Meaning
Process optimization programs in injection molding aim to minimize the volume of wasted plastic generated during a production run. This initiative is known as molding scrap reduction, which governs the recycling of sprues, runners, and rejected parts. The term does not apply to metal stamping or subtractive machining processes.
Process Optimization
Minimizing waste requires a systematic analysis of the start-up and steady-state phases of the molding cycle. Achieving molding scrap reduction is often accomplished by optimizing the hot runner system to eliminate the sprue entirely. This design change removes the primary source of excess material from the process.
Additionally, using sensors to monitor cavity pressure helps prevent the production of short shots and flashed parts.
Material Recovery
Regrinding rejected parts and runners allows manufacturers to reuse some of the plastic material. Within a molding scrap reduction program, the ratio of regrind to virgin resin must be carefully controlled to prevent the degradation of mechanical properties. Too much recycled plastic can make the finished parts brittle and prone to failure.
This control ensures that the cost savings from recycling do not come at the expense of product quality.
Economic Consequence
Reducing the amount of material sent to the grinder improves the overall profitability of the factory. A successful molding scrap reduction campaign lowers both raw material costs and the energy required to process the resin. This improvement is particularly important for high-volume automotive or medical packaging runs where material costs make up most of the product price.
