Device for induction heating

Abstract

A heating device is presented comprising an induction coil for heating an electrically conductive target. The induction coil comprises an electrical conductor of a substantially planar configuration arranged in a form of a number TV (N>1) of windings, defining a heating surface of the induction coil having a substantially planar shape by which it faces a surface of the electrically conductive target during heating. Each winding defines first and second circumferential portions, the first circumferential portion being a heating portion forming a portion of said heating surface of the coil and the second circumferential portion being a periphery portion with respect to the electrically conductive target. At least one of the N windings of the induction coil is configured with the heating portion thereof having a first resistance (Ri) smaller than a second resistance (R2) of the periphery portion, thereby providing that, when said induction coil is operated, the heating portion of said at least one winding has an electric current density Ji higher than an electric current density J2 in the periphery portion of said winding.

Description

[0001] DEVICE FOR INDUCTION HEATING

[0002] TECHNOLOGICAL FIELD

[0003] The present invention is in the field of induction heating techniques and relates to an induction heating device and method utilizing an induction coil.

[0004] BACKGROUND

[0005] Induction heating is known as a fast and efficient technique for heating electrically conductive materials, such as metals and semiconductors, by applying a magnetic field and generating Joule heating.

[0006] Induction heating is widely used in industrial, medical and domestic applications, as being advantageous over traditional heating techniques (resistance heating, flame heating, ovens, furnaces, etc.). Induction heating is used also for many applications including metal surface treatment and additive manufacturing. Some of the advantages of induction heating are the ability to perform heating which is selective (i.e., only conductive materials), non-contact, flameless and having high energetic efficiency.

[0007] GENERAL DESCRIPTION

[0008] There is a need in the art for optimizing inductance heating processes for heating electrically conductive surfaces towards desired temperatures. In particular, there is a need in the art for enabling to improve the heating efficiency, thus shortening the heating time required to achieve the desired temperature under a given electric current through an induction coil and / or allowing operation with a lower electric current to heat the surface to the desired temperature, as well as allowing to produce a higher temperature gradient (sharper temperature profile) on the target being heated.

[0009] The present disclosure provides a novel heating device utilizing a novel configuration of an induction coil, enabling the achievement of the above improvements.

[0010] Thus, according to one broad aspect of the present disclosure, there is provided a heating device for heating a target, the heating device comprising an induction coil having a near-target heating segment and a far-from -target segment, such that the resistance of the near-target heating segment is smaller than the resistance of the far-from-target segment. This provides that when the induction coil is operated, the near-target heating segment has an electric current density that is higher than the electric current density in the far-from-target segment of the coil.

[0011] The difference in the resistance of the near-target heating segment and the far- from-target segment may be achieved by configuring / manipulating coil's geometry and / or material properties to thereby divert current distribution within the coil to receive more current (or higher current density) closer to the target being heated. Heating efficiency (heat deposited into target for given current in coil) at the near-target heating segment is thus achieved, however, the overall resistance of the coil is inevitably increased.

[0012] Embodiments of the present disclosure will be described with reference to providing coil segments with a different effective length and / or different effective resistivity for a given cross-section area in which the current is flowing.

[0013] Embodiments of the present disclosure will be described with reference to a solenoid-type coil for heating a target being surrounded by the induction coil (external coil) or engulfing the coil (internal coil providing bore heating); or a coil of a substantially planar configuration, e.g., a pancake-type configuration, for heating a target located adjacent to the surface of the induction coil outside thereof. Other coil types and configurations can be exploited within the scope of the present disclosure.

[0014] The induction coil of the present disclosure can be configured as a solid-profile conductor or as a hollow-profile conductor. The hollow profile conductor may or may not accommodate a cooling fluid running therethrough. Other cooling configurations, such as a heat sink, may be used.

[0015] The induction coil of the present disclosure may be supplied with AC current supply.

[0016] The heating device of the present disclosure may generally be used to heat any electrically conductive target. In the description below, such an electrically conductive target is at times referred to as "metal target" or "metallic target". It should, however, be understood that the principles of the present disclosure are not limited to the purpose of heating metal targets, but all electrically conductive surfaces / targets. The technique of the present disclosure can advantageously be used for heating metal surfaces during the manufacture of metal objects by additive casting. Various techniques of metal object production by additive casting are described, for example, in WO2019053712A1, WO22243921, W02023002468, all assigned to the assignee of the present application and incorporated herein in their entirety. According to these techniques, a series of production layers are created forming a vertical stack of production layers, wherein the production layer includes also mold regions surrounding the metal object regions according to the metal object shape. Such manufacture utilizes heating of e.g., a metal rod towards its melting temperature, thus depositing molted metal onto object region(s) of the production layer (source heating). Such manufacture further includes heating of the object region(s) before, during and / or after the metal deposition (surface heating).

[0017] Various heating applications are required to control the heating process to achieve and keep precise temperature conditions of the target being heated, as well as control the time pattern of alternating heating and cooling stages. Further, the duration of heating (the length of time needed for heating) of the metal target to the desired temperature is important, and for some applications, short heating times are preferred.

[0018] For example, in the case of metal object production by additive casting, as described in the above publications, it is critical to control the heating of the fabrication area, where the molten metal (being in droplet form, in the form of a narrow molten metal stream, or a flow) meets / interacts with the previously deposited metal which has solidified. This small fabrication area (on the scale of millimeters) is where the added metal becomes part of the cast object. Relying on the thermal energy of the added molten metal to bond it to the previously deposited metal is sometimes inadequate to properly control the metallurgical transition from the liquid phase to a fully integrated solid phase and results in poor bonding, irregular grain microstructure, anisotropic properties, and other casting defects. Precise control enables to remelt the fabrication area and allows the added molten metal to seamlessly integrate and bond with the pre-existing metal.

[0019] Thus, according to one broad aspect of the present disclosure, it provides a heating device comprising an induction coil for heating an electrically conductive target. The induction coil comprises an electrical conductor arranged in the form of a number N (N>1) of windings defining a heating surface of the coil having a substantially planar shape by which it faces the electrically conductive target, each winding comprising first and second circumferential portions, the first circumferential portion being a heating portion forming a portion of said heating surface of the coil and the second circumferential portion being a periphery portion with respect to the electrically conductive target. The configuration is such that at least one of the N windings of the induction coil is configured so that the heating portion thereof has a first resistance Ri smaller than a second resistance R2 of the periphery portion. This provides that, when said induction coil is operated, the heating portion of said at least one winding has an electric current density Ji higher than an electric current density J2 in the periphery portion of said winding.

[0020] In some embodiments, the induction coil has a pancake-type configuration.

[0021] In some embodiments, the conductor is configured such that at least one winding has a cross-section defining heating and periphery segments of said heating and periphery portions, respectively, and having different first and second widths W1 and W2, respectively, such that W1>W2.

[0022] In some embodiments, the conductor is configured such that at least one winding has heating and periphery portions of different first and second circumferential lengths LI and L2, respectively, such that Z7<Z2.

[0023] Thus, according to another broad aspect of the present disclosure, it provides another heating device comprising an induction coil for heating an electrically conductive target, the induction coil comprising an electrical conductor arranged in a form of a number N (N>1) of windings defining a heating surface of the coil by which it faces the electrically conductive target, each winding defining integrally made first and second circumferential portions, the first circumferential portion being a heating portion forming a portion of said heating surface of the coil and the second circumferential portion being a periphery portion with respect to the electrically conductive target, wherein at least one of the N windings of the induction coil is configured such that the heating portion thereof has a first resistance Ri smaller than a second resistance RS) of the periphery portion, such that, when said induction coil is operated, the heating portion of said at least one winding has an electric current density JI higher than an electric current density J2 in the periphery portion of said winding.

[0024] The heating and periphery portions of at least one winding may comprise first and second different material compositions providing the first and second resistances Ri and R2 satisfying a condition RI<R2. For example, each of the first and second material compositions has a relatively highly-conductive component and a relatively low-conductive component, and a percentage of the relatively highly-conductive component in the first material composition is larger than the percentage of the relatively highly-conductive component in the second material composition.

[0025] In another example, the heating and periphery portions are made of first and second materials having first and second resistivities pi and p2, respectively, such that pi<P2.

[0026] In a yet further example, the periphery portion of the winding is made of an electrically conductive material of said conductor, further comprising a plurality of relatively less-conductive particles (as compared to the electrical conductivity of the conductor material) embedded in said electrically conductive material. As for the neartarget heating portion, it may be made of the electrically conductive material of the conductor, being either free of such particles or including the particles but of a smaller concentration than that of the periphery portion. Hence, the effective resistivity (p2)eff the periphery portion is higher than the effective resistivity (pi)effd the heating portion.

[0027] In some embodiments, the induction coil is configured for the improvement of heating efficiency of the electrically conductive target to a desired temperature as compared to the conductor having the same resistance for all portions of the windings. Such improvement provides at least one of the following: (1) shortening the heating time of the electrically conductive target to the desired temperature under a given electric current, (2) use of a smaller electric current to heat the electrically conductive target to said desired temperature, and (3) producing a higher temperature gradient on the target.

[0028] Preferably, the first resistance Ay is at least 10% smaller than the second resistance R2.

[0029] The conductor of the induction coil may be configured with an array of two or more windings (N>2) arranged in a spaced-apart relationship along a longitudinal axis of the induction coil and thus along its surface by which the coil faces the electrically conductive target. These are typically concentrically arranged windings.

[0030] In some embodiments, the induction coil has a solenoid-type configuration defining a cylindrical shape of the heating surface, thereby being operable to heat the electrically conductive target extending along an axis of the solenoid. Considering the induction coil whose at least one winding has the solenoid-type configuration, it is configured such that it has an elongated cross-section whose longitudinal axis extends substantially perpendicular to the axis of the solenoid, thereby providing the heating and periphery portions of the winding having different first and second circumferential lengths LI and Z2, respectively, satisfying the condition that L1<L2. For example, this cross-section has a substantially parallelogram shape or a substantially oval shape, or a substantially trapezoidal shape such that a wider side of a trapeze forms said heating portion of the winding. The cross section of the conductor may or may not have rounded corners.

[0031] In some embodiments, the induction coil may have a solid profile of the N windings.

[0032] In some other embodiments, the electric conductor has a hollow profile. The hollow profile of the electric conductor may define a cavity for a cooling fluid to flow therethrough, wherein the induction coil comprises at least one cooling fluid inlet and at least one cooling fluid outlet. For example, at least one from among the at least one cooling fluid inlet and at least one cooling fluid outlet is / are located at an interim winding on a periphery portion thereof.

[0033] The windings are preferably isolated between them. In some embodiments, a transition area between adjacent windings of said N windings has a rounded shape to reduce a near-surface flow regime of a coolant liquid component of said cooling fluid within said hollow cavity of the conductor.

[0034] Considering at least one winding of the induction coil has a substantially planar configuration, the cross-section of the winding may be oriented such that an axis thereof is inclined with respect to a normal axis to the heating surface of the coil at a tilt angle a that satisfies a condition that 5° < | a\ < 85°, thereby providing that the heating portion of the winding has a length LI smaller than a length L2 of the periphery portion of said winding.

[0035] For example, the cross-section of at least one winding has a substantially parallelogram shape, where two opposite sides of the parallelogram define heating and periphery segments of said heating and periphery portions, respectively, the cross-section of the winding being oriented such that said heating and peripheral segments are substantially parallel to the target and other parallel sides of the parallelogram are inclined with respect to the normal axis to the heating segment at said tilt angle a. Alternatively, the cross-section of said at least one winding has a substantially oval shape, and said cross section is oriented such that a long axis of the oval is inclined with respect to the normal axis to the heating surface of the coil at said tilt angle a.

[0036] Similarly, the electric conductor may have a hollow profile defining a cavity for a cooling fluid to flow through the cavity. The tilt angle a is selected to reduce near- surface flow regime of a coolant liquid component of said cooling fluid within said hollow cavity of the conductor.

[0037] The induction coil of the present disclosure may be integrally made, but this is not necessarily so.

[0038] The induction coil of the present disclosure may be implemented as a 3D printed structure. Such 3D printed structure may be manufactured by a direct energy deposition (DED) method, e.g., utilizing two metal powders with different percentages of highly- conductive metal.

[0039] The conductor having hollow winding(s) may be of a wall thickness of about 1 mm.

[0040] The heating device further typically comprises a power supply unit for operating electric current passage through said conductor.

[0041] According to another aspect of the present disclosure, it provides a heating system comprising at least one heating device configured as described above, further comprising a cooling fluid system configured and operable for operating fluid flow through said cavity of the hollow conductor.

[0042] According to a yet further aspect of the present disclosure, it provides a heating system configured for heating during the formation of a metallic object by additive casting.

[0043] In some embodiments, the heating system comprises at least one source heating device configured to apply surface heating to a molten metal source surrounded by the induction coil towards a melting temperature thereof to affect molten metal deposition onto a region of a production layer of the metallic object being formed; at least one region heating device to apply surface heating to said region before and after said molten metal deposition on the region; and a control system configured and operable to selectively operate the at least one source heating device and the at least one region heating device in accordance with a predetermined production plan, wherein one or more of the at least one source heating device and the at least one surface heating device are configured as described above with respect to the induction coil having portions with different material compositions.

[0044] In other embodiments, the heating system comprises at least one source heating device configured to apply surface heating to a molten metal source surrounded by the induction coil towards a melting temperature thereof to affect molten metal deposition onto a region (fabrication area) of a production layer of the metallic object being formed; at least one region heating device to apply surface heating to said region before and after said molten metal deposition on said region; and a control system configured and operable to selectively operate the at least one source heating device and the at least one region heating device in accordance with a predetermined production plan, wherein one or more of the at least one source heating device and the at least one surface heating device are configured as described above with respect to the induction coil having planner configuration with elongated cross section.

[0045] In yet other embodiments, the heating system comprises at least one source heating device configured as described above with respect to the induction coil having a solenoid-type configuration defining a cylindrical shape of the heating surface, being thereby operable to heat an electrically conductive target extending along an axis of the solenoid, said at least one source heating device being configured and operable to apply surface heating to a molten metal source surrounded by the induction coil towards a melting temperature thereof to affect molten metal deposition onto a region of a production layer of the metallic object being form; at least one region heating device configured as described above with respect to the induction coil having a substantially planar configuration, defining a substantially planar shape of the heating surface of the coil by which the induction coil faces a region of an electrically conductive target, to apply surface heating to said region before and after said molten metal deposition on the region; and a control system configured and operable to selectively operate the first and second heating devices in accordance with a predetermined production plan.

[0046] The technique of the present disclosure also provides a method for heating an electrically conductive target to a desired temperature by an induction coil, the method comprising: providing at least one heating device configured according to any of the above described embodiments and examples, being located at a predetermined working distance between the heating surface of the induction coil and a surface of the electrically conductive target, operating said induction coil with a given electric current therethrough, resulting in that electric current density Ji in the heating portion of the at least one winding of the induction coil is higher than electric current density J2 in the periphery portion of said at least one winding, thereby providing improvement of heating efficiency of heating the electrically conductive target to a desired temperature as compared to a conductor having same resistance for all portions of all windings thereof, said improvement providing at least one of the following: (1) shorten a heating time of the electrically conductive target to the desired temperature under a condition of said given electric current, (2) use of a smaller value of said given electric current to heat the electrically conductive target to said desired temperature, and (3) produce a higher temperature gradient on the target.

[0047] The metallic target may be composed of any one of metal-based materials or material compositions, e.g., being one of the following: aluminum, copper, gray iron, ductile iron, steel, Inconel alloys, titanium alloys, Monel alloys, and wherein the desired temperature is near or equal to a melting temperature of the material composition.

[0048] It should be noted that the induction coil of the present disclosure may or may not be integrally made. Here, the term 'integrally made' signifies that the induction coil can be produced within a single manufacturing process and / or by the same production device. As described above, the induction coil may be realized through a 3D printing technique. Such a 3D printed structure can be manufactured using a direct energy deposition (DED) method, wherein two metal powders with varying percentages of highly-conductive metal are employed. Joining methods (non-integrally made) such as welding, gluing, soldering, brazing, and similar techniques can also be utilized in the manufacturing of the induction coil discussed in this disclosure.

[0049] The induction coil of the present disclosure, having two portions with different resistivities, was discussed with reference to two materials with different properties. It should, however, be understood that the principles of the present disclosure are not limited to this implementation. Rather, the technique of the present disclosure allows for incorporating more than two portions as needed. Moreover, the resistivities of two or more portions can be gradually varied, e.g., providing a smooth transition between the different resistivity levels of the portions. Additionally, variations of the resistivity within a segment - either the near-target heating segment, the far-from target segment, or both, may be provided. Generally, the variation of resistivities may be distinct or gradual along any of the X, Y, and Z axes. This flexibility allows for designing and optimizing the induction coil to meet specific requirements and achieve desired performance characteristics.

[0050] Aspects of the present disclosure were presented with reference to a solenoid-type coil configuration and a pancake-type coil configuration. The innovative concepts of the present disclosure may be implemented with any coil geometry, shape and type. For simplicity of explanation, air core types were discussed, however, other cores may be used.

[0051] BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0053] In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described by way of non-limiting examples only, with reference to the accompanying drawings, in which:

[0054] Fig. 1A schematically illustrates a part of an induction coil conductor configured according to the principles of the present disclosure for use in a heating device for heating an electrically conductive (e.g., metallic) target;

[0055] Figs. IB to IE show schematically three exemplary embodiments of the heating device comprising an induction coil for heating a conductive target (e.g., a metallic target) according to the principles of the present disclosure, wherein Fig. IB shows two examples of an induction coil of a substantially planar configuration exemplified with a hollow conductor profile, Fig. 1C shows examples of an induction coil of a solenoid-type configuration exemplified as having a hollow- or solid-profile conductor, Fig. ID exemplifies a solenoid-type induction coil having a hollow-profile conductor, and Fig. IE exemplifies a pancake-type induction coil with solid conductor;

[0056] Figs. 2A to 2E show an exemplary induction coil according to the principles of the present disclosure, wherein Fig. 2A is a photo of a pancake-shape induction coil with slanted cross-section; Figs. 2B and 2C show perspective views of the periphery and heating portions of the coil, respectively, as well as the periphery and heating segments of the coil's winding; and Figs. 2D and 2E show sectional views illustrating, more specifically, the cross-sections of the windings; Figs. 3A and 3B show, in an axisymmetric view, the results of electromagnetic and thermal simulation of a conventional induction coil having a pancake-type configuration with a substantially rectangular cross section of the conductor (only one half (right half) of the cross-section is shown), illustrating the magnetic flux lines around the coil, the metallic target temperature, and the current density on coil windings (zoomed in Fig. 3B);

[0057] Figs. 3C to 3D show the results of electromagnetic and thermal simulation (the magnetic flux lines around the coil, the metallic target temperature, and the current density on coil windings (zoomed in Fig. 3D)) for a similar induction coil of a pancaketype shape having a substantially parallelogram-shaped cross section of the conductor but modified to provide a slanted cross-section of the coil windings (slanted coil shape) in accordance with some embodiments of the present disclosure;

[0058] Figs. 4A to 4E demonstrate the results of a comparison simulation of the efficiency of heating at several coil angles, wherein Figs. 4A and 4B show, respectively, the simulation results (the magnetic flux lines around the coil and the metallic target temperature) and the respective current densities of the heating and periphery segments for the conventional induction coil with rectangular profile (similar to that of Fig. 3 A); Figs. 4C and 4D show the simulations performed for the induction coil configured according to some embodiments of the present disclosure (similar to Fig. 3C), and show, respectively, the simulation results (the magnetic flux lines around the coil and the metallic target temperature) and the respective current densities of the heating and periphery segments for the induction coil slanted at 45 deg.; Fig. 4D further shows the current densities of the heating and periphery segments for the induction coil slanted at several other coil angles; and Fig. 4E indicates the precise location of the respective periphery and heating segments of the inner winding of the induction coil used for simulation ;

[0059] Figs. 5A to 5C show further simulation results for the induction coils configured according to some embodiments of the present disclosure (similar to Fig. 3C), namely the maximal temperature of the metallic target heated by induction coils having different slant angles as a function of the heating time on a linear and logarithmic time scales, respectively, wherein Fig. 5B is an insert showing the temperature distribution inside the metallic target 45 sec after activation of the heating with a coil having a slant of 45 degrees, and Fig. 5C demonstrates that the faster heating rates of the slanted coils can also be observed during the initial heating stage due to the fact that the magnetic field on the metal target is higher as the slant increases;

[0060] Fig. 6 exemplifies the total resistance and inductance of a slanted induction coil (pancake shape, e.g., Fig. 2A) as a function of the slant angle; and

[0061] Figs. 7A and 7B exemplify the use of the heating device of the present disclosure in an additive casting system; wherein Fig. 7A exemplifies the use of the induction coil of pancake-type configuration for heating the fabrication area (object region) of the production area (surface heating), and Fig. 7B exemplifies the use of a first heating device with the induction coil of pancake-type configuration for heating the fabrication area (object region) of the production area (surface heating), and a second heating device with the induction coil of solenoid-type configuration for heating the metal rod (source heating) towards the melting temperature to assist in deposition of the molten metal onto the fabrication area to form the object region.

[0062] DETAILED DESCRIPTION OF EMBODIMENTS

[0063] Reference is made to Fig. 1A, showing schematically a part of an induction coil (conductor) 104 configured according to the principles of the present disclosure for use in a heating device for heating a conductive target such as metallic target MT (constituting an electrically conductive surface / target / object). Generally, the induction coil conductor 104 is arranged in the form of a number 7V(N>1) of windings, a part of the single i-th winding Wi being shown in the figure.

[0064] Each winding Wi of the induction coil 104 includes first and second circumferential portions 104h and 104p, where the first circumferential portion 104h, by which the winding Wi faces the metallic target MT, is a heating portion, and the second circumferential portion 104p of the winding Wi is a periphery portion with respect to the metallic target MT.

[0065] In the schematic illustration of Fig. 1A, such first and second circumferential portions 104h and 104p are actually parallel facets of coil 104, both being substantially (almost) parallel to the metal target MT. The facet placed close to the metallic target MT is referred to as the "near facet" and defines the heating portion 104h. The facet placed far away from the metallic target MT is referred to as the "far facet" or "peripheral facet" and defines the periphery portion 104p. The induction coil conductor 104 defines a heating surface HS by which the conductor 104 faces a metallic target MT to be heated. If a plurality of coil windings are used (not shown in Fig. 1 A), the heating segment HS is defined by the plurality of heating portions 104h of the windings. In the same manner, a periphery segment PS is defined by the periphery portions 104p.

[0066] In response to feeding the coil 104 with electric current, magnetic fields generated in the near facet - the heating portion 104h - heats the metallic target MT. Magnetic fields generated in the far facet - the periphery portion 104p - also contributes to heating the metallic target MT. However, the heat generated due to magnetic fields generated in the near facet - heating portion 104h - is considerably higher as compared to that of the the far facet - the periphery portion 104p.

[0067] According to the present disclosure, the winding Wi is configured such that the heating portion 104h has a first resistance Ri smaller than a second resistance2of the periphery portion 104p, such that, when the induction coil 104 is operated (i.e. electric current passes therethrough), the electric current Ii flowing through the heating portion 104h of the winding Wi is higher than an electric current I2 flowing through the periphery portion 104p of the winding Wi.

[0068] The first resistance Ay is preferably at least 10% smaller than the second resistance R2.

[0069] The inventors have found that an induction coil configured with an electrical conductor satisfying the above condition of Ri < R2 provides an improved heating efficiency of the metallic target MT to a desired temperature as compared to the conductor having the same resistance for all portions of the windings. The inventors realized that such a difference in resistances between the heating portion 104h and the periphery portion 104p is beneficial for the intended use of heating the metallic target MT since it makes the heating portion 104h, which is close to the surface being heated (metallic target MT), favorable to the electric current. The improved heating efficiency provides for shortening the heating time of the metallic target to the desired temperature under a given electric current and / or for the use of a smaller value of the electric current to heat the metallic target to said desired temperature and / or for producing sharper temperature profile on the target being heated.

[0070] The conductor of the induction coil 104 can be configured with a solid profile or hollow profile. The induction coil 104 and the respective Heating Segments and Periphery Segments may or may not be planar. These, as well as other details and examples, are described further below.

[0071] Reference is now made to Figs. IB to IE showing non-limiting examples of a heating device 100 according to the principles of the present disclosure. To facilitate understanding, the same reference numbers are used to identify functionally similar elements common for all the examples.

[0072] The heating device 100 includes an induction coil 104 for heating a metallic target MT. The induction coil 104 is associated with / connected to a power supply unit 120, which is associated with a controller 130. As also shown in the non-limiting examples of Figs. IB and 1C by dashed lines and is relevant also for the example of Fig. ID (although not being specifically shown there), the heating device 100 may be further associated with a cooling fluid system 140, the possible purpose of which will be described further below.

[0073] As mentioned above, the induction coil 104 is an electrical conductor which is generally arranged in a form of a number N (N>1) of windings, wherein, for clarity, a schematic cross-sectional view of i-th winding Wi only is shown in Figs. IB and IE, and a few windings are exemplified in Fig. 1C (windings W1-W3) and in Fig. ID (windings W1-W5). The number N of windings of the coil defines a heating surface HS of the coil 104 by which it faces the metallic target MT (also referred to as near-target coil segment).

[0074] Thus, as described above with reference to Fig. 1A, each winding Wi of the induction coil 104 is composed of first and second circumferential portions (substantially parallel facets), where the first circumferential portion 104h (near-target facet / heating portion or, in short, near facet or near heating portion), being the portion of the heating surface HS, by which the winding Wi faces the metallic target MT, is a heating portion 104h, and the second circumferential portion 104p (far-from-target facet / portion or, in short, far facet / portion) of said winding Wi is a periphery portion 104p with respect to the metallic target MT. According to the present disclosure, at least one winding of the coil (winding Wi in this example) is configured such that the heating portion 104h has a first resistance Ri smaller than a second resistance R2 of the periphery portion 104p, such that when the induction coil 104 is operated, the heating portion 104h of the winding Wi has an electric current density Ji higher than an electric current density J2 in the periphery portion 104p of the winding Wi.

[0075] In the examples of Figs. IB and IE, the induction coil 104 has a substantially planar configuration (e.g., pancake-type configuration), where the heating surface HS by which the induction coil 104 (conductor) faces the metallic target MT, as well as the opposite surface of the coil, are substantially planar.

[0076] Fig. IB illustrates three examples of arrangements of a pancake-type configuration: (1) a parallelogram-shape cross-section; (2) an oval shape cross-section; and (3) a rectangular-shape cross section coil with segments having different resistivity.

[0077] As shown in Fig- IB, the induction coil / conductor 104 has a parallelogram-shape cross-section 110. According to the parallelogram-shape cross-section example of the pancake-type configuration of the induction coil / conductor 104, the winding Wi is configured such that the above-described difference in the resistance (RI<R2) for the neartarget heating portion 104h and the periphery portion 104p is achieved by configuring and orienting the cross-section 110 of the winding 104 to provide a first circumferential length Li of the near-target heating portion 104h of the conductor shorter than a second circumferential length L2 of the periphery portion 104p of the conductor, i.e., Li < L2. This is shown in the figure by solid (red) lines.

[0078] The two opposite sides of the parallelogram cross-section 110 define a near-target heating segment IlOh and a periphery segment IlOp of, respectively, the near-target heating portion 104h and periphery portion 104p, which are substantially parallel to the heating surface HS (and to the metallic target MT).

[0079] To this end, the cross section 110 of the winding has an axis A and is oriented such that said axis A is inclined with respect to a normal axis NA to the heating surface HS of the coil at a certain tilt angle a.

[0080] The other parallel sides 112 of the parallelogram 110 are inclined at said tilt angle a with respect to the normal axis NA to the heating segment.

[0081] The tilt angle may be in a range of 5° < |a| < 85°.

[0082] The provision of the slanted / tilted orientation of the cross-section of the winding results in that the near-target heating portion 104h of the winding has a length Li smaller than the length L2 of the periphery portion 104p of said winding.

[0083] Another example of a pancake-type configuration 104A, with an oval-like shape cross section, is shown in Fig. IB Two windings - Wi and Wi+i - are shown. The abovedescribed slanted / tilted configuration of the cross-section 110 of the winding may be achieved by configuring the cross-section with an oval shape 110A.

[0084] Thus, such "tilting" / "slanting" configurations 104, 104A (either of oval-like or parallelogram shape) provides that the near-target heating portion 104h and the periphery portion 104p, when being made of the same material compositions (i.e., the same specific resistivity), have, respectively, smaller and larger lengths Li and L2, and thus smaller and higher resistances Ri and R2 (Ri< R2) for the given electric current passing through the conductor.

[0085] As also shown in Fig- IB, in another example of the substantially planar induction coil (e.g., pancake-type coil) - 104B, the required difference between the resistances Ri and R2 of the near-target heating portion 104h and the periphery portion 104p is achieved while using the winding cross-section HOB (dashed line) of a non-tilted (e.g., a rectangular) configuration. The exemplified rectangular configuration is symmetric with respect to the normal axis NA (length Li of the heating portion 104h and length / A of the periphery portion 104p (dashed line) are substantially equal), but the winding is configured with respective first and second different material compositions for these portions 104h and 104p having different specific resistivities pl and p2, respectively, such that pl<p2.

[0086] The required difference between the resistances Ri and R2 of the near-target heating portion 104h and the periphery portion 104p may be achieved with different effective resistivities: the different material compositions may be such that each has a relatively highly-conductive component and a relatively low-conductive component, and wherein a percentage of the relatively highly-conductive component in the first material composition of the near-target heating portion 104h is larger than the percentage of the relatively highly-conductive component in the second material composition of the periphery portion 104p. Hence, the near-target heating portion 104h and the periphery portion 104p have different effective resistivities (pl)eff and (p2)eff, respectively, such that (pl)eff <(p2)eff.

[0087] For example, the conductor 104B can be made of the basic conductive material having specific resistivity pl, and the periphery portion 104p contains a plurality of relatively less-conductive particles embedded in the electrically conductive material, while the heating portion 104h is either made of the electrically conductive material of the conductor 104B free of said particles or including said particles but of concentration smaller than that of the periphery portion 104p. Such configurations provide effective resistivity (p2)eff of the periphery portion 104p higher than that of the near-target heating portion 104h. The non-tilted cross-section of the coil with different effective resistivities may be a rectangle, circle, oval, etc.

[0088] It should be noted that the pancake-type induction coil 104 of the present disclosure (e.g. exemplified in Fig. IB and Fig. IE) may include a combination of the above features (tilting / slanting of the cross section and / or different material compositions of the heating and periphery portions) to achieve the resistance difference condition Ri< R2.

[0089] Figs. 1C and ID show schematically the heating device 100 according to the principles of the present disclosure, where the induction coil 104C has a solenoid-type configuration operable to heat a conductive surface (metallic target MT, e.g., a metallic rod), extending along an axis of the solenoid and being thus surrounded thereby. The electrical conductor / coil 104C has first and second circumferential portions being, respectively, a circumferential near-target heating portion 104h by which it faces the metallic target, and a circumferential periphery portion 104p.

[0090] In the embodiment of the induction coil illustrated in Fig. 1C as 104C, which is also depicted in Fig. ID, the inner side of a circular solenoid-type coil is designated as the near-target heating portion 104h. The technique of the present disclosure is not limited to this embodiment. For example, to effectively heat a tubular electrically-conductive target having a ring-shape cross-section, the circular solenoid-type coil may be placed inside the tubular target and thus the outer side of the circular solenoid-type coil is designated as the near-target heating portion.

[0091] It should be understood that with the standard solenoid-type configuration of the induction coil 104C - having, e.g., a rectangular cross-section HOC, the near-target heating portion 104h and the periphery portion 104p have different length lengths Li and L2 such that / . / < Z2, thus providing some difference in the respective resistances Ri and R2 (RI<R2). However, in order to provide the desired resistance difference (at least 10% difference), thereby obtaining the improvement in heating efficiency as described above, the solenoid-type induction coil 104C of the present disclosure has a modified configuration.

[0092] In some examples of such modified configuration, as shown more specifically in Fig. ID, the near-target heating portion 104h and the periphery portion 104p of the conductor / winding(s) are made of different materials or material compositions MCi and MC2, similar to that described above with reference to Fig. 1A. For example, the near- target heating portion 104h and the periphery portion 104p may be made of materials of different specific resistivities or material compositions having different effective resistivities. This is exemplified more specifically in Fig. ID. The different materials / material compositions provide that the near-target heating and periphery portions 104h and 104p have different specific resistivities pi and p2 / different effective resistivities (pi)eff and (p2)eff, respectively, such that pi<p2 or (pl)efi<(p2)eff. For example, conductor 104C can be made of the basic conductive material having specific resistivity pi, and only the periphery portion 104p further contains a plurality of relatively less conductive particles embedded in the electrically conductive material of said periphery portion, thereby providing effective resistivity (p2)eff of the periphery portion 104p higher than that of the heating portion 104h made of said electrically conductive material.

[0093] As described above, the circumferential heating portion 104h and the circumferential periphery portion 104p may be integrally made. For example, these portions can be integrally made by the same production device using known in the art 3D printing techniques for fabricating the solenoid-type induction coil 104C.

[0094] The present disclosure is not limited to coils fabricated using 3D printing techniques. The circumferential heating portion 104h and the circumferential periphery portion 104p may be made from two materials that are attached together, e.g., by welding, coating and the like. For example, a conventional solenoid-type coil or planar coil may be used. The near-target segment of the conventional solenoid-type coil or the planar coil may be removed (e.g., by milling) and replaced by a new near-target segment, made from a different material with higher electric conductivity. The amount of material to be removed or added depends, among other factors, on the desired skin depth. The new neartarget segment may have a thickness equal to, x2, x3 or more of the desired skin depth. In some applications, a skin depth of 50, 100, 150, 200 microns is desired.

[0095] In some other examples, as shown in Fig. 1C, the cross-section HOD of the solenoid-type conductor 104D is elongated (indicated by dashed lines), extending along an axis substantially perpendicular to the solenoid axis, thereby further increasing the length difference between the heating and periphery portions 104h and 104p, such that Li « L2, where L2 is the increased length of the periphery portion 104p.

[0096] The increase of the aspect ratio of such elongated cross-section may be implemented for different shapes of the cross-sections 110, for example, a rectangular shape (e.g., HOC, HOD), trapezoid shape (e.g., HOE) or oval shape (e.g., HOF). With the trapezoid cross-section 110E, the configuration is such that the heating and peripheral segments IlOh and IlOp have different first and second widths Wi and W2, respectively, such that Wi>W2. The difference in the segment widths provides the heating portion 104h with a first resistance Ri smaller than a second resistance R2 of the periphery portion 104p of the winding. As a result, when the induction coil is operated, the heating portion 104h of the winding Wi has an electric current density Ji higher than an electric current density J2 in the periphery portion 104p of the winding Wi.

[0097] It should be noted that the solenoid-type coil can include a combination of the above-described features of 'widths' difference and 'materials' / material 'compositions' difference.

[0098] As also exemplified in the non-limiting examples of Figs. IB to ID, the induction coil conductors 104 of the present disclosure may be configured with a hollow profile defining a cavity 108. This can be used to allow for a cooling fluid to flow through the hollow conductor. In this case, the induction coil has at least one cooling fluid inlet and at least one cooling fluid outlet (not shown in Figs. 1A-1E). Considering the conductor configuration with the tilted / slanted cross-section of the winding as described above with reference to Fig- IB, the tilt angle a is selected to reduce a near-surface flow regime of a coolant liquid component of the cooling fluid within the hollow cavity 108 of the conductor. For example, tilt angles up to |a| < 45°, 55° and 65° may reduce a near-surface flow regime of the cooling fluid within the hollow cavity 108 of the conductor. Effective cooling fluid flow can be achieved also by optimizing the area / circumference ratio of the conductor cross section.

[0099] Fig. IE exemplifies the heating device 100, in which the induction coil conductor 104E is configured generally similar to that of Fig. IB, i.e., has a planar (e.g., pancaketype) configuration, but has a solid profile. Also, in this non-limiting example, the conductor 104E is configured with the tilted / slanted cross-sections 110 of the windings, exemplified as being in the form of a tilted parallelogram. It should, however, be noted, as also indicated above with respect to Fig. IB, that the technique of the present disclosure is not limited to such tilted configuration, as well as is not limited to the parallelogram shape of the cross-section, and any of the above described features, as well as any combination of these features, can be used to provide the required resistance difference condition RI<R2 for the heating and periphery portions 104h and 104p of the conductor. The conductor 104E of the example of Fig. IE differs from that of Fig. IB in that the conductor of Fig. ID has a solid profile. For solid-profile applications requiring cooling, conductor 104E may be cooled e.g., by a cooling-jacket (not shown in Fig. IE).

[0100] It should be noted that, generally, the use of the tilt / slant feature in the planar- type winding, while providing the required resistance difference between the heating and peripheral portions, affects the total resistance of the coil. This is taken into consideration to properly select the electric current parameters supplied to the coil. More specifically, the adverse effect of slanting the coil winding is an increase in AC resistance, which means more voltage is required to drive the coil at a given current, and in increase in coil inductance, meaning that for a given power supply, the resonant frequency decreases, resulting in less inductive heating; this can be addressed by adequate redesign of the power supply's capacitor bank.

[0101] For hollow-profile conductors (pipes), the slant angle is selected as an optimum for several operational factors: current, cooling rate, conductor dimensions, coolant properties, etc.

[0102] Reference is made to Figs. 2A to 2E exemplifying an induction coil 104 configured according to the principles of the present disclosure for the embodiments of pancake-type coil having slanted cross-section and the hollow-profile windings (e.g., Fig. IB). Fig. 2A shows a photo of a pancake-shape, being a multiturn (multi-windings) induction coil.

[0103] Such a pancake-type coil may be manufactured by known in the art 3D printing methods. Alternatively, such a pancake-type coil may be manufactured by the following process: winding a copper coil to form a cone-shape structure, heating the copper coil of said cone-shape structure in an oven (e.g., to temperature of about 600° C), and applying pressure to the copper coil being heated to thereby distort a shape of the copper cone from the cone-shape to a substantially planar shape.

[0104] Figs. 2B and 2C show, respectively, the top and bottom perspective views of the induction coil 104. Figs. 2D and 2E show sectional views of the coil, illustrating more specifically the configuration of the cross-sections 110 of the coil's windings.

[0105] The induction coil 104 is made of hollow windings (pipes) defining cavities, e.g., forming a fluid flow line for a cooling fluid (e.g., water). In these examples, the induction coil has one (generally at least one) cooling inlet CI and two (generally at least one) cooling outlets CO1 and CO2. The sectional views of Figs. 2D and 2E show electrical conductor 104 arranged in multiple windings - five windings Wi, Ws in this non-limiting example, defining a substantially planar winding surface (heating surface). The cross-section 110 of each i-th winding Wi has a substantially parallelogram shape, where two opposite sides of the parallelogram define heating and periphery segments IlOh and IlOp of the heating and periphery portions 104h and 104p, respectively. The cross-section 110 of the winding is oriented such that the heating and peripheral segments IlOh and IlOp are substantially parallel to the heating surface defined by the coil 104 (and substantially parallel to the target's surface being heated). The other parallel sides 112 of the parallelogram define a longitudinal axis A, which is inclined with respect to a normal axis to the heating surface of the coil at a tilt angle a.

[0106] As described above, when the longitudinal axis LA is inclined with respect to the normal axis to the winding surface at a tilt angle a, the induction coil, when operated, has lower resistance and thus higher electric current density at the heating (bottom) segment IlOh (and thus the heating portion 104h of the coil) as compared to the periphery (top) segment IlOp (and thus the periphery portion 104p of the coil), thereby providing higher heating efficiency of the metal surface to a desired temperature.

[0107] In the following, the term "slanted coil" will at times be used to describe a coil with an inclination / tilting of the longitudinal axis of the cross-section of the winding(s).

[0108] Reference is made to Figs. 3A-3B and 3C-3D demonstrating thermo- electromagnetic simulations performed by the inventors for induction coils with similar properties and arrangements, except for their coil slant angle. Figs. 3A-3B show axisymmetric thermo-electromagnetic simulation for an induction coil having a conventional pancake-type shape with substantially rectangular cross section 110, (coil angle=0 deg.) of a conductor. Non-tilted sides 112A and 112B are shown. Figs. 3C-3D show axisymmetric thermo-electromagnetic simulation for an induction coil having a pancake-type shape with substantially parallelogram cross section 110 of conductor of a tilted / slanted orientation (coil angle=10 deg. in this example) according to the principles of the present disclosure as described above.

[0109] In this comparison, the slanted coil shape was altered so that the profile area (cross section area) was maintained (rectangular profile area = parallelogram profile area), and the perimeter of the slanted coil profile is extended. Coil height and placement (working distance above the surface of the metallic target) were maintained. In these simulations, the induction coil is operated with an AC current of about 1.6kA at 150 kHz. The simulations demonstrate the heating of a metallic target made of grey iron (melting temperature of 1150°C). In Figs. 3A and 3C, only one half (right half) of the cross-section is shown, although an axisymmetric model was calculated.

[0110] Figs. 3A and 3C show, in the respective upper part of Figs. 3A and 3C, the magnetic flux lines and magnetic flux density around the coil (grey scale), the current density in the coil windings (Red-White-Blue scale, better seen in the zoomed windings shown in Figs. 3B and 3D). Figs. 3A and 3C further show, in the respective lower part of Figs. 3 A and 3C, the temperature distribution and melting front inside the heated target (equi-temperature lines and color scale). The equi-temperature line of 1150°C (melting temp, for grey iron) is emphasized.

[0111] It should be understood that the current flow along segments 112B and the other half-segments HOh and HOp of adjacent windings is in opposite directions, thus cancelling the respective magnetic field components.

[0112] As clearly shown in Figs. 3A and 3B, with the conventional pancake-type induction coil, very similar (or even equal) current densities are obtained along the heating and periphery segments HOh and HOp. The dashed circles in Fig. 3B direct attention to the magnetic flux lines density in the vicinity of the heating and periphery segments HOh and HOp. It can be seen that a maximum current density of about 2.5e9 A / m2is achieved, and a melting temperature of 1150°C (gray iron) is obtained at a depth of about 5 mm below the metal target surface.

[0113] The simulations demonstrated in Figs. 3C and 3D were performed for the coil configuration of Figs. 2A to 2E above. The dimensions in the simulation match those of the coil shown in Fig. 2A with a slant of 45 deg. It can be seen that at the same current applied, the resulting maximum current density is significantly higher at the heating segment HOh than that of the peripheral segment HOp of the conductor (6.1e8 vs. 5.5e8 A / m2) and is higher than that achieved by the conventional coil (Fig. 3 A). Fig. 3C further shows that the melting temperature of 1150°C (gray iron) is obtained at a depth of about 10 mm below the metal target surface using the same current as in the coil of Fig. 3A. The dashed circles in Fig. 3D direct the attention to that the magnetic flux lines' density in the vicinity of the heating segment is substantially higher as compared to that of the peripheral segment. The results of the thermo-electromagnetic simulations show that the induction coil configured according to the principles of the present disclosure (e.g., exemplified by Figs. 2A to 2E and Fig. 3C) is characterized by a higher efficiency, i.e., smaller electric current needs to be supplied to achieve the desired temperature at the desired depth within a desired time inside the target as compared to the conventional pancake-type induction coil (having identical and non-tilted top and bottom segments of the winding's crosssection).

[0114] Figs. 4A to 4E show simulations of the current density obtained along the coil's top and bottom segments of the innermost winding, under the same simulation conditions as described with reference to Figs. 3A-3D. The top and bottom segments of the innermost winding have each a flat segment of 2mm length. The results of the current density simulation along the top and bottom segments are shown in Fig. 4A for a nontilted coil (coil angle = 0); in Fig. 4C for a slanted coil with a coil angle of 45 deg., and in Fig. 4D, a comparison graph for a variety of coil angles between non-tilted (coil angle = 0) to coil angle of 45 deg.

[0115] Fig. 4A is an axisymmetric view showing, in the upper part of the figure, the magnetic flux lines around the rectangular-shaped coil (grey scale), where only the right half of the coil cross-section is shown for clarity, the current density in the coil windings (Red- White-Blue scale), and showing, in the lower part of the figure, the temperature distribution inside the heated target after 120 sec. of heating (equi-temperature lines and color scale). Fig. 4B shows the current density in the near-target heating segment IlOh (solid line) and far-from target peripheral segment IlOp (dashed line) of the innermost winding of the non-tilted coil. The calculation was performed for a 2 mm length of the heating / periphery segment, and "0 mm" in the figure corresponds to the innermost flat edge of the respective near-target heating segment and the far (periphery) segment. It can be seen that in the vicinity of the highest magnetic flux, at the innermost coil winding, the current density of the heating segment IlOh is higher by about 15% than the current density of the periphery segment IlOp. The same behavior is obtained along the segments' length.

[0116] The results of a similar simulation for the slanted induction coil are shown in Figs. 4C to 4E. Fig. 4C is an axisymmetric view showing, in the upper part of the figure, the magnetic flux lines around the parallelogram-shaped coil with a slant angle a of 45 degrees (only the right half of the coil cross-section is shown for clarity), the current density in the coil windings (Red-White-Blue scale). Fig. 4C further shows, in the lower part of the figure, the temperature distribution inside the heated target at 120 sec after activation of heating (temperature lines and color scale). Fig. 4E is an enlarged view of an area of Fig. 4C, zooming on the innermost coil winding. Fig. 4E indicates the precise location of the bottom heating segment IlOh of a 2mm length, where the current density is compared with the respective periphery segment IlOp on the same coil winding. Similar to Fig. 4B, Fig. 4D shows the current density along a 2 mm long periphery segments (dashed line) and heating segments (solid line) of the innermost coil winding for 0, 5, 10, 30 and 45 deg. coil angles. The results for 45 deg. coil angle are highlighted. It can be seen that in the vicinity of the highest magnetic flux at the innermost coil winding the current density of the heating segment IlOh is about 3 times higher than the current density of the periphery segment IlOp. The same behavior is obtained along the segment length.

[0117] Thus, the inventors have shown that inclining / tilting the coil cross-section provides lowered resistance of the heating segment IlOh of the induction coil compared to the peripheral segment IlOp, leading to higher heating efficiency.

[0118] Looking at the current densities for coil angles 0, 5, 10, 30 deg. in addition to the 45 deg. coil angle results in Fig. 4D, it can be seen that as the slant (coil angle) increases, the difference between the current densities of the heating segment (solid line) and the periphery segment (respective dashed line) increases. More current is diverted to the heating segment due to its lower resistance.

[0119] As stated above, the induction coil of the present disclosure provides higher heating efficiency which is also characterized by faster heating to a target temperature of the metallic surface under given electric current conditions.

[0120] Faster heating to a target temperature of the metallic surface under given electric current conditions is favorable for additive metal manufacturing techniques, for example, as described in WO2019053712, WO22243921, and WO23002468. During the addition of a new metal layer, previously-cast metal bulk is heated before metal deposition, during metal deposition and / or after metal deposition. Faster heating contributes to improved manufacturing efficiency and throughput.

[0121] Figs. 5A to 5C exemplify this efficiency by simulation and showing the maximal temperature of the metallic target as a function of the heating time on a linear and logarithmic time scales, respectively. The stages of heating, as indicated in Fig. 5A, include stage (a) of skin-depth heating, stage (b) of heat diffusion onset into previously cast bulk, and stage (c) of semi-steady state flow heating of the metal.

[0122] The dash-dotted lines in Fig. 5A indicate that the time from the activation of the heating to reaching the melting temperature (1150°C for gray iron) is shorter with the induction coil configuration of the present disclosure. For example, 26 sec. for a coil with a slant angle of 45 degrees, compared to 70 sec. for a coil with a non-slanted (zero slant angle) rectangular profile.

[0123] Fig. 5A further indicates that at the same time after activation, the maximal temperature of the workpiece achieved with slanted coils is higher and linearly depends on the coil angle. For example, at about 70 seconds from activation, the maximal temperature achieved with a slanted coil of 45 deg. is above 1450 deg. C; the maximal temperature achieved with a slanted coil of 15 deg. is about 1300 deg. C; and the maximal temperature achieved with a non-tilted coil (coil angle = 0) is above 1150 deg. C. Also, after the stabilization of heat diffusion into the bulk of the heated metallic target, the heating rates of the coils with slanted profiles are faster (stage (c) in Fig. 5A).

[0124] Fig. 5B shows the distribution of temperature inside the metal target after about 44 sec from the activation of the heating, and the solid line on the cross-section of the metal target being heated delineates the region of melting (for gray cast iron). Fig. 5B further shows the measurement location at which the maximal temperature of the workpiece is obtained.

[0125] Fig. 5C shows that as in stages (b) and (c) of heating, the faster heating rates of the slanted coils can also be observed during the initial heating stage (a).

[0126] The results shown in Figs. 5A-5C, indicating the faster heating rates and their dependency on the slant angle are obtained due to the fact that the magnetic field on the conductive target is higher as the slant increases.

[0127] Reference is made to Fig. 6 exemplifying the total resistance and inductance of the slanted coil 104 as a function of the slant angle a. As described above, slanting the cross-section of the coil winding leads to a change in the coil properties, comparing the non-tilted coil, and this change in the coil properties needs to be considered when integrating the coil into a heating system. Slanting the cross-section of the coil winding leads to an increase in total AC resistance, which means higher voltage is required to drive the coil at a given current. Slanting the cross-section of the coil winding further leads to an increase in total coil inductance, meaning that for a given power supply, the resonant frequency will decrease, resulting in less efficient inductive heating. These changes can be addressed by properly modifying the power supply's capacitor bank.

[0128] Reference is made to Figs. 7A and 7B exemplifying how the heating device of the present disclosure can be advantageously used in a system of metal object manufacture by additive casting. Additive casting involving the deposition of molten metal with one or both of pre-deposition heating and post deposition heating of the already-cast metal is described in WO2019053712, WO22243921, and WO23002468 which are incorporated herein by reference in their entirety.

[0129] Fig. 7A exemplifies the use of a surface heating device including the induction coil 104 of pancake-type configuration for heating the fabrication area (object region) FA of the production area (pre-deposition heating and / or post deposition heating). Fig. 7B exemplifies the use of the surface heating device including the induction coil 104Source of pancake-type configuration for heating the fabrication area (object region) FA of the production area (pre-deposition heating and / or post deposition heating), and a second heating device including the induction coil 104Source of solenoid-type configuration for heating a source in the form of metal rod MR towards the melting temperature to assist in deposition of the molten metal in the form of e.g., metal drops MD, onto the fabrication area FA to form the object region.

[0130] In the specific non-limiting examples of Figs. 7A-7B, the slanted coil design of the pancake-type coil 104SUrface is used. However, as mentioned above, the technique of the present disclosure is not limited to this example, and thus, this illustration should be interpreted broadly.

[0131] More specifically, the manufacturing system may include a Preparation- Deposition-Post treatment (PDP) unit, including a molten metal depositor operative to deposit molten metal in a fabrication area of an obj ect region (defined by the mold region) of the current production layer. The PDP unit performs at least one of: pre-deposition heating the fabrication area to a pre-deposition temperature before molten metal deposition on said fabrication area (pre-heating), and post-deposition heating the fabrication area after molten metal deposition thereon, to a post-deposition temperature (post-heating).

[0132] Aspects of the present disclosure are exemplified herein with reference to a production scenario of combining the currently-deposited molten metal with the previously-cast bulk when the currently-deposited molten metal and the fabrication area of the previously-cast bulk are at a temperature above the melting temperature, and preferably have the same temperature.

[0133] Such pre-heating and / or post-heating processes can be realized using induction heating. The pre-heating is applied to the fabrication area of the object region of a previously fabricated production layer, and the post-heating is applied to the fabrication area of a current production layer. The fabrication areas of the previous production layer and the current production layer constitute a melt pool that solidifies in a homogeneous manner. For example, a melt pool of a few millimeters (5, 10, 50, 100) up to a few centimeters (1, 2, 3, 4, 5, 10, 15) is created.

[0134] The combined operation of metal source (e.g., metal rod) heating, and pre-heating and / or post heating of the fabrication area FA of metal deposition is required for proper casting with perfect bonding between the already cast object layer to the next one to ensure homogeneous bonding with uniform and isotropic micro grain structure throughout the cast product, eliminating the casting voids and other defects.

[0135] Typically, pre-heating is applied to melt the fabrication area in the previous production layer. Metal rod heating is applied to melt the metal and facilitate its deposition at the proper temperature. Post-heating is applied to enable controlled cooling of the resultant metal area.

[0136] The integrated PDP unit not only deposits the additive molten metal, but also precisely controls the thermal properties of both the additive molten metal and the target region of the solidified metal. Precise control enables to eliminate or at least significantly reduce thermal shock and allows the molten metal to seamlessly integrate and bond with the pre-existing metal. Physical coupling of the molten metal depositor to the heating units in the PDP unit according to the above publication allowed precise control over this small time-interval, to minimize its effects.

[0137] In additive casting involving molten metal deposition with pre-heating of the target region, rapid heating of the target area is an advantage as it minimizes the remelting of previously deposited material. The pace of pre-heating addresses heat dissipation to the previously-deposited bulk of the metal.

[0138] One of the advantages of using the heating device of the present disclosure in the PDP unit is a significant shortening of the time that elapses e.g., between pre-heating (and post heating) of the target area and the deposition of the added molten metal, by providing faster heating of the metallic surface under given electric current conditions. Referring to Fig. 7A, an exemplary casting system includes a heating system 100 including a heating device / PDP unit 700, which performs at least one of: pre-heating the fabrication area before molten metal deposition to a pre-deposition temperature and postheating the fabrication area after molten metal deposition to a post-deposition temperature. The heating device 100 or the induction coil 104 may be integrated into the PDP unit 700 by using a common frame 710. By using a common frame, the gap in time between the end of pre-deposition and start of the deposition of molten metal into the same fabrication area is shortened. Similarly, the gap in time between the end of deposition and the start of post-deposition heating of the same fabrication area is shortened.

[0139] The use of the same induction coil 104SUrface for both pre-heating of the fabrication area FA before molten metal deposition thereto and post-heating of the metal surface in said fabrication area FA after deposition can be implemented by movement of the induction coil 104Surface along the heating surface. This is better described with reference to Fig. 7B below.

[0140] The metal deposition module 730 may be positioned in the central opening of the induction coil 104 and configured to deposit the molten metal drops / stream from the metal depositor 720.

[0141] Considering the use of hollow-profile coil for the purposes of cooling fluid flow therethrough, the PDP unit 700 is configured to provide a coil cooling inlet / outlet 750.

[0142] Fig. 7B exemplifies a heating system 200 configured for surface heating during the formation of a metallic object by additive casting. The heating system includes a first heating device 700A having a solenoid-type induction coil 104Source configured as described above (e.g., Figs. 1C and ID), and a second heating device 700B, having a planar coil (e.g., pancake-type coil) 104SUrface configured as described above (e.g., Figs. IB, IE, 2A-2E). The induction coil 104Source applies heating to a metal source (e.g., a rod, as shown in Fig. 7B, or a bottom part of a liquid-holding crucible) MR (constituting the metallic target), extending along and surrounded by the induction coil 104Source, towards a melting temperature thereof to affect molten metal deposition onto a region FA (fabrication area) of a production layer of the metallic object being formed. The induction coil 104surface applies heating to said region FA before and / or after said molten metal deposition on the region. The heating system 200 is associated with (includes or is connectable to) a control system 230 configured and operable to operate the first and second heating devices (namely, source heating and surface heating) in synchrony in accordance with a predetermined production plan (illustrated in Fig. 7B as progression direction D). This example can be used for integration of the technique of the present disclosure in a molten metal depositor 720 and also pre- and / or post-treatment system 700B for treatment of the fabrication areas in the successive produced production layers. The electric power level provided to the induction coil 104Source ensures melting of the metal in a portion of the molten metal depositor 720, whereas the pre-processing and the post-processing units may be realized by induction coil 104SUrface, as described above.

[0143] As mentioned above, the use of the same induction coil 104SUrface for both preheating of the fabrication area FA before molten metal deposition thereto and postheating of the metal surface in said fabrication area FA after deposition can be implemented by movement of the induction coil 104pan along the heating surface. Hence, while moving, a leading portion 200A of the induction coil 104Surface pre-heats the previously fabricated object region (i.e., of the preceding production layer) to a first temperature, and a trailing portion 200B post-heats the just-deposited object region in the current production layer to a second temperature. Physical coupling the molten metal depositor to the induction coil 104Surface in the PDP unit allows precise control over this small time-interval, to minimize its effects.

[0144] Embodiments of the present disclosure are not limited by the target melting temperatures. In the context of additive metal casting as described above, embodiments of the present disclosure are not limited by the target temperatures of deposition, predeposition, and post deposition heating.

[0145] Embodiments of the present disclosure are not limited by the frequency that is applied. Embodiments of the present disclosure can be used within the electric current frequency range applicable for induction heating.

[0146] Embodiments of the present disclosure are not limited by the number, type, shape, geometry, and special configuration of the induction coil / s responsible for pre-heating and post heating.

[0147] Embodiments of the present disclosure were discussed for ease of explanation, mainly with reference to a circular pancake-type configuration and a round, solenoid-type configuration. Other coil shape configurations may be used. For example, non-circular single turn or multi-turns planar shapes can be used, including but not limited to square, hexagonal, octagonal, and mesh planar shapes. Similarly, non-planar non-round multitum shape types may be used including, but not limited to rectangular, spiral-helical, and U- shapes. The shapes may have sharp corners or rounded corners. Squircle shapes may also be used.

[0148] Embodiments of the present disclosure were discussed, for ease of explanation, mainly with reference to multitum coil configurations with even turn spacing. However, multiturn coil configurations with varied turn spacing may be used.

[0149] Embodiments of the present disclosure were discussed, for ease of explanation, mainly with reference to a single induction coil that performs pre heating and post heating. However, pre-heating may be carried out by one induction coil, while post-heating may be carried out by another induction coil. By another example, the height above the previously-fabricated layer of the induction coil responsible for pre-heating may differ from the height above the previously-fabricated layer of the induction coil responsible for post-heating. Pre-heating and post heating were described as performed on a slice, while trailing the deposition path (a thin line, represented in Fig. 7B as progression direction D), but this is not necessarily so. Pre-heating and post heating are not limited to a slice configuration. Thus, by yet another example, Pre-heating and post heating may be provided off-trail.

[0150] Embodiments of the present disclosure were discussed mainly with reference to additive casting of metal involving pre-heating of the target region up to the creation of a melt pool ready to receive the deposited molten metal. The invention is applicable for additive casting involving overheating the molten metal before deposition to thereby convey heat carried by the molten metal drops / stream to the target area.

[0151] Embodiments of the present disclosure were discussed mainly with reference to additive casting of metal and exemplified with reference to iron. The invention is not limited to this application and can apply for the additive casting of many other metal alloys and other conductive materials. Further, the invention is not limited to additive manufacturing and may apply to other applications involving induction heat treatment.

[0152] Embodiments of the present disclosure were discussed mainly with reference to applications involving moving one or more heating units over a surface. Embodiments of the present disclosure are not limited to these applications. For example, embodiments of the present disclosure are applicable to the use of stationary heating unit / s and a moving surface (e.g., a drum). Embodiments of the present disclosure are further applicable for using stationary heating unit / s for heating stationary targets.

[0153] While certain features of embodiments of the present disclosure have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the present disclosure.

Claims

CLAIMS:

1. A heating device comprising an induction coil for heating an electrically conductive target, the induction coil comprising an electrical conductor of a substantially planar configuration arranged in a form of a number N (N>1) of windings, defining a heating surface of the induction coil having a substantially planar shape by which it faces a surface of the electrically conductive target during heating, each winding defining first and second circumferential portions, the first circumferential portion being a heating portion forming a portion of said heating surface of the coil and the second circumferential portion being a periphery portion with respect to the electrically conductive target, wherein at least one of the N windings of the induction coil is configured with the heating portion thereof having a first resistance (Ri) smaller than a second resistance (R ) of the periphery portion, thereby providing that, when said induction coil is operated, the heating portion of said at least one winding has an electric current density Ji higher than an electric current density J2 in the periphery portion of said winding.

2. The heating device according to claim 1, wherein said induction coil is configured for improvement of heating efficiency of the electrically conductive target to a desired temperature as compared to a similar conductor having same resistance for all portions of the windings, said improvement providing at least one of the following: (1) shorten a heating time of the electrically conductive target to the desired temperature under given electric current, (2) use of smaller electric current to heat the electrically conductive target to said desired temperature, and (3) produce a higher temperature gradient on the target.

3. The heating device according to claim 1 or 2, wherein said first resistance Ri is at least 10% smaller than said second resistance R2.

4. The heating device according to any one of the preceding claims, wherein said conductor of the induction coil is configured with an array of two or more windings (N>2).

5. The heating device according to any one of the preceding claims, wherein the induction coil has a pancake-type configuration.

6. The heating device according to any one of the preceding claims, wherein said conductor is configured with at least one winding having a cross-section defining heating and periphery segments of said heating and periphery portions, respectively, said heatingand periphery segments having different first and second circumferential lengths LI and Z2, respectively, such that Z7<Z2.

7. The heating device according to claim 6, wherein said cross-section has a substantially parallelogram shape.

8. The heating device according to claim 6, wherein said cross-section has a substantially trapezoidal shape such that a wider side of a trapeze forms said heating portion of the winding.

9. The device according to any one of the preceding claims, said electrical conductor has windings having a solid profile.

10. The heating device according to any one of the preceding claims, wherein said electric conductor has windings having a hollow profile.

11. The heating device according to claim 10, wherein said hollow profile of the windings defines a hollow cavity of the conductor for a cooling fluid to flow therethrough, and wherein the induction coil comprises at least one cooling fluid inlet and at least one cooling fluid outlet.

12. The heating device according to claim 11, wherein at least one from among the at least one cooling fluid inlet and at least one cooling fluid outlet are located at an interim winding on a periphery portion thereof.

13. The heating device according to any one of the preceding claims, wherein the windings are isolated between them.

14. The heating device according to any one of claims 11 to 13, wherein a transition area between adjacent windings of said N windings has a rounded shape to reduce a near- surface flow regime of a coolant liquid component of said cooling fluid within said hollow cavity of the conductor.

15. The heating device according to any one of claims 5 to 14, wherein said at least one winding of the induction coil having substantially planar configuration has an oriented cross-section having an axis thereof, said axis being inclined with respect to a normal axis to the heating surface of the induction coil at a certain tilt angle <z, thereby providing that the heating portion of the winding has a length LI smaller than a length L2 of the periphery portion of said winding.

16. The heating device according to claim 15, wherein said certain tilt angle a satisfies a condition that 5° < |a| < 85°.

17. The heating device according to claim 15 or 16, wherein said cross-section of said at least one winding has a substantially parallelogram shape, where two opposite sides of the parallelogram define heating and periphery segments of said heating and periphery portions, respectively, said heating and peripheral segments being substantially parallel to the surface of the target being heated and other parallel sides of the parallelogram being inclined with respect to the normal axis to the heating segment at said tilt angle a.

18. The heating device according to claim 15 or 16, wherein said cross-section of said at least one winding has a substantially oval shape, and a long axis of the oval is inclined with respect to the normal axis to the heating surface of the coil at said tilt angle a.

19. The heating device according to any one of claims 15 to 18, wherein said electric conductor has a hollow profile defining a cavity for a cooling fluid to flow therethrough, the tilt angle a being selected to reduce near-surface flow regime of a coolant liquid component of said cooling fluid within said hollow cavity of the conductor.

20. The heating device according to any one of the preceding claims, wherein said first and second circumferential portions are integrally made.

21. The heating device according to any of the preceding claims, wherein the induction coil is a 3D printed structure.

22. The heating device according to 21, wherein the 3D printed structure is manufactured by a direct energy deposition (DED) method.

23. The heating device according to claim 22, wherein said DED method utilizes two metal powders with different percentages of highly-conductive metal.

24. The heating device according to any of claims 10 to 23, wherein said conductor has a wall thickness of about 1 mm.

25. The heating device of any one of the preceding claims, further comprising a power supply unit for operating electric current passage through said conductor.

26. The heating device according to any of the preceding claims, configured and operable to control operation of the induction coil to provide desired temperature conditions of the heating surface.

27. A heating system comprising at least one heating device configured as the heating device of any one of claims 1 to 26, and a control system configured and operable to operate the at least one heating device in accordance with a predetermined production plan.

28. The heating system according to claim 27 wherein said at least one heating device has an electric conductor with a hollow profile defining a cavity, the heating system further comprising a cooling fluid system configured and operable for operating fluid flow through said cavity.

29. The heating system according to claim 27 or 28 configured for heating during formation of a metallic object by additive casting, wherein said at least one heating device being configured and operable to apply the surface heating to a fabrication area of a production layer before and after deposition of a molten metal on said fabrication area to form an object region of said metallic object in said production layer.

30. A heating system configured for heating during formation of a metallic object by additive casting, the system comprising: at least one surface heating device configured as the heating device according to any one of claims 1 to 26 to apply the surface heating to a fabrication area of a production layer before and after deposition of a molten metal on said fabrication area to form an object region of said metallic object in said production layer; at least one source heating device comprising a solenoid-type heating device configured and operable to apply surface heating to a molten metal source surrounded by said solenoid-type heating device towards a melting temperature thereof to affect molten metal deposition onto said fabrication area of the production layer; and . a control system configured and operable to selectively operate the at least one source heating device and the at least one surface heating device in accordance with a predetermined production plan.

31. A method for heating an electrically conductive target to a desired temperature, the method comprising: providing at least one heating device configured as the heating device of any one of claims 1 to 26, located at a predetermined working distance between the heating surface of the induction coil and a surface of the electrically conductive target, operating said induction coil with a given electric current therethrough, resulting in that electric current density Ji in the heating portion of the at least one winding of the induction coil is higher than electric current density J2 in the periphery portion of said at least one winding, thereby providing improvement of heating efficiency of heating the electrically conductive target to a desired temperature as compared to a conductor having sameresistance for all portions of all windings thereof, said improvement providing at least one of the following: (1) shorten a heating time of the electrically conductive target to the desired temperature under a condition of said given electric current, (2) use of a smaller value of said given electric current to heat the electrically conductive target to said desired temperature, and (3) produce a higher temperature gradient on the target.

32. The method according to claim 31, wherein the electrically conductive target is composed of any one of the following materials and material compositions: aluminum, copper, gray iron, ductile iron, steel, Inconel alloys, titanium alloys, Monel alloys.

33. The method according to claim 31, wherein the desired temperature is near or equal to a melting temperature of the material composition.

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