In general, precision casting parts dimensional accuracy is influenced by structure of casting, casting material, moulding, shell making, roasting, pouring the influence of various factors, such as any one link set, unreasonable operation can make the casting shrinkage rate of change, has led to the deviation of dimension accuracy of castings and requirements.Below is the defects can cause precision casting dimension accuracy of factors:(1) the influence of the casting structure: a. casting wall thickness, shrinkage rate is large, thin wall castings, the shrinkage rate is small.B. free shrinkage, hinder the little shrinkage.(2) the influence of the casting material: a. materials of carbon content is higher, the line of the smaller shrinkage rate, the lower the carbon content, the line, the greater the shrinkage rate.B. common material casting shrinkage rate is as follows: casting shrinkage ratio K = (LM - LJ)/LJ x 100%, LM for the cavity dimension, LJ for casting size.K by the following factors: the wax models K1, K2, alloy casting structure types K3, K4 pouring temperature.