Induction welding of workpieces

Abstract

An inductor unit for controlled induction welding of at least one fiber-reinforced thermoplastic composite workpiece includes at least one coil unit (110, 210), at least one conductive element (120, 220), and at least one soft magnetic element (130, 230). The conductive element (120, 220) has a generating side (120a, 220a) and an active side (120b, 220b). The active side is configured to face at least one workpiece (20, 21) to be welded and has a smaller cross-sectional area than the generating side. The at least one coil unit is configured to induce a current in the conductive element, and the at least one soft magnetic element is at least partially disposed on the at least one conductive element such that the induced current is directed from the generating side to the active side of the conductive element and concentrated there

Description

【Technical Field】 【0001】 The present invention relates to an inductor unit for controlled induction welding of at least one fiber-reinforced thermoplastic composite workpiece. The present invention also relates to a system for induction welding and a method of providing such a system. 【Background Art】 【0002】 Over the past few years, in, for example, the automotive and aerospace industries, reducing carbon emissions during transportation has been a major goal, and there has been an increasing interest in using lightweight materials. For example, it is becoming increasingly common for components of vehicles or aircraft to be made of fiber composite materials. By newly switching from thermosetting resins to thermoplastic matrices, it becomes possible to weld parts together, for example, by induction welding. 【0003】 Several systems directed towards induction welding of such materials are commercially available. The drawbacks of these systems are that they often use coils with high current levels of about 300 - 1000 A, require significant cooling, and use single- or multi-turn copper tubes that are inefficient, or use machined or 3D printed copper structures with high losses and current levels. Other systems use litz wire, which can be efficient but is often difficult to cool. A difficult problem associated with induction welding is to achieve a uniform temperature at the welding interface while applying a specific consolidation pressure to the heating area without accompanying local hot spots or cold spots and without remelting undesirable areas of the composite part. 【Prior Art Documents】 【Patent Documents】 【0004】 【Patent Document 1】 European Patent No. 2801472 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0005】 The drawback of the prior art system is that it requires a high current level to provide sufficient heating, resulting in large losses and low efficiency. Typically, this also means that it is necessary to place nearby a bulky and heavy workhead consisting of a transformer, a resonant capacitor, and copper busbars, which is not desirable to be placed on the end effector of a robotic arm. There are other similar examples of inductors, for example, combined with rollers as described in Patent Document 1, or the inductor itself is usually not able to withstand pressure in a good way and thus is combined with other devices applying a compaction pressure. The problem in these designs is to achieve a desirable heating pattern. 【0006】 Therefore, there is a need to improve the induction welding apparatus that can be used to better control the welding of fiber-reinforced plastics, improve the welding quality, and reduce the power used in the process. 【0007】 The object of the present invention is to solve or at least mitigate the problems associated with the prior art. This object is achieved by the technology described in the appended independent claims, and the preferred embodiments are defined in the related dependent claims. 【Means for Solving the Problems】 【0008】 According to one aspect of the present invention, an inductor unit for the controlled induction welding of at least one fiber-reinforced thermoplastic composite workpiece is provided. The inductor unit comprises at least one coil unit, at least one conductive element having a generative side and an active side, the active side being configured to face at least one workpiece to be welded, the active side of the conductive element having a smaller cross-sectional area than the generative side, and at least one soft magnetic element. The at least one coil unit is configured to induce a current in the conductive element, and the at least one soft magnetic element is at least partially disposed on the at least one conductive element such that the induced current is directed from the generative side of the conductive element towards the active side and concentrated therein. 【Advantages of the Invention】 【0009】 An advantage of the inductor unit is that the required current is considerably low because the current density becomes high at the active side of the inductor unit facing the workpiece to be welded, thereby increasing the power density in the workpiece. 【0010】 Another advantage of the inductor unit is that the need for cooling is low. Accordingly, the need for an external cooling system is reduced. 【0011】 Yet another advantage of the inductor unit is that it can be designed to precisely conform to the shape of the workpiece to be welded. This also applies to complex geometric shapes of the workpiece. The inductor unit can be used or endured to apply a consolidation pressure to the welding seam area, either as a rigid structure or with a specific flexibility that conforms to the part geometry of the workpiece to be welded. It can be used for both continuous welding and discrete welding including spot welding. A common need for induction welding equipment is the flexibility to handle different geometries in a fast and cost-effective way. The proposed inductor design can be easily and automatically adapted to handle, for example, wide and narrow welds, flat and curved geometries, various weld lengths, etc. 【0012】 Unlike copper tubes, due to the high degree of freedom in geometry, the constraints in design optimization are reduced. The conductive and soft magnetic elements enable induction of current in an optimal way to achieve the desired temperature pattern. In contrast to the prior art, due to the high power density, the cycle time can be shortened and the heat affected zone can be limited. 【0013】 Another advantage of the inductor unit is that it can be arranged to contact or be close to the workpiece to be welded. In this way, losses can be reduced and efficiency can be improved. 【0014】 The inductor unit can ensure concentrated heating at the required location, reduce unwanted heating of areas outside the welding seam area, cool the surface, and prevent remelting of unwanted areas. Furthermore, the material of the inductor unit can provide the heat load or cooling of the welding zone, also called the welding seam area, adjusted by the inductor unit design, not only for generating a specific temperature pattern but also for facilitating the temperature profile for improving material properties such as matrix crystallinity. 【0015】 Furthermore, when combined with a processing means, the high-efficiency inductor unit can help predict the temperature of the welding interface. 【0016】 According to another aspect, a system for induction welding of at least one fiber-reinforced thermoplastic composite workpiece comprising the above-described inductor unit is provided. 【0017】 According to yet another aspect, a method of providing a system for induction welding the above-described at least one fiber-reinforced thermoplastic composite workpiece is provided. BRIEF DESCRIPTION OF THE DRAWINGS 【0018】 As an example, embodiments of the present invention will now be described with reference to the accompanying drawings. 【0019】 【Figure 1】 FIG. 1 is a perspective view of a part of an induction welding system according to one embodiment. 【Figure 2】 FIG. 2 is a schematic block diagram of a part of the system of FIG. 1. 【Figure 3a】 FIG. 3 is a perspective view of an inductor unit according to one embodiment. 【Figure 3b】 FIG. 3a is a cross-sectional view of the embodiment of FIG. 3. 【Figure 3c】 FIG. 3b is a perspective view of a part of an inductor unit according to another embodiment. 【Figure 3d】 FIG. 3c is a cross-sectional view of the embodiment of FIG. 3c. 【Figure 3e】 FIG. 3c and FIG. 3d are perspective views of a part of the inductor unit. 【Figure 3f】 FIG. 3e is a perspective view of a part of an inductor unit according to still another embodiment. 【Figure 3g】 FIG. 3f is a cross-sectional view of the inductor unit of FIG. 3f. 【Figure 3h】 FIG. 3g is a perspective view of an inductor unit according to another embodiment. 【Figure 3i】 FIG. 3h is another perspective view of the inductor unit of FIG. 3h. 【Figure 3j】It is a cross-sectional view of the inductor unit of FIG. 3i. 【Figure 3k】 It is a perspective view of the inductor unit according to one embodiment. 【Figure 4a】 It is a perspective view of the production side of a part of the inductor unit according to another embodiment. 【Figure 4b】 It is a perspective view of the active side of a part of the inductor unit of FIG. 4a. 【Figure 4c】 It is a schematic top view of the inductor unit of FIGS. 4a - b. 【Figure 4d】 It is a perspective view of the active side of the inductor according to FIGS. 4a - b. 【Figure 4e】 It is a cross-sectional view of the embodiment of FIG. 4d. 【Figure 5a】 It is a perspective view of half of the inductor unit according to yet another embodiment. 【Figure 5b】 It is a perspective view of a part of the inductor unit of FIG. 5a. 【Figure 5c】 It is a cross-sectional view of an inductor unit that is twice the inductor unit shown in FIG. 5a. 【Figure 6a】 It is a perspective view of a part of the inductor unit according to another embodiment. 【Figure 6b】 It is a perspective view of a part of another type of inductor unit according to the embodiment shown in FIG. 6a. 【Figure 6c】 It is a cross-sectional view of the inductor unit according to one embodiment. 【Figure 6d】 It is a cross-sectional view of the inductor unit according to another embodiment. 【Figure 6e】 It is a cross-sectional view of the inductor unit according to still another embodiment. 【Figure 7a】 It is a perspective view of the inductor unit according to another embodiment. 【Figure 7b】 It is a cross-sectional view of the embodiment of FIG. 7a. 【Figure 8】 It is a schematic block diagram showing a system for induction welding. 【Figure 9】 It is a schematic block diagram of a welding method according to one embodiment. 【Best Mode for Carrying Out the Invention】 【0020】 Embodiments of the present invention will be described below with reference to the drawings. However, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The terms used in the detailed description of the specific embodiments shown in the accompanying drawings are not intended to limit the present invention. In the drawings, like numbers refer to like elements. 【0021】 FIG. 1 shows a part of a system 1 for induction welding according to the present invention, the purpose being to achieve a process temperature sufficient to weld at least one workpiece 20, 21 without overheating or underheating the material or workpiece to be welded. The induced power 2 is caused by inductor units 100, 200 that induce an electric current in at least one workpiece 20, 21. 【0022】 Apply pressure to at least one workpiece 20, 21 to ensure proper consolidation. The pressure can be applied to the workpiece through the inductor unit or by other means such as a vacuum bag or an external fixture. 【0023】 Before moving on to a detailed description of the disclosed embodiments of the inductor units 100, 200, an exemplary environment in which the inductor units can be implemented will be briefly described here. 【0024】 Referring to FIG. 1, two surfaces of two workpieces 20, 21 are welded to each other. The workpieces 20, 21 are configured to be induction welded in a weld seam region A. The weld seam region A is defined by a first portion 20' of the first workpiece 20 disposed on, adjacent to, and facing a second portion 21' of the second workpiece 21. The inductor units 100, 200 are disposed in relation to or in proximity to at least one of the two workpieces 20, 21. In one embodiment, the two workpieces 20, 21 are disposed in relation to the inductor unit by directly contacting each other. In a further embodiment, the two workpieces 20, 21 are disposed in relation to the inductor units 100, 200 without directly contacting each other. Thus, at least one of the workpieces 20, 21 may be in direct or indirect contact with the inductor units 100, 200, or may not be in physical contact with each other. The distance between the inductor units 100, 200 and the workpiece is preferably less than 5 mm for good electromagnetic coupling, but may be about 10 - 15 mm if the weld zone is wide. 【0025】 For example, a heat conductive or insulating material may be disposed between the inductor units 100, 200 and at least one workpiece to control heat transfer and cause indirect contact. In one embodiment, the inductor units 100, 200 are at a predetermined distance from at least one of the workpieces 20, 21, and the densification pressure can be obtained by other means. The smaller the distance, the better the electromagnetic coupling. Preferably, the distance is less than 5 mm, but may be about 10 - 15 mm. For example, by mechanically clamping outside the weld seam region A, the densification pressure is maintained even after heating is completed. 【0026】 The inductor units 100, 200 induce current in at least one of the workpieces 20, 21 that are susceptible to electromagnetic heating. Alternatively, an embedded susceptor is present within or in proximity to the workpiece, typically near the weld seam region A. When the workpieces 20, 21 are induction heated, the material within the weld seam region A melts or fuses when it reaches a predetermined melting or processing temperature corresponding to the material properties of the workpieces 20, 21. The time required to melt the workpieces 20, 21 in the weld seam region A is determined by the material properties and geometric shape of each workpiece. 【0027】 In the embodiment shown in FIG. 1, the workpieces 20, 21 are rectangular. However, as will be understood by those skilled in the art, they may have any shape. For example, they may be beams and outer panels of aircraft components. The workpieces 20, 21 may also be fixed elements attached to automotive components or two similar parts to be joined (see, for example, FIG. 3k). The workpiece to be welded may have a complex geometric shape and its thickness may vary from submillimeter to several tens of millimeters. 【0028】 Workpieces 20, 21 should be regarded as susceptors, which means they have the ability to absorb electromagnetic energy and convert it into heat. Typically, they are carbon fiber composite materials such as carbon fiber reinforced plastics (CFRP). The fiber reinforcement material may be any type of industrial fiber such as glass fiber, linen, aramid, PET, ultra-high molecular weight polyethylene (UHMWPE), etc. Also, the composite material can be a hybrid fiber reinforcement material containing multiple fiber types, for example, glass and carbon fibers. The fibers can be continuous or chopped, unidirectional, multi-axial or woven fabric lay-up or randomly oriented fibers. Different types of fibers and lay-ups have specific advantages such as rigidity, density, cost, appearance, environmental impact, dielectric properties, etc. The susceptor material can be any conductive or magnetically permeable material, for example, carbon fiber and any kind of metal. For example, as will be apparent from the following description, a steel mesh may be added so that non-conductive fiber composite materials can be welded. 【0029】 Workpieces 20, 21 may be made, for example, from a unidirectional laminate in which each layer is arranged at a different angle with respect to the adjacent layer. As a non-limiting example, each workpiece may include, for example, 10 layers of carbon fiber embedded in a thermoplastic matrix. Alternatively, workpieces 20, 21 are made from a woven web of carbon fibers such as chopped or ground, organized, or randomly oriented carbon fibers. The matrix may be an amorphous or semi-crystalline thermoplastic material, for example, polyethylene terephthalate (PET), polypropylene (PP), polyamide (PA), polycarbonate (PC), or a high-end type, for example, polyphenylene sulfide (PPS), polyetherimide (PEI) or polyetheretherketone (PEEK), etc. Carbon fiber composite materials are usually classified as semiconductors and can be directly heated throughout the thickness of the material. The thermoplastic matrix enables the workpieces 20, 21 to be melted, thereby forming a weld seam in the weld seam region A shared by the two workpieces 20, 21. 【0030】 The workpieces 20, 21 may also be fiber glass composite materials. The fibers may also be any other technical textile such as linen fibers, aramid, ultra-high molecular weight polyethylene, etc. As a non-limiting example, glass fibers can be used as a reinforcing agent in a polypropylene-based matrix. If the workpieces 20, 21 to be welded are glass fiber composites, it may be necessary to introduce an additional layer (not shown) at the interface between the two workpieces 20, 21. This is because glass fibers have no electrical conductivity and magnetic permeability. The additional layer disposed at the interface may be referred to as a susceptor. This susceptor may be, for example, a woven web of metal or carbon fibers. The web constituting the additional layer may be a non-woven fabric. The additional layer may be something other than a web. For example, the additional layer may be randomly oriented carbon fibers applied to one or both surfaces of the workpieces 20, 21 to be welded. 【0031】 Note that the two workpieces 20, 21 may be of different materials. Thus, the first workpiece 20 may be of a first material and the second workpiece 21 may be of a second material. In the above-described embodiments, one workpiece may be made of a fiber glass composite material and one workpiece may be a susceptor. The composite material can also be constructed with hybrid fiber reinforcements such as glass fibers and carbon fibers, and typically the carbon fibers are disposed at least on or near the surface of the material. The workpiece can also be welded to a thermoplastic part or a metal component, for example, a fixing element. 【0032】 In the above example, welding has been described as welding two surfaces of two separate workpieces. However, as will be understood by those skilled in the art, it is also possible to weld two surfaces of a single workpiece. In other words, the two workpieces may belong to the same part if they have a closed cross-section component such as an open tube welded to each other along the length, for example. 【0033】 The workpieces 20, 21 may also include non-consolidated materials such as fabrics, organosheets, other types of semi-finished or pre-consolidated carbon fiber thermoplastic prepregs based on co-mixed or spun carbon and thermoplastic fibers, or may be technical fibers with thermoplastic or thermally activated binders. Typically, in these cases, welding is used to maintain the layers in place during layup, after which they are placed in a mold and consolidated, sometimes referred to as preforming. Furthermore, it should be understood that in certain cases, even the surfaces of three or more different workpieces can be welded to each other. Other combinations of materials may be a reinforcing material welded to a core material, for example, a metal or carbon fiber sheet welded to a foamed PET material, which is commonly used in lightweight structures to increase rigidity and is often referred to as a sandwich structure. In another example, a thermoplastic composite panel can be welded to a metal frame for quick attachment. 【0034】 Returning to FIG. 1, pressure is applied to the workpieces 20, 21 to ensure good contact between the two workpieces to be joined. The pressure can be applied through external pressure means 50 (see FIG. 8) or by a force resulting from the inherent characteristics of the inductor design, for example, through geometric expansion, which will be understood in connection with FIGS. 3 - 6 below. Generally, the pressure means 50 can be applied from either side of the workpiece welded to the inductor units 100, 200, and preferably includes a fixing device (not shown) on the opposite side. The inductor units, pressure means, and fixtures can be either fixed or movable depending on the settings and applications. The consolidation pressure may result from any type of force generation such as a spring load, a press unit, a robotic device, or expanding parts or materials. As an alternative, the consolidation pressure may result from a vacuum bag / membrane covering the workpieces at atmospheric or high pressure, or the equivalent. For example, an autoclave or a water tank can be used to apply the consolidation pressure, and in the case of water or other fluids, cooling of the workpieces 20, 21 is also provided. 【0035】 FIG. 2 shows a schematic view of the inductor units 100 and 200. Some reference numerals appear in the description of FIG. 2 but are not explicitly shown in FIG. 2. These features will become apparent when read in connection with the remaining drawings. The inductor units 100 and 200 include a coil unit 110, conductive elements 120 and 220, and soft magnetic elements 130 and 230. Further, the inductor units 100 and 200 are preferably operably communicating with the processing means 30. Here, the different parts will be described in more detail. 【0036】 The inductor units 100 and 200 have a generating side 100a, 200a and an active side 100b, 200b (see FIGS. 3 to 7). Both the generating side 100a, 200a and the active side 100b, 200b include or form a part of the conductive elements 120 and 220. The generating side 100a, 200a of the inductor units 100 and 200 may correspond to the generating side 120a, 220a of the conductive elements 120 and 220. Correspondingly, the active side 100b, 200b of the inductor units 100 and 200 may correspond to the active side 120b, 220b of the conductive elements 120 and 220. 【0037】 On the active side 100b, 200b of the inductor units 100 and 200, the conductive elements 120 and 220 preferably have a smaller cross-sectional area than the generating side 100a, 200a of the inductor units 100 and 200. The cross-sectional area relates to the area through which the current passes. 【0038】 The cross-sectional area can be defined by the width of the place where the current can flow × the skin depth. Since the skin depth can be assumed to be the same at any place on the conductive element (effective when the conductive element is made of the same material, for example, copper, at any place), it is the same as the cross-sectional width of the surface where the current can flow. Therefore, at least a part of the active side 120b, 220b may have a narrower surface width than the generating side 120a, 220a. In other words, the cross-sectional area may also be called the cross-sectional width. 【0039】 The conductive elements 120, 220, or at least parts thereof, may be replaceable. It may have a curved or bent shape on the generating sides 100a, 200a, thereby increasing the cross-sectional area on the generating sides 100a, 200a as compared to the surface area on the active sides 100b, 200b. Conversely, the conductive elements 120, 220 may have a narrower shape towards the active sides 100b, 200b of the inductor unit, creating a smaller cross-section for the current, thereby creating a more concentrated electromagnetic flux density and power density. Further, the conductive elements 120, 220 may be deformable by a pressurizing medium or the like. For example, when the conductive elements 120, 220 are at least partially hollow and the wall thickness of the active sides 120b, 220b of the conductive elements 120, 220 is small, it deforms when the hollow volume is expanding, thereby applying pressure to the workpiece. This operation is achieved when the hollow volume is pressurized, for example, by air or water. 【0040】 Briefly stated, the conductive elements 120, 220 have generating sides 120a, 220a and active sides 120b, 220b. The active sides 120b, 220b are configured to face at least one workpiece 20, 21 to be welded and have a cross-sectional area that is at least locally smaller than that of the generating sides 120a, 220a. When the width of the active sides 120b, 220b of the conductive element varies, the highest power density is generated in the narrow cross-section with the highest current density. Illustrated in the shape of an hourglass, if the distance between the active sides 120b, 220b of the conductive element and the workpieces 20, 21 is the same everywhere, the central part (where the current concentrates) gets the warmest. 【0041】 The cross-sectional area of the active sides 100b, 200b may be described as the area of the inductor units 100, 200 facing the workpiece to be welded, and the cross-sectional area of the generating sides 100a, 200a may be described as the area of the inductor units 100, 200 facing away from the workpiece to be welded. 【0042】 Parts of the conductive elements 120 and 220 that connect the generating sides 120a, 121a, 220a and the active sides 120b, 121b, 220b are referred to as transmission parts 120c, 121c, 220c, 221c, 222c. Hereinafter, the transmission parts are also referred to as the transfer side. The transfer sides 120c, 121c, 220c, 221c, 222c may have substantially any shape. In a particular inductor design, the size of the transfer side may be negligible. Preferably, the transfer side is not covered by the soft magnetic elements 130, 230. 【0043】 The coil unit 110 may include one or more coils that together form at least two turns, preferably more turns. The turns may be at least partially wound around the generating sides 120a, 121a, 220a of the conductive elements 120, 220 and / or at least one soft magnetic element 130, 230. Each coil preferably consists of a low-loss Litz wire. The Litz wire comprises a plurality of individual strands. The strands typically consist of thin insulated wires arranged with respect to each other. In one embodiment, the strands are twisted in parallel. In an alternative embodiment, the strands are twisted together as a single bundle. In a further embodiment, a plurality of bundles of strands are twisted together. 【0044】 Litz wire is used to reduce the skin effect. The skin effect is a term that refers to the phenomenon in which high-frequency current tends to flow near the surface (or skin) of a conductor. This is caused by the magnetic field induced in the conductor by the high-frequency alternating current. The magnetic field makes it difficult for the current to flow anywhere other than the outer surface. Since the current is forced to flow only through a part of the wire, the effective resistance of the wire increases. The higher the frequency, the greater the loss of the wire due to this increase in effective resistance. The winding pattern of the Litz wire equalizes the ratio of the total length of each strand on the outside of the conductor. This has the effect of evenly distributing the current among the wire strands, thereby reducing the resistance. Similarly, the Litz wire also reduces the proximity effect, whereby the current is forced to concentrate in specific regions of the regular wire due to the current in adjacent wires or conductors. 【0045】 The conductive elements 120, 220 are made of a highly conductive material. The material may be, for example, copper or aluminum. The advantage of using copper is that it has excellent thermal and electrical conductivity among commonly used metals. The advantage of using aluminum is that in addition to good electrical conductivity, high-temperature-resistant electrical insulation can be easily applied in terms of aluminum oxide by anodization, so that, if necessary, the inductor can be brought into direct contact with the workpiece surface without the need for direct electrical contact. The electrical contact between the conductive elements 120, 220 and the workpieces 20, 21 may not be a problem from a functional perspective due to the large difference in electrical resistivity between different materials, but it may cause undesirable arc discharge. Even with direct electrical contact between the conductive elements 120, 220 and the workpieces 20, 21, the welding results may be improved, as will be further described below with reference to Fig. 3k. The conductive elements 120, 220 may comprise a plurality of parts, as will be described in more detail with reference to Figs. 3 to 7. Further, the inductor units 100, 200 may also include an electrical and / or thermal insulator (not shown) between at least one workpiece 20, 21 welded to the conductive elements 120, 220. 【0046】 As described above, the inductor units 100, 200 further include soft magnetic elements 130, 230. The soft magnetic elements 130, 230 are made of any kind of soft magnetic material having a relative permeability exceeding 10. The soft magnetic material should also preferably have a high bulk electrical resistivity and should have an electrical resistivity thousands or millions of times higher than that of the conductive elements. The bulk electrical resistivity is defined as the overall electrical resistivity in the direction in which an induced current can flow, rather than a micro-level property. The bulk resistivity of the soft magnetic material is preferably at least 0.01 Ω·m. 【0047】 The soft magnetic materials 130, 230, also called magnetic flux concentration elements, may preferably be a composite material or ceramic with low magnetic hysteresis loss. It includes amorphous and semi-crystalline alloys, and may be any one of soft magnetic ferrites, and / or powder-based cores, bundles or stacks of individually insulated soft magnetic wires, strips, or laminates. Preferably, the soft magnetic elements 130, 230 are at least partially disposed on the interface surface of the inductor units 100, 200. More specifically, the soft magnetic elements 130, 230 are preferably at least partially disposed on the surfaces of the conductive elements 120, 220. This is to enhance the magnetic flux and prevent current from flowing in the region of the conductive elements covered by the soft magnetic elements. The soft magnetic elements 130, 230 disposed on the conductive elements 120, 220 preferably face the environment rather than the workpiece. The interface surface of the inductor unit may be described as the outer surface of the inductor unit facing the environment. 【0048】 The purpose of arranging the soft magnetic elements on top of the conductive elements is to direct the current induced by the coil units 110, 210 from the generation sides 120a, 220a of the conductive elements 120, 220 towards the active sides 120b, 220b and concentrate the current therein. Further, the soft magnetic elements 130, 230 are provided to strengthen the magnetic flux and prevent the current from being conducted over the regions of the conductive elements 120, 220 covered by the soft magnetic elements 130, 230. The soft magnetic elements 130, 230 may also be arranged within the inductor units 100, 200 for the purpose of concentrating and strengthening the magnetic flux in the desired regions of the inductor units, as will become apparent from the following description. Also, the soft magnetic elements 130, 230 are configured to concentrate the induced current on the active sides 100b, 200b of the inductor units 100, 200 to heat a predetermined weld seam region A within at least one workpiece 20, 21. 【0049】 In one embodiment, the soft magnetic elements 130, 230 are made of soft ferrite. In an alternative embodiment, the soft magnetic elements 130, 230 include a powder-based core of a flux material or other similar type of soft magnetic composite. In a further embodiment, the soft magnetic elements 130, 230 include a laminated soft magnetic structure. Generally speaking, the soft magnetic elements 130, 230 are configured to concentrate the electromagnetic flux and thereby assist in inducing the current in the desired direction. This can be seen as a shield that helps with the concentration of the current. 【0050】 The soft magnetic elements 130, 230 may comprise a plurality of parts, as will be described in more detail with reference to FIGS. 3 to 7. Preferably, the soft magnetic elements 130, 230 surround at least a portion of the conductive elements 120, 220. The soft magnetic elements 130, 230 are configured to act as a conductor for the magnetic field but not as a conductor for the current. 【0051】 The soft magnetic elements 130, 230 may contribute to the concentration of current in predetermined parts of the inductor units 100, 200 by providing a path for magnetic flux. The induced current in the conductive elements 120, 220 of the inductor units 100, 200 is enhanced by magnetic flux concentration, particularly by the current in the active sides 100b, 200b of the conductive elements. This principle may be explained as follows. 【0052】 The induced current in the conductive elements 120, 220 aims to minimize the stored energy of the circuit, i.e., the inductance of the circuit. Therefore, the current preferably flows on the surfaces not covered by the soft magnetic materials 130, 230 such as the transmission sides 120c, 121c, 220c, 221c, 222c, etc., and avoids the regions covered or separated by the soft magnetic materials 130, 230. The direction of the induced current is defined by the coil units 110, 210. The current is also forced to generate a closed current loop according to the laws of physics. When the conductive elements 120, 220 come into contact with at least one workpiece 20, 21 during welding, a closed current loop is formed for the current flowing from one region to another region of at least one workpiece 20, 21. 【0053】 In some embodiments, the conductive elements 120, 220 may be formed with a tapered surface area in a direction configured to face the workpieces 20, 21 to be welded. Alternatively or additionally, the conductive elements 120, 220 may have recesses such as slits extending radially outward from the central axes of the inductor units 100, 20 in a direction configured to face the workpieces 20, 21 to be welded. In either of these two cases, or in an alternative configuration, the current induced in the inductor unit via the coil units 110, 210 may be guided through the inductor units 100, 200 in a direction towards the workpieces 20, 21 to be welded. The presence of the soft magnetic elements 130, 230 enhances this current density formation according to the aforementioned principle. 【0054】 As described above, referring to FIG. 2, the inductor units 100 and 200 communicate operably with the processing means 30 such as a frequency converter. The processing means 30 is configured to generate a high-frequency current in the coil units 110 and 210. The system 1 shown in FIG. 8 including the inductor units 100 and 200 further includes the processing means 30. 【0055】 Preferably, the processing means 30 is a frequency converter or includes a frequency converter. The processing means 30 is configured to generate an electromagnetic field through the inductor units 100 and 200 by applying an alternating current to the inductor units 100 and 200 so as to inductively heat the workpieces 20 and 21 in the welding seam region A. As a result, the workpieces 20 and 21 are welded to each other. 【0056】 The processing means 30 may further include an interface (not shown) for transmitting data obtained by the inductor. The interface may be of any suitable type including simple wiring, serial interfaces such as Ethernet (registered trademark), RS485, USB, wireless interfaces such as Bluetooth (registered trademark) or WiFi. The processing means 30 may include a programmable device such as a microcontroller, a central processing unit (CPU), a digital signal processor (DSP) or a field programmable gate array (FPGA), a discrete digital synthesizer (DDS) having appropriate software and / or firmware, and / or an application specific integrated circuit (ASIC) or other dedicated hardware. The processing means may be connected to or include a computer-readable storage medium such as a disk or memory. The memory may be implemented using any well-known technology for computer-readable memory, such as ROM, RAM, SRAM, DRAM, FLASH, DDR, SDRAM, or some other memory technology. 【0057】 The processing means 30 may further include a display unit for providing process information to an operator or user. The processing means will be further described with reference to FIG. 8. 【0058】 An advantage of the inductor units 100 and 200 of the present invention common to all embodiments is that they can be driven with a low current due to the multi-turn structure of the coil units 110 and 210. By integrating the coil units 110 and 210, the conductive elements 120 and 220, and the soft magnetic materials 130 and 230 as one unit, a relatively high power density may be achieved in the portion of the workpiece to be induction welded. 【0059】 Compared with conventional coils and work heads, the inductor units 100 and 200 are small and lightweight units and can be easily attached as the end effector of any type of robot. Also, a long flexible wire between the processing means and the inductor unit 100 can be handled with stable operation and without substantial loss or EMC interference. 【0060】 As described above, the inductor units 100 and 200 are configured to be arranged near the workpieces 20 and 21 to be welded and to inductively guide a heating current to specific positions above / around the workpieces 20 and 21. The inductor units 100 and 200 may be in direct or indirect contact with the workpieces 20 and 21 to be welded, depending on the thermal design, material selection, and application. The inductor units 100 and 200 may include a heat insulating material covering the active side of the conductive element to prevent excessive heat from being transmitted to the inductor units 110 and 200. In a specific fixed configuration, the inductor units 100 and 200 do not necessarily need to be in contact with the workpiece, but a densification pressure can be obtained by other means that are particularly useful in the case of continuous welding. 【0061】 As shown and described with reference to FIGS. 3 to 7, the inductor units 100 and 200 may be designed to have different shapes. Therefore, the inductor units 100 and 200 can be adapted to different workpiece configurations, enabling selective and precise heating of the workpieces to be welded. Non-exhaustive examples of the inductor configuration are shown in the accompanying drawings. Note that there are also other embodiments not captured by the drawings. 【0062】 The movement of the inductor units 100 and 200 can be in multiple directions in a single embodiment as long as the inductor units 100 and 200 are close to at least one workpiece 20, 21. Preferably, the translational movement of the inductor is actuated by a moving means (not shown). This will be further described in relation to FIG. 8. The inductor units 100 and 200 may be applied to spot welding, static line welding, piece-by-piece static line welding, or continuous or dynamic welding along a programmed track, depending on their design and use. 【0063】 Referring to FIG. 3a, an inductor unit 100 according to a first embodiment is shown. The inductor unit 100 in FIG. 3a may also be referred to as a longitudinal flux inductor 100. In this embodiment, the inductor unit 100 has a shape that extends longitudinally. The inductor unit 100 has a generating side 100a and an active side 100b and includes three main components (coil unit 110, conductive element 120, and soft magnetic element 130). This schematic diagram of the inductor unit shows the concept of the present invention in an educational way and can function as a reference for other embodiments described below. 【0064】 As shown in FIG. 3a, the coil unit 110 is preferably a Litz wire wound around the coil a plurality of times. The coil unit 110 extends along the longitudinal direction of the inductor unit 100. 【0065】 The conductive element 120 may be integrally formed. However, in relation to FIG. 3a, it is more easily explained as having a first part, a second part 122, and a third part 123. In this case, the first part 121 corresponds to the part including the active side 100b of the inductor unit 100, and the other parts 122, 123 serve to reduce the inductance of the circuit. Joining the three parts together enables a more optimized design. Typically, the different parts of the conductive element 120 are of the same material, but may be, for example, a combination of copper and aluminum. The first part 121 of the conductive element 120 has a generation side 121a facing the coil unit 110 and an active side 121b corresponding to the active side 100b of the inductor unit 100. In practice, the active side 100b of the inductor unit 100 faces the workpieces 20, 21 during welding. As seen in FIG. 3a, the generation side 121a of the first part 121 of the conductive element 120 has a larger surface area than the active side 121b. The first part 121 of the conductive element 120 tapers from the generation side 121a to the active side 121b via the transmission side 121c. In this embodiment, the first part 121 of the conductive element 120 tapers from the generation side 121a to the active side 121b in a direction perpendicular to the longitudinal extension of the inductor unit 100. Thus, the current flowing through the generation side 121a of the conductive element 120 is forced to flow to the active side 121b, forming a closed current loop using the transmission side 121c not covered by the soft magnetic material 130. The transmission side 121c can be seen as the end or the gable of the inductor unit 100 in FIG. 3a. 【0066】 Furthermore, the first part 121 of the conductive element 120 has a first opening 125 and a second opening 126, which can be seen on the transmission side 121c of the inductor in FIG. 3a. The smaller the cross-sectional area of the active sides 100b, 121b, the higher the current density, and thereby the higher the power density. 【0067】 Due to the operation of the transformer and the minimization of current leakage in the conductive element 120 by the soft magnetic element 130, the total current passing through the cross-section of the active side 121b is approximately equal to the magnitude of the coil current × the number of turns of the coil unit. These openings 125, 126 are configured to extend into the first part 121 of the conductive element 120 along most of the length of the inductor unit 100 to form a U-shaped channel. The first and second openings 125, 126 may be useful for cooling the conductive element 120. The first and second openings 125, 126 are sometimes referred to as cooling channels. The cooling channels are configured to receive a fluid medium such as a gas or a liquid medium. 【0068】 In particular, the need for cooling the inductor unit 100 of the present invention is reduced because the heating efficiency of the workpieces 20, 21 to be welded is high. However, cooling is beneficial for reproducibility and continuous operation. Despite being efficient, due to heat transfer from the workpiece, certain losses occur in both the coil unit 100, the soft magnetic element 130, and the conductive element 120. 【0069】 In FIG. 3a, the second part 122 of the conductive element 120 is optional, has a substantially block-like shape, and is disposed inside the inner part of the coil unit 110. This feature can be seen more clearly in FIG. 3b. Below the second part 122 of the conductive element 120, that is, in the direction towards the active side 100b of the inductor unit 100, a soft magnetic element is disposed, which will be further described below. Optionally, the soft magnetic element is disposed above the second part 122. 【0070】 The third part 123 has a shape similar to that of the second part 122 of the conductive element 120 and is disposed on the side facing the generating side 100a of the inductor unit 100 of the coil unit 110. The third part 123 is optional and is configured to reduce the inductance of the circuit, simplify the application of pressure to the inductor unit 100 in use (and thus the workpieces 20, 21 heated thereby), and contribute to the cooling of the inductor unit 100. 【0071】 The soft magnetic element 130 may be provided in one or more parts of the inductor unit 100. In FIG. 3a, a first part 131, a second part 132, a third part 133 and a fourth part 134 are shown. These parts are substantially rectangular in shape. The soft magnetic parts 131, 132, 133, 134 are arranged on each side of the inductor unit 100. As described above, the soft magnetic element 130 is typically a powder-based core of soft magnetic ferrite or flux wire configured to conduct magnetic fields but not electric currents. Thus, the soft magnetic element 130 may be regarded as a barrier to electric current. The parts 131, 132, 133, 134 of the soft magnetic element are arranged along the sides of the funnel-shaped / tapered conductive element 120 to assist in concentrating the induced current on the active side 100b of the inductor unit 100. Optionally (not shown), the soft magnetic element 130 may also be arranged on the generating side 100a of the inductor. The preferred position and geometric shape of the soft magnetic element 130 relative to the conductive element 120 depend on the application, geometric shape, material selection and design. The soft magnetic material 130 is often made into shapes with limited sizes, and some soft magnetic materials are difficult to machine and require the use of several pieces rather than one large unit. In certain configurations, it may be beneficial to use one-piece soft magnetic elements or different pieces assembled together. Sometimes, depending on the design and material selection, it may be beneficial to introduce gaps between different parts of the soft magnetic element to reduce high magnetic flux density concentration. 【0072】 The inductor unit 100 extending in the longitudinal direction of FIG. 3a is shown in cross-section in FIG. 3b. Here, it shows that the inductor has a laminated structure. Below the second part 122 of the conductive element 120, the fifth part 135 and the sixth part 136 of the soft magnetic element 130 are shown. The litz wire 110 surrounds the second part 122 of the conductive element 120, and the fifth part 135 and the sixth part 136 of the soft magnetic element are sandwiched between the first part 121 and the third part 123 of the conductive element 120. 【0073】 In the inductor unit 100 shown in FIGS. 3a and 3b, the induced current flowing through the inductor unit 100 is concentrated on the active side 100b of the inductor unit, which also corresponds to the active side 121b of the conductive element 121 described above. 【0074】 As a result of the inductor arrangement shown in FIGS. 3a and 3b, a relatively small current concentration entering the coil unit 110 can be achieved at the active side 100b of the inductor unit 100 configured to be disposed near the workpieces 20, 21 to be welded. When the induced current moves through the conductive element 120 (or a part thereof), it is pushed downward toward the tapered portion of the first part 121 of the conductive element 120 extending in the longitudinal direction, that is, the current moves from the generation side 100a of the inductor unit 100 to the active side 100b via the transmission side 121c. In other words, the current concentrates from a relatively large surface area (i.e., a larger cross-sectional area) at the generation side 121a corresponding to the space directly below the coil unit 110 to a narrower surface area at the active side 121b of the conductive element 120 corresponding to the active side 100b of the inductor unit 100. 【0075】 Figure 3c shows a part of the inductor unit 100, which is also called a longitudinal flux inductor, like the inductor shown in relation to FIGS. 3a - b. In FIG. 3c, compared with FIGS. 3a - b, the surface expands at the generating side 120a of the conductive element 120, and the cross-sectional area of the current becomes relatively large without consuming the widthwise space that may interfere with the workpiece or other equipment. Instead, the height of the inductor unit 100 increases, allowing more space to be utilized. The expansion of the surface can be explained as being achieved by bending or wrinkling the generating side 121a of the conductive element shown in FIGS. 3a - b. 【0076】 The coil unit 110 is wound around the recess provided in the conductive element 120. In FIG. 3c, two coils are used. Further, in this figure, the coil unit 110 is substantially square. In reality, the corners of the square may be more rounded. The coils may be connected in series or in parallel according to the desired inductance and / or impedance matching and setting. Inside the coil unit 110, a square piece is formed, which is shown as one piece of the soft magnetic element 130 consisting of a plurality of small pieces. The large flat side surface of the conductive element 120 is covered with a soft magnetic material to induce magnetic flux around the active side of the inductor unit 100. When the active side 120b of the soft magnetic element 120 converges to a small tip, the output density becomes very high and it can function, for example, like a spot welder useful for preforming carbon fiber fabrics. 【0077】 Figure 3d is a cross-sectional view of the inductor unit 100 of Figure 3c. Here, an enlarged view of the surface of the generation side 120a with respect to the inductor unit of Figures 3a - b is shown. The generation side 120a in Figure 3c may be interpreted as being defined by two U-shaped recesses or sides in the conductive element 120. Together, the U-shaped generation side 120a contributes to a relatively long cross-sectional surface area, or cross-sectional width as described above, compared to that of the active side 120b. The generation side 120a can also be described as the internal surface area of the conductive element 120, which is larger than the cross-sectional area of the active side 120b of the same conductive element 120. As is clear from Figure 3c, the current moves from the generation side 120a through the transmission side 120c without a soft magnetic element to the active side 120b. 【0078】 An advantage of the technology described herein is the flexibility and opportunity to adapt the heating pattern etc. to achieve a desired heating profile. This can be done by changing the conductive element 120, for example, by narrowing the cross-sectional area at a specific location, i.e., the active side 120b, 220b, or by locally removing the material between the conductive element 120 and the workpiece to increase the distance to that workpiece, thereby contributing to heat generation. 【0079】 When the conductive material 120 is further away from the workpiece to be heated, a non-conductive material may be added to the interface between the conductive material and the workpiece for mechanical support and also to cool the surface of the workpiece. The interface material can typically be a polymer, ceramic, or composite material and may have any kind of heat conduction properties. Another option for changing the heating pattern is to provide mechanical pockets in the active side 120b of the conductive element 120, where materials such as soft magnetic materials can be added for the purpose of inducing current paths and thereby controlling the heating pattern. Alternatively, materials with completely different thermal properties may be beneficial in changing the thermal load on the workpiece. These types of actions are shown in Figure 3e. 【0080】 The supports or fixtures for the workpiece on the opposite side of the inductor units 100, 200 may also affect the heating pattern due to the heat load and material selection. Non-magnetic and non-conductive fixtures do not affect the electromagnetic field from the inductor, but conductive materials induce reverse currents, reducing efficiency and heating depth, i.e., pushing the heating towards the surface closest to the inductor units 100, 200. They may also be used to reduce the edge effect or the heating of unwanted areas. Soft magnetic materials in the fixture can be used not only to control the heating pattern but also to increase the depth of heating, i.e., to move the heat generation away from the inductor units 100, 200, which is useful, for example, in welding thick workpieces. 【0081】 When space constraints are in the height direction, according to FIGS. 3f to 3g, it is possible to bend the generating side 120a of the inductor away from the welding seam area. In this particular case, a slit, also called the end 140, is added to the conductive element, and current is forced to flow from the generating side 120a to the active side 120b through the transmission surface 120c, which is the wall of the slit 140, and in this case, it is perpendicular to the active side 120b of the conductive element 120 to form a closed current loop. In FIG. 3f, the conductive element 120 is substantially L-shaped. It should be noted that the geometric shape of the inductor unit 100 can have a complex shape, although it is illustrated with a geometric shape having straight sides and a perpendicular angle. The soft magnetic element 130 may be composed of a single piece or multiple pieces. In FIG. 3g, for manufacturability purposes, it is three pieces. Also, from a performance perspective, it may be beneficial to divide the soft magnetic element into several pieces and introduce small gaps between different parts of the soft magnetic element 130 to distribute the magnetic flux more uniformly within the material, thereby reducing the risk of losses and electromagnetic saturation. Saturation is a phenomenon in which the material becomes non-magnetic when the magnetic flux density reaches a magnetic flux density that is too high. This limit varies with different materials and temperatures. 【0082】 By completely encapsulating the coil unit 110 in the conductive element 120, the efficiency is improved and the parasitic inductance of the circuit is reduced. In this case, the inductor unit 100 consists of two different coils, and these coils may be connected in parallel or in series in order to obtain the best results from the viewpoints of impedance matching, voltage, etc. 【0083】 Another version is sometimes called the upright version of the inductor unit and is shown in FIGS. 3h to 3j. In this case, the coil is encapsulated inside the conductive element. This embodiment is similar to the embodiment of FIGS. 3c to 3e, and a square coil unit including two coils surrounds a soft magnetic element that further extends to the active side 120b of the conductive element 120. The main difference is that the conductive element 120 extends to the generation side 120a so as to substantially surround the coil unit 110, similar to FIGS. 3f to 3g, has a small slit at the top, and the current flows from the generation side 120a through the transmission side 120c, which is substantially longer in this configuration than in the configuration of FIGS. 3c to 3e, and is forced to flow to the active side 120b, which is more similar to FIGS. 3f to 3g. It should be noted that the opening or slit may be made larger to create an embodiment between FIGS. 3c to 3e and FIGS. 3h to 3j. In the latter embodiment, for example, in a robot actuator or a press, a mechanical structure is also added to support and fix the inductor unit 100. 【0084】 In FIGS. 3i to 3j, yet another conductive part 122 is added together with two additional soft magnetic elements 130, and the new elements are arranged in a non-conductive structural support or tray 150. The added elements mean that the inductor can be adapted to the geometric shapes of different workpieces 20, 21, for example, different materials, lengths, widths, thicknesses, or curvatures, without changing the entire inductor unit. Typically, the configuration is sensitive to the above parameters, among others, and this solution creates a cost-effective way to handle this. For example, the notches, curvatures, etc. described in relation to the conductive element 120 of FIG. 3e may be implemented with the additional conductive element part 122. 【0085】 The tray 150 may be manufactured from a high thermal conductivity material or a low thermal conductivity material, such as a polymer, composite material, or ceramic material, depending on the desired heat load on the workpieces 20, 21. The added conductive element 122 should be in electrical contact with the other conductive element 121 or more reasonably insulated from each other, and the current in the first conductive element 121 induces a corresponding current in the second conductive element 122. The parts can be insulated by any ceramic or polymer material having sufficient dielectric properties, such as polyimide, aramid, or sintered aluminum oxide or aluminum nitride. Improving the thermal contact between the two different electrical conductive elements 121, 122 can be beneficial as it eliminates the need for cooling in the second electrical conductive element 122. The tray 150 also provides mechanical support outside the weld seam area and functions as a heat sink to prevent delamination if unwanted excessive heat occurs. The tray 150 is also adaptable to different inductor units and the size of the weld seam area. 【0086】 In FIGS. 3i - 3j, the two different conductive elements 121, 122 are joined to each other using flat surfaces, but it may be beneficial to expand the surface to reduce resistive losses, such as by bringing two comb shapes together or making male and female shapes of any geometric shape. It is preferable to have a certain gap between the two conductive elements 121, 122 because the proximity effect allows the current to be advantageously dispersed, minimizing the losses in the two parts. 【0087】 The principle of the inductor illustrated and described in FIGS. 3a to 3k is that a current is induced into the workpiece along a line or an open curve, and that current moves from one end to the other, often referred to as a longitudinal magnetic field inductor. As discussed previously, since all current loops need to be closed, the current in the workpiece needs to find a return path that is not substantially part of the welding area. In the case of smaller workpieces, this has been a problem causing edge effects or other undesirable heating. Since the area to be welded is thermally loaded or cooled by fixtures and the inductor unit, already a slight heat generation outside the welded or clamped area can cause problems with overheating and delamination. One solution to overcome this problem is to provide an easy return path for the current. 【0088】 In Figure 3k, the inductor unit includes a conductive return part 160. The return part 160 is preferably made of copper. Conductive electrodes 161, 162, which are electrically insulated from the conductive elements 120 of the inductor unit 100, are attached to each end of the inductor. The electrodes 161, 162 may be in contact with the surface of the workpiece, or more beneficially, they may be connected or clamped to the side surface of the workpiece either directly through their design or via spring-loaded electrodes that can ensure proper contact between, for example, the current feedback loop and the side surface of the workpiece. The short ends of the workpieces 20a, 20b and / or 21a, 21b are particularly well-suited for transmitting current from the workpiece to the electrodes as they allow the current to flow along the entire length of the weld without affecting the heating uniformity. Also, the short ends are typically cut, and the cut surfaces allow for good electrical contact to the different layers of carbon fiber, although in other areas, a thin layer of plastic from the manufacturing reduces the electrical connection. Also, the electrodes may be attached along the entire long edges of the workpieces 20c, 20d, 21c, 21d to reduce the edge effect by cooling the surface and strengthen the current path. The return path of the current is preferably a feature of the inductor unit but may also be part of the fixture. 【0089】 The conductive return part 160 provides a return path for the current with low electrical resistance and is itself a passive part of the setup as in Figure 3k. Alternatively, the conductive return part 160 may be part of the conductive elements 121, 122 having generation sides 121a, 122a, and a voltage is induced that forces at least a part of the return current to flow through the conductive return part 160 instead of the workpieces 20, 21. 【0090】 Another way to mitigate the problems associated with unwanted heating due to the return current path is to use the induced voltage within the workpiece to control the movement of the current. Similarly, since the current can be induced along a line or an open curve, the inductor unit may form a closed current loop by inducing both positive and negative current directions simultaneously at different positions. This type of inductor unit may be referred to as a transverse flux inductor. 【0091】 The inductor unit 100 of FIG. 3k includes a non-magnetic element 170 located at the ends of a conductive element (not shown). These ends may also be referred to as short sides. The purpose of the non-magnetic element 170 is to cool the surface of the workpiece closest to the inductor unit 100 during welding and, at the same time, apply pressure to the workpiece materials 20, 21. The non-magnetic element 170 may be conductive. Optionally, the non-magnetic element 170 is not conductive. In some cases, the non-magnetic element 170 is preferably electrically insulated from the conductive element 120 of the inductor unit 100 to prevent the occurrence of a short circuit between the conductive elements 120. Preferably, the non-magnetic element 170 has a thermal conductivity of 1 W / mK or more, such as 10 W / mK, or even more preferably 100 W / mK. This is to prevent the upper surface of the workpiece 21 facing the inductor 100 from melting unnecessarily during welding. 【0092】 A non-conductive structural support or tray 150 is also provided in the embodiment of FIG. 3k, which has the same purpose as described above in connection with FIGS. 3i - 3j. 【0093】 FIGS. 4a - e are perspective views of an inductor unit 200 according to another embodiment. In this embodiment, the inductor unit 200, which may also be referred to as a transverse flux inductor 200, may have a substantially square shape. 【0094】 Similar to the inductor unit 100 shown in FIGS. 3a and 3b, the inductor unit 200 in FIG. 4a has a generating side 200a and an active side 200b, and includes three main components (coil unit 210, conductive element 220, and soft magnetic element 230). 【0095】 The coil unit 210 is preferably a litz wire that enters the inductor unit 200 through the recess 227 of the conductive element 200. The coil unit 210 is wound around a trace or groove of the conductive element 200 in a direction centered on the central axis (not shown) of the inductor part 200. The trace of the conductive element 200 encloses the coil unit 210, which can also be called a wire, and forms a large cross-sectional area for the induced current on the generating side 220a of the conductive element, which minimizes losses and circuit inductance. The coil unit 210 may be completely enclosed within the conductive element, for example, by adding a lid to the open surface of the trace including the coil unit 210. Alternatively, the coil unit may be wound inside a drilled or machined hole or groove of the conductive element 220. 【0096】 The conductive element 220 may be integrally formed. Typically, the conductive element 220 is made of the same material, but may also be a combination of two or several materials. For example, the conductive element 220 may be a coated structure such as copper-coated aluminum. The conductive element 220 has a first side 220a corresponding to the generating side 200a of the inductor unit 200 and a second side 220b corresponding to the active side 200b of the inductor unit 200. In practice, it is the active side 200b of the inductor unit 200 that faces the workpieces 20, 21 during welding. As seen in FIG. 4a, the first surface 220a of the conductive element 220 has a larger cross-sectional area than the second surface 220b. In FIG. 4b, a stepped shape is shown between the first side 220a and the second side 220b of the conductive element 220. 【0097】 In particular, in all the illustrated embodiments, the second side 200b of the inductor unit 200 appears substantially flat and smooth. However, the surface of the active side 200b may have a certain degree of surface roughness or even a pattern. Further, the surface is not limited to being square. For example, the cross-section may vary across the active side and the corners may be smooth. Some of these are shown in FIG. 3e. 【0098】 On the side of the conductive element 220 shown as the opposite side of the recess 227 in FIG. 4a, corresponding ends or slits 240 are provided, forming two transmission sides 221c, 222c that extend between the generation side 200a and the active side 200b of the inductor unit 200 along a direction perpendicular to the active side 220b of the inductor unit 200. It should be noted that while still providing the same functionality, multiple slits may be provided to create more transmission sides 221c, 222c, 223c, etc. Some transmission sides may be convenient in some designs, as seen below in other embodiments. The slits may have any shape and direction, i.e., the transmission sides 221c, 222c are not limited to being straight or perpendicular to the active side 220b. 【0099】 For all embodiments described herein, the slit may also be defined as an end portion, short side, or gable of the inductor units 100, 200. The end portions 140, 240 are also part of the conductive elements 120, 220. The slits 140, 240 are preferably not covered by the soft magnetic materials 130, 230. In FIGS. 3a - 3b, the end portion 140 or gable may be regarded as a slit with an infinitely large radius extending longitudinally along the active side 100b of the inductor unit 100. Further, the end portions 140, 240 extend at least partially along the active sides 120b, 220b of at least one conductive element 120, 220, preferably between the production sides 120a, 220a and the active sides 120b, 220b of at least one conductive element 120, 220. The current induced by the coil units 110, 210 is preferably conducted through the end portions 140, 240 to the active sides 100b, 200b of at least one conductive element 120, 220 facing the workpiece to be welded. 【0100】 Referring again to FIG. 4a, through the slit 240, i.e., in the gap (end portion) between the transmission sides or between the components 221c and 222c, at least one coil unit 210 can be seen. The current flowing through the production side 220a of the conductive element 220 is forced to flow through the transmission sides 221c, 222c to the active side 220b and is returned to form a closed current loop. In particular, the total cross-sectional area of the production side 220a is substantially larger than the total cross-sectional area of the active side 220b of the conductive element 220. During use, the workpieces 20, 21 to be heated / welded will be placed under the active side 200b because the current (and thus the heat) concentrates in this region of the inductor unit 200. 【0101】 Furthermore, a first opening 225 and a second opening 226 are provided on the conductive element 220. The first and second openings 225, 226 may extend into the inductor device 200 and be integrated into the structure of the conductive element 220. The first and second openings 225, 226 may extend in the form of channels throughout the inductor unit 200. The first and second openings 225, 226 may also be referred to as cooling channels. The cooling channels are configured to receive a fluid medium such as a gas or a liquid medium. In particular, the need for cooling the inductor unit 100 of the present invention after use is reduced due to the high heating efficiency of the workpieces 20, 21 to be welded. Alternatively, the cooling channels 225, 226 may share space with the coil unit 220 within the inductor unit 200. 【0102】 The first and second openings 225, 226 are useful while cooling the conductive element 220, the coil unit 210, the soft magnetic material 230, and potentially the workpiece with a liquid or a gas. The openings 225, 226 may comprise joints or other connecting means for supplying a cooling fluid. There may be a plurality of cooling channels, and for manufacturing purposes, some openings 228 are required for channel perforation and can be sealed or plugged before use of the inductor unit 200. 【0103】 In the case of 3D printed conductive elements, not only the electrical design but also the thermal and mechanical designs can be optimized, and the cooling channels and support structures may have very complex shapes and cannot be manufactured using conventional manufacturing methods. However, the coil unit and the soft magnetic element must be adaptable to the inductor unit according to the description herein. 【0104】 Surrounded within the center of the conductive element 220, a soft magnetic element 230 is disposed. In the illustrated embodiment, the soft magnetic element 230 has a generally rectangular shape extending along the central axis of the inductor portion 200. 【0105】 The soft magnetic element 230 may be arranged along the entire boundary surface of the inductor unit 200 when current is not desired (see FIG. 4d). To prevent a short circuit through the slit 240 for the current in the conductive element 220, the soft magnetic element 230 may have a slit (not shown) or at least be electrically insulated from the conductive element 220 near the slit, depending on the type of soft magnetic material. The voltages at both ends of the slit depend on the size and geometry, operating frequency, current level, workpiece characteristics, etc. To prevent malfunction due to a short circuit, it is necessary to consider the width of the slit and the electrical insulation with respect to the voltages at both ends of the slit. Similarly, the electrical insulation between turns of the coil, or between different coils of the coil unit 210, and between the coil unit and the conductive element 220 must be sufficient. 【0106】 FIG. 4b shows the active side 200b of the inductor unit 200 of FIG. 4a. From FIG. 4b, it is clear that the slit 240 provided in the conductive element 220 extends between the generating side 200a and the active side 200b of the inductor unit 200. The transmission side 220c between the generating side 200a (facing downward in FIG. 4b) and the active side 200b (facing upward in FIG. 4b) of the inductor is shown as a stepped configuration. However, other transitions are possible. For example, the transition may be curved or have any other smooth shape. A smooth transition is preferable from the viewpoints of efficiency and heat, but a stepped configuration may be easier to manufacture. The soft magnetic element 230 shown in FIG. 4a can be seen on the active side 200b of the inductor unit of FIG. 4b. Therefore, it is clear that the soft magnetic element 230 penetrates the inductor unit 200 and provides a path through which the electromagnetic flux passes. 【0107】 In use, the current induced by the coil unit 210 within the conductive element 220 concentrates on the active side 200b of the inductor unit 200 via the slit 240, or rather via the transfer sides 221c, 222c of the slit shown in FIG. 4b. As is apparent from FIGS. 4a and 4b, the slit 240 extends into the inner region of the inductor unit 200 and around the inductor unit. The slit 240 forms two transfer sides 221c, 222c which may also be referred to as the slit 240 / end walls. The transfer sides are not covered by the soft magnetic element 230. Further, two pipe joints (not shown) may be provided in the regions corresponding to the openings 225, 226 in FIGS. 4a and 4b, for example, to facilitate connection of cooling air or cooling water as briefly described above. 【0108】 To better visualize the production parts 200a of the inductor unit 200 and the internal parts of the inductor unit 200 arranged in relation to the coil unit 210, a top view of the inductor unit 200 is shown in FIG. 4c. Here, the inductors in FIGS. 4a and 4b are shown from different viewpoints. A top view of the slit 240 provided in the conductive element 220 is shown. 【0109】 Referring to FIG. 4d, the active side 200b of the transverse inductor unit 200 is shown, where the soft magnetic element 230 is present not only inside the inductor unit 200 but also around the entire circumference of the inductor unit 200. For example, the soft magnetic element 230 may be a soft magnetic ferrite material or a powder core, or any other suitable material mentioned above. 【0110】 The embodiment of FIG. 4d is shown in cross section in FIG. 4e. Here, the slit 240 is oriented in a direction opposite to that in the case of FIG. 4d. As shown in FIG. 4e, the coil unit 210 is disposed in a groove, trace, or space of the conductive element 220. Here, the conductive element 220 is formed in a single piece. Optionally, it may be an assembly of two or more parts. The two openings 225, 226 described previously in connection with FIGS. 4a and 4b extend in a direction corresponding to the shape of the conductive element 220 around the central axis (not shown) of the inductor unit 200. Briefly stated, the two openings 225, 226 are configured to transfer a cooling medium to maintain a steady temperature throughout the inductor unit 200. 【0111】 The inductor unit 200 functions as follows. The coil unit 210 induces a current in the generation side 220a of the conductive element 220. When the induced current reaches the slit 240, since the other surfaces of the inductor unit 200 are covered by the soft magnetic element 230, it is forced to pass through the transfer sides 221c, 222c and reach the active side 220b, forming an adjacent current loop. The soft magnetic material forms a soft magnetic element having a deformed form of what is usually called a pot core, a central leg, a bottom, and a peripheral portion. The soft magnetic element 230 flows around the entire coil unit 210 and the conductive element 220, forming a path for the electromagnetic flux that induces a current in the workpieces 20, 21. 【0112】 On the active side 200b of the inductor unit 200 corresponding to the second side 220b of the conductive element 220, the current density is substantially higher than that on the generation side 200a of the inductor unit 200. In other words, the current concentrates on the active side 200b of the inductor unit 200 due to the difference in surface area between the generation side and the active side of the conductive element 220. As described above, since the current (and thus heat) concentrates in this region of the inductor unit 200 during use, the workpieces 20, 21 to be heated will be disposed under this active side 220b. 【0113】 The soft magnetic element 230 may be a single piece or may include multiple parts. Both soft ferrites and powder cores are typically manufactured by pressing and are limited in size. Also, some soft magnetic materials are difficult to machine, which is another reason to construct the soft magnetic element 230 from multiple parts. Dividing the soft magnetic element into multiple pieces can also be a way to reduce losses and prevent magnetic saturation by reducing local concentration of the electromagnetic flux density. Utilizing materials with different properties, particularly relative permeability, is another way to control losses, prevent saturation, and optimize the heating pattern. 【0114】 As described above, in some designs, multiple slits can be beneficial. FIGS. 5a - c show an inductor unit 200 having two slits in the conductive element 220, thereby having four transmission sides and forming first and second conductive elements 221, 222. In contrast to FIG. 4a, this embodiment is constructed as two separate units in FIGS. 5a, b and then assembled as two mirror or rotational parts in FIG. 5c. Instead of having a coil unit 210 where the coil intersects the slit, in this case the coil is restricted to cover each section of the inductor unit 200. Specifically, it covers one of the multiple pieces of the conductive element 220. Different coils may then operate individually or together, continuously or simultaneously, at different frequencies or the same frequency. When the coils operate at the same frequency, the current may have a phase shift between 0 degrees and 360 degrees or may alternate, for example, between 0 degrees and 180 degrees. The coils may be connected alternately between different configurations, for example, in parallel, in series, or in inverse series, or using, for example, a mechanical switch, or a network of inductors and / or capacitors. 【0115】 By operating the coils within each conductive element with a phase shift defined as 180 degrees at the same frequency, currents in different directions are generated on the active sides 220b of the two different conductive elements 221 and 222, which has the advantage of avoiding an undesirable return path of the induced current within the workpiece associated with the transverse flux inductor. 【0116】 By setting the phase shift to zero degrees, corresponding to all currents on the active side 220b flowing in the same direction, longitudinal field operation is achieved, generating heat at the center of the inductor unit but with the risk of unwanted heating outside the welding area A. However, by alternating the phase shift during the welding operation, a uniform heating pattern in the weld seam area can be obtained, making it possible to limit or manage heat generation outside the weld seam area. By using different phase shifts, the heating pattern in the welding area can be distorted in either direction. Similar to the previously implemented transverse flux inductor shown in FIGS. 4d and 4e, the soft magnetic element 230 covers the sides and the center of the conductive element 220 and can be seen as being constructed by the two conductive elements 221 and 222, leaving only the active sides 221b, 222b, the generating sides 221a, 222a, and the transmission sides 221c, 222c uncovered. In longitudinal field operation, as shown in FIGS. 3a - 3k, there is little magnetic flux towards the center of the soft magnetic element, while in transverse flux operation, the maximum magnetic flux density is typically shown at the center of the soft magnetic element depending on the geometric shape. 【0117】 Another embodiment of the concepts described herein is shown in FIG. 6a, where the coil unit 210 is further encapsulated inside the conductive element 220, similar to FIGS. 3h-3j, to reduce the magnetic flux density within the soft magnetic element 230, lower the inductance, and increase the efficiency. Also, in FIGS. 6a-b, the current flows from the generation side 221a through the transmission side 221c to the active side 221b. To further enhance the flexibility regarding the adjustment of the heating pattern and improve the flexibility to accommodate different geometric shapes of the workpiece, three or more different coils and conductive elements may be used (see FIG. 6b). As described above, different types of operating modes or interactive modes, including different phase shifts between the currents in different coils, may be used to change, adjust, or move the heating pattern within the welding seam region A. 【0118】 As shown in FIG. 6b, the conductive element 220 can be divided into a plurality of dependent or independent parts 221, 222, 223, 224. The presence, amplitude frequency, and phase shift of the current can be controlled individually or collectively in each conductive element part 221, 222, 223, 224. In FIG. 6b, the conductive element parts 221, 222, 223, 224 are separated parallel to the main direction of the current. However, it should be understood that the current can be directed in any direction, as briefly shown in FIG. 3e, which illustrates the curved and smooth surface of the active side of the inductor unit. For example, a zigzag pattern of the conductive element 220 on the active side 220b (not shown) may be beneficial for a specific material layup of the CFRP workpiece. 【0119】 Figures 6c to 6e show the active side 220b of the inductor unit 200. In particular, FIG. 6c shows an embodiment in which the conductive element 220 is divided into eight independent parts 221 to 228. Optionally, the conductive element 220 may be divided into fewer or more parts than those shown and described in FIG. 6c, depending on the design of the coil unit 210. The conductive elements 221 to 228 are separated by the soft magnetic element 230 and / or the non-magnetic element 270. In this inductor design, the current direction can be selected in different ways. For example, refer to FIGS. 6d and 6e, which are indicated by arrows pointing in different directions for different current directions. 【0120】 In FIG. 6d, the current flows in opposite directions on each active side 220b of adjacent conductive element portions 221, 222, 223, etc. The induced current in the workpieces 20, 21 is forced to flow in small loops or figure-eight patterns, as indicated by the dotted lines in FIG. 6d. In this way, the temperature uniformity of a specific material layup of the CFRP workpiece can be improved. 【0121】 Alternatively, as shown in FIG. 6e, three inductor units 200 of the type described in FIGS. 6c to 6d are arranged side by side. In this configuration, in a specific region of the workpiece to be welded, different parts of this region can be heated at each time point. Alternatively, different frequencies may be used with each separate inductor unit 200 to heat the workpiece simultaneously. Optionally, the same frequency may be used to heat the workpiece simultaneously, but the phase shift of the current is different. For example, the region of the workpiece to be welded may be near the edge of the workpiece. 【0122】 The inductor configuration shown in FIG. 6e can be beneficial for both continuous or dynamic welding and static welding. For example, it can be beneficial for static welding where the length of the welding zone changes, or to overall improve the temperature uniformity of the welding zone. 【0123】 Figures 7a - 7b show further embodiments of the transverse flux inductor. The inductor unit 200 of Figures 7a - 7b shares similar features with the inductor unit 200 illustrated and described in relation to Figures 4 - 6. 【0124】 The coil unit 210 of Figure 7a is surrounded by a soft magnetic element 230 over a wider range than the conductive element 220. The advantage of this configuration is that the inductor unit 200 becomes more space - efficient. Similar to the inductor unit 200 of Figures 4 and 5, the coil unit 210 of Figure 7a is constructed by only one coil and represents a more compact version than Figures 6a - e. 【0125】 Similar to Figure 3k, the inductor unit 200 of Figure 7a includes a non - magnetic element 270 located at the ends of the conductive element. These ends can also be called short sides. The purpose of the non - magnetic element 270 is to cool the surface of the workpiece closest to the inductor unit 200 during welding and at the same time apply workpiece material pressure. The non - magnetic element 270 may be conductive. Optionally, the non - magnetic element 270 is non - conductive. In some cases, the non - magnetic element 270 is preferably electrically insulated from the conductive element 220 to prevent the occurrence of a short - circuit between the conductive elements 220 of the inductor unit 200. Preferably, the non - magnetic element 270 has a thermal conductivity of 1 W / mK or more, for example 10 W / mK, or even more preferably 100 W / mK. This is to prevent the upper surface of the workpiece facing the inductor 100 from melting unnecessarily during welding. 【0126】 The inductor unit 200 of Figures 7a - 7b also includes a fixture 250, which can also be called a non - conductive structure support. The purpose of the fixture 250 can be to prevent the inductor unit 200 from coming into contact with the workpiece to which it is welded. Other examples of the purpose of the fixture 250 are described above in relation to Figures 3i - 3j, which have similar features called the tray 150. 【0127】 FIG. 8 shows a system 1 in which the inductor units 100, 200 can be used. For example, the system 1 includes a moving means 40. The moving means 40 may be operatively coupled to both the processing means 30 and the inductor units 100, 200. The moving means 40 is configured to cause the movement of the inductor units 100, 200 based on the process information received and / or determined by the processing means 30. In other words, the processing means 30 is configured to control the movement of the inductor units 100, 200. Alternatively, the inductor units 100, 200 are stationary, and the moving means 40 is configured to move the workpieces 20, 21 relative to the inductor units 100, 200. 【0128】 The processing means 30 may be configured to control the pressure applied by controlling the pressure means 50. Typically, the pressure is applied in a direction substantially perpendicular to the welding seam region A of at least two workpieces 20, 21 to be welded. 【0129】 The moving means 40 is configured to move the inductor units 100, 200 while welding or between different welds with respect to the workpieces 20, 21 to be welded. The moving means 40 may communicate operatively with the processing means 30 and may communicate operatively with a drive unit 70 that causes the movement of the inductor units 100, 200. The drive unit 70 may be part of the moving means 40 or may be disposed outside the moving means 40. The drive unit 70 may be a motor such as an electric motor or a pneumatic actuator. Alternatively, the drive unit 70 may be a brushless DC electric motor. The brushless DC electric motor may be a stepping motor. The stepper motor divides a full rotation into several equal steps. The advantage of the stepper motor is that it is possible to move and hold at one of these steps without having a position sensor for feedback. The drive unit 70 may be any type of servo motor. 【0130】 The processing means 30 may command the drive unit 70 to move the inductor units 100 and 200 along a predetermined path. The drive unit 70 can be controlled wirelessly by the processing means 30, or can be controlled by wire or by an optical fiber. The drive unit 70 may be configured to follow a predetermined protocol stored in a memory associated with the processing means 30, and / or the drive unit 70 may be configured to follow commands given by the user of the processing means 30. The drive unit 70 may be arranged as part of the system 1 or as a separate external component that communicates operably with the system 1. 【0131】 Optionally, the moving means 40 may be part of the processing means 30 or may be arranged outside the processing means 30. The moving means 40 may include, for example, a track, a frame, a rod, or a similar configuration that enables precise control of the movement. The moving means 40 may further be a robotic arm, a parallel kinematic robot, or a gantry. The moving means 40 can move stepwise to control the welding process. The moving means 40 can also move continuously. The moving means 40 may be driven manually. For example, the moving means 40 may be arranged within a housing and may, for example, be arranged longitudinally (not shown) so as to be able to move along the housing to enable the movement of the inductor units 100 and 200. In one embodiment, the moving means 40 may include a telescopic arm that can be lengthened or shortened during welding to enable different positions of the inductor units 100 and 200. 【0132】 System 1 may further comprise cooling means 60 configured to cool system 1 during and / or after use. Cooling means 60 is configured to cool workpieces 20, 21 during and / or after reaching the processing temperature at which the welded portion is formed. The area to be cooled may include both the weld seam area A and the remaining portion of the workpiece due to unwanted heat generation, for example, along the edges or intersection toes of the laminate of workpieces 20, 21. Cooling may be controlled by processing means 30. For example, if the welding process is continuous, system 1 may comprise a roller or a cooling cylinder configured to cool the weld seam area A. This roller or cooling cylinder may then be arranged behind the inductor units when the inductor units 100, 200 move across workpieces 20, 21. Cooling may alternatively be derived from a liquid or gaseous fluid, for example, air. 【0133】 Alternatively, the inductor units 100, 200 may cool the newly welded area by heat conduction. Different from the conventional welding inductor design, the inductor units 100, 200 described herein may be composed of a solid block of a thermally conductive material, i.e., the conductive elements 120, 220, which may be designed to provide a uniform or desired heat load to the heating area corresponding to the welding seam area A in FIG. 1. The robust design also enables it to be clamped directly or indirectly to the workpiece to form good thermal contact. The inductor units 100, 200 may be characterized by other non-conductive thermally conductive materials designed to cool the workpiece in areas along the edges of the conductive elements 120, 220 or areas not intended to be heated. To achieve the desired heat load on the surface, a material with specific thermal conductivity or heat insulation can be introduced between the conductive element and the workpiece. These materials may be loosely arranged therein or may be part of the inductor units 100, 200. Since the conductive elements can be provided with cooling channels, their temperature can be controlled, for example, by the processing means 30. Similarly, the support structure of the workpiece on the opposite side of the inductor unit can also be designed to provide active or passive cooling of the workpiece. 【0134】 In another embodiment, the inductor may comprise vibration means (not shown) aimed at reducing the friction between the inductor units 100, 200 and the surface of the workpiece. More specifically, the inductor may include the mechanical part of the vibration means or may be operably communicable with the vibration means as a whole. Typically, at least the electronic means or the processing means of the vibration means are external and may be the same as or similar to the processing means of the inductor unit. The vibration means may be piezoelectric, magnetostrictive, mechanical or electromagnetic to facilitate continuous welding by the pressure from the inductor unit. 【0135】 For example, in the case of continuous welding, a densification force is always desired, but this force is generated from the inductor unit and prevents the inductor unit from moving. By means of vibrations with a small amplitude, friction is reduced and the inductor unit can move despite the high pressing force. The vibration means can be constituted by a mechanical vibration unit such as an electrodynamic unbalanced rotating mass, or a piezoelectric actuator or a magnetostrictive actuator. The vibration means is typically driven by a power electronic drive unit that supplies, for example, a controllable DC or AC voltage or current. Specific heat generation may also result from the vibrations. 【0136】 One possible way to do this, either to clamp the workpiece or to apply a densification pressure to the workpiece, is to make the active parts 120b, 220b of the conductive elements 120, 220 thin enough to expand when pressurized. By utilizing the membrane effect, even if the surface is non-uniform, the pressure distribution in the welding area can be made uniform. The membrane effect can be defined as a flexible deformable part or surface that is constrained along the outer boundary and applies a force to the surface. For example, a pressurized balloon pressed against the surface can deform and, under certain circumstances, apply a moderately uniform pressure over a specific surface area even if the surface does not conform to the original shape of the balloon. As another example, an inflatable and expandable bladder, similar to the inner tube of a tire, is generally used to compress composite materials. This can be interpreted as a mechanical clamp for maintaining the densification pressure during welding. 【0137】 Alternatively, the tray 150, also referred to as a non-conductive support, may be constructed of a material that can expand as a membrane, typically a polymeric material. The expansion of such a membrane is preferably effected by pressurization achieved by a gas of a liquid such as air or water, independently of whether it is part of the conductive element 120 or the tray 150. Typical pressures range from less than 1 bar to a few tenths of a bar or up to a few bars. When the pressure is high, a support is required to prevent the extrusion of the molten material during the welding process. 【0138】 Another advantage of the proposed inductor concept is the opportunity to construct an openable inductor unit for round objects. For example, for pipe joints, it can be advantageous to have an inductor unit that surrounds the diameter of the pipe to be welded and yet can be easily removed after welding. By using a conductive element that includes two or more parts, this can be achieved without cutting the coil unit, for example, using the inductor variations shown in FIGS. 3f - 3g. 【0139】 FIG. 9 shows a method 300 for induction welding at least two workpieces 20, 21 using the system 1 described above. This method begins with a step 310 of preparing inductor units 100, 200 and a step 315 of positioning it in relation to at least one of the workpieces 20, 21 to be welded. Processing means 30 are also provided 320. An alternating voltage V is applied to the inductor units 100, 200 by the processing means 30 330, whereby a current is induced in the conductive elements 120, 220 of the inductor units 100, 200 via the coil units 110, 210. The current in the conductive element further induces a current in the workpieces 20, 21 that are at least partially susceptible to influence. The aim is to induction heat at least two workpieces 20, 21 to form a weld seam in the weld seam region A between the two workpieces 20, 21 (see FIG. 1). The alternating voltage V is an input signal to the inductor units 100, 200 and is applied via the processing means 30. However, this method is not limited to applying only the input voltage to the inductor. Other electromagnetic signals such as current I or frequency F can equally be applied. 【0140】 More specifically, the induction welding method is performed as follows. First, the inductor units 100, 200 according to any of the above-described embodiments are provided 310. The inductor units 100, 200 are arranged in relation to at least one workpiece 20, 21 315. Next, processing means 30 is provided 320 to control the overall function of the process and the movement of the inductors 100, 200 relative to the workpieces 20, 21 to be welded. The inductor units 100, 200 may be positioned by a moving means 40 such as a robot arm. The robot arm may be controlled by the processing means 30 as described above. Before starting the heating process, a step 325 of applying a consolidation pressure to at least one workpiece may be provided. 【0141】 For example, by applying an alternating voltage to the inductor units 100, 200 330, an electromagnetic field is generated, inducing a current in the conductive elements 120, 220 of the inductor units 100, 200. The current in the conductive elements 120, 220 further induces a current in the weld seam region A, thereby generating an electromagnetic field that heats the workpieces 20, 21, and after reaching the process temperature, a weld seam is generated in the weld seam region A. 【0142】 Optionally, a step 340 of providing a moving means 40 configured to move the inductor units 100, 200 and a step 350 of providing a cooling means 60 configured to cool the inductor units 100, 200 after the welding process is completed are provided. 【0143】 The processing means 30 generates current in the coil units 110, 210. This current preferably generates a magnetic field that induces currents in opposite directions within the conductive elements 120, 220 made of copper and / or aluminum or their alloys, thereby counteracting the electromagnetic field and reducing the magnetic flux density of the circuit. As described above, the soft magnetic elements 130, 230 are provided around the conductive elements 120, 220 to induce the resulting electromagnetic flux into the workpieces 20, 21 and cause the currents in the conductive elements 120, 220 to flow on the desired surfaces, thereby improving efficiency and inducing the desired heating pattern. Since the soft magnetic elements 130, 230 have a high electrical resistivity and low magnetic hysteresis losses, the heat generation amount of the inductor devices 100, 200 is small. Therefore, in most settings, the heating efficiency is improved by providing the soft magnetic elements 130, 230 around the conductive elements 120, 220. 【0144】 As a result of the different inductor units shown in FIGS. 3 to 6, the currents induced in the conductive elements 120, 220 are led from the generation sides 100a, 200a of the inductor units 100, 200 to the active sides 100b, 200b located close to the workpieces 20, 21 to be welded. 【0145】 In other words, by combining the elements of the inductor units 100, 200 as described above, the current initially supplied to the coil units 110, 210 is quite small, so that the workpieces 20, 21 in the welding seam region A can be intensively and highly efficiently heated. 【0146】 When the welding process is completed, the inductor units 100, 200 are transferred away from the welding zone, also referred to as the welding seam region A, via the moving means 40. Cooling is achieved fairly easily due to the characteristics of the inductor design. More specifically, the copper or aluminum (or the like) used as the conductive elements 120, 220 contributes to fairly rapid and controlled cooling. Also, the setup support or fixing device located on the side opposite to the inductor unit 100 also contributes to the cooling of the workpiece. The cooling means described herein also prevents remelting of the outer surface of the workpiece. 【0147】 In particular, the welding method may be performed by a continuous process or by a stepwise static process. Optionally, a loading force is applied to the generating sides 100a, 200a of the inductors facing away from the workpieces 20, 21 before an electromagnetic field is applied through the processing means 30. Further, as long as current concentration can be achieved, the bottom of the inductor unit facing the workpiece may have different cross-sections. The cross-section may be, for example, patterned and / or may have a cross-section that varies across the entire bottom surface. For example, the surface may be rounded. The force transmission from the inductor units 100, 200 to the workpieces 20, 21 may be direct from the conductive elements 120, 220 or may be indirect via an electrically and / or thermally insulating material. Alternatively, a consolidation force can be applied from the opposite side of the workpiece while the inductor unit is fixed to provide mechanical support. As described above, also, for example, a force may be applied from a vacuum bag covering the workpiece, or other mechanical support, that does not act on the inductor unit. The vacuum film, which is part of the inductor unit, is another alternative means of achieving a clamping force and is particularly useful for welding small workpieces or attaching small workpieces to relatively large workpieces. In the case of relatively thick workpieces such as 10 mm or more, it may be beneficial to arrange one inductor unit 100, 200 on each side of the workpiece to facilitate heat generation up to the welding seam region A. 【0148】 In all embodiments of the present invention where an air gap exists in the inductor design, the isolation of the air gap may be required to avoid short circuits. 【0149】 In particular, the soft magnetic element is arranged and configured to concentrate the current induced in the conductive material and to direct the current in a predetermined direction across the inductor unit. In this way, when the inductor units 100, 200 heat the workpiece during use, small self-generated losses occur.

Claims

[Claim 1] An inductor unit for controlled induction welding of at least one fiber-reinforced thermoplastic composite workpiece (20, 21), At least one coil unit (110, 210) and At least one conductive element (120, 220) having a generating side (120a, 220a) and an active side (120b, 220b), wherein the active side (120b, 220b) is configured to face the at least one workpiece (20, 21) to be welded, and the active side (120b, 220b) of the conductive element (120, 220) has a smaller cross-sectional area than the generating side (120a, 220a), At least one soft magnetic element (130, 230) and Equipped with, The at least one coil unit (110, 210) is configured to induce current in the conductive elements (120, 220), An inductor unit in which the at least one soft magnetic element (130, 230) is at least partially arranged on the at least one conductive element (120, 220) such that the induced current is directed from the generating side (120a, 220a) of the conductive element (120, 220) to the active side (120b, 220b) and concentrated therein. [Claim 2] The inductor unit according to claim 1, wherein the conductive elements (120, 220) further comprises ends (140, 240) that at least partially extend between the generating side (120a, 220a) and the active side (120b, 220b) of the at least one conductive element (120, 220), and the induced current is led from the generating side (120a, 220a) to the active side (100b, 200b) of the at least one conductive element (120, 220) via the ends (140, 240). [Claim 3] The inductor unit according to claim 1, wherein the coil unit (110, 210) comprises at least one coil forming at least two turns, the turns being at least partially wound around the generating side (120a, 220a) of the conductive element (120, 220) and / or the at least one soft magnetic element (130, 230). [Claim 4] The inductor unit according to claim 1, wherein the at least one soft magnetic element (130, 230) has a relative permeability of 10 or more, and preferably a high bulk electrical resistivity of 0.01 Ω·m or more. [Claim 5] The inductor unit according to claim 1, wherein the at least one soft magnetic element (130, 230) is at least partially disposed on the interface of the inductor unit (100, 200). [Claim 6] The inductor unit according to claim 1, wherein the inductor units (100, 200) are operably communicating with processing means (30) configured to generate current in the coil units (110, 210). [Claim 7] The inductor unit according to claim 1, wherein the coil unit (110, 210) comprises at least one Litz wire. [Claim 8] The inductor unit according to claim 1, wherein the conductive elements (120, 220) include copper or aluminum. [Claim 9] The inductor unit according to claim 1, wherein the soft magnetic elements (130, 230) include amorphous and semicrystalline alloys and are selected from the group consisting of soft magnetic ferrite and / or powder-based cores, individually insulated soft magnetic wires, strips, or bundles or stacks of laminates of soft magnetic composite materials. [Claim 10] The inductor unit according to claim 1, further comprising an electrical and / or thermal insulator between the conductive elements (120, 220) and the at least one workpiece (20, 21) to be welded. [Claim 11] The inductor unit according to claim 1, further comprising a cooling channel for a fluid medium. [Claim 12] The inductor unit according to claim 1, wherein at least a portion of the conductive elements (120, 220) is replaceable. [Claim 13] The inductor unit according to claim 1, wherein the conductive elements (120, 220, 160) come into contact with the at least one workpiece (20, 21) during welding and form a closed current loop for current to flow from one region of the at least one workpiece (20, 21) to another region. [Claim 14] The inductor unit (100, 200) is deformable, as described in claim 1. [Claim 15] The inductor unit according to claim 1, further comprising a mechanical clamp for maintaining a compaction pressure during welding. [Claim 16] The inductor unit according to claim 1, further comprising a vibration means. [Claim 17] A system for induction welding at least one fiber-reinforced thermoplastic composite workpiece (20, 21), The inductor unit (100, 200) according to claim 1, At least one workpiece (20, 21) to be welded, Processing means (30) that communicates with the inductor units (100, 200) in an operable manner, A system equipped with these features. [Claim 18] A method for providing a system for induction welding at least one fiber-reinforced thermoplastic composite workpiece (20, 21), Step (310) of providing an inductor unit (100, 200) having the coil unit (110, 210) described in claim 1, The steps include providing at least one workpiece (20, 21) to be welded, Step (315) of arranging the inductor units (100, 200) in relation to the at least one workpiece (20, 21), The steps include providing a processing means (30) that communicates operably with the inductor units (100, 200), Methods that include...

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