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How Electrification Affects Manufacturing of Transmissions

Without a doubt the automotive industry has seen very challenging times recently. Considering the revolutionary electrification of the automobile powertrain, requiring a paradigm shift of OEMs and suppliers, it is probably the most challenging time within its history.

Despite increasing popularity of Battery Electric Vehicles (BEV), which commonly utilize rather simple transmissions, there are many indicators that hybrid technology will serve as the dominant powertrain for the foreseeable future. In light of ever tightening regulations and the push to abandon fossil fuels to reduce carbon emissions, Internal Combustion Engines (ICE) and transmissions need to evolve to prevent another "ICEage." Besides interesting developments like synthetic fuels and hydrogen-based concepts, the electrification of the powertrain will play a major role in this evolution. The result will be a large variety of diversified hybrid powertrains used in modern automobiles for decades to come. A key element within this development will be Dedicated Hybrid Transmissions (DHT).

While there are numerous versions of DHT, many of them share a few key components including high precision pinions and newly developed hollow shafts. While these workpieces are not entirely new to OEMs and suppliers, the increasing requirements are asking for new cost-efficient manufacturing solutions. Noise, vibration and harshness (NVH) requirements, overall quality, and changing production criteria like smaller lot sizes and higher mix of variants are just a few of the challenges. "Fortunately, innovative machine tool builders like Bahmueller Technologies, Inc. recognized this trend and developed new solutions to overcome these challenges," said a company spokesperson.

Pinions, for example, have been produced and used in conventional automatic transmission for many years. But the increasing variety of transmissions like DHT requires a more flexible manufacturing approach. The traditional production method often separates the grinding and honing process, which in turn requires more machines, workpiece handling, part buffers, floor space and more operator intervention, which may result in an inferior quality product and higher cost per piece.

Following the principle of lean manufacturing, Bahmueller has developed a solution that finishes the bore and faces of pinions in a single in-line grinding and honing cell. The workholding is specifically designed to clamp the part in the pitch line of the gear teeth, minimizing the stock allowance for the final gear teeth finish operation. "The in-line pinion cell from Bahmueller increases the flexibility of our whole value chain and allows us to easily scale production and accommodate customer requirements," said a transmission OEM spokesperson.

Another key component often found in DHT is the hollow shaft. Bahmueller's solution for this workpiece is centered around a special workholding, called mid-clamping, that chucks the part in the middle, allowing operators to grind the exposed sides of the workpiece simultaneously using two independent tools. The first operation is the I.D. grinding of multiple diameters in combination with face grinding. The second operation is performed subsequently in the very same clamping and consists of O.D. grinding a journal and a shoulder while finish grinding another I.D. feature at the same time. After this the workpiece is unloaded via the integrated robot, a new part is presented to the chuck and the cycle repeats. "By going from rough to finish in a single clamping in conjunction with using a smart robot inside the ULTRA grinder, we significantly improved the flexibility of our grinding process," said a Bahmueller customer.

This ULTRA machine is customized specifically for the grinding of hollow transmission shafts featuring an array of one O.D. and three I.D. grinding spindles on independent slides controlled by six CNC axes. Automated post-process gauging of the finished workpiece with a closed loop feedback to the machine ensures trend correction and reduces the need for any manual SPC. Multiple high-frequency dressing units with acoustic emission technology allow for automatic conditioning of all grinding wheels. The machine concept and Bahmueller's extensive experience with super abrasives like cubic bore nitride (CBN) yield higher performance and reduce the cost per part even further. Utilizing a single clamping ensures perfect geometry, especially the runout between the I.D. and O.D. features of the workpiece. And by finishing all grind operations of the hollow shaft in a single machine, Bahmueller provides customers with a solution that is easily scalable and offers flexibility even for smaller batch sizes.

Bahmueller incorporates the latest technology such as direct drives, linear motors, polymer concrete base and connectivity for Industry 4.0 features which, in conjunction with state-of-the-art automation and gauging, enable lights-out manufacturing in the factory of the future.

Authored by Bahmueller

For more information contact:

Bahmueller Technologies, Inc.

10815 John Price Rd, Suite A

Charlotte, NC 28273

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