Mold thimble material introduction

The thimble of the mold is generally made of high-speed steel, and then needs heat treatment. At present, there are many grades, commonly used SKD61, SKH51. Its hardness is 50--55 degrees. Surface hardening and nitriding treatment. There is also a kind of ordinary high-speed steel. The thimble is used in places where the requirements are not high.
The mold thimble is easy to break during the stamping process. What is the reason?
Broken needles must be too much resistance when punching, beyond the limit of the thimble endurance of the mold. First check the hardware for the deformation of the mold, and properly improve the draft angle; if there is still no improvement, the change from the mold thimble, such as increasing the thimble diameter of the mold thimble, or the mold thimble with a better material SKD61 heat treatment. And from the perspective of whether the process can be improved.
In fact, the Secretary is just a kind of thimble - only when you are doing the mold, you have to design a column that is relatively deep, and you can use it when you are not able to top it out when you are out. Needle to solve this problem ~ Among them, the cylinder in the mold and the thimble will move, and there is a small needle in the middle of the cylinder, which is called the cylinder needle, it is not moving, generally fixed on the bottom plate. The cylinders are generally more than the PL surface of the mold.