Monitoring of laser metal deposition height by means of coaxial laser triangulation

TL;DR

This paper introduces a coaxial optical triangulation system for real-time, non-intrusive monitoring of deposition height in laser metal deposition, improving process control and quality in additive manufacturing.

Contribution

It presents a novel coaxial, non-intrusive optical triangulation method integrated into LMD for accurate height monitoring during the process.

Findings

Successfully monitored stainless steel deposition height.

Reconstructed spatial height variation maps.

Identified self-regulating layer thickness mechanism.

Abstract

Laser metal deposition (LMD) is an additive manufacturing technique, whose performances can be influenced by several factors and parameters. Monitoring their evolution allows for a better comprehension and control of the process, hence enhancing the deposition quality. In particular, the deposition height is an important variable that, if it does not match the process growth, can bring to defects and geometrical inaccuracies in the deposited structures. The current work presents a system based on optical triangulation for the height monitoring, implemented on a LMD setup composed of a fiber laser, a deposition head, and an anthropomorphic robot. Its coaxial and non-intrusive configuration allows for flexibility in the deposition strategy and direction. A measurement laser beam is launched through the powder nozzle and hits the melt pool. A coaxial camera acquires the probe spot, whose position is converted to relative height. The device has been demonstrated for monitoring the deposition of a stainless steel cylinder. The measurements allowed to reconstruct a spatial map of the height variation, highlighting a transient in the deposition growth which can be explained in terms of a self-regulating mechanism for the layer thickness.