Semi Hot / Warm Forging
In semi hot/warm forging the tool parts are subjected to very high mechanical loads and intensive cooling. This leads to high degrees of wear and thermal fatigue. To avoid this use materials with good hot strength like Bohler W303 Isodisc, Bohler W60 Isobloc, or Bohler W403 VMR. When extremely good ductility is required, use Uddeholm Dievar.
Warm forging is a precision forging operation carried out at a temperature range between 550-950ºC. It is useful for forging of details with intricate shapes, with desirable grain flow, good surface finish and tighter dimensional tolerances than if hot forged. The weight of the forged piece is between 0,1-50 kg and the production rate about 10-40 pieces per minute. The contact time is about 200 ms and the mechanical loads at 600ºC are 3 to 5 times higher than in hot forging. Automatic multi-station presses with integrated cooling/lubricating systems are often used.
During the warm forging operation the tool parts are exposed to rather high temperatures, high mechanical loads and intensive cooling. As a result of this alternate heating and cooling the tool parts are subjected to high thermal fatigue. An additional factor is the degree of hot wear of the material, which depends on the surface temperatures and the mechanical stresses on the tool.
Tool material properties
The tool parts are subjected to both high mechanical stresses and high thermal stresses. For these reasons a tool steel has to be chosen which has a good temper resistance, good wear resistance, high hot yield strength, good thermal conductivity and good thermal fatigue resistance. A warm forging steel must exhibit a properties profile, which is in between the typical properties profiles for hot work and cold work steels.