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hot runners | DFM

Hot runners can offer many benefi ts to manufacturers. But their use, placement and gating type should be considered early in the product development process to gain maximum advantage, says André Eichhorn

integrating hot runners

Tips for

Hot runner technology has been with us for more than 40 years and while hot runners could be challenging to work with in the early days this is no longer the case – hot runner suppliers have made huge technical improvements over the past decade or so. That said, it remains the job of the component and mould designer to decide whether a hot runner system or gating style is appropriate for the specifi c task and, if so, to ensure the system is executed correctly. The fi rst point to consider is that not all moulding

applications are suitable for hot runner technology. The volume of parts required each year is often the key driver as the cost of a hot runner system has to be justifi ed. But sometimes it can be advantageous to have a cold runner attached to the component where post moulding operations such as painting or plating are required as it can simplify handling. The typical principle advantages of using a hot runner system include:  material savings due to elimination of the cold runner;  shorter cycle time;  improved moulding system effi ciency;  better part quality;  higher level of moulding automation;  greater design fl exibility;  better balanced melt fl ow. Once the decision has been made to incorporate a hot runner system into a mould, the question to be

asked is: What kind of system is required? The hot runner suppliers themselves are the specialists in this regard and they have the most experienced people to help. So in general, the mouldmaker will place the design of the hot runner system in the hands of the supplier. What the hot runner designer will need in terms of information will include details of the compo- nent geometry, weight and material, and the pitch between the cavities. Normally the supplier will be provided with the complete tool design. However, there are some key elements a product designer should consider during the DFM phase. The fi rst is a commercial consideration - it does not make sense, for example, to work with a supplier that offers a good price and quality but has no service available in the area of the world where production will be carried out. After that, there are a number of major design aspects to consider. Direct gate points are most often placed in areas

where they are visible to the customer so the appear- ance of the gate point can be an issue, especially where the position is dictated by the need to achieve the best fi lling and packing of the component. There are two basic gating principles to consider: the open gate and the needle valve type. The most common hot runner gate option is the open

system, where the hot tip is placed on the component surface. This is the simplest option but the downside is

July/August 2013 | INJECTION WORLD 51

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