In addition to heat and lubrication of the billet prior to warm extrusion, the extrusion punch and die must be preheated. Generally preheated to 150 ~ 300 °C and then extrusion production. Mold preheating is mainly to ensure:
1. When the extrusion blank is placed into the mold, the temperature of the blank is not too fast, so as to avoid plasticity reduction and increase the deformation resistance; at the same time, the temperature difference between the surface of the blank and the center layer is prevented from being too large, so as to prevent defects of the extrusion due to non-uniformity of the deformation or Damaged mold.
2. Reduce the temperature difference between the mold and the blank, to avoid the rapid increase in the temperature of the mold surface and cause the internal temperature difference of the mold is too large to produce a large internal stress, in order to reduce the risk of mold damage in the work.
The specific method of mold preheating is to install a special resistance preheater on the mold, or use a torch or place a red iron block on the mold for preheating. The preheating temperature depends on the extrusion blank temperature.