What should be paid attention to in different types of polishing

Polishing can effectively improve the surface roughness, eliminate the defects such as scratches, ash inclusions and fine cracks; reduce the surface friction coefficient, improve the wear resistance; improve the physical and mechanical properties of the part surface, improve the surface stress distribution of the part; improve the accuracy of the part, ensure the assembly process, etc., but in the process of polishing, we need to pay attention to many problems Let's get to know more about it.

1. Matters needing attention in 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 number level during grinding, the hands of the workpiece and the operator must be cleaned to avoid taking the coarse sand particles to the next finer grinding operation.

(3) In each grinding process, the sandpaper shall be polished from different 45 ° directions until the upper sanding grain is eliminated. After the upper sanding grain is removed, the grinding time must be extended by 25% before the next finer sanding number can be changed.

(4) When grinding, changing different directions can avoid unevenness such as waves.

2. Points for attention in diamond grinding and polishing

Diamond grinding and polishing must be carried out under light pressure as far as possible, especially when polishing pre hard steel parts and polishing with fine grinding paste. When polishing with 8000 × abrasive paste, the common load is 100-200 g / cm2, but it is difficult to maintain the accuracy of this load. To facilitate this, a thin and narrow handle can be made on the wood strip, or a part of the bamboo strip can be cut to make it softer. This helps to control the polishing pressure to ensure that the die surface pressure is not too high. When diamond is used for grinding and polishing, not only the working surface is required to be clean, but also the hands of workers must be very clean.

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3. Points for attention in plastic mold polishing

The polishing of plastic mold is very different from the surface polishing required by other industries. Strictly speaking, the polishing of plastic mold should be called mirror machining. It not only has high requirements for polishing itself, but also has high standards for surface flatness, smoothness and geometric accuracy.

It is difficult to precisely control the geometric accuracy of parts by electropolishing, fluid polishing and other methods, while the surface quality of chemical polishing, ultrasonic polishing, magnetic abrasive polishing and other methods can not meet the requirements, so the mirror machining of precision molds is mainly mechanical polishing.

Precautions in polishing are as follows:

(1) When a new mold cavity begins to be processed, the surface of the workpiece shall be checked first, and the surface shall be cleaned with kerosene, so that the surface of the oilstone will not be stuck with dirt, resulting in the loss of cutting function.

(2) When grinding coarse grain, it should be carried out in the order of "hard first, easy later". Especially for some dead corners that are hard to grind, the deeper bottom should be first grinded, and finally the side and large plane.

(3) Some workpieces may have several pieces assembled together for polishing. First grind the coarse grain or spark grain of a single workpiece, and then grind all workpieces together until they are smooth.

(4) For workpieces with large plane or side plane, after grinding off the coarse grain with oilstone, use flat steel sheet for light transmission test to check whether there is any unevenness or bad condition of reverse buckle. If there is reverse buckle, it will lead to difficulty in demoulding or drawing of workpieces.

(5) In order to prevent the die work piece from developing the reverse thread or having some bonding surfaces to be protected, it can be pasted with saw blade or with sandpaper on the edge, so as to obtain the ideal protection effect.

(6) The surface of the grinding die is pulled back and forth, and the handle of the dragging oilstone is placed as flat as possible, not more than 25 °. Because the inclination is too large, the force is punched from up to down, which is easy to lead to many coarse grains on the workpiece

(7) If the plane of the workpiece is polished by pressing a piece of copper or bamboo 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 grinder to repair the parting surface, because the parting surface of the grinding wheel head is rough and has uneven waves. If necessary, the grinding wheel head must be pasted 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 is not deformed by grinding.

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