Tools for Improving Machine Tool Volumetric Accuracy

Independent Quality Labs, Inc.Independent Quality Labs, Inc. 11© 2005© 2005

CTMA 2005CTMA 2005

Tools for Improving Tools for Improving Machine Tool Volumetric AccuracyMachine Tool Volumetric Accuracy

Robert (Buz) Callaghan

Chief Engineer

22Independent Quality Labs, Inc.Independent Quality Labs, Inc.© 2005© 2005

Why ImproveWhy ImproveMachine Tool Volumetric Accuracy?Machine Tool Volumetric Accuracy?

Measuring machine performance

Allows process improvements before parts are made.

Allows predictive repairs of machines.


Why ImproveWhy ImproveMachine Tool Volumetric Accuracy?Machine 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.


What are the Tools?What are the Tools?

Machine Error Budgets

Machine Parametric Measurement


HowHow did these tools evolve?did 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.


squareness level

HowHow did these tools evolve?did these tools evolve?

Schlesinger’s book, Testing Machine Tools, contains parametric tests, such as

limited to the characterization of machine spindles and moving components

roundness straightness


How did these tools evolve?How did these tools evolve?

Engineers at Lawrence Livermore National Labs found these methods inadequate for specifying their machines.


How did these tools evolve?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.

© 2005© 2005 99Independent Quality Labs, Inc.Independent Quality Labs, Inc.

“parametric error budgeting”

“parametric error measurement”

What were their solutions?What were their solutions?

They developed techniques to aid in specification, design & production of the world’s most accurate machine tools.


Identify machine axis relation parameters

Identify machine thermal error parameters

Identify machine environmental error parameters

Sum error parameters

Parametric Error BudgetingParametric Error Budgeting

Identify machine motion error parameters


Motion Error ParametersMotion Error Parameters


Motion Error ParametersMotion Error Parameters


Relation ParametersRelation Parameters


Machine Error BudgetMachine Error BudgetFULL VOLUME ERROR MODEL

X Y ZStart -289.0000 0.0000 -55.6700End 0.0000 161.0000 0.0000

Travel 289.0000 161.0000 55.6700

Error Description Error Comments Ang Error Offset Full ErrorDir (AS) (in/ft) (in) (in)

1 eXx Lin Acc x Systematic Deviation (E) 0.0016002 erXx Repeat x Unidirectional Repeatability (R) 0.0002003 eYx Str Y y 0.0023004 eZx Str Z z 0.0021005 eAx Roll z Offset Y Travel 8.0 0.00047 90 0.0034926 eBx Pitch x Offset Z Travel+ W Travel - Tool Length 4.8 0.00028 90 0.0020957 eCx Yaw x Offset Y Travel 4.1 0.00024 31 0.0006168 eoCxy Sq x Offset Y Travel 6.0 0.00035 90 0.0026259 eYy Lin Acc y Systematic Deviation (E) 0.003200

10 erYy Repeat y Unidirectional Repeatability (R) 0.00010011 eXy Str X x 0.00030012 eZy Str Z z 0.00040013 eBy Roll x Offset Z Travel+ W Travel - Tool Length 12.4 0.00072 31 0.00186414 eAy Pitch y Offset Z Travel+ W Travel - Tool Length 8.1 0.00047 10 0.00039315 eCy Yaw y Offset Scale Distance from S C/L 10.6 0.00062 10 0.00051416 eoAyz Sq y Offset Z Travel - Tool Length -55.0 -0.00320 90 -0.02400017 eZz Lin Acc z Systematic Deviation (E) 0.00060018 eZz Repeat z Unidirectional Repeatability (R) 0.00010019 eYz Str Y y 0.00010020 eXz Str X x 0.00040021 eCz Roll x No Offset 2.3 0.00013 90 0.00100422 eBz Pitch x Offset Z Travel - Tool Length 2.5 0.00015 31 0.00037623 eAz Yaw y Offset Z Travel - Tool Length 1.6 0.00009 31 0.00024124 eoBxz Sq x Offset Z Travel - Tool Length 4.6 0.00027 31 0.00069825 eXs Rad Err X x 0.00010026 eYs Rad Err Y y 0.00009327 eZs Axial Err Z z 0.00011028 eoAxs Sq SX x or z Offset Tool Length 4.3 0.00025 8 0.00016729 eoBys Sq SY y or z Offset Tool Length 5.3 0.00031 8 0.000207

Sum = 0.005514


Extending Budgeting MethodsExtending Budgeting Methods

Part Feature Assessment

Process Error Budget


Part Feature AssessmentPart 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.



Length

Width

HeightSize

Diameter

Straightness

Flatness

Circularity

For Individual Features

Form

Cylindricity

Of a LineFor Individual or Related Features Profile

Of a Surface

Position

ConcentricityLocation

Symmetry

Angularity

PerpendicularityOrientation

Parallelism

Circular

For Related Features

RunoutTotal



Feature Tolerance Ratio (FTR)

determined by dividing the feature tolerance bandwidth by the distance over which it is applied




Process Error BudgetProcess Error Budget

The development of a Process Model from the Full Volume Model involves four steps.



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



3. determine the effect of squareness and angular errors

4. compare the sum of all errors to feature tolerance bandwidth = Part Tolerance Ratio (PTR)



Part Tolerance Ratio (PTR) should be greater than 4




Parametric Error MeasurementParametric Error Measurement

Methods specified by ANSI Standards

Methods require full documentation to assure repeatability

Errors exceeding budgeted values must be corrected



Roll with Electronic Level



Accuracy with Laser


Parametric Error CorrectionParametric Error Correction

Proper measurement and presentation of errors

Leads to rapid error correction


Yaw ErrorsYaw Errors

Loose Saddle



Before Gib Adjustment



After Gib Adjustment


Tools Under DevelopmentTools Under Development

Computer Aided Process Specification (CAPS)

LOCUSw Machine Measurement and Correction Software


CAPSCAPS

Objective:

To integrate the existing budgeting methods with CAD/CAM to produce Machine Performance Specifications


Current CAPSCurrent CAPS


New CAPSNew CAPS


CAPS How will it work?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.


LOCUSwLOCUSw

Objectives;

1. Create data for CAPS.

2. Incorporate error correction.

3. Facilitate training


LOCUSw Define MachineLOCUSw Define Machine


LOCUSw Select SequenceLOCUSw Select Sequence


LOCUSw Setup TestLOCUSw Setup Test


LOCUSw Run TestLOCUSw Run Test


LOCUSw Review ResultsLOCUSw Review Results


How do these tools affect Weapon How do these tools affect Weapon System Sustainment? System Sustainment?

Many parts are produced on Computer Numerically Controlled (CNC) Machines.

Using digitally transferred programs to produce a single part.

One reject means 100% scrap.

Worn parts from existing Weapon Systems must be replaced by the Depots.


How do these tools affect Weapon How do these tools affect Weapon System Sustainment? 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.


How do these tools affect Weapon How do these tools affect Weapon System Sustainment?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.


How can these tools improve CNC How can these tools improve CNC Machines? Machines?

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.

Each CNC machine has it’s own unique capability.


How does LOCUSw Software help Weapon How does LOCUSw Software help Weapon System Sustainment?System Sustainment?

To reduce the time of machine performance measurement and correction.

To capture, analyze and diagnose CNC machine errors.


How does LOCUSw Software help Weapon How does LOCUSw Software help Weapon System Sustainment?System Sustainment?

Adding knowledge based software for diagnostics.

Improving hands-on training at Weapons Depots.

Documents

Tools for Improving Machine Tool Volumetric Accuracy