Tech Focus Chrome components in a single shot
With its Flexflow technology, Italian hot runner specialist HRS Flow has developed an innovative solution for the injection moulding of high-quality parts primarily for the automotive industry.
Flexflow is a servo-driven, finely regulated valve gate system for hot runner systems. The precise control of the melt flow of each individual hot runner nozzle permits a very balanced filling of all cavities and uniform pressure distribution during packing stage, even with multiple gating and widely varying cavity volumes. The radiator grille from the HRS Flow test mold measuring 580 mm x 330 mm with a total parts weight of 297 g and different wall thickness, from 2 mm to 3 mm, on cavities is subsequently chrome-plated and must therefore meet very high demands in terms of surface quality. Several car component suppliers have already positively tested this ABS and ABS/PC part on their electroplating equipment. The first chrome-plating applications are due to go into series production shortly.
Different shot weights in one filling process
With the Flexflow valve gate system, even large-area parts can be molded with high-grade surfaces. With the cascade injection molding process that is normally used for this purpose, the electrically driven needle valve nozzles allow the precise, sequentially coordinated opening and closing of the valve pins with variable velocity over stroke length. This in turn permits accurate control of the melt flow on each hot gate and of the volume flow in the cavity as a whole. With the customized opening of the valves, the dreaded pressure loss that occurs with conventional cascade injection molding methods is avoided, and, with it, the accompanying marks on the molded part. Moreover controlled position of pin during packing stage allow to reach independent pressure control on each gate and thus desired shrinkage for each cavity, speeding-up matching of tolerance requirement and avoiding expensive modification of tools.
The injection-molded radiator grille is produced in a single shot over ten gating points with nozzles from HRS Flow's MA series. The system layout consists of a compact runner and is designed expressly not symmetrical. The volumes of the cavities for the individual molding elements of the radiator grille have a ratio of 1:20 from the smallest to the largest mold cavity, with 30% of thickness variation from thinner to thicker. The injection time is 2.9 s, the holding time is 6 s, the hot runner temperature is 255 °C and the mold temperature 60 °C.
In the past, to achieve the different shot weights and still meet the demands for chrome-plating and assembly tolerances, separate molds would have been needed to produce this high-quality part. The aim of this hot runner system layout was to prove the strengths of the Flexflow technology with the aid of this multi-cavity application. Mr. Nicola Pavan, CAE department coordinator and project leader at HRS Flow says: "To prove Flexflow capability we intended to mold the components only with simultaneous opening of the electrically driven needle valve nozzles with a previously defined opening stroke setting.
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