The roundness precision of the plastic ball is a very important link. Generally, the roundness precision has several grades of 0.01MM for the first grade, 0.02MM for the second grade, and 0.03MM for the third grade. The roundness of the plastic ball should start from the mold design. For example, the mold steel selection 718, P20, S136 and 420, etc. The mold structure design is very important, directly related to the roundness of the plastic ball. Press the injection molding, try to choose high-precision plastic ball machines imported from Japan, Germany and Italy. During the production process, mold temperature, injection molding pressure holding time, molding time, and cooling time should be carefully debugged.