Things are on the move
 
SIEBER became particularly well known through its founder Karl SIEBER, who set in motion new concepts using reinforced tools for cold forging more than 50 years ago.
 
Reinforced, pre-stressed tools can absorb much higher forces and this triggered an enormous surge forwards in cold forging.
 
This has now become part of standard engineering practice. The challenge consists in providing even higher levels of accuracy, using higher tensile materials, having short warm-up times and, quite naturally, a greater degree of flexibility, in order to be able to manufacture smaller batch sizes cost-effectively.

Figure 1: Matizenverband laboratory setup
 
It would be great if the tool, which should really be very stiff, could be somewhat more flexible, especially if you need to work with greater degrees of accuracy or be able to adjust measurements sensitively and flexibly even in a closed loop cycle or even respond to material features.
 
Inspired by forging splines, where operators normally remould the cores to guarantee levels of accuracy in order to make minute changes to the drilling measurements to respond to effects caused by the material or heat treating processes, a tool concept was developed, with which the drill hole can be flexibly adjusted by up to 0.06 mm without altering the initial stress levels. The tool does not have to be dismantled or activated mechanically.
It is even possible to adjust settings during operations so that no interruption is required in the process – which could lead to the tools cooling down.
 
The task was resolved by simultaneously heating and cooling a shrink joint.
 
While the core can be heated to a temperature of up to 500 °C, the reinforcement is cooled down at the same time in order to adjust the shrink joint.

The heating procedure uses a new kind of induction process, which takes less than 5 minutes to operate from a cold start and guarantees real time processes to manage and control the drilling diameter.
A temperature change of 10 °C leads to a change in diameter of 0.001 mm.
 
In contrast to other solutions on the market, which only resolve the adjustment of the drill hole by the initial stress applied, this concept allows the initial stress to be largely retained by using a separately controlled cooling cycle or it can even be actively used to expand the working area.
 
In the experiment, a composite tool with a core drill hole of 27.8 mm and a reinforcement outer diameter of 200 mm is used.
Fig. 2 shows a test run that lasted 75 minutes. The temperature of the core is dark blue and the outer temperature of the reinforcement is light blue.

After approx. 7 minutes, the core temperature was already 250°C. The reinforcement temperature was set at approx. 80°C, which leads to the drill hole opening by 0.05 mm.
Tungsten carbide was used as the core metal.

Tungsten carbide would only expand by approx. 0.035 mm in the drill hole at these temperatures. By heating the reinforcement to 80°C, the assembly expanded by an additional 20%, which means that the core roughly opened a further 0.015 mm. This means that the core drill hole opened by approx. 0.05 mm at below 300°C.
 
Figure 2: Development Team
 
he core temperature was increased to approx. 350°C after 20 minutes and the reinforcement temperature followed suit to the same ratio.
After 45 minutes, a temperature ratio of approx. 300°C to approx. 50°C was set, which created an opening in the drill hole of just 0.02 mm. Despite the 300°C in the core, the huge temperature difference of more than 200°C between the core and reinforcement provided greater initial stress, which means that the opening in the drill hole was only slight.

This tool concept opens up new dimensions, not only to be able to respond to process or material fluctuations in a much more flexible manner; but it also allows the user to reach a new level of accuracy, embedded in a closed control cycle.
           
The temperatures that can be obtained create options for combining processes ranked between cold and semi-hot forging, so that other materials with higher degrees of deformation can now be used.
 
The pre-heated tool also provides the advantage that warm-up processes, which are based on reaching the operating temperature of the tool, can be shortened to a major degree and can even be eliminated.
 
However, it should be noted that the effect of the temperature on complex shapes – e.g. splines – must naturally be taken into account when designing tools.
 
The corrections to the geometry are very complex, especially in the case of splines, and this must be taken into account when designing the tools.
 
Assuming that the work area is designed for 100 C° - 500C°.
 
Figure 4: Workspace
 
The tool should be designed for temperatures exceeding 100C°, which means that the tool cannot be produced with a mould, as would be used at room temperature. The spline mould has to be pre-corrected.
The important quality features for splines are not only the thickness of the teeth, but also the mould for the involute profile and the mould for the pitch line in the direction of the axis. These parameters are normally measured using a spline measuring device as Fig. 5 shows.
(Pitch line
Profile)
Figure 5: Determination of quality parameters with a gear meter
 
Using measured or ideal points, it is using software to analyze possible deviations of the teeth to simulate effects and to determine correction parameters. Figure 6 explains how to change the basis of theoretically exact dates to a selected gear the profile and flank line when a contraction is simulated.

This simulation is very simple mouse click. The relevant quality characteristics of the teeth are calculated and displayed online.

For an optimal control strategy of Use / can be created for a specific tooth sensitivity matrix, which maps the relationships between quality parameters and the process and material parameters
 
Figure 6: Simulation of the shrinkage effects with ideal measurement points
 
The presented simulation possibilities exist for measured curves, such as picture explains 7th
 
Figure 7: Calculation of correction parameters of the teeth from measured Darte
 
The presented simulation possibilities exist for measured curves, such as picture explains 7th As an alternative to the shrinkage correction can gradually change the values of the teeth or through an offset account directly the optimal set points are determined so that the deviations are minimized. This approach is interesting when the production of the tools is via Verzahnungssollwerte and corrections are taken into account. The particular advantage of this software lies in the iterative calculation, which allows all Verzahnungssollwerte in a step to correct the same time exactly.
 

In addition, the analysis software for many functions for graphical comparison of measurements or to determine the axis position. It thus represents an important tool for the development, design and operation of forming processes of gearing production dar.


With these measures described precorrection the form essential factors to be considered. The influences from the Durchmesserfeineinstellung in the work area can thus not be compensated, such adjustments must be covered by the tolerance range for the form.

 
The concept allows a diameter setting without mechanical intervention, thus offering the possibility of integration in a closed loop. Figure 8


As seen in the picture, can the heating and cooling of the core of the reinforcement are controlled separately, which, unlike other non-market principles, the change in diameter is used at the expense of bias. Even the temperature and / or the geometry of the workpiece can be captured to be used as a guide or control variable for the tool. The control parameters resulting from the levels found in the simulation sensitivity matrix.
Figure 8: Closed loop
 
The development is currently in the testing of prototypes. It is planned to offer a complete assembly that is to be retrofitted to virtually any press.
The tool concept and the procedure was applied for a patent.