Deepankar Pal

Comparison of 3DSIM thermal modelling of selective laser melting using new dynamic meshing method to ANSYS

Abstract Selective laser melting (SLM) is an additive manufacturing (AM) process in which parts are fabricated by selectively melting regions of the surface of a metallic powder bed in a layer-by-layer fashion. Various thermal phenomena such as heat conduction, convection, radiation, melting and solidification, dynamic phase changes, and evaporation occur during the SLM process. In addition, laser intensity and powder bed scan speeds during processing complicate understanding of the process due to complex dynamic interactions between the powder bed and laser. In order to study these dynamic interactions, a finite element model has been developed which uses a dynamic mesh with spatial non-linear thermal properties to track the point of laser exposure on the powder bed to study thermal evolution during SLM. The model is able to achieve a refined, localised mesh in the melt zone and heat affected zone (HAZ), surrounded by a relatively coarse mesh outside of the HAZ regions. The dynamic meshing for this implementation is achieved using both the sub-modelling functionality in ANSYS and a new set of algorithms being commercialised by 3DSIM, LLC. It was found that dynamic meshing reduces the model size and computational burden. In this paper, the use of the sub-modelling approach for dynamic meshing was verified by comparing it against a uniform fine mesh model. The results of the two models match within an acceptable tolerance. Also, a mesh sensitivity analysis was carried out in order to show solution convergence as a function of increasing mesh density. The results of this analysis were also validated using experiments to show a match between experimental and simulated melt pools. Finally, the ANSYS solution was compared with a new set of dynamic meshing finite element analysis algorithms running in Matlab. It was found that these new algorithms were significantly faster than their ANSYS counterparts for solving problems using a dynamic mesh.

A Generalized Feed Forward Dynamic Adaptive Mesh Refinement and Derefinement Finite Element Framework for Metal Laser Sintering—Part I: Formulation and Algorithm Development

A novel multiscale thermal analysis framework has been formulated to extract the physical interactions involved in localized spatiotemporal additive manufacturing processes such as the metal laser sintering. The method can be extrapolated to any other physical phenomenon involving localized spatiotemporal boundary conditions. The formulated framework, named feed forward dynamic adaptive mesh refinement and derefinement (FFD-AMRD), reduces the computational burden and temporal complexity needed to solve the many classes of problems. The current study is based on application of this framework to metals with temperature independent thermal properties processed using a moving laser heat source. The melt pool diameters computed in the present study were compared with melt pool dimensions measured using optical micrographs. The strategy developed in this study provides motivation for the extension of this simulation framework for future work on simulations of metals with temperature-dependent material properties during metal laser sintering.

Modelling of ultrasonic consolidation using a dislocation density based finite element framework

A dislocation density based constitutive model has been developed and implemented into a crystal plasticity quasi-static finite element framework. This approach captures the evolution of dislocations and grain fragmentation at the bonding interface when boundary conditions pertaining to the Ultrasonic Consolidation process (UC) are prescribed. The model is initially calibrated using experimental data from published refereed literature for simple shear deformation of a single crystal pure aluminum and uniaxial tension of a polycrystalline Aluminum 3003-H18 alloy. The model has then been extended to predict the results of an Al 3003- H18 alloy undergoing UC. Good agreement between the experimental and simulated results has been observed for the evolution of linear weld density and embrittlement due to grain substructure evolution. For computational time efficiencies, a novel time homogenisation approach has been followed which significantly reduces the computational overhead.

An Efficient Multi-Scale Simulation Architecture for the Prediction of Performance Metrics of Parts Fabricated Using Additive Manufacturing

In this study, an overview of the computational tools developed in the area of metal-based additively manufactured (AM) to simulate the performance metrics along with their experimental validations will be presented. The performance metrics of the AM fabricated parts such as the inter- and intra-layer strengths could be characterized in terms of the melt pool dimensions, solidification times, cooling rates, granular microstructure, and phase morphologies along with defect distributions which are a function of the energy source, scan pattern(s), and the material(s). The four major areas of AM simulation included in this study are thermo-mechanical constitutive relationships during fabrication and in-service, the use of Euler angles for gaging static and dynamic strengths, the use of algorithms involving intelligent use of matrix algebra and homogenization extracting the spatiotemporal nature of these processes, a fast GPU architecture, and specific challenges targeted toward attaining a faster than real-time simulation efficiency and accuracy.

Microstructures of Friction Surfaced Coatings – a TEM Study

Abstract The microstructures of dissimilar metal welds between 9Cr-1Mo (Modified) (P91) and austenitic stainless steel (AISI 304) with Ni-based alloy interlayers (Inconel 625, Inconel 600 and Inconel 800H) are reported. These interlayers were deposited by the friction surfacing method one over the other on P91 alloy, which was finally friction welded to AISI 304. In this paper, the results of microstructural evolution in the friction surfaced coated interlayers (Inconel 625, 600, 800H) are reported. For comparative purposes, the microstructures of consumable rods (Inconel 625, 600, 800H) and dissimilar metal base metals (P91 and AISI 304) were also reported. Friction surfaced coatings exhibited dynamic recrystallization. In friction surfaced coatings, the carbide particles were found to be finer and distributed uniformly throughout the matrix, compared to their rod counterparts.

The effects of material property assumptions on predicted meltpool shape for laser powder bed fusion based additive manufacturing

The objective of this study was to provide guidance on material specifications for powders used in laser powder bed fusion based additive manufacturing (AM) processes. The methodology was to investigate how different material property assumptions in a simulation affect meltpool prediction and by corrolary how different material properties affect meltpool formation in AM processes. The sensitvity of meltpool variations to each material property can be used as a guide to help drive future research and to help prioritize material specifications in requirements documents. By identifying which material properties have the greatest affect on outcomes, metrology can be tailored to focus on those properties which matter most; thus reducing costs by eliminating unnecessary testing and property charaterizations. Futhermore, this sensitivity study provides insight into which properties require more accurate measurements, thus motivating development of new metrology methods to measure those properties accurately.

A study of transverse laser modes using a novel multi-scale simulation architecture for laser-based manufacturing technologies

The present work presents an investigation of transverse laser modes in Selective Laser Melting (SLM). It includes detailed descriptions of process physics and various simulation tools that were developed at 3DSIM for SLM simulation. The SLM process depends on a focused laser directed towards a powder bed to selectively melt and solidify layers of powder to create a complex three dimensional geometry. The thermo-mechanical interaction of laser, powder bed and partially solidified part involves various nonlinear phenomena leading to final part microstructure, mechanical properties and geometrical accuracy. One important aspect of these interactions is the laser beam profile. Traditionally, Gaussian laser profiles with 00 transverse modes are used for SLM, since these are the only modes readily available for commercial purposes. The present work utilizes the SLM simulation tools at 3DSIM to study the potential for the use of transverse mode lasers for SLM. The interaction of transverse laser modes with characteristic thermal Eigenmodes of a typical powder bed has been modeled to further understand the effects of higher order laser modes on SLM performance.