Introduct material selection and heat treatment of cold punch

- Sep 12, 2017 -

Force analysis of cold punch

The cold punch should mainly consider the strength, toughness and wear resistance of steel.

The common cold punch can be divided into three kinds, namely, cold heading punch blanking punch and cold extrusion punch according to the operating conditions.

Blanking punch is largely driven by smaller impact load and the heavier friction. The premature failure mode is wear, Improving the strength and abrasion resistance should to be considered in particular when choose material and heat treatment.

Cold heading punch is mainly by the large impacted load and strong friction. The premature failure mode is fracture.
Improving toughness should to be considered in particular when choose material and heat treatment, at the same time, improve the wear resistance in binding surface. 

Cold extrusion punch was very main compression load and friction. The premature failure mode is fracture crushing and wear. Improving yield strength should to be considered in particular when choose material and heat treatment, at the same time, improve the wear resistance in binding surface. 

Cold punch material selection and heat treatment case

Cold heading punch

A customer product bicycle parts using cold heading die, the original SKH51 material through 1180 ℃ quenching, 560 ℃ tempering hardness up to 63 HRC, service life is only a few thousand times, failure mode is the fracture.

Analysis: because the main material toughness is not enough, then changed to DC53 with better toughness through 1030 ℃ quenching, 530 ℃ tempering, the hardness is HRC 61. Considering that DC53 wear-resisting than SKH51 abrasion resistance, so PVD coating treatment on surface, service life increased to 200000 times.

Cold extrusion punch

A customer manufacturing automotive parts use of cold extrusion die, the punch diameter is φ38, the original material is SKH51 through 1180 ℃ quenching, 560 ℃ tempering, and hardness is up to 62 HRC. When test die pressuring only once, short 2 mm, outside diameter also coarsen. After fine grinding, the punch is broken only use 1000 times.

Calculated, the punch to withstand the pressure up to 2600 mpa, when working, close to SKH51 compressive yield strength, coupled with the punch coarser, due to uneven material or heat treatment volume effect, it is difficult to achieve internal and external uniform, lead to punch the compressive strength is lower than the theoretical value. After using HAP40 material with higher strength and better uniformity, through 1180 ℃ quenching, 560 ℃ tempering, hardness reaches 66.5 HRC, service life is increased to more than 200 million times.


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