Makes possible punches with long life-spans!-An introduction to HW coating punches-What is HW coating?

In order to make possible punched products that are lighter, stronger, higher in performance, and lower in cost, there has been an increase in the use of high-tensile steel sheet as well as demanding punching with micro clearance punching, heavy-load punching and small hole punching. Because of the high stress of the load on each of these punches, the wear, breakage and chipping of punch tips have become a problem. We at MISUMI have developed HW coating punches for the purpose of meeting demanding punching conditions of this kind. Since launching these products, we have been receiving high evaluation from customers centered around the automobile industry. This is how we are contributing to the extension of punch life-spans.

Feature 1: Increased hardness of the base material (increased wear resistance)

Though TiCN coating provides superior hardness of about 3000HV, it can crack and peel when undergoing high-stress punching, as the base material experiences miniscule deformation that the high hardness coating film cannot keep up with. The hardness of the base material can be increased to about 1000HV with WPC® pre-treatment before TiCN coating (see fig. 1). Not only is the hardness of the base material increased, but also the best features of TiCN coating are brought about by making it possible to control cracking and peeling.

Fig.1 The differences between MISUMI TiCN and HW coating treatment

Feature 2: Improved fatigue strength

One cause of the breakage and chipping of punch tips is a lack of fatigue strength in the base material. HW coating makes it possible to enhance the residual compression stress of the base material surface through WPC® treatment (see fig. 2). It is difficult to achieve increased residual compression stress with any other surface improvement technology. For example, nitriding, a technology used a lot for increasing the strength of base material, can achieve residual compression stress of no more than 200-300N/mm². Because HW coating makes possible a high residual compression stress of around 1000N/mm², the fatigue strength is dramatically increased (see fig. 3) and the breakage and chipping of punch tips is brought in check.

Fig.2 Surface residual compression stress due to WPC® treatment

Feature 3: Improved seizure resistance

In the case of a punch with an ordinary polished finish, streaks in the direction of polishing are left on the surface. In contrast, WPC® treatment creates fine convex and concave surface irregularities. Because machining oil collects in these irregularities when punching, you can expect improved seizure resistance (see fig. 4).
The above features make HW coating provide punches with greater life-span. We at MISUMI will continue to focus our efforts on the development of press die standard components that meet the needs of our customers. Please direct all inquiries about our products to the contact below.

Fig.4 Surface comparison of normally polished and WPC® treated product

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