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Layer-to-Layer Melt Pool Control in Laser Powder Bed Fusion

Dominic Liao-McPherson, Efe C. Balta, Mohamadreza Afrasiabi, Alisa Rupenyan, Markus Bambach, John Lygeros

Abstract

Additive manufacturing processes are flexible and efficient technologies for producing complex geometries. However, ensuring reliability and repeatability is challenging due to the complex physics and various sources of uncertainty in the process. In this work, we investigate closed-loop control of the melt pool dimensions in a laser powder bed fusion (LPBF) process. We propose a trajectory optimization-based layer-to-layer controller that adjusts the laser power input to the next layer to track a desired melt pool depth and validate our controller by placing it in closed-loop high-fidelity multi-layer smoothed particle hydrodynamics simulator of a 2D LPBF process. Detailed numerical case studies demonstrate successful regulation of the melt pool depth on brick and overhang geometries and provide first of its kind results on the effectiveness of layer-to-layer input optimization for the LPBF process as well as detailed insight into the physics of the controlled process. Computational complexity and process performance results illustrate the method's effectiveness and provide an outlook for its implementation onto real systems.

Layer-to-Layer Melt Pool Control in Laser Powder Bed Fusion

Abstract

Additive manufacturing processes are flexible and efficient technologies for producing complex geometries. However, ensuring reliability and repeatability is challenging due to the complex physics and various sources of uncertainty in the process. In this work, we investigate closed-loop control of the melt pool dimensions in a laser powder bed fusion (LPBF) process. We propose a trajectory optimization-based layer-to-layer controller that adjusts the laser power input to the next layer to track a desired melt pool depth and validate our controller by placing it in closed-loop high-fidelity multi-layer smoothed particle hydrodynamics simulator of a 2D LPBF process. Detailed numerical case studies demonstrate successful regulation of the melt pool depth on brick and overhang geometries and provide first of its kind results on the effectiveness of layer-to-layer input optimization for the LPBF process as well as detailed insight into the physics of the controlled process. Computational complexity and process performance results illustrate the method's effectiveness and provide an outlook for its implementation onto real systems.
Paper Structure (21 sections, 8 equations, 13 figures, 1 table, 1 algorithm)

This paper contains 21 sections, 8 equations, 13 figures, 1 table, 1 algorithm.

Table of Contents

  1. Introduction
  2. High-fidelity Multi-layer LPBF Process Model
  3. Powder Layer Generation Module
  4. Melt Pool Simulation Module
  5. Control Design
  6. Control Architecture
  7. Control-oriented Modeling
  8. Optimal Control Problem
  9. Numerical Experiments
  10. Simulation Setup
  11. Controller Model Identification
  12. Depth Tracking Results with L2L Control
  13. Comparison between open and closed-loop
  14. Runtime
  15. Geometry and Temperature
  16. ...and 6 more sections

Figures (13)

  • Figure 1: In an LPBF process, a thin layer of metal powder is selectively melted using a high-power laser. The melted powder material then solidifies and bonds to the underlying solid volume.
  • Figure 2: LPBF closed-loop control architecture considered in this work.
  • Figure 3: Consecutive steps of the multi-layer LPBF simulation in our SPH-based modeling framework: (A)-(F). Fraction of fluid and temperature distributions at layer 2 are shown for a time-step in which the melt pool has reached a steady state. The color spectrum from red to blue in the two images below the subfigure F depicts the transition from hot to cold temperatures.
  • Figure 4: Print of a 10-layer part with constant 125W input. As each layer is printed the laser deposits thermal energy in the part. As this energy builds up, the melt pool becomes larger and more energetic leading to non-uniformities in the part. This heat buildup could be avoided by allowing the part to completely cool between layers but at the cost of significantly increasing the build time for the part.
  • Figure 5: The proposed layer-to-layer control architecture
  • ...and 8 more figures

Theorems & Definitions (1)

  • Remark 1