How to solve the common problems in the polishing of injection molds ?

- Apr 01, 2019-

How to solve the common problems in the polishing of injection molds ?


(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: “peeling” and “pitting”. Excessive polishing occurs mostly in mechanical polishing.


(2) Reasons for the appearance of " peeling" on the work piece


  Irregularly rough surfaces are called " peeling". There are many reasons for producing "peeling". 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 " peeling". For example: polishing wheel polishing, the heat generated by the polishing wheel can easily cause "peeling". 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 "peeling" of the work piece


  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) Remove the defective surface. The particle size of the grinding is slightly higher than the previous sand number, and then the grinding is performed. The polishing intensity is lower than the previous one.


2) Perform stress relief at a temperature lower than the tempering temperature of 25 °C, and grind it with the finest sand number before polishing until a satisfactory effect is achieved, and finally polish with a lighter force.


(4) Reasons for the formation of "pitting" on the surface of the work piece


   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 not enough and the content of hard impurities is high.


3) The surface of the mold is rusty.


4) Black leather is not removed.


(5) Measures to eliminate pitting corrosion of the work piece


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


2) The softest polishing tool should be avoided when the grit size is less than 1 mm.


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


   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.

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