Magnetics are often critical to a winning automotive or otherwise motor-based project. Some engineers don’t even realize they need a component with magnetic properties for their design (or that powdered metal can offer those properties).
Those who do recognize the need for magnetism still may simply think of it as “magic” -- that’s probably what the ancient Greeks thought when they were lugging around lodestone. Well, it’s not magic -- it’s some pretty serious science that is actually in the same family tree as electricity.
Trying to develop a strong metal product with the right magnetic qualities? Let’s break it down in simple terms.
The Basics of Magnetics
Magnetic materials are essential to today's electronics. From the motors that power industry to transformers that make your Dell turn on, magnetics are becoming increasingly crucial to consumer goods. When used properly, they offer:
- Lower manufacturing costs
- Greater reliability
- Higher energy efficiency
How do you produce electricity from magnetism? In layman’s terms, you place a metal wire near a magnet (and therefore inside a magnetic field). Moving the wire or magnet will cause the magnetic field to fluctuate and, in turn, electricity to head through the wire. As long as you keep one or the other moving, you’ll continue to make electricity.
(DYK? We measure magnetic field strength in units called teslas, named for electricity pioneer Nikola Tesla. You can also use kilogauss: 10 of them = 1 tesla.)
Everything with an electric motor in it (i.e. your lawn mower) uses that magnetoelectricity to create motion. The magnetic field you create pushes against the field of a permanent magnet, causing the inside part of your motor to rapidly spin. This motion is your source of massive machine power!
Powdered Metal: Permanent (Hard) Magnetics Vs. Soft (Temporary) Magnetics
In many applications, it pays to know the difference between permanent and soft magnetics.
Hard and soft magnets come in varying sizes and strengths. The term “permeability” refers to how easily a material can be magnetized. Note that high permeability is ideal for applications in which you need lightning-fast response to an applied current.
Anyway, that custom magnet of your kid’s awkward school photo that’s hanging stuff up on your fridge? It’s a permanent magnet. It always keeps its magnetism.
High-carbon steel is an example of a hard magnetic material, especially when heat-treated. Alloys of iron and rare-earth metals retain much of their magnetism, even if away from a magnetic field, so they make good permanent magnets, too.
But not all magnets work this way.
Soft magnetic materials are those that can easily be both magnetized and demagnetized. Compared to their hard counterparts, soft magnetic materials have:
- Increased permeability
- Higher saturation induction
- Lower coercive force values
Examples of soft magnetic materials include iron and nickel. Even steel can be a soft magnetic -- a good example is the alternator in your car, which uses a low-carbon version of steel. It’s cheaper than using a low-carbon hard magnetic steel.
(DYK? Heating a permanent magnet to a certain point can rearrange its atoms and turn it into a temporary magnet.)
Materials like iron turn into lovely temporary magnets when you put a magnet nearby, but tend to lose some or all magnetism when you take that magnet away.
Soft magnetic materials are great for powder metallurgy and are typically classified as either DC or AC applications:
DC (Direct Current)
These applications use consistently applied magnetic fields.
The most common DC projects are automobile-related. These applications typically use a press and sinter process. Your choice of alloy system, density, and sintering practice will impact what sort of magnetic quality ensues.
AC (Alternating Current)
AC applications require a constantly changing applied magnetic field. Once upon a time, these applications were limited to steel lamination processes. Today, powdered metal can be used in AC projects thanks to high-performance polymer- and oxide-coated powders.
Where Powdered Metal Comes In
In powder metal parts, magnetic performance is a function of
- Alloy system used
- Density of final part (Compaction can improve density and, in turn, magnetic properties.)
- Saturation induction and permeability
- Sintering temperature
- Carbon and nitrogen contents after sintering
Note: Sintering is for DC applications only. Soft magnetic composites are not sintered, but are instead low-temperature annealed.
Advantage of Magnetics in PM
The use of powder metal parts continues to grow. The automotive industry in particular has embraced the technology. This despite a lot of misconceptions and lack of knowledge about powdered metal among some designers!
The advantages of the powder metals parts making process in magnetic applications are similar to the advantages offered in structural applications. Specifically, these include:
- Greater material usage
- Ability to produce complex shapes to net shape
- Ability to tailor magnetic properties to your application by controlling material and processing parameters.
Thanks to insulated particle materials, it’s now possible to define a 3-D magnetic field. You and your powder metal component vendor can improve a current concept or even create an entirely new one!
Powder metal processing is unique in that your desired magnetic properties can be adjusted via part density and sintering to meet certain requirements.
A few words of caution: Repressing a powder metal part severely hampers its magnetic properties. Following up with annealing will eliminate the decrease in magnetic performance a restrike causes.
Now That You’ve Got the Basics ...
Congrats! You’ve got an intro to magnetics under your belt. Hopefully you’ve also gained an understanding of how they work hand in hand with powder metal parts.
If you have any more questions about how magnetics impact part performance -- and how powder metal components solve these issues -- let us know.