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The standard dimensional tolerance for the majority of permanent magnets is +/-0.1mm. The best dimensional tolerance usually available is +/-0.05mm (on rare occasions +/-0.04mm is possible) but the improved tolerance carries an additional cost. These tolerances apply for low and high quantity magnets. For larger magnets +/-0.1mm tolerances may be perfectly acceptable but for very small magnets this could be more problematic particularly in sensitive applications such as, for example, sensors (as size variations may cause a variation in magnetic output from magnet to magnet).
The standard production procedure requires randomly selected samples from each production batch to be measured for dimensional accuracy (amongst other quality control checks); statistical analysis determines whether the magnets in each batch will all fall within tolerance (sometimes a batch may be 100% inspected). Where tighter dimensional tolerances are required, 100% testing is more likely to be the only reliable method of testing - only the magnets that pass the tolerance requirements are retained and the remainder would be scrapped for recycling. This can lower the yield to the point where either the process is not cost effective which is why +/-0.05mm is usually the minimum tolerance range) or the high scrap rate plus additional testing costs is reflected in an increase in cost per magnet.
However, we are now able to offer Precision NdFeB Magnets with tolerances better than +/-0.05mm through an improved production process. These Precision Magnets are only available in small sizes and are only available in minimum order quantities - typically 100,000 magnets is the minimum order quantity (MOQ). As the factory is streamlined for mass production (batch quantities in millions of magnets per month), we may have to charge for samples (there may also be a MOQ on samples).
The magnet material, shape, size and magnetisation pattern will affect how accurately the magnets can be produced. The best tolerances we can offer is down to +/-0.005mm. That is down to 1/20th of the standard tolerance – hence our calling it Precision Magnetics. The tighter the tolerance on the Precision NdFeB Magnet, the higher will be the cost.
The shapes we offer for the Precision NdFeB Magnet range are disc magnets, ring magnets and rectangular magnets. We currently offer these magnets in SmCo and NdFeB (Neodymium Iron Boron, Neo, NIB) and the coatings we offer include Nickel, Gold and Zinc. The magnets are offered with axial and diametric magnetisation patterns. Each Precision Magnetic product is bespoke to the customer.
As these magnets are bespoke, we will require information on the exact requirements including desired tolerances. If the shape can be produced we will contact you with a price, lead time and confirmation on tolerances that can be achieved (if the required tolerances are too tight, we will advise on the nearest realistic tolerances that can be achieved).
Example sizes (we may be able to produce smaller or larger upon request - please contact us with your requirements):-
NdFeB ring:- OD 0.9mm x ID 0.25mm x 0.5mm through to OD 4.5mm x ID 1.2mm x 3.65mm.
NdFeB disc:- D 1.0mm x 0.5mm through to OD 6mm x 0.7mm.
NdFeB rectangle:- 1.0mm x 1.0mm x 1.0mmA through to 22.0mm x 2.75mm x 1.05mmA.
We were asked to supply axially magnetised N35 disc magnets that were rated to 120 deg C, having a diameter of 3mm but with a 0.15mm thickness. Even with +/-0.05mm tolerances, the potential variation in thickness could be problematic for magnetic output variation (the thickness would vary from 0.1mm to 0.2mm). We offered +/-0.02mm tolerances on a Ni plated N35H magnet. The tests results on a randomly selected sample of 20 of our Precision NdFeB Magnets were as follows:- average 2.9980mm diameter (2.990mm to 3.000mm range) by average 0.1547mmA (0.150mm to 0.158mm range).
If you would like Precision NdFeB Magnets, please contact us with your requirements and we will provide you with a quotation.