A Long Journey from the First Hair-pin Stator Line to Continuous Flow Winding

Edoardo Freschi, EV-Traction Sales Director, IMA EV-TECH

It was early in 2009 when ATOP started developing the first fully automatic line to produce hair-pin stators. Being a medium-sized company and not having, at that time, the capacity to support such a wide range of solutions, it was necessary to make a choice between the well-known, state-of-the-art coil insertion technology or exploring the brand-new copper bar technology with a pioneering approach. With a focus on the future, the choice was to explore this new territory and today we can say the decision was the right one.

As has always been the case in over 30 years of IMA EV-TECH – ATOP history, process equipment must preserve some of the unique characteristics that have always distinguished our machines: they must be innovative, flexible and compact in design.

The main focus was on hair-pin forming process, considered the true key to the success of this new solution. The innovation requirement was met through the introduction of a CO₂ laser for enamel removal on the wire combined with a fully programmable 3D forming robot used to bend copper wire. This solution perfectly matched the second prerequisite of flexibility. In fact, like for the pin forming, all machines in the line had to be suitable for different products with varying dimensions, slot geometries, and conductors per slot.

The application of QCO (Quick Change Over) technology to the new machines in stage of development, appears as a perfect combination. New machines are born with the natural predisposition to receive different sets of tooling for different products. The idea was to have a complete tool installed in the machine with fixed references,requiring no fine-tuning or adjustments to start production. Given the high value of EV motor components, it was defined that, after all quality checks, the first part produced must be a good part. The presence of electric axes to control all process functions definitively helped engineers in their work.

With the experience gained in the electric motor manufacturing field, it was considered an added value to approach the third pre-requisite: compact design. We integrated the electrical and pneumatic cabinets inside the machine frame. Further on, we had chance to learn how automotive industry standards were different in this field. While Tier and Tier 2 customers accepted this solution, OEMs required a more conventional external electrical cabinet. To satisfy both philosophies, today both configurations are available.

In over 15 years of experience with copper bar stators for e-Mobility applications, we have grown our experience thanks to the scientific approach always applied even through a close cooperation of our R&D with universities. Nonetheless, events and reaction of the copper that initially appeared to be inexplicable, have gradually found their explanation. Experience taught us to define the copper “the alive material” because, like a chameleon is capable to change his characteristics so quickly and sometime without any apparent reasons.

Welding is keen while producing the hair-pin technology. From the very beginning the idea to use a mask to align the couple of wires was developed and applied. This solution was later abandoned in all those cases of high slot numbers and small diameters. Where it was preferred clamping by gripper. Today, the alignment by mask is made using a three-effect mask that allows to make tangential and radial wires alignment while providing axial containment. The new mask, thanks to its reduced thickness, perfectly meets the needs of extremely short wire leads, those known in Asia as “minipins”. This is not a novelty, since we already have high-capacity lines in serial production with wire terminals below 6 mm in straight path.

The current state of the art is the ATOP machines generation that represent the fourth generation of machines developed for hairpin stator technology. Maintaining the original pre-requisites, achievements of this latest generation, are the condensation of all experiences matured in those year, with higher process speed and productivity.

What about the future of e-mobility motor design? It is a widely shared opinion that hair-pin stators may represent a transitional solution toward a simpler and more cost-effective process.

Here at IMA EV-TECH, we continue to monitor developments and, just as we did 15 years ago, try to explore possible alternatives. Wave winding, as it stands today, presents clear limitations in terms of motor design constraints, lack of process control, cost, floor space occupation of the production lines and difficulties in achieving a fully automated process.

An interesting alternative to traditional wave winding is the CFW solution, acronym for Continuous Flow Winding. This technology was developed to meet the requirement of the motor from MAVEL. This already solved most of the criticality typical of a wave winding:

• Closed-gap inner diameter, because the insertion is made from outside
• Helicoidal slot profile, offering a well-distributed magnetic flow distribution and helps tremendously on having in a smooth wire insertion process
• Small waves development, that leads to compact footprint equipment. A complete line having the floor space occupation similar to an hair-pin stator line
• Low-height copper headers outside the slots, with crown height contained below 24 mm thanks to outer-slot insertion

Applications with Litz-wire have been developed in recent years, with flexible conductor used to wind single poles stators as well as rigid bars for hair-pin production. It is hard to define what the future will bring, but one thing is sure: IMA EV-TECH will be there supporting the growth of our customers.

Safe and Sustainable-by-Design: Setting New Standards for EV Coolants

Dr. Sander Clerick, Development Chemist, Arteco

The automotive industry is rapidly shifting to low- and zero-emission solutions. Electrification, including hybrid, battery, and fuel cell electric vehicles (EVs), is driving innovation in powertrain and thermal management systems. Moving away from internal combustion engines is crucial to reducing greenhouse gases, air pollution, and their impact on the climate. With transportation accounting for ~28% of global emissions, reducing its impact is essential to achieving global decarbonisation.

Effective thermal management plays a key role in maximising performance and durability. Arteco develops high-performance engine and electric vehicle coolants designed to meet strict safety and environmental standards, with a focus on long-term durability. These formulations are specifically engineered for modern vehicle systems where thermal control is essential.

By applying safe and sustainable-by-design (SSbD) principles during R&D, Arteco ensures its solutions are aligned with future environmental and regulatory standards. This approach balances technical expertise with human and environmental safety, supporting the industry’s shift towards sustainability. The introduction of specialised product ranges marks a significant step forward, setting a new benchmark for minimising environmental impact by embedding safety and sustainability at the heart of product design.

Safe-by-Design

Water–glycol-based engine coolants are widely used in electric vehicles for indirect liquid cooling. Their excellent heat transfer properties, proven automotive performance, compatibility, and ease of handling make them a commercially preferred solution for thermal management. In EV systems, the coolant is physically separated from electrical components, often by using a battery bottom cooling plate, to ensure safe and reliable operation.

For demanding scenarios such as fast charging, the industry is trending towards increased battery-to-coolant integration. Closer contact between the fluid and battery, with higher heat exchange surface, enhances thermal management by improving heat transfer efficiency. As a result, the coolant’s electrical properties become increasingly critical. Traditional engine coolants, while robust and corrosion-resistant, typically have electrical conductivities between 2.000 and 10.000 µS/cm. If leakage occurs within the battery pack, this level of conductivity can pose a serious electrical safety risk. Eects can range from external short circuits triggering rapid battery discharge to internal cell Damage and even thermal runaway if the situation is not properly managed.

To address this challenge, there is a growing focus on dedicated EV coolants that not only deliver thermal performance and material compatibility, but also fulfil a safety-critical function throughout the product’s lifecycle.

Recognising this need early, Arteco’s pioneering work led to the development of Freecor® EV Milli coolants with low electrical conductivity, specifically designed to enhance the safety of battery systems.

To demonstrate the eect of coolant leakage into battery cells, Arteco collaborated with leading academic research institutions and independent specialised testing institutes to conduct controlled abuse testing. The experimental setup (Figure 1) featured a 57 Ah Li NMC prismatic cell at 100% state of charge (SoC), partially submerged in water–glycol coolants of varying electrical conductivity. A 1 cm gap was maintained between the battery’s negative terminal and a copper busbar, across which a 400 V potential was applied, simulating a worst-case short-circuit event at the pack level.

When exposed to a conventional engine coolant (pink, 5.000 µS/cm), the system immediately exhibited short-circuit behaviour. The coolant boiled locally at the electrode, and electrical arcing was observed. Battery surface temperature rose rapidly, to levels potentially initiating thermal runaway. The combined effects of hydrogen generation via coolant hydrolysis and electrical arcing created a severely hazardous scenario within a very short timeframe.

In contrast, testing with a low-conductivity coolant (blue, 100 µS/cm) demonstrated substantially improved safety characteristics. Electrical arcing was entirely suppressed, and the battery surface temperature increased only gradually under identical abuse conditions. While hydrogen evolution could not be fully prevented due to the high applied voltage, the overall risk profile was significantly reduced. This delay in escalation provides critical time for users to evacuate and for emergency responders to intervene.

In light of these findings, industry standards have begun to impose stricter limits on electrical conductivity. For example, ASTM D8566 specifies a maximum electrical conductivity of 100 µS/cm for fresh coolants used in battery Electric vehicle applications. A significant regulatory step was taken with the implementation of China’s GB29743.2 standard in October 2025. This regulation mandates that as-supplied coolants used in newly developed vehicle platforms in the People’s Republic of China must not exceed 100 µS/cm, particularly for systems using water–glycol battery cooling.

Maintaining low levels of electrical conductivity, a parameter often overlooked or insufficiently emphasised in existing specifications, is essential to ensure system robustness. During controlled atmosphere brazing of aluminium components, such as radiators, cold plates, and other battery cooling structures, brazing aids and fluxes leave behind ionic residues on internal surfaces. Once the cooling system is assembled and filled, these residues dissolve into the coolant as residual salts, leading to a sharp increase in electrical conductivity. If the coolant is not specifically formulated to counteract this effect, the resulting conductivity spike may compromise the intended safety improvements (see Figure 2, 300 µS/cm).

Freecor® EV Milli technology resists such electrical conductivity spikes upon contact with brazed aluminium surfaces (Figure 3). Ist formulation helps maintain the initial safety benefits by stabilising conductivity levels, ensuring continued electrical insulation throughout the vehicle’s operational life.

Sustainable-by-Design

While EV-specific coolants are developed to meet safety and performance requirements, Arteco has gone further by addressing their climate impact. Recent life cycle assessment (LCA) studies show that the most significant climate Impacts associated with coolants are largely attributable to raw material extraction and end-of-life treatment. In response, Arteco has prioritised resource efficiency in its development strategy, leading to the creation of the Freecor® EV ECO coolant range.

Freecor® EV ECO coolants incorporate base fluids linked to bio-based or recycled feedstocks, allocated via a certified mass balance approach. This method enables the integration of alternative raw materials into existing production systems, while ensuring full traceability and third-party certification across the supply chain. The base fluids used, Monoethylene Glycol (MEG) or Monopropylene Glycol (MPG), are traditionally virgin-grade materials linked to fossil resources. The Freecor® EV ECO product line helps reduce reliance on virgin fossil resources. To confirm the traceability and reliability of this process, Arteco has received the International Sustainability and Carbon Certification (ISCC) PLUS certification for its mass balance approach towards bioeconomy and circular economy.

The benefits of the ECO coolants are reflected in their significantly reduced Product Carbon Footprint (PCF) compared to their traditional virgin fossil-based equivalents.

Arteco’s strategy involves identifying a strong supplier network capable of meeting stringent sustainability and quality standards. Sustainable sourcing plays a central role in this strategy, supported by thorough evaluation of all Input materials to ensure coolant performance and reliability are never compromised.

Interpreting environmental data remains inherently complex, particularly in quantifying carbon savings. Variables such as feedstock origin and methodological assumptions can substantially influence the outcome of impact assessment. To strengthen data quality and transparency, Arteco collaborates with accredited external partners to develop a scientifically grounded, reliable database of product environmental information.

Developing sustainable coolants is a shared responsibility across the value chain. A proactive strategy focused on climate action, responsible resource use, and stakeholder collaboration is essential to achieve meaningful progress.

Arteco’s advancements in EV coolant technology contribute to the evolution of safe, sustainable mobility. Its solutions specifically designed for indirect liquid cooling in EVs, address the industry’s increasingly stringent safety and performance requirements. With the introduction of ECO coolants, Arteco is raising the bar for decarbonisation eorts across the entire value chain.

Disclaimer: Statements regarding environmental benefits, CO reductions and other sustainability-related performance characteristics of the product(s) referenced herein are based on recognised scientific evidence and internal and/or external data available to us at the time of publication. Actual environmental performance may vary depending on use, conditions, and context. Supporting data and methodology are available on request (info@arteco-coolants.com). This information is provided for transparency purposes and does not constitute a guarantee of performance in all circumstances.

Effective Solutions for Bearing Insulation to Prevent Electrical Corrosion in E-Drive Systems

Philippe Pauchard, Application Engineers at DuPont (Switzerland)
Christoph Berger, Application Development Manager, DuPont (Germany)
Ruth Jackowiak, Application Engineers at DuPont (Switzerland)

The automotive industry is progressing toward high-voltage systems for electric vehicles (EVs) with enhanced efficiency. Reliable and durable components are increasingly critical, particularly bearings in electric motors, which can suffer from electrical erosion due to parasitic currents, causing significant damage and premature failure. This challenge is addressed by using insulation provided by DuPont™ Vespel® polyimide parts.

Vespel® polyimide insulating bearing sleeves

Vespel® S is a sintered polyimide which has no observable glass transition temperature or melting point. Its high-temperature resistance allows it to be used as an insert in die-cast aluminum parts. Its unique property is key for applications where high loads and elevated temperatures can occur, as may be the case in traction motors in critical drive modes or in the case of malfunction.

Vespel® polyimide insulating bearing sleeves, can be used to electrically insulate the rotor from the housing and suppress discharge currents. They offer a versatile and cost-effective solution for mitigating electrical corrosion in e-motor bearings. These sleeves can be installed during final assembly by press-fitting onto either the rotor shaft or one of the bearing rings (Figure 1). In all cases, standard steel ball bearings can be utilized with Vespel® sleeve, eliminating the need for expensive ceramic
rolling elements such as hybrid bearings. Vespel® polyimide insulating layer between 1 and 2 mm offers robust insulation by significantly increasing electrical impedance. This effectively attenuates high-frequency currents traversing the bearing, thereby reducing the risk of electrical erosion. Vespel® polyimide also exhibits mechanical
damping properties that may help reduce noise, vibration, and harshness (NVH) in electric motor systems.

Figure 1: Vespel® bearing insulation sleeves (left) and Stress analysis of the Vespel® sleeve press-fitted over the shaft and assembled on the inside diameter of the bearing (right).

Existing solutions, such as ceramic and polymeric coatings provide adequate insulation in DC environments, they often fail to prevent electrical discharge under AC conditions, particularly at higher frequencies, and may suffer from mechanical fragility.

Electrical insulation performance

Various tests have been conducted to support the use of Vespel® sleeves in addressing electrical corrosion issues. The electrical impedance has been measured by IMKT (Institut für Maschinenkonstruktion und Tribologie at Leibniz Universität Hannover). Results indicate that the electrical insulation performance of Vespel® SP-1, although
slightly lower than that of the hybrid bearing, remains in the same order of magnitude and significantly higher than the ceramic-coated bearing solution [8], even when compared to the thickest layer of ceramic coating (Figure 2).

Figure 2: Comparison of Electrical Impedance Across Various Insulated Bearing Solutions

Designing Vespel® polyimide Insulating sleeve

The design of the Vespel® polyimide sleeve requires studying the different press-fitting scenarios and checking that the loads resulting from the press-fitting of the various parts, combined with thermal expansion, are acceptable (Figure 1). Bearing manufacturers typically provide maximum hoop stress and radial stress; this information is used to properly dimension the Vespel® polyimide sleeve. Although proper testing needs to be conducted on the final system to ensure the parts behave appropriately, simulations are used to build confidence and quickly design a working prototype (Figure 1).

Other polymeric solutions could be used, but they need to be reinforced with fibers to enhance mechanical strength. The fibers are abrasive and easily cause wear issues when they are in contact with aluminum. In EV cars, this phenomenon is amplified with the vibration generated by electrical motors causing fretting wear issues on aluminum housing.

Unlike standard polymers, Vespel® polyimide, with extreme temperature capabilities, does not require fiber reinforcement to maintain its mechanical performance and withstand the maximum temperature of 150°C, observed at the bearing position for traction motors. Tests conducted at the DuPont Tribological Laboratory under similar conditions revealed that fiber-reinforced thermoplastics caused significant wear on aluminum components, whereas Vespel® polyimide resulted in no measurable wear (Figure 3).

Figure 3: Wear performance of Vespel® polyimide vs polymeric solution against die cast aluminum

Aluminum die-casting insert

Another innovative solution involves the use of Vespel® polyimide as an insert in aluminum die-casting, leveraging its exceptional high-temperature resistance and lack of a melting point, which enables it to withstand aluminum processing temperatures up to 680 °C. By integrating a Vespel® insert directly into the mold, an electrically insulating barrier is formed between the traction motor housing and the bearing. Following the die-casting process, the insert can be machined to achieve precise tolerances – a standard step prior to bearing assembly.

In collaboration with Swiss aluminum die caster Aluwag AG, the feasibility of this concept was successfully demonstrated through the production of aluminum housings incorporating a 90 mm diameter Vespel® insert (Figure 4). Notably, the interface exhibited no structural or dimensional changes after multiple thermal cycles ranging from –40 °C to 150 °C, underscoring its suitability for long-term use in demanding application environments.

Figure 4: Cross section of bearing seat with Vespel® insert (© DuPont)

Recyclability of aluminum components with Vespel® polyimide inserts

Die cast aluminum housings containing Vespel® polyimide inserts are currently being evaluated by companies for use in electric vehicle driveline components. In addition to performance testing, there is a need to recycle aluminum housings that exhibit defects. During the casting process, a skimming operation is typically performed to eliminate impurities such as oxides, slag, and other contaminants that form at the surface of the molten aluminum. Preliminary tests have shown that Vespel® polyimide components float on the surface of the molten aluminum, which could simplify their removal during the skimming operation.

Most electric motor housings use steel sleeves to protect aluminum from bearing-induced fretting wear. However, these inserts complicate recycling due to material separation. Vespel® polyimide could offer a more sustainable alternative, replacing steel sleeves used with ceramic bearings while maintaining electrical insulation and simplifying recycling.

Figure 5: Vespel® Inserts Floating on the Surface of Melted Aluminum

Summary

As electric vehicles evolve, the need for reliable and durable components, particularly bearings, is paramount due to their susceptibility to electrical erosion in high-voltage systems. DuPont™ Vespel® polyimide offers a groundbreaking solution with its insulating bearing sleeves, which can enable the use of standard roller bearings instead of costly ceramic alternatives, thereby helping to reduce material costs significantly.

Additionally, Vespel® polyimide inserts can be integrated within aluminum die-casting processes, providing effective electrical insulation and enhanced performance in demanding environments. The combination of these innovative solutions positions Vespel® polyimide as an essential material for the future of electric vehicle technology, promoting safer, more efficient, and sustainable electrified drivetrains.

References
[1] Rösel, G.; Moenius, P.; Daun, N.; Spas, S.; Hackmann, W.; Schmitt, B.; Reich, A.: Konzept für einen Hocheffizienten 800 V Achsantrieb. 41st International Vienna Motoren Symposium, Vienna, 2020
[2] Power Electronics New Zealand: The principles of managing dV/dT in AC variable frequency drives. Online: https://www.power-electronics.co.nz/blog/the-principles-of-managing-dvdt-in-ac-variable-frequency-drives/, access: August 13, 2024
[3] Saucedo-Dorantes, J.; Zamudio-Ramirez, I.; Cureno-Osornio, J.; Osornio-Rios, R. A.; Antonino-Daviu, J. A.: Condition Monitoring Method for the Detection of Fault Graduality in Outer Race Bearing Based on Vibration-Current Fusion, Statistical Features and Neural Network. Online: https://www.mdpi.com/2076-3417/11/17/8033, access: July 17, 2024
[4] NTN: Elektroerosion. Online: https://waelzlagerwissen.de/waelzlagerschaeden/elektroerosion/, access: July 17, 2024
[5] Franquelo, L. G.; Rodriguez, J.; Leon, J. I.; Kouro, S.; Portillo, R.; Prats, M. A. M.: The age of multilevel converters arrives. In: IEEE Industrial Electronics Magazine 2 (2008), No. 2, pp. 28-39
[6] Eireiner, D.; von Petery, G.; Völkel, F.: Bearings Reinvented – Contribution of Rolling Bearings to Improving Ranges and Charging Times of Electric Vehicles. 20th International VDI Congress Dritev – Drivetrain for Vehicles, 2020
[7] Preisinger, G. Cause and Effect of Bearing Currents in Frequency Converter Driven Electrical Motors: Investigations of Electrical Properties of Rolling Bearings. Ph.D. Thesis, TU Wien, Vienna, Austria, 2002

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