Research On Preparation And Application Technology Of Environmentally Friendly Composite Wax Powder For Selective Laser Sintering

Traditional investment casting is also called lost wax casting.In the wax mold manufacturing process,the mold cost is high and the delivery time is long,making it difficult to produce wax molds with complex shapes.Rapid investment casting(RIC)technology based on selective laser sintering(SLS)can be widely used in production because it can quickly produce "wax molds" without molds.Since the 1990 s,polystyrene(PS)has been widely used as a low-cost material commonly used in the preparation of wax molds for SLS.However,PS will pollute the environment when demolding,and its ash content is difficult to remove,which often causes the quality of castings to drop.In this paper,an environmentally friendly composite wax powder suitable for the RIC process is prepared through the selection of base materials and the optimization of the formula for the SLS process;on this basis,the application of the SLS process optimization,the post-processing process of sintered parts,and the adaptability of investment casting process are prepared.The technology was studied and the following conclusions were reached:(1)In the thesis,EVA3 wax powder was selected as the matrix material,and white carbon black,sodium dodecylbenzene sulfonate and carbon black were used as additives,and the influence of white carbon black and sodium dodecylbenzene sulfonate on the fluidity of EVA3 wax powder was studied.,And use the mechanical mixing method to prepare the composite wax powder,and use the orthogonal experiment to determine the optimal ratio of the composite wax powder: the content of carbon black is 0.15wt%,the content of silica is 0.9wt%,dodecylbenzene The content of sodium sulfonate is 3wt%.The results of differential thermal analysis showed that the addition of fillers did not affect the melting range of the wax powder;the results of thermogravimetric analysis showed that the thermal stability of the composite wax powder was better than that of the matrix material,and the results of thermogravimetry-mass spectrometry showed that the composite wax powder could be used as an environmentally friendly material in the RIC process.The thesis tested the reflectivity of the composite wax powder and EVA3 wax powder base material to the carbon dioxide laser with a wavelength of10.6?m,and the results showed that by adding carbon black as a light absorber,the reflectivity of the composite wax powder to the carbon dioxide laser was reduced by 1%.(2)The paper studied the influence of SLS process parameters on the quality of composite wax powder sintered parts.Appropriate preheating temperature can reduce the shrinkage of the sintered part,reduce the heat-affected zone of the sintered part,and facilitate the cleaning of the sintered part;Within a certain range,the higher the laser power,the higher the energy received by the powder,and the greater the melting degree of the powder.At the same time,the shrinkage of the molded part will increase;the scanning speed and laser power will affect the melting and solidification of the sintered part.The influence law is basically the opposite;the smaller the thickness of the powder,the higher the accuracy of the sintered part.According to the particle size of the composite wax powder,the minimum thickness of the powder is 0.1mm.Using the orthogonal experiment method,taking the accuracy in the height direction and the density of the sintered parts as indicators,the optimal SLS process of the composite wax powder was determined: the laser power was 8W,the scanning speed was 2000mm/s,the powder thickness was 0.15 mm,and the heat temperature is 50°C.The tensile properties of the sintered parts under the optimized process are about 2.2 MPa,which is increased to about 3.0 MPa after the wax immersion treatment.(3)The paper conducted an investment casting process adaptability experiment on composite wax powder SLS molded parts,and the results showed: The investment mold prepared by the composite wax powder has good coating properties and good demolding performance.It can be demolded by the steam dewaxing process and the shell does not burst and crack,and there is no ash.This material is suitable for the RIC process,and the whole process does not produce toxic gas.(4)According to the higher requirements of the wax mold strength for ultra-thin parts with a wall thickness of less than 1mm,the paper carried out a carbon fiber/composite wax powder modification study.The effect of carbon fiber powder on the melt viscosity of composite wax powder and the properties of sintered parts was studied.The results showed that with the addition of carbon fiber,the viscosity of the composite wax powder melt increased,and it was positively correlated with the content of carbon fiber.And the greater the melt viscosity of the sintered material,the more unfavorable for sintering molding.When the content of carbon fiber is 5wt%,the carbon fiber-modified composite wax powder can be sintered smoothly.The tensile strength of the sintered part is 3.3Mpa,which is better than that without post-treatment.The tensile strength of SLS composite wax powder sintered parts has increased by about 50%.SEM shows that the carbon fibers are uniformly distributed in the sintered parts,and the mechanism of the carbon fiber reinforced composite wax powder sintered parts is the debonding and pulling out of the carbon fibers.