Magnetic assembly problems rarely show up during design review. They show up in validation testing, in the field, or on a production lot that measures differently than the approved sample. By then the fix is expensive, because the tooling exists and the program has a date.
The six below account for most of what we see when a customer brings us an assembly that is not working. All of them are cheaper to prevent than to diagnose.
1. The assembly weakens at temperature and does not recover
This is the most common of all magnetic assembly problems and the easiest to prevent. Every permanent magnet loses output as temperature rises. Some of that loss is reversible and returns on cooling. Some of it is not.
When a magnet goes above the maximum operating temperature for its grade and geometry, the loss is permanent. The part works at ambient, goes through one hot cycle in service, and comes back measurably weaker for good. Teams often discover this after environmental testing, when the failing unit is the one that already passed.
Prevention: specify the highest temperature the magnet sees, not ambient, and select the material against it. The published maximum operating temperature for a grade assumes a particular geometry, so check the number against your actual part and circuit rather than reading it off a chart.
2. The bond fails before the magnet does
The magnet is fine. The adhesive holding it is not. Adhesive temperature limits are often well below the magnet’s, and the assembly sees temperature, vibration, thermal cycling and sometimes solvent exposure that were never checked against the bond.
Prevention: treat retention as a design decision with its own requirement list. If the environment is demanding, consider a mechanical retention feature carrying the load with adhesive as a secondary, rather than adhesive alone.
3. Field goes somewhere other than the working face
A magnet by itself sends flux in every direction. In an assembly, surrounding steel decides where that flux goes, and surrounding steel includes parts that are not on your magnet drawing. A bracket, a mounting plate, or the machine frame can pull a significant share of the field away from where the design needs it.
The usual symptom is an assembly that measures correctly on the bench and underperforms once installed. The usual reaction is to specify a stronger magnet, which is the expensive fix for a geometry problem.
Prevention: describe the full installed environment during design. Adding or repositioning steel is often cheaper and more effective than upgrading material.
4. Performance varies lot to lot
The first production run measures at the top of the acceptable band. The third measures at the bottom. Nothing changed in the process.
Magnet properties are published as ranges and minimums, not single values, because real material varies within a specification. An assembly designed with no margin against the low end of the range performs inconsistently even when every magnet conforms.
Prevention: design against the low end of the published range rather than the midpoint, and agree an acceptance criterion tied to the functional requirement instead of to a nominal value.
5. Magnets get damaged or misplaced during assembly
High-energy magnets are difficult to handle in an assembly operation. They attract each other and every ferrous tool nearby, they can chip on impact, and aligning them against their own attraction is slow and inconsistent work.
This is a manufacturing problem that originates in design, and it is one of the reasons the sequence of operations matters. Magnetizing after the assembly is built, rather than assembling already-magnetized parts, changes what is practical during handling, alignment and bonding. We do this in house where the application allows it. Whether it suits a given part depends on the construction, so it is worth raising early.
Prevention: involve the people who will build the assembly during design, and ask your supplier what the assembly sequence looks like before you lock the geometry.
6. The magnetic problem surfaces after the mechanical design freezes
The other five problems all get worse with timing. Changing a magnet grade at concept stage costs a conversation. Changing it after the housing tooling exists costs the tooling.
Prevention: bring in magnetic input while the geometry is still soft.
Catching these earlier
Adams Magnetic Products reviews customer designs for these failure modes as part of our engineering support, whether or not the part is already ours. If you have an assembly that is underperforming, or a design you would like a second opinion on before you freeze it, Talk to a Magnet Expert.
Already have a drawing? Send Us Your Drawing and we will review the magnetic side and come back with what we would change and why.
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