Design guidelines for laser powder bed fusion in Inconel 718

Abstract

Additive manufacturing (AM) has been leveraged across various industries to potentially open design spaces allowing the design of parts to reduce the weight, cost, and integrated design. Over the past decade, AM has sped up fast enough to penetrate various industry offering potential solutions for multiple materials, such as metals, alloys, plastics, polymers, etc. However, challenges lie to best utilize the opened design spaces as current generation engineers are trained to design parts for the conventional manufacturing process. With this lack of design guidelines for the AM process, users are limiting themselves to best utilize the offering made by advanced manufacturing. For aerospace parts, the design freedom of additive manufacturing is attractive mainly for two purposes: for weight reduction through lighter, integrated design concepts as well as for functional optimization of parts aiming at an increase of performance, e.g., by optimizing flow paths. For both purposes, it is vital to understand the material-specific and manufacturing process design limits. In AM, combination of each material and manufacturing process defines the design space by influencing minimum thickness, angle, roughness, etc. This paper outlines a design guideline for the laser powder bed fusion (also DMLM, direct metal laser melting) AM process with Inconel 718 material. Inconel 718 is a superalloy with superior mechanical properties and corrosion resistance at elevated temperatures up to 700 °C and is, therefore, used in several applications including aerospace engine parts. Due to its weldability, the alloy has also been extensively investigated in laser powder bed fusion and other additive manufacturing processes. A comprehensive study is provided both analytically and experimentally suggesting how parts can be designed having critical design features, manufacturing direction/orientation to meet design requirements, design accuracy, and quality. Design features presented include walls, overhangs, bore holes, and teardrop shapes, with their minimal feature sizes and effects on accuracy and roughness of the build parts. For the light-weight design of parts, different concepts such as lattices and stiffener structures are discussed. For gas or liquid carrying flow channels, the geometrical form and size are highlighted. Based on an approach by Kranz et al., design guidelines for Inconel 718 are derived from the experiments and provided in the form of a catalog for easy application.