Coordinated motion control of a wire arc additive manufacturing robotic system for multi-directional building parts

TL;DR

This paper presents a coordinated control algorithm for wire arc additive manufacturing robots that enables precise deposition on complex shapes by aligning build direction with gravity, improving surface quality and structural integrity.

Contribution

It introduces a novel task augmentation control scheme for multi-robot WAAM systems to handle complex geometries and optimize build orientation.

Findings

Successful fabrication of complex geometry parts using the proposed control method

Enhanced surface finish and layer integrity in produced parts

Effective alignment of build direction with gravity during deposition

Abstract

This work investigates the manufacturing of complex shapes parts with wire arc additive manufacturing (WAAM). In order to guarantee the integrity and quality of each deposited layer that composes the final piece, the deposition process is usually carried out in a flat position. However, for complex geometry parts with non-flat surfaces, this strategy causes unsupported overhangs and staircase effect, which contribute to a poor surface finishing. Generally, the build direction is not constant for every deposited section or layer in complex geometry parts. As a result, there is an additional concern to ensure the build direction is aligned with gravity, thus improving the quality of the final part. This paper proposes an algorithm to control the torch motion with respect to a deposition substrate as well as the torch orientation with respect to an inertial frame. The control scheme is based on task augmentation applied to an extended kinematic chain composed by two robots, which constitutes a coordinated control problem, and allows the deposition trajectory to be planned with respect to the deposition substrate coordinate frame while aligning each layer buildup direction with gravity (or any other direction defined for an inertial frame). Parts with complex geometry aspects have been produced in a WAAM cell composed by two robots (a manipulator with a welding torch and a positioning table holding the workpiece) in order to validate the proposed approach.