Optical 3D Scanning and X-Ray Tomography Accurately Measure AM Part Geometry

Medical and Aerospace companies count among the early adopters of metal Additive Manufacturing (AM). The usually highly innovative automotive industry, however, so far struggles with the high manufacturing cost of Additive Manufacturing. An exception are high performance cars with low production volumes and demand for customization.

With metal Additive Manufacturing, two competing powder bed fusion technologies have been brought to industrialization in the past years. While typically Electron Beam Melting (EBM) is offering high productivity, Laser Beam Melting (LBM) offers higher resolution and geometrical freedom. However, LBM is closing in on productivity with multi laser systems.

A case study, supplied by Ampower, provides a deep dive into the manufacturing route of high performance automotive components by considering both Laser Beam Melting (LBM) and Electron Beam Melting (EBM) and evaluates the manufacturing feasibility of a Porsche GT2 RS tail pipe blend along the whole process chain from data preparation to surface finishing.

Tail pipe blends are the visible part of the engine exhaust system. Optical requirements are high since the component reflects the engine’s performance to the customer’s eye. Conventionally, the blends are manufactured from stainless steel or titanium alloys. Two metal sheets formed by deep drawing are joined by a welding seam. Requirements for the mechanical properties are driven by vibration and corrosion which put high stress on the welding seam. Additionally tail pipes are subject to major design iterations. This leads to remanufacturing of deep drawing tools with high cost and typical lead times of over 12 months.

The study analyzes the effect of process inherent distortion along the manufacturing route. X-ray tomography is used to reveal large part deformation after hot isostatic pressing if placed incorrectly. The results show that correct placement and orientation of the part during the process reduces such distortions. To finish the part both surface vibration grinding and micro machining are applied. As expected, the as build rough EBM surface proves to be challenging for both processes resulting in Ra values of around 3,6 µm. Using equal finishing operations on the LBM part yields a polished surface with Ra values below 0,1 µm.

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X-ray scan of the tail pipe blend revealed powder remains between the walls of the EBM part. The preheating of the powder during the EBM process to several hundred degrees causes the powder particles to expand and adhere to each other to form a powder cake. Removal of parts requires mechanical work to loosen the particles. A common method is to use a blasting process. For such processes to work successfully, hollow structures require suitable access for the blasting nozzle.

The study closes with an evaluation of the cost structure and lead time of the process chain including pre- and post-processing. The LBM technology proves to be more cost efficient, if multi laser systems are employed. The thin walled structure leads to lower effective build rates on the EBM machine. It turns out that the fast lead time of around 25 days is a game changing benefit of AM produced automotive parts such as the reviewed tail pipe blend compared to traditional tool-bound production.

Download the full study

for more information: www.am-power.de

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