Factors affecting the surface polish ability of injection molds
(1) Surface condition of the work piece
During the machining process, the surface layer may be damaged by heat, internal stress or other factors, and improper cutting parameters may affect the polishing effect. The surface after EDM is more difficult to grind than the surface after machining or heat treatment. Therefore, the EDM should be finished before the end of EDM, otherwise the surface will form a hardened thin layer. If the EDM is not properly selected, the depth of the heat affected layer can be up to 0.4 mm. The hardness of the hardened layer is higher than the hardness of the substrate and must be removed. Therefore, it is best to add a rough grinding process to provide a good basis for polishing.
(2) Quality of steel
High-quality steel is a prerequisite for good polishing quality, and various inclusions and pores in the steel will affect the polishing effect. In order to achieve a good polishing effect, the work piece must be marked with the surface roughness of the polishing when starting the machining. When a work piece is determined to require mirror polishing, the steel with good polishing performance must be selected and heat treated. High polishing steel such as P20HH, NAK 80 and S136 steel. the S136 steel is a stainless mold steel with excellent polishing ability, it is sidely used for the high quality and mirror polishing project.
(3) Heat treatment process
If the heat treatment is not proper, the surface hardness of the steel is uneven or the characteristics are different, which may cause difficulty in polishing.
(4) Polishing technology
Since polishing is mainly done manually, human skills are still the main reason for the quality of polishing.
It is generally believed that the polishing technique affects the surface roughness. In fact, the good polishing technology is matched with the high-quality steel and the correct heat treatment process to obtain a satisfactory polishing effect. Conversely, the polishing technique is not good, even if the steel is good, the mirror effect is not achieved.