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Of all things, a Bicycle manufacturer in the car industry, where it’s at: thanks to a process called Thixomoulding, significantly lighter weight components can be made of Magnesium. In the Dutch two-Wheeler forge Flevobike technology is already in use, Car producers could follow suit.

Gregor Honsel

Friday, 12.10.2007
At 08:59

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It is not easy to distinguish at a trade show with 868 exhibitors, but Johan Vrielink has managed to do: At this year’s Eurobike in Friedrichshafen, the chief of the Dutch Bicycle manufacturer, Flevobike for his recumbent bike “the green machine”, the Gold award was awarded in the category “bike mobility”. The most visible highlight of the send Kurzliegers: The entire chain is maintenance-free and Trouser leg for sure – within the framework of the 14-speed hub gear is completely integrated in the swing arm bearing. “Perfect industrial design in its best Form,” praised the Jury.

Less obviously, a further Innovation is made, the Vrielink for the green machine given: their wheels are made by Magnesium injection molding (“Thixomoulding”). Thus, Vrielink is a pioneer of a technology that is also used for the car industry, are increasingly of interest to you.

So far, major components made of aluminum or Magnesium to be produced almost exclusively by die-casting, in which a piston liquid pressed light metal into the casting mold. In Vrielinks Thixomoulding, however, the Magnesium is not melted alloy completely, but only up to about a hundred degrees below the melting point of 650 degrees Celsius. In a up to a tenth of a degree defined temperature window, the Magnesium is then in a so-called “thixotropic” state – it is like quicksand and Ketchup, are all the more thinner, the more it is stirred. By the shearing force of a screw, which transports the Magnesium mass to the mould, can change the viscosity of honey-like to watery.

This has a number of advantages. “The fact that I can set before the injection is very specifically the structure of the material, I can make more precise and thinner-walled structures,” says Andreas Lohmüller from the research firm New materials Fürth GmbH. Vrielink itself speaks of up to 0.5 mm thin walls which, thanks to Thixomoulding pour. In addition, the workpiece shrinks due to the lower temperatures, less porous, and more alloys can be used. Further plus points: the Magnesium Thixomoulding is cast more environmentally friendly than print, because it requires less heating energy. In addition, the highly reactive Magnesium gets little or no contact with air and must be surrounded, therefore, less expensive shielding gas.
These benefits take advantage of Asian producers since the nineties in the production of mobile phone shells or camera housings. But so far, could establish the procedure hardly in the case of components that are greater than, for example, a television. “The limiting factor is the clamping force of the machines,” says process engineer Lohmüller – the force with which the two halves of the mold together to be pressed. Currently the largest machine for this purpose has a holding force of a thousand tons. The ranges for components of approximately 1300 cubic centimeters in volume and nearly three kilograms of weight.

So far, the market for Thixomoulding-machine is in the Hand of the manufacturer Japan Steel Works, supplies mainly to the Asian region. Lohmüller is estimated that in Asia, currently about 300 Thixomoulding machines are in use in Europe, however, “only a few”. The canadian plastics specialist, Husky Injection Moulding Systems would like to but are now strengthened in the light metal business, and has, in particular, the car industry in the visor. “

The next generation of machines will probably have the 2000 tons of clamping force and four to six kilograms of Magnesium alloy can handle,” says Zac glass Ford, Product Manager for metal injection moulding Husky. Thus all the transmission housing could be injection molding. Lohmüller speaks to the Thixomoulding a good chance on a second career with the machine builders: “the point will come when the Magnesium injection molding, is a serious competitor for the pressure casting. In the car industry, a relatively large interest in Magnesium injection molding reigns, and because of this the quality of the Magnesium parts is larger, but as well as to replace by means of new Magnesium alloys of aluminum.”

Even in the distance of the spray casting of other metals such as aluminum or steel. The reasons for this: steel has a high melting temperature that it would damage the tools; aluminum, in turn, is in a liquid state to be more aggressive than Magnesium. According to its website is to be expected that it could be so only with expensive ceramic tools.

Flevobike-chief Vrielink is in any case fully to the Magnesium – card. As soon as the green machine is optimized down to the last Detail and piece of figures waving from a few Thousand, he wants to have components like the bottom bracket and the swing arm housing, which are currently machined from aluminum, Magnesium injection molding – to-weight advantage over aluminum: from 30 to 35 percent. An English Bicycle manufacturer, Flevobike is working together, had the first 200 copies of the 1.2-kilogram Magnesium frame for a city Bike pour.

Currently, that happens even in the case of partner companies in Canada, Malaysia and Taiwan. But as soon as the lucrative contracts to sign, would Vrielink with the company Thixotech Europe BV, whose partner he is casting, and injection machinery. In this way, his Green Machine to get another title: Know-how for the automotive industry.

© Technology Review, Heise Zeitschriften Verlag, Hannover

Heise Zeitschriften Verlag, Hannover

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