FIEED 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 (A/M).

[0004] The present invention can be leveraged to meet with the various requirements of the soft magnetic alloy electromagnetic component: Fabricating parts in whatever complex design it is required to be made to. Processing a wide variety of magnetic materials in customised chemical composition. Tuning the functional properties to match the targeted performance. 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 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 O, 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 pm.

[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. [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 J/mm3.

[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 pm.

[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 pm to 500 pm. [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 10°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 l-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 pm to about 500 pm. [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 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 Ihr 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 FeSi6.5 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. [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 IKgF 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 DO3 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. [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. [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 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 objects, 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 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 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.%

O - 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 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:

(i) 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 [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. 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 (pm) - about 20 to about 60 pm;

(iii) Scan Speed (mm/s) - about 700 to about 1200 mm/s; and

(iv) Hatch Spacing (pm) - about 40 to about 100 pm.

[0084] The above process variables determine Volumetric Energy Density, VED (J/mm ³ ) 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 pm, Layer Thickness - about 20 pm, 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/mm ³ . 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. [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 Ihr 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 l-2°C/min. In some embodiments, the cooling is performed in an argon gas-controlled atmosphere of up to 300°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 AM 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 manufactured-------magn component refers to an additively manufactured magnetic component that has not been subjected to an additional heattreatment step besides the fusing steps employed during the additive manufacturing technique, 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 2.7 imaging software based on ASTM 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 pm. 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 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, microhardness 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 IKgF employed to create the indents. 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. Most of the samples had an increase in HV after annealing. At VED of 110 and 120 J/mm3, 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 FeSi6.5sample 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/DO3. Figure 11(b) illustrates a unit cell structure of a FeSi6.5 sample showing A2, B2 and DO3 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/DO3 ordering observed in the annealed FeSi6.5 sample. Small diffraction peaks at 26 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 IT, 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 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.