Study On Dinensinal Accuracy And Transitive Law Of Rapid Investment Casting Based On Selective Laser Sintering

Rapid Investment Casting (RIC) is very useful technology to fabricate complexmetal castings. It realizes the shift form rapid prototyping to rapid manufacturing bycombines Selective Laser Sintering (SLS) with investment casting, has a broadapplication prospect. Dinensinal accuracy is the key to RIC technology, but RIC ismultistep technology, the dimensions of parts passing through several steps, and thereare many factors which influencing the dinensinal accuracy of parts and it is hard tocontrol. There is significant academic value and practical meaning to study thedimensional accuracy and transitive laws of dimensions of RIC.In terms of dinensinal accuracy of SLS, experiment were implemented underdifferent part orientation, different laser power and differernt layer thickness.Dimensions of sample were measured. The results show: there is relative highdimension accuracy when dimensions parallel to XY axis because there is no influenceof step effect. The dimension error is0.67%; Dimensions of SLS prototype increase firstand then decrease with increasing of part orientation when the dimensions are notparallel to XY axis. Peak value of dimension error occurs when the part orientation is60degree, and the peak value is1.78%, because the step effect is most significant. It can beseen that try to keep important dimensions parallel to XY axis is necessary.Dewaxing and roasting process is very important in RIC technology and willinfluence the dinensinal accuracy of shell. In terms of dewaxing and roasting process ofRIC technology, experiments were implemented under four different dewaxingtemperature and time. The results show: there are more outflows of SLS pattern withhigh dewaxing temperature, but the shell is easy to crack when dewaxing temperature istoo high, the best dewaxing temperature is250℃, the SLS pattern outflow rate is94.28%under this temperature; The optimal dewaxing time is100min. the shell is noteasy to crack with high heating rate; in roasting process, it is better to heat preservationfor2hours at400℃, then heating to800℃after SLS pattern is completedecomposition, in order to prevent residual pattern burning in the shell cause shellcracking.In terms of research on dimensional transitive laws of RIC technology, five kindsof shells were fabricated based on RIC technology. The dimensional transitive laws form CAD model to the SLS prototype, form SLS prototype to SLS pattern and fromSLS pattern to casting in RIC technology were studied. The results show: dimension ofCAD model has great influence on dinensinal accuracy of SLS prototype, highestdimensional accuracy of SLS prototype occurs when the dimension of CAD is79mmbecause secondary sintering and sintering shrinkage is balanced; Different dinensinalaccuracy for different kinds of dimensions. Dimensions of outer surface appear aspositive deviation and inner surface appears as negative deviation; Dinensinal accuracyof different kinds of shells is not significant, which is about1.58%; Shrinkage ofdimensions of inner surface, which is0.62%, is lower than that of outer surface becauseresistance of shell.Effect of part orientation on dinensinal accuracy of SLS prototype, dewaxing androasting process of RIC technology and dimensional transitive laws of RIC technologywas studied in this paper, RIC process was optimized, and effect of RIC processparameters on dinensinal accuracy and transitive laws of RIC technology was obtained.It can be used to control the dimensions of RIC technology, which had laid a goodfoundation for rapid casting of complex structures.