In addition to the original air in the cavity, there are low molecular volatile gases produced by heating or solidification of plastics, which must be considered to be discharged sequentially. Generally speaking, for complex mold, it is difficult to estimate the exact location of gas resistance in advance. Therefore, it is often necessary to confirm its position by trial mode and then open the exhaust slot. The exhaust slot is usually placed in the cavity and finally filled. The way of exhausting is to use mold parts to match clearance exhaust and vent exhaust. Exhaust is the need for molding parts, and air entraining is needed for plastic parts. For large-scale deep cavity shell plastic parts, after injection molding, the gas in the cavity is removed, and a vacuum is formed between the surface of the plastic part and the core surface during the demoulding process, which makes it difficult to demould. If forced demoulding, the plastic parts will be deformed or damaged, therefore, it is necessary to introduce gas, that is, air between the plastic parts and the core, so that the plastic parts smoothly demoulding. At the same time, several shallow grooves are processed at the parting surface to exhaust.