Correlation between the productivity and mechanical performance of AISI 316L parts produced via Laser powder bed fusion process

Laser Powder Bed Fusion (LPBF) is an Additive Manufacturing (AM) process, able to generate parts of a quality comparable to those produced through conventional manufacturing methods. The technology allows the production of complex objects directly from metal powder, exploiting a layer-by-layer build-up methodology. Among the many advantages of SLM, low productivity is still one of the most difficult challenges to address since it drastically increases the overall production time. Consequently, the ability to manufacture components with enhanced accuracy and quality is counterbalanced by high manufacturing costs. This thesis aims to study the relationship between productivity and mechanical properties of AISI 316L parts. Process productivity depends on many factors; one of them is the Build Rate (BR) that directly depends on Volumetric Energy Density (VED). In this work, a procedure to select a process parameter combination with an increased BR is presented and experimentally validated, exploiting the VED lumped parameter. This thesis is divided into five chapters. The first one, “Introduction”, presents a general overview of AM. Chapter 2, “State of Art”, deals with the main findings reviewed during the research activity. First, the main process parameters and their effects on productivity and mechanical features are studied, providing a suitable productivity and cost equation model. In addition, it describes the principal procedures to select a set of process parameters with optimized BR, as well as some case studies with the support of previous works. Chapter 3, “Materials and methods” includes the experimental part of the thesis. To run the experiment, different combinations of process parameters were used to produce 24 test samples. The methods and the procedures used for the characterization of the samples are there described in detail. The purpose of the characterization was to identify the relation between the porosity percentage of the samples and the VED values used to print them. Once identified the most promising parameter sets which showed the best results in terms of porosity, tensile specimens were produced with those characteristics to test the mechanical properties. Chapter 4, “Results and discussions”, discusses the influence of process parameters on porosity, density, surface quality and roughness, tensile properties, and build time of 316L parts. The tensile test results only showed a slight difference in Yield Strength and ultimate tensile strength between specimens produced with high VED and those built with low VED. Despite this difference, two case studies are presented in an effort to highlight the significant advantages that the use of optimized parameters has, both in terms of time and costs: the low VED level allows to build products with an 18% faster build time. Finally, chapter 5 summarizes the conclusion of the whole work, clearly underlining the fact that the build time can be improved while maintaining good mechanical properties by adjusting the process parameters.