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Design helps Germany compete with Far East

European producers cannot match the labour costs of some Far East manufacturing nations but intelligent design means the shift eastwards is not inevitable. That, at least, is the view of key plastics engineering specialists within the German operations of appliance makers Bosch Siemens and Braun.

Speaking at the VDI injection moulding conference in Baden-Baden earlier this year, Brigitte Furth, manager of the technology department at Bosch Siemens Hausger?te (BSH) in Bad Neustadt, described how the appliance maker has halved the cycle times for production of plastics parts for its latest VS5A series floor vacuum cleaners - sold under the Siemens name as the "Super XS dino e" model - through design of optimised injection moulding tools.

The BSH plant is the company's centre of competence for its floor care product lines and is claimed to be the largest vacuum cleaner plant in Germany. It produces a wide range of vacuum cleaners, ranging from compact hand models up to its latest cylinder cleaners.

Furth says the optimisation of the part designs has resulted in an almost 20% reduction in production cost compared with the company's earlier equivalent model, enabling it to reduce the premium over a comparable cleaner from China to just 6% after accounting for freight cost from China to Germany.

Around 65% of all vacuum cleaners sold in Germany in 2008 were imported from China but, with such a low premium, Furth said the company decided to produce the VS5A in Germany.

Part of the savings are attributed to shorter cycle times, says Furth, but integration of assembly supports and the introduction of assembly directly beside the injection moulding machine also help keep down production costs.

Furth said the new design also cut investment cost for tools to produce the three large housing parts (cover, underbody and cap) by 42% compared with the preceding model. And a saving of 45% on machinery and ancillary investment cost was achieved.

The optimised tooling design achieved, on average, a cycle time reduction for the three housing parts from 60s for first sampling to 38s for series production.

At the outset of the process, for example, the cover required a cycle time of 38s. The introduction of higher thermal conductivity tool materials, reduction of wall thicknesses in critical areas of the moulding and optimisation of cooling reduced the cycle time by a further 8s.

Furth says mould fill simulation was used to optimise the placement of cooling channels for both the fixed and moving mould halves, with laser-cused mould inserts used where close-contour cooling was required for critical areas.

Close attention was also paid to wall thicknesses. Furth says the housings of the previous vacuum cleaner model had walls up to 5mm thick at some points. For the new model a 2mm wall thickness limit was set, with areas requiring more rigidity simply strengthened by the addition of rib structures.

Further cycle time reductions were made by ejecting parts at higher temperatures than was standard practice in the past. This was made possible by paying careful attention to release angles, by polishing ribs in the direction of ejection, and by placing ejectors at or very close to the areas likely to require the most force. Aside from reducing cycle time, Furth says these measures also result in more even heat distribution in the mould.

Speaking at the same VDI event, Gerald G"rich, plastics processing manager at personal care product maker Braun's headquarters in Kronberg, explained how it used component optimisation, material selection, process development and tool design factors to develop the three-component "layer technology" housing for its new Silk épil Xpressive depilation appliance.

Launched in February this year, the Silk épil parts have been designed to create an impression of "layered" depth. They are moulded in a four-station 90° rotary indexing tool at the Braun plant in Walldürn in Germany.

PTC's Pro/Engineer software was used to engineer the part, followed by Moldflow Plastics Adviser studies to determine filling of the three polycarbonate housing components. Braun has been using Pro/Engineer since 1994 and was a pioneer in evaluating the Wildfire 4.0 version introduced in 2007.

At the VDI conference, G?rich said that in this case the company used Sigma 3D software for 3-D flow simulation. This allowed it to simulate melt temperature profiles during the filling stage, as well as the cooling and reheating characteristics, enabling it to avoid moulding problems such as clouding and bleeding of the first component.

Aside from the Silk épil, Braun also recently introduced the "bodycruZer" product for men that won a 2009 product of the year award at the Pro-K consumer plastics goods trade association.

Combining an electrical trimmer with a wet shaver, a key feature of the device is its use of a polycarbonate-based blend polymer with TPE and polyamide to provide a firm grip and complete seal against water ingress while under a shower.