Autos opt for the hydro cure

As the technology sweeps through the automotive industry, Anna Kochan discovers that hydroforming is not only a strengthener, but also produces big cost savings on exotic and more mundane applications

Hydroforming is being adopted across the automotive industry at an extraordinary speed. The technology has been used for decades, but hit the headlines last year when the Ultra Light Steel Automotive Body project heralded it as a production process to take weight out of a steel car and delay the replacement of steel by aluminium.

The benefits go far beyond a simple weight loss, and include increased strength, reduced tooling investment and overall lower cost.

Hydroforming can be used for forming tubular parts such as engine cradles and sheet parts such as bonnets, but it is the application with tubes which is generating most interest.

The process involves placing a tube inside a die in a hydraulic press, filling it with water, or other fluid, and increasing the hydraulic pressure until the tube expands to fill the die.

It is capable of achieving intricate forms with high dimensional repeatability. The body of Audi’s new A2, for example, is partly constructed from extrusions which have been calibrated in a hydroforming press to give them the required accuracy. But this is an exotic application.

On the mundane side, Mercedes makes several million hydroformed exhaust parts for the A- and E-Class models every year. The Astra engine cradle is hydroformed, as is the Rover 75’s. Rear axle components for the BMW 5-Series and Volkswagen Golf and Bora, Audi A3 and Audi TT are also hydroformed. Frame components, instrument panel beams and roof rail inners are further examples of parts produced by the application.

With each component, one hydroformed part replaces several pressings spot welded together – as many as 17 in the case of a radiator closure assembly, according to Vari-Form, a specialist hydroforming company in the TI Group.

Fewer parts mean simpler logistics. Reduced spot welding eliminates the need for flanges and results in weight benefits. And better strength properties and greater accuracy are possible through eliminating spot welding.

Hydroforming the Ford Winstar engine cradle produces a 15% saving in weight and price, says Mike Green, vice-president of structural products at Dana, which supplies the cradles to Ford. He explains that Ford saves a further $2 a vehicle because the cradle incorporates two body mount brackets that would otherwise have to be bolted on.

At General Motors, the process is valued mainly for its potential to cut down on tooling by reducing the number of parts. Bill Surber at GM’s Advanced Portfolio Exploration Group in Warren, Michigan, says this cuts the investment needed with each engineering change or model introduction. He suggests that a ten-fold reduction in the number of tools employed might be possible.

GM is a leader in the process among vehicle manufacturers. Its Pontiac facility has a centre of expertise in the technology and produces many of its own parts. Ford is setting up its first hydroforming installation at its Dearborn frame plant. In Europe, all the German car companies are playing a pioneering role and BMW places special focus on aluminium hydroformed parts. The technology can be applied equally well to steel or aluminium parts.

Perhaps most impressive are the installations that have been set up by first-tier suppliers. Magna’s highly automated facility cost hundreds of millions of dollars. It uses six hydroforming presses, more than 500 robots and 52 YAG lasers to produce 1.2 million fully-assembled frames a year for GM pick-up trucks.

The huge growth in the use of hydroforming by the auto industry in the past five years looks set to continue, with more vehicle makers expected to use the technology for a wider range of parts. Charles Bruggemann, manager of Body Structure at GM, says only 15-20% of the technology’s potential has been exploited. Ford also plans to make greater use of the technology.

At the same time, new applications are also being developed. Mercedes has created a camshaft which is being fitted on diesel engines for the Smart city car. By replacing a conventional forged or cast camshaft with a hydroformed one, a 40% weight reduction and 30% lower total investment can be achieved, says Matthias Schroeder of DaimlerChrysler’s hydroforming development centre in Hamburg.

In the Mercedes process the cams are assembled loosely on the tubular shaft before it is loaded to the hydroforming press.

There is even talk of creating a hydroformed camshaft entirely from a tubular component. `We are working very closely with three customers on a single component hydroformed cam-shaft,’ says Horst Prelog, vice-president of operations at Magna’s chassis group. `Cars with these camshafts should be on the roads within a couple of years.’