Combined with the rule of dimension error transfer from CAD model to one-time wax impregnation, the dimension shrinkage in X and Y directions is the same in theory for this revolving part. According to the formula, the rule of dimension error transfer from CAD model to one-time wax impregnation is as follows:
Therefore, the X and Y transfer coefficients from CAD model to wax pattern are 0.99015, and the Z transfer coefficient is 1.01576. According to the specific dimensions of the parts, the negative deviation of the corresponding X and Y dimensions should be -0.40789mm 12361mm, and the actual diffuser impeller size deviation is greater than the theoretical value, which is mainly due to the large size of the diffuser parts. Therefore, under the same rapid process, because the outer powder bed of the sintered parts dissipates heat faster, and the powder bed can not be fully heated in the subsequent sintering process, the outer dimension shrinkage of the parts is greater than the theoretical value, so the outer blade shrinkage is greater. The inner side of the impeller shrinks less than the outer side due to the heat transfer of sintered parts to the powder bed.
Through calculation, the positive deviation of Z-direction dimension should be 1.9519mm after one wax immersion, However, the actual dimension deviation is negative, which is mainly due to the influence of secondary sintering on Z-direction when the z-direction dimension of the specimen is small, and the influence of SLS prototype volume shrinkage when the z-direction dimension is larger than 22mm. Therefore, in the selection of the dimension error rule of the specimen, the corresponding Z-direction dimension error is calculated by using No. The specific formula is shown in.
Where,
The results show that the relative error of No. 5 test dimension of ε z15-sls prototype relative to the wax pattern;
Epsilon z25 – relative error of wax pattern compared with SLS prototype No.
According to the above formula, the deviation in Z direction is -0.4204mm, which is less than the actual measured value. The main reason is that the size of diffuser parts is large, and the sintered area of the bottom layer can not get effective heat source compensation at the beginning, resulting in large volume shrinkage. Finally, the correction coefficient of X and Y dimensions is 1.00985, and the correction coefficient of Z dimensions is 1.00339 when Z dimensions are larger than 22mm, At the same time, in view of the problem that the actual deviation is greater than the theoretical deviation, it is necessary to compensate the heat source at the outer side and blade of the complex parts to reduce the actual size shrinkage.
