3 Fundamentals of press design

438 Solid forming (Forging)
the corresponding values for cold forging. When hot forging, even lower
flow stress values can be achieved, corresponding to as little as one
fifth of the flow stress level during cold forging. Again depending on
the material used, in warm forging and hot forging respectively forgeability
is two or six times higher than that in cold forging. In the higher
temperature range from around 700 °C upwards, the increase in scale
formation which has a detrimental effect on dimensional accuracy and
surface quality of the parts must be taken into account. The temperature
required for warm forging must be carefully selected as in its “lower
range” it is limited by the size of the press force and the achievable
degree of deformation and in its “upper range” by scale formation.
Table 6.1.1 provides a comparison of the advantages of all three
methods on the basis of processing engineering criteria. The weight
of the components produced using hot forging ranges between
0.05 and 1,500 kg, in warm and cold forging between 0.001 and 50 kg.
Dimensional accuracy and surface quality decrease with increasing
scale layer
μm
80
60
40
20
0
fracture strain ϕ B
5
4
3
2
1
0
flow stress k f
N
mm 2
1500
1000
500
0
0
X8CrNiTi1810
C60
X10Cr13
C15
.
ϕ=0,7
Ck45
.
ϕ = 90s-1
16MnCr5
.
ϕ=70s
42 MnV7
15 min
200 400 600 800 1000 1200
[°C]
forming temperature
Fig. 6.1.5 Flow stress, scale formation and achievable degree of deformation (forgeability) in
function of temperature
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
-1
C60
Ck 15
5 min