Reference Target Placement for Flexible Plastic Parts
Position reference targets on flexible plastic parts at high-stiffness rib intersections using explicit 3-2-1 restraint forces to eliminate gravity sag and inspection disputes.
Mechanical Restraint Force
Meaning
Physical pressure applied by jigs or fixtures prevents a part from warping as it reaches thermal equilibrium. Mechanical restraint force holds the plastic against a known datum while the internal stresses from the moulding process relax. This technique allows a moulder to ship parts that meet tight tolerances even when the material is prone to shrinking.
Clamping Pressure
Application of force must be high enough to resist the internal tension of the polymer but low enough to avoid surface marking. If the pressure is uneven, the part may develop new stresses that cause it to warp in a different direction. Standardized gauges monitor the load across the fixture.
Springback Resistance
Deformation occurs when the part is released from the restraint and attempts to return to its distorted state. Engineers must calculate the amount of over-bending or the duration of the hold time to minimize this effect. The material type determines how much permanent set is achieved during the cooling period.
Fixturing Load
Structural integrity of the measurement gauge must exceed the force exerted by the plastic. If the fixture frame flexes under the weight or the tension of the part, the resulting measurement will be incorrect. Heavy steel or aluminum bases provide the necessary rigidity for this application.