MIMCOIL vs. wound coils vs. hairpins.

Comparison

#1 → Type 1

This page summarizes how MIM copper coils compare to conventional wound coils and hairpins for traction motor applications. The scores are based on theoretical potential and typical design practice – not on a specific motor design.

#2 → Type 4

Visual rating – how the three technologies stack up

The dot scale is qualitative: more filled dots indicate higher potential or suitability in that category under the given assumptions (high-purity copper, good process control, automotive use case).

Criterion Wound Hairpin MIM coil
Slot fill factor ●●●●● ●●●●● ●●●●●
AC loss optimization ●●●●● ●●●●● ●●●●●
Thermal homogeneity ●●●●● ●●●●● ●●●●●
HV suitability (800–1200 V) ●●●●● ●●●●● ●●●●●
Cross-section design freedom ●●●●● ●●●●● ●●●●●
#3 → Type 4

How we arrived at these ratings

The comparison is based on a typical traction motor context (e.g. automotive) and assumes optimized designs for each technology. The focus is on physical potential, not on today’s average implementation.

  • Slot fill factor: wound coils are often limited to roughly 50–70 % effective slot fill, hairpins to ~75–80 % in practice. A MIM coil can theoretically approach 95–100 % because the slot volume is filled by a single, shaped copper body.
  • DC and AC losses: more copper in the slot means either lower DC resistance or more current at the same losses. On top of that, MIM allows you to tailor the cross-section (segmentation, widths, shapes) to reduce skin and proximity effects for the relevant frequency range and PWM strategy.
  • Thermal behavior: wound coils have air gaps between wires, hairpins have corners and local hotspots at joints. A MIM coil behaves more like a quasi-solid copper body with a defined interface to the lamination stack and cooling system, which leads to more homogeneous temperatures and better hotspot control.
  • High-voltage capability: at 800–1200 V, controlled radii and distances between conductors become critical. Hairpins tend to have sharp bends and welds; MIM coils can provide smooth 3D geometries and defined creepage/clearance distances, which helps to reduce partial discharge risk.
  • Design freedom: both wound coils and hairpins are constrained by bending radii, tooling and process limitations. MIM, in contrast, offers almost full 3D freedom of the conductor path and cross-section – as long as it is compatible with the molding and sintering process.
#4 → Type 4

Key technical advantages of MIM motor coils

 

  • Up to ~30 % lower copper losses (theoretical): by combining near-full slot fill with resistance-optimized cross-sections, MIM coils can reduce copper losses or increase power density at a given loss level.
  • Superior thermal behaviour: MIM copper behaves like a nearly homogeneous block inside the slot – no significant air pockets, better contact to the lamination stack and more predictable heat paths. Ideal for oil- or water-cooled stators.
  • Full 3D design freedom: you can use conductor profiles that are impossible to wind or bend: curved cross-sections, locally thicker regions for heat spreading, segmented areas to influence AC losses, integrated positioning features for assembly.
  • High-voltage ready (800–1200 V): smooth surfaces, controlled radii and defined insulation distances support partial-discharge-robust designs, more predictable than classic hairpin layouts.
  • Industrializable and precise: once the MIM tool is validated, the geometry is highly reproducible. Combined with post-machining of key reference surfaces, this supports automated stator assembly at tight tolerances.
#5 → Type 4

Typical application examples

The benefits of MIM coils are most relevant where power density, efficiency and thermal limits are highly constrained.

  • 800 V traction motors for passenger cars and trucks: maximum slot fill and optimized cross-sections support higher continuous power and better efficiency at high speed.
  • Compact two-wheeler and powersports drives: limited installation space and high torque density requirements benefit from near-full copper utilization in the slot.
  • Industrial servo motors: reduced copper losses at continuous load, improved temperature control and more compact machine designs.
  • Generators and wind turbine drives: improved thermal cycling behaviour and more homogeneous temperature profiles help with lifetime and reliability.