How Do You Achieve High Accuracy Precision in Critical Manufacturing Processes?

High accuracy in critical manufacturing is not achieved by using one “high-precision” instrument.

It comes from controlling the entire measurement process — the engineering requirement, coordinate system, measurement technology, environment, inspection method, analysis and final reporting.

For aerospace, manufacturing, tooling and other critical applications, the first question should not be:

“What instrument should we use?”

The better question is:

“What engineering decision must this measurement support?”

Innovative Measurement Solutions builds the measurement strategy around that requirement.

Start With the Engineering Definition

Before measurement begins, the project requirements need to be understood.

That can include:

• CAD geometry
• Engineering drawings
• Required tolerances
• GD&T requirements
• Datum reference frames
• Coordinate systems
• Component size
• Feature relationships
• Accessibility
• Environmental conditions
• Acceptance criteria
• Required deliverables

A measurement can be repeatable and still fail to answer the engineering question if it is referenced to the wrong coordinate system or evaluated against the wrong requirement.

That is why IMS approaches Dimensional Inspectionfrom the engineering definition first.

Select the Right Measurement Technology

No single metrology technology is right for every critical manufacturing process.

Laser Tracker Measurement

Laser Tracker Measurementis useful when accurate coordinate measurement is required across large components, tooling, machinery and assemblies.

Applications can include:

• Large assembly measurement
• Tooling and fixture verification
• Machinery positioning
• Precision alignment
• Datum establishment
• Feature location
• Installation verification

3D Laser Scanning

3D Laser Scanningis valuable when dense surface geometry is required.

Instead of measuring only selected points, scanning can capture detailed surface information for:

• CAD-to-part comparison
• Reverse engineering
• Surface inspection
• Tooling inspection
• Deformation analysis
• Complex geometry measurement

Dense data can help identify bow, twist, distortion, interface mismatch and other geometric conditions that may not be obvious from a limited number of discrete measurements.

The correct method still depends on the tolerance and engineering requirement.

Establish a Stable Coordinate Framework

High-accuracy measurement depends on knowing what the measurement is referenced to.

Depending on the project, IMS may establish the coordinate framework from:

• Engineering datums
• Tooling points
• Physical features
• Reference targets
• Monuments
• Customer-defined coordinate systems
• CAD geometry

For large or accuracy-sensitive inspections, control points may also be remeasured during the project to confirm that the reference network remains stable.

Environmental Conditions Matter

Temperature, vibration, airflow, equipment stability and material expansion can influence dimensional measurements.

NIST has documented the effect that temperature and coefficient of thermal expansion can have on dimensional measurement uncertainty.

For critical work, relevant conditions can include:

• Part temperature
• Ambient temperature
• Thermal gradients
• Material coefficient of thermal expansion
• Vibration
• Line of sight
• Surface condition
• Measurement duration

Portable metrology is often required because large tooling, machinery and assemblies cannot be moved into a controlled inspection laboratory.

The measurement strategy therefore has to remain appropriate to the real environment in which the work is performed.

Calibration Is Only Part of Traceability

A calibrated instrument is important, but calibration alone does not automatically make every measurement result traceable.

NIST defines metrological traceability as a property of a measurement result that connects it to a reference through a documented, unbroken chain of calibrations, with each link contributing to measurement uncertainty.

For critical manufacturing, confidence in the result depends on the complete measurement process — not simply the calibration sticker on the instrument.

Measurement Uncertainty Matters Near Tolerance Limits

Measurement uncertainty becomes especially important when a result approaches an engineering tolerance limit.

ISO 14253-1 addresses conformity and nonconformity decisions while taking measurement uncertainty into account.

That matters because a measured value close to a specification limit may require more careful evaluation than a result comfortably inside or outside the tolerance.

The required tolerance should therefore be considered before selecting the measurement method.

Measure During Manufacturing — Not Only After

Waiting until a component or assembly is finished before discovering a dimensional problem can make correction more difficult and expensive.

In-process Dimensional Inspectioncan support:

• Machining setup
• Fabrication verification
• Weldment inspection
• Tooling adjustment
• Assembly positioning
• Interface verification
• Equipment installation
• Large assembly integration

Measurement does not replace manufacturing engineering or automatically determine the root cause of a problem.

It provides objective dimensional information that engineering, manufacturing and quality teams can use to make better decisions.

Verify the Tooling That Controls the Product

Critical manufacturing accuracy often depends on tooling and fixtures.

Production tooling can settle, twist, shift or respond to environmental conditions over time.

Tooling & Fixture Certificationcan evaluate whether the tooling that controls production remains consistent with its engineering requirements.

Precision Alignment Matters Too

Manufacturing accuracy is not limited to an individual part.

The position and orientation of machinery, tooling and assemblies can also affect the final result.

Precision Alignmentuses portable metrology and established coordinate references to evaluate those relationships and support physical adjustment when required.

Turn Measurement Data Into Engineering Information

Collecting coordinates or point clouds is only part of the job.

The final information must be usable by engineering, manufacturing and quality teams.

Depending on the application, IMS deliverables can include:

• Dimensional inspection reports
• GD&T results
• CAD-to-part comparison
• Deviation maps
• XYZ coordinate data
• Alignment reports
• Point clouds
• Meshes
• Reverse-engineered CAD
• Tooling certification results
• Customer-specific reporting

The deliverable should be considered before measurement begins so the measurement plan is built around what the customer actually needs.

High Accuracy Is a Process

Achieving high accuracy precision in critical manufacturing requires more than selecting an accurate instrument.

It requires a controlled process:

1. Define the engineering requirement.
2. Select the appropriate measurement technology.
3. Establish the correct coordinate framework.
4. Account for environmental conditions.
5. Understand measurement uncertainty.
6. Measure at the appropriate stage of manufacturing.
7. Analyze the data against the engineering definition.
8. Deliver results that support the required decision.

Innovative Measurement Solutions provides portable 3D metrology for complex parts, tooling, equipment and large-scale assemblies from Florida’s Space Coast, supporting projects throughout Florida, nationwide and internationally.

Have a Critical Measurement Requirement?

Send IMS your available CAD, drawings, photographs, approximate dimensions, tolerances, project location and required deliverable.

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Related IMS Services

References

• NIST — Metrological Traceability
• NIST — Metrological Traceability (Metrology)
• NIST — Uncertainties in Dimensional Measurements Made at Nonstandard Temperatures
• ISO 14253-1 — Inspection by measurement of workpieces and measuring equipment

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