How to solve common problems in polishing

The polishing of the cavity during the mold manufacturing process is a very important process, which is related to the quality and life of the mold, and also determines the quality of the product. Mastering the working principle and process of polishing, and selecting a reasonable polishing method can improve the quality and life of the mold, and thus improve the quality of the product.

1, over-polishing

The biggest problem encountered during daily polishing is “over-polishing”, which means that the longer the polishing time, the worse the quality of the mold surface. There are two phenomena of over-polishing: “orange peel” and “pitting”. Excessive polishing occurs mostly in mechanical polishing.

2. The reason why the workpiece appears "orange peel"

Irregularly rough surfaces are called "orange peels". There are many reasons for producing "orange peels". The most common cause is due to overheating or excessive carburization of the mold surface. Excessive polishing pressure and long polishing time are generated. The main reason for "orange peel". For example: polishing wheel polishing, the heat generated by the polishing wheel can easily cause "orange peel". Harder steels can withstand higher polishing pressures, and relatively softer steels are prone to over-polishing. Studies have shown that the excessive polishing time will vary depending on the hardness of the steel.

3. Measures to eliminate the "orange peel" of the workpiece

When surface quality is found to be bad, many people increase the polishing pressure and extend the polishing time. This practice tends to make the surface quality worse.

The following methods can be used to remedy:

(1) The defective surface is removed, and the particle size of the grinding is slightly thicker than that of the previously used sand number, and then the grinding is performed, and the polishing force is lower than the previous one.

(2) Stress relief at a temperature lower than the tempering temperature of 25 °C, grinding with the finest sand number before polishing until a satisfactory effect is achieved, and finally polishing with a lighter force.

4. Reasons for the formation of "pitting" on the surface of the workpiece

Due to some non-metallic impurities in the steel, usually hard and brittle oxides, which are pulled out from the surface of the steel during the polishing process to form micro-pits or pitting, the main factors causing "pitting" are as follows:

(1) The polishing pressure is too large and the polishing time is too long.

(2) The purity of the steel is insufficient and the content of hard impurities is high.

(3) The surface of the mold is rusted.

(4) The black leather material is not removed.

5, measures to eliminate pitting corrosion of the workpiece

(1) Carefully re-grind the surface, the grit size is slightly thicker than the previously used particle size, and the final step of grinding is performed with soft and sharp oil stone before the polishing process.

(2) When the grit size is less than 1 mm, the softest polishing tool should be avoided.

(3) Use the shortest polishing time and the minimum polishing force as much as possible.