Abstract
Producing components using metal additive manufacturing processes, such as powder bed fusion, presents manufacturing and measurement challenges, but also significant opportunities. The as-built surface may include overhanging (re-entrant) features not intentionally included in the design, but that aid in component functionality. In addition, the additive manufacturing process presents opportunities to design and manufacture re-entrant features intentionally. Re-entrant features increase the specific surface area and, in addition, produce mechanical locking to the surface. These re-entrant features may be intended to improve surface performance in areas such as biological cell attachment, coating adhesion, electrical capacitance and battery plate design, fluid flow and material cooling. Re-entrant features may prove difficult or impossible to measure and characterise using conventional line-of-sight surface metrology instrumentation, however the correct measurement of these surfaces may be vital for functional optimisation. X-ray computed tomography does have the ability to image internal and re-entrant features. This paper reports on the measurement of re-entrant features using X-ray computed tomography and the extraction of actual surface area information (including re-entrant surfaces) from sample additively manufactured surfaces. A proposed new surface texture parameter, Sdrprime, is discussed. This parameter is applicable to true 3D data, including re-entrant features, and is intended to relate directly to the component surface functional performance. The errors produced when using line-of-sight instruments and height map parameter generation per ISO 25178-2 to evaluate surfaces that include re-entrant features are discussed. Measurement results for electron beam melting and selective laser melting additively manufactured components, together with simulated structured surfaces, are presented.
Highlights
IntroductionOne significant advantage additive manufacturing (AM) systems have, when compared to conventional subtractive processes such as milling and turning, is the ability to manufacture components with intentional, designed-in, re-entrant features at scales matched to the functional requirements
Introduction of a Surface Characterization ParameterSdrprime for Analysis of Re‐entrant FeaturesA
Powder bed fusion additive manufacturing processes are capable of producing complex freeform surfaces and reentrant features that significantly enhance the designed function of the component in industrial applications including medical bio-attachment, electrical battery design, heat exchanger systems and paint and coating adhesion applications
Summary
One significant advantage AM systems have, when compared to conventional subtractive processes such as milling and turning, is the ability to manufacture components with intentional, designed-in, re-entrant features at scales matched to the functional requirements. Manufacturing components with these features will provide advantages based on two properties produced by such features: firstly, re-entrant features increase the specific surface area: that is, an increase in the total surface areas for a given planar envelope area or component volume and secondly the ability to mechanically lock to the re-entrant surface. There may be applications in cooling and fluid flow where an increase in contact surface area provides greater volumetric efficiency [2] and medical applications such as orthopedic and dental implants where osseo integration between implant and tissue may be enhanced by the increased surface area
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