In the process of polishing, we need to pay attention to many problems. Now let's have a detailed understanding.
1. Precautions for mold sandpaper grinding and oilstone grinding
(1) For the mold surface with high hardness, only clean and soft oilstone grinding tools can be used.
(2) When changing the sand grade during grinding, the workpiece and the operator's hands must be cleaned to avoid bringing coarse sand particles to the next finer grinding operation.
(3) During each grinding process, the sandpaper should be polished from different 45 ° directions until the sand lines of the previous level are eliminated. After the sand lines of the previous level are removed, the grinding time must be extended by 25% before switching to the next finer sand number.
(4) Changing different directions during grinding can prevent the workpiece from generating waves and other unevenness.
2. Precautions for diamond grinding and polishing
Diamond grinding and polishing must be carried out under light pressure as far as possible, especially when polishing pre hardened steel parts and polishing with fine grinding paste. When polishing with 8000 × grinding paste, the common load is 100 ~ 200 g/cm2, but it is difficult to maintain the accuracy of this load. In order to facilitate this, you can make a thin and narrow handle on the wooden strip, or cut a part on the bamboo strip to make it softer. This can help control the polishing pressure to ensure that the pressure on the mold surface is not too high. When using diamond grinding and polishing, not only the working surface is required to be clean, but also the hands of workers must be very clean.
3. Precautions for polishing plastic mold
The polishing of plastic mold is very different from the surface polishing required in other industries. Strictly speaking, the polishing of plastic mold should be called mirror processing. It not only has high requirements for polishing itself, but also has high standards for surface flatness, smoothness and geometric accuracy.
Because electrolytic polishing, fluid polishing and other methods are difficult to accurately control the geometric accuracy of parts, and the surface quality of chemical polishing, ultrasonic polishing, magnetic polishing and other methods can not meet the requirements, so the mirror processing of precision molds is still dominated by mechanical polishing.
Precautions in polishing are as follows:
(1) When a new mold cavity is processed, the surface of the workpiece should be checked first, and the surface should be cleaned with kerosene, so that the oilstone surface will not stick with dirt, resulting in the loss of cutting function.
(2) When grinding coarse grain, it should be carried out in the order of difficult first and then easy, especially for some difficult dead corners, the deeper bottom should be studied first, and finally the side and large plane.
(3) Some workpieces may be polished by multiple pieces assembled together. First, grind the coarse grain or spark grain of a single workpiece respectively, and then grind all workpieces together until smooth.
(4) For workpieces with large plane or side plane, grind off the coarse lines with an oilstone and then use a flat steel sheet for light transmission detection to check whether there is any unevenness or bad condition of backtracking. If there is backtracking, it will cause difficulty in demoulding or strain of the workpiece.
(5) In order to prevent the die workpiece from being knocked out or there are some bonding surfaces that need to be protected, you can paste it with a saw blade or paste it on the edge with sandpaper, so as to get an ideal protection effect.
(6) When grinding the plane of the die, pull it back and forth. The handle of the drag oilstone should be as flat as possible, and should not exceed 25 °. Because the slope is too large, the force will rush from top to bottom, which will easily lead to many coarse lines on the workpiece.
(7) If the plane of the workpiece is polished with copper or bamboo pieces pressed with sandpaper, the sandpaper should not be larger than the area of the tool, otherwise it will be grinded to the place that should not be grinded.
(8) Try not to use a grinding machine to repair the parting surface, because the parting surface repaired by the grinding wheel head is rough and uneven, if necessary, the grinding wheel head must be glued to the concentricity balance.
(9) The shape of the grinding tool should be close to the surface shape of the die, so as to ensure that the workpiece will not be grinded and deformed.