Microform calibrations in surface metrology

Abstract

Microform calibrations include the measurement of complex profile forms and position errors of micrometer scale in combination with the measurement of deviations from a specified profile and surface texture of profile segments. Tolerances on the profile form are specified and may correspond geometrically to surface texture parameters. One example of microform calibration is the calibration of Rockwell diamond indenters used for hardness testing of materials. Previously reported measurement techniques do not meet the stringent microfonn calibration requirements for Rockwell diamond indenters. Inadequate microform calibration of hardness indenters may be one factor resulting in significant interlaboratory differences in results from Rockwell hardness tests. By using a stylus instrument, in combination with a series of calibration and check standards and calibration and measurement uncertainty calculation procedures, we have calibrated Rockwell diamond indenters in accordance with the definitions specified in ISO and ASTM standards. Our procedures for conducting microform calibration yield total measurement uncertainties less than ten percent of the tolerance values specified in ISO and ASTM standards. In this paper, the general calibration requirements, calibration and check standards, and calibration and uncertainty procedures that we use in performing microform calibrations are introduced. Some general considerations on stylus radius correction, data fitting, calibration traceability, uncertainty and reproducibility are also discussed.