Many people have the misconception that the smoother the surface of the heavy gauge vacuum forming aluminum mold, the brighter the product surface formed by the aluminum mold will be. In fact, it should be better explained in this way: to maintain the molding effect of the plastic aluminum mold, mold surface should have appropriate smoothness.
The plastic-aluminum mold maintains a certain temperature, and the surface of the plastic-aluminum mold also needs appropriate roughness. If the surface of thermoforming aluminum mold is processed into a mirror state, this will cause the result that gas can not escape from the mold and material well.
Plastic sheet will stick to the blister aluminum mold and will leave marks. It will be difficult to extract air. This will eventually lead to the formation of air accumulation. And the marks become ripples. Releasing mold is difficult. Certain roughness, in fact, will help both air relieve and mold release to some extent.
The decisive factors for the roughness of the blister aluminum mold are: the characteristics of the thermoplastic sheets and the requirements for the products transparency. The roughness is usually Ra = 0.8～1.6μm, and Ra 0.8μm is used for products with high transparency requirements.
Sandpaper polishing process can use 600 ~ 800CW oil sand or sandpaper to treat the surface of the mold. If the molded product is colored or divided, 240-320CW sandpaper can be used. If the processing roughness is selected according to the characteristics of the sheet, PVC, PS, PET parts, can use finer 600-800CW sandpaper, and PP parts can use 240-320CW sandpaper and coarser sandpaper.
The forming function of the surface roughness is to sandblast the surface of the mold. Using sandblasting process, the surface roughness of the blister aluminum mold is relatively uniform. The roughness of the blister aluminum mold should be selected according to the molding material and effect. When using sandpaper, the surface is prone to streaks (sandpaper texture), which affects the appearance of the product. If sanding, it must be parallel and in the same direction from end to end to reduce clutter in the sandpaper pattern. A good mold will be good for vacuum forming machine to operate on.