Three kinds of Dieless manufacturing processes, including laser selective sintering of coated sand, laser selective sintering of PS powder and wax infiltration, digital dieless casting and NC processing of sand mold, were studied, and the optimal processing parameters were determined. The rapid casting process design of aluminum alloy cylinder head, cast iron cylinder block and aluminum alloy chain chamber cover of automobile engine was optimized, the pouring of three kinds of sand castings was completed, and qualified sand castings were obtained. The research work completed includes:
(1) In the process of selective laser sintering coated sand, the effects of process parameters such as laser power, preheating temperature and scanning speed on the initial strength of sintered sand mold were studied. The optimal process scheme of laser sintering coated sand was obtained as follows: powder layer thickness 0.25, laser power 24W, preheating temperature 65 ℃, scanning speed 1600 mm / s.
When this process parameter is used for laser selective sintering, there is no obvious sand sticking on the surface of the sample and no hardening on the bottom layer. The average tensile strength of the cast sand mold sample can reach 0.58mpa, which meets the strength requirements of post-treatment and is easy to clean.
(2) The effects of laser power and scanning speed on the sintering depth in the laser selective sintering process of PS powder are analyzed. Combined with the analysis results, the effects of different process parameter combinations on the dimensional accuracy of PS samples are compared and analyzed. It is determined that the optimal processing process is layered thickness of 0.2mm, excitation power of 25W and scanning speed of 2000mm / s. Using this process parameter, the maximum relative error of PS powder sample sintered by laser selective sintering is 1.2%, and the bending strength can reach 2.6MPa, which meets the strength requirements of cleaning and post-treatment.
(3) The performance of sand mold manufactured by laser selective sintering, digital Moldless mold NC machining and 3D inkjet printing are tested and compared, so as to provide reference for the selection of subsequent sand mold manufacturing process. The comparative analysis shows that the properties of 3D inkjet printing sand and self hardening sand are close, with low gas generation and good air permeability, while the gas generation of laser selective sintering sand mold is high and poor air permeability. During casting, the laser selective sintering sand mold is easy to produce casting defects such as pores. The tensile strength of 3D inkjet printing sand and self hardening sand is lower than that of laser sintering. If these two processes cast thin-walled complex sand cores such as engine cylinder block and cylinder head water jacket core, there is a risk of core breakage in the process of sand casting. Laser sintering coated sand has higher strength and is more suitable for manufacturing thin-walled and complex sand cores.
(4) Through sand casting process analysis and design optimization of engine aluminum alloy cylinder head, aluminum alloy chain chamber cover and cast iron cylinder block. By defining a database close to the actual mold parameters, improve the accuracy of simulation analysis, predict the casting defect trend in the actual production of castings by means of simulation analysis, and formulate effective solutions to improve the qualified rate of sand castings. The casting of cast iron cylinder block and aluminum alloy cylinder head was completed by sand mold sand casting process, and the casting of chain chamber cover was completed by wax mold rapid casting process. All qualified sand castings were obtained.