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Optimization of the Injection Molding Cycle

SpecialChem / Oct 4, 2006

An optimised injection molding process is one that is only restricted by the physics of the process and not by the capability of either the mold or machine. There is an optimum filling time for any mold. The optimum filling speed is close to that which requires the least pressure. Fig 1 shows a typical relationship between filling time and pressure to fill. However faster filling speeds are often compromised by problems such as 'gassing' - the burning of the melt front due to entrapment of cavity air. Vents should be cut where the 'gassing' occurs. If vents do exist, and they are properly sized and clean, then reducing the locking force can help with venting and enable faster injection time. But the process should not be compromised because of the poor venting - the venting should be properly engineered to do the job required.It is common for filling times to be too long. Probably 95% of all molds should have a filling time between 1.5 and 3 seconds. If a mold takes longer than 3 seconds to fill it should be investigated.

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