1.factors affecting the plastic parts size. The size of plastic parts mainly depends on the use of requirements, such as color TV shell, it is subject to the standard series of CPT constraints, and some plastic parts as a part and other parts are installed together, it is subject to the relevant parts of the restriction. The flow of plastic has influence on the plastic part dimension, the fluidity of plastics, such as PC, PSF, HPVC or glass fiber reinforced plastic, design size is not too large. For the thin wall and the size is not too large, because of the large and thin plastic parts, melt filled cavity is difficult, there is not yet filled cavity before curing, or just full of plastic parts, but is not very good fusion and the formation of weld line, affecting the appearance of plastic parts and strong degree. Effects of injection volume, injection molding machine clamping force, template size to the size of injection molding products have different degree.

2.factors affecting the plastic parts size precision. Forming the search rate, characteristics of plastic and its forming conditions of plastic molding search rate and search the fluctuation rate, such as plastic mold, liquidity, elastic modulus, melt temperature, and mold temperature, injection pressure, holding pressure, plasticizing backpressure, forming period. All have different degrees of influence on the search rate. For the same kind of plastic, conditions of molding plastic products, reasonable structure reasonable, rational die structure and manufacturing precision plastic molding, can reduce the search rate, obtain higher size accuracy. The die structure and its manufacturing precision. In the die design, not only to the type of surface to consider mold, plastic molding and demoulding, but also consider the liquidity of plastic molding weld material, namely the distribution of runner, position, exhaust, mold gate cooling or heating. In injection molding, the mold cavity to withstand high pressure, if the mould stiffness is not enough, will cause the deformation, thereby reducing the dimension precision of plastic parts. In addition, the structure of the cavity has a large influence on the stiffness, the best overall model, frame, insert die the worst. But the machining precision is highest, framework of insert die the whole die, the worst, therefore, to consider both collaborative. Die, die dynamic positioning with guide column and guide sleeve, but due to a clearance exists, therefore the cavity may shift, the plastic part dimension accuracy, therefore, can be adopted to eliminate the gap between the positioning of the original, in order to improve the positioning precision mould. Die, die will be subject to different degrees of wear in use process, mainly refers to the cavity and the moving parts, such as the guide post and the guide sleeve and the abrasion of the. When the plastic contains hardware packing, fiberglass, wear the cavity is particularly prominent, the mold cavity should choose the material of good wearability, or hardening on the surface.