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