Development of an Eddy Current Testing Method as Process Control for Additive Manufacturing of Metallic Components

Abstract

Eddy current testing is one of the main nondestructive testing methods. It provides essentially information on surface and subsurface state of a structural component. Industrial non-destructive testing includes techniques such as X-rays, ultrasound and vibration analysis besides eddy current testing. These technics are absolutely crucial for safety and reliability of vital machinery components such as e.g. airplane wings or turbine blades, which are monitored at regular intervals by eddy current techniques to detect micro fatigue cracks. In this contribution, we discuss a new potential application of eddy-current testing which appeared while doing our research. Our research on future eddy current testing methods and instruments lead us to a new field, the online monitoring of additive manufacturing (3D printing). The industry is lately quite interested in additive manufacturing of metallic structures. These metallic structures could be used in near future directly as parts and not just as prototypes or models. The two main production processes are “Selective Laser Melting” (SLM) and “Selective Laser Sintering” (SLS). The component is manufactured from several hundreds or thousands of metal powder layers. These layers are deposited individually and a high-power laser fuses them. Many parameters influence this complex process and can lead to different types of defects or even to a complete failure of the manufactured part. Two of the main defects observed are delamination and porosity differences within the part. Partial delamination or porosity changes usually affects the mechanical strength of the part and a full delamination; a full delamination usually leads to a part failure, so there is obvious need to detect it as early as possible. In this paper we will present two main experiments for eddy current on-line monitoring and quality control. We will present tests on samples with different porosities and further eddy current testing on partly delaminated samples. The results of these tests will be presented and along with a method on how to differentiate these two failure modes. This work is part of an industrial cooperation with Sensima Inspection Sarl.