Hybrid and Multi-Metal Part Concepts in Laser Powder Bed Fusion

Abstract

A hybrid part in Laser Powder Bed Fusion (LPBF-H) is a composite joined in situ during the primary shaping of the additive manufactured joining partner. A comprehensive examination of the product development process for Hybrid Part Concepts in Laser Powder Bed Fusion (LPBF-H) is presented in this thesis. This framework comprises insights and methods as a knowledge database. A workflow to make these insights accessible in future development projects is described. The workflow covers conceptual design, the embodiment of the design and the process, and concludes with a verification step ahead of the production phase. The theoretical considerations of the product development process are accompanied by two case studies of fluid-conducting components: A servo valve, and a heat sink in a multi-metal design are examined. A conceptual design criterion database is introduced to assess whether – and if so, which – sub geometries of the component can be identified as potential LPBF structures. A hybrid part concept makes sense if there is heterogeneity between sub-geometries in the suitability of the process, and production-readiness criteria – additionally introduced – do not recommend an assembly instead. The suitability of the elements for LPBF is hypothesized by a suitability score, assigning the most unambiguous scored elements as poles. A scoring matrix and a dual system representation are developed to enable a process-specific aggregation and rearrangement of functional elements to LPBF and non-LPBF sections. A component concept variant selected in the conceptual phase must be subjected to embodiment design. Three sub-geometries are considered in the design process: The LPBF section, non-LPBF sections, and their interface. The generalized design guidelines for the LPBF-H variant are structured as applied to the design of these three sub-geometries. Special attention is paid to the manufacturing process for LPBF-H. A success criterion is deduced that models effects that determine the build success holistically. It is used as an onset for analytical indicator models to rationalize the extent of interface process modification. A theoretical analysis of the morphological dimensions of interface modifications complements this investigation. The presented interface architectures aim to develop interface processing based on a holistic consideration of existing options. The subsequent exploration of the aluminum alloy AlSi10Mg and copper material combination builds on these general concepts. The final chapter covers the quantitative property and performance evaluation of hybrid and multi metal LPBF components. Again, this evaluation is based on the case studies mentioned and the materials required for them, the stainless steel 1.4404, aluminum alloy AlSi10Mg, copper, and silver. Thermophysical property analyses show quantitatively that the intermetallic phase transition between aluminum and copper exhibits significantly poorer conductivity than the bulk material. However, the heat sink case study shows that improving functional performance characteristics is feasible when a hybrid and multi-metal part concept is applied and the LPBF design freedom is exploited. Component tests show this improvement regarding pressure loss in the cooling medium and heat dissipation. For 1.4404, the question arises as to whether cyclic loads can be safely endured at the interface and whether hybrid components can even be designed against them. Fatigue analyses were carried out to clarify this. Based on process- and parameter-specific data, a fatigue strength model, is calibrated and verified using the servo valve mentioned at the beginning. Dedicated tests on hybrid LPBF fatigue specimens show typical geometric notch errors at the interface and the validity of design recommendations developed against these. By applying these recommendations, the fatigue strength of the interface can be increased, and its computer-aided predictability can be achieved.