Research On Carbon Fibers Reinforced The Coated Sand By Selective Laser Sintering

Selective Laser Sintering(SLS) is a key branch of rapid prototyping technology(RP). It has been widely applied in aerospace, automotive industries and medical treatment due to the diversity of SLS material, and needn’t special fixture, free from limitation through complex degree of drip molding shape. Selective Laser Sintering combined with casting technology could reduce the design and manufacture of wood pattern, shape, etc, which realize the sand/core integration manufacturing and manufacture the complex casting require high technical. Early strength of laser sintered parts is relatively low currently and the poor collapsing limits its application in complex precision castings. The prototyping performance of carbon fibers reinforced coated sand by selective laser sintering has studied by using carbon fibers as reinforced material and coated sand as based material. The main research contents and conclusions are as follows:The surface of the carbon fibers has been modified by gas phase oxidation, nitric acid oxidation, silane coupling agent with nitric acid, and its effect on the early strength and the curing strength of the sintering parts is investigated. The modified carbon fibers treated by nitric acid with silane coupling agent groove etching and roughness are more significant than the other modified methods by means of the microstructure, which improved the combination between carbon fibers and the coated sand, also realized the uniform distribution in the coated sand. The early tensile strength and early bending strength are 0.372 MPa and 0.56 MPa respectively, and the curing tensile strength and bending strength are 6.385 MPa and 8.011 MPa respectively through the mechanical properties testing,The effects of different proportion of carbon fibers on the early strength, the curing strength, collapsibility, gas evolution and permeability have studied. The results show that the early strength improves when carbon fibers with 3wt% added in the coated sand, the early tensile strength and the early bending strength increase by 23.18% and 31.46% respectively compared with those not add carbon fibers. With the increase of carbon fibers content, the curing strength increase firstly than decrease rapidly, which reach the highest when carbon fibers content is 3wt%, the curing tensile strength and the curing bending strength increase by 24.71% and 24.71% respectively compared with those not add carbon fibers. When the roasting temperature at 280℃, the residual strength of the coated sand increase firstly, then decrease with further increase in the carbon fibers content, when roasting temperature is above 380℃, the residual strength of the coated sand decrease with the increase of carbon fibers content. The addition of carbon fibers has a little influence on gas evolution of the coated sand, but has great effect on permeability, with the increase of carbon fibers content, the permeability of coated sand reduce gradually.Various parameters of SLS forming process on the influence of the quality of the sintered parts have studied. The SLS process parameters has optimized by orthogonal test, and the best process parameter combination is gained determined by orthogonal test and extreme difference analysis, preheating temperature 60℃, laser power 42 W, scanning speed 3m·s-1, spread powder thickness 0.15 mm.