Optical Profilometry and ISO 25178 Parameters for Cavity Wear
ISO 25178 areal parameters like Ssk, Sku, and Vvc measured via optical profilometry quantify cavity wear, predicting ejection failures before part dimensions drift.
Core Void Volume Vvc
Meaning
Core void volume vvc is a physical measurement specifying the trapped air percentage within a polymer injection mould before clamping forces seal the cavity. This metric governs clamping pressure thresholds and determines the maximum injection velocity achievable without diesel effect burns on the moulded part surface. Measuring this volume requires high precision laser displacement sensors mounted across parting line faces during dry cycle operations.
The boundary where this specification ceases to apply is found in open atmospheric casting methods lacking hermetic seals. Uncontrolled fluctuations in core void volume vvc alter packing efficiency and generate internal voids in thick walled structural components.
Thermal Drift
Tool steel expansion during high throughput production cycles changes the physical gap geometry inside the press. Heat transfer from molten feedstock expands cavity blocks and reduces total available capacity by measurable fractions of a millimetre. Monitoring thermocouples embedded near the parting line provides real time feedback for automated press controllers adjusting clamp tonnage.
Cooling channels operating below optimal flow rates intensify thermal growth and accelerate dimensional deviation across long production runs.
Resin Specification
Virgin polyolefins demand tighter dimensional tolerances on tooling gaps than post consumer regrind materials containing variable molecular weight fractions. Melt flow index instability shifts the viscosity profile and changes how rapidly polymer fronts fill residual air spaces. Supplier changes introduce additives that alter surface tension and modify gas entrapment tendencies during high pressure injection phases.
Purchasing departments balancing cost reduction against scrap rates frequently miscalculate how regrind variability widens process windows.
Part Defect
Gas burning appears on finished components when trapped air compression generates localized temperatures exceeding polymer thermal degradation limits. Inadequate venting channels prevent proper gas evacuation and force residual atmospheres into dead corners of the geometry. Short shots occur when compressed air pockets resist forward advance of the viscous polymer front and freeze prematurely against cold cavity walls.
Correcting these surface blemishes requires systematic adjustment of injection speed profiles rather than arbitrary increases in barrel temperature. Plant engineers track scrap reduction figures to verify that tooling modifications successfully eliminate internal porosity without creating flash along parting lines.