Liebherr has introduced new technology for the automotive and commercial vehicle industry: Chamfer Cut unit for workpieces up to 180 mm and a newly designed gear grinding machine for both profile and generating grinding.
New Chamfer Cutting Capability
Liebherr-Verzahntechnik's hobbing machine, when equipped with a separate Chamfer Cut unit, has opened up a long- and well-established procedure to new applications, according to the company. "After hobbing with the usual one-cut strategy, the Chamfer Cut tool additionally generates precise and reproducible chamfers that are increasingly demanded by the market," said a company spokesperson.
According to the company, the newly developed solution eliminates the main disadvantage of Chamfer Cut: prolonged machining time during the chamfering process. "In the past, hobbing and chamfering took too much time at the same setting," said the spokesperson. "We have solved this by integrating a complete second machining unit for Chamfer Cut tools - two machines in one, so to speak," said Dr.-Ing. Oliver Winkel, Director of Application Technology. Winkel is responsible for technological development of gear cutting at Liebherr-Verzahntechnik.
"The main design engineering challenge was to execute the Chamfer Cut unit at a reasonable cost," said Dr.-Ing. Hansörg Geiser. "We thus integrated the deburring unit within the existing machine dimensions without any impact on space requirements."
"Functionality, operation and CNC programming are based on familiar machine design," said the spokesperson. "The operating changeover from the existing machine is relatively simple once standard user training has been provided."
According to the company, chamfering no longer prolongs machining time by taking place in a separate unit within the same machine while the next workpiece is already hobbed. Both chamfer tools are no longer located directly next to the hobbing tool but in the separate unit. "We know from gearbox design development that the subject of chamfering is becoming more and more important," said Winkel. "This innovation enables the machine to combine high chamfering quality, provided by the Chamfer Cut procedure, with cycle times that correspond to the demands of the automotive industry."
The spokesperson added, "This technology is worth considering by all users, for whom alternative procedures are too time-consuming, whose tooling costs are too high or those who especially need to take follow-up processes such as honing into consideration."
According to the company, Liebherr offers all common chamfering procedures. "Compared to press deburring and chamfering with finger mills, the chamfer cut process has the lowest chamfering costs," said the spokesperson. "Cycle time is the central parameter by which we are judged," said Winkel. "Speed is a must-have. Process reliability, controllable quality and lowering costs are also givens."
"For all chamfering processes, it is a matter of precisely chamfering the face edges of gear workpieces as consistently and reproducibly as possible - free from burrs and warps," said the spokesperson. "Yet, especially with press deburring, rolling requirements at the tooth root are not optimal for the chamfer quality. With the Chamfer Cut principle and the new chamfering unit, adjustments of the chamfer to varying flank corrections are possible."
The size of the chamfer, according to the company, can be reduced compared to the previous standard; the chamfer tool is no longer dependent on the size of the hobbing tool. "Chamfering tools with diameters of 40 mm are possible, which helps to solve the collision problem and facilitates accessibility," said the spokesperson. "In view of further downsizing trends in industry, this technology meets the technical requirements to be able to generate even smaller, more precise chamfers for transmission components. As the importance of a reproducibly generated chamfer increases, the smaller the gear will be.
"Parts frequently do not conform to drawings due to imprecise chamfering procedures, which is especially true the thinner the gear face width becomes. The transmission designer calculating to the limits of design feasibility is gaining importance. The chamfer is becoming more and more of an engineering factor. The importance of chamfer quality has increased due to the fact that its actual impact can now be calculated and also due to the ever tighter design of transmissions. For example, it makes a huge difference in a gear from an automotive transmission that is only about 12 mm wide, whether the chamfer is 0.5 or 1 mm, and consistently throughout high-volume production.
"Partnering with the tool manufacturer, it is now possible for the first time to chamfer both face edges of the workpiece without the usual change of rotation direction, creating an additional time advantage." A further advantage, according to the company, results from having two separate machining positions. The workpiece is machined on different devices: gear hobbing on a stable device designed for maximum rigidity, and chamfering on a simple fixture designed for optimized collision. "The length of the hobbing tool can also be maximized, enabling total tool costs to be further reduced," said the spokesperson.
The following are additional advantages of the new machine concept, according to the company:
- No material deformation
- Very long service life if dry machining is involved
- No needle chips (from the chamfer) in the main work area
- Settings via CNC axes
- Simple set-up
- Ease of regrinding Chamfer Cut
- Separate setting for hobbing and chamfering (more chamfering options).
Grinding Machine
Liebherr's new machine for profile and generating grinding is designed to combine short grinding times with consistent high large-scale production quality. "This machine gives users fast processing combined with the advantages of a one-table solution," said Dr.-Ing. Andreas Mehr, Grinding and Shaping Technology Development and Consultancy at Liebherr-Verzahntechnik.
For this reason and given its compact dimensions, according to the company, the machine is especially suited to vehicle and transmission manufacturers and their suppliers. "To facilitate installation of production lines for a complete series, making optimum use of the available space, the machines for both 180 and 280 mm have the same external dimensions," said the spokesperson. "Vehicle manufacturers can thus develop a complete production line in which all gearing components for a passenger vehicle transmission can be ground: planetary and sun gears, bore-type gears, as well as drive and pinion shafts with lengths of up to 500 mm."
"Choosing a one-table solution means one setting, one geometry," said Mehr. "The advantage is higher quality throughout the entire production. Every machined part is manufactured under the same conditions for the highest reproducibility. A key argument in favor of the one-table solution is the statistical capability and reliability in continuously producing controlled µ-range finish quality."
According to the company, the machine bed has been manufactured using a thermally stable material in order to minimize any thermal impacts. The core of the machine is the newly developed grinding head. "Conventional solutions have been chosen here in several areas in order to be prepared for yet higher quality requirements," said the spokesperson.
The new grinding head is designed to allow for rotation speeds up to 10,000 RPM and has spindle power of 35 kW. "Given this performance data, the head enables high cutting speeds and high feed rates," said the spokesperson. "This top-rate performance makes the machine future-proof. There are also reserve capacities for new developments and coming higher demand. The new grinding machine can exploit the considerable potential of the abrasive Cubitron II.
"The machine will enable undulations to be applied specifically to gear wheel flanks for noise optimization purposes for the first time. The ability to produce sub-µ range waviness cost-effectively gives designers a whole new range of optimization options."
Further features of the machine are, according to the company:
- Twist-free grinding (according to Liebherr's Dr. Sulzer)
- Grinding of stimulus-optimized corrections (amplitude, wavelength, phase, orientation)
- Trueing up of lines
- Grinding of conical gear teeth (beveloids).
For more information contact:
Liebherr Automation Systems Co.
1465 Woodland Drive
Saline, MI 48176-1259
734-429-7225
www.liebherr.us