Conference Paper

Improving metal additive manufacturing part design and final part precision using feedback from X-ray computed tomography

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Abstract

Additive metal manufacturing processes, such as laser powder bed fusion, still show difficulties when producing overhang features or internal structures such as channels or bores. Channels are often mutilated by sag defects and dross formation at their upper part, when the channel-axis is close to parallel to the base plate and in the particular case when support structures cannot be used as it would be impossible to remove them after the build. The problem is still not completely solved, although various design guidelines have been developed for various processes and materials in use. So far, a general approach is to tweak the processing parameters or to orient the design on the build plate to reduce downfacing regions at the most critical features of the parts. This work proposes to use feedback from X-ray computed tomography measurements and a new evaluation approach for the additive manufacturing process-chain to obtain improved geometrical accuracy of internal channels. Preliminary results on the evaluation are presented, with the future scope of reducing sag and dross defects by adapting the channels and bores during the design stage.

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Book
Additive manufacturing (AM) is a fast-growing sector with the ability to evoke a revolution in manufacturing due to its almost unlimited design freedom and its capability to produce personalised parts locally and with efficient material use. AM companies, however, still face technological challenges such as limited precision due to shrinkage, built-in stresses, and limited process stability and robustness. Moreover, often post-processing is needed due to the high roughness and remaining porosity. Qualified, trained personnel are also in short supply. In recent years, there have been dramatic improvements in AM design methods, process control, post-processing, material properties and material range. However, if AM is going to gain a significant market share it must be developed into a true precision manufacturing method. The production of precision parts relies on three principles: 1. Production is robust (i.e. that all sensitive parameters can be controlled). 2. Production is predictable (for example, the shrinkage that occurs is acceptable because it can be predicted and compensated in the design). 3. Parts are measurable (as without metrology, accuracy, repeatability and quality assurance cannot be known). AM of metals is inherently a high-energy process, with many of sensitive and inter-related process parameters, making it susceptible to thermal distortions, defects and process drift. The complete modelling of these processes is beyond current computational power and novel methods are needed to practicably predict performance and inform design. In addition, metal AM produces highly textured surfaces and complex surface features that stretch the limits of contemporary metrology. With so many factors to consider, there is a significant shortage of background material on how to inject precision into AM processes. Shortage in such material is an important barrier for a wider uptake of advanced manufacturing technologies and a comprehensive book is thus needed. This book aims to inform the reader how to improve the precision of metal AM processes by tackling the three principles of robustness, predictability and metrology, and by developing computer-aided engineering methods that empower rather than limit AM design.
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