Study On Digital Design And Direct Fabrication Of Functional Parts Based On Selective Laser Melting

Selective Laser Melting (SLM) is one of the major Rapid Prototyping (RP) technologiesthat can directly fabricate metal functional parts. SLM is the research focus and thedevelopment trend of RP since the SLM part is metallurgical bonded and has high relativedensity, high dimensional accuracy and good mechanical properties. The current research onSLM has been focused on material, process, equipment, application and fabrication of singlepart. The design of SLM part and the direct fabrication of mechanisms have been seldomstudied.Due to the research status, this paper investigates the digital design and direct fabricationof functional parts based on SLM. The main contents and results are as follows:(1) Freeform design of functional parts was studied. The design frame for functional partswas established, then the timing relationship between structure elements was analyzed. Theprinciple constraints of freeform design were studied, considering the aspects of laser deeppenetration, slic ing of model and focus diameter. The design guidelines for functional partswith freeform structure were proposed, which included the principle constraints and thegeneric freeform structures. Functional parts could be designed according to the genericfreeform structures, which had the advantages of nonstandard form of raw materials, nonetool feature, none fixture feature, freeform hole and freeform surface.(2) The expression of utilization rate of energy during SLM process and its correctionfactor were obtained according to the principle of themodynamics and the geometry ofpowder packing. Three types of overlapping mechanism, intra-layer overlapping mechanism,inter-layer overlapping mechanism and mix overlapping mechanism, were introducedaccording to the geometrical relationship between tracks under interlayer-staggered scanningstrategy. Some experiments have been carried out to study the relationships between scanningspace, scanning speed and relative density and to test the mechanical properties of parts.Result showed that the tensile strength and the yield strength of part by SLM werecomparable to the counterparts from casting. The powder laying device of the SLMequipment was also improved to obtain better powder laying effect.(3) A new concept was proposed that non-assembly mechanisms was digitally assembledand subsequently directly fabricated by SLM as assembled. After introduction of clearancefeature, the design skills for non-assembly mechanisms were proposed that the mechanismcomplexity could be reduced by reducing the part count and simplifying the part shape andthe processability could be improved by adjusting the clearance feature. The major factors in direct fabrication of non-assembly mechanism were studied and some solutions werepresented: (a) Using drum shaped pin and drum shaped hole to optimiz e the clearance feature;(b) Adjusting the assembly angle and display to improve the surface quality of mechanism; (c)Using tilting display to reduce the number of supports within the clearance feature; (d)Increasing scanning speed to improve the fabrication quality of clearance feature. Forexperimental verification, a number of mechanisms have been designed and directlyfabricated.(4) The digital design of customized parts was studied. The design efficiency wasimproved by classifying the structure elements of customized part as common structure andcustomized geometry. Then, a method was proposed to quickly design customized bracket,which was assembled using structure features. For experimental verification, a mouth ofcustomized brackets has been designed and directly fabricated by SLM, then been testedusing Typodont simulative experiment. Result showed that the brackets could express theexpected orthodontic force accurately.(5) Two design guidelines for optimization of parts with complicated cavity was proposedthat the powders within the cavity could be cleared and the supports within the cavity couldnot affect the performance by classifying the structure elements as base structure and cavitystructure. Then, the Hole coaxial nozzle has been optimized using the design guidelines basedon SLM since the current one had several defects such as unwell cooling effect and unwellseal.