Variations in temperature, residual stress, and distortion in collaborative robot-assisted patterned additive manufacturing

Abstract

Collaborative robots (COBOT) offer advantages over traditional robots by reducing the need for path programming, enhancing safety for human interaction, and improving user-friendliness and productivity, making them suitable for additive manufacturing of large and complex parts. COBOT simplifies path planning in patterned additive manufacturing by using teaching points where a complex deposition pattern can be represented by a few key coordinates. However, the selection of teaching points significantly affects the temperature fields, deposit geometry, residual stresses, and distortion, and these effects are not well understood. Here we use a combined experimental and computational approach to study the effects of four patterns with different teaching points (4, 5, 6, and 8) during wire arc-directed energy deposition (WA-DED) of stainless steel. Experiments are performed using an in-house COBOT-assisted WA-DED system. Finite element modeling is done to compute temperature fields, deposit geometry, residual stresses, and distortion. We concluded that the distribution of residual stress varies notably with different deposition patterns, even though the maximum stress values are not significantly different. Stress tends to accumulate at sharp corners where the arc heat source stays longer. In addition, thermal distortion is present in all parts due to variations in the temperature field, with the highest distortion occurring farthest from the molten pool. However, overall distortion remains comparable across parts due to a consistent total heat input.