Polishing can be roughly divided into 3 categories, rough polishing, semi-finishing polishing, and fine polishing.
Rough polishing
The surface after turning, grinding, NC, spark machine, wire cutting and other processes is generally rough, and needs to be polished with oilstone, using kerosene as a lubricant. The general order of use: #180~#240~#320~#400~#600~#800~#1000. Oilstone polishing method, this operation is the most important and difficult operation. According to the different specifications of the processed products, cross-grinding is performed at an angle of about 70 degrees. The ideal round-trip range is about 40 to 70 mm.
Semi-finishing polishing
Mainly use sandpaper and kerosene. After the oilstone operation, the sandpaper operation is completed. When sandpapering, pay attention to the round edge and sharp corner position of the mold core, the round corner and the generation of orange peel. Therefore, the oilstone process should be processed as finely as possible. Sandpaper is used with a harder wooden stick, and cross-grinding is performed like oilstone operation. The number of sandpaper grinding times on one side is about 10 to 15 times. If the grinding time is too long, the grinding force of the sandpaper will decrease, which will cause uneven processing surface. When sandpaper is used, bamboo pieces are generally used for grinding. In fact, it is most ideal to use a wooden stick with low elasticity or an aluminum stick with low hardness to grind at an angle of about 45 degrees. Rubber or highly elastic materials cannot be used for the grinding surface. Shapes that cannot be ground at a 45-degree angle can be ground at an acute angle. The numbers of sandpaper are:#220~#320~#400~#600~#800~#1000~#1200~#1500. In fact, #1500 sandpaper is only suitable for hardened mold steel (above 52HRC) and not for pre-hardened steel, because this may cause burns on the surface of pre-hardened steel parts.
Fine polishing
Fine polishing mainly uses diamond grinding paste. If a polishing cloth wheel is mixed with diamond grinding powder or grinding paste for grinding, the usual grinding order is 9 μm (1 800#) → 6 μm (3 000#) → 3 μm (8 000#). 9 μm diamond grinding paste and polishing cloth wheel can be used to remove the hair-like wear marks left by 1200# and 1500# sandpaper. Polishing with sticky felt and diamond grinding paste, the polishing process with precision requirement of Ra0.2 can be carried out in a clean polishing room in the mold processing workshop. For more precise polishing, an absolutely clean space is required. Dust, smoke, dandruff and saliva foam may scrap the high-precision polished surface obtained after several hours of work.