Making mistakes is not an option
For the serial production of planet carriers for gearboxes for commercial vehicles, the American gearbox manufacturer Allison Transmission has shifted to the gear skiving method. With Skiving3, Liebherr was able to implement several special requests within a short time due to good coordination between machine, tool and technology, significantly increasing the tool life and productivity.
Allison Transmission Holdings, Inc, based in Indianapolis, is a US manufacturer of automatic gearboxes with integrated braking systems and hybrid drives for commercial vehicles. The company’s drive systems are in use in trucks, buses, off-road and military vehicles all over the world.
Allison Transmission Inc.
Industries:
Automatic transmissions for medium- and heavy-duty commercial vehicles
Company size:
2,700 employees
Founded:
1915
Headquarters:
Indianapolis, Indiana (United States)
Website:
www.allisontransmission.com
Allison Transmission – a traditional company with a commitment to quality
Founded in 1915 by James Allison, the company initially built race cars and airplane engines. Further milestones in manufacturing were, for example, the first powershift transmission for the navy, the angle drive for track vehicles, integrated hydraulic retarders, fully automatic truck gearboxes, and gearboxes equipped with double turbines for transport vehicles. Today, Allison Transmission is the world’s largest developer, manufacturer and distributer of fully automatic gearboxes for medium-duty and heavy-duty commercial vehicles and hybrid drive systems.
Allison’s demands of the quality and service life of their fully automatic gearboxes are high. From the beginning, the company’s philosophy was based on quality and workmanship. “Whatever leaves this shop under my name must be of the finest work possible”, states the inscription on a sign in the company which its founder, James Allison, put up. Today, customers still value the reliability and economic efficiency of Allison gearboxes, which ensure low downtimes and maintenance cost with minimum maintenance requirements.
Tandem machining of a planet carrier
Investment in gear skiving technology
In the course of a substantial machine investment in 2017, the company was searching for productive and economically efficient alternatives for the manufacturing of planet carriers – sophisticated components with an interfering contour, which had previously been shaped. At this point, Liebherr was able to convince the company’s management that these components could be ideally manufactured using gear skiving technology. Furthermore, the Liebherr machine can combine two gear manufacturing machining tasks into one single machine, significantly reducing the overall cycle time.
Gear skiving is significantly faster than shaping and more economical than broaching, but it is also a demanding process which relies on perfect coordination between machine, tool and technology. “For successful gear skiving, users need more than just a good machine”, explains John Hartford, Regional Sales Manager at Liebherr. “With our Skiving3 design, we offer a complete customer solution, which includes not only the actual gear skiving machines but also the matching tools and technology for the process.”
Liebherr LK 300: innovative and productive
Liebherr LK 300: innovative and productive
With the LK 300 gear skiving machine, Liebherr had the ideal machine for Allison’s requirements. It is characterized by high machine rigidity with directly powered tool and table spindles. Additional functions such as a tool loading device for particularly heavy tools and an adaptable deburring steel on the gear skiving head extend the application possibilities. Optionally, a fully automatic tool changing system for up to twelve tools can be integrated. It is operated via the LHGearTec control software, which also includes the mathematical formulas for tooth thickness, lead and profile angle modifications. This means that quality improvements can be easily achieved via the kinematics of the machine.
Liebherr’s strength lies precisely in implementing individual customer requests.
Specialist for special requests
However, for the machining of the planet carriers, special features had to be realized, which are not included in the machine as a standard. Until now, both gears of the component had been manufactured using different methods on two different machines: The outer gear of the component was hobbed, while the spline was shaped. This meant that, on the LK 300, tandem machining of both gears had to be realized in one workpiece clamping. The customer also requested integrated tool measurement in the machine. “Liebherr’s strength lies precisely in implementing individual customer requests”, says John Hartford. “Our customers come to us because they know that we can do better than the standard.” Despite the implementation of the desired special features, Liebherr was able to deliver the machines within the usual timeframe. During commissioning, the service team supported the customer on site. “We have optimized the process and tool conditioning together. The result was a significant improvement to the tool life and a threefold increase in productivity compared to the previous process”, explains Philipp Kohler, responsible for technology application for gear skiving at Liebherr.
Tool loading device for particularly heavy tools
Investment that paid off
In this case, two gear skiving machines were able to replace four shaping machines – an investment that paid off. After the successful commissioning of the first two gear skiving machines, Allison decided to purchase a third machine. There is even a further integrated option: A tool changing system, which can also change large tandem tools. “More than anything, Liebherr rises to the individual challenges and is also able to react flexibly and at short notice and implement special requests as part of a machine delivery”, emphasizes John Hartford.
