Lightweight is the focus of the auto industry as new fuel economy regulations loom on the horizon. The new standards mandate an average fuel economy of 54.5 miles per gallon for the 2025 model year. This increases the pressure on auto manufacturers to step up development of electric vehicles and improve mileage on all of their models through more efficient engines and lighter car parts.
For example, the Chrysler Group ZF-sourced TorqueFlite 8HP transmission has been installed in more than one million vehicles around the world. When compared with its 5- and 6-speed predecessors, the 8-speed automatic is estimated to save 700 million gallons of fuel over the lifetime of those one million vehicles, according to Chrysler. In addition, the auto maker expects a reduction in CO2 emissions by more than 6 million metric tons.
“Big V8 engines and big cars used to be in demand, but now CO2 efficiency, fuel efficiency and environmental compatibility are the most important factors,” says Dr. Andreas Mootz, managing director of EMAG Automation GmbH, Heubach, Germany.
On a hybrid car, for example, reduced fuel consumption means you have to integrate an electrical engine, the battery and power electronics,” Mootz says. “That requires weight and space, thereby creating a need to make the remaining components, such as those for the transmission, more efficient. You have to reduce weight and size to give room for these additional electrical components.”
With new materials and altered geometries, designers optimize the functionality of one part of the transmission – the gearwheels. “The lightweight trend creates a need for new materials, such as high-speed steels, because they allow us to design a gear that is less wide, for example,” Mootz says. “The overall size of the transmission shrinks. We used to use lower-strength steel, which is easier to machine and weld, but it doesn’t work anymore for the lightweight.”
Laser welding
While laser welding technology has been used in automatic transmission components, such as sun gears and planetary carriers, for years, the lightweight trend also means laser welding use is growing in other automotive applications.
One look at a typical gearwheel shows the manufacturing challenges involved. Even a small wheel with integrated synchronous gearing represents a relatively complex design.
To manufacture it efficiently and at the highest precision calls for the two components, the gear itself and the synchronizer used to transmit the torque through the transmission, to be machined separately first, followed by the joining and welding laser process that combines them,” Mootz explains.
Otherwise, it is typically mechanically joined, increasing part size and requiring more machining for that joining process.
Manufacture of the differential housing is another example of possibilities for the laser welding technology. Auto companies have been replacing the screw-type connection between the differential housing and crown gear with a welded seam. The result is the weight of the differential housing has been reduced by approximately 1.2 kg or 2.65 lbs. This process has been established for a while in Europe, and now American automakers are beginning to use it, according to Mootz.
Laser welding allows you to concentrate a carefully dosed amount of the energy emitted by the laser beam on the welding point, minimizing possible warping, while still achieving high welding speeds,” Mootz says.
Furthermore, the welding process from EMAG uses solid-state lasers, which makes it energy efficient. Whereas a classic CO2 laser achieves an efficiency factor of about 8 percent, EMAG solid-state lasers produce an efficiency factor of approximately 20 percent. In other words, the power used to achieve the same optical performance is noticeably less, with energy costs reduced.
However, each type of laser does have its benefits, depending on the application. Some materials are more prone to weld cracks with a fiber laser versus a CO2 laser. And fiber lasers can splatter more welding material.
Joining a gear and a synchronous ring using laser welding.
Making the station
Knowledge of the production processes used for many transmission components adds to EMAG’s competency in machine development. The EMAG Laser Cell (ECL) family of laser welding systems features compact laser machines that can be configured, on the basis of standardized platforms and their relevant modules, to form customized manufacturing systems.
The ELC 160 is a modular laser welding machine that can be configured to suit a variety of applications, such as driven gears, carriers and sun gears. At the heart of this machine is a 3-axis NC machining module. By adding process modules, such as assembly units, induction equipment for preheating, laser markers and gauges, a production solution is created using standardized modules. The ELC 160 also has auto-changeover ability, making it a flexible solution for part families.
The ELC 250 DUO is a compact laser welding system that features two spindles. The twin-station operation allows for cycle time concurrent loading and unloading of the work spindles. As the machining stations can be used independently of each other, this allows for simultaneous production of different components, such as differential housings.
The laser beam sources, combined with an optimized clamping technology, make for a welding process with little distortion, which is a precondition for quiet transmissions. The laser welding machine relies on a stationary beam control while the workpiece is transported to the various machining stations.
The work spindle uses the pick-up principle to load itself. The components to be welded are then clamped and pressed together in the joining press. The clamping technology used ensures the highly accurate positioning of the components for the welding process.
You always have to live with some tolerances introduced by the machining process in the welding process,” Mootz says. “With welding, you want to have very slim weld seams to reduce the amount of energy you put into the part. Additional energy means additional heat input and distortion, which adds additional tolerances to the finished part.”
But to do a slim weld, you have to hit the proper position for welding very accurately. It requires accurate positioning and precise workholding to reduce all the tolerance buildup. “If you have bad workholding, you cannot produce a very slim weld. The ELC systems allow that. It does not have a welding jig, but a precise workholding like machine tools use.”
Laser welding the differential housing and the crown gear has meant a weight reduction of 1.2 kg or 2.65 lbs for this assembly.
Machining area of the ELC 160 laser welding machine. On up to three stations, the gearwheel assembly is preheated, joined and laser welded.
Need for gears
EMAG Automation in Heubach has sold more than 50 ELC systems in the last decade. “We have a lot of know-how in the manufacture of these components. We understand the entire process, from turning and grinding and welding right up to the concluding ultrasound testing,” Mootz explains. “We can develop and construct the whole process chain. This significantly simplifies the planning of new production sites and the expansion of existing ones.”
The general market does play into the hands of the German machine builder. It is not only the successful dual-clutch transmission that ensures the need for more gears. Conventional transmissions also tend to have more speed gears, owing to the fact that the number of speed gears in many passenger cars is on the increase.
We are offering a well-proven welding technology that provides an energy-saving, high-precision manufacturing process and, at the same time, helps to advance lightweight construction and reduce production costs. This is no doubt a very successful and persuasive combination,” Mootz concludes.
The Mercedes-Benz GLA is one of many vehicles on the road today that are benefiting from laser welding technologies.
