Role of contour scanning speed on the lateral surface quality of TC1 alloy printed by selective laser melting
Selective laser melting(SLM)process is one of the key three-dimensional printing technologies,which has been widely applied into the manufacturing of components with geometrically complex structures.Most of the selective laser melting printed components should subject to machining operation to satisfy the requirement of surface quality,like polishing and grounding.It is attractive that the comparatively low demand of printed component surface quality can be met through tailoring the parameters of printing processes.The subse-quent machining procedure can be thus reduced with shortened production cycle and optimized cost-effectiveness of manufacturing.So it is vitally important to elucidate the effect of SLM parameters on the surface quality of printed components.In the current study,a series of distinct contour scanning speed were utilized to prepare SLMed specimens of TC1 titanium alloy.The sections of specimen lateral surface were observed by Axio Oberver 3M microscope.The printing defects in the lateral near-surfaces of specimens were also characterized.The corresponding outline of near-surface boundaries were further extracted and processed.The data of outline was then statistically obtained to quantitatively calculate the roughness of the printed specimen surfaces.The Vickers hardness variation in the area within the range of 0.05 to 0.8 mm away from the lateral surface was measured by Wilson VH3100 hardness tester.It is found that the roughness(Ra)of the SLMed specimens lateral surfaces increases from 8.09 μm to 12.27 μm with the rise of contour scanning speed,which can be primarily attributed to the balling behavior and incomplete melting of powder adherent with the surface.To be specific,a large amount of air pore defects form around the near-surfaces of the components due to the keyhole effect of melted powders.The air pores mainly distribute in the areas 80 μm to 130 μm away from the near-surfaces.The size of these air pores varies from 20 μm to 50 μm.On the other hand,unfused defects occurred in the near-surfaces of specimens can be ascribed to the low energy density at high contour scanning speed(900 mm/s).The unfused defects locate at the areas 100 μm to 115 μm away from the near-surfaces.The dimension of the unfused defects long axis varies from 10 μm to 50 μm.In addition,relatively lower contour scanning speed leads to the increment of energy density.The cooling rate of the melting pool in the contour area consequently reduces.As a result,the hardness of the near-surfaces decreases.Therefore,it can be deduced that high contour scanning speed benefits to the maintaining of hardness around the near-surfaces areas.On the basis of the above research results,it is thus concluded that tunning the contour scanning speed of selective laser melting process can effectively amelio-rate the lateral surface quality of the SLMed specimens of TC1 titanium alloy.While a moderate contour scanning speed is proposed as an appropriate printing parameter.
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