In this master thesis, the magnetic properties of SiFe laminations after cutting and welding
are studied. The permeability and the iron loss density are investigated since they are
critical characteristics for the performance of electrical machines. The magnetic measurements
are conducted on an Epstein frame for sinusoidal variations of the magnetic ux
density at frequencies of 50, 100 and 200 Hz, according to IEC 404-2. Mechanical cutting
with guillotine and cutting by means of ber and CO2 laser are performed. The inuence
of the ber laser settings is also investigated. Especially the assisting gas pressure and
the power, speed and frequency of the laser beam are considered.
In order to increase the cutting e ect, the specimens include Epstein strips with 1,
2 and 3 additional cutting edges along their length. It is found that mechanical cutting
degrades the magnetic properties of the material less than laser cutting. For 1.8% Si
laminations, mechanical cutting causes up to 35% higher iron loss density and 63% lower
permeability, compared to standard Epstein strips (30 mm wide). The corresponding
degradation for laser cut laminations is 65% iron loss density increase and 65% permeability
drop. Material of lower thickness but with the same Si-content shows lower
magnetic deterioration. Additionally, laser cutting with high-power/high-speed characteristics
leads to the best magnetic characteristics among 15 laser settings. High speed
settings have positive impact on productivity, since the cutting time decreases.
The inuence of welding is investigated by means of Epstein measurements. The test
specimens include strips with 1, 3, 5 and 10 welding points. Experiments show an iron
loss increase up to 50% with a corresponding 62% reduction in the permeability.
A model that incorporates the cutting e ect is developed and implemented in a FEMbased
motor design software. Simulations are made for a reference induction motor.
The results indicate a 30% increase in the iron losses compared to a model that does
not consider the cutting e ect. In case of laser cut core laminations, this increase reaches
50%. The degradation prole considers also the deteriorated magnetizing properties. This
leads to increased nominal current up to 1.7% for mechanically cut laminations and 3.4%
for laser cut la