Finishing - March-April 2022

NEW
42 SUPERFINISHING
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 regard-less of
the type of drive, including steering racks and
nuts, for example." Automotive supplier ZF
Friedrichshafen AG at its standard location in
Thyrnau near Passau, where transmission
shafts for e-vehicles, among other things, are
produced, confirms the trend: Finishing is an
increasingly required manufacturing process in
the area of e-mobility, according to the statement.
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. Because only this type of
superfinishing is capable of eliminating the
ripples.
When it became apparent at ZF in Thyrnau
that the need for superfinishing capacity was
increasing, the company decided to purchase
a new superfinishing centre. The choice fell on
a NaShaft Eco 612 machine from Nagel. "This
machine proved to be the best system for our
application," explains the process planner
responsible on site. "It is loaded by a gantry
loader through the roof hatch and will be fully
integrated into a belt linking system at a later
stage," he says, outlining the automation
concept. "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. These are
therefore products 'Made in Germany' - and
that goes down well with customers,"
emphasizes Christian 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
centres. After grinding, the values for cylinder
shape and surface finish are around 8 µm and
Rz 2.5 µm. The targets for superfinishing are