Good Morning!
Thank Magnetics Magazine
for successfully organizing
this event and I am
honored to be here today.
Today’s topic:
Economic Manufacturability of
Quality Magnets and
Assemblies
Custom Made Magnets
Most motor magnets are custom made.
First, they are custom made to the drawing
specifications which include the similar
contents of any other mechanical
components.
Second, they are magnets. There are some
significant differences between a magnet
and a regular mechanical component in
terms of specifying and making them.
Some Differences Between Regular
Mechanical Components and Magnets
Regular Mechanical
Components
Magnets
Material
e.g. A Stainless Steel Shaft
e.g. An N45SH 14 Arc Rotor
Mechanical
properties
Tensile Strength, Yield Strength, Young's
Modulus, Elongation and ETC.
Typically not Specified
Heat Treatment
Typically Specified
Typically not Specified
Typically not Specified
Typically Specified
N/A
Could be Specified
Magnetizing
N/A
Always specified
Coating
Depending on material
Typically Specified for
NdFeB
Magnetic
Properties
Magnetic
Orientation
Let’s Focus on the Magnets
1 Magnetic Properties Br, Hc, Hci, BHmax, ETC
2 Magnetic Orientation Could be specified
3 Magnetizing or not
Always specified
4 Coating or Plating
Typically specified
5 Surface Finish
Typically not specified if it is
coated or plated
1. Magnetic Properties
Different suppliers may specify
differently: some offer minimum
value while others give ranges or
just some nominal values
How to correlate the magnetic
properties to the performance of
motor or other magnetic device
is the focus of design engineers.
1.1 A True Story
1.1.1 Specified N42H is rejected.
1.1.2 N48H is eventually accepted
1.1.3 Specs are still not changed.
1.2 Why there is a gap?
1.2.1 BH curve is the simplified proof.
1.2.2 Accumulated dimensional variations
1.2.3 Possible impact of high temperature
1.2.4 The geometry effects the operating
point or the load line
1.2.5 Impact of manufacturing method
1.2.6 The variations of other motor parts
1.3 Suggestion to Specify on Drawing
1.3.1 Do your due diligence, FEA
1.3.2 Check with suppliers’ specs.
1.3.3 Being flexible to adopt suppliers’
magnetic specifications
1.3.4 Closely monitor and evaluate the
prototype and make necessary
adjustment
1.3.5 Use your magnet supplier for
manufacturability review
2. Magnetic Orientation
2.1 In most case, it’s not specified
if the magnet is supplied to be
magnetized and it’s in the same
direction of magnetization.
2.2 It must be specified if the
magnet is supplied un-magnetized
2.3 It must be specified if the magnet is
supplied magnetized in more than
one direction. e.g. 2 poles on 1 face
3. Magnetizing (1/3)
3.1 Always specify the magnet
to be supplied magnetized or not.
3.2 If the range of magnetism is
tight, try to establish a way to
measure so both customer and
supplier can use it.
3. Magnetizing (2/3)
3.3 Inspect Gauss versus Flux
3.4 Inspect Gauss or Flux plus BH curve
3.5 Establish the correlation between
the Gauss or Flux and magnetic
properties to the performance of
motor or device
3. Magnetizing (3/3)
4. Corrosion Resistance
4.1 Mainly NdFeB magnets need to be
plated or coated.
4.2 Plating or coating will effect the
dimensional tolerance
4.3 Typically +/-.002” after plating and
tighter can be held but costs more
5. Dimensional & Geometric Tolerances
5.1 Suitable Tolerances
The most relaxed tolerance but
still will function in the application
5.2 Tighter tolerance can be held but
that could cost more.
5.3 Over 7.25 million pcs have been
delivered with tolerance of +/.00025” on inner diameter without
any incidence.
6. Simplify the Geometry
6.1 Most magnets are hard and brittle.
6.2 The typically ways to machine them
are grinding and EDM from blocks.
6.3 In most case they can’t be
machined like other metal
components.
Summary
Because of the differences between
regular mechanical components and
magnets, use your magnet supplier to
review your magnet design for
suitable tolerances and the economic
manufacturability.
THANK YOU!
Questions?
Please visit www.ppactech.com for more details.