PRODUCTION
Tool work thermocouble
This technique is based on the principle of thermocouple (seebeck effect).According to this principle, when
two different electrically conducted material joined together at two different places, one junction then emf
will be generated and current flow takes place from hot junction to cold junction. The magnitude of current
depends upon the difference in temperature between two junctions. The magnitude of current flow can be
measured with the help of millivoltmeter which is placed at the cold junction. Now to measure the tempera-
ture developed at machining area, a calibration curve is used which is already prepared.
x
x
x
(voltage x
change)
temp. >
Compound rake method
This method is applicable for that tool material which is not a good coductor of Electricity like ceramic.
www.ascentgateacademy.com Copyright : Ascent Gate Academy 101
MECHANICAL ENGINEERING
To find out the chip tool inter Face temperature, a small hole can be provided from the flank face.A
small strip of material having eqnivalent properties to that of ceramic tool material, is inserted to the hole and
a thermoconple is attached to their cold junction having millivoltmeter also. Now with the help of thermo-
couple & calibration curve we can measured the temperature over speified region. To another region where
we are interested to find out the temperature, we grind the flank face. Due to grinding, the position of small
strip inside the hole can be changed and corres ponding temperature can be measured with the help of
thermocouple and calibration curve.
TOOL FAILURE
when the cutting tool is unable to cut, consuming reasonable energy and can not produce an acceptable
finish, it is considered to have failed. The failure of a cutting tool may be due to one or combination of the
following modes :
I) Mechanical breakage of the tool due to large force, insufficient strength and toughness.
II) plastic deformation of the tool due to high temperature and large stress.
III) Blunting of the cutting edge of the tool through a process of gradual wear.
Wear : Wear is defined as the progressive loss or removal of material from a surface. wear has great
technologic & economic significance became it changes the shape of tools and dies and consequently.
affects the size and quality of the parts produced.
Types of wear mechanism
Diffusion : The favourable condition for the diffusion is the localized temperature over the actual area
between the chip underside and the tool face. In that condition the metal atom will transfer from the tool
materal to the chip material at the points of contant. This weakens the surface structure of the cutting tool and
may ultimately lead to tool failure. The amount of diffusion depends upon -
1. Temperature 2. Bonding affinity between the chip and work 3. Large gradients of various elements.
Adhesion wear :- Due to the excessively high temperatures high pressure and intimate contant between the
chip & tool, welding takes place at the high points of asperities. when the chip slides, the small amount of
tool carried awaybythe sliding chip. Thus small particles will continue to separate through this phenomenon
called adhesion wear.
Abrasion wear : Since there will be thousands of faylite pockets inside the work material and as these
faylite pockets come in contant with the cutting edge, there will be a shock. As a result of that a portion of
cutting egde will be eroded.
Fatigue wear : when two surface slide in contact with each other under pressure, asperities on one surface
inter lock with those of the other. Due to friction, compressive stress is produced on one side of each inter
locking asperity and tennile stress on the other side After, the above stresses are relieved. New pair of
asperities are formed and stress cycle is repeated. This phemomenon causes surface cracks lead to erosion
of tool, called fatigue wear.
www.ascentgateacademy.com Copyright : Ascent Gate Academy 102
PRODUCTION
Types of wear
1- Flank wear : The flank wear occurs on the flank face under the cutting adge the to rubbing of machined
surface with the tool. This wear produces wear lands on the side and end flank of the tool. In the beginning,
The tool is sharp and the wear land on the flank has zero width. However very soon. the wear land develops
and grows in size on account of abrasive wear.
We not that wear land is not of uniform width. it is widest at a point farthest from the nose.
After a critical wear land has formed further wear takes place at an accelerating rate. it is advisable
to change the tool well before the onset of rapid wear in order to avoid tool failure. During the steady wear
phase, flank wear is caused mainly through abrasion, where as during the rapid wear phase it is caused by
diffusion
Crater wear :
It occure on the rake face of the tool. The crater is formed at some distance from the cutting edge.
careful measurements have shown that the locations of maximum crater wear and maximum chip tool inter-
facial temperature coincides and it is clear that the crater wear is a temparature dependent phenomenon
caused by diffusion, ad hesion etc. crater significantly reduces the strength of the tool and may lead to its
failure.
www.ascentgateacademy.com Copyright : Ascent Gate Academy 103
MECHANICAL ENGINEERING
This is generallyobserved while machining ductile materials which produces continuous chips.
***************
www.ascentgateacademy.com Copyright : Ascent Gate Academy 104
PRODUCTION
FACTOR INFLUENCING HEAT GENERATION
1) Work material :- Hard material - more power req. consequently more heat generated soft material - less
power required the refore less heat generated
2) Tool material :- If cutting speed is high, temperature is also high
2) Cutting condition :- speed , temp.
feed temp.
depth of cut temp
4) Use of cutting Fluid
5) Tool geometry : more rake - less heat
less rake - more heat
Tool life : Tool life can be defined as the time elapsed between two successive grinding of the tool.
Tool life can be expressed in
1) Minutes - in gereral
2) No. of pieces produced - in mass production
3) Volume of metal removed - in rough machining
Tool life equation : The tool life is mainly affected by cutting speed means higher the cutting speed the
smaller the tool life - Tougler gave the relation between cutting speed and tool life that is
VTn = C
where V = cutting speed
T = Tool life
C = Machining constant
n = Tool life exponent (depends only on tool material)
For HSS n = 0.25
For carbides n = 0.3
For ceramics n = 0.4
Low alloy steels n = 0.14 - 0.16
C depends upon tool and work material as well as widthof wear land on side flank i.e. VB.
Taylor’s tool life equation is empirical formula and completely based on experience and experimen-
tal work. But we can prove the tool life equation with the help of the following example.
Example :- Select cutting speed Take feed. Depth of cut, lool & work pair constant.
www.ascentgateacademy.com Copyright : Ascent Gate Academy 105
MECHANICAL ENGINEERING
form ACB tan = n = AB = AD - BD
BC EC - EB
Where n is the slope of the straight line and is called tool life exponent.
n = log V2 - log v1
log T1 - log T2
n = log (V2 / v1)
log ( T1 / T2 )
n log ( T1 / T2 ) = log ( V2/V1)
log T1 n v2
= log
T2 v1
log (T1 / T2 ) n =0
( V2 / V1 )
log (T1 n. T2 ) n = log 1 log (T1 / T2)n - log (V2/V1) = log 1
( V2 n . V2 )
V .T n T1n V
11 T2n x 1 = log 1
=1
V2 . T2 n V2
V1 . T1 n = V2 . T2 n = C V1 T1 n = V2 V2n = C
VT n = C Tool life equation
www.ascentgateacademy.com Copyright : Ascent Gate Academy 106
PRODUCTION
Modified Taylor’s tool life equation
VTn f p dq = C, Where F, d are feed and depth of cut
also P > q indicates that tool life is more sensitive to uncut chip thickness than to the width of cut.
For orthogonal machining, feed is equal to uncut chip thickness and depth of cut is equal to width of cut.
Effect of tool life on cutting parameters
V>F>d
Machinability The ease with which a given material may be worked with cutting tool nuder a given set of
cutting condition is machinability. Machinabilitycan be evaluated using the following criteria.
1) Tool life :- more the tool life better the machinability.
2) Surface finish :- Better the surface finish better the machinability
3) Force and power consumption :- more the force, poor the machinability
4) Shear angle :- larges the shear angle better the machinability.
5) MRR :- Higher the MRR better the machinability.
6) specific energy :- lower the specific energy better the machinability.
7) Ease of chip disposal
8) Temperature of tool work interface more the temperature, poor the machinability
Machinability index :- The parameters that affect machinability are numerous. Machinability appears to
be difficult concept to reduce to quantitative terms. Inspite of this, many attempts have been made to obtain
a quantitative measure of machinabilityin terms of a ‘Machinabilityindex’ - a single unique index to Describe
the relative ease with which a material could be machined.
Machinability index = Vt x 100
Vs
Where VS = Cutting speed of standard free cutting steel for 20 minutes tool life
Vt = Cutting speed of metal for 20 minutes tool life.
Free cutting steel - free machining steels having 0.13 % carbon, 0.06 to 1.1% manganese, 0.08 to 0.03%
sulphur. Its machining index is relativelyfixed at 100%
Representative machinability index for some materials
Materials Machinability index
Low carbon steels 55 to 65
Copper 70
Brass 180
Aluminum alloys 300-1500
Magnesium alloys 500-2000
Mn steels 60
www.ascentgateacademy.com Copyright : Ascent Gate Academy 107
MECHANICAL ENGINEERING
Factors affecting machinability
Machine variables :-
1) Power
2) Rigidityof the machine & holding device.
Machine variables indirectly affecting the machinability The machine should be rigid and have sufficient
power to with stand the induced cutting force and to minimize deflection. If not so then, both tool life and
surface finish are affected.
Tool variables :-
1) Tool material
2) Tool geometry
The cutting tool has to optimized to obtain a reasonable value of tool life and remove maximum
material.
Proper tool geometry is essential for efficient machining and it depends on the work material and
machining condition, surface finish greatlyinfluenced bythe tool geometry.
Cutting condition :
1) Cutting speed
2) Feed rate
3) Depth of cut
4) Cuttingfluid
Cutting speed has great influence on tool life. The surface finish normallyimproved byincrease in the
cutting speed, due to continuous reduction of BUE.
We have, cutting temperature Vafbdc
Where a, b, c are constants and a > b > c
The above expression indicates that cutting temperature is greatly influenced by cutting speed. The
impact of feed rate is moderate and depth of cut has least influence. This discussion reveals that higher the
cutting velocity, higher the cutting temperature and lower the tool life.
The cutting fluid reduces the cutting temperature and friction between the chip tool interface and
hence increases machinability.
Work material variables :
1) Hardness
2) Microstrucutre
3) Tensile strength
4) Chemical composition
Cutting tool materials :
Cutting tool must be 35 to 50% harder than work material. The improtant qualities expected of a good
cutting tool are :-
www.ascentgateacademy.com Copyright : Ascent Gate Academy 108
PRODUCTION
1) High hardness for easy penetration into the work
2) High mechanical resistance to bending and compression so that it can withstand cutting forces.
3) Hot hardness for maintaining the hardness at the elevated temperature
4) wear resistance
5) High toughness
6) High thermal conductivity
7) Low coefficient of friction
8) Low coefficient of thermal expansion
9) Low specific heat
10) Cost and easiness in fabriction
CHARACTERISTICS OF CUTTING TOOL MATERIAL
High Carbon Steel :-
Composition C = 0.6 to 1.5% , Si = 0.1 to 0.4%, Mn = 0.1 to 0.4%
Chromium and vanadium are also added
Easy to manufacture and cutting edge can be easily sharpened.
Hot Hardness is 2500C
Hardness is about RC = 65, VH = 750
Cutting speed is 5m/min
Application - wood working, machining soft metals like free cutting steel, brass
High Speed Steel
General used HSS is 18 - 4 - 1 (Tungsten based)
18% - Tungsten - used is increase hot hardness and stability
4% - Chromiun - used to increase strength
1% - vanadium - used to maintain keenness of cutting edge
In addition : 2.5 to 10% cobalt - used to increase hot hardness
0.8% - carbon , Rest - iron
8 - 4 - 1 (Molybdenum based)
Cutting speed - 28 to 30 m/min
Hardness value - 850 HV
Hot hardness - 6000C
Application - Machining non Ferrous materials
Non Ferrous Cast alloys (stellites)
It is an alloy of cobalt - 40 to 50% , chromium - 27 to 32%
Tungsten - 14 to 29% , carbon - 2 to 4%
It can not be heat treated and are used in the as cast form
Hot hardness - 8000C
Cutting speed - slightly higher than HSS tool
Weak in tension
www.ascentgateacademy.com Copyright : Ascent Gate Academy 109
MECHANICAL ENGINEERING
Cemented carbides :
Produced by powder metallary technique with sintering at 15000C.
Carbides are classified into two main types :
1. Straight tungsten carbide
2.Alloyed tungsten carbide
Straight tungsten carbide - Finely powedered Tungsten carbide (85 - 95%) + cobalt (5 - 15%), cobalt
acts as a bonding medium. cobalt, decreases hardness, strength, wear resistance but increases toughness.
Alloyed Tungsten carbide has addition of carbide of titanium and niobium.
Titanium carbide reduces BUF formation & increase hot hardness. Tantalum carbide improves resis-
tance to crater wear.
High compressive strength, High wear resistance
High modulus of elasticity, low coefficient of thermal expansion, High thermal conductivity
Working temperature - upto 10000C
Maximum cutting speed - 150 m/min
Application - steel cutting & Machining cast iron & non ferrous material
Hardness value - 1800 HV to 3100 HV
According to ISO the various grades of carbide tool materials grouped as
* for cutting CI and non Ferrous metals are Designated as K01 to K40
* for cutting steels are designated as P01 to P60
* for geneeral purpose application are designated as M10 to M30
Note :
P type - 30% Tic + 60% (WC + TaC) + 10% Co
M type - 15% Tic + 75% (Wc + TaC) + 10% Co
K type - 90% (WC + TaC) + 10% Co
Harder and brittle materials have low in number, less hard and more tough have higher number.
Ceramics and Sintered Oxides
Produced by powder metallurgy technique
Ceramics -Al2O3 (Alumina) + upto 10% addition of oxides of magnesium, titanium, chromium
High abrasion resistance
less tendency of BUE formation
Ceramic tool tips are highly brittle so they are usually attached to the shank by means of epoxy resins.
Low coefficient of friction against work material
Working temperature - upto 14000C
Hardness value - 2200 HV
Maximum cutting speed - 400 m/min
Application - Machining for heat treated steel, monel stellite, gray cast iron.
Generally used ceramic is sintered carbides and another ceramic tool is silicon nitride which is mainly
used for CI
The tool life silicon nitride is effective over 1500 CI pieces, but for same work tungsten carbide tool
lasted only for 250 pieces.
www.ascentgateacademy.com Copyright : Ascent Gate Academy 110
PRODUCTION
Cermets
Combination of ceramics and metals
Produced by Powder metallurgy process
When they combine ceramics give high refractoriness and metals will give toughness and thermal shock
resistance.
for cutting tools usual combinations as Al2O3 + W + Mo + Boron + Ti etc.
Usual combination 90% ceramic, 10% metals
Increase in % tage of metals reduces brittelness some extent and also reduces wear resistance.
Diamond : It has
Extreme hardness
Chemically inert and high thermal conductivity
Low thermal expansion
Low coeffiecient of friction
Poor electrical conductor
Oxidation starts at about 4500C and thereafter it can even crack, for this reason the diamond tool is kept
flooded by the coolant during cutting.
Used as an abrasive in grinding wheel
Hardness value - 7500 HV
Maximum cutting speed - 1000 m/min
Application - for machining non-ferrous metals likeAl, Cu, brass & bronze, plastics, glass, gold, silver,
platinum, zinc, Mn
Working temperature - 20000C
On ferrous metals diamonds are not suitable because of the diffusion of carbon atoms from diamond to
work.
Cubic boron nitride (CBN)
Hardest material next to diamond
Used as abrasives in grinding wheel
Consists of atoms of Nitrogen and Boron and produced by PM
Excellent surface finish is obtained
Hardness value - 4700 HV
Maximum cutting speed - 600 - 700 m/min
Melting temperature - 13000C
Application - Machining for stainless steel and high speed steel
UCON
Developed by union carbide company
Consists of 50% columbium, 30% titanium, 20% tungusten
Produced by rolling process
Application - Machining of steel with high speeds and feeds.
****************
“Success is often the result of taking misstep in the right direction”
www.ascentgateacademy.com Copyright : Ascent Gate Academy 111
MECHANICAL ENGINEERING
6 SHEET METAL OPERATION
The following are the operation involved during metal working.
1. Punching or piercing
2. Blanking
3. Deep drawing
4. Bending
The first two involves shearing action and the last two involves plastic deformation
The process of shear starts with the punch sinking into the metal and stressing the metal to its elastic
limit.As the punch penetrates further into the metal, the elastic limit of the material is exceeded and a rupture
appears at the cutting edge of the punch. There is rupture at the cutting edge of the die also.As the punch
penetration continues, the fractures meet and a clean break results.
Penetration brick
...................................
...>.................
clearance
Clearance is the space between the punch and die. For a round punch and die opening it is the differ-
ence of the two radii. If the clearance is correct, based on the type and thickness of material, the two
fractures will met as stated above and a blank having good clean edges will result. The edge of the blank will
appear burnished for about one third of its edge length. This is thedepth to which the punch penetrated
before complete fracture took place.
Punching or Piercing:- Here the hole produced on the sheet is useful one. In this punch is made to the
correct size and clearance is provided on die.
Size of punch = size of hole to be produced
Size of die = size of punch + 2C
Where C = Clearance on radius
* Shear is provided on punch
Blanking : Here blank coming out during punching is useful one. In this die is made to correct size and
clearance is provided on punch
Size of die = size of blank
Size of punch = size of - 2 c
* Shear is provided on die
* Clearance = C = 0.0032 . t. . mm
www.ascentgateacademy.com Copyright : Ascent Gate Academy 112
PRODUCTION
Where is in N/mm2 , ‘t’ is in mm (or) 10% of ‘t’.
Cutting force (or) load estimation :
Force required for blanking or punching = As x = Fmax
Where As = Sheared area = perimeter x thickness = D t ................ for circular blanks
= 4.a.t......... for squar = 2 (a + b) t ................. for rectangle
Energy required for punching or blanking = E = Force x punch travel = Fmax.K.t.
Where K = % penetration required for rupture; t = thickness of sheets
Note: Some times a factor ‘x’ is considered to account extra enegry required due to friction etc. the value
of x = 1.16 in genral.
E = F K.t.x
max
Methods of reducing cutting force:
In the above case, of calulating force we assumed that the bottom of punch and top of die are flat
and parallel. but due to this a very high punch forces are required in short time. To avoid this and making
smooth punching operation two methods were adopted.
1. by providing shear 2. By staggering of punches.
a) shear : The working faces of the punch or die are ground off so that these do not remain parallel to the
horizontal plane but are inclined to it. This angle of inclination is called shear. This has the effect of reduc-
ing the sheared area at any one time and the max force is much less. This may be reduced by as much as
50 % .
The amount of shear to be applied is matter of compromise. If the shear is quite big, say 2t or 3t,
then the cutting edges of tool will become too acute and liable to break away easily. However, the shear
must be at least equal to the percentages penetration
Let I = Shear provided on punch or die
F = actual force with shear on punch (or) die
F max = max. force to be applied without shear on punch or die = As
Energy required for completing punching or blanking operation = F K.t = E
max
Punch travel required for completing punching with shear is = K.t + 1
Energy required if shear is provided = F (K.t +I), always F < Fmax Theoretically, the energy required
for punching or blanking to particular size is same with and without providing shear..
F max K.t = F (K.t + 1)
F = [(Fmax .K.t) / (K.t + I)] (or)
I = [( Fmax - F) K.t] / F
If we go for more and more amount of shear, no doubt operation is smooth but the dimesions of
the cut tend to increase inproportional to the angle of shear
Note: Shear chosen should provided a change in punch length of about 0.5 to 2 t
Note: In piercing the direction of shear angles must be such that the cut proceeds form outer extremities
of the contour towards the center. This avoids stretching the material when it is cut free.
b) Staggering of punches : An effect similar to shear can be obtained by staggering two or more
punches that all operate in one stroke of press. For staggering the puches are arranged so that one does
www.ascentgateacademy.com Copyright : Ascent Gate Academy 113
MECHANICAL ENGINEERING
not enter the material until the one before it has penetrated through. In this manner, the cutting load may
be reduced to 50 % if two punches are taking part in one stroke,
Minimum size of punching : = shear of sheet
Let fc = Crushing stress of punch
By assuming hole produced is in circular shape
Force reduired for punching = .d.t.
Force that can be withstand by punch = (/4) d2 .fc
For min size of hole.
Force on punch = force required for punching
(/4) d2 .fc = .d.t. , Let fc = the equation becomes d = 4t
if fc = 4 , d = t
a = edge of blank to side of the strip
= back or front scrap = t + 0.015 h
b = scrap bridge
= 0.8 mm ; when t < 0.8 mm ;
= t ; 0.8 < t < 3.2 mm ;
= 3.2 mm ; t > 3.2 mm
Feed (or) advance = S = w + b
No. of blanks = N = L - b0 / S
Scrap remaining = L - (NS + b)
% Utilization = Area of material used / Total area of sheet
= h.x = h.x
(h + 2a) S (h + 2a) (x + b)
Drawing :
Drawing is the process of forming a flat piece of material (blanks) into a hallow shape by means
of punch which causes the blank to flow into the die cavity.
The depth of draw may be shallow, moderate or deep.
If depth /diameter < 0.5 ---- called shallow drawing
If depth /diameter > 1 ---- called deep drawing
www.ascentgateacademy.com Copyright : Ascent Gate Academy 114
PRODUCTION
Note : The blank between die wall and puch surface is subjected to pure tension and tends to stretch and
become thinner. This is called “necking”
Note : Due to blank holding force the outer portion of blank become thicker during drawing. If the
clearnace is not enough to accomodate this increased thickness, then the “ironing” will takes place. This is
useful if uniform thickness of part of required.
Draw ratio : It is the ratio of max blank diameter to the diameter of the cup drawn from the blank, that is
D/d. For a given material there is a limiting draw ratio (LDR) after which the punch will pierce a hole in
the blank instead of drawing the blank.
This ratio depends upon many factors such as type of material, amount of friction present etc. the
usual range is 1.6 to 2.3
Venting (i.e. hole is provided in punch) in puch serves as
a) Eliminates suction, which would hold the cup on punch during return stroke
b) Providing passage for lubricants
No. of draws : it can be done in two ways
a) draw reduction ratio b) limiting draw ratio
In draw reduction ratio method
Ist draw reduction = 45 to 50% = (D - d )/D
1
d1 = dia. of Ist draw punch
IInd draw reduction = 30% = (d1 - d2) / d1
IIIrd draw reduction = 25% = (d2 - d3) /d2
IVth and above draws = 16%
Whenever dia. of purch is less than or equal to the required dia of component, the corresponding
draw number is the no. of draws.
Blank size in drawing : The basic assumption in calculating blank size in drawing is the area of the
developed blank before drawing should be the same as the surface area of the shell after drawing, pro-
viding the thickness of the material remains unchanged.
Blank dia = D d2 + 4th ------------------ for d/r > 20
d = dia of part h = height of port r = corner radius
T = bottom thickness
D = d2 + 4th --- 0.5 r ......... if 15 < d/r < 20
D = d2 + 4th --- r ......... if 10 < d/r < 15
D = d2 + 4th (t/T) , .......... t = wall thickness
Drawing force = P = .d.t.fy [(D/d) - c] ...... Newton
Where t = thickness of blank ;
d = dia of punch; fy = yield strength N/mm2
C = constant to cover friction and held = 0.6 or 0.7
Blank holding force = 1/3 drawing force
www.ascentgateacademy.com Copyright : Ascent Gate Academy 115
MECHANICAL ENGINEERING
Note : Corner radius of punch and die is more for first draw and become equal to the corner radius of
required part at the draw. Generally for Ist draw corner radius is 10t.
Bending :
Bend allowance = (/ 180) (r + K)
Where = bend angle in degrees
= part which makes angle with horizontal plane
R = inside radius of bend ;
K = distance of neutral axis from inside surface of the bend.
If r < 2t k = 1/3 t = 0.33 t
r 2t k = ½ t = 0.5t
Bending pressure = F == C. l . fy . t2 / W Newton’s
l = length of part fy = yield strength W = width of die opening
t = blank thickness
C = die opening factor = 1.2 for die opening of 16 f
= 1.33 for die opening of 8 t.
Note : - For “U” or channel bending, the pressure will be twice as for “V” bending and for edge bending
it will be about one - half of that for V -bending
Types of dies: According to the method of operation the dies are classified as
a) Single operation (or) simple dies
b) Compound dies c) Combinaton dies d) Progressive dies
Simple dies : These will perform single operation for each stroke of the press slide. The operation may
be a cutting operation like blanking, punching etc (or) forming operation like bending, drawing etc.
Compound dies : In these dies two or more operations may be performed at one station and at one
stroke. Also these are considered only as cutting dies. The example is washer is provided by blanking and
piercing operations simultaneously. These are accurate and economical in mass production.
Combination dies : In this die also two or more operations will preformed at one station and one stroke.
But the operation area not only cutting, here the cutting operation is combined with forming operation for
example blanking is combined with bending or drawing operations.
Progressive die : It is also called follow on die. It is like a compound die, but the difference is here all
the operation will be completed in one stroke but not at one stage. Between the strokes the strip is
transferred or moved to the next stages, but finally one component or product will comes out per stroke.
But the advantage here is we can stagger the punches to reduce the max force capacity of a punch press.
Transfer die : unlike the progressive dies where the stock is fed progressively from one station to
another, in transfer dies the already cut blanks are fed mechanically from station to station.
Multiple dies : Multiple or gang dies produce two or more work pieces at each stroke of the press.
**************************
“Success is nothing more than a few simple disciplinees,
practiced every day”
www.ascentgateacademy.com Copyright : Ascent Gate Academy 116
PRODUCTION
7 UNCONVENTIONAL MACHINING PROCESS
“UNCONVENTIONAL MACHINING PROCESS”
Present day techonology needs to develop some non conventional machining process because the
available traditional manufacturing processes can not serve purpose such as
(i) New materials with a low machinability
(ii) Dimensional accuracyrequirements
(iii) A higher production rate and economy
Example of those types of jobs are machining a complicated turbine blade made of super alloys and
producing holes and slots in materials such as glass and semiconductors. Some times job becomes difficult
due to dimensional complications such as drilling a non - circular hole or a micro hole. In addition to above,
higher production rate and economic requirements maydemand use of Non-Traditional Machining (NTM).
ULTRASONIC MACHINING (USM) :
The basic process involves a tool vibrating with a very high frequency and a continuous flow of an
abrasive slurry in the small gap between the tool and the work surface. The impact of the hard abrasive
grains fractures the hard and brittle work surface resulting in metal removal in the form of small wear par-
ticles, which are carried away by slurry . Feed force
Ultrasonic vibration
frequency = 20 kw
Amplitude = 15-20
work
The reasons of MR during USM are
* Hammering of the abrasive particles on the work surface by the tool.
* The impact of the free abrasive particles on the work surface.
* The erosion due to cavitation.
* Chemical action associated with the fluid used.
The MRR in USM is given by Q V Z f
Where Q = volume of MRR, V = volume of material dislodged/impact,
Z = no. of particles making impact/cycle, f = frequency
On simplification of the above equation Q = 5.9 f (Ry ) 1/2 (/H) mm/sec
0
Where R = radius of grit in mm y = amplitude of vibration
0
www.ascentgateacademy.com Copyright : Ascent Gate Academy 117
MECHANICAL ENGINEERING
= stress developed in tool in kg/mm2 or N/mm2
H = surface hardness of work piece in kg/mm2 or N/mm2
= X compression facture strength of abrasive particles
The summary of USM characteristics are
1. Mechanics of M.R. Brittle fracture caused by impact of abrasive grains due to tool vibrating at
high frequency.
2. Medium Slurry (abrasives mixed with water, paraffin etc.)
3. Abrasives Al2O3, B4C (Boron Carbide), SiC, diamond
Usually B C with water as slurry
4
Si C with paraffin as slurry
100 - 800 grit size.
4. Vibration frequency - 15 to 30 KHz
amplitude - 25 to 100 m
Application of USM :
* Used to produce holes as small as 0.1 mm.
* Used for drilling, grinding, profiling, coining etc on materials like SS, glass, ceramic, carbide quartz,
semiconductors etc.
* Also used for piercing of dies and for parting off operations.
Limitations: Low MRR, high tool wear, Sp. MRR on brittle materials is 0.018 mm3/joule.
Normal hole tolerances are 25 m and surface finish is 0.5 to 0.7 m.
Electric Disharge Machining (EDM) :
When a discharge takes place between two point of anode and the cathode, the intense heat generated
near the zone melts and evaporates the meterials in the sparking zone. For improving the effectiveness the
work piece and the tool are submerged in a dielectric fluid (hydrocarbon or mineral oils). If anode and
cathode are of the same materials, it has been found that greater erosion takes place at anode (positive
terminal). So in EDM, work is made the anode.
Let C = capacitance in relaxation circuit R = resistance in relaxation circuit
V0 = supply voltage Vd = discharge or sparking voltage (or) voltage during
sparking
W = power input in KW Q = MRR
Energy released per spark = (1/2) CVd2. Joules = E
Cycle time = tc = RC loge [Vo / (Vo - Vd)] sec
Avg. power input = W = E/t
c
NOTE : Cycle time denotes charging time which is equal to time required to reach a value Vd .
For machining of steels under normal conditions, MRR = C 27.4 W 1.54
For maximum power delivery, Vd = 0.72V0
www.ascentgateacademy.com Copyright : Ascent Gate Academy 118
PRODUCTION
* So MRR increases as ‘R’ decreases, but ‘R’ can not be decreased below critical value, other-
wise arcing instead of sparking will take place.
Rmin = L / C where L = inductance of discharge circuit,
Surface roughness = Hrms = 1.11 Q ,0.384 where Q = MRR, H rms = R.M.S. value of roughness
* Discharge time is about 10% of the charging time, and frequencey of sparking = == 1/tc
The commonlyused principles for supplying the pulsating DC can be classified into
(i) Resistance - capacitance relaxation circuit with a constant DC sourec.
(ii) Rotary impules generator
(iii) Controlled pulse circuit
The R-C relaxation circuit methodology is explained above. It has disadvantage that
MRR is very less. For improving MRR, a pules generator is used for spark generation.
In Rotary Impulse generator, type, the capacitor is charged through the diode during the
first half cycle. During the second lalf cycle, the sum of the voltages generated by the generator and the
charged capacitor is applied to the work tool gap. Though the MRR is higher in this system, but surface
finish is pool.
In the above two systems, there is no provision for an automatic prevention of the current
flow when a short circuit is developed. To achieve such an automatic control, a vacuum tube is used as
the switching device. This system in known as a controlled pulse circuit.
MRR depends upon current density and it increases with current. But, high MRR pro-
duce poor surface finish. So, in EDM, a roughing cut with a heavy current followed by finishing cut with
less current.
Summary of EDM characteristics are
Mechanics of MR Melting and evaporation aided by cavitation (spark erosion)
Medium Dielastic fluid (generally kerosene)
Tool
Materials Cu, Brass, Cu - W Alloy, Ag - W- Alloy, Graphite
Wear Ratio 0.1 to 10
Gap 10 to 125 m
Max. MRR 5 X 103 mm3/min
Sp. power consumption 1.8 W/mm3 / min
Advantages EDM can be usedto any material, it does not leave any chips or burrs on
work and no cutting forces.
Disadvantages Used only for electrically conductive materials, electrode wear is more,
rehardening takes place due to heat generated during machining and
perfactly square corners cannot be made.
Applications Blind cavities and narrow slots in dies, min. dia hole produced is 0.13
mm and L/D is as high as 20 can be done. So, due to this, EDM is particularly useful in machining of
small holes, orifices, slots in diesel fule injection nozzles, airbrake valves, aircraft engines etc.
Wire Cut EDM : It is similar to EDM, but
www.ascentgateacademy.com Copyright : Ascent Gate Academy 119
MECHANICAL ENGINEERING
1. Instead of moving electrode, a moving wire is used.
2 Instead of submerging work in dielectric fluid, the working zone is supplied with co-axial jet of
dielectric medium.
3. In this the work table should have moments in x and y-axis to cut the plate in desired shape.
Electric Discharge Grinding (EDG) : It is also similar to EDM except that the electrode is rotating wheel
(usually graphite). Here also the complete workpiece is immersed in dielectric fluid and is fed past the wheel
by servo-controlled machine table. The metal chips are flushed away by normally held at 0.013 to 0.076
mm and wheel speed is 0.5 to 3 m/s.
E.D.G. is generally used for operations such as
(a) Grinding carbide and steel without wheel loading
(b) Grinding thin sections without distortion
(c) Grinding brittle and fragile parts without fracturing
Electro Chemical Machining (ECM) :
ECM uses principle of electrolysis is remove metal from the workpiece. Electrolysis is based on fara-
days laws of electrolysis which is stated as “weight of substance produced during electrolysis is proportional
to current passing, length of time the process used and the equivalent weight of material which is deposited.”
ECM is just reverse of electroplating (anode loses metal to cathode). So in ECM work is made anode and
tool is made cathode. So work loses metal, but defore depositing it on to tool, it is carried away be electro-
lyte.
* In ECM the tool is provided with a constant feed motion and electrolyte is pumped at a high pressure
through the tool and the small gap between tool and work piece.
* The current used is few thousand amperes and voltage used is 8-20 volts and gap is of the order of to
0.2 mm.
* MRR = 1600 mm3/min for each 1000 amperes. So, approximately 3 KWH is needed to remove 16 X
133 mm3 of metal, which is 30 times the energy required in conventional machining process.
* Practically no tool wear in ECM.
* MRR is independent of hardness of work.
According to Faraday’s 1st Law’s of electrolysis, mass of ions liberated by the substance.
M = Z . I. t.
Where I = current flowing in amperes t = time in sec
Z= constant known as electrochemical equivalent
‘Z’ is also equal to mass of ions liberated by the substance by the passage of one ampere of current for one
second through the electrolytic solution.
According to Faraday’s IInd law
Also Z = (1/F) x (At /) = (1/F) .M.
Where F = Faraday’s constant = 96500 coleuses = 26.8 amp - hours, = Valences of metal dissolved
M=Z.I.t At = atomic weight of material in gms.
= (I . t / F) . (At / )
www.ascentgateacademy.com Copyright : Ascent Gate Academy 120
PRODUCTION
MRR = M / (A . t) cm/sec
Where A = machined area, cm2, = density of work piece, gm/cm3 , t = time, sec
MRR = (I . t. / F) . (At /) . (1 / A. .t) = (I . At) (F.) cm3/sec
Current density = VK/y = . f / Z
Where y = gap between tool and work, V = applied voltage, K = conductivity of electrolyte (mho/mm)
= density of work material kg/mm3, f = tool feed rate (mm/sec)
Characteristics of ECM are Tool Electrolysis
Mechanics of Material removal Conducting electrolyte
Medium
Cu, Brass, Steel
Materials (infinite)
Wear ratio 50 - 300 m
Gap 15 X 103 mm3/min
Max. MRR 7 W/mm3 /min
Sp. Power Consumption High sp. Energy consumption (about 150 Times
Limitations that required for conventional Process). Not ap
plicable to non conducting materials.
Electrochemical Grinding : The work is machined by combined action of electrochemical effect (90%) and
conventional grinding (10%). The features of ECG process are
1. Gap between tool and work is 0.25 mm.
2. Accuracy 0.01 mm, surface finish 0.1 m and MRR is 15 mm3/s.
3. D.C. voltage of 5 to 20 V and current density of 100 to 200 A/cm2.
4. Tool wear negligible and so more tool life.
5. No surface stresses and distortion.
6. Used for shaping and sharpening of carbide cutting tools.
Abrasive Jet Machining (AJM) : In this material removal takes place due to the impingement of fine
abrasive particles with a high speed air or gas stream.
Air+ Abrasive particles (velocity = 150 to 300 m/sec)
www.ascentgateacademy.com Copyright : Ascent Gate Academy 121
MECHANICAL ENGINEERING
features of abrasive jet machining are
* Size of abrasive particles re about 0.025min.
* Mechanism of material removal is due to brittle fracture by impinging abrasive grains at high speed.
* This process is more suitable when the work material is brittle and fragile.
* MRR = Q = KZd3v1.5 (/12HW)3/4
Where K = constant, Z = no. of abrasive particles impinging per unit time
d = mean dia of abrasive grains V = velocity of abrasive grains
= density of abrasive materials Hw = hardness of work material
* Media for of abrasives is air or CO , abrasive material is Al O or SiC. Normally no. of grains per unit
2 23
time are 2 to 20 g/min with non-recirculating type and size of grains is 15 to 20 m.
* Pressure of air/gas normally used is 2 to 10 MPa and nozzle is made by WC with orifice area or 0.05
to 0.2 mm2 and its life is 12 to 300 HR.
MRR characteristics inAJM are
* Nozzle is generally having contact with abrasives, so it should be made by very hard material to avoid
wear. Shape of orifice is circular or rectangular.
* Nozzle tip distance is the distance between nozzle tip and workpiece, it affects not only the MRR but
also shape and size of cavity produced. As the nozzle lip distance increases velocity of abrasive particles
impinging on work surface increases due to their acceleration after they leave the nozzle, which in turn
increases the MRR. But with further increases in nozzle tip distance velocity decreases due to drag of the
atmosphere. MRR
Nozzle tip distance
* Applications ofAJM are cutting, cleaning and for machining of semi-conductors such as silicon, gallium
or germanimum, for making holes and slots in glass, quartz mica and ceramics.Adimensional tolerance of
0.05 mm can be obtained with a surface finish of 0.5 to 1.2 m.
* Limitation are low MRR (40 mg/min or 15 mm3/min) embedding of abrasive in work piece, tapering of
drilled holes etc. Tapping is about 7o if nozzle top distance is 15 mm.
Water Jet Machining : Water jets alone (without abrasives) can be used for cutting. Thin jets of high
pressure and high velocity have been used to cut materials such as wood, coal, textiles, rubber, rocks,
www.ascentgateacademy.com Copyright : Ascent Gate Academy 122
PRODUCTION
concrete, asbestos and leather.
* The machanism of MRR is by erosion. When high pressure water jet emerges of a nozzle, it attains a
large kinetic energy. When this high velocity jet strikes the work piece, its KE is converted into pressure
energy inducing high stresses in the work material. When the induced stress exceeds the ultimate shear stress
of the material, rupture takes place.
* The pressures normally used are 1500 to 4000 MPa.
* Nozzle is made by sintered diamond, WC and the exit dia of nozzle is about 0.05 to 0.35 mm.
* No moving parts in the system, so less operating and maintence costs and safe process.
* No thermal damage to work and intricate shapes can be cut.
* The process in convenient for cutting soft and rubber like materials because teeth will get clogged in
conventional methods.
* The limitation of the process is high intial cost and hard materials cannot be cut.
* The second limitation of cutting hard materials have been over come by introduing abrasives in water in
WJM also called AWJM.
* InAWJM abrasives below 0.45 micron size is mixed with water and compressed to 420 MPa with this
machine a 25 mm thick Al has been cut for 100 mm/min. On zinc-nicket steel of 25 mm thick the rate of
cutting is 35.5 mm/min, but on the same work EDM can cut 2.5 mm/min.
Electron Beam Machining (EBM) : Basically EBM is a thermal process. Here a stream of high speed
electrons impinges on the work surface so that the KE of electrons is transferred to work producing intense
heating. Depending upon the intensity of heating the work can melt and vaporize. The process of heating by
electron beam is used for annealing, welding, or metal removal. Veryhigh velocities can be obtained byusing
enough voltage, for example 15000 V can produec electron velocity of 228, 478 km/sec, and it is focused
on 10 - 200 m dia, power density can go upto 6500 billion W/mm2 . Such a power density can vaporize
substance immediately.
* EBM is suitable for producing fine holes and cutting norrow slots.
* Complex contours can be easily machined bymaneuvering the electron beam using magnetic deflection
coils.
* To avoid a collision of the accelerating electrons with the air molecules, the process has to be con-
ducted in vacuum (10-5 mm of Hg). So EBM is not suitable for large work pieces.
* MRR in EBM is
Q = area of slot or hole X apeed of cutting = A X V mm3/min
Beam power for ‘Q’ MRR is P=C.Q
Where C = specific power consumption
= 12 (W/mm3 /min) for tungsten
= 7 (W/mm3 /min) for iron
= 6 (W/mm3 /min) for titanium
= 4 (W/mm3 /min) for aluminium
Thermal velocity acquired by on electron of the work material due to EB is
Vw = 2b./Mw
www.ascentgateacademy.com Copyright : Ascent Gate Academy 123
MECHANICAL ENGINEERING
Where = Boltzmann constant = 1.38 x 10 -23 J/oK/atom
b
rise is temperature of work for vaporization oK
Mw = mass of one atom of work, in gm.
* The circular area of diameter ‘D’ where the beam is concentrated is given by
D = ( /V) [0.1 .k. ] cm
Where = thermal diffusivity = K / Cp in cm2/sec
K = thermal conductivity in J/cm/oK
= density Cp = specific heat at constant pressure (J/kg/oK)
V = velocity of transverse of electron (cm/sec) P = power of the beam (watts)
I = depth of penetration (cm) = temp. attained at the work piece (oC)
* Absolutely no effects on work piece because about 25-50 m away from machining spot remains at
room temperature and so no effects of high temperature on work. Also the process is accomplished with
vacuum so no possibilityof contamination.
* The limitation of this processs is very high sp. energy consumption, vacuum is compulsory and ma-
chines are so expensive.
Laser Beam Machining (LBM) : Laser - light amplification by simulated emission of radiation.
LBM is similar to EBM. Laser is a highly coherent beam of electromagnetic radiation with wavelength
varying from 0.1-70m. But due to limitation in power availability the usable wavelength is 0.4 to 0.6 m.
Because the laser beam is perfectly parallel and monochromatic, it can be focused on to a very samll
diameter and so we can obtain a power density of 107 W/mm2 (10 MW/mm2). The machining by a laser
beam is achieved through the following phases.
(a) interaction of laser beam with work material.
(b) heat conduction and temperature rise.
(c) melting, vaporization and ablation.
* Energy released by flash tube is much more than the energy emitted by the laser head in the form of
laser beam, so the system must be properly cooled.
* Efficiency of EBM is very low i.e. 0.3 to 0.5%
* Divergence of beam is about 2 x 10-3 radians.
* Like EBM, LBM is also used for drilling micro holes and cutting very narrow slots. Holes upto 250 m
dia can be easily by laser.
* The dimensional accuracy is 0.025 mm, when the work thickness is more than 0.25 mm, a taper of
0.05 mm/mm is noticed.
* The time required to rise the surface to melting temperature is tm = ( ) (mK / 2H)2
Where = thermal diffusivity = K/ C
K = thermal conductivity, J/moC
H = heat flux = heat absorbed = melting point temperature of work
* The critical value of ‘H’ is given by m
Where d = focused dia of incident beam. Hcr = K m/d
If H = Hcr, power intensity is the minimum value.
If H < Hcr, the supplied power intensity will never melt the work.
www.ascentgateacademy.com Copyright : Ascent Gate Academy 124
PRODUCTION
* H = VL Where L = amount of energy to vaporize the unit volume of the material.
V = velocity of penetration of beam
H = rate that input required to vaporize the material
= heat flux = heat absorbed by work
* The advantage of LBM when compared to EBM is it does not need vacuum as medium.
* Max. MRR is 5 mm3/min and sp. power consumption is 1000 W/mm3/min.
* Limitations of LBM are, verylarge power consumption and can not cut material with high ‘K’ (Thermal
conductivity) and high reflectivity.
****************************
“Success is simply a matter of luck, Ask any failure”
www.ascentgateacademy.com Copyright : Ascent Gate Academy 125
MECHANICAL ENGINEERING
8 “NUMERICAL CONTROL (NC) MACHINES”
“NUMERICAL CONTROL (NC) MACHINES”
- Numerical control is a form of programmable automation in which the processing equipment is con-
trolled by numbers, letters and other symbols.
- NC is suitable for low and medium volume production.
- In NC machines the input information for controlling the machine tool motion is provided by means of
punched paper tapes or magnetic tapes in coded language.
- When program changes NC is capable to change the sequence of operations to accommodate differ-
ent product configutations.
- Operating principle of NC is relative position of a tool (or) processing element with respect to the work
part being processed.
- Application of NC is drilling, milling, turning, assembly, drafting and inspection.
- Program is coded into punched tape and is fed into control unit, which directs the processing equip-
ment accordingly; NC is also called the tape control.
- Machine control unit (MCU) consists of the electronics and control hardware that read and interpret
the program of instructions and convert it into mechanical action of the machine tool.
NC machine tool is most appropriate where parts are processed frequentlyand in small to medium lot sizes.
The other applications are
• For parts which are complex geometry and it will not be possible to manufacture them very accu-
rately on conventional m/cs due to human error involved
• For part which are subjected to frequent design changes
• Repetitive and precision quality parts which are to produced in low to medium batch quantity
• To require 100% inspection
• it is expensive part where mistaken in processing would be costly.
The main elements of NC machine tool
• the control unit, also called NC console
• the drive unit
• position feed back package
• magnetic box
• manual control
In the control unit, the instructions for manufacturing the component are written in a coded language,
are read by a tape reader. The instruction undergo electric processing and the control unit sends command
signals to the drive units of machine tool and also to the eletrical cabinet called magnetic box. Command
signals sent to the drive units of the m/c tool, control the lengths of travel and the feed rates, while the
command signals sent to the magnetic box control other functions such as spindle motor starting and stop-
ping, selecting spindle speeds, actuation of tool change, coolant supply etc.
www.ascentgateacademy.com Copyright : Ascent Gate Academy 126
PRODUCTION
Feed back transducer is provided to check whether the required lengths of tool travel has obtained.
The feed back transducer sends the information of the actual position achieved to the control unit. If there is
any diff between the input command and the actual position achieved, the drive unit is actuated by suitable
amplifier from the error signal.
Some times few functions can be done by operator such as motor strart, stop, coolant suplly, speed
change, feed change etc.
Advantages of NC is
- greater accuracy can be obtained
- less production cost due to reducation in lead time and up time.
- highly repeatable and improved product quality
- huge production rates due to optimized machining conditions and reduced non productive time.
- less scrap due to consistent accuracy and no operator errors
- reduced WIP
- less operator skill is required to run NC m/cs
- better m/c utilization
- lower tooling cost and changes in part design can be incorporated very easily.
Disadvantages
- high cost of m/c
Classification of NC machine tools
a) Based on control system features
- point to point control
- straight line control
- contour control
b) Based on feed back
- open loop control
- closed loop control
c) Base on no. of simultaneous control axis or slide control
- 2D, 2 1/2 D, 3D, 5D etc
In point to point control, the machining is done at specific positions, here work is stationary and tool
moves from point to point. The simple example is drilling holes at diff positions on a plate
In straight line control, the tool moves at a controlled feed rate in one axis direction at a time. Some
times we can move the tool in two axis also as a straight taper. Examples are stepped turning on lathe,
pocket milling etc.
In contour control, there are continuous, simultaneous and co-ordinate motions of the tool and the
work piece along diff co-ordinate axes. Examples are various profile, contours, curved surface etc.
In open loop system, there is no feed back and no return signal to indicate the actual position of the
tool. So we do not know whether there is an error between the input signal and the actual movement of tool.
In closed loop control system, it gives the actual distance traveled by tool and so we can know the
www.ascentgateacademy.com Copyright : Ascent Gate Academy 127
MECHANICAL ENGINEERING
error between input and output signal. The common position feed back devices in NC m/cs are encoders,
potentiometers, inductance, synchros, digitizers, tacho generators etc.
In contour machining, the velocity control is also essential, to ensure that the cutter path is as required
by the profile. Generally velocity feed back is provided by tacho generator.
Some times m/cs utilize only semi-closed loop system in which the exact position of the tool slide or
table is not measured as the linear distance directly, but by the rotary position of a lead screw or pinion gear.
The linear displacement of the tool slide or table is inferred from the rotary displacement. The accuracy of
position depends on the accuracy of the lead screw or a gear train.
Capability of machine tool can be specified is in terms of the control available on the slide movements,
like 2D, 3d, 21/2 D are the commonly used terms. 2D and 3D refer to machines with continuous path control
in 2 and 2 axis respectively, 21/2 D mean continuous path control is applied to two axis and the third axis is
capable of traversing at a controlled feed rate to a specified position. But in advanced m/c tool it is 4D, 5D,
6D etc are used to identify m/cs controlled in 4, 5, and 6 axes.
NC codes: a suitable pattern of perforations on a tape or a code is to be evolved to present each instruction
to be imparted to the m/c. the elements or the symbols of a code are either the absence or presence of a hole
punched on the tape.Acode is the series of combinations of these symbols, it represents either a figure or an
alphabet.
A hole in the first column has a weighted values of 1, in 2nd it is 2, in third it is 4, 4th it is 8. Suppose in
a row the holes are there in 1st , 2nd, 4th columns is equal to 1+2+8 = 11
Redundant information is anyinformation contained in the data which in not essential to enable the data
to be understood like “tape feed”, “end of block” etc.
The standard code for machine tool control are
TAB - separates axes information with in a block
EOB (end of block) - indicates the end of block and is specified on track 8
DELETE - used for erasing code
END OF RECORD/REWIND/STOP - it is placed at the beginning of program to indicate
rewinding of tape.
Tape : Eight channel punched tape is very common and popular means by which control instructions are
given to an NC m/c tool. The paper or paper plastic or aluminum plastic laminates are suitable medium for
storing data. It has on inch width and has 8 channels and has a line of sprocket holes to feed the tape
conveniently. In the same way magnetic tapes also can be used and which can store voluminous information
in small apace and fast reading and durable.
The track numbers on paper tape are
Track number 1 to 4 - alphabets
5 - parity check
6 to 7 - numerals
8 - end of block
- Track or channel is the line of holes or spaces parallel to the edge or the tape. The tracks are
numbered from 1 to 8, reading from right to left.
- Row is the line of holes or spaces perpendicular to the edge, each row contains one character.
www.ascentgateacademy.com Copyright : Ascent Gate Academy 128
PRODUCTION
- Bit is defined as a condition or two possible states, on or off. With respect to the tape, it means the
presence or absence of a hole.
- Character is a group of holes across one row on the tape which represents a number, a letter or a
symbol.
- Block is a word or group of words considered as a unit. Two blocks can be separated b EOB. It
generally indicates one complete instruction for a designated machine movement.
CNC (Computer Numerically Controlled) machines
In conventional NC system, the entire data input and data handing sequence including control functions
are determined only by the fixed circuit inter connections of decision elements and storage elements.Any
modification in part requires a preparation of new tape, so NC system is a hard wired or rigid system.
In CNC there is a dedicated mini computer in whose memory, the control program is stored which
performs all the basic NC functions. So in this the machine control data is directly coming from mini com-
puter and so it is called “software system”. The advantages are
- design changes of part can easily be incorporated
- no error in reading program
- no chance of destruction of program
- can be easily copy program into the another machine
The various elements of CNC system are
Control unit
>Input unit> Output unit
>>
>
> Memoryunit
Arithmetic unit
Operator & m/c interface>
INPUT UNIT : It receives all the commands from operator interface and feed back o status of m/c in the
form of AC, DC and analog signals.All the input signals are made compatible to be understood by control
unit.
CONTROL UNIT : It takes instructions from the memory unit and interprets them one at a time. the
information received from operator and m/c interface is interpreted and manipulated with hardware logic
and computer programs. It acts as a mediator between I/O units and memory unit.
MEMORY UNIT : It stores instructions and data received from input and performs arithmetic operation
and supplies information to the output unit.Amount of memory required is based on the no. of programs and
instructions to be stored.
www.ascentgateacademy.com Copyright : Ascent Gate Academy 129
MECHANICAL ENGINEERING
ARITHMETIC UNIT : It performs calulations makes decisions and results are stored in memory.
OUTPUT UNIT : It takes the data from memory and commands from control unit and made it compatible
with output devices. For this digital signals are first converted to analog form to control axis drive servomotros.
OPERATOR INTERFACE : The operator can interface with input and output units and gives commands
and data through punched tape or tape writers.
M/C INTERFACE : Consists of all devices used to monitor and control m/c tool like extreme travel limit
switches, solenoids for hydraulic and pneumatic control valve, servomechanisms etc.
Usually two limit switches are provided to detect end of travel on any axis. A servomechanism is a
group of elements which convert the NC O/P into precision mechanical displacements.
DNC (Direct / Distributed Numerical Control)
In DNC several NC or CNC m/cs can be controlled by a large central computer. Here direct link is
established between mini computer at the m/c and central computer, so that data and instruction can be
down load or upload to and from mini computer through computer networking.
At beginning of DNC, CNC use to have very small memory, so every time when a part to be made,
first the existing program is uploaded and then down load the next program, this is called direct NC. here
there there is traffic jam in the network.
Later days the memory capability of NCN m/c has increased and so the part programs are stored at m/
c, with specified numbers, so that the host computer will give command to use so and so program for next
part etc. this is called distributed NC.
ANC (adaptive NC) / Adaptive control
In general speed feed and depth of cut will be indicated in the program. Some times the indicated variable
may not be optimal, so inANC as the component is being manufactured, the important variables are mea-
sured and if needed the variable are changed.
For example in drilling, torque on drilling is measured and speed and feed or both are adjusted with in
programmed limits. The limits set by the process are surface finish, max feed, speed, depth of cut, cutting
force, torque etc.
ANC system can be classified into two categories
i) Adaptive control with optimization (ACO)
ii) Adaptive control with constraints (ACC)
inACO system , the performance is optimized according to the prescribed index of performance which
maybe an economic function likeminimum machining cost (or) maximum production rate usuallyit is difficult
to develop the comprehensive indexes of performance and sensors to measure parameters pose limitations.
ACO is basicallya sophisticated closed loop control system which automatically works in optimum condi-
tions even though work piece and tool material may very.ACO uses an optimization computer unit (OCU)
which calculates the performance index according to the formula told to it. The various variables are so
adjusted by it so that optimum values of performance index is obtained.
The optimization strategy used in OCU is based upon the gradient method. Each step of this strategy
begins with explanation to the region of the actual point to determine local gradient. For example, in case of
speed and feed variables, first an exploration step of 0.001 mm/rev of feed is made and followed by a
www.ascentgateacademy.com Copyright : Ascent Gate Academy 130
PRODUCTION
second exploration step of 10 rpm and the performance index calculated. The local gradient and the oper-
ating point is then moved a single step in the direction of this gradient and cycle of steps repeated until the
maximum value of performance index is obtained.
InACC system, the machining conditons are maximized with in the precribed limits of m/c and tool
constraints like spindle speed, max torque, max cutting force and power, maximum feed, max vibration
amplitude etc. the advantage of this system is that the cutting tool is protected against catastrophe failure
simultaneously with keeping the highest possible feed rate.
TRANSFER MACHINES
The problems faced in time to time production system are
- For increasing the production rate, it is possible with increase in speed, feed and depth of cut.Also for
quick setting we have to use jigs and fixtures.
- The problem facing in industry is handing of components during their passing from one operation to
another. For this unnecessary movements lead to operator fatigue and which in turn lowers the output
- Occupation of considerable floor space for handing or work from m/c to m/c
- Labour problems
A transfer machine is an automated machine which indexes or transfers the work piece and its fixture
from station to station while many operations are performed on it. Work pieces are loaded at one end and
are automatically transferred along with their fixtures, from station to station. At each station machining
operations are perfomed on the pieces and the completed work pieces leave at the other end. Thus transfer
machine is a combined material handing and material processing m/c.
These are basically special purpose m/cs and are often the most suitable method for continuous manu-
facture of identical or very similar parts in mass production.
The most common types of transfer machines are
i) In - line transfer machines
ii) Rotarytransfer machines
In in-line transfer machines, the machining heads are arranged in a line and the component is automati-
cally transferred from one machining station to the next one of follwing 3 methods.
- by pulling along supporting rails by means of an endless chain conveyor
- by pushing along continuous rails by air hydraulic pistons
- bymoving an overhead chain conveyor, which may lift and deposit the work at the machining stations.
The various geometric arrangements of machining deads, in in-line transfer machines are straight line, L,
U, square, Rectangular etc.
In case of jam up of components, automatic safety device operates and all m/cs come to stop. Thisis
more popular in case of automoble industry.
Rotary transfer machine is used when, only 6 to 10 or fewer machining stations need to be employed.
The table rotates about a vertical axis and its movement may be continuous or intermittent. For indexing,
Geneva type indexing mechanism is used. it is very compact and requires very less space. It is best suited for
automatic assembly of a product.Almost all the operations can be done on the transfer machine.
www.ascentgateacademy.com Copyright : Ascent Gate Academy 131
MECHANICAL ENGINEERING
Advantages of transfer machine :
- can handle very heavy components and components of extremelyawkward size and shape no manual
handling is involved expect loading and unloading
- fewer operations are needed
- considerable floor space is saved
- greater accuracy of job is achieved
- alignment of the job at each machining station is simplified and atomized
- it is flexible and can be arranged to suit modifications in the design of the components.
Disavabtages of transfer machines
- system is justifiable only for high producation rates
- initial cost is very high
- breakdown of one machine will stop all the machines
- electrically the system is very complex.
Machining center :
A machine center consists of a single, but sometimes, two m/c tools with the specific feature of an
automatic tool changer and capable of performing a no. of operations (drilling, tapping, milling, boring,
turning etc) on a work piece. Most of the m/cs are numerically controlled.
The major advantage is that the job needs clamping on the work holding surface only once, the m/c
then performs a variety of machining operations, on all the faces except the base. Work handling is mini-
mized because there is no movement of the work. Some m/cs have work tables, so that when work on one
table is undergoing., on second one the job is loaded.
Various tool magazine systems are used for storing the preset tools. These reset tools are removed
from their slots by a hand arm mechanism. When a particular machining operation is completed, the tool is
removed from the spindle and returned to its storage slot, then another tool is picked up and mounted in the
tool spindle.
Machining center is mainly used for batch production of main components of a product. The main
components of a product are usually small but are expensive because they have considerable material value
and usuallyrequire a large amount of machining. For such components, the machining center must economi-
cal.
Machining centers have high MRR capability. The high degree of accuracy and multi operation in the
same set up, make the machining centers highly versatile and increase productivity.
CAD-CAM :
- CAD deals with the modeling and details design of a part or total product.
- CAM deals with the fabrication of the part using the design data base.
- CAD-CAM means an intergrated approach to the creation of CAD data base, transfer of CAD data
base to CAM software and creation of programs to handle the work piece, machining and inspecting
a component using CAM and CMM respectively.
- CAD-CAM includes integration of three different technical and management activities like design,
manufacturing and computing.
www.ascentgateacademy.com Copyright : Ascent Gate Academy 132
PRODUCTION
Activities of CAD-CAM are
- 3-D modeling (Ideas,Ansys, proengineer, CADDS, solid works etc)
- Analysis and optimization
- 2-D drafting and drawing preparation
- Database management
- Process planning
- Tool design
- NC programming
- Inspection
From the above the major activities are modeling, analysis and NC part programming.
Application of computers in design
The various design related tasks performed by modern computers is
- geometric modeling
- engineeringanalysis
- design review and evaluation
- automated drafting
Geometric modeling is concerned to the computer compatible mathematical description of the geom-
etry of an object. The mathemataical description allows the image of an object to be displayed and manipu-
lated on a graphic terminal through signal from the CPU of the CAD system. The geometric modeling can be
done by using 3 types inputs commands, first is the generation of basic geometric elements such as points,
lines and circules. The second one is used to accomplish the scaling, rotation, or other transformations of the
elements. The third cause the various elements to be joined into desired shape of the object being created on
the ICG system. During this geometric modeling process, the computer converts the commands into a
mathematical model, stores it in the computer data files and can be reviewed and modified if it requires.
Once the modeling has been completed, the next step is the engineering analysis, it may stress-strain
analysis, heat transfer analysis, or the use of differential equations to decribe the dynamic behaviour of the
system being designed. The computer can be aid in this analysis work. The analysis can be done by using
two ways,
1. Analysis of mass properties: it provide properties of solid object being analysed, such as the surface
area, weight, volume, center of gravity, and moment of inertia.
2. FEM : it is most powerful tool in the analysis. With this technique, the object is divided into a large
number of finite elements (usually rectangular or triangular), which forms an interconnecting network of
concentrated nodes. Byusing computer with significant computational capabilities, the entireobject is analysed
for stress-strain, heat transfer, and other characteristics, by calculating the behavior of each node. By deter-
mining the correlation behavior of all the nodes, in the system, the behavior of the entire object can be
assessed.
The next step is the design review and evaluation. In this different part drawing can be assembled to get
the final assembly and check whether the assembly is possible or not, if possible what is the amount of
clearance or interference is coming etc can be checked here.And also here we can do dimensioning of the
www.ascentgateacademy.com Copyright : Ascent Gate Academy 133
MECHANICAL ENGINEERING
part correctly after checking the interfacing. But in the evaluation stage we can check the kinematics of
mechanisms and linkages.Among the different soft - wares,ADAMS is the most powerful software for this
purpose.
The last step is the automated drafting, which involve the creation of hard copy engineering drawing
directly from CAD data base.
FMS (Flexible manufacturing system)
FMS is an integrated approch to automating a production operation. The primary characteristic of an FMS
is that it is a computer controlled manufacturing system that ties together automated production machines
and materials handling equipment. The FMS is designed to be flexible so that it can fabricate a variety of
different products of relatively low volumes.
We need a flexible manufacturing system to the variety at small batch at lowest cost
Benefits of FMS
- LOW ORDER VOLUME
- Better utilization of resources
- Greater variety
- Reduction in stocks
- Shorter reaction times to market shifts
CAPP (computer aided process planing)
One the design of a comonent is over, then the next activity is process planning. It uses computer for
generating process plan for the given product. The output of CAPP is
- Bill of materials
- What machines and processes are to be used
- The sequence of operation
- Date of completion etc
It takes input as
- comonent design and drawings
- materials to used
- capacity and loading schedule of machines
- priority schedule etc
DFM (Design for manufacture)
Due to competitive market any company will try to redue the cost of producing a component, to
compete in the market. If we do the complicated design, which needs more time to manufacture, and cost
goes up. To reduce this manufacturing costs we have to reduce the complexity of design at the cost of
functioning. For example a complicated design improves efficiency of an IC engine by 1% (66KMPH
instead of 65KMPH) and if this complicated design costs about Rs. 5000 more it is absolutely waste.
So in the above context we have to design the components and assemblies with greater care to manu-
facture very easily with low cost.
The general guide lines for DFM approch are
• Take advantage of economics of scale
- design parts to be capable of being used in multiple products
www.ascentgateacademy.com Copyright : Ascent Gate Academy 134
PRODUCTION
- minimize the no. of separate part types to reduce inventory
•Aim to standardize as much as possible
- use of known capability and from known suppliers
- try to develop part families
• Use simple, low cost operations
- use established technologies as for as possible
- avoid high cost technologies unless technically essential
- choose simple, regular shapes and part assemblies
• Choice of production processes
Group techonology
GT is an operation management philosophybased on the recognition that similarities occur in the design
and manufacture of discrete parts. Similar parts can then be arranged into part families.
It uses mass production layout and technique for producing small batch production systems. GT re-
places traditional job shop manufacture bythe analysis and grouping of work into families and the formation
of groups of machines to manufacture these families on a flow line principle of minimizing setting times.
GT is a technique for identifying and bringing together related or similar components in a production
process in order to take advantage of their similarities by making use of the aim of GT is
- rduce WIP
- improve delivery performance
In GT the layout design is not according to the functional characteristics of machines, but rather by
groups of different machines called cells that are necessary for the production of families of parts.
GT based clasification and coding consists of about 10 to 20 code. The optiz system which was
designed to incorporate the encoding of design and manufacturing features has 3 elements
- 1st element consists of 5 digits which decribe the geometric form of the component
- 2nd element consists of 4 digits and known as supplementary code classifies the size, material, original
raw material form and the required accuracy of the component.
- 3rd element used to encode information of a process planning nature for example operation sequences,
required m/c tools, fixtures etc.
PART PROGRAMING
NC part programming language consists of a software package plus the special rules, conventions and
vocabulary words for using that language. it is used to communicate part geometry and tool information to
the computer, so that the designed part program can be prepared. There are more than 100 NC part
www.ascentgateacademy.com Copyright : Ascent Gate Academy 135
MECHANICAL ENGINEERING
program languages available. but many of them were specifically developed for a particular component etc.
among them some important one are
APT (automatically programmable tool) it is developed by MIT and even now it is popularly used in
USA. First it was developed as a contouring language but modern versions can be used for both positioning
and continuous path programming in upto 5 axes. The different versions are APTURN (for lathe opera-
tions),APTMIL(for milling and drilling),APTPOINT (for point to point control).
ADAPT (adaptation ofAPT) developed by IBM. The fullAPT requires a larger computer system. The
ADAPT was intended to provide many of the features ofAPT but utilizes a small computer.ADAPT is not
as powerful asAPT but can be used to program both positioning and contouring.
EXAPT (extended APT) developed in Germany based on the APT. the versions are EXAPT1 - for
positioning, EXAPT 2- for turning, EXAPT - 3 for limited contouring. The important features for EXAPT is
attempts to compute optimum feeds and speeds automatically.
UNIAPT (because it was developed by united computing corporation, USA), it uses a small; com-
puter forAPT. it is allowing many smaller shops to posses computer assisted programming capacity.
SPLIT (standard processing language internally transferred), it can handle upto five axis positioning
and processes contouring capability as well. One of the useful features of SPLIT is that the post processor
is built into the program.
COMPACT - ii :developed by MDSI (manufacturing data systems Inc.) it is similar to SPLIT in many
features
PROMPT : It is an interactive part programming language offered byWeberNC systems. It is designed
for use with a variety of machine tools, including lathes, machining centers, flame cutters and punch presses.
CINTURN - II : it is a high level language to facilitate programming of turning operations.
APT LANGUIAGE
APT is not only an NC language , it is also computer program that performs the calculations to generate
cutter positions based onAPT statements.APT is a 3D system that can be used to control up to five axes.
There are 4 types of statements in theAPT language.
- Geometry statements
- Motion statements
- Post processor statements
-Auxiliary statements
In geometry statements, the tool is subsequently directed to move to the various point locations and
along surface of work part which have been defined by these statements. The definition of work part ele-
ments must precedes the motion statements. The definition ofAPT geometry statement is
Symbol = geometry type/decriptive data
EXAMPLE : P1 = POINT / 5.0, 4.0 , 0.0
The statement is made up of 3 sections. the first is the symbol used to identify the geometric element.A
symbol can be any combination of six or fewer alphabet and numeric charcters, but at least one of the six
must be alphabetic character.
The second section of the geometry statement is an APT vocabulary word, related to geometry for
example POINT, LINE, PLANE, CIRCL;E etc.
The third section consists of descriptive data that define the geometry data as dimensional data, posi
www.ascentgateacademy.com Copyright : Ascent Gate Academy 136
PRODUCTION
tional data etc.
Generally alash separates surface type from the descriptive data. commas are used to separate the
words and numbers in decriptive data.
The point can be defined as
- P 1 = POINT/ 5.0, 4.0, 0.0 (X = 5.0, Y = 4.0, Z = 0.0)
- P2 = POINT / INTOF, L1, L2
(here L1, L2 must be previously defined and the point is an intersection of
L1 and L2 line
- the symbol must be used for defining only one geometric element
- only one symbol can be used to define any element for example
P1 = POINT / 1.0, 1.0, 1.0
P2 = POINT / 1.0, 1.0, 1.0
The above is wrong
- lines defined inAPT are considered to be of infinite length in both directions. Similarly,
planes extent indefinitely and circles defined inAPT are complete circles.
The general format of motion statement is
Motion command/decriptive data
For example GOTO/P1
Here two statements are separated by flash. The first is the basic motion command which tells the tool
what to do. The second section contains data, which tells the tool where to go.
At the beginning of motion statement, the tool must be given a starting point. This point likely to be the
target point, the location where the operator has positioned the tool at the start of the job. This is done by
FROM / TARG
The FROM is anAPT vocabularyword which indicates that this is the initial point from which others will be
referenced. in above TARG is the symbol given to starting point. The above also can be written
FROM / -2.0, 2.0, 0.0
The point to point motions can be defined in two ways
GOTO - indicates go to so and so point
GODLTA- specifies an incremental move for the tool. also useful in drilling and related operation.
For example
GOTO / P2
GODLA/0,0,-1.5
GODLATA/0,0,+0.5
In contouring motions, there are 3 types of surface used
- drive surface: Is the surface that guides the side of the cutter
- part surface: Is the surface on which bottom of cutter rides. It may not be the actual surface of the
www.ascentgateacademy.com Copyright : Ascent Gate Academy 137
MECHANICAL ENGINEERING
work part.
- Check surface : Is the surface that stops the movement of the tool in current direction. That is it checks
the forward movement of the tool
The part programmer must define the drive surface and part surface for the purpose of maintaining continu-
ous path control of the tool.
The check surface can be defined by 4 words called, TO, ON, PAST, TANTO
The other motion commands are
GOLFT, GOFRD, GOUP, GORGT, GOBACK, GODOWN
We must have to define motion command after check surface.
For example
FROM/TARG
GO/TO, PL1, PL2, TO PL3
The Go command instructs the tool to move the intersection of the drive surface (PL1), the part surface
(PL2), and the check surface (PL3). The periphery of the cutter is tangent to PL1 and PL3 and the bottom
of cutter is touching PL2. in GO statement we have to maintain same order, that is drive, part, check surface
respectively.
GOTO - used in PTP
GO/TO - initialize the sequence of contouring motions
The post processor statements are those which indicate the control of the operation of the spindle, feed and
other feacture of m/c tool. the commonly used postprocessor statements are
COOLNT/
RAPID
END
SPINDLE/
FEDRAT/
www.ascentgateacademy.com Copyright : Ascent Gate Academy 138
PRODUCTION
TURRET/
MACHIN/
Statements without slash are self contained and no other data is required. But with slash statements require
further data
The auxiliary statements are used for cutter size definition, part identification etc. the words used are
CLPRNT
INTOL/
CUTTER
OUTTOL/
FINI
PARTNO
THE MACRO STATEMENT IN APT
The MACRO feature is similar to a subroutine in FORTRAN and other computer languages. This is gener-
allyused when certain motion sequences are to be repeated several times within a program. So with MACRO
we can reduce the size of program drastically. The MACRO statement is defined
as
Symbol = MACRO / parameter definition
The symbol is similar to other statements like six or less characters and at least one of the character must be
a letter of the alphabet. At the end of MACRO we can give TERMAC, so that it terminates the MACRO.
To activate the MACRO, a cell statement used as
CAll/ symbol, parameter definition.
The symbol would be the name of the MACRO that is to be called. The parameter secification identifies the
particular values of the parameters that are to used in this execution of MACRO subroutine.
DRILL = MACRO/PX
GOTO/PX
GODLTA/ 0,0,-1.0
GODLTA/ 0, 0, 1.0
TERMAC
FROM/P0
CALL/DRILL, PX = P1
CALL/DRILL, PX = P2
CALL/DRILL, PX = P3
GOTO/P0
SAME WAY FOR MILLING
MILL = MACRO/DIA
CUTTER / DIA
FROM / P0
GO/TO, L1, TO, PL1, TOL3
GORGT/L1, TANTO, CI
GORGT/L1, PAST, L2
www.ascentgateacademy.com Copyright : Ascent Gate Academy 139
MECHANICAL ENGINEERING
GOFRD/L2, PAST, L3
GOLFT/L3,PAST, L1
GOTO/P0
THE MAIN PROGRAM IS
CALL/MILL,DIA = 0.570
CALL/MILL,DIA = 0.500
APT statements
ATANGL: at angle
CALL : used in main program
CENTER : used to indicate center of circle
CIRCLE : used to define a circle
a) by co-ordinates of center and if radius
C1 = CIRCLE/CENTER, 4.0, 3.0, 0.0, RADIUS, 2.0 (or)
C1 = CIRCLE/4.0, 3.0, 0.0, 2.0
b) by center point and radius
C1 = CIRCLE/CENTER, P1, RADIUS, 2.0
c) center point and tangent to a line
C1 = CIRCLE/CENTER, P1, TANTO, L1
d) 3 points on the circumference
C1 = CIRCLE/ P!, P3, P4
e) by two intersecting lines and the radius
C2 = CIRCLE?XSMALL, L2, YSMALL, L3, RADIUS, 0.375
C3 = CIRCLE / YSMALL<L2, YSMALL, L3, RADIUS, 0.375
CLPRNT : Cutter location print (auxiliary statement) can be used to obtain a computer print out of the cutter
location sequence of the NC tape.
COOLNT : Coolant (post processor statement) for on and off the coolant
CUTTER: (AS) defines cutter dia to be used in tool offset computations, CUTTER/1.0
END : used to stop the m/c at the end of the section of the program. Can be used to change the tools
manually.
FEDRAT : (PPS) feed rate, mm/min
FINI : Finish (AS), must be the last word in APT program. Used to indicate the end of the complete
program.
FROM From tool staring loacation (motion command) used to specify starting point of cutter
GO : (motion start up command in contouring) used to bring the tool from starting point.
GO/TO, L1, TO, PL1, TO, L2
Drive surface L1, past surface PL1, check surface L2
(Or)
GO/TO/L1,TO,PL1,TO,L2
www.ascentgateacademy.com Copyright : Ascent Gate Academy 140
PRODUCTION
GODLTA: (PTPmotion), instructs the tool to move in increments as specified from the current tool loaction.
Ex: GODLTA/2.0,3.0,-4.0
Say the tool to move 2.0 in x-direction, 3.0 in y-direction and -4.0 in z-direction from the present
position
GOBACK contour motion comman) intructs the tool to move back relative to its previous direction of
movement.
Ex: GOBACK/P15, TO L1
It moves the drive surface PL5 until it reaches L1.
Same way
GODOWN
GOFRD
GOLFT
GORGT
GOUP
GOTO: PTP command, ex GOTO/P1 (or) GOTO/2.0,5.0,0.0
INTOF: intersection of (decriptive data)
INTOL: inside tolerance (AS)
Ex. Intol/0.005
LEFT : left
LINE (GS)
a. by co-ordinates of two points
L1 = LINE/2, 0,5,3,0
b. by two points
L1 = LINE/P1, P2
c. by point and tangent to a circle
L1/LINE/P1,LEFT,TANTO,C!
L2+LINE/P1,RIGHT,TANTO,C1
d. by point and angle of the line to the x-axis or another line
L3 = LINE?P1, LEFT, ATANGL, 20
L4 = LINE/P1, LEFT, ATANGL,30,L3
e. by appoint and parallel to or perpendicular to another
L5 = LINE/P2, PARLEL, L3
L6 = LINE/P2, PERPTO, L3
f. by being tangent to two circles
L7 = LINE/LEFT, TANTO, C3, LEFT, TANTO, C4
L8 = LINE/LEFT, TANTO, C3, RIGHT, TANTO, C4
L9 = LINE/RIGHT, TANTO, C3, LEFT, TANTO,C4
L10 = LINE/RIGHT, TANTO, C3, RIGHT, TANTO, C4
www.ascentgateacademy.com Copyright : Ascent Gate Academy 141
MECHANICAL ENGINEERING
MACHIN: (PPS), used to secify the m/c tool and to call post processor for that m/c tool
for ex: MACHINE/MILL,1
Machine is mill, I is the particular machine and post processor
MACRO : is subroutine
ON : used motion modifier word
OUTTOL : Outside tolerance
Ex. OUTTOL/0.0025, INTOL/0.0025
PARLEL: Used to determine line parallel to the other to
PARNO: (AS) 1 to 6 number commonly
PAST : As seen earlier
PERPTO: Perpendicular to, it is line statement
PLANE : To define a plane
a. 3 point that to not lie on the same straight line
PL1 = PLANE/P1,P2,P3
b. point and being parallet to another plane
PL2 = PLANE/P4, PARLEL, PL1
c. two point and being perpendicular to another plane
PL3 = PLANE / PERPTO, PL1, P5, P6
POINT :
a. can be defined using x, y and z coordinates
P1 = POINT/3.0,1.5,0.0
b. intersection of two line
P1 = POINT ? L1, L2
c. intersection of a line and a circle
www.ascentgateacademy.com Copyright : Ascent Gate Academy 142
PRODUCTION
P2 = POINT / YLARGE, INTOF, L3, C1
d. by two intersection circles
P4 = POINT / YLARGE, INTOF, C1, C2
P5 = POINT / YSMALL, INTOF C1, C2
e. Center of a circle
P6 = POINT / CENTER, C1
RADIUS
RIGHT
TANTO
TERMAC: Termination of MACRO.
TO:
TURRET: (PPS) used to specify a turret position on a turret tathe
XLARGE: In the +ve direction, used to indicate relative position of one geometric element w.r.t. another
when there are two alternatives
XSMALL
YLARGE
YSMALL
PART PROGARMING
The generally used codes in the part program are
G00 - rapid traverse
G01 - linear interpolation
G02 - clockwise circular interpolation
G03 - CCW circular interpolation
G04 - dwell
G05 - hold
G09 - speed reduction exact stop
G17 XY plane selection
G18 - YZ
G19 - ZX
G33 - thread cutting constant lead
G34 - thread cutting with increasing lead
G35 - thread cutting with decreasing lead
G63 - tapping
G90 absolute progamming
G91 - incremental programming
M00 - program stop
M01 - planned stop
M02 - end of program
M03 - CW spindle rotaion
M04 - CCW spindle rotation
M05 - spindle off
www.ascentgateacademy.com Copyright : Ascent Gate Academy 143
MECHANICAL ENGINEERING
M06 - tool change
M07, 08 - coolant on
M09 - coolant off
M10 - clamp
M11 - unclamp
M17 - end of sub program
M30 - end of main program
I - interpolation parameter for X - axes (0.001 to 99999.9999)
J - interpolation parameter for Y - axes (0.001 to 99999.9999)
K - interpolation parameter for Z - axes (0.001 to 99999.9999)
L - Subroutine number
H - auxiliaryfunction
P - number of subroutine passes
****************************************
“Success is simple. Do what’s right, the right way,
at the right time”
www.ascentgateacademy.com Copyright : Ascent Gate Academy 144
PRODUCTION
9 LIMITS FITS & TOLERANCES
LIMTS : The variation permitted on given dimension is called limit.
TOLERANCE : The total variation permitted on given dimension is called Tolerance.
* Manufacturing of components to the exact dimension is difficult & costly. So, the variation on the given
dimension is permitted.
Reasons for difficulty in manufacturing of component of exact dimension :-
i) The Machine errors present on the machine tool will be transferred to the components. So, it is difficult to
manufacture components to exact dimension.
ii) Man : During maching of components manually, it is difficult to set the process parameters exactly.
iii) Material : During maching of soft w/c pcs, even though given layer of material is removed but the imme-
diate vicinity layer will try to come along with the removing layer and produces loose structure.
functionality
cost
>
Tolerance functionality
cost
>
During design & manufacturing of components, it is always aimed that the assenbly should have a
highest functionality & cost of manufacturing should be lowest. It is impossible to manufacture the compo-
nents with highest functionality & lowest cost. So, we have to make a compromise between cost & function-
ality. Wherever the functionality is more important, it is preferable to provide the smallest amount of toler-
ance.
Eg. : Piston & cylinder of a high capacity hydaulic press.
Wherever the cost is much important & functionality will not change much due to change in toler-
ance, large amount of tolerances can be selected. Wherever both are important, it is preferable to select the
medium amount of tolerance.
Eg. : Piston cycle of I.C. Engine.
Type of Tolerances :
i) Unilateral tolerances
ii) Bilateral tolerances
www.ascentgateacademy.com Copyright : Ascent Gate Academy 145
MECHANICAL ENGINEERING
i) Unilateral : If total variation is permitted on onlyone side of given dimension, it is called unilateral tolerance.
Eg. : +0.08 +0.06 +0.00 -0.02
50+0.00 50+0.02 50-0.05 50-0.10
50.00 to 50.08 50.02 to 50.06 49.95 to 50.00 49.9 to 49.98
It can be provided either on the mating parts or on non mating parts but preferabley on mating parts
. If the part is moving inside the other part, it is called as mating assembly, the party in the assemblyare called
mating parts.
Eg. : Piston cycle of ICE, shaft in a journal bearing etc.
ii) Bilateral : If total variation is permitted on both sides of given dimension, it is called as Bilateral tolerance.
Eg. : 50 + 0.05 , +0.02 +0.08
50 - 0.06 , 50 - 0.03 ,
It is provided only on non mating parts.
Tolerance Accumulation
If a component has more than one dimension or an assumbly has more than one component, the
total tolerance on the component or assembly = sum of the individual tolerances. It is called as tolerance
accumulation. Because of tolerance accumulation, the overall component dimensions are getting increasing
or decreasing by large. So, it is not preferable to have the tolerance accumulation.
Tolerance accumulation can be eleminated by progressive dimensioning of the components.
If each & every component dimension & it’s tolerance is specified with referance to only one single
reference plane or point, it is called as progressive dimensioning.
Compound Tolerances
It a component has more than one dimension so that one of the dimensions on it’s limits & tolerances
depends on other dimension & tolerances of the same component.
FITS
The relationship between two components i.e. hole & shaft during the assembly is called as FIT.
Types of Fits :
1) Clearance fit : Dimensions of hole & shaft are such that the clearance or gap is always present during the
assembly.
Eg. : Mating assemblies like piston & cycle of ICE, shaft in journal bearing etc.
www.ascentgateacademy.com Copyright : Ascent Gate Academy 146
PRODUCTION
<< >
<< >
<< >
<< >
XXXXXXXXXX XXXXXXXXXX
L Shaft
Hole L - H -
H. Shaft Shaft hole hole
-0.02 + 0.06
30 - 0.08 30 + 0.00
Hshaft < L - Hole (for producing clearnace fit)
Maximum clearance = H . hole - L. shaft
= different between minimum material limit
Minimum clearance = L . hole - H. shaft
= different between maximum material limit
2) Interference fit :
Dimensions of hole & shaft are such that without interference of external agency, it is not possible to
assemble hone & shaft.
Eg. : Shaft = 70.05 L shaft < H hole
hole = 70.00
Maximum interference = H . hole - L. shaft
= difference of maximum material limit
Minimum interference = L . shaft - H hole
= difference of minimum material limit
3) Transition fit : The dimensions of hole & shaft are such that sometimes the clearance fit is produced &
sometimes interference fit is produced, such a fit is called transition fit.
www.ascentgateacademy.com Copyright : Ascent Gate Academy 147
MECHANICAL ENGINEERING
If H limit of one of the comp. is lying in between H & L limit of other components, it produces
transition fit.
Allowance = different between maximum material limits of the comp.
Allowance = minimum clearance (in case of clearance fit) &
Allowance = maximum interference (in case of interference fits)
Eg. :
i) Hole = 50 + 0.05
-0.07 Clearance fit
Shaft = 50 - 0.11
Maximum clerance = 50.05 - 49.89 = 0.16
Minimum clearance = 49.95 - 49.93 = 0.02
ii)
+0.03 Transition
Hole = 80 - 0.06
+0.10
Shaft = 80 - 0.04
Allowance = 80.40 - 79.94
= 0.16
System of limits, fits & tolerances
Standard method of designating the hole shaft pair is called system of limits, fits & tolerances.
Nomal size : Size detected based on the design considerations of the component.
Basic size : Near to the nomial size which is rounded off to the full dimension and based on which limits &
tolerances can be specified.
Deviation : Difference between limit of a component and basic size is called Deviation.
Difference between upper limt & basic size is called upper deviation, difference between lower limit
& basic size is called lower deviation.
Fundamental deviation : Upper or lower deviation which is fixed & conveniently chosen for specifying the
limits, fits & tolerances.
Hole based system : If the hole is made first approximately near to the required dimension, the shaft can be
made slowly such that it can be assembled into the hole according to the required assembly conditions. { If
we use Hole “H” it is hole based system}.
www.ascentgateacademy.com Copyright : Ascent Gate Academy 148
PRODUCTION
Shaft based system : Shaft “h” is called shaft based system.
Hole based system is most commonlyused system because reducing the dia. of shaft slowly is easier
when compared to the enlarging the hole slowly, because it needs many number of reamers.
Indian system of Limits, Fits & Tolerances
Holes : Capital letteres
Shafts : Small letters
25 fundamental deviation holes & shafts
18 grades of tolerances
Holes : A, B, C, D, E, F, G, H , J, Js, K................. ZA, ZB, ZC
Shafts : a, b, c, d, e, f, g, h, j, js, k.......................... za, zb, zc.
18 grades of tolerances :
I to 1, I to 0, I T 1, I T 2, I T 3 ............................... I T 16
Hole A : A to 1, A 0, A 1, A 2, A 3 .......................... A 16
Shaft D : D01, D0, D1, D2, D3 ..............................D 16
No. of holes = 18 x 25 = 450
No. of shaft = 18 x 25 = 450
No. of assemblies produces = 450
Even though holes & shafts have been standardised but many varieties of assembling can be pro-
duced.
www.ascentgateacademy.com Copyright : Ascent Gate Academy 149
MECHANICAL ENGINEERING
Holes : Ato H - Unilateral tolerance
J & Js - Bilateral tolerance
K to Zc Unilateral tolerance
Only J & Js are bilateral tolerance components all other things are unilateral tolerance components.
The limit of a component shown with straight line is considered as a fixed limit. The limit shown with
variable line, the limit is getting varying as the grade of tolerances vary.
> tolerence
<< > tol. A 02 A 10
< < >< >
H
(L
(
<< >
< < >< >
(
(
Types of Assemblies
i) Make to suit assembly :
If one of the component is made approximately near to the required dimension, the other compoent
is made slowly such that it can be assembled on to the existing component according to required assembly
conditions.
Advantage : No rejection, less wastage.
Disadvantage : During the usage, if one part in assembly fails, the total assembly has to be brought to the
industryfor manfucaturing.
ii) Interchangable assembly :
The parts manufactured as per the designed limit of the component, any acceptable hole can be
assembled with any acceptable shaft & during the usage if one part fails in the assembly, it can be inter-
changed by using another part manufactured under similar conditions.
iii) Selective assembly : If only selected group of components are interchangable, it is called as selective
assembly. Selelctive assembly is used when very closed tolerence of components are to be manfucatured on
a mchine which has very poor process capability.
www.ascentgateacademy.com Copyright : Ascent Gate Academy 150
The words you are searching are inside this book. To get more targeted content, please make full-text search by clicking here.
PE theory
Discover the best professional documents and content resources in AnyFlip Document Base.
Search