Meaning
Manufacturing efficiency in plastics processing is calculated using a ratio that compares the weight of high-quality finished parts produced to the total amount of raw material consumed. This metric is known as the yield factor and it accounts for material lost to sprues, runners, scraps, and defective parts during a production run. A high value indicates that the moulding process converts raw resin into sellable products with minimal waste.
It does not measure the chemical yield of polymerization reactions.
Material Efficiency
Production runs of moulded parts generate waste in the form of cold runners and purging material that must be subtracted from the total resin used. The yield factor is determined by dividing the weight of approved parts by the total weight of the resin bags or boxes opened for the run. This calculation helps moulding shops identify which parts or tools are generating excessive scrap.
Process Control
Optimizing the startup phase of the injection moulding machine is necessary to maintain a high yield factor. During the initial cycles, the machine produces unstable parts that must be discarded until the process reaches thermal equilibrium.
Economic Impact
Raw materials represent the largest cost component in plastic moulding, making the tracking of material conversion critical for profitability. A low yield factor increases the cost per part because more virgin resin is required to meet the order quantity, which reduces the margin on the job. Moulding shops often grind down the runners and non-defective scrap to reuse as regrind, which helps recover some material value and restores the overall profitability of the run, provided the mechanical specifications of the customer allow for recycled content.
