When the mold is injected, the molten plastic in the mold cavity produces a huge back pressure, generally 600 ~ 1000 kg/cm2. Mold makers sometimes do not pay attention to this problem, and often change the original design size, or replace the moving template with low-strength steel plates. In the mold with ejector ejector, due to the large span between the seats on both sides, the template bends down during injection. Therefore, the moving formwork must be made of high-quality steel, with sufficient thickness. A3 and other low-strength steel plates must not be used. When necessary, support columns or support blocks should be set under the moving plate to reduce the thickness of the plates and improve the bearing capacity.