Hollow shafts for Continental - New production process for drive components

To produce the hollow shaft of a Continental electromotor for servo steering systems, the experts at Felss Rotaform have developed a completely new production sequence that takes the geometry, material, weight and surface hardness into account. The gearbox component is manufactured by means of rotary swaging, axial forming and other processing steps that are optimally adjusted with each other with high precision and are also particularly efficient.

Given the required geometry, the designated material and the surface hardness of the hollow shaft, there were two factors at the center of the new development for Felss Rotaform Switzerland: the high precision of the drive component and the exact 90-degree shoulder at the end of the hollow shaft.

“We need a whole process that on the one hand exceeds the rotary swaging and axial forming of a tube”, explains Georg Jecklin, technical manager at Felss Rotaform Switzerland. “On the other hand we wanted to carefully introduce the strengths of our processes and develop them further.”

A Felss rotary swaging system with a 150 ton press has been specifically developed for this purpose. “First, we carried out a series of basic experiments in Switzerland and at Felss in Germany”, says Jecklin. The focal point was then pressing the 90-degree shoulder onto the blank: How much force is needed for this? Can the material withstand the pressure? And how does its microstructure change?

Optimally adjusted process steps

The ambitiousness of the production of the hollow shaft is already illustrated by the first process step: the actual rotary swaging. The formed blank must present a near-net-shape geometry after the forming process – with tolerances that are smaller than a tenth of a millimeter. The hardening process comes during the second process step: During the thermal treatment, the component is gas-nitrided, thereby tempering the surface. “The aim here is not just to define the necessary optimum thermal process. We must also construct the blank and its material correctly for the nitriding process in order to guarantee the required surface hardness”, explains Jecklin. The hollow shaft is then machine cut. After the grinding and rotating operation, it then meets the highest precision requirements.

Newly developed production process

The whole production process, from selecting the material for the hollow shaft via the performance description of the forming press that is used, to the final tempering and metal cutting, had to be redeveloped. Only the demands on the component had initially been determined, for example the necessary surface hardness and its highly accurate geometry. “We have tailored every process step to the next one and have developed a solution ready for series production for our Continental customer”, summarizes Rolf Käser, Managing Director at Felss Rotaform.