Tooth Flank Grinding Solution

Gear grinding is currently attracting a lot of attention, especially in the production of components for electric drives.

"Production planners are demanding new solutions for a perfect surface that assures smooth running at high speeds and heavy torque loads," said an EMAG spokesperson. "To see how a high-tech niche machine builder implements these requirements, one need look no further than EMAG SU tooth flank grinding machines. The gear grinding machine specialist developed the G 160 model, for example, that features a virtual axis concept for microscopically near-perfect surfaces. At the same time, the integrated material handling technology keeps the cycle times down to a minimum."

Electromobility is booming and the competition to have the best solution is accelerating. Almost all automotive manufacturers launched new EV models in 2022. What does this mean for the production planning by OEMs and suppliers?

"They have to effectively deal with growing production quantities, yet, still have to guarantee an ever-increasing level of quality, because the high torque load of an EV electric motor results in special requirements for tight tolerance dimensions and surface finish," explained Alexander Morhard, Technical Gear Support Specialist with EMAG SU. "This development is particularly noticeable in the machining of tooth flanks on shafts and gears. Here, it is important to achieve dimensionally accurate results in the micron range, because even minimal ripple in the surface finishing of the components can cause interference noise in the drive performance."

G 160: Minimal Chip-to-Chip Times

With a wide range of technological innovations, EMAG SU demonstrates how quality can be improved in this extremely precise application. The company offers a large range of machine tools that cover the entire gear tooth cutting process. Tooth flank grinding, with the alternative cornerstone procedures of "generating grinding" and "profile grinding" is a key area of application. With generating grinding, for example, the gear geometry is continuously "generated" by a combination of multi-axes, high performance machine motions and well-maintained grinding wheels. EMAG SU's G 160 model is a fast machine for components up to module 3 with a maximum outside diameter of 160 mm. The G 160 speed is made possible by a slide axis concept with two parallel workpiece tables that take turns moving at high speed (with the help of durable, high performance linear motors) to the grinding wheel. During the time that one component is being machined, the loading robot inserts a blank into the other spindle, after first unloading the completed part, as needed. Self-centering alignment, or "meshing," of the grinding wheel to the rough-cut gear component takes place directly on the workpiece spindle, at load position, in parallel with the main machining operation. This results in a chip-to-chip time between the grinding processes of only 1.6 seconds (a very small value compared to grinding machines with turntables, where in some cases up to five seconds pass for the same process, according to EMAG). Here, it is important to note that the actual grinding time needed for a typical component, such as a planetary gear wheel, is only about 10 seconds.

"The difference between the chip-to-chip times between grinding is therefore a real game changer," said the spokesperson. "The floor-to-floor time is significantly reduced by about 3 seconds (more than 20%), and the output quantity is massively increased. This is a decisive factor in the planning of high-volume manufacturing in the growing electromobility market."

Axis Concept Prevents Ghost Frequencies

"What also sets apart the technology of EMAG SU is the enhanced surface qualities that the innovative axis concept that the G 160 makes possible," continued the spokesperson. "Unlike many other generating grinding machines, it has no tangential axis. Instead, the Y- and Z-axis generate a virtual tangential axis through a simultaneous movement. As a result, the point of contact between the grinding wheel and workpiece is around 100 mm closer to the pivot point of the swiveling axis, which is beneficial for the swiveling behavior during the grinding process."

The wheel point of contact varies, thereby smoothing the gear form for better mesh and higher bearing ratios. The result is visible in the surface structure of the finished component, as the ghost frequencies in the micron range mentioned previously vanish almost entirely. Additionally, gear form Profile Deviation is very low, as measured by the force-field approximation (FFA) value. The improved finish and form of the gears is due to the rigidity of the G 160 and other EMAG SU innovations. Numerous shafts and gears wheels of the electric drive systems benefit from this quality.

G 250: Short Cycle Times/Maximum Flexibility

Another interesting machine concept can be found in the G 250 machine of EMAG SU, which is suitable for components up to module 7, with an outside diameter of 250 mm. Axle drive gears, gear wheels or shafts with a maximum length of 550 mm can be produced with this solution, using generating grinding or profile grinding, with short cycle times. To this end, the machine is equipped with two table spindles to minimize idle time during the manufacturing process.

"Additionally, the flexibility of the machine was very important to us," explained Morhard. "For example, the G 250 can also be equipped with very small grinding wheels and worms." The G 250 HS variant also has a high-speed grinding head, which makes 20,000 RPM possible, if a small grinding worm is used.

Other advantages of this machine concept:

• Generating grinding and profile grinding are performed on the same main grinding spindle, so the machine does not suffer from heat development (like when auxiliary spindles are used for profile grinding). Additionally, the machine can be re-tooled for the alternative procedure within a matter of minutes.
• Generating grinding can also be used for machining workpieces with interfering contours by using generating worms with a root diameter up to 68 mm. This results in very short grinding times. All other components can be finished with a small profile grinding wheel with a size of up to 30 mm.
• Centering takes place in the loading position, in parallel with the main machining operation.
• The integrated dressing unit provides process reliability.

For large components in trucks or in general gear manufacturing, the cost-efficient G 400 rounds off the upper end of EMAG SU's product range for generating grinding. It is equipped with a tool table for components with a max. diameter of 400 mm and a shaft length of up to 750 mm. A feature that is important to many users: The machine can also be loaded from above, because the housing has an over-the-corner door.

To accommodate various grinding wheel sizes and types, a variety of spindles with corresponding power and performance are available. Additionally, the technology can easily be combined with different automation technologies.

"We consider ourselves ideally equipped to supply machines for the grinding tasks needed in the field of electric mobility, as shown by a well-known French automotive manufacturer currently successfully using several EMAG SU grinding machines to generate gears," said Morhard. "In the coming years, we want to continuously improve our contribution to the global requirement for precision gear grinding machines for the ever-increasing quality demands for electric vehicles."

Authored by EMAG

For more information contact:

EMAG L.L.C.

38800 Grand River Ave.

Farmington Hills, MI 48335

248-447-7440

info@usa.emag.com

www.emag.com