Cluster Design for Injection Molding Tooling
The cluster design developed by Schöttli AG Mould Technology, Diessenhofen, Switzerland, is a tooling concept for symmetrical side gating that is not available from standardized mold systems. The concept is particularly suitable for rotationally symmetrical tube shaped parts in multi-cavity tools. In the past round parts were often only injected on one side in order to save the cost of additional nozzles and control zones and to keep the mold compact in size. By circular arrangement of the clusters of four, double sided symmetrical gating of the components can be realized without increasing the complexity of the tool. The number of nozzles and thus control zones is kept low with just four nozzles for four cavities.
The symmetrical advance of the melt front prevents a single sided bending load on the core and eliminates core deformation. This has a decisive effect on part quality minimizing circumferential variations in wall thickness and deviations in straightness due to warpage. In addition arranging in clusters of four simplifies the precise centering of the two halves of the mold.
By using side gating with injection nozzles Schöttli continues to promote the advantages of open side gating systems, which unlike needle valve systems have no wear parts. The sprue is cleanly parted during de-molding and is often not visible. The cluster construction has proved itself in many applications such as syringe bodies, pipettes and tampon applicators. Typical tool sizes are between 4 and 128 cavities.
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