The spline of an input hub - rethinking rotary swaging and axial forming
As shown by the example of an input hub for a double clutch transmission, it is often the small drive train components of a car that are complex to manufacture. The gear element that is only a few centimeters in size not only has a relatively complex geometry but also needs an external and internal spline. The traditional method used to produce an input hub is very time-consuming and costly as different, and in part metal cutting processes are used. Two parts are produced first and are then assembled at a later stage. The machine manufacturers and process specialists at Felss have suggested a very different process to a customer: one that is quicker, more accurate, simpler.
The internal spline of a so-called central shaft for a machine drive train was to be produced in a company of the automobile supplier industry using a new axial forming system. “Somewhere along the line we then saw the input hub for the double clutch transmission for the first time and heard about the rather complicated production process”, says Philipp Grupp of Felss Business Development. At that point in time, the two splines on the component were manufactured in several stages: First the external spline was rolled, then the internal spline was mounted as a separate sleeve into a pre-drilled thread. “We were only supposed to make one suggestion as to how the external spline could be pressed on through axial forming. One thing was for sure though: There must be an easier way to do this. The internal spline therefore became the focus of attention too.”
Using the rotary swaging process intelligently
It is technically possible to manufacture internal splines during axial forming. The forming tool presses the spline into a pre-drilled hole. Felss process planners went further though this time with the intelligent approach of carrying out multiple steps at the same time. Werner Michi, Project Manager of Process Development at Felss explains the approach: “To press on an external spline axially, you often need an internal mandrel anyway that supports the material. In this case, this could be the tool for the internal spline.”
Guaranteed performance breakthrough in tests
A series of tests then provided confirmation: Regardless of its relatively small diameter, the tool was able to withstand the pressure during the axial forming of the internal spline of the input hub. The cycle time for the simultaneous manufacturing of two splines on the machine was only about 20 seconds. The cold formed transmission component also has a continuous grain structure and excellent surface quality. All this from just one clamping that achieves an excellent concentricity. In conclusion, the combined manufacturing process represents a measurable improvement in performance for customers.
Breaking the mold with rotary swaging
The experts at Felss have enabled automobile manufacturers to use to capacity their existing axial forming systems. Larger investments were not needed. “The example is typical of our approach. Together with our customers, we also try to scrutinize run-in processes. In the case at hand we have radically simplified a complicated production process by producing two splines at the same time – in other words, tacking both ‘problems’ at the same time. This was once considered to be too complicated”, concludes Grupp.