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Laser-welded oil pipe of DuPont Zytel in VW’s dual-clutch gearbox

10 July 2006

A tube of hot-oil-resistant DuPont Zytel nylon carries oil from the filter to the six-speed direct-shift gearbox’s control unit of Volkswagen’s trend-setting dual-clutch gearbox. To produce the complex-shaped tube cost-effectively and at the same time avoid demoulding problems, German automotive supplier IBS Filtran combines injection-moulding with laser-transmission welding to join separately moulded parts without risk of producing loose particles that might contaminate the oil. A ring of heat- and oil-resistant DuPont™ Vamac® ethylene acrylic elastomer seals the oil tube from the gearbox.

Markus Beer, IBS Filtran’s general manager, says: “The oil tube just fits into the tight space available, whether the oil is at minus 40 °C or +140 °C. The Zytel 70G30 HSLR type we chose, reinforced with 30 percent glass fibre, makes weight-saving thin-wall mouldings possible, but still has very high strength. Even when the temperature and the vacuum in the system reach peak values, and vibration and impacts create high acceleration forces at the same time, deformation remains minimal. As a result, the upstream filter always works optimally and there is no risk of collision with gearbox parts which are very close.”

IBS Filtran ruled out blow-moulding, which seemed the obvious way to produce this part. “This process would not have met requirements for a constant flow cross-section and even wall-thickness,” Michael Jacob, the design manager, explains. “There was also a danger of glass-fibre particles coming loose from the inner surface and damaging the delicate system of valves into which the tube carries the oil.

“So we decided on injection-moulding. For this we had to divide the tube into separate parts, to make demoulding easier. However, we could not make two equal halves joined by conventional welding techniques, because the necessary contact surface area would have been too broad and welding-waste particles could have come loose; this had to be avoided.”

IBS Filtran’s solution was a tube with offset open areas. “One part made of a laser-absorbent variant of Zytel 70G30 HSLR can be moulded in a tool with a single parting line,” Jacob continues. “Onto the open areas we then laser-weld two other injection-moulded tops of the same nylon but using a laser-transparent variant. The weld-seam is very precisely defined and reliably air- and oil-tight. As the welding process does not involve oil-contact surfaces, there is no danger that particles of the plastic material come loose and enter the oil-stream. All in all, laser-transmission welding provides an optimum combination of cost-effectiveness and reliability.”

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