DJJ 1043 WORKSHOP TECHNOLOGY CHAPTER 7: Welding Nama Penulis e-Book: 1. Sharudin B. Hassan 2. Sarimah Bt. Atan 3. Mohd Helmi B. Salleh 4. Akmal B. Ismail. 5. Khairul Anuar Shah B. Hassan 6. Azlan Shah B. Katiman
Learning Outcome Upon completion of this chapter, students should be able to:- Explain Gas Metal Arc Welding (GMAW) Explain Gas Tungsten Arc Welding (GTAW) Distinguish defect & distortion in Welding
Learning Outcome Upon completion of this chapter, students should be able to:- Explain Gas Metal Arc Welding (GMAW) Explain Gas Tungsten Arc Welding (GTAW) Distinguish defect & distortion in Welding
Gas Metal Arc Welding (GMAW)
Gas Metal Arc Welding (GMAW) • An arc welding process that uses an arc between a continuous filler metal electrode and the weld pool to produce a fusion (melting) together of the base metal • The process is used with a shielding gas supplied from an external source without pressure.
Gas Metal Arc Welding (GMAW) ALSO KNOWN AS: • Wire Feed • MIG = Metal Inert Gas – Inert Gas= Inactive gas that does not combine chemically with base or filler metal • MAG= Metal Active Gas – Active Gas= Gas will combine chemically with base or filler metal
Gas Metal Arc Welding (GMAW) GMAW Safety • Cover all skin to prevent Radiation burns • Cover hair to prevent sparks setting hair on fire • Wear ear plugs to protect from noise and burning ear drums with sparks • Use a 14 shade welding helmet to protect eyes • Wear safety glasses at all times • Make sure pants pockets are empty
Gas Metal Arc Welding (GMAW) GMAW Equipment • Power Supply – Direct Current Electrode Positive (DCEP) • (Electrons flow from – to +) • Wire Feeder – Electrical mechanical device that feed required amount of filler material at a constant rate of speed
Gas Metal Arc Welding (GMAW) GMAW Equipment • Welding filler electrode Small diameter consumable electrode that is supplied to the welding gun by the roller drive system • Shielding Gas Gas used to protect the molten metal from atmospheric contamination 75%Argon (inert gas) & 25% Carbon Dioxide most common gas used for GMAW
Gas Metal Arc Welding (GMAW) Principle of GMAW Process
Gas Metal Arc Welding (GMAW) GMAW Set Up • Plug ground wire into (Neg) Terminal • Plug Wire Feeder into (Pos) Terminal • Select CV-Wire mode • Hot start is not used • Set Arc Control to “-5” – -10= soft arc (for use with inert gases) – +10= crisp arc (for use with CO2 )
Gas Metal Arc Welding (GMAW) Min. Arc Control • Soft Arc • Thicker Materials • Deeper Penetration • More Fluid Weld Pool • Flatter / Smoother Weld • Reduce Spatter • Stainless Steels Max Arc Control • Crisp Arc • Thin Materials • Arc Stability On Open Gaps • Convex Weld Bead • Increased Spatter • Colder Arc • Improved Weld Pool Control
Gas Metal Arc Welding (GMAW) GMAW Set Up • Set Volts – See Chart for proper setting • Set Wire Speed – See Chart for proper setting – Increase wire speed = Increase amps – Decrease wire speed = Decrease amps • Set gas flow – See Chart for proper setting – Pull trigger to get gas flowing then adjust regulator
Gas Metal Arc Welding (GMAW) RUNNING A BEAD Hold tip 1/16” to 1/8” from work piece Angle of tip should be 10-15° Can push or pull bead • Pull (preferred) • More stable arc • Less Spatter • Deeper penetration • Push • More spatter • Less penetration • Good cleaning action
Gas Metal Arc Welding (GMAW) BEAD FORMATION
Gas Metal Arc Welding (GMAW) GMAW Process Parameters Steel Material .035” wire Short-Arc Mode Thickness Gas 75%AR25%CO2 Amps Wire Speed Volts 1/8” 18-19 140-150 280-300 23-24 3/16” 18-19 160-170 320-340 24-25 1/4” 21-22 180-190 360-380 24-25 5/16” 21-22 200-210 400-420 25-26 3/8” 23-24 220-250 420-520 26-27
Gas Metal Arc Welding (GMAW) ADVANTAGE DISADVANTAGE Not required the high degree of operator skill Welding equipment is more complex & more costly Continuous welding at higher speeds and in all position Mechanical properties of the joint may be affected due to high cooling rate Thick & thin, both type of workpieces can weld effectively Difficult to weld in small corners Process can be easily mechanized Process variable are more No flux: more visibility, cleanliness
Learning Outcome Upon completion of this chapter, students should be able to:- Explain Gas Metal Arc Welding (GMAW) Explain Gas Tungsten Arc Welding (GTAW) Distinguish defect & distortion in Welding
Gas Tungsten Arc Welding (GTAW) ► What is GTAW? Gas Tungsten Arc Welding ► Also referred to as TIG Tungsten Inert Gas ► In TIG welding, a tungsten electrode heats the metal you are welding and gas (most typically Argon) protects the weld from airborne contaminants
Gas Tungsten Arc Welding (GTAW) ► TIG welding uses a non-consumable tungsten ► Filler metal, when required, is added by hand ► Shielding gas protects the weld and tungsten
Gas Tungsten Arc Welding (GTAW) Electric shock can kill. – Always wear dry insulating gloves – Insulate yourself from work and ground – Do not touch live electrical parts – Keep all panels and covers securely in place Fumes and gases can be hazardous to your health. – Keep your head out of the fumes – Ventilate area, or use breathing device SAFETY PRECAUTION
Gas Tungsten Arc Welding (GTAW) SAFETY PRECAUTION Welding can cause fire or explosion. – Do not weld near flammable material – Watch for fire; keep extinguisher nearby – Do not locate unit over combustible surfaces – Do not weld on closed containers Arc rays can burn eyes and skin; Noise can damage hearing. – Wear welding helmet with correct shade of filter – Wear correct eye, ear, and body protection
Gas Tungsten Arc Welding (GTAW) SAFETY PRECAUTION • Hot parts can cause injury. – Allow cooling period before touching welded metal – Wear protective gloves and clothing • Magnetic fields from high currents can affect pacemaker operation. • Flying metal can injure eyes. – Welding, chipping, wire brushing, and grinding cause sparks and flying metal; wear approved safety glasses with side shields
Gas Tungsten Arc Welding (GTAW) EQUIPMENT Welding power source Tungsten electrode Filler metal Welding torch High frequency unit suppressor & cable Inert gas cylinder Pressure regulator Cooling water supply Water & gas solenoid valve
Gas Tungsten Arc Welding (GTAW) EQUIPMENT
Gas Tungsten Arc Welding (GTAW) EQUIPMENT
Gas Tungsten Arc Welding (GTAW) EQUIPMENT
Technique for basic (GTAW) Arc Length • Arc length normally one electrode diameter, when AC welding with a balled end electrode • When DC welding with a pointed electrode, arc length may be much less than electrode diameter
Technique for basic (GTAW) Gas Cup Size • Inside diameter of gas cup should be at least three times the tungsten diameter to provide adequate shielding gas coverage • Picture on right shows example of gas cup size and torch position 1-Workpiece, 2-Work clamp, 3-Torch, 4-Filler rod, 5-Gas cup, 6-Tungsten electrode
Technique for basic (GTAW) Electrode Extension • Refers to distance the tungsten extends out beyond the gas cup • May vary from flush with the gas cup to no more than the inside diameter of the gas cup • Longer the extension, the more likely it may contact something by accident • General rule would be to start with an extension of one electrode diameter
Technique for basic (GTAW) Manual Torch Movement
Technique for basic (GTAW) Butt Weld and Stringer Bead • Be sure to center weld pool on adjoining edges • When finishing a butt weld, torch angle may be decreased to aid in filling the crater Torch and rod position for welding the butt weld and stringer bead
Technique for basic (GTAW) Lap Joint • Pool is formed so that the edge of the overlapping piece and the flat surface of the second piece flow together • Torch angle is important because the edge will become molten before the flat surface • Enough filler metal must be added to fill the joint as illustrated on the right Torch and rod position for welding the lap joint
Technique for basic (GTAW) T-Joint • Edge will heat up and melt sooner • Torch angle illustrated will direct more heat onto the flat surface • Electrode may need to be extended further beyond the cup in order to hold a short arc Torch and rod position for welding the T-joint
Technique for basic (GTAW) Corner Joint • Both edges of the adjoining pieces should be melted and the pool kept on the joint centerline • Sufficient filler metal is necessary to create a convex bead as shown Torch and rod position for welding the corner joint
(GTAW) Shield Gases • Argon • Helium • Argon/Helium Mixtures
(GTAW) Shield Gases Argon ► Good arc starting ► Good cleaning action ► Good arc stability ► Focused arc cone ► Lower arc voltages ► 10-30 CFH flow rates Helium ► Faster travel speeds ► Increased penetration ► Difficult arc starting ► Less cleaning action ► Less low amp stability ► Flared arc cone ► Higher arc voltages ► Higher flow rates (2x) ► Higher cost than argon
(GTAW) Shield Gases Argon/Helium Mixtures ► Improved travel speeds over pure argon ► Improved penetration over pure argon ► Cleaning properties closer to pure argon ► Improved arc starting over pure helium ► Improved arc stability over pure helium ► Arc cone shape more focused than pure helium ► Arc voltages between pure argon and pure helium ► Higher flow rates than pure argon ► Costs higher than pure argon
(GTAW) Parameter Aluminum weld parameters
Tungsten Electrode Selection Guide to selecting a tungsten electrode based on amperage range
POLARITIES DCSP (Direct Current Straight Polarity) Tungsten electrode (-ve), work (+ve) used for mild steel, stainless steel, copper & titanium. DCRP (Direct Current Reverse Polarity) Tungsten electrode (+ve), work (-ve) used for welding aluminium and heavy oxidized aluminium castings. ACHF (Alternating Current High Frequency) it is used for Al and Mg. High frequency also helps in oxide cleaning action. Gas Tungsten Arc Welding (GTAW)
Gas Tungsten Arc Welding (GTAW) ADVANTAGE DISADVANTAGE Welds more metals and metal alloys than any other process Lower filler metal deposition rates High quality and precision Good hand-eye coordination a required skill No sparks or spatter Brighter UV rays than other processes No flux or slag Slower travel speeds than other processes No smoke or fumes Equipment costs tend to be higher than other processes
Learning Outcome Upon completion of this chapter, students should be able to:- Explain Gas Metal Arc Welding (GMAW) Explain Gas Tungsten Arc Welding (GTAW) Distinguish defect & distortion in Welding
Defect & Distortion in Welding WELD DEFECT
Defect & Distortion in Welding WELD DEFECT According to the American Society of Mechanical Engineers (ASME) welding defect causes are broken down into the following percentages: 41% poor process conditions, 32% operator error, 12% wrong technique, 10% incorrect consumables, and 5% bad weld grooves.
Defect & Distortion in Welding WELD DEFECT Crater crack Crater cracks occur when a crater is not filled before the arc is broken This causes the outer edges of the crater to cool more quickly than the crater, which creates sufficient stresses to form a crack
Defect & Distortion in Welding WELD DEFECT Hat crack Hat cracks get their name from the shape of the cross-section of the weld, because the weld flares out at the face of the weld The crack starts at the fusion line and extends up through the weld.
Defect & Distortion in Welding WELD DEFECT Hot cracking Hot cracking, also known as solidification cracking, can occur with all metals, and happens in the fusion zone of a weld To diminish the probability of this type of cracking, excess material restraint should be avoided, and a proper filler material should be utilized
Defect & Distortion in Welding WELD DEFECT Underbead crack An underbead crack, also known as a heat-affected zone (HAZ) crack,is a crack that forms a short distance away from the fusion line; it occurs in low alloy and high alloy steel The other factor that affects this type of crack is internal stresses resulting from: unequal contraction between the base metal and the weld metal.
WIRE BURNBACK Possible Causes Corrective Actions * Drive Rolls in Poor Condition *Tighten, Clean, or Replace Drive Rolls * Excessive Welding Voltage * Reduce Voltage * Insufficient Electrical Stickout * Increase Contact Tip to Work Piece Distance * Contact Tip in Poor Condition * Clean or Replace Contact tip * Spatter on Contact Tip * Remove Spatter Defect & Distortion in Welding