Steering system - dimensional stability for steering spindles from one tube

High quantities are not the only important aspect for many parts of the steering system, such as a steering spindle. Another important aspect for each component in automobile manufacturing is the dimensional tolerances in the smallest possible area.

The manufacture of a new steering spindle by the component manufacturer Felss Rotaform is an impressive example of how process developers master these different challenges. On behalf of ZF Lenksysteme, the Swiss forming specialists manufacture the steering component from just a single tube. During rotary swaging, tool segments that rotate around the workpiece, form the component in quick succession. The use of additional mandrels means that complex and high-precision internal contours can be manufactured – all while the outside diameter is being machined. The material starts to flow. The machining quality therefore also depends on the accuracy of the internal mandrel. “The mandrel as it were is the negative form for the internal geometry. With the steering spindle, it maps cams inside the tube”, explains Georg Jecklin, Technical Manager at Felss Rotaform Switzerland.

Rotary swaging and axial forming: many parameters for a perfect steering shaft

The correct mandrel design is of course only one detail in the overall process. In order to be able to perfectly manufacture the external and internal form of the steering spindle, the rotary swaging specialists at Felss Rotaform must guarantee the correct flow behavior of the material during forming – a difficult task, as Jecklin explains: “There are of course a great deal of parameters on the machine, on the internal and external tool or on the component, that play their role. We determine for example how much forming force the machine has to apply. Then, it’s a question of controlling the forces that occur in a process-safe procedure.” During production, a total of seven machining steps are performed. The blank – a tube section – is hammered over the mandrel during the first two steps, it is then inductively hardened during the third step, then it is rotated and machine cut. During the sixth step, the required external spline is pressed on through the axial forming process and finally, the steering spindle is cylindrically ground.

Common rotary swaging system solution

The shape of a steering spindle is very complex. This is precisely why rotary swaging and axial forming have the edge over many other processes, because they guarantee a very efficient and economical production. “It is nevertheless a constant challenge to adapt the technology to the respective component conditions”, adds Jecklin. Felss Rotaform – the component manufacturer within the Felss Group – thereby also benefits from the close cooperation with the machine manufacturers at Felss. Together, the specialists from Switzerland and Germany have aligned and run in the required rotary swaging system. Even for the ongoing optimization of the system for manufacturing the steering shafts, the machine manufacturer’s know-how and the knowledge of the component supplier are equally important to the production processes. Both come together in the Felss Group. The result is an ideal solution for the customer and a component.