Motor Laminations

motor lamination examples

Magnetic Metals specializes in the manufacturing of standard and custom precision stamped rotor and stator laminations for the aerospace, electrical, industrial, and medical markets. With over seventy years of experience and our engineering expertise, the laminations are manufactured to meet and exceed the customer's expectations on quality and performance.

Magnetic Metals is your partner for high volume to low volume niche applications. In addition Magnetic Metals provides expertise in coating, stamping, annealing, testing, assembly, and bonding.

For prototype, development work, and production lamination shapes please contact us at .


Grades and Gauges

The rotor and stator shapes are available in a wide variety of high performance magnetic materials. Table 1 lists the various lamination material designations and trade names of similar material furnished by steel manufacturers.

All Standard grades and gauges are available. Since a single tool will not stamp all grades and gauges, contact us at  for the availability of special grades and gauges to meet your specifications.



Materials for precision rotating components are selected for their isotropic magnetic properties. After stamping, proprietary heat treating processes ensure that the most uniform magnetic properties are developed.


TABLE 1 - General Classification of Magnetic Grades

Material Type Material Description Mainly Used In:
Iron-cobalt alloys
Highest flux density
Magnetic bearings
SuperPermTM 49 49% Ni, Fe (isotropic)
Alloy type 2 ASTM A753
Moderate permeability
Low core losses
Highest flux density of all nickel alloys
Magnetic bearings
SuperPermTM 80 80% Ni, Fe
Alloy type 4 ASTM A753
Highest permeability
Low core losses
Low flux density
Magnetic bearings
Amorphous and Nanocrystalline Alloys Iron based
Low flux density
Low core losses
0.001" material thickness
Motor laminations


Surface Insulation

Magnetic Metals provides material coating to prevent laminations from fusing together during heat treatment. The applied coating provides resistance between layers on the stacked assembly, reducing eddy current losses. After heat treatment, the coating is a magnesium oxide (MgO).

Magnesium oxide can be interpreted to mean:

  1. MMX (magnesium methylate) pure MgO after heat treatment. This coating is very thin (approx. 0.0001" per side after heat treatment); It is the coating most used on cobalt-iron alloys.
  2. MLC, pure MgO with some Al2O3 after heat treatment. Thickness is approx. 0.0003" per side after heat treatment.
  3. Upon request, finished parts may have oxide coating for electrical insulation by annealing in oxygen. Thickness is approx .0002" per side.

Magnetic Metals is also capable to measure surface insulation with the Franklin Test Method as per ASTM A717.


Quality Assurance

Magnetic Metals' laminations are manufactured to a high level of magnetic quality and mechanical tolerances. The Quality Assurance Program is compatible with MIL-Q--9858A. Continuous in-process checks of mechanical and magnetic characteristics throughout the manufacturing process insure a consistent and superior product.

Magnetic Metals has the capability to perform magnetic testing using hysteresis graphs. Special tests and reports are available upon request.

Information on standard test methods can be found in the American Society for Testing and Materials Standard Method of Test for Alternating Current Properties of Laminated Core Specimens (ASTM Designation A346-74), available from the American Society for Testing and Materials, 100 Barr Harbor Drive, West Conshohocken, PA 19428.


Process Control

Laminations for small, precision rotating components are produced by Magnetic Metals Corporation to the highest standards of accuracy. Our process and Quality Control concentrates on the attainment of the following properties:

  1. Availability of isotropic soft magnetic materials.
  2. High degree of mechanical accuracy for stampings, involving close tolerances in the stamping dies, as well as in the stamping operation itself.
  3. Minimum burrs on the finished laminations.
  4. Carefully established heat treating processes.
  5. Good machining properties where required through the use of special annealing.
  6. Post stamping operations such as testing, bonding and machining.


Quality Control - Nominal Tolerances Material and Gages

  Nickel Iron & Cobalt Iron Alloys
Measure of tolerance 0.014" 0.006"
Burr 0.001" 0.00075
Concentricity 0.001" TR
Dimensional ± 0.005"
Flatness See Below

Flatness bridge gage - motor laminations

Flatness of 'X' equals (length of X' in inches)(0.005) + Material Nominal +0.001 Gage Allowance = Flatness Bridge Gage

Example, X is 2" Diameter, Material .025 thick (2)(0.005) + 0.025 + 0.001 = .036 Flatness Bridge Gage


Engineering Terminology

Performance characteristics of rotating components depend on the design and configuration of the lamination. Certain terminology describing the rotor and stator lamination is used.

Slot Pitch: Slot pitch is the circumferential distance at the air gap surface from the center line of one tooth or slot to the center line of the adjacent tooth or slot. It can also be expressed as an angle.

Slot Area: The total slot area is the area between the teeth which can be filled with copper windings. It is defined by the open area between the teeth less the rectangular area between the slot bridges which, in general, cannot be filled with copper wire. The total slot area is given both in circular mils and in square inches. To convert square inches into circular mils multiply the area in square inches by 1.272 x 106. For practical applications, the total slot area must be reduced to account for slot insulation and the possible area loss caused by skewing of the lamination stack.

Slot insulation subtracts directly from the slot area by an amount equal to the slot perimeter multiplied by the thickness of the insulation.

Tooth Width: The tooth width gives the minimum width of the tooth which is important in the design calculation as saturation might occur in this area. Calculations for the maximum flux density may be made using this dimension.

Motor laminations - terminology