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Understanding build failures in metal AM
Understanding build failures in Laser Powder Bed Fusion: An overview Build failures remain a major challenge in metal Additive Manufacturing, particularly on large parts for which build times are measured in many days rather than hours. They come at a high price in lost machine time, wasted material and delayed deliveries. Olaf Diegel and Terry Wohlers explain a number of reasons for such failures in Laser Powder Bed Fusion processes. In many cases, one can reduce their risk through effective part and support design, parameter control and machine maintenance.
Contrary to much of the marketing hype of the past, it is not easy to make absolutely anything with AM. Producing good parts by AM requires a detailed understanding of the different processes and how to design for them. In fact, making parts by metal AM can be difficult and, in the majority of cases, using metal AM to manufacture parts should only be considered if the process adds value to the product. Every operator of metal AM systems knows that build failures are not uncommon, and learning how to predict and minimise them is a critical part of the process. To be able to do this, it is important to understand the causes of metal AM build failures. Also important is gaining an understanding of the strategies used to minimise the chance of failures.
Part distortion An estimated 70% of all metal AM failures occur from physical distortion of the part. These failures can occur from thermal stresses and distortion caused as the part distorts enough to
Vol. 5 No. 1 Š 2019 Inovar Communications Ltd
interfere with the recoater. Another cause are support structures, also referred to as anchors, when they are insufficient and detach from the part or build plate, allowing the part to rise and interfere with the recoater (Fig. 1).
In general, thermal and distortion-related failures affect the outcome in two ways: the distorted part breaks away from the support material during the build. It then rises enough to crash into the powder-spreading mechanism. If
Part Support structure failure
Support structure Fig. 1 Distortion example: this part exhibits support structure failure and excessive distortion (Courtesy Autodesk, as published in ‘Distortion in metal Additive Manufacturing: Modelling and Mitigation’, Metal AM Vol. 3 No. 1)
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