How to Specify Magnetization on a Drawing

Magnetization is often under-specified on magnet drawings. Two parts can share a drawing and a material and still behave differently, because the direction of magnetization, the pattern of the poles and the face the poles sit on were never written down. This guide explains the terms and lists what a drawing has to fix, so a requirement can be described in a message instead of guessed.

Magnetic orientation is not magnetization

Orientation happens while the part is being made: the easy axis of the material is aligned during forming or pressing, and for hard ferrite that alignment is what gives the part its usable direction. Magnetization happens after the part exists: an external field is applied and the part keeps the pole pattern that field leaves in it. A part can be well oriented and still magnetized in a pattern that does not match the circuit, so the two are described and confirmed separately.

Three decisions, not one

Direction is where the field runs through the part. Pole pattern is how many poles there are and how they are arranged. Pole location is the face the poles appear on. They are separate: axial, diametrical and radial are directions, bipolar and multipole are patterns, and an end face, an outer circumference and an inner circumference are locations. Writing “multipole” on its own tells a factory almost nothing, and radial orientation is not the same thing as multipole magnetization.

The basic directions

• Through-thickness — the field runs across the thickness of a flat part, so one large face is N and the other S.
• Axial — the field runs along the axis of a cylinder or ring, so the poles sit on the two end faces.
• Diametrical — the field runs across a diameter, so each half of a disc or ring face is one pole.
• Radial — the field runs from the centre outward, so a ring carries one pole on the outer circumference and the other on the inner one.

Common pole patterns

• Bipolar — one N area and one S area.
• Multipole sectors on one face — alternating N and S sectors around a face, used in sensor and small-motor rotors.
• Multipole around a circumference — alternating poles around the outer or the inner circumference.
• Striped — alternating bands across one face.

The pole count and the pole pitch are project parameters: they follow the tooling and the circuit, and they are not a range that can be promised across a material family.

What the drawing has to fix

A magnetization requirement is readable when the drawing states these five points. Anything left out is a question the factory has to answer by assumption.

• Geometric datum — the face, bore or axis the poles are dimensioned from. Without it, “top”, “outer” and “radial” can mean different faces to the drawing office and to the magnetizing fixture.
• Direction — which way the field runs through the part: through-thickness, axial, diametrical or radial.
• Pole count — how many poles, and the pole pitch where the circuit defines it.
• Pole location — the face, circumference or bore the poles appear on, and whether they alternate around it.
• Requirements still to be evaluated — the material and route, the tooling, the magnetizing fixture and the assembly. These are confirmed per project; the drawing describes what the part has to do, not what the factory will achieve.

The same shape can be magnetized more than one way

A disc can be magnetized axially or diametrically; a ring can be radially oriented, or magnetized as a multipole ring around a circumference; an arc segment is normally magnetized across its thickness or radially, depending on where it sits in the stator. Whether a particular combination can be made depends on the material, the route the part is produced by, the geometry and the tooling, so it is confirmed per project rather than promised from a table.

What to send us

• A sketch with N and S marked, and the datum the poles are dimensioned from.
• The face the poles have to appear on, and the direction of the field in the assembly.
• The pole count and the pole pitch, where they are already defined.
• A sample, or a photograph of the existing part with N and S marked on it.
• How the magnet is held in place, because clips, adhesive and overmoulding all affect what the assembled field looks like.

If the terms are not familiar

Send the sample. A physical part, or a photograph with N and S written on it, is a useful starting point for identifying the direction and the pattern, which is then confirmed in the drawing review, and a project does not need a complete magnetization specification before the first message. “Not sure” is a usable answer.

Magnetization feasibility depends on the material, manufacturing process, geometry and required pole pattern. Send us your drawing, sample or magnetization diagram for evaluation.