Surface Topography: Metrology And Properties
A study of surface-specific additive manufacturing test artefacts by Andrew Townsend, Radu Racasan and Liam Blunt, highlights that test artefacts of additive manufacturing are de-signed to provide a simple access for measurements using conventional surface measure-ment techniques. Surface-specific test artefacts can be more compact because they don’t need the larger dimensions need for accuracy of measurements. A series of measurement test artefacts were designed for use of verification of this process. These three artefacts are small enough to be included in every build and include built in manufacturing traceability, making it easier to build records. Additive manufacturing allows you to create physical 3-dimensional objects directly from a design file. This design file is used to build up the piece in layers by depositing material, ra-ther than machining a piece from a solid block.
The first artefact contains three measurement areas the first is a flat area, which is parallel to the base, designed for profile characterisation for example per ISO 4287, this ISO standard was to provide methods for general calculation of surface textures by means of stylus profilometers which typically record profiles. The second are includes a 1: 25 plane. Which allows examination of the build layer change. (Moylan, Cooke and Jurrens, 2012) The third area on the artefact is a series of ten round bosses. The heights of these unma-chined bosses allow a calculation of the actual material. The second artefact includes ISO 25178-70 Type ASG another standard of surface finish that has been designed for “assessment and correction of systematic errors”.
The shaped on this surface has been used previously in AM research. Three of the AMSA3 artefacts were in-cluded in the electron beam melting build, each with different measurements this was for identification purposes between each artefact. (‘Default @ www. imagemet. com’,2018) The third artefact (fig. 4) like the ASMA1 included three sections, “each with a constant am-plitude, decreasing wavelength structured sine wave”. The reason behind this design was to give a way to see the resolution limit when compared to the design model. EMB artefacts results The false colour height maps of the evaluated areas of the smoothed and filtered horizon-tally and vertically- built surfaces are shown. The melt pool produces a significantly better finished surface than the build side surface.
Future work of this study will include further investigation of the sensitivity of the surface texture parameters to AM build variation and ultimately to functional performance. This will include evaluation of ISO 25178-2 parameters, along with parameters applicable to freeform and re-entrant surfaces, such a those proposed by Pagani. This information will influence the amount and location of the additional material require to be added prior to the build to assure complete clean-up of any post processed surface, such as sealing or bearing surfaces. Unsupported vertical surfaces (the side of the bosses) have linearly greater than 0. In conclusion, a suite of surface specific AM measurement artefacts has been pro-posed.
These artefacts are small and cost saving to build and to include in every AM build. They include built-in manufacturing traceability and have been de-signed for easy measurement on standard metrology equipment. The artefact de-sign may be custom designed to the application to produce the greatest sensitivity to pro-cess changes. They may be used for process checking, to determine the worth, amount or quality of best build orientation and to create information about the amount and loca-tion of added material required to allow the complete clean-up of the surfaces during post-processing.
