Nagel Maschinen- und Werkzeugfabrik GmbH in Nürtingen offers its NaShaft series superfinishing centers. The automotive supplier ZF in Thyrnau uses this system for e-transmission shafts.

"We are noticing that demand for our superfinish technology is by no means slowing down with the trend toward e-Mobility; on the contrary," said Christian Feuchter, technical sales at Nagel. "The typical workpieces for combustion engines are becoming fewer, but those for e-drives are increasing, especially transmission and rotor shafts. At the same time, machining requirements are also increasing. Other components are also on the rise regardless of the type of drive, including steering racks and nuts, for example." 

Automotive supplier ZF Friedrichshafen AG confirms the e-Mobility trend: Finishing is an increasingly required manufacturing process in this area. The aim is to increase the load-bearing capacity of the workpieces and to reduce short wavelengths.

E-drives, unlike combustion engines, generate operating noise at a very low level. On the other hand, the surrounding bearing points become audible with a whirring noise. This is caused by the waviness of the bearing journals, which is inevitably left behind by the pre-processes of turning and grinding. Where components make themselves heard in this way, friction and losses are also higher. Another undesirable side-effect. As a consequence, drive manufacturers are raising their quality requirements for dimensional accuracy and surface finish. After all, the vehicles are supposed to roll along the streets as quietly as a whisper, without passers-by wondering about strange sounds. Against this background, superfinishing is becoming a key technology in the production chains of e-drive components. 

ZF in Thyrnau purchased the NaShaft Eco 612 machine from Nagel. 

"The NaShaft series is a highly flexible machine platform with a modular design and is therefore a cost-effective solution. We manufacture this series as well as all other machines according to our high quality standards in Nürtingen," said Feuchter.

ZF uses the NaShaft Eco 612 for various transmission shafts with overall lengths from 150 to 380 with bearing journals in the range D = 30 to 60 mm. Tension is applied between centers. After grinding, the values for cylinder shape and surface finish are around 8 μm and Rz 2.5 μm. The targets for superfinishing are <5 μm and Rz <0.7 μm. Nagel developed a hybrid process for this task. "There is a stone process and a tape process. The stone process ensures an improvement of the waviness on the bearing journals, it therefore optimizes the cylinder shape or the shape accuracy. The subsequent tape process improves the surface quality," Feuchter added.

The NaShaft Eco finishing center is equipped with four finishing modules. The shafts to be machined have two bearing locations. Consequently, both bearing journals can be machined simultaneously, first in the stone process, then in the tape process. The pure machining time for one shaft is 15 s. 

"Our Superfinish center meets all the user's quality and productivity specifications. The application example is proof that flexibility and a modular design are important criteria. In order to meet high quality requirements, it is not always necessary to have high specifications," Feuchter said.