Meaning
Mechanical contact probes exert localized contact pressure that elastically or plastically deforms delicate surface features during coordinate measurements. A stylus contact force deformation distorts reported surface profiles by pushing probe tips into soft substrates or thin wall structures. Hertzian contact stress theory calculates local surface displacement based on stylus tip radius, measuring force, and material elastic moduli.
Measurement corrections fail when contact forces exceed material yield strength, causing permanent surface scratching or plastic flow.
Contact Stress
Small spherical probe tips concentrate measuring forces onto tiny surface contact areas, generating high mechanical contact stress. Elastic compression depresses surface features during measurement scans, producing false negative dimensional readings on compliant parts. Prototype trials evaluate deformation magnitude across varied probe tip radii and force settings to establish baseline correction factors.
Confusing static mechanical stiffness with dynamic probing capability leads to dimensional errors on flexible production components.
Deformation Compensation
Calibration algorithms compute elastic surface displacement to correct raw coordinate measurements according to known material elastic constants. Accounting for stylus contact force deformation restores true geometry measurements on soft polymers and thin-walled metallic precision parts. Production yield metrics verify that probing force settings balance signal stability against workpiece surface damage.
Releasing CMM inspection routines without contact force calibration results in systemic dimensional errors across soft material production runs.
Yield Envelope
High contact forces exceeding substrate yield points cause irreversible plastic indentations along the scanning track. Dynamic force spikes during rapid probing movements fracture delicate micro-structures or brittle surface coatings.
