In order to obtain high quality polishing effect, the most important thing is to have high quality polishing wheel, sandpaper and diamond grinding paste. The choice of polishing process depends on the surface conditions of pre processing, such as machining, EDM, grinding and so on.
        The general process of mechanical polishing is as follows: (1) the surface of rough throwing after milling, electric spark and grinding can be polished at 35000 - 40000rpm rotating surface polishing machine or ultrasonic grinding machine. The commonly used method is to remove the white electric spark layer by using wheels with diameters of 3mm and WA#400. Then hand grinding, strip oil and kerosene as lubricants or coolants. The general usage sequence is #180~#240~#320~#400~#600~#800~#1000. Many die makers choose to start with #400 in order to save time. (2) Sandpaper and kerosene are mainly used in semi-precision and semi-precision casting. The number of sandpaper is #400~#600~#800~#1000~#1200~#1500 in sequence. In fact, #1500 sand paper is used only for hardened die steel (more than 52HRC), but not for pre hard steel, because it may cause surface burns of pre hard steel. (3) fine polishing and polishing is the main use of diamond grinding ointment. If the polishing wheel is mixed with diamond grinding powder or abrasive paste, the usual grinding sequence is 9 m (#1800) ~6 m (#3000) ~3 m m (#8000). The diamond grinding cream and polished cloth wheel of 9 m can be used to remove the abrasion marks left by #1200 and #1500 sandpaper. Next, it is polished with adhesive felt and diamond grinding paste. The order is 1 m (#14000) ~1/2 m (#60000) ~1/4 m m (#100000). The polishing process with accuracy above 1 m (including 1 m) can be carried out in a clean polished chamber in the mold shop. For more precise polishing, there must be an absolutely clean space. Dusts, fumes, dandruff and saliva are all likely to scrap high precision polished surfaces after hours of work.
        Attention should be paid to the problems in mechanical polishing. Sandpaper polishing should pay attention to the following points: (1) polishing with sandpaper requires the use of soft sticks or sticks. When polishing round or spherical surfaces, cork rods can better match the radians of the circular and spherical surfaces. Hard wood bars, like cherry wood, are more suitable for polishing flat surfaces. The end of the trimming of the bar makes it fit with the shape of the steel surface so that the sharp angle of the bar (or bamboo strip) can be avoided to contact the surface of the steel parts and cause a deep scratch. (2) when different types of sand paper are used, the polishing direction should be changed to 45 ~90 degrees so that the Striped shadow of the former model of sand paper can be resolved. Before changing the different types of sand paper, the polishing surface must be carefully wiped on the polishing surface with 100% pure cotton with alcohol, as a small gravel will destroy the entire polishing work on the surface. This cleaning process is also important when polishing the sand paper for diamond polishing paste. All particles and kerosene must be thoroughly cleaned before polishing continues. (3) in order to avoid scratching and burning the surface of workpieces, special care must be taken when polishing with #1200 and #1500 sandpaper. Therefore, it is necessary to load a light load and polish the surface by two step polishing. Polishing with each type of sandpaper should be done two times in two different directions, and 45 degrees ~90 degrees each time in two directions.