ISSUE 012 Winter 2021 Sigma Powertrain EMAX transmission dossier l In conversation: David Hudson l 48 V systems focus l 2021 Battery Show North America and Cenex-LCV reports l Everrati Porsche 911 digest l Switching insight l Motor laminations focus

are given a higher priority than thermal conductivity, so waste heat has to be managed by other means. However, the thermal conductivity of the stack as a whole can be increased by full-face bonding of the laminations using backlack, because the varnish (which is also an electrical insulator) has a higher thermal conductivity than the air left in the gaps between individual laminations that don’t have full-face bonding. Laminations themselves have evolved significantly over the past decade, with thinner grades becoming available and losses for a given thickness reduced, particularly at higher frequencies, the electrical steel supplier says. It adds that new steels that exhibit better combinations of mechanical strength and magnetic losses have also been developed. In laminate manufacturing, the biggest development over that period relates to the strip thickness it is possible to use in high-volume production, the supplier adds. Around 10 years ago, the limit was generally considered to be about 0.3 mm, but these days many projects are looking at 0.2 mm and are aiming to start production in the near future. In current new projects, the stack manufacturer notes, laminate thicknesses of between 0.25 and 0.3 mm are already being used in stators, with up to 0.35 mm for rotor applications because of the need to resist rotational forces. Demand for higher strengths, meanwhile, is being driven by engineers’ decisions to use the same material for both stator and rotor for the reasons outlined above. For niche applications, however, even thinner grades of electrical steel are already in use, with some specialised and highly efficient motors containing laminations as fine as 0.1 mm, the electrical steel supplier says. Inevitably, industry looks for ways to expand the application of technologies initially suited only to narrow niches. To that end, the alloys provider says it has optimised the cost and performance of 0.1 mm laminations for mass production, pushing the practical processing limit for niche applications down to half that figure. Drawbacks to slimming In principal, the thinner the laminations the better, because of their beneficial effect on eddy-current losses at higher switching and commutating Focus | Motor laminations these parameters in EV traction motors is by using soft magnetic materials, such as the aforementioned iron cobalt, that exhibit high-induction and low-loss characteristics, according to the alloys provider. Over the past decade, the lamination tooling expert says, the pursuit of greater efficiencies and higher rotational speeds has seen much higher demand for advanced means of ensuring the structural integrity of laminate stacks through the use of bonding varnish (also known as backlack) and glue-dot bonding, with implications for thermal management. Managing heat lows Heat in motors and generators comes mainly from the losses in the electrical steel in the rotor and stator, although the copper losses from resistance in the windings is also important. Although using steel with low electrical losses reduces waste heat at source, the alloying elements used to achieve this are principally silicon and aluminium, which unfortunately reduce the steel’s thermal conductivity. In most cases, the steel supplier points out, low losses Some suppliers of motor lamination services Austria Voestalpine +43 50304 15 0 www.voestalpine.com Germany Andritz Kaiser +49 7252 91001 www.andritz.com Schuler Group +49 7161 660 www.schulergroup.com Tata Steel Europe +49 211 4926 0 www.tatasteeleurope.com Vacuumschmelze +49 6181 38 0 www.vacuumschmelze.com Italy Aussafer Due +39 0431 66501 www.aussafer.it Dema +39 019 9354711 www.demasassi.it Euro Group +39 02 35 0001 www.euro-group.it Switzerland Feintool +41 32 387 5111 www.feintool.com UK Brandauer +44 121 359 2822 www.brandauer.co.uk HV Wooding +44 1303 264471 www.hvwooding.co.uk USA Arnold Magnetic Technologies +1 585 385 9010 www.arnoldmagnetics.com Carpenter Electri ication +1 610 208 2000 www.carpenterelectri ication.com LH Carbide +1 260 432 5563 www.lhindustries.com Oberg Industries +1 724 295 2121 www.oberg.com Tempel +1 773 250 8000 www.tempel.com With rotors requiring higher mechanical strength than stators, one option is to use a material optimised for strength and annealing the stator core (Courtesy of Voestalpine Automotive Components Nagold) 68 Winter 2021 | E-Mobility Engineering