The wall thickness obtained is too small, causing the plastic parts filling flow resistance is very big, making the shape complex or large plastic parts molding difficult. Wall thickness is too big, not only waste plastic raw materials, but also to the molding will bring certain difficulties. The wall thickness of the same plastic part should be as uniform as possible, and the ratio of wall thickness should not exceed 3:1 if different wall thickness is required in the mechanism, and between different wall thickness should adopt appropriate modification radius to make wall thickness part transition slowly.