Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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A METHOD FOR THE ADDITIVE MANUFACTURE OF MAGNETIC MATERIALS
FIELD OF THE INVENTION
[0001] The present invention relates generally to the field of magnetic
materials, particularly
soft magnetic alloy and methods for the production of the same.
BACKGROUND OF THE INVENTION
[0002] The following discussion of the background to the invention is intended
to facilitate an
understanding of the present invention. However, it should be appreciated that
the discussion
is not an acknowledgment or admission that any of the material referred to was
published,
known or part of the common general knowledge in any jurisdiction as at the
priority date of
the application.
[0003] Soft magnetic alloys fall under a specialized group of functional
materials in which
magnetic performance properties define the end products. These types of
magnetic products
have been traditionally fabricated from sheet magnetic material using stamping
process
Unfortunately, these materials also tend to be brittle because of the
formation of B2 and D03
chemically ordered phases during slow cooling, making it difficult to machine
these materials
Moreover, the magnetic properties are very sensitive to their processing
methods and can
significantly deteriorate during such processing. Soft magnetic materials in
powder form are
isotropic and thus possess 3D magnetic flux lines compared to a planar that
allows in two
dimensions only. Typical magnetic properties of consideration for a soft
magnetic core in
highly efficient electrical machines are high magnetic saturation,
permeability, low coercivity,
specific hysteresis/eddy current losses and magnetostriction wherein
permeability (p.) is the
result of magnetic flux density (B) divided by applied magnetic field or
magnetic force (H).
Magnetic flux density (B) is expressed as in Tesla (T) whereas magnetic force
(H) is expressed
as amperes per meter (AIM).
[0004] The present invention can be leveraged to meet with the various
requirements of the
soft magnetic alloy electromagnetic component:
D Fabricating parts in whatever complex design it is required to be made to.
D Processing a wide variety of magnetic materials in customised chemical
composition.
D Tuning the functional properties to match the targeted performance.
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Topology Optimization tools to lightweight or miniaturize the parts without
compromising on its functionality.
)> Customize production "On demand" and in as small a batch size as a single
unit.
[0005] To address the issues that arise in working with these materials during
manufacture,
some groups have attempted to manufacture parts from such magnetic alloys via
additive
manufacturing (AM), or 3D printing, from designing alloy powder compositions
using direct
energy deposition or similar laser-based AM process. The chemical composition
and
crystallographic orientation of the soft magnetic alloy directly influence the
hysteresis losses
of the additively manufactured material. Small hysteresis losses and high
electrical resistivity
are important factors in designing the electric machine core because it is
subjected to thermal
and magnetization/demagnetization cycles during service that result in large
energy losses from
iron dissipation and magnetostriction effect of the material. However, the
prior arts have met
with mixed results. Although elements having near-net shape were formed, the
magnetic
properties of elements formed using such techniques were determined to be sub-
optimal.
[0006] The present invention attempts to overcome at least in part some of the
disadvantages
and to provide a key enabling technology for implementing additive
manufacturing techniques
to enable near net fabrication of magnetic materials for components such as
stators for specific
implementations.
Summary of the Invention
[0007] The following presents a simplified summary of one or more
aspects in order to
provide a basic understanding of such aspects. This summary is not an
extensive overview of
all contemplated aspects, and is intended to neither identify key or critical
elements of all
aspects nor delineate the scope of any or all aspects. Its sole purpose is to
present some
concepts of one or more aspects in a simplified form as a prelude to the more
detailed
description that is presented later.
[0008] In a first aspect, the present disclosure provides a method
for forming an additively
manufactured magnetic component comprising: preparing a feedstock material of
a powderized
ferrosilicon alloy; configuring process parameters for obtaining the
additively manufactured
magnetic component with a predetermined property; applying a suitable additive
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manufacturing process on the feedstock material to form the additively
manufactured magnetic
component; and heat treating the additively manufactured magnetic component
wherein the
heat treating comprises the following steps: annealing the additively
manufactured magnetic
component at an increasing temperature of 10 C ¨ 30 C per minute beginning at
about 700 C
and ending at about 1150 C; applying stress-relief annealing on the additively
manufactured
magnetic component for at least 3 to 5 hours at a temperature of about 700 C
to about 850 C;
annealing the stress-relieved annealed additively manufactured magnetic
component for about
1 hour at a temperature of about 1050 C to about 1150 C; and cooling the
annealed additively
manufactured magnetic component to a temperature of up to 300 C in an
atmosphere of an
inert gas.
[0009] In some embodiments, the additively manufactured magnetic
component comprises
a magnetic alloy including iron and silicon.
[0010] In some embodiments, the powderized feedstock of the
ferrosilicon alloy consists
of 6.2-6.8wt% of Si, trace elements 0.002 to 0.02 wt% of C, .02 to 0.07 wt% of
0, and 0.001
to 0.012 wt% of S; and the balance Fe.
[0011] In some embodiments, the powderized feedstock of
ferrosilicon alloy consists
6.5wt% Si.
[0012] In some embodiments, the powderized feedstock of the
ferrosilicon alloy is gas
atomized, spherical and has a particle size ranging from between about 10 to
53 1.un.
[0013] In some embodiments, the powderized feedstock of the
ferrosilicon alloy has a
Hausner Ratio of less than or equal to about 1.15.
[0014] In some embodiments, the step of preparing the powderized
feedstock material of
the ferrosilicon alloy includes heating the powderized feedstock material of
the magnetic alloy
at a temperature of between about 70 C to about 200 C for about 2 hours in a
vacuum furnace.
[0015] In some embodiments, the suitable additive manufacturing
process is selected from
a group of powder bed fusion (PBF) processes.
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[0016] In some embodiments, the additively manufactured magnetic
component is made
from a plurality of successive layers of a deposited feedstock material
comprising a powderized
ferrosilicon alloy using a thermal energy source having a volumetric energy
density of between
about 70 to about 160 Jimm3.
[0017] In some embodiments, the thermal energy source is a laser.
[0018] In some embodiments, the thermal energy source is controlled
by modifying at least
one or more of the following parameters: spot size, scan speed and power.
[0019] In some embodiments, the step of modifying an internal
energy of the powderized
magnetic alloy prior to the heat treating is such that a grain structure is
formed in the heat-
treated additively manufactured magnetic component.
[0020] In some embodiments, the step of annealing performed on the
additively
manufactured magnetic component is in an inert gas ambient controlled furnace.
[0021] In some embodiments, the step of annealing is performed at a
minimum annealing
temperature of at least 700 C.
[0022] In some embodiments, the step of cooling is conducted in an
argon gas ambient up
to 300 C and thereafter cooled in a normal atmosphere.
[0023] In some embodiments, the annealed additively manufactured
magnetic component
comprises a body having a porosity level of less than or equal to about 0.5%
and maximum
crack length of less than or equal to 100 [tm.
[0024] In some embodiments, the step of modifying the internal
energy comprises varying
the grain structure of the powderized magnetic alloy to obtain a desired grain
structure in the
additively manufactured magnetic component.
[0025] In some embodiments, the predetermined property of the
additively manufactured
magnetic component comprises a body having an average grain size range between
350 jAm to
500 um.
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[0026] In some embodiments, the varying of the grain structure
leads to a variance in one
or both of a magnetic property of the additively manufactured magnetic
component, selected
from the group of coercivity, permeability, magnetic saturation, core loss and
flux density; and
a mechanical property selected from the group of hardness and strength.
[0027] In some embodiments, the predetermined property of the
additively manufactured
magnetic component includes a hardness value in the range of 350 to 430 HV.
[0028] In some embodiments, the predetermined property of the
additively manufactured
magnetic component includes a core loss comparable to commercial non-oriented
electrical
steel in specific grades.
[0029] In a second aspect, the present disclosure provides a method
for heat treating an
additively manufactured magnetic component. The method comprises: annealing
the additively
manufactured magnetic component from 700 C to 1150 C with the heating rate
ranging from
C ¨ 30 C per minute; applying stress-relief annealing on the additively
manufactured
magnetic component for at least 3 to 5 hours at a temperature of about 700 C
to about 850 C;
annealing the stress-relieved annealed additively manufactured magnetic
component for about
1 hour at a temperature of about 1050 C to about 1150 C; and cooling the
annealed additively
manufactured magnetic component to a temperature of up to 300 C in inert gas
ambient at a
cooling rate of 1-2 C/min.
[0030] In some embodiments, the additively manufactured magnetic
component comprises
a magnetic alloy including iron and silicon.
[0031] In some embodiments, the additively manufactured magnetic
component further
comprises Carbon, Sulphur, or a combination thereof
[0032] In some embodiments, the additively manufactured magnetic
component is heat
treated at a temperature in a range of 700 C to about 1150 C.
[0033] In some embodiments, the heat-treated additively
manufactured magnetic
component has a median grain size in a range from about 350 lam to about 500
lam.
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[0034] In some embodiments, the saturation flux density of the heat-
treated additively
manufactured magnetic component is about 1.00 Tesla.
[0035] In some embodiments, the additively manufactured magnetic
component has a
saturation flux density at 1.00 Tesla at 50 Hz and average microhardness
values in the range of
350 to 430 HV.
[0036] In some embodiments, the additively manufactured magnetic
component is at least
a component of an electrical machine.
[0037] In some embodiments, the additively manufactured magnetic
component is selected
from any one from the group of: motors, stator or rotor cores, generators,
inductors and
solenoids.
[0038] In a third aspect, there is provided an additively
manufactured magnetic component
formed by the method as disclosed in the first aspect above, comprising: a
body formed from
a plurality of successive additively bonded layers of at least a magnetic
alloy comprising at
least Fe and Si, wherein the body has a density of at least 99.988%; and a
saturation
magnetization of at least 1.00 Tesla at 50 Hz, a coercivity of less than 20
Oe, a maximum
relative permeability of approximately 16,000 at 1.4 Tesla, 5000 A/m under DC
condition and
approximately 2,100 at 1 Tesla, 50 Hz under AC condition.
[0039] Additional benefits and advantages of the disclosed
embodiments will become
apparent from the specification and drawings. The benefits and/or advantages
may be
individually obtained by the various embodiments and features of the
specification and
drawings, which need not all be provided in order to obtain one or more of
such benefits and/or
advantages.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] In the drawings, like reference characters generally refer to the same
parts throughout
the different views. The drawings are designed for purposes of illustrations
only, and not as a
definition of the limits of invention, emphasis instead generally being placed
upon illustrating
the principles of the invention. The dimensions of the various features or
elements may be
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arbitrarily expanded or reduced for clarity. In the following description,
various embodiments
of the invention are described with reference to the following drawings, in
which:
[0041] Figure. 1 is a flow-chart of the process for forming an additively
manufactured
magnetic component in accordance with embodiments of the invention.
[0042] Figure. 2 is a flow-chart of the process for heat treating an
additively manufactured
magnetic component in accordance with embodiments of the invention.
[0043] Figure. 3 is a schematic diagram on the annealing cycles conducted on
the additively
manufactured magnetic component from initial room temperature of 23 C up to
700 C with a
hold time of 3 to 5 hrs, thereafter from 700 C to 1075 C with a hold time of
lhr subjected to a
heating rate of 10 to 30 C/min ending at 1150 C under protective Argon gas in
accordance
with embodiments of the invention.
[0044] Figure. 4(a) is the OM micrograph of a FeSi 6.5 powder morphology in
accordance with
embodiments of the present invention.
[0045] Figures 4(b)-(c) illustrate a plurality of mounted FeSi6.5 powder
samples in accordance
with embodiments of the present invention.
[0046] Figures 5(a)-(c) illustrate a plurality of stator core geometries
according to various
embodiments of the present invention.
[0047] Figures 6(a)-(c) illustrates a cube, a ring and a stator core
respectively according to
various embodiments of the present invention.
[0048] Figure 7(a) provides a porosity and crack analysis of the as-printed
sample in
accordance with embodiments of the present invention.
[0049] Figure 7(b) provides a porosity and crack analysis of an annealed
sample in accordance
with embodiments of the present invention.
[0050] Figure. 8(a) provides a melt pool analysis of the printed sample in
accordance with
various embodiments of the present invention.
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[0051] Figure. 8(b) provides a grain size analysis of an annealed sample in
accordance with
various embodiments of the present invention.
[0052] Figure. 9(a) provides a table that provides the test conditions and
indentation force of
1KgF employed to create the indents in accordance with the various embodiments
of the
present invention.
[0053] Figure. 9(b) show the changes in hardness (HV) from the as-printed
magnetic coupons
to annealed magnetic coupons respectively in accordance with various
embodiments of the
present invention.
[0054] Figure. 10 (a) provides an OM image of the elemental mapping's location
on as-built
FeSi6.5 sample and (b-c) EDX spectrum of as-fabricated FeSi6.5 sample in
accordance with
various embodiments of the present invention.
[0055] Figure. 11(a) illustrates a phase diagram of a FeSi6.5 sample based on
a
crystallographic phase analysis using XRD Analysis in accordance with various
embodiments
of the present invention.
[0056] Figure. 11(b) illustrates a unit cell structure of a FeSi6.5 sample
showing A2, B2 and
D03 phases based on a crystallographic phase analysis using XRD analysis in
accordance with
various embodiments of the present invention.
[0057] Figure. 11(c) illustrates a XRD pattern of a FeSi6.5 sample based on a
crystallographic
phase analysis using XRD analysis in accordance with various embodiments of
the present
invention.
[0058] Figure. 12 illustrates a table of results on the DC and AC magnetic
properties of a
FeSi6.5 alloy sample in accordance with various embodiments of the present
invention.
[0059] Figures. 13(a) and 13(b) and 14(a) illustrates the graphs of DC
hysteresis curves of
FeSi6.5 alloy samples in accordance with various embodiments of the present
invention.
[0060] Figures. 15 (a-b), 16 (a-b) and 17(a) illustrate graphs of the AC
hysteresis curve of a
FeSi6.5 alloy sample in accordance with various embodiments of the present
invention.
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[0061] Figure. 18 illustrates a top view of a stator core component that is
additively
manufactured in accordance with various embodiments of the present invention.
DESCRIPTION OF THE INVENTION
[0062] The following detailed description refers to the accompanying drawings
that show, by
the way of illustration, specific details, and embodiments in which the
invention may be
practiced. These embodiments are described in sufficient detail to enable
those skilled in the
stated-of-the-art practice in the invention. Other embodiments may be
utilized, and structural,
and logical changes may be made without departing from the scope of the
invention. The
various embodiments are not necessarily mutually exclusive, as some
embodiments can be
combined with one or more other embodiments to form new embodiments.
[0063] In order that the invention may be readily understood and put into
practical effect,
particular embodiments will now be described by way of examples and not
limitations, and
with reference to the figures. It will be understood that any property
described herein for a
specific product may also hold for any product described herein. It will be
understood that any
property described herein for a specific method may also hold for any method
described herein.
[0064] Furthermore, it will be understood that for any device or article or
method described
herein, not necessarily all the components or steps described must be enclosed
in the product
or device or method, but only some (but not all) components or steps may be
enclosed.
[0065] Approximating language, as used herein throughout the specification,
may be applied
to modify any quantitative representation that could permissibly vary without
resulting in a
change in the basic function to which it is related. Accordingly, a value
solidified by a term or
terms, such as "about", and "substantially" is not to be limited to the
precise value specified.
In some instances, the approximating language may correspond to the precision
of an
instrument for measuring the value. Similarly, "free" may be used in
combination with a term,
and may include an insubstantial number, or trace amounts, while still being
considered free
of the solidified term. Here and throughout the specification, range
limitations may be
combined and/or interchanged, such ranges are identified and include all the
sub-ranges
contained therein unless context or language indicates otherwise.
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[0066] In the specification the term "comprising" shall be understood to have
a broad meaning
similar to the term "including" and will be understood to imply the inclusion
of a stated integer
or step or group of integers or steps but not the exclusion of any other
integer or step or group
of integers or steps. This definition also applies to variations on the term
"comprising" such as
"comprise" and "comprises".
[0067] Embodiments of the present disclosure address the shortcomings in the
state-of-the-art,
including but not limited to the following. Complex designs and shapes cannot
be fabricated
from conventional stamping processes. The present invention provides a method
of fabricating
parts in whatever complex design it is required to be designed to:
= Conventional fabrication processes cannot make use of a wide variety of
magnetic
materials.
= Conventional fabrication processes cannot tune the functional properties
to match the
targeted performance.
= Conventional fabrication processes cannot miniaturize the parts without
compromising
on its functionality.
= Conventional fabrication processes cannot customize production "On
demand" and in
as small a batch size as a single unit.
[0068] Fe-Co alloys are alloyed with one or more materials have been used for
additive
manufacturing due to its high magnetic permeability, low coercivity, high
saturation and high
Curie temperature, for forming near net shape magnetic elements with high
magnetic
performance. However, this comes at the expense of higher production and
manufacturing
costs. The present invention intends to address this shortcoming as explained
in detail
hereinafter.
[0069] The present invention relates specifically to a soft magnetic alloy
having high density
(> 99.988%), reduced power losses and good mechanical properties for DC
applications and to
the production of the same. The present invention also relates to the novelty
of alloy design
composition and process/post-processing parameters optimization via Laser
Powder Bed
Fusion (L-PBF) of Additive Manufacturing. The soft magnetic alloy component
such as the
stator core is well suited in the manufacturing of high-performance permanent
magnet rotating
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motors such as the permanent magnet DC motors (PMDC) operating at high
frequencies
between 50 Hz up to 1000 Hz.
[0070] Inventors of the present application have found a heat treatment
procedure that provides
an ability to improve the magnetic properties of additively manufactured
magnetic components,
particularly with respect to ferrosilicon alloys, to substantially match the
magnetic properties
of commercially-produced motor components used for electric machines,
including but not
limited to stator cores, a 3 phase pulse motor stator, a claw pole, a Francis
turbine rotor, a
Halbach stator, a brushless DC motor stator, a DC motor stator, a rotor, a
brushless out runner
motor shell, a drum motor stator, and axial flux rotor, a windmill rotor, a
transversal flux rotor,
a dual tone mini siren stator, a transversal motor case, an axial rotor and a
3 phase motor
generator stator These magnetic properties are attained despite a marked
difference in
microstructure between the additively manufactured and conventional
manufactured
components. In some embodiments, an electric machine refers to an electric
motor that converts
electric power to mechanical power or to an electric generator that converts
mechanical power
to electric power.
[0071] Advantages of processing soft magnetic alloy powder via L-PBF AM are:
= Freedom to design material composition to match targeted performance and
build
very complex parts.
)> Control of processing and post-processing conditions to realize targeted
material
properties.
= Printing of net-shape parts eliminating the need for final machining
resulting in very
low scrap.
.> Most environmentally friendly process as there is no emission of gases and
generates
negligible scrap.
= Customized low volume production order can be done at a lower cost than
prevailing
methods.
[0072] To achieve the stated features, advantages and obj ects, the present
invention is directed
to an additively manufactured magnetic component, in accordance with the
embodiments
described herein, and is manufactured using an additive manufacturing
technique. The present
invention provides a method for forming an additively manufactured magnetic
component
comprising Iron (Fe) and Silicon (Si). The additively magnetic component
comprises FeSi6.5
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which is defined as comprising Silicon (Si) containing at least 6.5 wt.%Si.
The magnetic and
mechanical properties of the additively manufactured magnetic component can be
determined
based on one or more of the following parameters: core loss in W/kg, Flux
density (T),
operating frequency in Hz, Hardness of the material (HV) and operating
temperature range.
The present invention additionally provides a method of additively
manufacturing a magnetic
component comprising Fe and Si.
[0073] "Additive manufacturing" is a term used herein to describe a process
which involves
layer-by-layer construction or additive fabrication (as opposed to material
removal as with
conventional machining processes). Such processes may also be referred to as
"rapid
manufacturing processes". The additive manufacturing process forms net or near-
net shape
structures through sequentially and repeatedly depositing and joining material
layers. As used
herein the term "near-net shape" means that the additively manufactured
structure is formed
close to the final shape of the structure, not requiring significant
traditional mechanical
finishing techniques, such as machining or grinding following the additive
manufacturing
process.
[0074] In certain embodiments, suitable additive manufacturing processes
include, but are not
limited to, the processes known to those of ordinary skill in the art as
direct metal laser melting
(DMLM), direct metal laser sintering (DMLS), direct metal laser deposition
(DMLD), laser
engineered net shaping (LENS), selective laser sintering (SLS), selective
laser melting (SLM),
electron beam melting (EBM), fused deposition modeling (FDM), or combinations
thereof.
These methods may employ, for example, and without limitation, all forms of
laser radiation,
heating, sintering, melting, curing, binding, consolidating, pressing,
embedding, and
combinations thereof.
[0075] Figure 1 provides a flow-chart of the process for forming an additively
manufactured
magnetic component in accordance with embodiments of the invention. The
process begins
with step 20 by preparing a feedstock material comprising a powderized
ferrosilicon alloy
material In some embodiments, a gas atomized FeSi6 5 soft magnetic alloy
powder is used
Ferrosilicon alloys typically have lower porosity levels, higher density, a
better average grain
size, and better magnetic properties. Typically, powderized ferrosilicon alloy
material is an
iron-based powder. However, compared to iron-silicon, the inclusion of Silicon
makes the
ferrosilicon alloy possess very high electrical resistivity compared to other
alloying elements
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such as cobalt. This is an attractive property to have while designing
electromagnetic
components. Silicon is also a much cheaper alloying element compared to other
alloying
elements such as cobalt or nickel thus making the printed part economically
viable when
compared to the laminated steel part. The use of Cobalt as an alloying element
is its much
superior magnetic and thermal properties, however, this comes at a prohibitive
cost for most
applications so it is not normally used. In some embodiments, the composition
of the
powderized Ferrosillicon (Iron-Silicon) alloy material comprises the following
(in wt.%):
Fe- Bal
Si ¨ about 6.2-6.8 wt.%
C ¨ about 0.002 to 0.02 wt.%
0 ¨ about 0.02 to 0.07 wt.%
S ¨ about 0.001 to 0.012 wt.%.
In some embodiments, the powderized ferrosilicon alloy consists of 6.5wt% Si.
[0076] In some embodiments, preparation of the feedstock material comprising
the powdered
ferrosilicon alloy material includes a powder characterization process in a
pre-processing stage
which involves investigating the powder morphology. In some embodiments,
powder
morphology such as granulometry (Particle Size Distribution Analysis) and
flowability
(Hausner Ratio < 1.15) properties are determined to ascertain its suitability
for use. In some
embodiments, the powder must be gas atomized, highly spherical and a targeted
particle size
range is within 10-53 microns. In some embodiments, sieving is done using a
multi-layered
mechanical sieving machine to recycle the powder multiple times to obtain the
desired particle
size range. Figure 4(a) provides an optical micro image of a FeSi6.5 powder
morphology of
mounted powder samples analysed under the Optical Microscope in accordance
with
embodiments of the present invention. Figure 4(b)-(c) illustrates a mounted
FeSi6.5 powder
sample. The aforesaid images are obtained to ascertain recyclability of the
powder after each
laser processing cycle. In some embodiments, a Hall Flow Test, Apparent
Density and Tap
Density collectively determine the powder flowability. These tests are
required to determine
the powder suitability to the additive manufacturing process.
[0077] Step 30 further describes configuring process parameters for obtaining
desired
magnetic and mechanical properties of a targeted magnetic component. To obtain
the desired
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magnetic and mechanical properties, one or more of the following parameters
are determined
accordingly: core loss in W/kg, Flux density (T), operating frequency in Hz,
Hardness of the
material and operating temperature range. In some embodiments, the desired
magnetic and
mechanical properties of the target magnetic component are that the
ferrosilicon alloy
component have achieved a porosity level of less than 0.5%, a near fully dense
99.988% high
silicon iron, an average grain size of between about 350 pm to 500 pm and a
core loss
comparable to commercial non-oriented electrical steel in specific grades.
[0078] In some embodiments, preparation of the powdered ferrosilicon alloy
feedstock also
includes preparing the data for use during the additive manufacturing step. In
some
embodiments, the data includes computer graphics of commercially produced
motor
components In some embodiments, the data is obtained in stl format using
Materialise Magics
Software. In some embodiments, the following steps are performed:
Importing Design File in. stl Format
Once the design file is ready from the CAD software, the design file is
imported to the
Materialise Magics software.
(ii) Editing of Data
Manual and automatic editing or fixing of the data is available once the
designed file is
imported. In some embodiments, minor editing could also be done such as adding
fillet to the
design, adding perforator, making hollow part, cut or punch. It will be
appreciated by a person
skilled in the art that this software is known in the art and any suitable
software can be utilised
for the preparation of the data to obtain the desired design specifications.
Figure 5(a)-(c)
illustrates a plurality of stator core geometries in .stl files using the
functions as noise shell
fixing, holes fixing, stitching etc.
(iii) Placement and Support Generation
[0079] Once the imported file is edited and the necessary editing is done,
placement of the
parts on the build plate is done. There is freedom to place the parts on the
build plates.
Otherwise, automatic placement option can be selected as one of the options.
After placement,
support generation is done for the part/s available in different types. Choice
of supports is
dependent on the part design and application and the software automatically
generates it
(iv) Slicing Parameters and File Calculation
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[0080] Various additive manufacturing techniques suitable for forming the
object are
employed. As in additive manufacturing, the parts are printed layer by layer
and profiles are
selected for slicing including selection of layer thickness and slicing
profiles. Once the
calculation is done, the file is sent to the machine for printing. It will be
appreciated by a person
skilled in the art that the choice of slicing parameters and file calculations
are known in the art
to obtain the desired design specifications.
(v) Powder Heating/Drying before Processing
[0081] In some embodiments, pre-heating of the powderized ferrosilicon alloy
is performed at
70-200 C for 2 hours in a vacuum furnace.
[0082] The method further includes a step 40 of applying an additive
manufacturing process
on the feedstock material to form an additively manufactured magnetic
component. In some
embodiments, the feedstock material comprising the powderized magnetic alloy
is deposited
through a suitable additive manufacturing process. In various embodiments, the
process may
be an energetic emission (eg. Laser) based process for example, powder bed
fusion (PBF) or a
Laser-Powder Bed Fusion (L-PBF). L-PBF is an additive manufacturing process in
which
focused thermal energy is used to fuse powder materials. Part of the process
of the L-PBF is
used to convert digital files of the part geometry into near net shape
components, as described
above. During the 3D printing process, the laser melting and part
solidification processes are
very tightly controlled to ensure development of the desired microstructure
and
crystallographic orientation of the material conducive to developing favorable
magnetic
properties in the final part. Optimum process parameters were evaluated from
iterative
experiments and printing outcomes. The energy density and magnetic performance
of 3D
printed cores are compared to the traditional laminated cores. Additive
manufacturing of soft
magnetic alloys is proposed as an innovative manufacturing method that allows
complex
design freedom and structure of stator cores which leads to an increase in the
efficiency of the
motor.
[0083] In some embodiments, various additive manufacturing techniques suitable
for forming
a desired object, layer-by-layer, at near net shape to finished dimensions may
be used. In some
embodiments, the process may be an energy emission-based process such as for
example,
powder bed fusion, in which focused thermal energy is used to fuse materials.
Other suitable
focused thermal energy sources, such as electron beam and plasma arc systems
may be used.
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In some embodiments, the feedstock material comprising the powderized magnetic
alloy is
processed using a laser-powder bed fusion technique. In some embodiments, a
Concept Laser
Mlab Cusing 100R system is used. In some embodiments, Design of Experiments
(DoE) are
carried out with controlling one or more of the following process parameters:
(i) Laser Power (W) ¨ about 70 to about 90W;
(ii) Layer Thickness (p.m) ¨ about 20 to about 60 p.m;
(iii) Scan Speed (mm/s) ¨ about 700 to about 1200 mm/s, and
(iv) Hatch Spacing (pm) ¨ about 40 to about 100 p.m.
[0084] The above process variables determine Volumetric Energy Density, VED
(J/mm3)
which is expressed as.
VED (E) = P I (v x d x t)
where v = velocity; d = hatch distance, t = layer thickness; P=laser power; E=
volumetric
energy density.
[0085] For each experiment, each process parameter was changed and evaluated
based on its
influence on the VED and the part quality. Through iterative experiments, an
optimum set of
parameters for achieving the best quality parts is obtained. In some
embodiments, the optimum
set of parameters include at least one or more of the following: Laser Power ¨
about 90 W,
Hatch Distance ¨ about 40 to about 100 p.m, Layer Thickness ¨ about 20 p.m,
and scan speed
of about 700 to 1200 mm/s. In some embodiments, at an optimum power of about
90W, the
optimum VED achieved is between about 70-160 J/mm3. Figure 6 illustrates
sample coupons
in the form of a cube, a ring and a stator core respectively, each of which
were printed for
detailed metallurgical and magnetic testing The method further includes a step
50 of heat
treating the additively manufactured target magnetic component with the
desired magnetic and
mechanical properties, as will be explained in detail hereinafter.
[0086] After the post-processing thermal treatments of the printed parts,
AC/DC magnetic
testing is carried out in step 60 to evaluate the AC/DC magnetic profiles and
verify the
functional properties whether the printed part meets with the conventional
core's mechanical
and magnetic properties.
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[0087] Turning to the heat-treating process, Figure 2 provides a method
comprising steps 41-
45 of additively manufacturing a magnetic component comprising Fe and Si. Step
41 provides
an additively manufactured magnetic component for forming targeted magnetic
properties.
Figure 3 is a schematic diagram on the annealing cycles which describe steps
41 to 45 on the
additively manufactured magnetic component from initial room temperature of 23
C up to
700 C with a hold time of 3 to 5 hrs, thereafter from 700 C to 1075 C with a
hold time of lhr
subjected to a heating rate of 10 to 30 C/min ending at 1150 C under
protective Argon gas in
accordance with embodiments of the invention.
[0088] The method further includes a step 42 of annealing the additively
manufactured
magnetic component at an increasing temperature of 10 to 30 C/min beginning at
about 700 C
and ending at about 1150 C. In some embodiments, annealing is performed on
additively
manufactured magnetic components in an atmosphere controlled or vacuum furnace
In some
embodiments, the additively manufactured magnetic component is annealed at
different
temperatures in the range of 700 C ¨ 1150 C at the rate of 10 - 30 C per min
under inert gas
in an atmosphere-controlled furnace to impart stress-relief, phase ordering
and improvement
in the grain structure.
[0089] The method further includes a step 43 of applying stress-relief
annealing on the
additively manufactured magnetic material for at least 3 to 5 hours at a
temperature of about
700 to about 850 C. In some embodiments, the stress-relief annealing is
performed at a heating
rate ranging from between about 10 C/min to about 30 C/min. In some
embodiments, argon is
fed to the annealing furnace. In some embodiments, the annealed magnetic
component placed
in the furnace to be heated at the rate of about 10 C/min at 700 C with a hold
time of 3 to 5
hours. In stress relief annealing, the stress-relieved annealed magnetic
component is heated to
a lower temperature and is kept at this temperature for some time in the
furnace to remove the
internal stresses produced in the annealed magnetic component.
[0090] The method further includes a step 44 of annealing the stress-relieved
annealed
magnetic component for about 1 hour at a temperature of about 1050 C to about
1150 C
[0091] The method further includes a step 45 of cooling the annealed magnetic
component to
a temperature of up to 300 C in an inert gas ambient with a slow cooling rate
of 1-2 C/min. In
some embodiments, the cooling is performed in an argon gas-controlled
atmosphere of up to
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3 00 C and thereafter cooled in normal atmosphere. The heating and cooling of
the magnetic
material during the additive manufacturing process and subsequent heat
treatment develops
and enhance the internal microstructure and the crystallography which
significantly improve
the magnetic and mechanical properties of the formed target magnetic
component. The heating
and cooling of the magnetic material create an energy history and stored
internal energy in the
formed component. Generally, the faster the material cools, the higher the
stored internal
energy in the material. This internal energy is used to recrystallize and grow
grains during
subsequent heat treatments. Therefore, when the internal energy is altered and
optimized to
form the part, the microstructure of the material changes with the combination
of subsequent
thermal post-processing. For as-printed parts, vertically columnar structures
are observed
whereas after desired thermal post-processing, the grains grow into more
equiaxed structure.
Part Characterization
[0092] The as-printed and annealed additively manufactured magnetic samples
are compared
to ascertain the effects of annealing on the structure of the magnetic
samples, namely changes
in porosity and cracks. It was observed that if the annealing temperature,
heating and cooling
cycle times and argon atmosphere are not controlled tightly then it can have
adverse effects on
porosity and cracks. Porosity, part density and crack analysis are performed
as part of a defect
analysis using Optical Microscopy ZEISS Axiolab 5, ZEN core v 2.7 imaging
software after
cross-sectioning, cold mounting, grinding and polishing the as-printed
additively manufactured
magnetic and annealed magnetic samples Figure 7(a) provides a porosity and
crack analysis
of the additively manufactured magnetic sample where average porosity =
0.013%, zero cracks
and part density = 99.987% as the as-built sample having good compromise of
porosity and
crack. These results meet with the positive analysis of an as-printed AI\4
magnetic samples
having criteria: porosity of less than or equal to 0.5% and maximum crack
length of less than
or equal to 100 pm. Figure 7(b) provides a porosity and crack analysis of the
annealed magnetic
sample in accordance with embodiments of the present invention. The post
annealed sample
has an average porosity = 0.022%, zero cracks and part density = 99.978%.
These results meet
with the positive analysis of an as-printed AM magnetic sample having
criteria: porosity of less
than or equal to 0.5% and maximum crack length of less than or equal to 100
pm.
[0093] The term "as-printed" additively m anufactured----m agneti c component
refers to an
additively manufactured magnetic component that has not been subjected to an
additional heat-
treatment step besides the fusing steps employed during the additive
manufacturing technique,
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as described herein above. The term "annealed" refers to an additively
manufactured magnetic
component that has been subjected to at least one additional heat treatment
step, after the
completion of the additive manufacturing process.
[0094] Microstructural Analysis is next performed which includes micro-etching
of Fe-based
alloys performed by immersion technique using a suitable etchant. Selection of
etchant depends
on the type of soft magnetic material composition. In the case of ferrosilicon
alloys, the grain
microstructure is revealed by using 5% HNO3 solution and immersed for up to
30s. For
revealing the melt pool structures or as-printed magnetic component
microstructure, 2% Nital
solution is used and immerse up to 2 min. The average grain size and grain
morphology were
analysed for both as built and annealed samples using Optical Microscopy ZEISS
Axiolab 5,
ZEN core v 27 imaging software based on A STM El 12-13 Intercept Method
[0095] Figure 8(a) provides a melt pool analysis depicting the as-built
microstructure of the
as-printed magnetic component in accordance with various embodiments of the
present
invention. Figure 8(a) shows uniform melt pool geometry and achieving coarse
grain and
columnar microstructure are desirable. The cross-sectional microstructure of
the as printed
SLM FeSi6.5 parts is a typical columnar structure with an orientation in the
build direction.
[0096] Figure 8(b) provides a grain size analysis depicting the grain size and
structure of an
annealed magnetic component in accordance with various embodiments of the
present
invention. In the post annealed sample, grain growth observed to be between
350 to 500 um.
A melt pool analysis is performed to determine the kind of melt pool developed
during the
rapid heating and cooling cycles. The geometry and size of the melt pool
determines whether
the heating cooling cycle was conducive to coarse or fine grain structure
development. The
grain size analysis determines whether there was sufficient grain growth
during the annealing
cycle or not.
[0097] Annealing induces stress relief in the material, thereafter, increasing
the grain size and
reducing lattice defects during recrystallization Grain growth improves the
magnetic
properties of the material.
[0098] Grain size is a major factor determining the magnetic property of the
printed part. Upon
sufficient post-process annealing up to 1150 C to optimize the microstructure,
columnar grains
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would develop into typical equiaxed grains through orienting towards the easy
axis (001) of
<100> crystal family of the ferrosilicon alloy.
Micro-Hardness Measurements using Vickers Hardness Tester
[0099] To evaluate the effect of the processing parameters on the mechanical
properties, micro-
hardness using a Vickers indenter was measured. For each sample, ten
indentations were
performed along the build direction (z-axis). Figure 9(a) provides a table
that provides the test
conditions and indentation force of 1KgF employed to create the indents.
Figure 9(b) show the
changes in hardness (NV) from the as-printed magnetic coupons to annealed
magnetic coupons
respectively in accordance with various embodiments of the present invention.
Most of the
samples had an increase in HV after annealing. At VED of 110 and 120 ilmm3,
hardness values
are varying between 404 to 407 HV and 396 to 430 HV respectively. Figure 9(c)
depicts the
change of hardness (HV) before and after annealing.
Energy Dispersive X-Ray (EDX) Analysis of 3D Printed Soft Magnetic Parts
[00100] An EDX analysis is conducted on the as-printed magnetic
component to verify
any change in elemental composition after the additive manufacturing process.
Particularly,
EDX analysis determines whether the additive manufacturing process introduced
some stray
elements to the magnetic element comprising a magnetic alloy that includes a
ferrosilicon alloy.
One major impurity that could get introduced is metallic oxides which are
detrimental to the
grain boundary movement and consequently to the development of magnetic
properties. EDX
analysis determines if there were any other impurities introduced in the alloy
or not after
processing. Figure. 10(a) shows the analysis of a printed FeSi6.5 sample
showing small dark
spots to reveal tiny voids or pores where an OM image of the elemental mapping
location
would be analysed and (b-c) EDX spectrum of as-fabricated FeSi6.5samp1e in
accordance with
various embodiments of the present invention. There is a slight improvement of
overall
compositional mix of the material as analysed by a third-party independent
laboratory.
Crystallographic Phase Analysis using X-Ray Diffraction (XRD)
[00101] Figure 11(a) illustrates a binary phase diagram of
FeSi6.5 magnetic alloy based
on a crystallographic phase analysis using XRD Analysis in accordance with
various
embodiments of the present invention. The purpose of showing the phase diagram
is to
illustrate the annealing temperature ranges where stress relief is happening
and the range where
the phase changes from A2 to B2/D03. Figure 11(b) illustrates a unit cell
structure of a FeSi6.5
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sample showing A2, B2 and D03 phases based on a crystallographic phase
analysis using XRD
Analysis in accordance with various embodiments of the present invention.
Figure 11(c)
illustrates a XRD diffraction pattern of a FeSi6.5 sample based on a
crystallographic phase
analysis using XRD Analysis in accordance with various embodiments of the
present invention.
Based on the XRD diffraction patterns in Figure 11(c), the summary of the
results are as follows:
A strong presence of B2/1303 ordering observed in the annealed FeSi6.5 sample.
Small
diffraction peaks at 20 value of 24.099, 35.699, 49.359, 57.599, 64.079,
66.519, and 67.839 are
unidentified, may arise from impurity. Although B2/D03 ordering causes to
improve the
magnetic properties, however, very high B2/D03 ordering can lead to the loss
of ductility.
Tuning the process parameters and controlling of annealing cycles had
contributed to the
B2/D03 phase shown in Figure 11(c) which is characterized by the easy axis in
the <001>
direction of the printed part. Thus, the magnetic properties and performance
of the FeSi6.5
magnetic alloy have been improved substantially.
Advanced Magnetic Characterization
[00102] We have characterized the built coupons and cores
multiple times using
Brockhaus type magnetic tester and B-H Magnetometer to measure the AC and DC
magnetic
properties and plot the hysteresis curve. Measurements were taken at B(T) at
5000 A/m and
1T, 50 Hz for DC and AC magnetic testing respectively. Figure 12 illustrates a
table of results
on the AC/DC hysteresis curves of a FeSi6.5 alloy sample. Figures 13 (a-b) and
14(a)
illustrates a graph of the DC hysteresis curve of a FeSi6 5 alloy sample in
accordance with
various embodiments of the present invention whereas Figures 15 (a-b), 16 (a-
b) and 17(a)
illustrates AC hysteresis curves of a FeSi6.5 alloy sample respectively in
accordance with
various embodiments of the present invention. FeSi6.5 is a soft magnetic alloy
used in AC/DC
fields applications. The B-H curve aka Hysteresis curve is a graphical
representation of how
the magnetic properties, B(T) of the material is changing with the changing
electrical field
expressed by H(A/m). This is the single most important chart predicting the
magnetic
behaviour of the part. The objective of the above is to show the relationship
between the
magnetic flux density which is a major magnetic property to the applied field
(current). This
relationship explains how good the material is magnetically and what kind of
performance it
will give if used as a magnetic component say for example in an electric
motor.
[00103] Figure 18 illustrates a top view of a stator component
that is additively
manufactured in accordance with various embodiments of the present invention.
The design of
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the stator component is different from any existing design of similar
component because
vertical slits have been introduced on the side to enhance the magnetic
performance. This kind
of geometry is possible only with the use of AM technology.
[00104] While the invention has been particularly shown and
described with reference
to specific embodiments, it should be understood by those skilled in the state-
of-the-art that
various changes in form and detail may be made therein without departing from
the spirit and
scope of the invention as defined by the appended claims. The scope of the
invention is thus
indicated by the appended claims and all changes which come within the meaning
and range
of equivalency of the claims are therefore intended to be embraced.
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