Tensile Strengths for Laser-Fabricated Parts and Similarity Parameters for Rapid Manufacturing

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Abstract
This paper presents a set of process parameter selection rules to deposit a good metal part. A CO2 laser is used to melt metal powder to achieve layer by layer deposition for fabricating three-dimensional parts. Dimensionless numbers characterizing this powder deposition process are identified using Buckingham’s Π-Theorem. These dimensionless numbers are used to identify a range of values for the process parameters, such as the laser power, spot diameter, speed of the xyz stage and powder flow rate, to achieve good quality layers for different materials. The yield and ultimate strengths are examined for parts fabricated with stainless steel 304 (SS 304) powder under three different processing conditions. These stresses are correlated to the operating conditions and physical dimensions of the deposit through the dimensionless similarity parameters. Experimental data indicate that the yield strength of the part is close to the value of standard sample (250 MPa, same as wrought stainless steel SS304). It is also observed that the direction of maximum yield strength is oriented very close to the dominant direction of material solidification. The ultimate strength is found to be considerably less than the ultimate strength of wrought SS 304 (540 MPa) which may be due to the residual stresses generated in the part.

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