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.
Four Way Locator Pin
Meaning
Alignment component found within an inspection jig that locates a specific hole or boss to prevent lateral movement. A four way locator pin features a cylindrical body that fits into a precisely sized hole in the moulded part. It establishes the exact center of a feature in two dimensions.
This component is usually paired with a two-way pin to prevent the part from rotating around the primary axis.
Positional Accuracy
Precision machining of the pin ensures that the nominal position of the part feature is captured during quality checks. The four way locator pin must be sized to account for the tolerance of the moulded hole. If the pin is too tight, it will stress the plastic and cause local deformation near the mounting point.
A loose fit introduces measurement uncertainty that can hide a drift in the injection moulding process.
Material Interaction
Hardened surfaces on the pin prevent wear during high volume production runs. Because resins like glass-filled nylon are abrasive, a four way locator pin often receives a coating like titanium nitride to extend its life. Friction between the metal and the polymer can cause small shavings to accumulate in the fixture.
Regular cleaning of these pins prevents the buildup of debris that would otherwise offset the part.
Tooling Cost
Standardized sizes reduce the expense of fixture building.