Transmission machining

Features - Cover Story

Power skiving, new insert grades, and advanced turning techniques can boost production of electric vehicle (EV) transmissions.

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Power skiving, with tools such as the CoroMill 180 indexable power skiving cutter, enables all machining to be carried out in one single setup.
Photo credits: Sandvik Coromant

The definition of insanity is repeating the same action and expecting better results. This could apply to machining gear components, around which the landscape is changing and demand for cost-reduction is rife. With gear machining, manufacturers want more flexibility, but achieving this while reducing costs is not straightforward. Traditionally, projects that involved machining gears would depend on special machines and processes, especially in mass production. This means limitations – and often higher costs – in the production process.

Harish Maniyoor, global product manager for automotive at Sandvik Coromant, explains new ways of machining transmissions that can help manufacturers do more with less, making getting beyond these limitations possible. Moreover, these advantages go beyond automotive into areas such as general engineering, wind power, aerospace, and robotics.

Power skiving

A rotary cutting technique where the tool meshes with the gear being made, power skiving is a continuous cutting process enabling all machining to be carried out in a single setup. It combines hobbing and shaping, and the intersecting angle between tool and gear axis and the revolution speed is decisive for productivity.

Power skiving has been around for more than 30 years. However, it’s becoming more important as the machining landscape changes with new products such as transmissions for electric vehicles (EVs).

Originally it was thought EVs didn’t need multiple gears or transmissions. However, this view has changed, and Tesla and Porsche are rolling out multi-gear EVs. Electric motors achieve much higher revolutions per minute (rpm) than conventional cars – 20,000rpm in electric motors versus 4,000rpm to 6,000rpm in conventional combustion engines. A reduction gearbox makes these rpms more manageable.

EV transmissions also must be hard-wearing to withstand higher rpms and are tougher to machine as a result. Less obvious is that manufacturers producing these parts must focus on the metal removal rate, which expresses the speed of machining the workpiece.

Another major demand for EV transmissions is lower noise from the gearbox, since there’s no noise from the engine. This means producing components with tighter tolerances which entails more challenging machining.

So, the question for machine shops should be: Is it fast productivity you’re looking for, or something else?

Such agility can’t depend on traditional transmission manufacturing processes. Instead, power skiving makes it possible to machine the complete component in a multitasking machine or machining center in a single setup. This shortens production time, improves quality, and reduces handling and logistics costs.

Sandvik Coromant demonstrated the advantages of power skiving when they supplied a large automotive customer in Sweden with component machining solutions. Working with the customer’s automotive development team, the project proved that power skiving is possible with two 5-axis machines, using Sandvik Coromant’s CoroMill 180 indexable power skiving cutter, a tool designed for high-output gear and spline production.

The customer had demanded 14 minutes-per-component cycle times but was able to machine parts in less than 1 minute.

Furthermore, Sandvik Coromant’s research shows that a 20% increase in machine utilization can provide a 10% higher gross profit margin.

Maximized output

Achieving these benefits requires more than using the CoroMill 180. A wider ethos is also needed which is where PrimeTurning comes into play.

PrimeTurning methodology is based on the tool entering the component at the chuck, and removing material as it travels toward the end of the component – prioritizing metal removal rates. This allows for smaller entry angles, higher lead angles, and higher cutting parameters. Conventional machining can be performed with the same tools, so machine shops can alternate traditional and new processes.

Some applications could realize more than 50% productivity increases with PrimeTurning. This is aided by CoroPlus Tool Path software which supplies programming codes and techniques to setup parameters and variables that maximize output.

Whether the answer lies in power skiving, new carbide inserts, or PrimeTurning, these new machining methods can deliver improvements to manufacturers’ processes and their bottom lines. Machine shops can break away from doing the same old thing and ensure the price of change really is worth it.

Sandvik Coromant
https://www.sandvik.coromant.com

Transmissions for electric vehicles (EVs) must be hard-wearing to withstand higher speeds, and are tougher to machine as a result.