Datum Target Placement Mechanics for Compliant Thermoplastic Parts
Datum target placement on compliant plastic parts requires locating pads on rigid structural features and using restrained-state inspection standards.
Vacuum Fixtures
Meaning
Tooling component designed to hold a plastic part securely in a fixed position using atmospheric pressure differentials. Use of vacuum fixtures is common during the secondary machining or inspection of thin-walled and flexible moldings. The system works by evacuating the air between the part surface and the fixture, creating a force that clamps the part without mechanical clips.
Surface Protection
Traditional clamps often leave marks or cause local deformations on soft polymer surfaces. Because vacuum fixtures distribute the holding force evenly across a large area, they prevent damage to cosmetic surfaces. This makes them ideal for high-finish automotive or consumer electronics components.
Accuracy Control
Consistent positioning is essential for repeatable measurement on a coordinate measuring machine. By pulling the part down into a precisely machined nest, vacuum fixtures eliminate the variability caused by manual clamping. This ensures that the measured dimensions reflect the actual part geometry rather than the influence of the operator.
Design Requirement
Effective operation requires a continuous seal around the perimeter of the part or the targeted area. Porous materials or parts with many holes may require specialized zones or high-volume pumps to maintain the necessary hold. The material of the vacuum fixtures must be rigid enough to resist deflection under the atmospheric load to maintain the accuracy of the operation.