The Study On Surface Roughness Of Metal Parts Fabricated By Selective Laser Melting And The Application On Non-assembly Mechanisms

SLM, which have the advantage of favorable mechanical properties and high processaccuracy, is able to fabricate complex structural metal parts directly. However, bad surfacequality of the fabricated parts is one of the biggest shortcomings of this technique and is alsothe main obstacle which prevents SLM from being putted into wide application. This paperaims at improving the surface quality of SLM parts. Systematic studies are conducted to topsurface and side surface roughness. This paper is divided into three sections: the first sectionis theoretical research of surface roughness. The second section is process parametersoptimization of surface roughness. The last section is designing, manufacturing andpost-treatment of Non-assembly Mechanisms with high surface quality. The main contentsand achievements are as follows:（1）The top surface roughness of SLM parts is determined by three factors in theory.They are the width of melting pool, scan spacing and layer thickness. As the width of meltingpool are mainly dependent on laser power and scan speed. Hence, surface roughness is mainlyinfluenced by laser power, scan speed, scan spacing and layer thickness. The roughness ofinclined surface is theoretically determined by inclined angle and layer thickness. The biggerthe inclined angle is and the thinner the layer thickness is, the smaller the roughness ofinclined surface will be.(2) The fluctuations of influencing factors such as scan speed, laser power and scanspacing is unfavorable in terms of improving roughness. During the process of SLMmanufacturing, these three parameters are interactive and interrelated. So when setting upparameters, the whole process of manufacturing should be comprehensively taken intoaccount. If the volume energy density is too high, the balling effect would be caused, which isvery detrimental in improving the product quality. During the manufacturing, the laser energydensity should be maintained between120J/mm3to160J/mm3. The impact of thickness ofpowder and angle of inclination on side surface of parts conforms to theoretical analysis. Dueto the effect of laser penetrating, the down side of the parts is rougher than upper side of theparts. The area scanning can effectively reduce the warp. The layer stagger orthogonalscanning strategy with after raster in higher scan speed is an ideal scanning strategy. Lasersurface re-melting can not only improve the surface roughness, but also can enhance thedensity of the parts.(3) In the instances of parts manufacturing, two non-assembly parts, coin abacus andbicycle, are designed and manufactured. The clearance of the non-assembly mechanism is improved, and the improved drum clearance structure can not only reduce the support, butalso make the powder in the clearance remove more easily. Cross type support and taperedcylindrical support manually added not only fully take the part overhanging face into accountand receive better strength, but also make it easy to remove support after fabricating.Sandblasting treatment and electrolytic polishing can greatly improve the surface quality ofthe parts.This research can provide a theoretical basis and guidance for improving surfaceroughness of SLM parts.