Designing Restrained State Quality Fixtures for Flexible Plastic Assemblies
Restrained state fixtures simulate final assembly fasteners with calibrated clamps on datum targets to measure flexible plastic profiles accurately.
Clamp Sequence
Meaning
Procedural logic used in secondary assembly or inspection fixtures to secure a polymer component without inducing internal stress. A precise clamp sequence ensures that the part settles against its primary datums before secondary constraints engage. If the order is reversed, the fixture might trap the part in a distorted shape, leading to false measurement failures.
This process becomes vital when handling thin walled polyolefin parts that lack high structural rigidity.
Mechanical Logic
Logical ordering prevents the accumulation of deformation. The clamp sequence usually starts at the most rigid point of the part and progresses toward the edges. It allows the material to slide into position rather than buckling against a fixed stop.
Incorrect execution often masks defects like gate blush or sink marks by forcing the surface flat during an inspection check.
Dimensional Accuracy
Measurement reliability depends on repeatable force application. When a clamp sequence is inconsistent, the resultant data from a coordinate measuring machine fluctuates even if the moulding process is stable. Consistency ensures that the gap and flush requirements of an automotive assembly are met across thousands of cycles.
A documented protocol allows different operators to achieve the same results on different shifts. Operators must verify that every toggle or pneumatic arm moves in the specified order to prevent part tilt. This rigorous approach eliminates the noise in quality data that comes from poor handling rather than resin shrinkage or thermal variation.
Stress Management
Internal forces in a part can be redirected by the clamping order. A poorly designed clamp sequence may lead to micro-cracking in brittle resins like glass-filled nylon. Excessive pressure at the wrong step overcomes the yield strength of the polymer.
This results in permanent deformation that stays with the part after it is removed from the jig.