Abstract
In this paper, an orthogonal experiment was designed to fabricate the selective laser melting cobalt-chromium alloy samples. The influence rules of varying process parameters on the samples’ relative density was studied. The type and distribution of pore defect in the forming part were observed, and the pore formation mechanism was analysed, then porosity prevention measures were proposed. Experimental results show that: powder thickness affects the density of SLM forming parts most. Pore defect is one of the most important defects that affect the density. Pore defect can be divided into two types: keyhole and gas hole pore. The former is larger and irregular, caused by the underlying part of powder not melting completely due to the spheroidization effect and volume shrinkage effect of uneven powder thickness. The latter is smaller and round, mainly caused by the bubbles of nitrogen and vaporization of low melting point constituents discharging not timely. Reducing the thickness of the powder can effectively eliminate keyhole pore defects, and pre-heating the substrate before forming can reduce the occurrence of gas hole pore defects.
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