cutting beveloid gears comple processes made asy · sigma report 20/2011 cutting beveloid gears...

14sigma RepoRt 20/2011

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

cutting beveloid gears comple processes made asy · sigma report 20/2011 cutting beveloid gears...

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