Meaning
Holding pressure profile optimization utilizes a sequence of different pressures during the packing phase of the injection moulding cycle. This pressure profile is the multi-stage pressure curve, which allows for precise control over the polymer density within the tool. It is used to distribute material evenly throughout the cavity as it solidifies.
Adjusting the pressures in stages prevents the typical defects associated with uniform packing forces, such as localized overpacking or underpacking.
Sink Prevention
Thick-walled sections of a part shrink more and cool slower than thin sections. Applying a multi-stage pressure curve ensures that high pressure is maintained during the initial phase to pack the thick areas, followed by a step-down to prevent overpacking the gate. Preventing sink marks is achieved without creating excess internal stress in the part.
Process Repeatability
Variations in melt viscosity can cause inconsistent part weights and dimensional fluctuations between shots. A carefully tuned multi-stage pressure curve compensates for these variations by adjusting the packing pressure at specific time intervals. Step-by-step control reduces the impact of raw material variation on the finished part quality.
Flash Reduction
High injection and packing pressures can force the mould open slightly, leading to plastic escaping along the parting line. Transitioning to a lower pressure using the multi-stage pressure curve prevents this flash while still maintaining enough pack to fill out the cavity. Lowering the pressure also decreases tool wear and clamp force requirements.
