Abstract
The ability to produce consistent material properties across a single or series of platforms, particularly over time, is the major objective in metal additive manufacturing (MAM) research. If this can be achieved, it will result in widespread adoption of the technology for industry and place it into mainstream manufacturing. However, before this can happen, it is critical to develop an understanding of how processing parameters influence the thermal conditions which dictate the mechanical properties of MAM builds. Research work reported in the literature of MAM is generally based on a set of parameters and/or the review of a few parameter changes, and observing the effects that these changes (i.e., microstructure, mechanical properties) have. While these articles provide results with some insight, there lacks a standard approach that can be used to allow meaningful comparisons and conclusions to be made concerning the optimization of the processing variables. This study provides a template which can be used for making comparisons across DED platforms. The tests are performed with a design of experiments (DOE) philosophy directed to evaluate the effect of selected parameters on the measured properties of the DED builds. Specifically, a laser engineering net shaping system (LENS) is used to build multilayered 316L coupons and analyze how build parameters such as laser power, travel speed, and powder feed rate influence the thermal conditions that will define both microstructure and microhardness. A fundamental conclusion of this research is that it is possible to repeatedly obtain a consistent microstructure that contains a fine cellular substructure with a low level of porosity (less than 1.1%) and with microhardness that is equal to or better than wrought 316L. This is mainly achieved by maintaining an associated powder flow to travel speed ratio at the power level, ensuring an appropriate net heat input for the build process.
Highlights
The past few decades have provided great improvement in metal additive manufacturing (MAM) [1,2,3,4,5], but the consistency of the fabricated components’ properties continues to be a matter of concern
These beads were chosen to represent a range of powder feed to travel speed ratio across (Pf:Ts Ratio) the PLENS 645 W power setting
The research conducted in this study demonstrates an experimental approach that defines the powder flow to travel speed ratio Pf:Ts at a given power level which provides a consistent microstructure and microhardness for metallic directed energy deposition (DED), regardless of travel speed
Summary
The past few decades have provided great improvement in metal additive manufacturing (MAM) [1,2,3,4,5], but the consistency of the fabricated components’ properties continues to be a matter of concern. To evaluate the effect of these unique thermal cycles seen in MAM, empirical methods are often used to correlate thermal cycles to a set of processing parameters, without grasping the complexity of the essential foundations of these effects (i.e., what role does the heat input have on solidification). This kind of approach in the evaluation of observed results is further compounded by the variety of MAM systems available, with each system having particular nomenclatures and frameworks for operational use. Efforts have been made and are assisting in the advancement, but without a comprehensive look at the fundamental aspects, it is difficult to make significant improvements that can lead to widespread adoption
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