Q&A with Mats Wennmo

Global Manager for Automotive Transmission Gear Solutions at Sandvik Coromant

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Mats Wennmo has been the global manager for Automotive Transmission Gear Solutions at Sandvik Coromant since 2017. He got his start in the industry in 1982 as a trainee at SAAB Automobile. Prior to joining Sandvik Coromant nearly 15 years ago, he was the CEO and 50 percent owner at Swedish tool producer, SVA AB. Wennmo is currently responsible for a global team of application specialists mainly working with power skiving applications. Gear Solutions recently talked with him about advances in using power skiving for EV-transmission gears.

How important is noise reduction in gears used in EV transmissions?

Noise reduction in EV transmissions, since there is no combustion engine noise, are decisive for the total customer experience of the EV, particularly those involving high frequency sounds and/or whining sounds.

Why is the ring gear in the planetary gear design of an EV more difficult to produce?

The ring gear blank is a thin ring where the roundness needs to be maintained during the complete machining. The clamping forces need to be well distributed over the complete surface of the ring gear. The gear profile cannot deviate by many microns of the specified quality. If there are deviations in the ring gear, it might influence transmission noise in a negative direction. It also means that the load between planetary gears and ring gear cannot be evenly distributed.

What problems arise when a workpiece is moved from machine to machine?

In a line production where you move the blank from, for example, a turning machine to a broaching machine, the quality of the gear component will be considerably reduced with every move since the centering deviations increase and the run-out deviations increase. These deviations are directly linked to the function of the planetary transmission. The load on the gear flanks between ring gear and planetary gears cannot be evenly distributed due to the deviations. That’s why a one-setup machining process resulting in improved quality in a multitask machine/machining center is superior compared with the line production. 

The Sandvik Coromant CoroMill®180 indexable power skiving cutter for gear and spline production with high output. (Courtesy: Sandvik Coromant)

What is being done to upgrade the traditional manufacturing process?

The main problem with the traditional, line-based, dedicated gear manufacturing process is that it adds quality deviations with every move of the component. Further, the traditional manufacturing line is not flexible. It´s made for a specific component, and the tools and machine tools are designed for this component. A broaching tool is not flexible; it’s designed for a specific component and cannot be used for any other component. A typical automotive broach has a delivery time of 16 to 24 months.

Upgrades are expensive, since the whole line of machine tools would need to be upgraded, and still, the decline of quality remains with every line production.

How can power skiving be used to produce ring gears more efficiently?

Power skiving together with internal/external turning in the same setup in a multitasking machine/machining center is the fastest growing machining method for ring gears. The small footprint, together with improved quality and component flexibility, are the main drivers.

What innovations does Sandvik Coromant offer for power skiving?

In tooling, Sandvik Coromant has three different types of solid tools: CM178H, CM178S, and CM178B.

The CM178H is a high-speed steel (HSS) tool with a module range of 0.5 mm-6mm (DP 50-5) that can be delivered as arbor or shank tools.

The CM178S is a solid carbide tool with a module range of 0.5 mm-5 mm (DP 50-5) that can be delivered as an arbor or shank tool.

The CM178B is a solid carbide shank tool, where the carbide grade can be optimized for each application with coolant supplied through the shank.

In addition to those, the CM180 is an indexable power skiving tool that can be delivered with a module range of 3.0-9.0 mm (DP 8-3).   

Together with those tools, Sandvik Coromant offers, for example, damped tool holders.

At Sandvik Coromant, each EV transmission producer or contractor can machine its own components with power skiving in modern multi-task machines without interference in a running production. At each Sandvik Coromant training center, skilled and experienced staff is ready to support customers’ investments to achieve productive, efficient, and flexible gear machining for EVs — all in one setup. As these trends show, the wider use of power skiving is now becoming a reality. 

MORE INFO  www.sandvik.coromant.com