Overhanging Features and the SLM/DMLS Residual Stresses Problem: Review and Future Research Need

Albert E Patterson,Phillip A Farrington,Sherri L Messimer

doi:10.3390/technologies5020015

Albert E Patterson, Phillip A Farrington + Show 1 more

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https://doi.org/10.3390/technologies5020015

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Abstract

A useful and increasingly common additive manufacturing (AM) process is the selective laser melting (SLM) or direct metal laser sintering (DMLS) process. SLM/DMLS can produce full-density metal parts from difficult materials, but it tends to suffer from severe residual stresses introduced during processing. This limits the usefulness and applicability of the process, particularly in the fabrication of parts with delicate overhanging and protruding features. The purpose of this study was to examine the current insight and progress made toward understanding and eliminating the problem in overhanging and protruding structures. To accomplish this, a survey of the literature was undertaken, focusing on process modeling (general, heat transfer, stress and distortion and material models), direct process control (input and environmental control, hardware-in-the-loop monitoring, parameter optimization and post-processing), experiment development (methods for evaluation, optical and mechanical process monitoring, imaging and design-of-experiments), support structure optimization and overhang feature design; approximately 143 published works were examined. The major findings of this study were that a small minority of the literature on SLM/DMLS deals explicitly with the overhanging stress problem, but some fundamental work has been done on the problem. Implications, needs and potential future research directions are discussed in-depth in light of the present review.

Highlights

Additive manufacturing (AM) technologies, commonly known as 3D printing tools, are a family of manufacturing processes that produce solid geometries by “joining [raw] materials to make objects from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing methods” [1].While most commonly-used and established AM processes use plastics and photopolymers as the initial raw material, a number of AM processes that can process metals are emerging and being rapidly developed and perfected
One of the most promising and flexible of these metal-printing processes is known as selective laser melting (SLM) or direct metal laser sintering (DMLS)
The collection of both general and regional residual stresses into parts without a way for them to naturally dissipate can be a major problem because this can initiate cracks, warpage and delamination if the part is not properly designed or has delicate features, both during and after processing, and can reduce the fatigue strength of the part by a factor of 10 or more when compared to bulk-formed parts [5,6,7,8]

Summary

Introduction

While most commonly-used and established AM processes use plastics and photopolymers as the initial raw material, a number of AM processes that can process metals (usually in the form of fine powder) are emerging and being rapidly developed and perfected. The availability of such fabrication tools offers great promise to many sectors of manufacturing, especially the aerospace, medical and automotive industries, in their ever-growing quest for lighter, stronger, tougher, more complex and more cost-efficient metal parts. The collection of both general and regional residual stresses into parts without a way for them to naturally dissipate (as they do in non-metal AM processes) can be a major problem because this can initiate cracks, warpage and delamination if the part is not properly designed or has delicate features, both during and after processing, and can reduce the fatigue strength of the part by a factor of 10 or more when compared to bulk-formed parts [5,6,7,8]

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