Effect of Peak Cavity Pressure on Unreinforced Polyamide Linear Shrinkage Rates
Elevating peak cavity pressure compresses unreinforced polyamide melt, suppressing specific volume and reducing post-moulding linear shrinkage rates.
Machine Cycle Time
Meaning
Total elapsed duration required to complete a single injection moulding sequence from mold close to mold close. The machine cycle time governs the overall productivity and piece-part economics of a high-volume manufacturing run. This variable consists of mold closing, injection, holding, cooling, mold opening, and part ejection phases.
Economic Impact
Hourly operating rates of capital equipment represent a major share of piece-part costs. Reducing the machine cycle time by even a fraction of a second can yield significant financial savings over a long production run. When a machine runs faster, it produces more parts per shift, which reduces the overhead cost allocated to each unit.
However, shortening this duration too much can lead to quality defects.
Cooling Limit
Solidification of the molten polymer is the most time-consuming step in the process. The machine cycle time is largely dominated by the cooling phase, during which the polymer must lose heat until it becomes rigid enough to withstand ejection forces. Thick-walled parts require longer cooling times than thin-walled parts due to the low thermal conductivity of plastic.
Optimizing the cooling channel design within the mould helps to minimize this phase and keeps the entire sequence highly efficient.
Quality Tradeoffs
Accelerating the cycle can introduce physical defects into the molded parts. When the machine cycle time is squeezed excessively, the part may be ejected before it is fully solidified, leading to warpage, shrinkage, or sink marks. If the mould opens too quickly, the ejector pins can punch through the warm polymer skin.
Moulders must therefore find the optimum point where productivity is maximized without compromising dimensional stability.