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Upsetting,upset forging
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
Introduction
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
Engine valve
Introduction
1 initial blank
2 pre-form
3 final heading
Limits: material and geometry
Limits - material
Material’s formability
Equivalent logarithmic strain 𝜑 = 𝑙𝑛ℎ0
ℎ1= 2𝑙𝑛
𝑑1
𝑑0
Permissible deformation for some materials
Limits - material
Material 𝝋𝒎𝒂𝒙
Al 99.88 2.5
Al MgSil 1.5 – 2.0
CuZn 37 1.2 – 1.4
St 42–St 50 1.3 – 1.5
34 CrMo 4 0.8 – 0.9
42 CrMo 4 0.7 – 0.8
Upsetting ratio
Limits - geometry
s =ℎ0𝑑0
h0 stock’s free length
d0 initial diameter
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
Limits - geometry
s =ℎ0ℎ𝑑𝑑0
< 2
h0hd stock’s free length
d0 initial diameter
Maximum upsetting ratio – forming in one step
s =ℎ0ℎ𝑑𝑑0
< 4.5
h0hd stock’s free length
d0 initial diameter
Maximum upsetting ratio – forming in two steps
Preforming
forming in two steps
Calculations
Upsetting force
F upsetting force
A1 surface after upset forging
Kstr1 flow stress at the end of upsetting
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
𝜑 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
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
Tolerances are approximately five times higer.
Cold upsetting
Hot upsetting
Defects
Defect Cause Solution
Buckling
Upsetting ratio s
too high
Reduce s by pre-
forming
Longitudinal crack in
the head Die scars or surface
damage in
the starting material.
Check the stock for
surface damage.
Shear cracks in the
head
Deformability
exceeded
Reduce degree of
deformation
Divide forming into two
operations.Internal cracks in the
head