“Getting rid of the air”, or how to maximize winding fill factor (ID 81)

We have experienced the unprecedented copper price rises in the recent years. With increased use in the automotive industry, it will become even more serious issue, possibly slowing down the wider application of the electric drives in the new vehicles. More efficient way to use the copper would bring substantial benefits to other industries, too - every high volume inductive device application included. In the ideal world inductive devices would have 100% active material in the winding, but in the real world it is much less. The insulation layer is one cause and the wire shape fill factor the other. Round shapes can only be wound with limited efficiency. Other cross sectional shapes (hexagonal, rectangular) can bring improvement, but have limited applications due to high cost and unsuitability for any but heavy gauge wires. This paper describes and discusses the available and/or possible technologies of post-forming the round wire windings, in order to achieve the maximum fill factor. The wound circular cross sections need to be transformed into hexagonal array (honeycomb) while the insulation remains fully functional. This will results in substantial improvement of the fill factor, opening up the wide range of the possibilities from higher power to weight ratio to cost saving, even substitution of copper with aluminum in some applications, enabling dramatic improvements in the cost reduction, vehicle dynamics and overall energy efficiency. The technologies presented and discussed in this paper are: direct mechanical compression; injection moulding, in two sub-technologies (hydro forming and explosion-forming). Some of the above technologies are ready for industrial applications, some would need further development to reach that stage. Currently one of the technologies shows to have the highest potential to be implemented in the high volume production, because of it's more development and compatibility manufacturing resources, making relatively straightforward. That does possible technologies should not be considered one needs to carefully consider every application vs. technological solution separately.