How does artifact comparison work?
• artifact dimensions measured on calibrated CMM • calibrated dimensions stored in CNC • artifact probed on the machine tool, and actual dimensions are computed – includes growth and distortion due to thermal effects, plus systematic errors in the machine structure • difference between actual and calibrated size is stored as a correction factor – either a specific correction for each feature, or a scaling factor • component is measured, and correction factors are applied to remove the current machine errors detected by measuring the artifact The ideal artifact comparison process! Factors that affect the level of measurement uncertainty using artifact comparison techniques: • artifact stored in machine all the time and flooded with coolant • same temperature as the workpiece • artifact made of same material as the part • same expansion coefficient • artifact measured in same part of the machine tool • same local machine growth and distortions • artifact and workpiece measured with minim
