Injection Moulding Asia

IMHP technique with improvements

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In contrast to standard injection moulding procedure, the required hold pressure is applied within the mould. This means that the plasticising unit can already be withdrawn from the mould at the start of the hold pressure phase and after injection of the material, dosing of the screw can be resumed.

As such, the two phases of applying hold pressure and dosing, which would traditionally follow on from each other, can now be carried out simultaneously. This reduces the cycle time from the entire dosing time, if this is shorter than the hold pressure time. The company says this can be up to 30%, in the case of large shot volumes or relatively short overall cycle times.

The company has conducted trials at its Swiss technical centre and says the process offers two different methods: each integrated within the mould, for applying hold pressure and the successive feeding of molten material. As part of the first method, a hydraulically-operated piston, which is integrated in the movable side of the mould, is immersed in a specially provisioned and appropriately-dosed melt cushion. Alternatively, the equivalent melt volume is available on the stationary side of the mould in the hot runner. In this case, the molten material is pressed into the cavity using a needle-valve-like mechanism.

Both methods are currently being trialled and refined by DuPont, with a current emphasis on minimising the additional space required. The company also says that IMHP technology proved itself to be particularly beneficial when moulding DuPont's Delrin acetal resin since the hold pressure time constitutes a large proportion of its overall cycle time.

The next step will be for the company to work with moulders, hot runner and machinery producers in refining the engineering aspects of the process.