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Optimally designed for the Industry 4.0 production environment, there is virtuallyno other machine design that realizes high performance generating grinding inlarge-scale production better than the Höfler Speed Viper cylindrical gear generating grinding machine. Not only has it earned the trust of the industry, it has also
won an iF Design Award. Klingelnberg has now taken this successful platform astep further, with new features focusing on the noise behavior of transmissions
and extending the service life of grinding wheels.

Cylindrical Gear TechnologyMaximum productivity,
reliable processes andease-of-operation are
the keys to success fora production system.
This is especially true for gear manufacturing, where not only the measurable
geometry plays an important role, but
so do softer factors such as noise perception. Thus in addition to hardening
distortions, many gear experts struggle
on a daily basis with higher harmonics
and ghost orders that acoustic engineers
find in transmissions. And when they
do manage to deliver good technicalresults, they find themselves confronted
with the next obstacle: cost pressure.

A Cyber-Physical
Production System
With the Speed Viper machine family,
Klingelnberg has launched an innovative concept that is embedded in a cyber-physical production system. Complete digitization of the system results
in a digital image for every step in thedevelopment and production process.
This eliminates the need for expensive
rework – and creates complete transparency by the way, beginning with thegear design stage. To develop high-per-formance gears, tooth flank modifications are used to ensure a good noise
behavior and high load carrying capacity
for all operating conditions in spite oftemperature and load-induced deformations of the components. These toothflank modifications are made based onfunctional aspects. Exactly how to implement this on an existing machine fleet
with the tools available is one of themany challenges in production.
The duality of a cyber-physical production system helps in this respect. The
Gear Designer software checks whether
the desired, geometrically ideal toothflank form can be manufactured economically. Based on a manufacturing
simulation and the degrees of freedom
in the production process, it calculates a
tooth flank modification that can actually be manufactured. Of course, there will
be discrepancies between this calculated
modification and the originally desired
modification. The advantage of the Gear
Designer software is that it shows thedesign engineer everything in advancethat is bound to happen later on during
production. Instead of long, drawn-out
and expensive prototype phases, thegears can be analyzed and optimized
ahead of time in the design phase. AtHIGHLIGHTS IN BRIEF
Three highlights of the Speed
Viper family at a glance:
The Speed Viper platform isembedded in a cyber-physicalproduction system that enables
a Closed Loop for both production as well as development.
With QSS – Quiet Surface Shifting – the roughness values of
the tooth flanks can be modulated to achieve a positive noisebehavior.
Using adaptive shifting,Klingelnberg has achieved a longer service life for the grinding
wheel and increased the numberof parts that can be ground.

FILM ABOUTGEAR DESIGNER:Fig. 1: Klingelnberg’s cyber-physical production system

Cylindrical Gear TechnologyCompact
QSS – Quiet
Surface Shifting
Evaluating the noise behaviorof gears by means of the order
spectrum alone simply is notenough. The psychoacoustic
parameters of sharpness andtonality are influenced to a great
extent by the roughness of the
tooth flanks – and this can be
modulated in a targeted mannerwith Klingelnberg’s QSS method.

Fig. 2: Transmission error and order spectrum in
identical teeth

the end of the development phase is thedigital twin of a toothed gear, which will
be able to be manufactured as an actual
component in this exact form. Welcome
to the world of cyber-physical production systems!
Another advantage of this principle isthat the pure production deviation isdetermined based on the measured
data from conventional cylindrical gearmeasurement. This alone allows theGear Corrector program to minimize
production deviations automatically by
calculating corrected setting values forthe machine movement or – if required– the dressing process. The result is one
Closed Loop for production, which automatically minimizes production deviations, and one Closed Loop for development, which generates tooth flankmodifications that are designed for easeof manufacture and to satisfy the requirements.
Now, everybody knows that even with
precise toothed gear geometry, noise
perception follows a different set ofrules. The more precisely a toothed gearhas been manufactured, the more prominently individual orders in the spectrum
appear. Is the answer therefore to produce toothed gears of poorer quality?
This certainly would change the noise
perception – but it is doubtful whether
this is the right approach. Nevertheless,any consideration of precision must also
include a consideration of the technically and economically feasible production
tolerances.

Roughness Made-toOrder: QSS – Quiet
Surface Shifting
Fig. 3: Order spectrum with ghost orders

Until now, the tooth geometry has been
(and continues to be) the focus of thedesign considerations: Simulation pro-grams predict the exact way in which
the rotary motion of one gear is transmitted to the other. Although practicalparameters such as loudness, sharpness,tonality, roughness, fluctuation strength,etc. are now used in psychoacoustics todefine the noise perception of a transmission, many experts today still relyon the order spectrum when evaluating
noise behavior. To do so, the deviationfrom the rotational error-free transmission is converted to an order spectrum
by means of a Fourier transform. Here,the first order corresponds to one rotation of the toothed gear to be evaluated.
Accordingly, the spectrum will consist
only of orders of the number of teeth
and its multiples – provided all teeth
have an identical geometry and there areno run out deviations.
Figure 2 shows an example of this: A
toothed gear has 15 identical teeth andexhibits no run out. Consequently, theorder spectrum shows the 15th orderand its multiples. The amplitude of theseorders depends on the profile of thetransmission error.
One aspect that has been neglected in
the analyses up to now is the surface
quality of the tooth flanks. How do different roughness characteristics affectthe order spectrum? Without entering into a philosophical debate about
whether roughness should be interpreted as a geometric modification of the
tooth flank or simply as an aspect of surface quality, roughness is characterized
by the presence of a slightly modified
behavior of the tooth contact and thus
a different transmission error.
This effect is demonstrated in figure
3: The amplitudes of the original higher-harmonic orders have become slightly
smaller, and the order spectrum exhibits so-called ghost orders. By definition,
ghost orders are orders that cannot beCylindrical Gear Technology

divided by the number of teeth. The energy that was previously in the higher
harmonics only is now distributed acrossseveral orders. This is why the noise perception changes, since the way in which
the higher harmonics are perceived isinfluenced by the ghost orders. This effect manifests itself in improved psychoacoustic characteristics of sharpness andtonality.
So how can a stochastic change inroughness characteristics be achieved on
the tooth flanks? The answer lies in thedressing process. The roughness of the
tooth flanks is determined by the properties of the grinding worm, which canbe influenced by the dressing process.
By changing the speed ratio between
the dressing roll and the grinding worm,
the properties along the axial expansionof the grinding worm can be modulated.
In the Speed Viper machines, the variation in speed ratios between the dressing roll and the grinding worm is notrealized simply by modulating the dressing roll speed, but rather by modulating
the shift speed. Of course, to obtain thecorrect form of the grinding worm, its
angle of rotation must be controlled
as a dependent variable based on theshift position. The desired modulationof the grinding worm properties canthus be achieved in this way. The fixed
kinematic link up between the shift position and the angle of rotation positionof the grinding worm is realized in themachine’s control unit. The accuracy ofthis kinematic link up is always limited.
This may seem disadvantageous at firstglance – but on closer examination, it
reveals itself to be a further advantageof this method. This is due to the factthat the smallest inaccuracies in the kinematic link up produce tiny geometrical errors, which are distributed along
the grinding worm. As a result, each
tooth looks slightly different and thetooth meshes are therefore no longer
absolutely identical. Accordingly, thetransmission error is subject to extremely
small variations. This has a positive effecton the noise perception.
The result is illustrated in figure 4: Side
bands to the higher-harmonic orders areproduced by the small geometric inaccuracies. Orders below the first toothmesh order also occur, as they otherwise
stem from run out. The psychoacoustic
parameters of sharpness and tonality
decrease. Klingelnberg has named thismethod QSS – Quiet Surface Shifting.
Although the purely physical soundfield parameters undergo only negligible changes, the human perception of
the sound is significantly more pleasantnonetheless. The inaccuracies generated
with QSS are not the result of chance,
however. They are instead measures thatcan be used in a targeted manner to improve noise perception.

Fig. 4: Order spectrum with modulated roughness
and minimally different flank topographies

Adaptive Shifting
Makes the Tool Last
Longer
The third specialty of Klingelnberg’s
generating grinding presented here is
aimed at reducing tool costs. The shift
strategy is typically designed to ensure
the process reliability of grinding withthe smallest grinding wheel diameter.
This fixed shift strategy is also used fora new, unused grinding worm. Figures5 a and 5 b illustrate the conditions on
a single-thread grinding worm. Shift-Fig. 5 b: Active grinding grains and shift jump

Fig. 5 a: Profile development zone on
the grinding worm

Cylindrical Gear Technology

Changing the shift strategy toadaptive shifting reduces tool
costs by over 18 percent.

sw = sv ·Lead angle:

tan(h) = 2 ·Helix distance:
Meshing density

Compact
Adaptive Shifting
The idea of adaptive shiftingchanges the shift ratio and theshift jump in such a way that thesame technological parameters
are always given, regardless ofthe grinding wheel diameter.
Klingelnberg has introduced
the meshing density as the keyparameter. (See formula to theright.)

FILMS ABOUT ...

... Speed Viperwith dual-spindle
concept... Speed Vipering is divided into two categories: shift
ratio and shift jump. Whereas with theshift jump, the grinding worm is shifted
axially by a specific amount before thenext component, with the shift ratio,
the grinding worm is shifted continuallywith each revolution of the workpiece.
The axial length lp of the grindingworm’s profile-defining area is independent of the diameter, but its length ofdevelopment is not. The lines shownin red (see figure 5 b) indicate whichabrasive particles are active during machining of a toothed gear. A larger shift
ratio is reflected in the development
diagram by a greater length and flatter inclination of the lines. With a shift
jump, the lines of consecutively ground
toothed gears are shifted in parallel toeach other.
The idea of adaptive shifting changes
the shift ratio and the shift jump in sucha way that the same technological parameters are always given. Klingelnberg
has introduced the meshing density asthe key parameter. The shift ratio is agood example of the adaptive shifting
principle: Shift ratio sv is the shift distance per workpiece revolution. Shiftratio sv is initially converted to a shiftdistance sw per tool revolution. Basedon this, the helix distance per tool revolution can be determined. The meshingdensity is then the inverse value of thehelix distance per tool revolution.

gz

Shift distance:

sv
gzm
D

π ·m
D

sw
sin(h)
d=sin(h)sw

Shift ratio
Number of starts on grinding worm
Number of teeth on workpiece
ModuleOutside diameter of grinding worm

Meshing density d therefore indicates
how high the load of the abrasive particles is on a millimeter flank length of
the grinding worm. A constant meshingdensity d is assumed for adaptive shifting. Meshing density d is calculated forthe proven shift ratio sv at the smallest
grinding worm diameter Dmin. Using
specified formulas, shift ratio sv(D) isthen calculated for the given meshingdensity d.
What exactly does this achieve? Theextent to which the grinding worm’s
service life actually improves is illustrated with an example (see table 1): If thegrinding worm has always been dressed
after 80 parts with a shift ratio sv = 0.3,
a shift ratio sv = 0.205 can now be usedwith a constant meshing density for thegrinding worm with maximum diameter.
This new shift ratio increases the numberof parts before a dressing process is required from 80 to 117 for the respective
shift ratios. With an average of 98 for theentire service life of the grinding worm,
the number of parts that can be groundwith one grinding wheel improves.

Cylindrical Gear Technology

Three Advantagesout of Many
The special features of the Speed Viperconcept presented here offer the greatest possible support in day-to-day production with respect to the challenges
mentioned at the outset – maximum
productivity, reliable processes andease-of-operation. All features of theSpeed Viper family are designed to realize high-volume generating grinding
in series production in an Industry 4.0
environment, with a focus on cost-effectiveness.

Gearing Example
Number of teeth

z29

Face width [mm]b40Module [mm]m2.5

Number of starts on grinding worm

g5

Smallest grinding worm diameter [mm]

Dmin

210

Largest grinding worm diameter [mm]

Dmax

308

Shift ratio [mm/workpiece revolution]sv(Dmin)

0.3

Number of parts before dressing

80

Meshing densityd(Dmin)

1.441

Shift ratio [mm/workpiece revolution]sv(Dmax)

0.205

Table 1: Sample calculation of the service life of a grinding worm

Constant Shifting

Adaptive Shifting

Grinding wheel diameter 210 mm

sv = 0.300 mm

sv = 0.300 mm

Grinding wheel diameter 308 mm

sv = 0.300 mm

sv = 0.205 mm

Radial dressing amount0.25 mm

Number of parts before dressing

80

117 … 80Number of parts per grinding wheel

15,68019,208Tool service life

100 %122.5 %

Table 2: Constant versus adaptive shifting

Dr.-Ing. Hartmuth Müller
Head of Technology & Innovation,
KLINGELNBERG GmbH

Copyright KLINGELNBERG GmbHIf a dressing amount of 0.25 mm isused, the grinding worm in this example can be used 196 times in total. Thus
with adaptive shifting, the tool costdecreases by over 18 percent (see table2), with absolutely no technological risk
involved. In addition, the processing
time is reduced on average, since thedressing frequency is significantly lower
from the start.