Precision Magnetic Sensor
An automotive company approached us for assistance on a sensor magnet application. Standard magnets can have a "Direction of Magnetisation" axis tolerance of up to +/- 5 degrees from the intended axis. The automotive company was having difficulties in reliably activating their sensor at the correct positions, affecting the performance of their product.
We suggested an improvement to the production process which would offer not only better control of the "Direction of Magnetisation" axis but also 100% test and inspection of the Direction of Magnetisation axis to provide the automotive company with sensor magnets which would be more reliable for their application.
When a magnet is first pressed, it is often pressed slightly oversize then it must then be sintered to fuse the magnet powder together and to also give the magnet its final magnetic characteristics. The shrinkage is actually uneven (due to production methods e.g. magnet shape, pressing, sintering in a vacuum, position in vacuum furnace, etc) which can warp the magnet shape and skew the Direction of Magnetisation. The magnet is then machined to finished dimensions – depending on the warping of the magnets, this is the reason why the "Direction of Magnetisation" can be different from the intended axis.
Our solution was to produce a much larger block than the required magnet shape, deliberately removing all the outer faces to remove any impurities from sintering and using the material in the centre which had better magnetic characteristics for the required magnet shapes. Each magnet was then 100% tested for "Direction of Magnetisation" (measurements in three axes to give a "Direction of Magnetisation" angle from intended axis).
This production method allows a better control of the "Direction of Magnetisation" variation for magnets used in critical applications such as sensors.