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Key Considerations

When using a magnetic workholding system there are several factors to consider which may affect the workholding performance.
 

An air gap between the magnetic surface and the workpiece will reduce holding performance. The highest performance is where air gaps are kept to a minimum and the magnetic hold is maximised.

Air gaps are determined by the profile of the workpiece and the surface finish. For example a lapped fine finished product will have the best workholding performance whereas a rough planed surface will have a much poorer holding force due to air gaps.

Air Gaps

The material type determines the magnetic clamping force. Some materials have less magnetic permeability and this will affect the hold. The chart below shows some examples of how the clamping force is affected by different material types.

Material Type

Stainless steel, brass and aluminium have no magnetic holding capacity so should not be used with these products.

The flux path within a workpiece is a semi-circle from the centre of one chuck pole to the centre of the next.

If the workpiece is thinner than this radius it cannot absorb all the flux and some passes through. The resultant pull is lower than that when all the flux is absorbed by a thick workpiece.

AX Chucks: Variation of pull with workpiece thickness:

Material Thickness

To hold a thin workpiece securely the pole pitch and radius of the magnetic flux must be reduced. There are two main methods of achieving this.

(a) Eclipse Fine Pole Chucks (b) Induced pole Chucks - please ask for details.

(a) Fine Pole Chucks

These chucks are ideally suited to small thin workpieces although they can also be used to hold larger workpieces for surface grinding applications.

The heat treatment of a material affects its physical structure and its ability to absorb flux. Annealed materials are best. Hardened materials do not absorb flux as easily and tend to retain some magnetism when the chuck is switched off, sometimes making it difficult to remove the workpiece from the chuck.

Residual (or retained) magnetism can be removed from a workpiece by wiping the workpiece across an Eclipse De-magnetiser, once it has been removed from the chuck.