The working condition of the plastic mold is different from that of the cold die. Generally, it must be operated at 150 °C-200 °C. In addition to being subjected to a certain pressure, it must also withstand the temperature influence. The same mold can have multiple failure modes, and multiple damages can occur even on the same mold. From the failure mode of the plastic mold, it is important to select plastic mold materials and heat treatment reasonably, because they are directly related to the service life of the mold. Therefore, steel for plastic molds should meet the following requirements:
(1) Heat resistance
With the advent of high-speed forming machines, plastic products are running faster. Since the molding temperature is between 200 and 350 ° C, if the plastic has poor fluidity and the forming speed is fast, the molding surface temperature of the mold portion exceeds 400 ° C in a very short time. In order to ensure the accuracy and deformation of the mold during use, the mold steel should have high heat resistance.
(2) Sufficient wear resistance
With the expansion of the use of plastic products, it is often necessary to add inorganic materials such as glass fibers in plastics to enhance plasticity. Due to the addition of additives, the fluidity of the plastic is greatly reduced, resulting in wear of the mold, so it is required to have good Wear resistance.
(3) Excellent machinability
Most plastic molding dies require a certain amount of cutting and fitter repair in addition to EDM. In order to prolong the service life of the cutting tool, the work hardening is small during the cutting process. In order to avoid the deformation of the mold and affect the accuracy, it is hoped that the residual stress can be controlled to a minimum.