Fiber Laser Sintering/Invalidating Compound Additive Manufacturing Technology And Equipment By Using Foundry Coated Powders

As a kind of powder bed-based laser additive manufacturing(LAM)technology,Selective Laser Sintering(SLS)is superior in such aspects as its high material utilization rate,short technological process,and the application of manufacturing parts in complex shapes and therefore has been widely used in the field of sand LAM in recent years.With the continuous upgrading and efficiency improvement of China’s foundry industry,castings have become larger in shape and therefore the conventional SLS technology can no longer meet the needs of foundry industry in terms of processing size,efficiency and strength.This paper aims to break through the bottleneck of low processing efficiency caused by low laser power and narrow linewidth scanning in conventional SLS method,and to reasonably balance the accuracy of the part with the initial strength of the part,focusing on the research of fiber laser sintering/invalidating compound based on coated powder(Fiber Laser Sintering and Invalidating Compound,FLSIC)additive manufacturing method and its supporting equipment,forming process and materials,and combined with traditional casting technology to verify engineering application examples.The research content and results are as follows:A new idea of sintering and forming the phenolic resin coated materials using 500 W fiber laser featured by higher power and stability and longer service life by replacing the 100 W carbon dioxide laser of the conventional SLS forming system is proposed in this paper.Based on this,an additive manufacturing method FLSIC is proposed,which combined high-efficiency sintering scanning with the internal wide line of a large spot(high-efficiency bonding)and high-accuracy invalidating scanning of small spot contour(high-accuracy cutting).The method not only improves the efficiency of the part,but also obtains a higher initial strength of the part,and can effectively eliminate the bad influence of the secondary sintered body on the accuracy of the part,and ensure the dimensional accuracy of the part.The laser additive manufacturing method is extended,especially for the high-efficiency preparation of large-size and complex structure sand cores,which has important theoretical significance and practical value.A series of forming equipment with large sizes have been developed based on FLSIC method and modular scheme.With a high-power fiber laser and mobile low-cost rear focusing galvanometer as the core,the use of partition stitching scanning technology to achieve high-efficiency variable spot large-format processing,reasonable balance of equipment processing efficiency,processing area and design/manufacturing/maintenance costs.The master-slave combination of low-cost and large-stroke XY belt module with high-accuracy and small-stroke translation stage supported by grating ruler guarantees the high-speed and precise positioning of the mobile galvanometer effectively,eliminates the following error of the belt module in course of high-speed fixed-point movement,and realizes the positioning featured by low cost,large size and high speed and accuracy.With all software and hardware independently developed,and all components from domestic manufacturers,the equipment is compatible to FLSIC and SLS forming method and has undergone long-term running to verify its stability and reliability.It meets the requirements of basic process experiment and engineering application production.The new FLSIC forming process is studied by using the coated ceramsite sand as the material and the fiber laser as the light source.The process above is also compared with the parts formed as per the SLS method.According to the experimental results,the sintering and forming via defocused large-spot laser which replaces the conventional SLS focused small-spot laser have higher power and wider filling line spacing.The experimental results also show that the secondary sintering body can be cut away from the high-green strength parts at the same time by using large spot laser to fill and sinter the inner part of the section with the laser energy density corresponding to the high-green strength parts(high-efficiency and high-strength bonding),and then using small spot with high laser energy density to scan the section profile to make it invalid(high-accuracy cutting).Through the process above,the problem of parts accuracy affected by the large secondary sintering area caused by laser high energy density sintering in the SLS method,which could bring high forming green strength,can be solved.To solve the problem of low absorption rate and poor formability of the fiber laser applied to the FLSIC process by coated silica sand,which is commonly used in sand mold printing,graphene is used to modify the raw materials in this paper.The preparation process of the modified material,as well as its forming performance with the effect of fiber laser is studied.The result shows that the strength and accuracy of the sand print can be ensured,besides improving the absorption capacity of coated silica sand for fiber laser.When graphene accounts for 0.1%of the mass of silica sand,the forming efficiency and strength reach the best status.Finally,the casting feasibility of this material in sand printing is proved by manufacturing qualified medium-sized pump casing castings,providing a low-cost and high-performance basic material for FLSIC forming of large sand molds.A new and light heat-insulating coated powder that can be used for LAM is developed.The coated material is made from the floating beads extracted from fly ash and composite powder is prepared through coating with phenolic resin thermal method.The preparation process of coated floating beads and the FLSIC forming process are studied in this paper.The effects of resin content on the strength,thermal conductivity,accuracy and specific strength of the part are also analyzed.The results show that the thermal conductivity,bulk density and flexural strength of FLSIC parts made of FP20 materials meet the requirements of casting insulation riser sleeves.This research,which realizes the recycling of wasted pollutants while expanding the scope of technical application,provides the basic materials for manufacturing the insulation risers with complex structures in the foundry industry.