Influence of Process Parameters in LMD for Geometrical Accuracy and Thin Geometry with AISI316L

Abstract

Laser metal deposition (LMD) industrial use demands research about the influence of the parameters in the built parts density, accuracy and mechanical properties. Especially for the thin-wall parts, knowledge about the correlations between processing parameters and the final result is indispensable. This study explores the relationship between process parameters and the quality of AISI316L stainless steel thin-walled parts produced by LMD. A six-axis robot equipped with a deposition head allowed relative spatial movement between the powder nozzle and laser beam and substrate with high accuracy. Controlled energy input provided by continuous wave Ytterbium fibre laser allows using less material flow rate and the production of thin layers in test samples. Three processing parameters were selected to investigate the effects on part characteristics using a BoxBehnken experimental design. Through this method, each parameter was evaluated between 600 W to 800 W laser power, 6 mm/s to 14 mm/s feedrate and 0.2 mm to 0.4 mm layer thickness. All remaining parameters were fixed using argon to provide an inert atmosphere, 8.8 g/min powder feeding rate and 1.5 mm spot diameter. The method was used to test the manufacture of thin-wall cylindrical specimens with 10 mm in height and 75 mm in diameter. Fabricated AISI316L samples were evaluated regarding the dimensional and geometrical characteristics. It was observed that higher energy input density during the laser additive manufacturing implies lower geometric precision. Feedrate and layer thickness has the highest impact on both the wall thickness and vertical accuracy. Given the inability to produce parts with an acceptable final surface, the process finds great applicability when complemented with additional finishing technologies