A new star is born - SWD AG Statorund Rotortechnik

A new star is born
The segmented stator is the answer to raising raw material
prices, higher performance and smarter production.

• Tailor made material selection for both your stator and your rotor
• Maximum level of material utilisation and highest precision
• Better magnetic performance due to elimination of straightening of
  the raw material
• Full automated production lines for economical series production

Economic production of efficient electric drives for e-
vehicles through new in-line technologies
Thomas Stäuble, Georg Senn, Hannes Weiss, SWD AG Stator- und Rotortechnik

Electro mobility is here and it is transforming the automotive market. Dynamism is accelerating the
move to hybrid and full electrical automobiles. Major changes in the vehicles themselves and in the
value chains already are both starting to pick up speed.

In a joint project between an OEM and SWD AG Stator- und Rotortechnik, a completely new way of
producing stators was devised and, more importantly, was proven to be able to be implemented in large-
scale production. Instead of using a traditional progressive die of stator and rotor laminations, the stator
was built up in segments, which were punched with the highest possible material utilization, high precision
stacking and high speed bonding. The utlized Backpaketiersystem® BPS® Technology from SWD AG is
already proven, having been used in many other applications. The precise and stiff segments have been
joined to a full stator. The tolerances achieved for the joined stator segments are comparable with a stator
punched from round laminations. The OEM has insulated the joined stator and inserted hairpins and
mounted everythig into the housing. In addition to achieving massive reductions of material costs, the first
measured and verified performance values on the test bench met the values of the reference motors.

Bondig of segments

Stator segmentation is used in mass production of electrical vehicles. Because the stator and rotor are no
longer punched out of the same strip of electrical sheet, separate production of each is possible, which in
turn allows for ideal material selection and maximum material utilization (Figure 1). In addition, with regard
to technical matters, optimization of the magnetic properties, the increase in the filling level of iron and the
increase in the copper filling can all be profitably implemented through segmentation. When the segments
are manufactured with such high precision and provided with a corresponding connection coupling (Figure
2), very tight tolerances are possible as is shown in the results section below. Production of such high-
precision, solid segments, though, requires a mastery of both bonding technology and tool making.
Since the electrical steel is not straightened in the punching process, its magnetic properties are not
affected, resulting in loss reduction of more than 10% (Figure 3). High-precision tools, modern tool materials
and new eroding processes allow a reproducible and precise production of the segments, meaning large-
scale serial production opens the door to previously unimagined opportunities.

Fig. 1: Segment punching     Fig. 2: Bonded segment with   Fig. 3: Minimized losses during production through
pattern                      interconnection               production without straightening

The project shows impressively, that, due to the segmentation, the slightly increased cutting edges do not
harm the performance of the motor. Reason for that is the elimination of magnetic defects due to the
straightening process. The early consideration of the segmentation in the development phase of the
stator unveils substantial advantaged of efficiency and power density in the electrical drive. As an
example it can be possible to reduce the active length of the lamination stacks or the increase of the
magnetic flux in the air gap and the corresponding increase of speed and torque due to better suitable
electrical sheet material in the stator and the rotor. To unveil the advantages of the segmentation fully, the
detailed know-how in design of the interconnection of the segments is required.

Joining the overmolded stator segments
The segments were pushed together with force - distance control in the joining unit. The recorded
diagrams and the consistently achieved range of joining forces show again the high precision of the
bonded segments. Figure 4 clearly shows how the individual lamination sheets of the segments are
interlocking when they are joined (“ripple”).

Fig. 4: Joining curve                                              Fig. 5: Partly joined stator

The achieved joining force is approx. 20 kN. This value can be adapted to the requirements of the
coupling design. The recorded joining curves also allow the constant monitoring of the component quality.
The assembled complete stator was geometrically measured afterwards in detail. The achieved diameter
tolerance and roundness are listed in the result section. The stator was delivered to the OEM for the final
assembly at the end (Figure 6).

Assembly of the joined stator
The OEM then equipped the stator with hairpin winding and assembled it into the housing. The stator,
which consists of overmoulded stator segment packages, was at that time analysed on test bench,
yielding results which were comparable to those of a conventionally produced stator with inserted
insulating paper. The winding configuration of both stators were the same. The results of these analyses
are very promising and do not indicate any impairment of engine performance due to segmentation.

Fig. 8: Finished stator                         Fig. 9: Detail of segment and coupling

Results
The following impressive results has been achieved with the new stator concept:

Geometric evaluation
Stator outside diameter                220 mm
Stator inside diameter                 157 mm
Rotor diameter                         155 mm
Stator height                          160 mm

Diameter tolerance                     0.05 mm
Roundness                              0.09 mm

Conclusion:                            Very high precision of diameter and roundness

Material usage and cost assessment
Material use full stator               64.7 kg (including rotor from the interior)
Stator material use, segmented         28.5 kg (56% saving)
Material used rotor                    31.5 kg (2-lane punched)
Material costs stator                  NO30-16, based on 1,800 EUR / t
Rotor                                  M800-50A, based on 1,100 EUR / t

Full stator material costs             EUR 116.50 / set (if stator and rotor are cut in a progressive die
                                       out of NO30-16)

Segmented stator and rotor             EUR 51.30 / stator made of NO30-16
                                       EUR 34.60 / rotor made of M800-50A

EUR 80.20 / set (saving 32%)
Conclusion:                 The analyses support the use of “ideal material” by
                            separating stator and rotor materials, which lead to a
                            significant reduction of material cost.

                            Furthermore, rotor material optimization, when adapted to the
                            casting process, especially with regard to the coating, also leads
                            to better motor characteristics. For instance, no cavitation forms
                            from excessive degassing of insulating varnish and there is better
                            conductivity by the squirrel cage rotor).

Process data information
Punching                    The segments are punched at up to 700 h / min.
                            No straightening process occured before punching, so there was
                            no additional magnetic impairment of the high-quality electrical
                            sheet NO30-16, which is built into the stator.
Bonding                     “High speed bonding” with Backpaketiersystem® BPS® in a time
                            range of a view minutes and 100% process monitoring leads to
                            maximum quality and traceability
Joining                     Joining of all segments in one process step with a joining force of
                            up to 20 kN, 100% process-monitored (force / distance control)
Winding                     Simply push of the hairpins into the slots

Performance data
Motor power                 250 kW (peak)
Torque                      500 Nm
Voltage                     400 V
Influence of segmentation   Advantage of bonding varnish vs. welding (see SWD website for
                            the advantages of bonding varnish) equalise the offsets of
                            segmentation
Iron fill factor            96%

Manufacturing the technology of the future
The aforementioned production technologies are proven suitable for serial production. Bonded
segments may be produced in a highly automated manner the SWD Backpaketiersystem® BPS® (see
SWD website for more information about the BPS® technology) either at SWD or on-site at the customer.
The segments are overmoulded in the next process by using the PVS stator insulation process (SIP).
With a combined production of the SWD bonding process (BPS) and the PVS stator insulation process
(SIP) the overmoulded segments can be manufactured in a complete in-line process. Because all data,
beginning with that of raw materials (electrical sheet and plastic) as well as their process and production
parameters are recorded by segment in a database, 100% traceability of each segment is achieved via a
data matrix code. The segments are assembled into a complete stator on a segment joining system
(SFS), developed and built by SWD which can be integrated into the BPS® system. The system then also
includes process monitoring and process data within the same database. Since the data matrix codes of
the segments will be read, supplemented by the data matrix code of the stator and connected to the
joined stator data, a unique database is created from which further improvements on processes, quality
assurance and traceability can be made.

SWD AG Stator und Rotortechnik is your partner for your next generation of electrical motors – “We
make your motors better”. As technology leader, we develop electrical sheet stacks, which ensure your
competitive advantage. We support from your idea to the efficient serial production and produce the
stacks in each phase.

                  “SWD AG – we make your motors better”