Multi-material Acceptance Testing for CT-Based Coordinate Measurement Systems

This contribution presents a multi-material acceptance test for computed tomography-based coordinate measurement systems (CT-based CMS). The multi-material test requirements and concepts – based on the international reference standard ISO 10360 – are presented. Also, a set of multi-material reference standards for the assessment of the probing error test (P-test) and length measurement error test (E-test) are presented. For the P-test, two half spheres made of different materials are assembled to a sphere. A multi-material hole cube standard is used for the assessment of the E-test. The hole cube consists of two symmetric half cubes made of different materials. For both, multi-material spheres and hole cube standards, the materials were selected to obtain two multi-material scenarios: (1) with high and (2) with at least a medium attenuation ratios. Thus, for the probing test, silicon nitride, aluminium oxide and lead-free glass N-SF6 were used. The hole cubes, however, were made by paring aluminium, a special ceramic material called carbon fibre silicon carbide (Cesic) and titanium. Form error and size measurements were evaluated in the multi-material spheres as well as hole-based centre-to-centre distances were evaluated in the hole cubes. The proposed test and multi-material reference standards were successfully tested, as they appear to be suitable for evaluating the multi-material error characteristic of CT-based CMSs.