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Multi-Robot Scan-n-Print for Wire Arc Additive Manufacturing

Chen-Lung Lu, Honglu He, Jinhan Ren, Joni Dhar, Glenn Saunders, Agung Julius, Johnson Samuel, John T. Wen

TL;DR

This paper tackles geometric imprecision in WAAM by introducing a closed-loop, multi-robot framework (6-DOF welding robot, 2-DOF trunnion, 6-DOF sensing robot with a wrist-mounted laser) that uses layer-wise height measurements to adjust deposition via the torch speed. A deposition-height model links torch speed to height, enabling per-layer and per-segment speed updates that are applied in either stepwise or continuous modes, with continuous feedback up to 100 Hz. Experimental validation on aluminum (ER 4043) and steel (ER 70S-6) alloys demonstrates substantial improvements in height uniformity and surface accuracy for wall and blade-like geometries, and confirms repeatability through velocity replay. The results indicate that the Scan-n-Print approach enhances near-net-shape WAAM quality and reliability, reducing edge defects and improving overall geometric fidelity for complex parts.

Abstract

Robotic Wire Arc Additive Manufacturing (WAAM) is a metal additive manufacturing technology, offering flexible 3D printing while ensuring high quality near-net-shape final parts. However, WAAM also suffers from geometric imprecision, especially for low-melting-point metal such as aluminum alloys. In this paper, we present a multi-robot framework for WAAM process monitoring and control. We consider a three-robot setup: a 6-dof welding robot, a 2-dof trunnion platform, and a 6-dof sensing robot with a wrist-mounted laser line scanner measuring the printed part height profile. The welding parameters, including the wire feed rate, are held constant based on the materials used, so the control input is the robot path speed. The measured output is the part height profile. The planning phase decomposes the target shape into slices of uniform height. During runtime, the sensing robot scans each printed layer, and the robot path speed for the next layer is adjusted based on the deviation from the desired profile. The adjustment is based on an identified model correlating the path speed to change in height. The control architecture coordinates the synchronous motion and data acquisition between all robots and sensors. Using a three-robot WAAM testbed, we demonstrate significant improvements of the closed loop scan-n-print approach over the current open loop result on both a flat wall and a more complex turbine blade shape.

Multi-Robot Scan-n-Print for Wire Arc Additive Manufacturing

TL;DR

This paper tackles geometric imprecision in WAAM by introducing a closed-loop, multi-robot framework (6-DOF welding robot, 2-DOF trunnion, 6-DOF sensing robot with a wrist-mounted laser) that uses layer-wise height measurements to adjust deposition via the torch speed. A deposition-height model links torch speed to height, enabling per-layer and per-segment speed updates that are applied in either stepwise or continuous modes, with continuous feedback up to 100 Hz. Experimental validation on aluminum (ER 4043) and steel (ER 70S-6) alloys demonstrates substantial improvements in height uniformity and surface accuracy for wall and blade-like geometries, and confirms repeatability through velocity replay. The results indicate that the Scan-n-Print approach enhances near-net-shape WAAM quality and reliability, reducing edge defects and improving overall geometric fidelity for complex parts.

Abstract

Robotic Wire Arc Additive Manufacturing (WAAM) is a metal additive manufacturing technology, offering flexible 3D printing while ensuring high quality near-net-shape final parts. However, WAAM also suffers from geometric imprecision, especially for low-melting-point metal such as aluminum alloys. In this paper, we present a multi-robot framework for WAAM process monitoring and control. We consider a three-robot setup: a 6-dof welding robot, a 2-dof trunnion platform, and a 6-dof sensing robot with a wrist-mounted laser line scanner measuring the printed part height profile. The welding parameters, including the wire feed rate, are held constant based on the materials used, so the control input is the robot path speed. The measured output is the part height profile. The planning phase decomposes the target shape into slices of uniform height. During runtime, the sensing robot scans each printed layer, and the robot path speed for the next layer is adjusted based on the deviation from the desired profile. The adjustment is based on an identified model correlating the path speed to change in height. The control architecture coordinates the synchronous motion and data acquisition between all robots and sensors. Using a three-robot WAAM testbed, we demonstrate significant improvements of the closed loop scan-n-print approach over the current open loop result on both a flat wall and a more complex turbine blade shape.

Paper Structure

This paper contains 16 sections, 5 equations, 19 figures, 6 tables.

Table of Contents

  1. INTRODUCTION
  2. Scan-n-Print Framework
  3. Overview
  4. Motion Generation and Execution
  5. Deposition Height Profile
  6. Motion Optimization
  7. Step-wise vs Continuous Scan-n-Print
  8. Welding Model
  9. Experiments and Evaluation
  10. Hardware Testbed
  11. Performance Comparison: Wall Structure
  12. Performance Comparison: Blade-like Structure
  13. Performance Comparison: Steel Alloy
  14. Continuous Scan-n-Print
  15. Repeatability Test
  16. ...and 1 more sections

Figures (19)

  • Figure 1: Scan-n-Print WAAM testbed
  • Figure 2: Scan-n-Print framework
  • Figure 3: Scanning path plan
  • Figure 4: Deposition height of the weld piece
  • Figure 5: Speed update of 40 motion segments. Dots: difference from the current height to the target height $\Delta h_d$. Lines: the updated torch speed.
  • ...and 14 more figures