Coherence Scanning Calibration Procedures for High Aspect Ratio Tool Steel Sidewalls
Calibrating optical coherence scanners on tool steel sidewalls requires specular tilt mapping, transfer function correction, and noise floor subtractive adjustment.
Demoulding Friction Coefficient
Meaning
Dimensional resistance measures the tangential force required to slide a polymer surface against a mould wall during the ejection phase. The demoulding friction coefficient determines the minimum force necessary for successful part release from steel or aluminium tooling surfaces. High values indicate a tendency for the plastic to adhere to the cavity or core, which leads to surface marring, deformation, or structural damage.
Lower values facilitate a smooth transition from the molten or solidified state to the final ejected part.
Ejection Mechanism
Mechanical pins apply force to the part base to overcome the gripping pressure of the cavity walls. The demoulding friction coefficient dictates the magnitude of this pressure because it quantifies the shear stress generated by the material contact against the metal. Tooling temperature variations alter this interaction by changing the thermal contraction rate of the resin.
A surface with a higher texture depth increases the effective area for contact and raises the total drag during the release phase.
Resin Specification
Material datasheets report the property as an average value derived from controlled sliding tests against polished metal standards. Virgin resins maintain predictable lubricity levels that shift when recycled content or fillers enter the formulation. Fibres often disrupt the surface profile of the polymer, changing the sliding characteristics and requiring higher ejection pressures.
Additives such as internal lubricants or slip agents modify the resin chemistry to lower the coefficient, which prevents sticking in high-speed production cycles.
Production Constraint
Tooling geometry directly influences the operational limits because draft angles must compensate for the material drag. Sharp corners or deep ribs trap the part, forcing the moulder to increase ejection speeds that potentially crack the plastic. Variations in packing pressure produce different densification levels at the surface, changing the actual coefficient observed on the shop floor compared to the value listed in the original design phase.
Excessive friction during extraction creates cost penalties through cycle time extensions, scrap generation, and increased wear on ejector pins.