Meaning
Excess wall thickness occurs when a mould cavity design or processing parameter forces more polymer into a part than the nominal engineering specification requires. Over-gauging describes this state where the dimensions exceed the allowed tolerance band. It shifts the weight of the final product upward and alters the cooling cycle requirements.
Designers control this by adjusting cavity volumes or injection pressures to maintain stable geometry.
Material Density
Resin viscosity fluctuations during high pressure filling lead to pack-out issues within the tool. Over-gauging arises if the controller maintains high gate pressure after the void space fills. Processors mitigate this by setting decoupling parameters that transition to holding pressure before the cavity reaches maximum volume.
Virgin resin often flows differently than regrind mixtures which forces the moulder to adjust these hold times during production runs. Accurate data sheets provide the baseline for these settings but real site conditions dictate the final machine inputs.
Tooling Impact
Cavity erosion or improper steel machining creates regions where molten plastic fills beyond the intended limit. Over-gauging leaves thick sections that create non-uniform cooling rates across the part surface. These gradients generate internal residual stresses that cause warpage when the component ejects from the tool.
Moulders check for this by measuring sample weights against the target value derived from the original cad file. A part weight consistently higher than the nominal calculation confirms that the tool or the injection cycle produces an unintended increase in wall thickness.
Economic Cost
High scrap rates follow when excessive wall thickness pushes a part outside the upper tolerance limit. Raw material usage rises because every cycle consumes more resin than the bill of materials allocates. This waste compounds over long production runs where narrow margins make excess polymer consumption a liability.
Production efficiency drops when cooling times lengthen to account for the additional heat sink created by the extra material. Proper calibration of injection setpoints prevents this variance and keeps the manufacturing process within the expected cost parameters.
