Raw Tooling Trial Witnessing Protocols for Multi Cavity Injection Moulds
Press side multi cavity trial witnessing mandates independent volumetric fill verification, gate seal determination, and 24 hour conditioned metrology
V P Transfer Point
Meaning
Velocity pressure transfer point defines the specific displacement of the machine screw where injection phase pressure transitions into holding phase force. A v p transfer point governs the shift from filling the mould cavity to packing the resin into the gates and runners. This calibration prevents excessive flash or short shots by managing the volumetric throughput of the molten plastic.
Precision in this setting ensures the repeatability of part weight and final dimensions across long production cycles.
Injection Dynamics
High melt flow indices require an early switchover to minimize internal stress and flash around parting lines. A v p transfer point set too late forces molten resin against the tooling walls with residual hydraulic pressure, often causing localized burning or degradation. Advanced controllers monitor the cavity pressure profile to determine the exact millisecond for this change.
Stable hydraulic response times remain essential for maintaining consistency between the set value and the machine reality.
Material Response
Crystalline resins often demand a precise switchover to accommodate the rapid solidification that happens as the melt hits cold steel. A v p transfer point behaves differently when moving from virgin pellets to high concentrations of regrind because the lower melt viscosity of the reclaimed material changes the flow front speed. Moulders adjust this setting during the initial setup of a new tool to compensate for the thermal expansion of the barrel.
Part specifications dictate the required density, which creates the physical boundary for where this transition occurs.
Tooling Interaction
Complex geometries with varied wall thicknesses force the calculation of this shift based on the slowest cooling region of the part. A v p transfer point acts as the primary tool for controlling internal voids that appear when the screw fails to maintain contact with the shrinking resin. Improper adjustment of this position leads to cosmetic sink marks or internal stress concentrations that weaken the structural performance of the part.
Control of this position represents the difference between a stable process and one that requires constant operator intervention.