Layer-to-layer Closed-loop Switched Heating and Cooling Control of the Laser Powder Bed Fusion Process

TL;DR

This paper presents a novel switched layer-to-layer closed-loop feedback control system for stabilizing interlayer temperature in laser powder bed fusion, improving thermal stability across complex geometries by dynamically adjusting laser power and dwell time.

Contribution

The study introduces a new control architecture combining feedback optimization and dwell time triggering to enhance temperature stability in laser powder bed fusion, especially for complex geometries.

Findings

Effective stabilization of interlayer temperature across varying geometries.

Supported parts reduce overheating but increase energy and material use.

Unsupported parts stabilize temperature faster but extend build time.

Abstract

This study investigates the stabilization of interlayer temperature in the laser powder bed fusion process through a novel switched layer-to-layer closed-loop feedback controller. The controller architecture aims to measure the interlayer temperature by a laterally positioned thermal camera and maintain a preset reference temperature by switching between the heating mode through dynamic laser power adjustment and the cooling mode by assigning interlayer dwell time to allow cooling between layers. The switching controller employs a feedback optimization control algorithm for the heating mode to adjust the laser power, and a triggering algorithm that increases the interlayer dwell time until the interlayer temperature reaches the reference value. Additionally, the study compares the performance of the proposed controller in both supported and unsupported overhanging parts to evaluate the effect of support structures on the controller performance as well as the thermal behavior of overhanging parts. Results demonstrate the controller's effectiveness in stabilizing interlayer temperature across varying cross-sectional areas while remaining within the material's stable processing zone. In the heating mode, the controller efficiently stabilizes temperature, even in geometries with significant cross-section variation. The study also identifies trade-offs among process efficiency, energy consumption, and build time. Supported parts exhibit reduced overheating but consume more energy and material, while unsupported parts stabilize interlayer temperature faster but with longer build times due to increased dwell time assignments. The research highlights notable improvements in interlayer temperature control for geometries prone to excessive thermal stresses. Moreover, the introduction of interlayer dwell time offers a practical solution to maintaining thermal stability in complex geometries.