Scalable Path Level Thermal History Simulation of PBF process validated by Melt Pool Images

TL;DR

The paper tackles scalable path-level thermal-history simulation for laser powder bed fusion by extending CAPL with three innovations: full-domain discretization using fictitious elements, Voronoi-based initialization to handle overlapping paths, and a refined conduction model to capture steep gradients near the melt pool. The PBF-CAPL method is validated against high-resolution AMMT melt-pool frames for IN625, achieving roughly 10% relative error in melt-pool length across multiple cases and revealing insights into how laser power influences melt-pool evolution. Key contributions include a robust discretization strategy for non-orthogonal paths, energy-conserving laser input handling under overlaps, and a conduction-cap model that better represents near-melt-gradient physics. The work demonstrates the practical potential of scalable, path-level thermal-history simulations to inform process planning and optimization in LPBF, and outlines future enhancements such as dynamic absorptivity and data-driven melt-pool prediction to further improve accuracy without sacrificing efficiency.

Abstract

In this paper we outline the development of a scalable PBF thermal history simulation built on CAPL and based on melt pool physics and dynamics. The new approach inherits linear scalability from CAPL and has three novel ingredients. Firstly, to simulate the laser scanning on a solid surface, we discretize the entire simulation domain instead of only the manufacturing toolpath by appending fictitious paths to the manufacturing toolpath. Secondly, to simulate the scanning on overlapping toolpaths, the path-scale simulations are initialized by a Voronoi diagram for line segments discretized from the manufacturing toolpath. Lastly, we propose a modified conduction model that considers the high thermal gradient around the melt pool. We validate the simulation against melt pool images captured with the co-axial melt pool monitoring (MPM) system on the NIST Additive Manufacturing Metrology Testbed (AMMT). Excellent agreements in the length and width of melt pools are found between simulations and experiments conducted on a custom-controlled laser powder bed fusion (LPBF) testbed on a nickel-alloy (IN625) solid surface. To the authors' best knowledge, this paper is the first to validate a full path-scale thermal history with experimentally acquired melt pool images. Comparing the simulation results and the experimental data, we discuss the influence of laser power on the melt pool length on the path-scale level. We also identify the possible ways to further improve the accuracy of the CAPL simulation without sacrificing efficiency.

Figures (28)

• Figure 1: System diagram of contact-aware path-level (CAPL) for laser powder bed fusion (LPBF) process. The components of the original CAPL are in dark blue and our modification and improvements for validation are shown in orange.
• Figure 2: The actual laser path is inside the red box. Fictitious elements are added as the paths outside the red box to represent the larger surface. The solid continuum is modeled as multiple such layers.
• Figure 3: Example of elements on the left top corner of the layer. Unexpected element overlaps with non-parallel overlapped path exists before modification (left). Elements generated by Voronoi diagram after modification (right): elements (in blue) approximately form a Voronoi diagram (in red) whose sites are the scanning paths (in black)
• Figure 4: Top view of the contact area (in red). The contact area is the smaller projected cross-section (in green) projected along the angle $\theta$ between two elements. $L$ and $W$ are the element length and width. Arrows indicate the scanning directions.
• Figure 5: An example of melt pool frame (left) acquired on the Additive Manufacturing Metrology Testbed by NIST and the binarized result (threshold is 80 out of 255).