Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting
Patent
1993-09-20
1996-11-26
Heitbrink, Jill L.
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
264 405, 2643281, 425145, B29C 4577
Patent
active
055782566
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to injection moulding of plastics, and relates particularly to a system and method for optimising operation of an injection moulding machine.
DESCRIPTION OF THE PRIOR ART
An injection moulding machine typically has a barrel and ram arrangement which must force a plastic melt into a die or mould through a nozzle to the runner and gate system by displacement of the ram, so to produce a particular article.
The procedure of moulding an item from a die involves three basic steps. These are the filling phase, during which the plastic flows into the cavity of the die, the pressurisation phase and finally the compensation phase. The pressurisation phase accounts for the compressibility of the plastic in its molten state, while the compensation phase accounts for the volumetric change in the transition between a molten and solid state of the plastic.
Design criteria of the injection moulding process often require that the time available to inject the plastic melt is very short, perhaps fractions of a second, which necessitates the need for close control over the ram of the injection moulding machine. Further, during the filling phase, the ram is required to move at high speed to obtain the required plastic flow velocity, whereas, during the pressurisation phase, the ram must move slowly to obtain the required plastic pressure. During the transition between the filling and pressurisation phases excessive pressure spikes can occur, which can cause significant difficulties affecting the moulding quality.
In this specification, the moulding of a single item is referred to as a shot. A single shot entails the execution of a number of sequenced steps constituting the moulding process, and which are repeated for each individual shot. One or more individual articles can be produced from the one shot.
Designers of conventional injection moulding machines have used sophisticated process controllers to regulate the speed or displacement of the ram of the machine according to a profile or characteristic which has been inputted to the process controller. This technique most often relies on the operator of the machine having to correct the ram input characteristic in accordance with a trial and error process. By such a technique one moulding is made, inspected, then appropriate or best-guess changes made based on that observation. Such a practice is cumbersome and wasteful of both time and materials.
Conventional techniques have been developed largely around control of the ram and all rely on the design variable (which is often guessed) being a property of the ram dynamics rather than considering the behaviour of the plastic melt itself. Therein lies one particular disadvantage with the prior art, in that the actual position of the plastic flow front as it enters a die is unknown. Therefore, in areas where slow injection ram speed is required (such as the gate region), the length of slow speed operation must be made long in order to ensure correct moulding. This can result in the plastic loosing temperature with a subsequent increase in the residual stresses within the article being moulded, even to the extent that the mould may not be completely filled.
The present applicant has developed computer design programs which simulate and optimize the injection moulding cavity, runner and gate design, as well as the flow of plastics into the mould. These programs are sold in many countries, and are identified by the trade marks: MOLDFLOW/FLOW or MF/FLOW.
The programs take into consideration the rheological, thermal and physical properties (such as pressure-volume-temperature relation and compressibility) of the plastic materials. The design procedure has recourse to the filling pattern of the plastic as it flows into a cavity as a function of temperature, pressure, shear rate, stress and other relevant factors to the process of injection moulding. The design programs therefore predict optimized moulding conditions in terms of melt and mould temperature, and the filling speed of the cav
REFERENCES:
patent: 3695800 (1972-10-01), Hutchinson et al.
patent: 3859400 (1975-01-01), Ma
patent: 3924840 (1975-12-01), Nelson, Jr.
patent: 4135873 (1979-01-01), Sone et al.
patent: 4146601 (1979-03-01), Bishop
patent: 4325896 (1982-04-01), Rodgers, Jr.
patent: 5062785 (1991-11-01), Stroud, III et al.
Heitbrink Jill L.
Moldflow Pty Ltd
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