Steering system: Steering shafts and steering rods for an automobile component supplier

Steering shafts that are produced using rotary swaging and axial forming are installed in most cars produced in Europe. System and machine manufacturers such as the rotary swaging specialists at Felss, are constantly developing the process. It is not only the efficiency of the systems that is optimized, but also the steering shaft itself is constantly being further developed.


Lighter and more cost efficient

The production planners of a Felss customer worked together with Felss to find out if it is actually possible to make considerable material and cost savings within a sophisticated production system when working with a component made from tubing. The answer was surprising: A new steering shaft is a further 30% more lightweight. “For an automotive component that has already been manufactured with the lightweight design, this improvement is like a transition into a new world”, explains Philipp Grupp, Head of Business Development at Felss. The weight of the steering system is very important within the overall context of fuel savings and reduction in emissions. Many parts of the steering system, including the steering shaft, are produced using a sophisticated process. During rotary swaging and axial forming, the tube blank is transformed into a component with a complex geometry and spline system. The workpiece is also elongated by up to nearly twice the length – the outer wall either becomes thinner (or even thicker in some places), whilst the strength of the material increases.

Lighter steering system = less fuel

At present, there are two reasons for developing this successful production process even further: First, the steering shaft should be lighter and its lighter weight should help reduce the fuel consumption of the car. Secondly, the aim was to reduce the amount of steel needed for each steering rod. “At the outset we only promised that we would be able to do it. The method used to manufacture a considerably lighter component, had however not yet been agreed”, explains Philipp Grupp. Machine manufacturers hereby focus on the wall thickness of the component: Until now, there were still parts of the actual steering rod model that had not been elongated during the rotary swaging process. “I know this may all sound quite straightforward: elongate the wall a bit more during rotary swaging and save on material. But, making changes to the process does raise some issues. To start with, it would need to be proven how the thinner steering rod would stand up to subsequent axial forming, during which the splines are applied. There must be no sign of distortion”, explains Werner Michi, Project Manager of Process Development at Felss. During axial forming, much force is applied to the splines to press them onto the ends of the rod. In numerous tests, Felss adapted the frequency of the axial forming process – in the process patented by Felss, the workpiece is not moved at a constant speed but is frequency modulated. This minimizes the forces of the spline pressing on the workpiece, for example. The clamping concept with which the component is positioned in the machine, is also changed here.

Steering system 30 percent lighter, material saved

The outcome of the tests performed by Felss was a quantum leap forward in the construction of steering shafts. The blank is elongated more than ever before and yet the function of the component remains unchanged. And by implication this means: Less steel is needed to manufacture a steering rod. The figures are impressive: The steering shaft is nearly 30% more lightweight. This means that approximately 400g less steel is needed for each component. By putting both components together, the customer saves a total of approximately 365 tons of steel a year!