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I am currently trying to hold a metal block in place with the magnets shown in the layout below. These magnets are permanent magnets which both expose one of their poles on the top side as shown below.

Magnet Layout

When placing a metal piece on the product I could think of the following strategies. Green lines are my expected ideal magnetic field lines while blue would be hindered by an air gap.

  • Case1: try to make straight magnetic lines which the thickest part of the product
  • Case2: Try to get as much coverage as possible and expect the magnetic lines to "curve" through the product.
  • Case3(no image): placing the product only on one pole, does not work due to air gap and I can push it over without a problem by hand.

Product layout on magnet

How could I calculate the magnetic force on the product for these cases? The magnets I am working with are designed for ~1500kg so I cannot physically feel the difference by hand. Factors I think are in play:

  • Magnetic field parameters of the manufacturer of the magnets (e.g. minimum and maximum height of the magnetic lines).
  • Part size and layout(height, width).
  • The kind of steel that is used for the part.

If the calculation also derives the resistence to forces in different directions that would be great, but only a force upwards would be sufficient for lifting the product. Note that my background is software engineering with a bit of electronic engineering, please try to account for this into the explanation / refer to literature I would need to learn.

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  • $\begingroup$ Check out magnetic tool clamps. $\endgroup$
    – Solar Mike
    Jun 15, 2022 at 19:25
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    $\begingroup$ How will that help me calculate the force? $\endgroup$
    – Maarten
    Jun 15, 2022 at 19:28

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If you wish free and open-source software, i can recommend ONELAB, which is combination of Gmsh (mesher and GUI) and GetDP (general purpose solver). You will have an exciting dive into physics and mathematics. There are examples of magnetic force calculations both via Maxwell tensor and virtual work method. I had optimized real linear electromagnetic actuator with it, couple years ago, using Maxwell tensor method.

Note that normal separation force will be calculated just from magnetism. Shear separation force will include friction caused by normal component of magnetic force and added planar component of magnetic force. This task is not as easy as it seems to be.

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  • $\begingroup$ I found this link as a tutorial which I'll look into the coming days. gitlab.onelab.info/doc/tutorials/-/wikis/Magnetic-forces I have not found a tutorial for the friction yet, could you explain this/add a reference for this? $\endgroup$
    – Maarten
    Jun 19, 2022 at 9:01
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    $\begingroup$ Friction in general is not a subject of finite-element computing. It is calculated by multiplying pressing force by friction coefficient of pair of materials, found from reference book. You can add computing of normal component of magnetic force and multiplying of it to the task file. There are many information in their mailing lists also, and in example files catalogue. $\endgroup$
    – Vladimir
    Jun 19, 2022 at 9:18

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