How to Design High Cavitation Tooling
Today's sophisticated dispensing closure tooling represents a significant capital investment and requires skillful selection of a mold supplier. This tooling is highly complex and requires a higher level of precision due to multiple product design functional requirements. Living hinges, linerless bottle plug seals, product shipping seals, dispensing orifices, internal or external threads, and mating component fits have a great impact on how the tool is designed.
Designing a product for high production tooling involves considerations that must be closely evaluated: gating location, part ejection, wall thickness, material flow characteristics, cycle time, hot runner feasibility and assembly at high rates. One overlooked area during product design is multi-cavity tooling requirements. Some very complex designs require a host of tool actions—such as side-action, automatic unscrewing and collapsible core, multi-material and two-shot features, sometimes all within the same tool—which can require large areas of space and limit mold cavitation.
New products are developed to test part function, provide marketing samples for consumer testing and aid in assembly equipment design, but they most likely will not uncover production tooling problems. A proven approach to reduce risk or delays for a complex production tool is to construct a representative single cavity, fully automatic tool of the intended production design to ensure the design concept will perform under production conditions.
Cycle time, shrinkage, venting, cooling, steel selection, and most importantly the tool's mechanical reliability are proven. The benefits are pre-production sample parts that meet customer specifications and delivery of the production tool on time without start-up delays. This process also benefits the moldmaker with insight into multi-cavity component manufacture. Special fixtures, tooling or equipment can be preplanned or purchased with this knowledge.
The capability of the injection molding machine requires thorough investigation. High cavitation tools can be extremely heavy and require molding machines with a rigid clamp design and well supported platens. Platen deflection during mold injection or platen tipping during mold opening or closing will have an effect on part quality and mold maintenance costs. Mold damage can occur rapidly when these guidelines are not followed. Plastizing of the resin is another area. Melt quality and shot-to-shot consistency will greatly impact part quality and cycle time. Injection molding technology of new machines can overcome issues related to processing.
Hot runner technology for dispensing closure designs may provide cost and manufacturing advantages over a cold runner; however, not all dispensing closures lend themselves to full direct hot tip gating due to part design constraints. In cases where complete elimination of the cold runner is not possible, a hot/cold combination system may be the answer and may also provide most of the available savings of a full hot runner while offering a lower cost solution.
Molders today are more conscious of purchasing higher quality tooling and implementing PM programs. Mold tryout and debugging by the moldmaker are strongly recommended, and open communication between the end user, molder and moldmaker will reduce errors and clarify delivery expectations. A well-engineered and developed product and tool design combination will guarantee success and greater profitability.
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