How to control the accuracy of plastic injection molding parts?Plastic shell or enclosure is generally produced by injection molding process (sometimes finished by two to more process like CNC milling the internal structure), product size control and manufacturing process are inseparable. In addition and the size of the product itself is also a relationship, the greater the product, the more difficult to control.
The effect of dimensional accuracy is divided into two parts: Injection mold making and injection molding production
1.The material of Mold steel, How to choose the right mold steel material that depends on the estimated order quantity in the near future. For example, the mold life can be 300k-500k shot if it is made if the high-quality steel like JIS S136 (DIN2136) , High-quality mold steel injection mold produce high-quality parts. Another factor is the additional mechanical properties to strengthen the treatment such as hardening. If the mold is made of poor mold steel, the wearing mold could not guarantee the accuracy.
2.The mold gate system design, plastic injection molding machines are pressure limit, and generally in the high-pressure high-speed, injection molding machine easy to instability, so a reasonable gate system should be easy to fill the mold cavity, the focus is Design and selection of gate system.
3, The part shrinkage rate, plastic thermal expansion, and contraction during the plastic molding, so the size of plastic products is certainly smaller than the mold size, so the mold size should be designed larger than the product size. How much is it? This depends mainly on the shrinkage rate of different kind plastic. According to the experimental data, we have a variety of plastic shrinkage rate, mold designers can refer to this data to design the mold size. Generally, take the middle value, the basic rules are: thin wall with small rate, thick arms take large rate, near the gate of the small rate. Shrinkage rate to obtain the more accurate, the more easily meet the size requirements of the product.
4.General plastic molds were adopted Moldflow simulation before making the mold. with the simulation it will found the parts deformation after plastic injection molding, then make some minor adjustment to the mold size in order to get the parts as high quality as possible.
High-precision machining equipment and testing equipment is to ensure the accuracy of the premise of the mold. Mold master's operating experience is also very important.