How To Solve The Problems In Yhe Mold Polishing Process
The biggest problem encountered in the daily polishing process 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, the grinding particle size is slightly thicker than the previous sand number, and then ground, and the polishing intensity is lower than the previous one.
(2) Stress relief is performed at a temperature lower than the tempering temperature of 25 °C, and the finest sand number is used for polishing before polishing until a satisfactory effect is achieved, and finally polishing is performed 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) 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 sand size is less than 1mm, the softest polishing tool should be avoided.
(3) Use the shortest polishing time and the minimum polishing force as much as possible.