Injection Mould Cavity Surface Roughness Measurement Using Silicon Replicas
Indirect silicone replica metrology resolves deep mould cavity roughness parameters non-destructively within five percent variance of direct steel scans.
Contact Force
Meaning
Physical interaction between two bodies signifies contact force. This mechanical phenomenon occurs when surface atoms repel or attract one another during physical engagement, transferring momentum or energy across the boundary. It governs the internal stresses experienced by polymers during injection moulding, specifically when a screw or plunger acts upon the resin melt.
The magnitude depends on the hardness of the materials involved and the acceleration of the components.
Process Dynamics
Friction and normal reaction represent the two primary vectors of this interaction in industrial settings. Precise control of contact force at the nozzle interface prevents backflow and maintains cavity pressure during the packing stage of a moulding cycle. Engineers measure the result by monitoring hydraulic pressure or load cell output against set parameters.
Deviations in the expected profile lead to dimensional instability or flash in the final part.
Material Response
Polymer granules and viscous melts behave differently under these loads due to their viscoelastic nature. A contact force applied too rapidly causes shear heating which degrades the molecular weight of sensitive resins like polycarbonate or acetals. Virgin pellets often demonstrate higher resistance to compressive loads compared to regrind because of their longer chain structure and uniform morphology.
Processors calculate the required load based on the projected area of the part to ensure the mould remains clamped.
Defect Mitigation
Excessive load causes tool deflection or permanent damage to the mould steel during high-speed production. Inadequate force results in incomplete filling of the cavity, known as short shots, or excessive sink marks across thick cross-sections. Practitioners maintain consistency by calibrating the stroke length against the density of the specific grade being processed.
A stable relationship between these parameters determines the long-term repeatability of the moulding operation.