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CMM AUDIT PROGRAMME - RESULTS AND LESSONS LEARNT

CMM AUDIT PROGRAMME - RESULTS AND LESSONS LEARNT. Speaker : F. J. van der Walt E-mail: fvdwalt@csir.co.za Tel.: (012) 841- 4799 07 September 2005. 3D Coordinate Measuring Machine (CMM). DEA Global Image CMM. Why a CMM audit programme ?. To identify/analyse CMM capabilities.

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CMM AUDIT PROGRAMME - RESULTS AND LESSONS LEARNT

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  1. CMM AUDIT PROGRAMME -RESULTS AND LESSONS LEARNT Speaker : F. J. van der Walt E-mail: fvdwalt@csir.co.za Tel.: (012) 841- 4799 07 September 2005

  2. 3D Coordinate Measuring Machine (CMM) DEA Global Image CMM

  3. Why a CMMaudit programme ? • To identify/analyse CMM capabilities. • To establish measurement traceability for CMM measurements. • Assess the influence of environmental conditions on CMM measurements. Scientific Research Council Act (Act No 46 of 1988, as amended by Act 71/1990)

  4. Audit Part Material = 7075-T6 CTE = 23,6 x 10-6K-1

  5. Top view X+ Y+

  6. Section A - A Z+ X+

  7. Evaluation of Measurements • All the measurements from the participating laboratories were recorded and evaluated. It was found that: a. Length measurements and Diameter measurements are acceptable. b. Roundness, angle, and concentricity measurements are cause for concern.

  8. Length Measurement 0,031 131,381

  9. Roundness Measurement

  10. Error Sources 1.Spatial errors are errors in the measured position of a point on the surface of the workpiece, and are caused by: a. guideways, scales, probing system, etc. b. environmental conditions. c. probing strategy. d. workpiece characteristics.

  11. CMM Errors Lxx Lyy Positional errors (3) Lzz Lxy, Lxz Lyx, Lyz Linearity errors (6) Lzx, Lzy

  12. CMM Errors(continued) Rxx, Rxy, Rxz Ryx, Ryy, Ryz Rzx, Rzy, Rzz 9 Rotation Errors

  13. CMM Errors(continued) Qxy Qyz Qzx Squareness errors (3)

  14. Error Sources(continued) 2. Computation errors are errors in the estimated dimensions and form deviations for the measured points on the surface of the workpiece, caused by: a. software used to estimate the geometry. b. the precision of the computer used. c. the number and position of the measured points. d. the extent to which the geometry departs from the ideal geometrical form.

  15. Tasks performed by the computer of the CMM Correction Transformation Controlling CMM Computer Computation Evaluation

  16. Causes ofMeasurement Errors • Probe system used. • Parameter settings. • Environmental conditions. • CMM errors. • Metrologist/operator skills.

  17. Operator Skills • The measured value for a distance of 5,0 mm was reported as 12,207 mm • The measured value for the overall length of 250 mm was reported as 131,381 mm • The measured value for the overall length of 250 mm was reported as 0,031 mm. NEGLIGENCE, CARELESSNESS, ………..???

  18. Uncertainty ofCMM Measurements • Machine Specification: ± (1,9 + 3L ) µm • Very few participants reported the uncertainty of measurement or even their machine spec! • Can not perform conformance testing without machine spec or estimated uncertainty. MAJOR CONCERN !!

  19. Conclusion • Length and diameter measurements are acceptable. • Inconsistency of roundness, angle and concentricity measurements. • CMM operators must know/estimate the uncertainty of measurement. • Need for CMM metrologist/operator training. • Participants with poor results should implement corrective actions. • Participate again.

  20. Upcoming CMM Course Presenter: Mr. Kostadin Doytchinov NRC Canada Venue: Pretoria and Port Elizabeth Date: November 2005

  21. Thank you for attending this presentation. Have a nice day.

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