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Robotic Wire Arc Additive Manufacturing with Variable Height Layers

John Marcotte, Sandipan Mishra, John T. Wen

TL;DR

This work tackles height deviations in aluminum WAAM when using variable-height, angled layers to form overhangs. It introduces a closed-loop approach that uses an IR camera on a separate robot to estimate the deposited layer height $oldsymbol{h}$ and adapt the torch-speed profile $oldsymbol{v_T}$ per layer through a constrained quadratic program, accommodating cold and hot bead-height models $ar f_{cold}$ and $ar f_{hot}$. The method yields substantial improvements over open-loop planning, with final-layer RMSEs as low as $0.57$ mm and no shielding-gas oxidation in closed-loop runs, validating the convergence analysis that error remains bounded under feedback. This framework enables more reliable, high-rate aluminum WAAM with angled layers and informs future enhancements such as in-process corrections, inclusion of the wire-feed rate as a control input, and considerations of material microstructure.

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.

Robotic Wire Arc Additive Manufacturing with Variable Height Layers

TL;DR

This work tackles height deviations in aluminum WAAM when using variable-height, angled layers to form overhangs. It introduces a closed-loop approach that uses an IR camera on a separate robot to estimate the deposited layer height and adapt the torch-speed profile per layer through a constrained quadratic program, accommodating cold and hot bead-height models and . The method yields substantial improvements over open-loop planning, with final-layer RMSEs as low as mm and no shielding-gas oxidation in closed-loop runs, validating the convergence analysis that error remains bounded under feedback. This framework enables more reliable, high-rate aluminum WAAM with angled layers and informs future enhancements such as in-process corrections, inclusion of the wire-feed rate as a control input, and considerations of material microstructure.

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.

Paper Structure

This paper contains 12 sections, 13 equations, 17 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Problem Statement
  3. Methods
  4. Overall Approach
  5. Process Model
  6. Nominal Process Plan
  7. Height of Layer from IR Camera during welding
  8. Correction Framework
  9. Convergence Analysis
  10. Experimental Setup
  11. Results and Discussion
  12. Conclusions

Figures (17)

  • Figure 1: Slicing methods for a bent tube using support structures (a), geometric decomposition (b), and non-uniform height layers (c).
  • Figure 2: Schematics of the multi-robot WAAM testbed.
  • Figure 3: Process input and output in the WAAM process
  • Figure 4: Control Architecture
  • Figure 5: Linear regression of $\ln(\Delta h)$ and $\ln(v_T)$ based on prior calibration data luMultiRobotScannPrintWire2024.
  • ...and 12 more figures