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Injection Molded Magnets - Pros and Cons · Geometry Large variety Determined by injection molding...
Transcript of Injection Molded Magnets - Pros and Cons · Geometry Large variety Determined by injection molding...
Injection Molded Magnets - Pros and Cons
Thomas Schliesch
Max Baermann GmbH, Bergisch Gladbach
Germany
1 Injection Molded Magnets – Pros and Cons
Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
• Injection molded magnets: Overview
• Aspects of magnetic strength in different sorts of applications
• Examples for motor and sensor applications
• Design and quality control
• Problems and future perspectives
Contents of Presentation
2 Injection Molded Magnets – Pros and Cons
Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
Injection Molded Magnets: Applications/Overview
Advantages •Complicated shapes (pro)
•High variety of field distributions (pro)
•High density of functions (pro)
•Large output rates (pro )
Disadvantages •Reduced fields and forces (con)
•Limited temperature range (con)
•Limited mechanical stability (con)
Industry •Automotive
•Household
•Computers and electronics
•Medicine
Injection Molded Magnets – Pros and Cons Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
3
Applications: •Field sources for sensors
•PM for electrical machines
•Magnetic couplings
•Magnetic bearings
•Gaskets
Injection Molded Magnets: Manufacturing
4 Injection Molded Magnets – Pros and Cons
Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
Injection Molded Magnets: Manufacturing by In-Mold-Magnetizing
5 Injection Molded Magnets – Pros and Cons
Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
pro
Mainly used
for Ferrites
pro
Injection Molded Magnets: Magnetization by Pulse Discharge Process
Injection Molded Magnets – Pros and Cons Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
6
Mainly used
for Rare Earth magnets
Features Values Remarks
Remanent polarization
Br
0.1T-0.8T Decreased by polymer delusion (con)
Intrinsic coercivity Comparable with bulk
materials
Application temperature -60°C - +200°C Mainly limited by polymer behavior (con)
Tensile strength 20MPa - 100MPa
(room temp.)
Large variations with temperature due to
polymer behavior (con)
Magnetization patterns
and fields
Large variety, any
locations
Tailoring of internal polarization patterns
and anisotropies possible (pro)
Combinability with
other parts
Easy By overmolding processes,
cost effective (pro)
Geometry Large variety Determined by injection molding (pro)
Injection Molded Magnets: Table of Characteristics
7 Injection Molded Magnets – Pros and Cons
Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
Injection Molded Magnets: Strength of Magnetization
=> Volume fraction of magnetic material determines performance !
E.g. a typical volume fraction is 60% (which means ~ 90% mass percent of
magnetic material for many sorts of compounds) => Mc ~ 0.6M0 (con)
C
i
0
C
i0
C
i
CV
V
MV
VM
V
m
M
iii
or
Injection Molded Magnets – Pros and Cons Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
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C
M0C
V
VMM con
Magnetic particles with raw material magnetization M0 diluted in a polymer matrix.
Vc compound volume, VM total magnetic volume, Vi volume of single particle,
Mc: Resulting magnetization of compound
Permanent Magnets – Strength of M Determines Strength of H and B
From Maxwell equations follows for the field H of permanent magnetic materials:
Example: Axial field above an uniaxially magnetized disc (center position):
22
a
22
a dr
d
)hd(r
hd
2
MH(d)
A V
'
'
''
'
'
dVrr
M
4π
1dA
rr
nM
4π
1)r(H
Injection Molded Magnets – Pros and Cons Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
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a0 MHμB )'r(fM)'r(M a
(Ma average strength of magnetization)
outside magnet
Magnetic Sensors and Injection Molded Magnets
Injection molded magnets are very popular for magnetic sensors due to:
- High variety of field shapes
- Geometry
- Combinability
- Fast production of large numbers
10 Injection Molded Magnets – Pros and Cons
Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
The lack of field strength of injection molded magnets often plays a minor role for magnetic
sensors due to:
- The development of more sensitive sensors
- Position sensors that detect or calculate field directions are independent
of field strengths over wide ranges of operation (pro)
- Field strengths can often be increased by slight dimensional changes (pole face) or by use of back iron
assemblies
0
rad
tan2 )
B
B(atan
p
1
pro
(measured angular position φ as a function of two field components,
p-> number of pole pairs)
Injection Molded Magnets for Magnetic Clamping and Coupling
Injection Molded Magnets – Pros and Cons Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
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dAnˆμμ
1F A
0r
)B2
1(BBBBB
BB)B2
1(BBB
BBBB)B2
1(B
ˆ
22
zyzxz
zy
22
yxy
zxyx
22
x
Maxwell Stress Tensor Θ:
2
aMF
0F 0.36 F
Magnetic Coupling, A-> air gap area, torque T:
if filling grade is 60% volume
e.g. for a clamping system
tanrad BBAT 2
aMT
Due to the dependence of the square of magnetization injection molded magnets
are used only for low strength couplings or clamping systems.
Magnetic Clamping, force F:
con
con
Injection Molded Magnets for Rotating PM Machines
MATH Maximum torque TH is proportional to strength of
magnetization M (and air gap area A) (con)
2
H
F )T
T(1η => Maximum efficiency decreases with decreasing strength of
magnetization (con), TF -> frictional torque
Even though the strength of injection molded magnets leads to inferior motor
performance, machines of lower power consumption are often built by using such
magnets. This is mainly done when:
- Complicated geometries of rotors are needed (pro)
- Special field shapes are demanded (pro)
- Magnet performance can be balanced by volume enlargement or increase of numbers
of windings
Injection Molded Magnets – Pros and Cons Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
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Examples: Sensor Magnets for Rotary Position Detection (On-Axis)
Off-axis position sensors: Sensor is located at or near the
center of rotation. 2D-Hall sensors or MR field direction
sensors are mostly used, two poles in the majority of cases
0
rad
tan2 )
B
B(atan
p
1
)sin(BB 0rad
)(cosBB 0tan
Injection Molded Magnets – Pros and Cons Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
13
1p
Examples: Sensor Magnets for Rotary Position Detection (Off-Axis)
Off-axis position sensors: Sensor is located radially
outside external circumference of cylindrical
specimen. 2D-Hall sensors or MR field direction
sensors in most cases. Amplitudes are usually not the
same for both field components, field shape is not
always sinusoidal. Number of poles starts with 2 but
can also be quite large.
0
rad
tan2 )
B
B(atan
p
1
)f(BB 1rad
)g(BB 2tan
Injection Molded Magnets – Pros and Cons Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
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1p
24 poles
4 poles
Examples: Rotor Magnets for Electrical Machines
Rotor magnets with different polarity
and field shapes and different inserts
(metal shafts or plastic bushes)
Different traces for torque and
signal generation are used fairly often
Injection Molded Magnets – Pros and Cons Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
15
FEM-Design Method for Field Oriented Magnets
Magnetizing Field
H’
Calculation of
Br and µr
mold magnet
Injection Molded Magnets – Pros and Cons Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
16
pro and con Optimization of magnet performance by tailoring field shapes raises the variety of technical solutions (pro)
but is fairly challenging (con)
FEM-Design Method for Pulse Magnetized Magnets
Magnetizing Field
H’
Calculation of
Br and µr
magnet
magnetizing coil
17 Injection Molded Magnets – Pros and Cons
Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
pro and con
Optimization of magnet performance by tailoring field shapes raises the variety of technical solutions (pro)
but is fairly challenging (con)
Magnetic Design by Analytical Software
A
dA''r-r
'nM
4π
1dV'
'r-r
M'
4π
1)r(
rr
V
rM
E.g. by solution of
Poisson equation: ΦH
Covers approx. 70%
of our daily design
work
Problem input and
solution are done
within a few seconds
only !
Treatment of many sorts
of different magnets
with up to 256 poles
Injection Molded Magnets – Pros and Cons Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
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Covers molded
and sintered magnets
Magnetic Quality Control
Automated sensor device with 4 different types of sensors for quality control in production sites
Injection Molded Magnets – Pros and Cons Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
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pro
Magnetic Quality Control
Check of each sort of magnet with own measuring routines, statistical data evaluation,
results accessible via intranet
Injection Molded Magnets – Pros and Cons Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
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pro
Mechanical Stability Issues and Their Solution
Different coefficients of thermal expansion
can lead to large internal stresses and
cracks. Solution is often an intermediate
layer made of low filled polymer for
damping
Injection Molded Magnets – Pros and Cons Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
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con
pro
Injection Molded Magnets – Pros and Cons Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
22
Mechanical Stability Issues and Their Solution
System design with the help of mechanical stability simulations
(pro and con). Attempts to develop materials with higher
elasticity/plasticity and comparable magnetic performance
to standard compounds (pro).
Maximum stress variation inside a magnet at
temperature cycle between -40°C and 125°C
Mechanical parameters of standard and improved
Ferrite/PA materials
Mechanical Stability Issues and Their Solution
- Rotors for water pumps made of PPS/Ferrite: Special PPS compositions can solve problems
to withstand temperature shock tests (pro).
- Mechanical stability control of magnetic compounds has to be applied continuously
for water pump magnets (con).
Injection Molded Magnets – Pros and Cons Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
23
Attempts to Solve the Strength Issue: Ferrites
Raise of remanence by increase of filling grade up to
70% of volume for a Ferrite-polyamide composition.
Filling grade enhancements are mainly limited by
mechanical strength issues.
Hybrid compounds: Compositions can be tailored to fill the gap between Ferrites
and Rare Earth materials by addition of e.g. NdFeB, but materials become expensive !
Injection Molded Magnets – Pros and Cons Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
24
pro
pro and con
Strength Issue: Anisotropic Rare Earth Compounds
-4000
-3000
-2000
-1000
0
1000
2000
3000
4000
0 40 80 120 160 200 240 280 320 360
Flu
x d
en
sit
y [
G]
Angle [°]Ferrite
NdFeB-anisotropic
Comparison of a multipolar rotor magnet made of
Ferrite and anisotropic NdFeB-HDDR powder
(PA-binder)
Injection molded anisotropic NdFeB-HDDR materials can originate large
remanences between 700mT (PPS based) and 800mT (PA based), but thermal stability
often does not meet automotive specifications. Similar results are valid for
SmFeN-materials
Demagnetizing curve of anisotropic NdFeB
compound with PPS binder
Injection Molded Magnets – Pros and Cons Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
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pro and con
Injection Molded Magnets - Pros and Cons
Injection Molded Magnets – Pros and Cons Magnetics 2017, Orlando, FL - Thomas Schliesch, Head of Research and Development
Email: [email protected], Phone: +49(0)22048309141
26
Thank you for your attention !