Robotic Wire Arc Additive Manufacturing with Variable Height Layers

TL;DR

This paper introduces a closed-loop control system for robotic wire arc additive manufacturing that uses IR imaging to adaptively correct layer height variations, improving geometric accuracy especially with aluminum.

Contribution

It presents a novel real-time feedback control method for layer height correction in wire arc additive manufacturing, addressing aluminum's temperature-dependent bead geometry.

Findings

Significant improvement in layer height accuracy with closed-loop control

Robustness to inaccuracies in model parameters demonstrated

Effective for complex geometries without support material

Abstract

Robotic wire arc additive manufacturing has been widely adopted due to its high deposition rates and large print volume relative to other metal additive manufacturing processes. For complex geometries, printing with variable height within layers offer the advantage of producing overhangs without the need for support material or geometric decomposition. This approach has been demonstrated for steel using precomputed robot speed profiles to achieve consistent geometric quality. In contrast, aluminum exhibits a bead geometry that is tightly coupled to the temperature of the previous layer, resulting in significant changes to the height of the deposited material at different points in the part. This paper presents a closed-loop approach to correcting for variations in the height of the deposited material between layers. We use an IR camera mounted on a separate robot to track the welding flame and estimate the height of deposited material. The robot velocity profile is then updated to account for the error in the previous layer and the nominal planned height profile while factoring in process and system constraints. Implementation of this framework showed significant improvement over the open-loop case and demonstrated robustness to inaccurate model parameters.