1. Excessive polishing: The problem encountered in the daily polishing process is "excessive polishing", which means that the longer the polishing time, the worse the quality of the mold surface. There are two phenomena that occur when overpolishing occurs: "orange peel" and "pitting". Overpolishing is more likely to occur in mechanical polishing.
2. Measures to eliminate the "orange peel" of the workpiece: When it is found that the surface quality is not good, many people will increase the pressure of polishing and extend the polishing time, which often makes the quality of the surface poor. The following methods can be used to remedy this:
(1) Remove the defective surface, grind the particle size slightly coarser than the previous use of sand number, and then grind, the polishing force is lower than the previous one.
(2) Stress relief is carried out at a temperature 25 °C lower than the tempering temperature, and a fine sand number is used for grinding before polishing, and polishing is carried out with a lighter force.
3. The reason for the formation of "pitting" on the surface of the workpiece
Since there are some non-metallic impurities in steel, usually hard and brittle oxides, they are pulled out from the surface of the steel during the polishing process, forming micropits or pitting corrosion, and the main factors that produce "pitting corrosion" are as follows:
(1) The polishing pressure is too large and the polishing time is too long.
(2) The purity of the steel is not enough, and the content of hard impurities is high.
(3) The surface of the mold is rusty.
(4) The black leather has not been removed.
5) Carefully re-grind the surface, the sand grain size is slightly coarser than the previous particle size, and use soft and sharpened oil stones for the subsequent grinding before the polishing procedure.
(6) When the size of the sand grain is less than 1mm, avoid using soft polishing tools.
(7) Use a short polishing time and small polishing force as much as possible.
Reasons for the appearance of "orange peel" in the workpiece: the irregular and rough surface is called "orange peel", and there are many reasons for the production of "orange peel", the common reason is caused by overheating or excessive carburizing of the mold surface, and the polishing pressure is too large and the polishing time is too long is the main reason for the production of "orange peel". For example: polishing wheel polishing, the heat generated by the polishing wheel will easily cause "orange peel". Harder steels can withstand greater polishing pressure, relatively soft steels are prone to overpolishing, and studies have proved that the time for overpolishing will vary depending on the hardness of the steel.
