Presence in Global Markets - arnesenmarketingcomps.com€¦ · sion-free return stroke. All in all, this results in an interrupted cutting movement of the shaper cutter. Because of

The Technical Magazineof the Gearing Partners Klingelnberg and Liebherr

No. 20/2011

Presence in Global MarketsProducts – Benefits – Service

2sigma RepoRt 20/2011

sigma RePoRT Nr. 20

Publisher

Sigma Pool

Klingelnberg GmbH Peterstrasse 45 · 42499 Hueckeswagen Germany

Liebherr-Verzahntechnik GmbH Kaufbeurer Strasse 141 · 87437 Kempten Germany

Klingelnberg AG Binzmuehlestrasse 171 · 8050 Zurich Switzerland

editorial Staff

Heinz Hoffmann Phone +49 2192 81-370 [email protected]

editorial Contributions

Dr.-Ing. Klaus Finkenwirth, Dr.-Ing. Hansjörg Geiser, Dr.-Ing. Andreas Mehr, Dipl.-Ing. Georg Mies, James Mitchell, Dr.-Ing. Hartmuth Müller, Dr.-Ing. Alois Mundt, Dr. Jamie Pears, Dipl.-Ing. (FH) Florian Schuon, Dipl.-Ing. Frank Seibicke, Dr.-Ing. Oliver Winkel

editing and Design

C&G: Strategische Kommunikation GmbH, Olper Strasse 10–12 · 51491 Overath Germany www.c-g-gmbh.de

Text: Tobias Hartmann Graphics: Viola Dreyling

Photos

C&G:, Klingelnberg, Liebherr, Winergy, ZF

IMPRINT

0403

2620

06

30

14

36

Partnership for Success

Presence in Global Markets

Complete Machining in a New Dimension

Efficient Software

Good Things Need Some Time

Measurement Technology

Customer Portrait Cutting Beveloid Gears

The New Hardness for Short Grinding Times


Presence in Global MarketsWorldwide Growth and Further Developments in Technology

Dear Readers,

The market is characterized by new challenges every day. This

is true not only for the further development of our technol-

ogies but also for our worldwide customer support. Liebherr

and Klingelnberg have been facing this challenge together for

almost two decades as partners in a joint association called

the Sigma Pool.

Globalization not only means the delivery of goods across

the world, globalization also means that global companies

produce and provide services on-site for local demand – prod-

ucts and services follow the markets. We have been responding

to this necessity for a long time through our own distribution

and sales offices in many countries.

The Sigma Pool has opened a site of its own in Shanghai for

service and spare parts in order to offer our customers rapid

and qualified support in China as well, where a number of

machine tools and measuring machines from Klingelnberg

and/or Liebherr are already in operation. We therefore follow

customer requirements with a view to geographic proxim-

ity and to technological progress. In this way, we successively

enhance the global availability of our services and applica-

tion technology.

In addition to services available all over the world, we focus on

technological innovation in this report: In the area of beveloid

cutting, Liebherr has achieved a technological breakthrough in

the process reliability of this procedure in production through

intensive development work and practical application. Much

the same is true for skiving: Even though the principle has

already been known for more than 100 years, Klingelnberg is

the first to be able to implement it in a cost-effective fashion

with respect to machinery, tools and production processes.

Dr. Alois Mundt, General Manager of Liebherr-Verzahntechnik GmbH

As you can see, the machines themselves are only one of

many factors which account for the achievements of the

Sigma Pool. Our solution package is made up of a combina-

tion of development work, consultation, machinery, software,

training, service and worldwide cooperation.

In order to understand the new challenges in terms of this

holistic approach, our approach is to think outside of exist-

ing models of products and markets. As the Sigma Pool of

today, we remain your partner for solving the problems of the

future. This is what we work on every day - around the clock,

around the globe.

I hope you have an interesting read.

Yours Alois Mundt


Rubrik

Service in China: Partnership for Success

In recent years, Sigma pool partners Klingelnberg and Liebherr have sold machine tools and measuring machines very successfully in China. Due to the wide variety of machines that have been commissioned on the Chinese market, the companies decided to establish their own service location in China.


Service Joint Venture

Service in China: Partnership for Success

In recent years, Klingelnberg has installed a great number of

measuring devices and cutting tools in China. Liebherr has

also sold numerous hobbing, shaping and grinding machines

to Chinese customers. Previously, Klingelnberg and Liebherr

have provided all of their services from Europe. Now the

Sigma Pool has established a joint venture in Shanghai – a

new service location that significantly reduces reaction times.

In order to cope with the growing significance of the Chinese

market and to do justice to the promising projects that will

lead to even more machines delivered to China, quick reac-

tion times for service and good, local spare parts supply are

necessary. In addition to Klingelnberg and Liebherr, DKSH is

the third partner in the joint venture. This company had

already represented the Sigma Pool in China. DKSH has a

comprehensive distribution network, which has contributed

significantly to the opening of the Chinese market for ma-

chines produced by Klingelnberg and Liebherr. In the future,

Information

DKSH is the leading Market Expansion Services provider with

a focus on Asia. The company helps other partner companies

to expand their business in existing or new markets. The DKSH

spectrum of services includes the entire value chain for all

types of products and services: sourcing, research

and analysis, marketing and sales as well

as distribution and after-sales service.

DKSH offers companies professional

expertise, well established local

logistics and solutions customized to

individual situations. A comprehensive,

unique distribution network completes the

spectrum. The business activities are orga-

nized into four highly specialized business

units, which reflect the DKSH fields of expertise in

specific industries: consumer goods, health care and

pharmaceutical products, specialized raw materials

and technology products.

Headquarters in Zurich, Switzerland•

Subsidiaries in 35 countries•

Locations: 590 in the Asia Pacific region •

and 20 in Europe and the Americas

Source/further information: www.dksh.de

China will remain one of the largest growth markets for the

Sigma Pool.

Under its own name, DKSH is currently providing services for

Liebherr and Klingelnberg. With the professional technical

support provided in the context of the new joint venture,

the manufacturing companies Klingelnberg and Liebherr are

moving directly into the customers’ focus. At the same time,

this expresses the tremendous importance of this market for

both companies.

The newly established company will provide the following services:

Installation and approval of new machines • and measuring devices

Inspection and maintenance work•

Calibration of measuring devices, • analysis and remedy of faults

Machine and measuring device repair•

Technical application consultation•

Each of the three partners has a one-third interest in the

service joint venture located in Shanghai. A local spare parts

storage location for all important components ensures the

customers access to quick supply.

In 2010, Klingelnberg and Liebherr already started training

eight Chinese employees with regard to servicing Sigma Pool

machines. Within three years, the joint venture will provide all

major services on site in China - independent of the European

locations. n

Dr.-Ing. Hartmuth Müller

Chief Technical Officer (CTO)Klingelnberg GmbH

[email protected]

Dr.-Ing. Klaus Finkenwirth

Managing DirectorLiebherr-Verzahntechnik GmbH

[email protected]

Good Things Need Some Time


It began more than 100 years ago: the story of skiving. on March 1st, 1910, Wilhelm von pittler registered a patent which was to revolutionize the manufacture of internal gears.


Skiving

the hob. The advantage of this procedure lays in its enormous

productivity. Even though the manufacture of such tools was

not simple, the short processing times and the high quality

of the gears manufactured in this fashion were convincing

enough to ensure that hobbing became the established stan-

dard toothing procedure for cylindrical gears.

Unfortunately, hobbing can only be applied to external cylin-

drical gears. In order to produce rings with internal gear-

ing, even today one is still forced to rely on broaching, form

cutting or shaping. It is precisely at this point that skiving

opens up new opportunities. An internal gear with cutting on

the abutting face is used as the tool. In contrast with shap-

ing, however, the cutting movement is not generated by an

oscillating stroke movement. It is far more the case that the

intersecting axis alignment of the tool and workpiece creates

an axial relative speed which makes the cutting movement

possible. During the rotation of the tool, each cutting edge

cuts through different tooth depths on the workpiece – a

movement which is required for the cutting process. The

intersection of the axes accounts for the fact that the helix

angle of the tool and the helix angle of the internal gear

to be manufactured differ by the amount of the axis inter-

section angle (see Fig. 1 sketch). Von Pittler thus developed

a continuously revolving toothing process which can drasti-

cally increase productivity for internal gearing. As a basic rule,

skiving makes it possible to generate any kind of periodic

structures on axially symmetrical lateral areas. ➔

Fig. 1.: Patent application of Wilhelm von Pittler and sketch, 1910

His patent for skiving with the title “Procedure for the cut-

ting of internal gears by means of a internal gear-like cutting

tool on which the faces of the teeth are provided with cutting

edges” was initially reminiscent of the method for shaping

internal gears that was already known at the time. The truly

revolutionary aspect of this idea required a second look.

Differentiation from shaping and hobbing

With shaping, the cutting movement is generated by means

of the stroke of the shaper cutter in an axial direction, which

rotates the workpiece and the tool somewhat further in accor-

dance with the number of their teeth during the oscillating

stroke movements. The tool is pulled back from the workpiece

in a radial direction to an extent sufficient to ensure a colli-

sion-free return stroke. All in all, this results in an interrupted

cutting movement of the shaper cutter. Because of the return

stroke, during which no cutting takes place, this shaping of

cylindrical gears always involves a time loss.

Approximately 50 years prior to the invention of skiving,

Christian Schiele obtained a patent for a screw-shaped hob

for the manufacture of cylindrical gears, the predecessor of


Skiving

Fig. 2 shows the degrees of freedom of the

kinematics of skiving. In addition to this gra-

dient for the axis intersection angle, there is

also a tilting angle, the gradient of which pro-

ceeds perpendicular to the axis of rotation of

the tool and perpendicular to the gradient for

the axis intersection angle. With this tilting,

a relief angle is achieved between the tooth

flanks of the tool and the tooth flanks of the

workpiece, which can also be referred to as

the kinematic relief angle. In addition, two

linear offsets are required. On the one hand,

the distance between the workpiece axis and

the tool axis must be adjusted, and on the

other hand, the tool must be traversed along

the workpiece axis. This traversing of the tool

along the workpiece axis requires a rotation

which overlaps the tool rotation or the work-

piece rotation which is dependent on the axis

intersection angle. It is usually referred to as

differential speed.

Classic tools for skiving

In accordance with the idea contained in

Pittler’s patent, shaping cutters have been

used for skiving in the past. This becomes

particularly evident when the tool is a

straight-toothed cylindrical cutting wheel.

The axis intersection angle must then cor-

respond precisely to the helix angle of the

internal gear to be manufactured. Such

tools can therefore only be utilized if the

helix angle of the internal gear to be manu-

factured is sufficiently large. The cutting

profile must be adjusted in accordance with

the helix angle. Because of the cylindrical

contour of the cutting wheel, it is manda-

tory to set a suitable tilting angle in order

for a usable relief angle to result from the

process. This tilting angle requires a renewed

adjustment in the tooth profile of the cutting

wheel (for an example of such tools, see

Fig. 3 above). The immediately recogniz-

able advantage of such tools is the simple

resharpening. It is sufficient to resharpen

after the stripping of the rake face and to

apply a new coating to the tool. The geome-

try does not change, which means that after

each resharpening with the original kine-

matics, the same tooth form is generated.

The longer the cutting wheel is, the more

often resharpening can be applied to it

and the lower the associated tool costs

becomes.

The decisive disadvantage to such tools

lies with the relief angle, which is always

way too small. The smaller the relief

angle, the higher the thermal load on

the cutting edge and the shorter the tool

life of the tool. The wearing characteris-

tics with cylindrical cutting wheels are

always exposed surface wear and cracks.

The problem of a relief angle which is too

small can be avoided through the utiliza-

tion of conical tools.

Furthermore, Fig. 3 shows a conical cut-

ting wheel. The relief angle is integrated

here in the tool. If the helix angle and the

axis intersection angle are different, then

one will obtain extremely different rake angles for the leading and trailing

flank of the cutters. In such cases, a step cut must be carried out on the rake

Fig. 3: Classic tools for skiving: cylindrical (above) and conical(Source: Bechle, A.: Beitrag zur prozessicheren Bearbeitung beim Hochleistungsfertigungsverfahren Wälzschälen, Dissertation WBK, University Karlsruhe, 2006)

Axis intersection angle

Common perpendicular

Sax

SD

Wz Wo

Rake face offset

Contact point

Tilt angle

Tool rotationWorkpiece rotation

Differential feed

Axial feed of tool parallel to workpiece axis

Fig. 2: Kinematics of the skiving process: The intersecting axis arrangement is achieved by a tilting around the distance of closest approach and base points of the perpendicular of the axes of tool and workpiece.


Skiving

faces. It is only that a similar rake angle can be

achieved for the leading and tailing flanks of

the cutters. This makes resharpening a difficult

process. In addition to that, a somewhat dif-

ferent profile is obtained after each time the

tool is resharpened. In order to produce the

same exact tooth space, adjustments to the

kinematics are necessary. Experience has

shown that conical tools can be resharpened

only a very few times.

Here the first dilemma becomes evident:

A cylindrical tool requires little effort for

resharpening, but always exhibits an inferior

behavior with respect to wearing. A conical

tool has a significantly better wearing behav-

ior, but it can be resharpened only a very few

times and this resharpening is a very diffi-

cult process.

Why has skiving been unsuccessful to date?

The productivity of a machining process

depends essentially on thickness and on

the number of cuts per time unit. The

great potential of skiving is evident in the

number of cuts per time unit. The required

cutting speed can be achieved by means of

suitable tool and workpiece rotation speeds

and through the suitable choice of the axis

intersection angle. For a dry cutting proce-

dure with a carbide tool, cutting speeds of

150 to 250 meters per minute are beneficial.

Simple approximate calculations make this

difference clear: With an assumed rotation

speed of 2,000 rotations per minute, which

leads to 200 meters per minute of cutting

speed, and with a tool with 25 teeth, 50,000

cuts are obtained per minute. A hob with

8 studs and two gears, which requires only

1,200 rotations per minute of tool rotations

for the same cutting speed, provides by con-

trast only 19,200 cuts per minute.

Naturally the question comes up of why, given

this potential, skiving has had a completely

unsuccessful existence to the present day. It

is certainly not for lack of scientific interest.

For more than 20 years, many investigations

have been carried out in this area, all of which are in agreement on one point:

skiving is a high-performance procedure, the success of which cannot take

hold because of the limited tool lives, excessive machinery vibrations and

critical chip removal.

The previously mentioned parameters of chip thickness and cuts per time unit

do indeed define the essence of productivity, but it is the cost-effectiveness of a

procedure which is of decisive importance for success in everyday practice. Short

processing times alone are not sufficient if the tool life is unsatisfactory.

In order to understand why the tools fail so rapidly, one must analyze the chip

formation in detail. Even though the kinematics of skiving can be described

in very simple terms, the relation between the cutting edge and workpiece

is a complicated movement for which suitable simulation tools are required

Fig. 4: Track of a cutter in relation to the workpiece from above (left) and viewed from the inner radius (below)

(Fig. 4). In this example, the workpiece has 48 teeth and the tool 17. After

every 17 teeth, this cutter machines the next tooth space of the workpiece.

Because the number of teeth is relatively prime, all of the tooth spaces of

the workpiece will actually be machined. If one numbers the tooth spaces

sequentially and counts them in counterclockwise order starting with the

tooth space at 9 o’clock, then the cutter depicted will machine the tooth

spaces in the sequence 1-18-35-4-21-38-7 etc., or to formulate this precisely

ix17mod48+1. ➔


Skiving

In the right-hand side of the image, one sees the movement

of the cutter within a tooth space. The cutter plunges into

the tooth space from the upper right. The radial movement

advances as far as the bottom of the tooth space and then

back again out of the tooth space. During the radial plung-

ing and emergence, the cutter moves axially along the face-

width of the workpiece. The curved course of the track is

significant. From it one can recognize that the tip rake angle

is continuously changing during the cutting in a tooth space

and can even take on a negative value at the end.

Starting results are obtained when simulation tools are used

for precise analysis of the dimensions relevant to the rake

and relief angles for chip formation. The rake angle is zero

degrees at best (0°) and during the process it can take on

negative values down to minus fifty degrees (-50°). It is easy

to appreciate that even the most suitable cutting material

is subjected to stresses in excess of its limits. This is intensi-

fied even more by the fact that negative rake angles always

lead to an increase in cutting forces and result in considerable

challenges to machine tools with respect to profile accuracy,

dynamics and stiffness.

It is because of this combination of tool problems, unfavor-

able chip formation and extremely high demands on the

machine tool that skiving, despite its benefits, has still not

become accepted.

Machine and tool – The success factors for skiving

Modern machine concepts, which are optimized with respect

to chip flow, stiffness, attenuation and geometric accuracy,

have made tremendous advances recently. An example is

the Oerlikon Spiral Bevel Gear Cut-

ting Machine C 29. This was originally

developed for the high-performance

dry cutting of bevel gears. In addition,

it offers ideal characteristics for skiving.

The outstanding stiffness, the highly

dynamic direct drives and the chip

flow which is optimized by the verti-

cal concept, along with precision axis

alignment, are necessary prerequisites

for the success of skiving.

In addition to the machine tool, the

tool itself is the decisive success factor.

As was shown above, chip forma-

tion is quite complicated with skiving

and always associated with disad-

vantageous conditions for the classi-

cal tools, no matter whether they be

cylindrical or conical in design. Usable

relief angles lead to conical tools

which cannot be implemented in a

cost-effective manner. Cylindrical tools

which can be resharpened in a way

which is acceptable from the point of

view of cost-effectiveness, do not offer

Fig. 5: Skiving on an Oerlikon Spiral Bevel Gear Cutting Machine C 29 – the machine axes are shown in red.


Skiving

The advantages of this tool are immediately evident:

Rake and • relief angles can be freely selected and can be optimized for chip

flow

Resharpening • is a reliable process which has been mastered worldwide for more than ten years for bevel gear

tools

Profile modifications can • be implemented immediately by grinding the bar blades

sufficient tool life. Under ideal circumstances the tool design

would only take the cutting edge into account. Any com-

promises with regard to the cutting wheel would become

obsolete.

This tool technology is already available and has been tested

worldwide for a very different application. The Oerlikon stick

blade system with the ARCON® and SPIRON® cutter heads

offer precisely these possibilities for spiral bevel gears. A rect-

angular carbide bar is ground to produce a cutting pro-file

and then coated and inserted in the core of the cutter head,

where it is built with high precision.

The solution is thus, in simple terms, to apply this stick blade

system to skiving. Instead of a cylindrical or conical completely

carbide cutting wheel, now only the cutting geometry is ground

into a carbide bar blade. These profiled bar blades are fastened

in a suitable cutter head core in order to form the cutters of a

stick blade cutting wheel (Fig. 6).

A tool system is thus created which for the first time per-

mits the optimization of the blades for skiving. Together with

the proven Oerlikon bevel gear cutting machines, a manufac-

turing system is available with which skiving can now finally

make a successful appearance on the market, 100 years after

its invention.

Closed loop production

Reliable processes require far more than reliable machines and

suitable tools. It is only the integration of all steps along the

process chain into a continuous data technology composite

which can guarantee stable and reliable results. This method

of approach is familiar to Klingelnberg. The closed loop has

been a proven standard worldwide for bevel gears for many

years. In order to ensure that the user profits from the same

process reliability with skiving that he has with bevel tooth cut-

ting, Klingelnberg has developed the closed loop for cylindri-

cal gear machining by means of skiving. ➔

Fig. 6: Stick blade cutting wheel


Skiving

The structure of closed loop production can be seen in Fig.

7. Everything begins with the design of the gearing. Here the

macrogeometry of the component is defined and the tooth

profile is modified in accordance with various optimization

criteria. In contrast to the approach with bevel gears, here

only one single internal gear, is observed. It is usual with

involute cylindrical gears to observe the topography devia-

tion between the optimized and the non-optimized tooth

flank instead of the ease-off. As soon as the complete

gearing geometry is calculated, the theoretical nominal data

of the tooth form is generated and the calculation of the tool

and of the kinematics begins.

Kinematics and the tool exhibit an influence on one another

in this iterative process. The user is shown the important

parameters for chip formation as the basis for the manufac-

turing simulation of the skiving process. He has the oppor-

tunity of optimizing the tip rake angle, the flank angle and

the relief angle at the head and flanks. As a by-product, he

obtains the appropriate kinematics for the machining equip-

ment and the form of the cutting edge. This software pack-

age supports not only stick blade cutting wheels but also just

as much the classical cylindrical or conical cutting wheels

with and without rake face offset. The gearing design is com-

pleted after these steps and the data for the component to be

produced, the data for the tool and the data for the machine

tool are all completed.

The next step in the process chain is the tool production. For

stick blade cutting wheels, it is here that the tool closed loop

comes into play, as has been known for many years for bevel

gear tools. The description of the tool contains not only the

number of teeth and the form of the cutting edge, but also

all of the geometric parameters of the tool. These include

all rake angle and relief angle information as well as all data

regarding the position of the stick blade in the cutting wheel.

Corrections

Corrections

Skiving

Finished gearing Match to the design

Gearing measurement

Stick blade cutting wheel adjustment

Exact tool

Toothed gear designTool authorization nominal data

Blade grinding

Stick blade measurement

Closed loop for skiving


Skiving

Once a stick blade has been ground, it can be dimensioned

geometrically. Even the smallest deviation of the stick blade

profile from the nominal form is recorded and processed in a

correction algorithm. The results are modifications to the set-

ting values of the grinding machine, so that the measured

deviations are minimized. There are now stick blades com-

pleted which exactly possess the specified profile. These are

positioned in the cutter head with micrometer exactitude

by the Oerlikon CS 200 cutter head adjustment device and

screwed in place. Starting here, it is ensured for the remain-

der of the process that a tool will be used which corresponds

precisely to required specifications.

The truly distinctive features of skiving a gear on an Oerlikon

cutting machine of the C series are the very short processing

times and the manufactured qualities. Once a part has been

milled, its dimensions are recorded in order to determine their

deviations from the theoretical form. Klingelnberg follows a

new path for the measurement of these parts. Instead of the

usual measurement of profile and lead trace as deviations

from an involute tooth form, measurement is carried out here

with a topographic grid. If the deviation at all grid points is

practically zero, then the manufactured component will cor-

respond to the specifications resulting from the tooth design.

Deviations will once again be fed into a correction algorithm

which calculates the correction values for the cutting machine

motions. As is the case with the machine tool, these are fed

per network to the machine control unit which then auto-

matically grinds the next part in such a way that the devia-

tions become minimal.

All closed loop users worldwide now agree that the main

advantage of closed loop production are the reliable processes.

In addition to process-capable machines and tools, it requires

control loops which keep the process stable. It is only when

one produces precisely what was designed that gearing opti-

mizations can occur.

So why skiving?

Internal gears which previously could only be manufactured

through the use of shaping can now be manufactured very

productively and with high precision when skiving is applied.

Even though the kinematics of the skiving process appears

simple at first glance, the chip formation is actually very

complex. Rake angles and relief angles which are subject to

continuous changes during the intervention lead to unfavor-

able chipping conditions with classical cutting wheels – no

matter whether they are conical or cylindrical in shape. This is

precisely the reason for the previous lack of success of skiving

during the last 100 years.

The decisive success factor for skiving is the stick blade tool-

ing system with its open design of relief angles and rake

angles. These kinds of tools have been successfully utilized

around the world for the dry cutting of spiral bevel gears for

more than a decade.

Thanks to the very short machining times and the high com-

ponent quality, it has become possible to reduce manufac-

turing costs drastically – while as a “by-product” the energy

consumption per component is falling and the stick blade

tool system is ensuring exceptionally short run-through times.

All prerequisites, both for large lots and for individual piece

manufacture, are thus fulfilled.

The system process reliability of the procedure is based on

the closed loop for the production. In terms of data, the tool

preparation and the skiving process are in a continuous data

network with the internal gear design. Thanks to the under-

lying quality control loops, it is ensured that that which is pro-

duced is also exactly what was designed.

The actual principle has not changed since the registration

of the Von Pittler patent. However, technical progress with

respect to machinery, tools and production processes in

general has ensured that it turned out well after all. n

Dipl.-Ing. Frank Seibicke

Chief Engineer Calculation SoftwareKlingelnberg GmbH

[email protected]



[email protected]


Cutting Beveloid Gears – Complex Processes Made Easy

Dry cutting, beveloid gears, ChamferCut – to begin with, the unusual combination of requirements was new territory for all involved. But today, ZF in Saarbrucken and Liebherr can already look back on five years of successful collaboration. From the initial enquiry to the complete setup of the complex machining application, the project progressed remarkably smoothly.


Cutting Beveloid Gears


implemented another technology change to Liebherr dry cut-

ting. No single machine or feature decided it. The overall con-

cept had to be right – and it was ideal.”

Cutting and deburring in a single step

“When we started looking for the right tool system to pro-

duce beveloid gears, we realized there was an important

factor to consider on which Liebherr was able to deliver. We

needed reliable, reproducible and economical deburring of

the gears”, explains Maurer. Previously the deburring process

was very time-consuming, particularly around the root.

“We knew that ChamferCut was a suitable system that could

help us progress”, Maurer says. The fact that cutting and de-

burring are performed in a single process increased overall

production efficiency. But the crucial point, says Maurer, was

finding the right machine technology and software.

In short, 2006 found ZF on the search for a dependable ma-

chine and software solution for the ChamferCut tool system.

Liebherr had not only the right technology, but also the know-

how to rise to the challenge. There followed a series of ex-

periments, joint development work and the in-depth discus-

sion of possible solutions, all of which resulted in a positive

outcome in several areas: “Today, there are three main pillars

to the partnership: ChamferCut, dry cutting on the Liebherr

Reinhold Driess


“Once our development department had completed the

necessary tests and approvals, the new Liebherr cutting tech-

nology was integrated into our production process in the space

of a few weeks. Then of course there was an internal phase

of optimization and fine-tuning”, says Department Head Gear

Production Hans-Joachim Maurer, recalling the start of the

collaboration between ZF and Liebherr. But how did the part-

nership first start, and what challenges did the two partners

encounter along the way?

Beveloid gears: the beginning

In 2005 the EU introduced a new directive on pedestrian

safety, which required a number of design modifications to

vehicles, including adaptations to the engine compartment.

To enlarge the crumple zone, the vertical gap between the

hood and engine block had to be extended. This produces

an offset, which can however be bridged with the help of a

beveloid or tapered cylindrical gear – which is associated with

particular design challenges of its own. In 2006, ZF became

the first manufacturer to use this solution for all-wheel drive

technology, in its 6HP six-stage automatic transmission.

Jürgen Roos, Department Head Advance Production, explains:

“For the beveloid concept, we basically modified two things.

Firstly, we converted the deburring process to ChamferCut

(from LMT Fette). Secondly, on this larger module scale we

Stefan BauerHans-Joachim Maurer

Jürgen Roos

We were speaking to (illustrations on page 16ff.): Stefan Bauer, CNC Programming/Tool Planning and Standardization, Car Driveline Technology DepartmentReinhold Driess, Department Head Process Planning Gear/Planet Carrier/Advance Production Automatic TransmissionsHans-Joachim Maurer, Department Head Gear Production/Automatic Transmissions Jürgen Roos, Department Head Advance Production and Machine Standards Automatic Transmissions All at ZF in SaarbruckenDr. Oliver Winkel, Head of Application Technology/Technology Development Gear Cutting, Liebherr-Verzahntechnik GmbH


LC series hobbing machines, and beveloid cutting. This com-

bination represented new terrain for all involved. What‘s

more, it meant changing our standard supplier”, says Rein-

hold Driess, Department

Head Process Planning at

ZF. The company required

not only the right equip-

ment, but a high standard

of technology know-how

and tool expertise.

Gears deburred with Cham-

ferCut exhibit a clean, de-

fined chamfer right down

to the root. This was a key

requirement, and one that

was not satisfied by the

previous ECM technology.

Unlike with ECM deburring,

there is no thermal stress and no deformation of the tooth

edges, which makes the process suitable for sensitive follow-on

processes such as honing. Stefan Bauer, from the ZF tool plan-

ning team, describes the complexity of the new tool system:

“Using ChamferCut is a complex task in itself. Applying it to

beveloid gears is even more so.”


Dr. Oliver Winkel

Optimizing the entire production process

Dry cutting: challenges and benefits

Setting up a new dry cutting system at a customer plant

was not a new challenge for Liebherr, but this project had

a unique feature in the special tooth design, which initially

presented a significant problem. The original tool design had

to be modified for dry cutting and put through its paces on

the test rig. “It was important that we could rely on the new

supplier”, says Maurer. “We chose to rely on the expertise of

Liebherr, and soon realized we had made the right decision

when the redesigned tools and solution were delivered in just

a few weeks.”

Bauer adds: “We had already used dry cutting for smaller

modules, so we knew a lot about the process. Thanks to

Liebherr, we learned even more.” ➔

Hobbing machineWet machining

Washing

Bottleneck, part jamECM deburring Washing

Electrolyte removal

Preservation

Washing for hardening

Hard end machining

Hardening

» Long throughput times and high volume of material in circulation

After integration of deburring in milling process and introduction of dry machiningLiebherrLC120

Hobbing (dry) with ChamferCut deburring

Hard end machining

Hardening

» Minimum throughput times and material in circulation


The adjustment of the workpiece clamping to allow access

to the tools also underlines the coherent concept of the sys-

tem – without impairing quality or machining efficiency. The

successful deployment of the technology is due not only to

the manufacturer‘s technology expertise and on-site support,

but its user-friendliness, which Bauer sums up as follows: “Our

staff likes working on Liebherr machines.”

“Significant improvements”

The ChamferCut technology has the apparant disadvantage

that it adds to the main processing time, but ZF compensated

for this by integrating it optimally into the overall process.

The introduction of dry cutting and deburring in a single pro-

cess has optimized the production process as a whole. Pre-

viously, parts had to be removed from the process, washed,

fed in again and then deburred, before being washed again

and preserved prior to hardening. “In this way we achieved

significant improvements in terms of logistics and through-put

times”, says Bauer (see illustration on page 17). Consequently,

ChamferCut was applied to other parts too.

With such finely optimized processes and very short lead

times in production, system availability is of the essence.

„We require 98 percent availability. Since the Liebherr LC 120

actually exceeds this, delivering 99 percent availability, we

eventually did away with our internal evaluation of

machine availability“, says Roos – testament to the

reliability of the machine and the stability of the

process.


Dr.-Ing. Oliver Winkel

Head of Application Technology Technology Development Gear CuttingLiebherr-Verzahntechnik GmbH

[email protected]

Promises kept

Driess concludes: “We always have to consider the system

as a whole, and in this respect Liebherr delivered on all its

promises from the development phase – in terms of the

technology, the economy of the machine and tool, and tech-

nical availability. That applies not only to the commissioning of

the system, but beyond.” Or in Maurer‘s words: “Both com-

panies view the collaboration as a partnership combining their

respective strengths. That includes maintaining an open dialog

on joint development projects, and delivering on promises.

In life, you often ask yourself `With the benefit of hind-

sight, would I make the same choice again?´ For this

partnership, the answer is unequivocally yes.” n

Dr. Oliver Winkel, Stefan Bauer and Hans-Joachim Maurer inspect the ChamferCut tool system in front of a Liebherr LC 120.

Cross-section of the 8HP eight-stage automatic transmission – the beveloid gears produced on the Liebherr LC 120 machines are used in the all-wheel drive design. (Source: ZF)



ZF Friedrichshafen AG(Saarbrucken plant)

The ZF Group is one of the world‘s leading suppliers of

driveline and chassis technology to the automotive indus-

try. The company develops and manufactures innovative,

high-quality products to improve the mobility of people

and goods and all associated technologies.

The Saarbrucken plant, where this project took shape,

belongs to the Car Driveline Technology division. Here are

some facts and figures about this division:

Sales: • € 2.3 billion (16 percent of group sales)

Founded: 1970•

Sites: • Saarbrucken, Brandenburg, Shanghai

Approx. 7,200 employees; • over 5,000 at Saarbrucken

5,000 transmissions manufactured per day•

Investments in R&D: € 646 million in 2010, laying the

foundations for the company‘s innovative force, driven by

the dynamism of the automotive industry; the continuous

development of the product portfolio; and the further

expansion of machine and employee capacities at all sites.

Products of the Driveline Technology division:

Manual transmissions•

Automatic transmissions•

Dual-clutch transmissions•

Hybrid systems•

Clutch systems•

Torque converters•

Dual mass flywheels•

Axle transmissions•

Bevel gear sets•

Differential gears•

ZF driveline and chassis technology helps to make driv-

ing more agile, safe and efficient. To take just one figure

as an example, each new generation of automatic trans-

missions reduces fuel consumption by up to 6 percent.

The company was the first to start volume production of

beveloid gears.

Each ChamferCut deburrs around 800,000 gears per year

(approximately 400,000 beveloid and 400,000 helical) –

that‘s around 3 to 3.5 million gears since it was first

introduced.

For more information, please visit: www.zf.com

The ZF plant at Saarbrucken produces around 5,000 transmissions every day.

Beveloid – dry-cut and chamfered

So many publications have been issued worldwide on the optimization of gear transmissions, one inevitably asks: “Is there any room left for more?”

Efficient Software for Realistic Simulation


942_sigmaREPORT_2011_20-25_GB.indd 20 01.09.2011 12:00:37 Uhr


New Software Solution

Efficient Software for Realistic Simulation

Klingelnberg has extensively investigated the subject of tooth

flank modifications for bevel gears and implemented trend-set-

ting developments. All possibilities for this kind of optimization

have been integrated not only in the motions of the gearing

machines but also in the KIMoS software in a manner suitable

for daily use. Actually, it would be possible to sit back, relax

and announce that everything has already been done to exploit

the entire potential available for gearing design.

Alternative production methods for the manufacture of bevel

gears have been presented recently which use 4-axis or 5-axis

free-form cutting for the machining of tooth flanks. The use

of this method permits the creation of unprecedented tooth

forms, because tool movements associated with the free-

form cutting of a bevel gear need not be oriented to the

kinematics of a bevel gear cutting machine. The opportuni-

ties of these occasionally outlandish tooth forms have been

presented with great pomp at conferences and in special-

ist publications – although no practical results have been

presented to date.

The more closely one studies what actually goes on in the

operation of a set of bevel gears – no matter which tooth

shape is involved – in the overall transmission system, the

more clearly it becomes evident that flank modifications can-

not be usefully applied unless the entire transmission system

has been subjected to sufficient analysis.

If one cannot describe this entire system with sufficient pre-

cision, then the inner workings of the transmission remains

unknown. All discussions about alternative tooth forms or

tooth flank modifications are for that reason obsolete: The

prerequisites required for the optimization are not in place.

Criteria for gear calculation

The key to the gear design lies in the tooth contact. In order

to ensure that a set of bevel gears can continue to work ef-

ficiently for many years, it must be ensured that the stresses

which occur at the tooth contact do not exceed the permit-

ted limit values for the material used. In addition to lubri-

cation conditions, the pressure, the tooth root tension and

the tensile and shearing stresses generated by sliding are the

most important parameters of a tooth contact.

The input variables of the operational conditions are load, ro-

tation speed, and the material and lubricant specifications.

Safety factors representing the relationship between opera-

tional conditions imposed on a gearset and the gearset limits

are output as the result. It is thus that one obtains very quick-

ly an approximate statement regarding the load-bearing ca-

pacity of a gearing under given load conditions. Fig. 1 shows

in graph form the typical resistances of various materials.

The calculation procedures based on the

standards proceed from several simplify-

ing assumptions. Thus, for example, it is

assumed – and quite reliably so – that

the load contact characteristic exhibits a

constant pressure distribution and that

normally 80 percent of the face width

is covered, along with the entire active

tooth depth.

These kinds of simplified assumptions,

however, do not take into account the

complex interactions between the load,

deformation and stress exhibited on

the curved tooth flanks found on bevel

gears. In order to take these kinds of

interactions correctly into account, the

mesh must be analyzed, along with its

actual geometry, as a surface contact

condition.

Surface contact conditions can be solved

with FE methods. Fig. 2 shows a tooth

contact analysis which is based on an FE

model. One recognizes the fine grid ➔

600

N/mm2 N/mm2

HRC

Surface hardness

500

400

Film

300

200

100

1200

1000

800

600

400

200450 500

50 55 60 65

600 700 800

ML

ME MQ

ML

ME

MQ 17CrNiMo6

15CrNi6

16MnCr5

Case-hardened alloyed steels

High core strength (≤ 40 HRC)Medium core strength (≤ 34 HRC)Low core strength (≤ 28 HRC)(DIN 17210)

Heat-treated, flame- / induction-hardened (including tooth root fillet)

FE

Fig. 1: Materials parameters

Fig. 2: Tooth contact analysis by means of FEM




in the area of the tooth flanks and the tooth base. It is a charac-

teristic of FE procedures that the finer the grid, the greater the

precision. Unfortunately, the computing time increases along

with it as well. The rapid BEM methods have been preferred

for years, because they provide results of comparable quality

while reducing computing time.

When the results from the standard calculation are compared

with the results of a stress analysis, it can be seen that, while

simplified assumptions can indeed lead to initial results, it is

not until the real conditions are completely taken into account

that the potential for optimization becomes evident.

Complete transmission analysis and gear optimization

For a complete stress analysis, it is not sufficient to mod-

el only the teeth and their immediate environment. Under

loaded conditions, it is not only the tooth flanks which

become deformed, but also the gear bodies, the shafts, the

bearings and the transmission housing. This results in altered

contact conditions for the tooth flanks: The tooth flanks are

displaced by the load deformations of the housing and the

gear bodies on one hand; and become deformed themselves

on the other. Detailed knowledge of these two effects is

necessary in order to be able to begin with the optimization

of the gearing.

KIMoS and RomaxDesigner are software packages, both of

which have been in worldwide use for many years. The utili-

zation of KIMoS has however been restricted to date to the

calculation of the actual gearing; any influences on the load-

dependent deflection of the relative position of ring gear and

pinion had to be calculated outside of KIMoS. RomaxDesigner,

on the other hand, is an analysis tool which focuses on the

housing, shafts and bearings of a gearbox. This means that the

two programs complement one another in an optimal man-

ner and finally provide the user with a software tool which

analyzes the entire gearbox and thus leads to the path to

optimization. This kind of optimization can be applied not only

to tooth flanks but also to bearings, shafts and housing.

The interface between the two program systems is the

deflection of the tooth flanks and considers both the load

spectrum and the geometry of the gearing. Fig. 3 depicts all

of the degrees of freedom of the deflection of tooth flanks.

The pinion may shift in an axial direction (H) or in the direc-

tion of the perpendicular of the axes of pinion and ring gear

(V). The ring gear may also be subject to axial shifting (J)

and the shaft angle between ring gear and pinion may also

change (Σ). All imaginable spatial deflections between ring

gear and pinion can be linked to these four offsets.

In order now to describe the interaction of these two pro-

gram systems for a complete gearbox analysis, the system

limitations of KIMoS and RomaxDesigner must be clearly

understood.

Fig. 4 shows the model upon which KIMoS is based. The

gear body is regarded as a rigid body with flexible teeth. Any

deformation of the gear body must be entered in KIMoS as

a relative deflection between the rigid bodies of ring gear

and pinion, so that the deformation of the teeth can be

calculated there.

Fig. 3: Displacement of the tooth flanks in 4 degrees of freedom

Fig. 4: Rigid gear bodies and flexible teeth in KIMoS




In RomaxDesigner, by contrast, the teeth are considered

rigid, which means that the tooth forces have a direct influ-

ence on the flexible gear body. Fig. 5 shows the interaction

which exists between KIMoS and RomaxDesigner. One begins

first with a bevel gear design in KIMoS. After the external

gearing geometry has been defined, the contact pattern and

the parameters of the load calculation are optimized in accor-

dance with the experiences of the user. At the end of the first

step, the tooth forces and the torsional rigidity of the set of

bevel gears are calculated by KIMoS in relation to the angle

of rotation and transferred together with the exact flank

geometry and the load spectrum to RomaxDesigner.

Now begins the calculation of the entire gearing environment,

which must be present in RomaxDesigner as a complete CAD

model. The tooth forces deform the gear bodies, the bear-

ings and the housing. This is calculated as an offsetting of the

tooth flanks in relation to one another for each load level in

accordance with the deflection definition shown in Fig. 3 and

made available to KIMoS.

Example: Automobile axle gearbox

The hypoid gear assembly of a sports car is presented here as

an example. The gearbox is first depicted in the CAD system;

the result is displayed in Fig. 6 as a solid model.

The macro-geometry of the hypoid gear set is known and

input into the dimensioning module of KIMoS. Then the

micro-geometry (EaseOff curve) is optimized. The objective is

to minimize transmission error, contact and bending stress-

es considering the load-dependent deflections expected at

established torque levels. Stresses must remain under limit

values given by the material used. Assembly tolerances are

also considered in the optimization. The results of the EaseOff

development are validated in the Load Tooth Contact Analysis

module for two load levels (200 Nm and 500 Nm), with cor-

responding deflections. ➔Fig. 5: Interaction between gearing and environment

KIMoS Bevel gear calculation

RomaxDesigner Powertrain analysis

• Dimensioning• Load spectrum• Contact geometry• Tooth forces• Load analysis under

displacements

• Bearings, shafts and housing deformation

• Gear body deformation

• NVH results• Load analysis under

displacements

Fig. 6

Now that the entire environmental situation is known in

KIMoS, the gearing geometry can be optimized for these con-

ditions. Precisely targeted flank modifications are performed to

guarantee acceptable contact conditions for the load-induced

deflections and therefore ensure the capacity of the gearing to

handle the required load.

The following shows an example in which one can recognize

the potential of this approach for the optimization of bevel

gearboxes.




Fig. 7 shows the de-

veloped, load-free

EaseOff; Fig. 8 the

results of the tooth

contact analysis un-

der load for the two

load levels.

Up to this point, the

development of the

gearing is based on

the model used in KIMoS, in which the environment of the

gearing is assumed to be infinitely rigid and modifications in the

relative position of the meshing flanks to one another is on the

basis of assumptions.

A new path was now selected for the application example.

The gear tooth profile was exported from KIMoS for reuti-

lization in RomaxDesigner. The data exchange takes place

by means of an XML file which, in addition to the geomet-

rical values, also contains the fine geometry, specifications

regarding stresses, rotational speeds and – if available- also

regarding deflections. Parallel to this, the CAD model of the

transmission housing was networked and imported into

RomaxDesigner. The imported data was integrated into the

complete model of the powertrain in RomaxDesigner. Shafts,

bearings, seals and other relevant components were com-

piled in RomaxDesigner and combined. The resulting model

is depicted in Fig. 9. A static analysis was carried out with

this model in order to determine the deformations of the

individual components. Evaluation is possible using graphic

representation, see Fig. 10, and in numerical values.

RomaxDesigner offers major opportunities for the detailed

analysis of the entire system or of individual components.

Critical for the development of the set of beveled gears, how-

ever, are the relative deflections between the tooth flanks

located in the mesh. RomaxDesigner describes an interface

file in which the deflections determined from the overall

analysis are transformed into the coordinate system required

for KIMoS calculations with its origin in the axis intersection

point. After these deflections have been imported into

KIMoS, a tooth contact analysis was carried out under

load and taking into account these deflections. It is clearly

evident that the previously developed EaseOff needs to be

improved.

The results of the tooth contact analysis under load, taking into

account the calculated deflections, are shown in Fig. 11.

Fig. 7: Developed EaseOff and contact pattern of the basic version

Fig. 8: Results of the TCA under load for the two load levelsFig. 10.: Graphic evaluation of the displacements, based on the static analysis of the hypoid gear assembly

Fig. 9: Transmission model in RomaxDesigner

Contact pattern for Mt = 200 Nm V=0.05mm, H=0.10mm, J=0.00mm

(Gear flank, Drive) 2mm

Tip

Root

Toe

Heel Max. pressure 1012 MPa0 MPa 110 Mpa 1100 Mpa



Tip

Root

Toe





After a few targeted iterations in the KIMoS EaseOff develop-

ment, results were achieved which are depicted in Fig. 12.

It will be seen that the value for the maximum surface pres-

sure with specification of the maximum torque of 1,512 Mpa

has been reduced to 1,334 Mpa in the result of the optimi-

zation, which corresponds to a reduction of 11.8 percent.

Naturally, in addition to the distribution of the Hertzian pres-

sure, the tooth depth tension, rotational error and meshing

rigidity under load are also considered for the analysis. The

EaseOff developed should always represent the best compro-

mise for all parameters.

The procedure described is applied in precisely the same way

for the thrust side as well.



Tip

Root

Toe




Tip

Root

Toe




Tip

Root

Toe




Tip

Root

Toe


Fig. 12: Results after the optimization

Fig. 11: LTCA results, taking into account the displacements determined in RomaxDesigner

James Mitchell

Lead Product EngineerRomax Technology Limited

[email protected]

Dr. Jamie Pears

Software Product ManagerRomax Technology Limited

[email protected]

Dipl.-Ing. Frank Seibicke

Chief Engineer Calculation SoftwareKlingelnberg GmbH

[email protected]



[email protected]

Considerable savings potentials through efficient data exchange

With the development of the interface between KIMoS and

RomaxDesigner a solution has been found to simplify the

data exchange between the two systems. The great advan-

tage for the user is to be able to perform the analysis of a

complete powertrain based on the exact tooth geometry ver-

sus the time consuming FEM calculation. But what pays off

the most is that the software provides a link between the

analysis of the system and the real behavior of the powertrain

which makes time consuming and costly trials (developments)

a thing of the past. n





LDF 350

Variety instead of monoculture – with the new Liebherr turning-milling machine LDF 350, “work-in-process” is permanently reduced for the production of toothed gears and toothed gear shafts. At the same time, the company is meeting a market demand, as for many users it is important that the competency for the entire process chain remains with the gearing expert.


The objective was to develop and design a combined turn-

ing and hobbing machine with which turning, drilling and

hobbing work could be carried out in the same clamping

arrangement as the hobbing of the gearings and the sub-

sequent chamfering and deburring processes. The result of

this new development, Liebherr‘s response to current trends

and demands of the market, is the LDF 350. This offers the

latest technical options for the machining of cylindrical gear

gearings, not only of wheels but also of shafts.

These kinds of innovative machine concepts are in demand

because of the increasing workpiece complexity and the

wish for increasingly smaller batch sizes, for reduced cy-

cle times and for intermediate layers in production to be as

small as possible. The turning and hobbing machine LDF 350

enables the combination of different machining processes

ranging up to complete machining in a single clamping

arrangement.

One special challenge that the Liebherr engineers faced was

the controllability of both processes (turning and hobbing) for

workpieces up to a maximum diameter of 350 mm, a total

length of up to 500 mm and a maximum module of 5 mm.

The most important component of the LDF is therefore the

workpiece table which fulfills two main requirements:

high rotation speeds of the turning process and•

high rigidity of the gear hobbing. •

Sequence of the fabrication steps

Aligned in the center of the rotation machine and perma-

nently connected with the machine bed, the table ensures

high-production turning and gear hobbing.

The gripper for loading the machine and the pressure de-

burring unit are also aligned on the revolver to the left of the

workpiece table, in addition to the necessary tools for the

turning and drilling processes. The gripper takes up the blank

directly from the storage belt and sets it down on the rapid

clamping system of the workpiece table. ➔


LDF 350

To the right of the workpiece table is the gearing hobbing

head. This absorbs the high forces of the hobbing pro-

cess. In order to absorb the forces of the gearing process,

Liebherr optimized the entire machine by means of FEM and

designed the guides of the radial infeed and of the stroke

and its drives to be extremely solid. This type of construction

guarantees a maximum of stability during the machining pro-

cess, so that even the highest of cutting speeds are possible

in dry machining.

New dimensions can be implemented

The combined machining enables new dimensions for the

workpieces – gearings up to module 5 mm with a maximum

diameter of 25 to 350 mm. This makes the utilization of the

LDF 350 of particular interest, even in the range of larger

gearings.

For tool changes, the hob head swivels the tool axis into

a vertical position so that the machine operator can insert

the hob mandrel in an ergonomically efficient manner. The

counterbearing is automatically tensioned and clamped.

After the gear hobbing, the revolver presses the pressure

deburring wheel into the gearing and thus eliminates the burrs

and/or applies a chamfer to the workpiece. Residual burrs on

the face sides can be eliminated by repeated stripping.

Lowering of investment expenditures, machinery and piece costs

In comparison with a conventional production line (Fig. 1)

with three individual processing machines for turning/drill-

ing, hobbing and deburring, the so-called combination cell

(Fig. 2, next page) also reduces, in addition to the logistics

outlays for loading and unloading, the non-productive times

between the machining processes. This results in a shorten-

ing of the through-put times and intermediate storage of the

workpieces is dispensed with. Product changes also proceed

more economically and more rapidly, as only one machine

needs to be retooled for this purpose. The LDF 350 can be

operated completely automatically and in conjunction with

one or more turning cells.

The machine enables the complete processing of a wide

spectrum of toothed gear shafts and toothed gears in only

one clamping arrangement. In comparison with the other

processes, this ensures a greater amount of flexibility and an

optimized throughput. Time-consuming retooling from one

workpiece type to the next with several individual machines

is dispensed with.

Given optimum conditions, the processing times of the LDF 350

can match those of the single specialized machines. This was

one of the most important objectives for the development of

the LDF 350.

As a result of the utilization of the LDF 350, the num-

ber of required machines, set up procedures and the over-

all throughput times for the complete machining of toothed Fig. 1: Conventional production line

turning

Deburring

Gear hobbing


LDF 350

LDF 350

gears is drastically reduced, which means that both the invest-

ment expenditures and the workpiece costs are considerably

lowered for the user.

Main advantages of the LDF:

no reclamping, no non-productive times•

no intermediate buffering•

High flexibility resulting from the considerably simpler conver-

sion for another workpiece: Only one machine needs to be

retooled and only one clamping fixture is required.

For maximum productivity, the workpiece axis must always be

kept in production operation wherever possible: Downtimes

are intended only for changing workpieces.

Additional qualitative improvements

Complete machining also opens up new qualitative possibilities:

It enables, for example, turning over the bearing seats once

more after gear hobbing. This makes it possible to minimize

deviations prior to hardening and any warpage which might

occur to be held out in an accordingly precise manner.

Result of joint development

As a specialist for gearing processes, Liebherr implemented

this innovation together with the lathe manufacturing com-

pany of Scherer from Mömbris, a professional partner who

has mastered the initial turning process. The result of this

joint development work, the Liebherr LDF 350, is expected to

be available from autumn 2011. n

Dr.-Ing. Hansjörg Geiser

Head of Development & Design Gearing MachinesLiebherr-Verzahntechnik GmbH

[email protected]

Technical datamax. Module mm Module 5

Drive performance kW 15

Hob rotation speed rpm 1,500

Tool diameter mm 30 to 110

Shift path mm 180

Path X axis mm 380

Path Z axis mm 600

Swivel angle -45° to +90° (90° for tool change)

Workpiece diameter mm 25 to 350

Workpiece length mm 500

Fig. 2: Complete production in the LDF 350


this industry has a tailwind: the wind power industry is growing at a rapid pace. the reasons for this are many: Ambitious climate targets, necessary Co2 emission reductions and the ongoing debate about atomic energy are ensuring a boom in the industry and thus also a flurry of activity in terms of technological advancement. Modern measurement technology for enhancing efficiency in quality assurance is an important part of this endeavor. optimum component quality is a competitive advantage which enables the wind turbine transmission manufacturers to be at the cutting edge of this technology.

Advancement Through Measurement Technology


Form and Position Measurement

The industry has considerably increased the performance of

the wind power plants in recent years – this is apparent to the

outside world from the sheer size of the systems. A central pri-

ority of all of the companies participating in the development

is therefore to enhance the performance density of the indi-

vidual components in order to avoid having the dimensions

and the weight of the nacelles increase to the same extent

as the output of the system.

Most of the wind power plants operate with a transmission

in order to transfer the relatively small rotation speed of the

rotor through several transmission stages to increase the rota-

tional speed suitable for the generator of around 1,500 rpm.

To accomplish this, typically several planetary gear stages are

arranged one after the other. The measurements of the trans-

missions have also increased along with the high outputs to

be transmitted, so that the internal gearings to be used some-

times have a diameter well in excess of 2 meters.

The transmission is thus one of the key components on

which, thanks to the clever design of all components, not

only the degree of efficiency, wear and the noise emissions

can be optimized, but also the size and weight of the nacelle

can be reduced. ➔



Innovative transmission designs

It is for this reason that certain components are deliberately

omitted, already during the development stages, in order to

obtain a transmission which is as compact and lightweight as

possible (Fig. 1). This is possible by having individual compo-

nents assume responsibility for various tasks simultaneously

which are distributed between several components in con-

ventional designs.

The internal gearing ring of the planet stages, for example,

is at the same time a load-bearing part and the outer shell

of the transmission – which means that machine holder and

housing can thus both be dispensed with. In addition, the

first of two transmission stages is integrated directly into the

main bearing.

The planetary bearing is located in turn in the

planet gear. Instead of separate external bear-

ing rings on the planet gears, correspondingly

formed bearing surfaces are ground into the

gearing component. The rolling elements of

the bearing thus run directly in the bore hole

of the gearing. The components not only

become more compact as a result, advantages

also arise at the time of assembly, sources of

errors are reduced and concentricity precision

is enhanced.

The requirements for the remaining compo-

nents are considerably increased, however –

new production processes become necessary.

As a result of the fact that the rolling elements

of the bearing run in the bore hole of the

planet gears, grinding work of bearing qual-

ity is required on the bearing surfaces. The geometry of these

bearing surfaces is in the meantime relatively complex and

has very low tolerances. This becomes clear with the example

planet gear with integrated bearing surfaces (Fig. 2).

Measuring under a different banner

As a result of the changed design, new processes are required

not only for the production of these components but also for

their quality assurance.

In order to check all of the functions of the component-

relevant parameters – which are now assigned several tasks –

measurements of dimension, form and position must now also

ø 500

0,008 C0,008 C0,015 C0,015 C0,015 B0,015 B0,015 A–B0,015 A–B

+0,08+0,06

ø 500 +0,08+0,06

580

0,008 D0,008 D0,015 D0,015 D0,015 A0,015 C0,015 A–B0,015 A–B

Fig. 1: Transmission and generator of a wind power plant (Source: Winergy)

Fig. 2: Gearing component (planet gear) from a wind turbine transmission with tolerances


Comparison of the Klingelnberg measurement system with the 3-D measurement systems of coordinate measurement machines

Measurement systems from

CMM (coordinate measure-

ment machine) are usu-

ally constructed in such a

way that the kinematics for

the three coordinate direc-

tions are physically arranged

behind one another. This de-

sign with serial kinematics

has the decisive disadvan-

tage that the moved mass

in the three coordinate di-

rections may differ from one

another and furthermore,

depending on the direction,

can even be very large. In or-

der to reduce the construc-


be carried out in addition to the complete gearing measure-

ment. The form measurements on the bearing surfaces are

thereby particularly challenging and are very demanding of

the measuring technology applied.

The solution for minimizing the overall cycle time for all mea-

surements, including tool time, is complete measurement

designed to run automatically on only one measuring device.

Towards this end, Klingelnberg has specially developed the

P 150 W for the requirements of the wind turbine trans-

mission components on the basis of the machines of the

P series. In contrast to the familiar P machines, the new 3-D

measurement system is fitted on a perpendicularly

aligned boom so that internal bore mea-

suring is possible (Fig. 3). This means that

not only external gears but also internal

gears can be measured to an equal extent

with short probe rods. This arrangement

also offers special advantages for form

measurements in bores.

Fig. 4: Diagram of a conventional 3-D measurement system with serial kinematics

Fig. 5: Diagram of the Klingelnberg 3-D measurement system with parallel kinematics

Fig. 3: Measurement center P 150 W

tion size, these measurements systems are designed to nest

inside one another. This does not influence the disadvantage

of serial kinematics, however. Fig. 4 shows this kind of 3-D

measurement system, simplified without nesting.

In the case of form measurement, it is well known that spe-

cial demands are made on the dynamics of the measurement

system. This is also true for gear tooth measurement, which

in principle is a combination of form and 3-D measurement.

It is for this reason that the Klingelnberg 3-D measurement sys-

tems (Fig. 5) have as a general rule unique, patented parallel

kinematics with three coordinate directions nested within one

another but which are arranged next to one another in physi-

cal terms. This construction provides decisive advantages: The

moved mass is not only identical in all directions, but also and

primarily considerably less than the conventionally structured

3-D measurement systems. As a result, the measurement sys-

tems of the Klingelnberg P series are suitable not only for gear-

ing measurement and general 3-D measurement but also for

other high-resolution form measurement tasks.

A further prerequisite for form measurements on axially sym-

metrical components is the use of a high-precision rotational

bearing. The bearing of the P 150 W, for example, possesses

a static strength of 20 tons while at the same time having a

concentricity precision which is less than 0.5 micrometers. Both

the development and the production and integration of ➔



Fig. 8: Cartesian measurement volume coordinates measurement device

Table: Schematic comparison of the Cartesian measurement volumes: The lesser volume of the P 150 W enables a very high basic precision.

this bearing is a core competency of Klingelnberg. No bear-

ing with this concentricity quality and the static strength of 20

tons is available on the market.

When a comparison is made between the conceptual structure

of the P 150 W with that of a conventional CMM (see table

above), it becomes clear which advantages can arise from the

structure of the P 150 W with three linear precision axes and

one high-precision axis of rotation.

In the case of the P 150 W, the Cartesian measurement vol-

ume set up by the three linear axes is deliberately consider-

ably smaller (Fig. 6) than is the case with a CMM. As a result,

a very high basic precision can be achieved in this measure-

ment volume, which is then additionally improved by a pat-

ented compensation procedure which was specially devel-

oped for this machine construction.

The combination of this measurement volume, which can

thus be mastered perfectly in geometric terms, and the high-

precision axis of rotation results as a whole in a considerably

larger, cylindrical measurement volume (Fig. 7) with a compa-

rably lower measurement uncertainty.

In contrast to this, the relatively large measurement volume of

a conventionally structured CMM must be compensated for

(Fig. 8). Due to the laws of physics, this is difficult to master,

very complex and must be repeated at certain intervals.

For the circular form measurement in the bore of the planet

gear described above, the circle must be generated by a com-

bined movement of two linear axes for this kind of CMM. In

doing so, a relatively large area of the measurement volume

P 150 W CMM

Volume size in mm (HxDxW)

1,500 x 600 x 800 1,500 x 1,500 x 1,500

Fig. 7: Total measurement volume P 150 W

Fig. 6: Cartesian measurement volume P 150 W


Dipl.-Ing. Georg Mies

Manager R&D Measuring TechnologyKlingelnberg GmbH

[email protected]

Fig. 9: Measurement of a sun gear from a wind turbine transmission on a P 150 W

will be intersected by both axes, with correspondingly negative

effects on measurement accuracy. This measurement strategy

may be suitable for a coordinate measurement, but not, how-

ever, for high-precision circular measurements.

Modern measurement technology as an important part of further development

Efficient and modern measurement machines are a decisive

part of the dynamics for ongoing and future developments

in the wind power industry. They support the companies who

contribute to keeping the tailwind blowing – so that climate

targets can be achieved, emissions reduced and an alterna-

tive to both nuclear energy and CO2-intensive energies will

be strengthened. n


The New Hardness for Short Grinding Times

the advantages of generating grinding with vitrified CBN grinding worms are particularly evident in comparison with established procedures. the reliable utilization of the extremely hard cutting material enables, among other things, shorter grinding time and longer tool life.


Generating grinding is an established process

for the hard finishing of gears. The use of

generating grinding is very widespread in the

range of up to Module 5 mm, particularly

in industrial gear manufacturing and in the

service vehicle and automobile sector. For

Module 5 to 8 mm, profile grinding is also

used in addition to generating grinding, and

the former grinding technique is always more

widespread with larger modules. Current

trends in machinery and tool development

are opening up an ever greater potential

here for generating grinding up to Module

14 mm. In the case of generating grinding,

the following process variants are encoun-

tered on the market, each with advantages

and disadvantages with respect to process

technology: ➔

Generating grinding with electroplated CBN grinding worms

Resistant to • hardness fluctuations

High process stability through • long tool life

2-cut process for allowances • of up to 0.18 mm/flank

Machining of collision-critical • gearings

No profile correction • opportunities possible

during ongoing process

Limitations with respect to • profile form and surface quality

Generating grinding with dressable grinding worms made of corundum

Excellent profile and • surface quality

resulting from dressing in the machine

Flexible correction • opportunities for profile angle deviation fhα

Influencing of the surface • roughness through targeted modification of the dressing speed ratio

Low tool costs per workpiece•

A 3-cut process is • necessary, depending on

the allowance situation and pre-machining quality

Proportionate dressing time • per workpiece

Combination grinding (roughing with grinding worm/ finishing with profile grinding disk) with both electroplated and dressable corundum tools

Resistant to • hardness fluctuations

Excellent profile and surface • quality resulting from finishing in the profile grinding process

Machining of collision-critical • gearings with the use of electroplated CBN tools

Longer machining • time during finishing

resulting from the single indexing process

Coordination of the tool life • with CBN or of the dressing cycles with corundum for the roughing worm and the finishing disk

Vitrified CBN


Vitrified CBN

Development of machining times for generating grinding with corundum

Grinding times overall have been considerably reduced with

a variety of further developments in procedures in the recent

past. Numbered among these developments are:

the development of high-performance corundum • grinding worms based on the SG corundum cutting materials or other special corundum

the further developments of ceramic bonding itself •

the optimum integration of these new, more • high-performance and/or of the proven corundum cutting materials in the ceramic matrix

One reason for the shortening of

the grinding time is that the cut-

ting speed has been increased

from 63 m/s to 75 m/s, and even

up to 80 m/s on the LCS machines.

However, the risk of thermal

joint damage also increases with

increasing cutting speed. In addi-

tion to the higher cutting speed,

increased feeds and greater cut-

ting depths per cut are also pos-

sible. This often opens up a 2-cut

process with a total allowance of

0.1 to 0.12 mm/tooth flank. At the

same time, though, the increased

grinding worm wear associated

with this must be compensated

for with greater dressing amounts. This is incorporated into

the proportional dressing time per workpiece and increases

the tool costs per workpiece.

All measures described for increasing performance when gen-

erating grinding with corundum grinding worms push the

grinding process to the limit. A different cutting material

must be selected to tap into further potential. CBN allows the

performance potential to be boosted in a risk-free and safe

way. The safety and stability limit of the grinding process is

increased and fluctuations avoided.

Table: Comparison of properties of different cutting materials important for machining

Corundum SG Corundum CBN

Structure Al2O3 Al2O3 SG-Al2O3 Chip space

Steel core Bonding (nickel)

Bonding (vitrified)

Pores Bonding (vitrified)

Pores

CBNAl2O3 Al2O3 SG-Al2O3 Chip space


Bonding (vitrified)


Pores

CBNAl2O3 Al2O3 SG-Al2O3 Chip space


Bonding (vitrified)


Pores

CBN

Bonding characteristics Multi-layer, dressing possible

Multi-layer, dressing possible

Single-layer, not dressable

Hardness [HK01] 1.850 2.150 4.500

Grain size [µm] 100–250 <1µm 100–250

Coefficient of friction[-] (with respect to steel) 0,34 0,19 0,19

Thermal conductivity[W/mK] e e

Temperature resistance[°C] 1.750 1.750 1.200

70–250

200–700

f.l.t.r.: - Tool set for combined generating and profile grinding- Vitrified CBN grinding worm- SG corundum grinding worm


Vitrified CBN

Cutting material with the greatest potential for high machining performance

Cubic boron nitride, better known as CBN, is the second-

hardest cutting material after diamonds – which due to their

chemical properties are either only of limited suitability or un-

suitable for machining hardened steels. In addition to its high

Knoop hardness, CBN is outstanding for its high thermal con-

ductivity and a low coefficient of friction with respect to steel.

The advantages of CBN in comparison with other corundum

cutting materials becomes clear in light of this criterion (see

table on the previous page). This makes CBN the ideal cutting

material for the machining of hardened toothed gears – with

the potential of reducing the grinding time even further and of

increasing tool life thanks to its high wear resistance. Further-

more, CBN offers the possibility of machining materials with

a high surface hardness in excess of 64 HRC.

Development from electroplated to vitrified CBN

30 years ago, Liebherr developed generating and combi-

nation grinding with electroplated grinding tools. With the

development of a dressing unit integrated in the machine,

the possibility was opened up of profiling and sharpening

grinding worms and profile grinding disks made of corundum

on the LCS. This LCS grinding machine type has been estab-

lished on the market since 1998.

As a result of the many years of experience and the know-

ledge of the performance potential of the CBN cutting ma-

terial with the grinding of gears, and in view of the dressing

unit available in the LCS, Liebherr developed together with

two tool suppliers the idea of bonding the cutting material

CBN in a dressable ceramic matrix for grinding worms for

generating grinding. The objective here is to achieve the

performance advantages of the CBN cutting material with the

positive characteristics of the chemical bond such as:

higher flexibility for profile angle corrections • by dressing

attaining the highest profile form and surface qualities•

combining multi-layer and dressable CBN cutting • material structure for a long tool life utilization.

This basic principle was already known on the market, but

vitrified CBN grinding worms have only been used only in a

few special applications to date. A cost-effective and efficient

utilization of these tools was still not yet successfully imple-

mented in large-series production. The reason for this was that

the manufacture of vitrified CBN grinding worms and their pro-

cess-reliable dressing involved a few technical difficulties. Two

different tool systems manufactured by the Wendt and Lapport

companies were introduced at EMO 2007 in Hanover. Together

with the dresser manufacturer Dr. Kaiser and two users, the

process was then developed in a joint project ranging from

basic research to the start of production. ➔

Fig. 1: Vitrified CBN grinding worm (Wendt Co.)

REM detail exposure of the bonding structure


Vitrified CBN

Challenges from the point of view of machinery and technology

For Liebherr as a manufacturer of gearing machinery, it was

important to develop the dressing and grinding process in

such a way that it would be employable on an already existing

LCS grinding machine with an integrated dressing unit. The

necessary additions with respect to machine technology

should be simple to retrofit as well.

One of the greatest challenges is represented by the dress-

ing of the vitrified CBN structure. Due to economic consid-

erations, it is on the one hand a prerequisite that the entire

dressing amount per dressing cycle is kept as low as possible.

On the other hand, the wear caused by the use of grinding

must be rectified by sufficient profiling. In order to ensure

this, the initial contact between dresser and grinding worm

must be detected down to a micrometer. In the case of the

individual infeeds for the entire dressing amount as well, only

up to 4 µm should be dressed per tooth flank in order to

ensure that the wear on the dressing tool does not become

too great. All this is made possible by the utilization of an

Acoustic Emission System (AE System). In addition to the AE

System, additional prerequisites are a very rigid dressing spin-

dle and the high-precision controllable tool spindle.

For the development of the dress-

ing technology, i.e. the dressing

speed ratio, a different strategy of

synchronus and asynchronus dress-

ing, and also the traversing speed

along the shift axis, it was advanta-

geous to carry out the single-flank

dressing usually used by Liebherr.

As a result, the processing forces

which arise when dressing the

CBN structure were considerably

reduced. It is only with the single-

flank dressing with the swiveling

dressing axis offered by the LCS

that precise adjustment or dressing,

respectively, of the pressure angle

at a point became possible.

A further focal point of develop-

ment from the point of view of

machine technology was to develop

a collision protection for the consid-

erably more expensive CBN grind-

ing worms which makes it possible

to protect the tool against either partial or entire break-outs of

worm segments or complete destruction. These kinds of colli-

sions could negate at one blow the very high tool life and the

economic efficiency associated with it. This collision protec-

tion developed by Liebherr on its own (see interview with Mr.

Florian Schuon on page 42) can be retrofitted on all LCS gear

grinding machines that have Siemens control units.

With respect to grinding technology, a new shift strategy

enabled an optimization of the tool life of the grinding worm.

For this new shift strategy, machining is not carried out in

segment shifts, as is usual on the LCS for dressable corun-

dum grinding worms, but instead is based on the example of

electroplated grinding tools with a roughing and a finishing

area. This does not involve two separate grinding worms, but

rather a mono-grinding worm which is divided into a finish-

ing area (main bearing side) and a roughing area (side oppo-

site the bearing) (Fig. 2). In each area, a prescribed number

of workpieces is ground in either axial or diagonal proce-

dure at one shift position, after which it is shifted further by a

defined offset. The following sequence is thereby maintained:

The first workpieces are each ground at the start positions at

Fig. 2: Function principle of the dynamic shift strategy

Finishing areaCounter bearing

Roughing area

Shift-Start Shift-Start

Direction Direction

Main bearing

Offset

30 P

ositi

on o

f w

orkp

iece

s 1

30 P

ositi

on o

f w

orkp

iece

s 2

diag

onal

, con

vent

iona

l

axia

l, cl

imb

50 P

ositi

on o

f w

orkp

iece

s 1

50 P

ositi

on o

f w

orkp

iece

s 2

Offset… etc. … etc.

Dyn

amic

ally

dis

plac

eabl

e SH

IFT

CEN

TER

Dep

endi

ng o

n th

e nu

mbe

r of

wor

kpie

ces

with

rou

ghin

g an

d fin

ishi

ng

Vitrified CBN

the ends of the grinding worm and then moved in the direc-

tion of the middle of the wheel by means of onward shifting.

The automatic dressing is triggered when the finishing and the

roughing areas meet in the middle of the worm.

The quantity of workpieces which can be ground for each

shift position is dependent on the grinding worm wear and

thus dependent on the allowance and the established grind-

ing parameters. The amount of the shift offset is dependent

on the respective gear geometry (module, pressure angle, ad-

dendum modification, etc.). Depending on the workpiece and

wear behavior, the length and the position of the roughing

and finishing area on the worm is managed dynamically by

the machine control unit and adjusted automatically.

This dynamic shift traversing can naturally only show its

strength if the grinding worm has a certain length and thus

makes sufficient shift positions available. In order to keep the

procurement costs of the grinding worm as low as possible,

the outside diameter can be reduced with corresponding worm

facewidth without any reduction in tool life. This is based on

the assumption of a tool spindle with high rotation speed and

one main bearing and one counter bearing. Both of these are

fulfilled by the LCS. ➔

Technology Comparison with a Machining ExampleWorkpieceModule 1.75 mm, z2 = 81

Worm facewidth 150 mm

Shift positions 24 per dressing cycle

Number of workpieces per shift position 40

24 x 40 = 960 workpieces per dressing cycle

Tim

e/Pa

rt [

min

.]

Process variation

With vitrified CBN, up to 40 times as many workpieces can be machined in a single shift position as with SG corunded worms – with a constantly high quality, as the comparison (on the right) between component no. 1 and no. 40 shows: The quality within one shift position is consistently high with all parts.

electroplated CBN: 2st, 66 m/s

SG corundum: 4st, 59 m/s

SG corundum: 4st, 75 m/s

vitrified CBN: 4st, 59 m/s

vitrified CBN: 4st, 75 m/s


1st Cut 2nd Cut Dressing Idle Time Total Time

1,60

1,40

1,20

1,00

0,80

0,60

0,40

0,20

0


Vitrified CBN

Collisions can result in high costs on gearing machines. Thus Liebherr offers a software solution which reduc-es the damages and their subsequent costs to a min-imum. This is particularly expedient with expensive tools and tool clamping fixtures. Florian Schuon, Con-trol Unit Development/CNC Development at Liebherr-Verzahntechnik GmbH, explains the principle of opera-tion and advantages of the unique collision monitoring in an interview.

sigma REPORT: Mr. Schuon, how do collisions happen

on gearing machines?

Florian Schuon: Collisions on gearing machines usually arise

from faulty operation or incorrect programming. Most collisions

occur as early as the setup stage when the attendant inadver-

tently selects an incorrect workpiece file that does not fit the

loaded workpiece or if the wrong direction key is pressed.

sigma REPORT: What are the difficulties in connection

with collision monitoring and how does your system

react to possible collisions?

Florian Schuon: The demand for ever-shorter machin-

ing times requires highly dynamic drives. Therefore a reduc-

tion of the torque is naturally unthinkable as a general solu-

tion. Furthermore, the monitoring should be active in manual

and automatic mode as well as in every phase of the axis

movement (rapid traverse, feed, running empty and machin-

ing). Naturally, we still continue to have a deliberate collision

during the gearing of the workpieces (hobbing, shaping,

grinding) to which the monitoring simply must not respond.

Our collision monitoring is purely a software solution which

can detect inadvertent collisions and which reacts to these

by quickly stopping the drive. Damages can be reduced to a

minimum or even prevented completely as a result.

sigma REPORT: How does your monitor function and how

does your system differ from systems of external suppliers?

Florian Schuon: The openness of new control unit genera-

tions permits the evaluation of drive signals in real time and

the initiation of reactions directly in the core of the control

unit. Rapid algorithms observe the current torque output of

the drives and link these to the process conditions. As a re-

sult of the direct assessment in the core of the control unit,

we have on the one hand the shortest reaction time, while on

the other hand we adjust our limit values dynamically to the

respective drive condition. In the event of an error, we effect

“ Reducing Damages to a Minimum or even Preventing them Completely”

Dr.-Ing. Andreas Mehr

Applications technology for grinding and shapingLiebherr-Verzahntechnik GmbH

[email protected]

Further development

Once the dressing and grinding technology and the grinding

machine technique were developed up to the start of produc-

tion, the next objective now is to optimize the tool life of the

grinding and dressing tools further in the series testing stage.

Initial reports from Production indicate that generating grinding

with vitrified CBN grinding worms on Liebherr gear grinding

machines can be implemented economically and with stable

reproducibility.

Currently, however, there is still no generally valid formula

which makes it possible to apply the experience gathered to

date with respect to wearing behavior and tool life to

other modules or applications. It is therefore in the interest

of Liebherr to expand its empirical knowledge in the future

in close collaboration with the users – through experiments

on other gears. n


Vitrified CBN

Dipl.-Ing. (FH) Florian Schuon

Control Unit Development/CNC DevelopmentLiebherr-Verzahntechnik GmbH

[email protected]

a standstill as rapidly as possible. Several axes are monitored

at the same time with this system.

External systems work with sensors. They thus have no access

to information in the control unit core. For me, the greatest

disadvantage is in the reaction speed of these monitoring

systems. Due to the scanning and evaluation cycles of this

kind of sensor, the reaction speed to a collision is much too

slow and it is difficult to prevent a larger-sized damage with

this. Furthermore there is also the problem that there is no

optimum position at which, for example, a 3-D acceleration

sensor of this sort could be fitted.

sigma REPORT: On which Liebherr machines do you

install the collision monitoring?

Florian Schuon: Fundamentally speaking, monitoring is

expedient on all grinding, shaping and hobbing machines.

Particularly useful however is monitoring on machines with

relatively expensive tools. This means that collision monitor-

ing is recommended in any event for grinding machines with

tools made of dressable CBN.

sigma REPORT: Mr. Schuon, thank you

for this discussion.� n

with monitoring without monitoring

Reaction path/time 0.04 mm / ≤1 ms 18.45 mm / 448 ms

Brake path/time 0.36 mm / 20 ms 01

Deformation path 0.4 mm / 21 ms 18.45 mm / 448 ms

max. torque 4.39 Nm 37.13 Nm

max. force at collision point

4.81 kN 93.83 kN

1) 0 because reaction (contour monitoring) takes place only with movement against an absolute fixed stop

Axis speed vX1 = 2,5 m/min

without collision monitoring

with collision monitoring

Consequences of a collision of the corundum worm (head against head), at a feed rate of 4 m/min.The activated collision monitoring detects the collision immediately, stops the drive as fast as possible and minimizes the damage.

Klingelnberg GmbH Peterstrasse 45

D-42499 Hueckeswagen Fon +49 2192 81-0

Fax +49 2192 81-200 Mail [email protected]

www.klingelnberg.com

Klingelnberg AGBinzmuehlestrasse 171

CH-8050 ZurichFon +41 44 2787979Fax +41 44 2731594

Mail [email protected]

Liebherr-Verzahntechnik GmbHKaufbeurer Strasse 141

D-87437 KemptenFon +41 831 786-0

Fax +41 831 786-1279Mail [email protected]

www.liebherr.com

www.sigma-pool.com

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