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Tools for Improving Machine Tool Volumetric Accuracy

CTMA 2005. Tools for Improving Machine Tool Volumetric Accuracy. Robert (Buz) Callaghan Chief Engineer. Why Improve Machine Tool Volumetric Accuracy?. Measuring machine performance. Allows process improvements before parts are made. Allows predictive repairs of machines.

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Tools for Improving Machine Tool Volumetric Accuracy

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  1. CTMA 2005 Tools for Improving Machine Tool Volumetric Accuracy Robert (Buz) Callaghan Chief Engineer Independent Quality Labs, Inc.

  2. Why ImproveMachine Tool Volumetric Accuracy? • Measuring machine performance • Allows process improvements before parts are made. • Allows predictive repairs of machines. Independent Quality Labs, Inc.

  3. Why ImproveMachine Tool Volumetric Accuracy? • Measuring finished part dimensions • Can only be done after the part is completed. • Causes reject parts to be repaired or thrown way. Independent Quality Labs, Inc.

  4. What are the Tools? • Machine Error Budgets • Machine Parametric Measurement Independent Quality Labs, Inc.

  5. Howdid these tools evolve? • For over 90 years, the builders determined machine performance standards. • Dr. Georg Schlesinger recognized the need to do measurements on machine tools. Independent Quality Labs, Inc.

  6. Howdid these tools evolve? • Schlesinger’s book, Testing Machine Tools, contains parametric tests, such as • roundness • straightness • squareness • level limited to the characterization of machine spindles and moving components Independent Quality Labs, Inc.

  7. How did these tools evolve? • Engineers at Lawrence Livermore National Labs found these methods inadequate for specifying their machines. Independent Quality Labs, Inc.

  8. How did these tools evolve? • The ISO 230 Specifications were for the assembly of machine tool components not the capability of machines to make parts. Independent Quality Labs, Inc.

  9. What were their solutions? • They developed techniques to aid in specification, design & production of the world’s most accurate machine tools. • “parametric error budgeting” • “parametric error measurement” Independent Quality Labs, Inc.

  10. Parametric Error Budgeting • Identify machine motion error parameters • Identify machine axis relation parameters • Identify machine thermal error parameters • Identify machine environmental error parameters • Sum error parameters Independent Quality Labs, Inc.

  11. Motion Error Parameters Independent Quality Labs, Inc.

  12. Motion Error Parameters Independent Quality Labs, Inc.

  13. Relation Parameters Independent Quality Labs, Inc.

  14. Machine Error Budget Independent Quality Labs, Inc.

  15. Extending Budgeting Methods • Part Feature Assessment • Process Error Budget Independent Quality Labs, Inc.

  16. Part Feature Assessment • Part features and tolerances are well defined by ASME Y14.5M-1994 Dimensioning and Tolerancing. • The definitions of size, form, profile, location, orientation, and run-out are used to relate features with processes. Independent Quality Labs, Inc.

  17. Length Width Size Height Diameter For Individual Features Straightness Flatness Form Circularity Cylindricity Of a Line For Individual or Related Features Profile Of a Surface Position Concentricity Location Symmetry Angularity For Related Features Perpendicularity Orientation Parallelism Circular Runout Total Part Feature Assessment Independent Quality Labs, Inc.

  18. Part Feature Assessment • Feature Tolerance Ratio (FTR) • determined by dividing the feature tolerance bandwidth by the distance over which it is applied Independent Quality Labs, Inc.

  19. Part Feature Assessment Independent Quality Labs, Inc.

  20. Process Error Budget • The development of a Process Model from the Full Volume Model involves four steps. Independent Quality Labs, Inc.

  21. Process Error Budget 2. determine which of the machine axes are moved and how far 1. use the FTR to identify the features and tolerances, which will govern capability Independent Quality Labs, Inc.

  22. Process Error Budget 3. determine the effect of squareness and angular errors 4. compare the sum of all errors to feature tolerance bandwidth = Part Tolerance Ratio (PTR) Independent Quality Labs, Inc.

  23. Process Error Budget • Part Tolerance Ratio (PTR) should be greater than 4 Independent Quality Labs, Inc.

  24. Process Error Budget Independent Quality Labs, Inc.

  25. Parametric Error Measurement • Methods specified by ANSI Standards • Methods require full documentation to assure repeatability • Errors exceeding budgeted values must be corrected Independent Quality Labs, Inc.

  26. Parametric Error Measurement • Roll with Electronic Level Independent Quality Labs, Inc.

  27. Parametric Error Measurement • Accuracy with Laser Independent Quality Labs, Inc.

  28. Parametric Error Correction • Proper measurement and presentation of errors • Leads to rapid error correction Independent Quality Labs, Inc.

  29. Yaw Errors Loose Saddle Independent Quality Labs, Inc.

  30. Yaw Errors Before Gib Adjustment Independent Quality Labs, Inc.

  31. Yaw Errors After Gib Adjustment Independent Quality Labs, Inc.

  32. Tools Under Development • Computer Aided Process Specification (CAPS) • LOCUSw Machine Measurement and Correction Software Independent Quality Labs, Inc.

  33. CAPS • Objective: To integrate the existing budgeting methods with CAD/CAM to produce Machine Performance Specifications Independent Quality Labs, Inc.

  34. Current CAPS Independent Quality Labs, Inc.

  35. New CAPS Independent Quality Labs, Inc.

  36. CAPS How will it work? 2. Select or build Machine Error Budget. 3. Scan CAM files to establish axis paths and tool selection. 4. Create Process Error Budget. 5. Print Parameter Specification 1. Scan CAD files and establish FTRs. Independent Quality Labs, Inc.

  37. LOCUSw • Objectives; 1. Create data for CAPS. 2. Incorporate error correction. 3. Facilitate training Independent Quality Labs, Inc.

  38. LOCUSw Define Machine Independent Quality Labs, Inc.

  39. LOCUSw Select Sequence Independent Quality Labs, Inc.

  40. LOCUSw Setup Test Independent Quality Labs, Inc.

  41. LOCUSw Run Test Independent Quality Labs, Inc.

  42. LOCUSw Review Results Independent Quality Labs, Inc.

  43. How do these tools affect Weapon System Sustainment? • Worn parts from existing Weapon Systems must be replaced by the Depots. • Many parts are produced on Computer Numerically Controlled (CNC) Machines. • Using digitally transferred programs to produce a single part. • One reject means 100% scrap. Independent Quality Labs, Inc.

  44. How do these tools affect Weapon System Sustainment? • Parts for new Weapon Systems are often made at the lowest cost. • This has caused the large Defense Contractors to out-source. • Resulting in smaller companies attempting to produce increasingly complex parts. Independent Quality Labs, Inc.

  45. How do these tools affect Weapon System Sustainment? • Parts for new Weapon Systems are also produced on CNC Machines. • Smaller companies do not always have the resources to solve complex problems. • Resulting in scrap, delays and cost over-runs. Independent Quality Labs, Inc.

  46. How can these tools improve CNC Machines? • Each CNC machine has it’s own unique capability. • CAPS matches capability with part requirements. • For selecting new machine vendors. • For selecting out-source vendors. • For selecting existing machines for new parts. • For determining the repair schedule. • For selecting machines to be retired or rebuilt. Independent Quality Labs, Inc.

  47. How does LOCUSw Software help Weapon System Sustainment? • To capture, analyze and diagnose CNC machine errors. • To reduce the time of machine performance measurement and correction. Independent Quality Labs, Inc.

  48. How does LOCUSw Software help Weapon System Sustainment? • Improving hands-on training at Weapons Depots. • Adding knowledge based software for diagnostics. Independent Quality Labs, Inc.

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