However, the company has experience with electric mobility: an in-house ePowertrain business unit is dedicated to electric powertrains, battery packs and battery management systems. However, the production of the sports car's transmission presented challenges that could not be met by the existing machine pool. The management contacted several suppliers and decided in favour of the proven partner KAPP NILES.

Microscopically small but crucial: surface structures

FPT has been working with KAPP NILES for a long time. The Italian subsidiary Bitek provides on-site support. Eight KAPP NILES KX 1 machines at the Turin site are used for dressing-free generating grinding. A new KX 300 P generating grinding machine was purchased specifically for the sports car transmission.

On this machine, the workpieces are machined with dressable corundum grinding worms, although this machine also allows the use of non-dressable CBN grinding worms or profile grinding wheels. Loading can be either manual or automated. In Turin, they have opted for the automated version with a ring loader to reduce loading times to a minimum. But why switch to ceramic generating grinding at all? ‘The surface has a different structure. In my opinion, the transmission will be significantly quieter when combined with the KAPP NILES structured shafts on the KX 300 P,’ explains Di Geronimo. For electric commercial vehicles, such as the Iveco Daily Trucks, the requirements for noise emission are not as strict. Furthermore, the effect is not as noticeable, since only speeds of up to about 6,000 rpm occur at the transmission input. At the sports car transmission, they are around three times as high at up to 18,000 rpm.

Even better than generating grinding: topological generating grinding

Compared to profile grinding, generating grinding offers a significantly higher machining speed combined with very good quality. As a rule, gears are ground with a crown. This results in slight deviations from the theoretically required tooth flank geometry due to the process. In technical jargon, this is called entanglement. For technological reasons, the gearing only has a perfect profile in the middle of the gearing width when using conventional generating grinding. Frank Holzheid, Manager Sales & Service at Bitek, explains the background: ‘In the case of conventional combustion engine transmissions, only the profile in the centre of the gearing was usually relevant as a quality criterion. The natural distortion that occurs at the ends of the gearing due to the process can generate a slightly higher noise level in the transmission. However, this is negligible compared to the much louder engine noise. The situation is different for electric vehicles. At low vehicle speeds, the gear noise is much more noticeable. That's why the wheel and the mating wheel must also be precisely matched in terms of their interlocking. We achieve this with topological generating grinding.’ Di Geronimo adds: ’Normally, we only check the involute in the centre of the facewidth, but for the sports car we now have three levels: the profile in the centre and two more at the beginning and at the end of the facewidth, as well as three levels for the flank line of the gearing.’

Partnership-based development

Well-engineered and reliable machines are available from a range of providers. However, this was not the only criterion for Di Geronimo. He emphasises: ‘Services, the availability of spare parts and the manufacturer's knowledge of our processes are just as important.’ Chiara Crosta, Administration Manager Sales & Service at Bitek, adds: ‘It was important for FPT to get a turnkey solution.’ Di Geronimo also analysed the manufacturing process itself in detail. This includes grinding and dressing times as well as the fastest possible set-up process between two different workpiece types. All this is incorporated into a precise calculation of the costs per workpiece.

Another important criterion: the development. KAPP NILES accompanied FPT from the prototype to series production. Di Geronimo: ‘We completed long test runs of the gearbox with the development department. This resulted in change requests for the process and the tools, which always had to be implemented under time pressure. I always had a contact person at KAPP NILES for this - even at weekends when things had to be done quickly. This meant that we had a new batch of prototypes in the shortest possible time, which we could use for testing. KAPP NILES helped us a great deal during the prototype phase of our new development for an all-electric transmission for a super sports car and was always an ideal partner for us.’

Holzheid adds: ‘Mr Di Geronimo also visited our main plant in Coburg several times. We reserved a machine for the tests there and assigned a specialist from the technology department for FPT.’

The example of helical gearing shows how even the smallest detail was examined for improvements. Normally, the thrust and drag flank have the same helix angle, in this case 30°. During the test run, however, the combination appeared too noisy. Changing the thrust flank angle by just 0.08° produced a significant improvement. Holzheid: ‘The requirement came in the prototype phase. We changed the technology data and it had the desired effect on the test stand. Different helix angles on both flanks are not unusual for e-transmissions and can be easily implemented on our machines from a technological point of view.’

As important as production: measurement technology

In addition to the generating grinding machines, FPT also uses a KAPP NILES measuring machine, the KNM 5X. The machines in this series have been specially developed for small and medium-sized workpieces. Wear- and friction-free air bearing technology in linear and rotary axes, large bearing distances and generously dimensioned guide cross-sections ensure accuracy, the best possible accessibility and a long service life. Linear motors are used in all feed axes. Rotary tables with air or hydrostatic bearings are equipped with direct drives. Controlled air spring elements under the base plates shield against shocks and vibrations and allow the measuring machines to be used close to the production area.

The final argument in favour of the purchase was the closed-loop process: the measurement and compensation data are automatically transmitted directly to the gear grinding machine via the GDE interface. This eliminates the need for time-consuming, manual and potentially error-prone transmission using a measurement protocol from the measuring room. In series production, this allows particularly fast conclusions to be drawn about the stability of the process. In particular, trends, i.e. gradually increasing deviations, can be detected at an early stage and automatically corrected accordingly. This is a major advantage for gears for electric drives with their extremely low tolerances. Crosta adds: ‘Mr Di Geronimo immediately realised that he could use this for other products as well. That convinced him.’

FPT has indeed invested in the entire production process: the largest gears in the sports car transmission have an outside diameter of 250 mm. However, the portfolio also includes the drives for an e-truck, a joint venture between FPT and a manufacturer of electric commercial vehicles. Here, the outside diameter is 600 mm. The measuring machine is designed for diameters of up to 650 mm.

Di Geronimo brings up another point on the subject of measurement: ‘In addition to the closed-loop technology, measurements can also be taken directly in the generating grinding machine; this saves even more time, especially when retooling the machine for a new component,’ he says, praising the equipment. With a measuring probe, it is possible to check whether the profile and line are correct immediately after setting up and grinding the first part. This saves the trip to the measuring room and thus long waiting times. Holzheid explains: ‘We cannot replace a measuring machine with this, because there is always oil or small particles in the working area that cause deviations of a few micrometres. However, the accuracy is perfectly sufficient for setting up and saves a lot of time.’

Zero tolerance for errors

The machine, grinding technology and measuring technology create the ideal conditions for error-free production. However, this does not rule out human error. That is why KAPP NILES has provided very effective measures to prevent operating errors. In addition to the aforementioned Closed Loop, the RFID labelling of tools and accessories is another such measure. Di Geronimo is happy to use this, as he explains: ‘A list of accessories for each workpiece is stored in the machine control. If I want to set up the machine for this product, I can identify each part with a reader. This reduces the margin for error to zero.’ Accessories include, for example, rolling screws, dressing tools, clamping devices, tailstock centres, coolant nozzles or gripper jaws for the ring loader. If the operator makes a mistake during setup, the machine detects that a part does not match the workpiece and does not start.

Holzheid adds: ‘We can do even more with the system. The built-in RFID chip, for example on the dressing roll, also always checks how many dressing cycles this tool has already performed. The machine issues a warning when the tool is approaching the end of its service life and a replacement is needed.’

The safety concept is rounded off by the Poka Yoke principle. It is based on the realisation that errors can never be completely ruled out, but that they can usually be avoided by simple technical precautions. For example, a contour mask is installed at the infeed of the ring loader to check the outer contour of the workpiece.