Study On Rapid Precision Casting Technology For Network Frame Parts Using Integral Plaster Mould

In recent years, various types of castings in the aviation industry develop to bethin-walled, complication, precision, lightweight and integration with the increaseddemands for product quality. Using traditional manufacturing process, airline engineparts with grid structure are not only difficult to meet the requirements of quality,precision and performance, but also generate the long test cycle and extremely high cost.With the combination of plaster mould precise casting technology and laser sinteringrapid prototyping technology, this paper developed a new fast method for the fabricationof complex network frame structure parts by using intergal plaster mould. ProCASTsoftware was applied to simulate the casting mold-filling and solidification processes soas to optimize the casting technology. Furthermore, network frame structure prototypesintering forming technology, integral plaster mould preparation technology and plastermould casting process technology were investigated systematically. The mainconclusions are given as follows:(1)In the current study, the optimized laser sintering process parameters forobtaining the network frame structure prototype with a clear outline, high dimensionalaccuracy, no deformation and easy to clear are determined as： the preheatingtemperature of Polystyrene powder88℃，the laser power23w, the layer thickness0.2mm, Scanning speed3.474m/s. With the permeability wax temperature as67℃, highsurface finish can be obtained for the network frame structure prototype.(2) The most suitable component of the plaster mould formula for polystyreneprototype is optimized as: the ration of α-hydrated gypsum and filler is40:60, where thefiller is composed of quartz powder, talcum powder and bauxite powder with the ratioof20:10:30. The ratio of plaster powder and water (ml/g) is37.5:100. The ratio ofsilicon sol and water is1:3. Moreover, powder alkali-free glass fiber should be added togypsum as type of strength agent with the amount of0.3%. Using Polystyreneprototype after wax process, the integral plaster mould can be prepared rapidly.(3) The stripping parameters for integral plaster without crack are chosen as:stripping temperature220℃and stripping time less than200min. In such a case, thedemould ratio can reach94.5%. (4) The roasting technology for obtaining high strength and crack-free integralplaster are given as: adopting step manner for temperature rise during roasting with thetemperature increasing rate5℃/min. The roasting temperature starts at150℃and holdsfor three hours. After then, the calcination temperature and corresponding heatpreservation time are chosen as:250℃two hours,400℃two hours,600℃two hours,and700℃two hours, respectively.(5)According to the simulation results of mould filling process precision castingfor the network structure of plaster, the ideal pouring plaster mould temperature andpouring temperature are determined as300℃and710℃. In such a case, shrinkage andother defects can be eliminated.(6) The external dimensions of the complex thin-walled network frame structure,which was fabricated successfully in laboratory, is95mm×45mm×70mm and net roddiameter is2mm. The surface of network frame structure is satisfactory with no internalcasting defects, which is consistent with the simulation results.