Complete Machining Large-Scale Production of Stators

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NILES-SIMMONS- HEGENSCHEIDT GmbH

MAPAL Fabrik für Präzisionswerkzeuge Dr. Kress KG

FAULHABER Drive Systems

Wuxi InfiMotion Technology Co., Ltd.

Niles-Simmons and Mapal are bringing their jointly developed process for the complete machining of stator housings for electric motors into series production. Suppliers and OEMs can now efficiently manufacture components for electric and hybrid vehicles from major manufacturers.

In a development project, the two manufacturers have demonstrated that it is possible to produce stator housings very economically and with high precision on a pick-up turning machine. The thin-walled aluminum components are required for the drive in electric vehicles. They have ribs on the outside for the cooling circuit and are installed in the larger motor housings.

While Niles-Simmons had been working with a converted modular lathe during the development phase, a machine designed specifically for stator production was now launched on the market. The development was based on the vertical machining center of the Rasoma brand, which, like Niles-Simmons, is a brand of the NSH Group (Niles-Simmons-Hegenscheidt GmbH). Both brands are jointly organized in the NSH Group subsidiary NSH Technology and have jointly driven the development. The designation Rasoma DZS 400-2 indicates that it works with two workpiece spindles.

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For use in series production, the machine was equipped with a pick-up area for the raw parts and a drop-down area for the finished parts on the sides. The components are fed in and out via conveyor belts. For manual assembly, a buffer of ten to 20 components can be used via the automation system. This makes it possible to operate several systems while the employee can pursue other processes during production.

We have thus implemented the simplest automation as standard, for which no robots or barriers are required on the machine. The operator can place the parts directly onto a pallet conveyor.

Thomas Lötzsch, Sales Manager at NSH Technology

Fully automated workpiece loading and unloading of several machines with a central conveyor system is possible as an option. The machine can be easily integrated into an existing production environment, which is also helped by its relatively compact footprint of 7.50 meters × 2.60 meters (~25 feet x 8.5 feet). The basis for the design of the Rasoma DZS 400-2 was developed in collaboration with LTH Castings, a partner with many years of experience in the field of casting and a specialist in the machining of complex, high-quality and thin-walled components made of die-cast aluminum. The design thus took direct account of practical experience and user requirements.

Complete Machining in Two Set-Ups

Between pick-up and drop-down, the components are completely processed on the vertical machine in two set-ups. A clamping device first picks up the workpiece from above and moves it to various processing stations in the machine one after the other. At a reclamping station in the work area, the part is rotated by 180 degrees and picked up by the second workpiece spindle for finishing. During the second clamping, machining of the next component begins in parallel at the first fixture.

The processing steps follow one another like a miniature transfer line. The process begins with roughing the various internal diameters of the component. The tool stands still and the workpiece rotates.

Machining with a four-edged ISO boring tool on an HSK-A 100 spindle requires only a quarter of the main time compared to conventional turning with one cutting edge.

André Ranke, Regional Sales Manager at Mapal

The next machining step, in which the rotating stator housing is machined internally and externally simultaneously with four cutting edges each, is also extremely efficient. The inner tool also rotates. The cutting speed on the inner cutting edges is determined by the difference between the tool speed and the workpiece speed. The bell-shaped outer tool is stationary. For machining, the component is moved into the gap between the inner and outer tool. This patented process reduces the forces acting on the clamping device. In order to machine thin-walled components precisely, a complex workpiece clamping device with vibration damping can be dispensed with.

When designing the tool, particular attention was paid to the large chip volume and the high forces involved, as the inner and outer diameters are typically machined simultaneously.

Michael Kucher, Component Manager E-Mobility at Mapal

During finishing, only the fine boring tool is driven while the component is stationary. This prevents imbalances from occurring in the material due to non-rotationally symmetrical workpiece shapes and having a negative effect. The workpiece is then reclamped in the machine and the outer area that was previously clamped in the flange area is machined. The reclamping station can also be used for another purpose: The workpiece is placed here to relax the material before fine boring. The machine also has two tool turrets for driven tools, which carry out further machining operations as required by the component.

The bottom line is that the Rasoma DZS 400-2 combines the best of both worlds, namely the speed of turning for pre-machining the inner and outer contour with the precision of fine boring for finishing the inner contour.

Daniel Pilz, Project Leader at NSH Technology

The machine tool manufacturer and Mapal have contributed their respective core competencies to this complete solution. With the serialization of machine, tool technology and process, the good results of the prototype were improved even further. The process stability achieved even exceeded expectations, which is why the targeted cutting speed of 700 meters per minute (~2,300 feet per minute) could be increased even further.

The experience that Niles-Simmons brings with it from its wide range of technologies has a positive effect on the overall stability of the tool technology and machine in this aluminum machining process.

Michael Kucher, Component Manager E-Mobility at Mapal

The Rasoma DZS 400-2 achieves a significantly shorter chip-to-chip time than a milling machining center. This is due to the fact that all tools are already in the working area and are only brought into working position by swiveling the turret disk. This eliminates all tool changes, which significantly reduces non-productive times. With the technology described, a cycle time reduction of 50 percent compared to standard turning was already expected in the studies. The increase in cutting speeds to 1,000 meters per minute (~3,300 feet per minute) using the most suitable cutting materials and the optimization of non-productive times resulted in a further 20 percent time saving.

The process is so stable that random sampling is sufficient for quality assurance. Whereas initially all manufactured components were measured, the recommendation is now only one part per shift. Daniel Pilz proves that this is more than sufficient with figures: "The Rasoma DZS 400-2 with the special tools from Mapal achieves a process capability index of over 1.67 for critical features such as cylinder shape, diameter and concentricities and therefore meets the industrial specifications." Customers who are already using the machine achieve an annual output of up to 180,000 produced components in three-shift operation.

Successful in Large-Scale Production

One of the first users of the series process for stator production on the Rasoma DZS 400-2 is LTH Castings in Slovenia. The long-established foundry company has more than 100 casting cells and processes the raw parts on more than 250 CNC machining centers. Around 3,800 employees work at a total of six locations.

With our all-in-one solutions from design to series production, we are an important strategic partner to the automotive industry. Our range of parts includes components for transmissions, motors for battery electric and hybrid vehicles, steering and braking systems.

Dr. Primož Ogrinec, CTO at LTH Castings

The Rasoma DZS 400-2 machines are loaded and unloaded by robots in the ultra-modern production facility.

Like most automotive suppliers, LTH Castings manufactures components for various vehicle models. The flexibility of the Rasoma DZS 400-2 is helpful in the production of stator housings, where only clamping devices and tools need to be converted. "With a single system and using the new process, an optimum solution was developed for the specific manufacturer in terms of both quantity and quality and made ready for series production," explains André Ranke. The production of stator housings is now possible up to a diameter of 500 millimetres and a component length of 500 millimetres (~20 inches).

The Rasoma DZS 400-2 can be used to produce all the housings we have seen so far, and we have already seen a great many.

Thomas Lötzsch, Sales Manager at NSH Technology

The project team was in for a surprise when an undercut on the inside of the component was required for the housing design of a major car manufacturer. The sample component from Mapal, which was specially designed and manufactured for the process design, did not present this challenge. However, Mapal and the specialists from the NSH Group very quickly came up with a joint solution: instead of the tried and tested fine boring tool, a high-precision actuating tool with four slides from Mapal's product portfolio was used to produce the required internal contour. On the machine side, an interface coordinated with Mapal was designed in just a few days, which was ready for series production during the current order. Thanks to the now very closely networked development design, the two companies are able to react quickly to newly developed contours.

New Benchmark for Low Cost per Part

The Rasoma DZS 400-2 with tool technology from Mapal has established itself for series production and solves quality problems that occur on conventional turning-milling machines and horizontal transfer lines. Thomas Lötzsch is aware of cases in which the required shape and position tolerances were not reliably achieved and rejects were produced instead - up to 50 percent. Where the quality was right, the cycle times left a lot to be desired and resulted in higher workpiece costs. There was no established process for manufacturing the components.

Because there is a tough price war among automotive suppliers, the development of the Rasoma DZS 400-2 focused on the lowest possible unit costs right from the start. This goal was achieved through the combination of high machine availability, short cycle times, quality of the machined components and reliable production processes. According to current calculations, this means that a particularly economical cost per part can be achieved for machining, including tool costs.