Upsetting, upset forging - Budapest University of ...

Upsetting,
upset forging

Introduction

Definition:
Upset forging is a bulk forming process where the effect
of the pressure is on the longitudinal axis of the workpiece.

Application:
Production of mass-produced parts :
screws, rivets, head bolts, valves etc.

Introduction

Production

0 shear off stock
1 pre-form head
2 finish head
3 reduce shank to diameter

for thread rolling
4 stamp out hexagon
5 chamfer shank (round off)
6 thread rolling

Introduction

Engine valve

1 initial blank
2 pre-form
3 final heading

Limits - material

Limits: material and geometry

Material’s formability

Equivalent logarithmic strain = ℎ0 = 2 1
ℎ1 0

Limits - material

Permissible deformation for some materials

Material
Al 99.88
Al MgSil 2.5
CuZn 37 1.5 – 2.0
St 42–St 50 1.2 – 1.4
34 CrMo 4 1.3 – 1.5
42 CrMo 4 0.8 – 0.9
0.7 – 0.8

Limits - geometry

a) free length of bolt not inserted in the die.
1 bottom die
2 ejector
3 stock before upset forging;

b) open-die upset forging, between parallel surfaces

buckling Upsetting ratio

s = ℎ0
0

h0 stock’s free length

d0 initial diameter

Limits - geometry

Maximum upsetting ratio – forming in one step

s = ℎ0ℎ < 2
0

h0hd stock’s free length

d0 initial diameter

Maximum upsetting ratio – forming in two steps

s = ℎ0ℎ < 4.5
0

h0hd stock’s free length

d0 initial diameter

Preforming

forming in two steps

Calculations

Upsetting force

F upsetting force

A1 surface after upset forging
Kstr1 flow stress at the end of upsetingng
µ coefficient of friction (0.1 – 0.15)

d1 diameter after upset forging
h1 height after upset forging

Calculations

Upset forging work

or

W upset forging work
V volume involved in the deformation
kstrm mean flow stress
p principal strain
ηF deformation efficiency (0.6 – 0.9)
h0 stock height
x process factor
Fm mean force
Fmax maximum force

Tooling

a) pressure plate
b) punch (snap die)
c) retaining ring (shrink fit)
d) counterpunch
e) ejector

Reinforced die

Tooling

a) shearing blade
b) shearing bottom die
c) pre-former
d) heading punch
e) bottom die / reducing die
f) reinforcement
g) ejector

1) bottom die
2) punch
3) ejector

Precision

Cold upsetting

Nominal size in mm 5 10 20 30 40 50 100
Head height tolerance in mm 0.18 0.22 0.28 0.33 0.38 0.42 0.5
Head diam. tolerance in mm 0.12 0.15 0.18 0.20 0.22 0.25 0.3

Hot upsetting

Tolerances are approximately five times higer.

Defects

Defect Cause Solution
Buckling
Upsetting ratio s Reduce s by pre-
too high forming

Longitudinal crack in Die scars or surface Check the stock for
the head damage in surface damage.
the starting material.

Shear cracks in the Deformability Reduce degree of
head exceeded deformation
Divide forming into two
Internal cracks in the operations.
head