Stator machining innovation ready for series production

Daniel Pilz (project leader NSH Technology) with the Mapal sample component, André Ranke (­Mapal regional sales manager) with a fine boring tool and Thomas Lötzsch (sales manager at NSH Technology) with a customer component. Picture courtesy of Mapal

A new benchmark in electric motor component manufacturing has been set by a collaboration between Chemnitz-based machinery manufacturer Niles-Simmons and precision tool specialist Mapal.

Their jointly developed process for machining stator housings has now transitioned from prototype to full-scale series production, offering suppliers and OEMs a highly efficient solution for producing critical components used in battery-powered and hybrid electric vehicles (HEVs). The stator housing, a thin-walled aluminium part with external ribbing for cooling, plays a vital role in the motor assembly and demands exceptional precision and structural integrity.

The breakthrough came during a development project where both companies demonstrated that complete machining of stator housings could be achieved cost-effectively and with high precision using a pick-up lathe. Initially, Niles-Simmons adapted a modular lathe for the task, but the success of the project led to the creation of a dedicated machine: the RASOMA DZS 400-2. This vertical machining centre (VMC), developed under the NSH Group umbrella, features two workpiece spindles and is designed specifically for stator housing production. Its compact footprint and modular automation options make it ideal for integration into existing production environments.

Pictured right: the difference in the tool speed and the workpiece speed produces the cutting speed at the inner blades. The bell-shaped outer tool stands still

The machine’s design reflects practical insights from LTH Castings, a long-standing partner with expertise in machining complex aluminium castings. Raw parts are fed into the system via a pick-up area, and finished components exit through a drop-down zone, both connected by conveyor belts.

Operators can manually load parts onto pallet belts, eliminating the need for robotic systems, while optional full automation allows for centralised loading and unloading across multiple machines. This flexibility enables manufacturers to scale production efficiently while maintaining high throughput.

At the heart of the process is a two-stage clamping system that enables complete machining in a single setup. The first spindle picks up the workpiece and guides it through several machining stations. Once initial operations are complete, the part is rotated 180deg and transferred to the second spindle for finishing. This simultaneous dual-spindle operation mimics a miniature transfer line, significantly boosting productivity.

The machining sequence begins with pre-roughing of the inner diameters using a four-blade ISO boring tool mounted on an HSK-A 100 spindle. According to Mapal’s André Ranke, this method is four-times faster than conventional turning. The next step involves simultaneous machining of the inner and outer surfaces using a patented tool system. The inner tool rotates while the outer bell-shaped tool remains stationary, with the stator housing positioned between them. This configuration reduces clamping forces and eliminates the need for vibration-damping devices, which are typically required for thin-walled components.

During the final finishing stage, only the fine boring tool is driven while the workpiece remains stationary. This approach prevents imbalances caused by non-symmetrical shapes and ensures high precision. Before this step, the component is briefly placed in the re-clamping station to allow the material to relax, further enhancing accuracy. The machine also features two tool revolvers equipped with driven tools for additional operations tailored to specific component requirements.

This innovative machining solution not only meets the stringent demands of electric vehicle production but also sets a new standard for efficiency, flexibility, and precision in aluminium component manufacturing. With its successful deployment in series production, the RASOMA DZS 400-2 is poised to become a cornerstone in the evolving landscape of e-mobility manufacturing.

The RASOMA DZS 400-2 has entered series production with a clear mission — to redefine the machining of stator housings for electric motors in the age of e-mobility. Developed through a close partnership between NSH Technology and Mapal, the machine combines high-speed turning with precision boring in a compact, automated VMC. The result is a process that not only meets the demands of modern automotive suppliers but also sets new standards for efficiency, reliability and cost-effectiveness.

Daniel Pilz, project leader at NSH Technology describes the machine as a fusion of speed and precision, where rapid pre-machining of inner and outer contours is followed by fine boring that delivers the required accuracy for critical features. The collaboration between the machine tool manufacturer and the tooling specialist has yielded a complete solution that has evolved beyond its prototype origins. With the machine, tool technology and process now fully serialised, performance has improved significantly. Cutting speeds that initially targeted 700m/min have been surpassed, thanks to the robust process reliability and the technological depth brought by Niles-Simmons.

The RASOMA DZS 400-2 achieves a chip-to-chip time far shorter than conventional milling centres. All tools are pre-positioned in the working area and brought into action by swivelling the revolver disc, eliminating the need for tool changes and slashing non-productive time. Studies had already predicted a 50% reduction in cycle time compared to standard turning, and further optimisation has pushed cutting speeds to 1,000m/min with the right cutting materials. Furthermore, additional refinements in non-cutting operations have delivered a further 20% time saving.

Pictured left: once the component has been turned, while OP 20 is being performed at the second spindle, OP 10 for the next stator housing can begin at the first spindle

Such process reliability has transformed quality assurance practices. Where every component was once measured, the system now requires only one part per shift to be inspected. Pilz points to a process capability index of over 1.67 for key characteristics such as cylinder shape, diameter and concentricity—well above industry requirements. In full production, customers are achieving annual outputs of up to 180,000 components in three-shift operation, a testament to the machine’s scalability and consistency.

One of the first adopters of the serialised process is LTH Castings in Slovenia, a company with deep expertise in aluminium casting and machining. With over 100 casting cells and 250 CNC machining centres across six sites, LTH Castings is a strategic supplier to the automotive industry, producing components for electric and hybrid drives, as well as steering and braking systems. In their advanced production facilities, the RASOMA DZS 400-2 is fully integrated, with robotic loading and unloading ensuring seamless operation.

Flexibility is a key advantage of the system. For suppliers like LTH Castings, who serve multiple vehicle platforms, the ability to retool clamping devices and tools allows for quick adaptation to different stator housing designs. Mapal’s André Ranke highlights how the process has matured into a manufacturer-specific solution that supports stator housing production up to 500mm in diameter and length.

The machine’s versatility was further demonstrated when a major OEM introduced a housing design with an internal indentation. Although the original sample component did not include this feature, Mapal and NSH Group responded swiftly, replacing the standard fine boring tool with a high-precision actuating tool featuring four slides. A compatible machine-side connection was developed within days and reached series maturity during the ongoing order, showcasing the agility of the development partnership.

The RASOMA DZS 400-2 has now firmly established itself in series production, solving quality and efficiency issues that have long plagued conventional turning and milling machines. Thomas Lötzsch of NSH Technology recalls instances where shape and position tolerances could not be reliably achieved, resulting in scrap rates of up to 50%. Even when quality was acceptable, cycle times remained inefficient, driving up per-part costs. The lack of a robust, repeatable process was a major barrier to competitiveness.

In a market where price pressure is intense, especially among automotive suppliers, the development of the RASOMA DZS 400-2 focused on minimising unit costs from the outset. This goal was achieved through a combination of high machine availability, short cycle times, consistent component quality and reliable processes. Current cost models confirm that machining with this system, including tooling expenses, delivers competitive per-part costs. The machine has not only met expectations — it has set a new benchmark for efficient, high-volume stator housing production in the EV era.