Machining EV transmissions

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Skiving cutter sharpening from ANCA supports precision gears needed for next-generation power transfer.

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Skiving cutters required for internal gear teeth cutting for electric vehicles (EVs) can be tougher to sharpen than traditional gear cutters.

Fossil-fueled cars may soon become a part of history. Many countries have set a deadline for ending the sales of fossil-fueled cars: France by 2040, the U.K. by 2030, and Norway aims to become the world’s first country to achieve this by 2025. Responding to green initiatives, and after investing billions of dollars into vehicle electrification, the automotive industry’s giants are pledging to stop making old fashioned internal combustion engine (ICE) vehicles. Volkswagen plans for 25% of sales to consist of electric cars by 2025. General Motors (GM) aspires to stop making gasoline-powered vehicles by 2035, and Ford (Europe division) will go entirely electric by 2030.

For cutting tool manufacturers serving the automotive industry, this electric transformation is an existential challenge and a revolutionary opportunity. In 2017, 11.8% of cutting tool consumption was for automotive manufacturing. Machining time for pure electric vehicles (EVs) is estimated to be up to 75% less than for traditional ICEs, resulting in overall cutting tool consumption decline as ICE vehicles’ production ceases.

Declining demand for cutting tools is a substantial threat, especially for cutting tool makers that depend heavily on the car industry. Meanwhile, EVs are providing many opportunities as the new skiving cutters required for their internal gears are significant.

Nearly half of all gear production (45%) is for vehicle transmissions. EVs have changed the gear industry’s requirements as engine speed up to 20,000rpm means a higher gear ratio is needed to reduce speed for efficiency. The planetary gear system is more prevalent in new transmission designs. In a planetary gear set, the external gears need to be ground, which the current production process of hobbing and then grinding can easily handle. The problem is with the internal ring gear. Traditionally, internal gears are produced with shaping or broaching; shaping is slow, while broaching relies on cumbersome tooling.

For EVs, efficiency – as well as noise emission – is a much higher priority for customers. Gears for EVs require greater precision and higher performance. The quality needs to increase from DIN 10 to DIN 6 for the internal gears; the gear industry sees hard skiving as the revolutionary process to produce the millions of internal ring gears needed for EVs.

Driven by EVs’ 28%-to-36% growth rate, the skiving cutter used in the skiving process is in high demand. Due to its complex geometry, producing solid carbide skiving cutters requires a series of technology and process developments. Released in 2019, ANCA’s GCX Linear provides a complete solution for manufacturing DIN AA quality solid carbide skiving cutters – the highest in the industry.

Skiving cutters are classified as a pinion cutter, consisting of the flank and rake face. After the flanks are produced, resharpening only grinds back the rake face. These tools are expensive and designed to have a long tool life, typically 6mm to 10mm of resharpenable depth. During resharpening, the rake face is ground back by 0.3mm to 0.5mm each time, depending on the level of damage. There can be as many as 50 resharpenings during the lifetime of a tool. Following the growing trend of EVs, there could be a need for hundreds of thousands of skiving cutters by 2024, which will equate to more than 1 million sharpenings.

To enable ANCA customers to tap into this fast growing market, ANCA released a new software package to sharpen skiving cutters and shaper cutters. Customers with MX and TX machines only need to purchase a software update and replace the standard probe with a ruby probe tip.

In the ToolRoom software package, the pinion-type cutter sharpening option contains operations for digitizing and sharpening two rake face styles: stepped rake face and conical rake face.

A conical rake face is part of a conical surface, defined by a rake angle and intersection with the flank to form the tool’s cutting edge. Sharpening a conical rake face requires an operation to digitize the end of the tool position, then regrind the conical surface with a 1A1 wheel. There is a plunge grinding method for the initial heavy grinding and oscillating grinding styles for subsequent resharpenings.

Photos credit: ANCA

A stepped rake face is a planar surface defined by a rake angle and a lead angle. To resharpen stepped rake face, finding and aligning with the tooth’s accurate index position is critical. ANCA software calculates the correct geometry to guide the ruby probe to find the right position. The process is automated, with no need for particular alignment and manual intervention. Sharpening the rake face plane takes place on one tooth at a time, either with a 1A1 wheel for speed or a cup wheel for improved surface finish.

The resharpening package is available for MX and TX machines. With minimal hardware change, the MX can accommodate tool diameters up to 105mm. The TX has a larger working envelope and more robust build, fitting a tool diameter up to 240mm. Hub-type and disk-type cutters can be mounted onto the collet with a fixture. The shank-type cutters can be clamped directly in the collet or with an adaptor for Morse taper.

This package is also a desirable solution for gear manufacturers who look to resharpen these tools regularly in-house.

ANCA https://machines.anca.com