Causes and Elimination of Pockmarks on Stamped Parts
Pocking is a common stamping defect on stamped parts, which is a small concave-convex pits on the surface of the parts, which are of different sizes, usually distributed in a certain pattern, resulting in surface roughness and significantly reducing the surface finish of the stamped parts. Pockmarking on stamped parts is a very common problem, it is especially obvious that after stainless steel sheet/coil is punch and bend, a large number of pokmarks are presented on the surface of stamped parts.
The causes of pockmarks on stamped parts may be divided into two categories, one is caused by lubricant, the other is caused by deformation of the formed parts.
1. Poor Punching Lubrication. Punching lubricants are essential for ensuring punch durability, reducing friction and thermal stress, removing chips and other functions. Improper choice or maintenance of lubricant will cause pock marks on the surface of the stamped parts. Insufficient punch lubrication or improper lubrication will result in increased friction and heat generated between the punch and the punched part, which can cause oxidation or other material changes on the punch surface, resulting in small pits and pockmarks on the surface of the punched parts.
2. Forming Deformation. Poor die design, improper die heat treatment, the thin area of the material is too large or a sharp inner corner will cause plastic deformation at the forming position, resulting in unevenness on the surface of the stamped parts.
To eliminate the pockmarks on stamped parts, there are two major steps that must be focused on:
1. Improve Punching Lubrication. First, we must choose the lubricants with better performance, that is, the lubricants with higher corrosion resistance, pressure resistance and oxidation resistance. Second, ensure sufficient punch lubrication. A good lubricating effect is maintained at the punch sliding direction of the punch, and the lubricating material is not leaking in the punching process to prevent the lubricant from binding into the punched part.
2. Reasonable Design. Reasonable design of the die itself must be carried out, such as reasonable design of the shape, size of the parts, smooth transition fillet, reasonable selection of punch and die materiel, proper optimization and reduction of the structure size and die parts should be adopted. and sufficient strength and stiffness of Die should be ensured by reasonable selection and design of technical parameters and heat treatment.
In conclusion, pockmarks on stamped parts are mainly a combined result of poor lubricants and poor design. To eliminate the pockmarks on stamped parts, therefore, we must not only improve the lubrication of punhcing parts, but also optimize the design of the die itself.
