Three-stage solution for the stator bore
In the pot-shaped version of the motor housing, the stator
carrier housing is inserted into the main housing as an
intermediate housing. Typical diameters for the thin-walled
aluminium part are between 200 and 240 mm on the inside and
between 240 and 260 mm externally. Concentricity of the
various bearing and mounting diameters is critical to the
performance of the electric motor, which requires very precise
machining within tight tolerances.
The first of three steps for machining the stator bore is pre-
machining with a boring tool. The blank has casting bevels that
result in cutting depths of up to 6 mm to be removed. For this
purpose, special indexable inserts with a supporting arc shaped
land are used to avoid vibrations. This also ensures that small
chips are produced, which can be easily removed. In the
subsequent semi-finish machining, the complex contour path of
the electric motor housing is pre-machined in such a way that
the complete fine machining with chamfers and radial
transitions can be produced to μm accuracy with the finishing
fine boring tool. The tools are individually designed for the
respective customer depending on the stock situation,
machinery and clamping setup. Different steps in the housing
are taken into account with the cutting-edge positions of the
tools, as are cast-in or pressed-in steel bushings for bearings.
While the majority of the workpiece is machined with PCD,
carbide cutting edges are used for the steel area.
World first for external machining
On the outside, the part features a helical circumferential
groove. Because the coolant later flows through this groove
after it’s been inserted into the outer housing, the stator carrier
is also known as the “cooling jacket”.
MAPAL is presenting new external machining tools at the EMO
in Milan. They are among the more unusual tools. After pre-
machining, a bell-shaped tool takes over the complete finishing
of the outside. The specifically designed lightweight tool is
equipped with indexable inserts and guide pads and was
provided with bars in the right places to save as much weight as
possible and to get rid of chips through large openings. The fine
machining tool promises high roundness and accuracy.
Complete machining on machining centre
Internal machining is possible very quickly and accurately with
the boring tools. In addition, the outside can also be machined
in the same clamping setup without moving. The machining
centre solution caters to customers who are embracing the
transformation to e-mobility with existing machinery geared to
machining large cubic aluminium housings.
Those who start their production on a greenfield site can, of
course, choose which machining strategy is best for them.
MAPAL has developed an alternative machining solution in a
joint project with a machine manufacturer. In this case, the
process was rotated 90 degrees for use on vertical lathes.
