Traceability of optical 3D scanner measurements on sand mould in the production of quality castings

This paper addresses the establishment of traceability of optical 3D scanner measurements on green sand mould in the production of quality castings. Optical measurements are subject to the influence of the workpiece material optical properties, which can be very different from those of conventional calibration artefacts, e.g. check boards, ball plates, etc. This means that an optical 3D scanner calibrated using a check board or a ball plate may give biased and unreliable results when used for dimensional measurements on a crystalline material such as sand. In order to use a tactile coordinate measuring machine as reference for optical measurements on a green sand mould, which cannot be probed directly, a hard furan sand cone plate was developed and substituted as reference workpiece for tactile as well as optical measurements. Systematic errors and measurement uncertainties were assessed for the optical measurements, and a maximum expanded uncertainty of 26 µm was estimated, which is acceptable for optical measurements on sand surfaces having single grains with an average diameter of 232 µm.