Correlating surface quality with internal defects of additively manufactured components

The development of additive manufacturing (AM) technologies, moving from a prototype and pilot technology into a mature manufacturing technology, has the potential to change the paradigm for manufacturing. AM will significantly shape the future of manufacturing towards a flexible and OnDemand approach and accelerate the transformation from the conventional manufacturing industry to Industry 4.0. To facilitate the uptake of AM technologies into a wider range of applications and foster AM’s full commercialisation, there must be focused attempts to overcome existing technical barriers. A major challenge among these is that AM processes are not robust enough and AM production machines lack sufficient process control, which consequently bring various shortcomings that are commonly seen in AM products, such as poor as-built surface finish, a lack of dimensional precision and repeatability, and mechanical properties not equivalent to those of bulk materials. Following a discussion with Dr James Hughes (research director AMRC North West), a targeted research topic of particular interest is to correlate the quality of external surfaces with the internal defects of AM components. Both surface texture and internal defects are closely linked with the AM process and have significant impacts on mechanical performance of AM products. For example, it is reported that the fatigue performance of AM components is often initiated either from deep surface notches or internal pores. X-ray Computed Tomography (XCT) has been proved a valid and valuable technique to inspect AM internal defects. XCT is, however, an expensive and time-consuming metrology technique, not affordable by every industry company, particularly SME. In comparison, surface texture measurement is more feasible in terms of both efficiency and cost. However, due to the light-of-sight restriction, tactile and optical surface measurement instruments cannot access internal defects without physically breaking AM parts. Preliminary research work recently done by the applicant (in collaboration with the MAPP Hub https://mapp.ac.uk/) found that there exists a link between external surface quality (Sa, Sq, Sv) and internal defect (e.g. porosity)1which implies a potentially very useful fact that surface quality might be used as an indicator to tell the internal quality of an AM part. This secondment will further exploit this research work with the AMRC AM group. Should it be successful, the research outcome will be further disseminated to industrial end-users with the help of AMRC.

Note 1: Z. Zhu, S. Lou, C. Majewski, 2020 Characterisation and correlation of areal surface texture with processing parameters and porosity of high speed sintered parts, Additive Manufacturing, 36 101402