Stator production – a complex processThe key elements of stator production are producing the winding and then drawing the preformed winding into the stator body. Various technologies are used for the winding process, including hairpin insertion and, more recently, flat wire wave winding. Depending on the application, the full stator production process also involves applying additional insulation prior to winding, applying cover strips, intermediate and final forming, and taping of the winding head.
For many manufacturers of electric motors, the name Elmotec Statomat is synonymous with their customized solution for the most complex and critical step in production – the manufacture of stators for energy-efficient e-motors. Users benefit from innovative, state-of-the-art technologies and the reliability of machinery built with decades of experience. All of Elmotec Statomat’s solutions have one thing in common: they are custom-tailored to meet the particular requirements of the motor manufacturer in question.
Anna Sadiku, responsible for sales and marketing, explains: “E-car motors need to be highly compact and light. They are also subject to stringent efficiency and energy density requirements. In the field of e-mobility – unlike the manufacture of industrial electric motors – all quality-related materials, process parameters and test results relating to each stator must be traceable. A stator without quality data is scrap! It cannot be approved for installation.” The fact that e-car motors generally require considerably shorter production periods than industrial motors complicates matters even more. The trend toward electromobility therefore demands flexible production facilities that can be switched over to new stator designs or design variants as easily as possible.
Challenge: flat wire
With the highest packing densities and copper space factors, flat wire and rectangular wire stators support efforts by car manufacturers to build highly compact and energy-efficient e-car motors. However, producing stators using rectangular wire requires mastery of significant additional technological challenges.
The wire must reliably lie on the designated side – usually the wider side of its profile. It must be guided as gently as possible so that the quality of the insulation, which is particularly exposed here, is not impaired by abrasion or breaks at the corners of the wire profile. Additional insulation reinforcement is also necessary at precise points on the wire, for example with Kapton tape, at points on the winding that are subject to particular mechanical stresses during operation. Due to the considerably denser structure of a winding made of rectangular wire, the maximum permissible manufacturing tolerances during each process step are also much stricter than when using round wire.
Bernhard Schnell, head of electrical design, explains what this technology means for machine building and electrical engineering design: “To ensure maximum repeat accuracy, complete documentation of the process, and simple switchover to new motor variants, we have taken a fundamental departure from mechanical cam disks, hydraulic positioning mechanisms, and ultimately also PLCs. Today, our entire control and drive technology for plants of this type are built on the Simotion motion control system; that, incidentally, now applies to 95% of our applications.
Even if, in an isolated case, motion control is not strictly necessary, we still benefit from the system’s high-level language capability and the flexibility of the servo technology. And – last but not least – from the drive-based safety functions of the Sinamics S120 drive controller, which is part of the motion control system. The system comprising Simotion control system and Sinamics drives considerably simplifies and expedites engineering work and reduces the invest.” The control quality and repeat accuracy achievable with integrated systems of this type is directly reflected in a high process quality and process reliability.
Motion control as a key technology
Today, the technology functions integrated in the Simotion control system handle complex tasks – for example, the control of constant wire drawing during winding when asymmetrically structured tools have a non-centered winding axis. Replacing the former wire drawing controller including the wire brake, motion control with Simotion generally suffices at Elmotec Statomat. As, however, the winder is controlled by Simotion, the system knows the current tool angle of rotation from the outset and at all times. This enables predictive, adaptive and constant wire drawing control – even at highly oscillating draw speeds. This, in turn, allows for faster winding, all to the benefit of throughput and quality.
Wave winding technology with rectangular wire
Elmotec Statomat has developed a model solution for the manufacture of e-car stators with rectangular wire using wave winding technology. In wave winding, several wires are wound onto the blade, which moves along one step for each winding. The winding formed on the winding blade is drawn off onto a linear magazine, from where it is transferred to a rotary magazine in several layers. This rotary magazine, together with the preformed winding, is guided into the stator body and expanded from the inside such that the windings are pushed precisely into the stator’s slots and compressed there.
“Every one of these process steps demands extremely tight tolerances – we’re talking about micrometers,” says Burkhard Schnell. “The individual coil windings need to be transferred to other carriers several times during production. That’s only achievable if all positioning actions are as exact and repeatable as possible in the process sequence. At the same time, the wire must not tilt or rub at any point. Thanks to Simotion motion control, we can realize all process steps with the required accuracy and offer an attractive product. In the process, all quality-related process forces are monitored, including drive data analysis. This allows us to prevent production of defective parts and supply the top-level MES system with all the data required for quality certification.”
Thanks to Simotion motion control, we can realize all process steps with the required accuracy.Burkhard Schnell, head of electrical design, Elmotec Statomat
Plant operation has also been updated, as Schnell explains: “With a view to e-car applications, we have updated our user software and in-house operator panel so that changes to new products are now primarily effected through software and parameter changes. The fact that we build the entire automation concept for a plant on a homogeneous automation system from a single source has also proven advantageous. It is, in other words, as simple as possible, without additional interfaces, and with Siemens’ established, high-quality and secure global supply of replacement components and service options.”
The adaptation of existing and new model variants of a motor family is already possible using recipe control in Elmotec Statotmat machines. It can be carried out directly by the set-up technician without the need to involve an engineer or developer. A true competitive advantage for the players in the e-mobility segment.