Inductive welding of workpieces

Abstract

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

Description

Technical Field

[0001] The invention relates to an inductor unit for controlled induction welding of at least one fiber reinforced thermoplastic composite workpiece. The invention also relates to a system for induction welding and a method for providing such a system. Background Art

[0002] Over the past few years, there has been growing interest in the use of lightweight materials, for example in the automotive and aerospace industries, with the main goal of reducing carbon emissions during transportation. For example, it is increasingly common for vehicle or aircraft components to be made of fiber composites. The emerging switch from thermosetting resins to thermoplastic matrices allows the parts to be welded together, for example by induction welding.

[0003] There are a variety of systems available on the market for induction welding of this material. The disadvantages of these systems are that they typically use coils with single or few turns of copper tubing that require high current levels of about 300A to 1000A, significant cooling and low efficiency, or they use processed or 3D printed copper structures that have high losses and current levels. Other systems use Litz wire, which can be effective but is generally difficult to cool. The difficulty with induction welding is to achieve uniform temperature across the weld joint without local hot or cold spots and without remelting undesirable areas of the composite part, while applying a certain consolidation pressure to the heated area.

[0004] A disadvantage of prior art systems is that they require high current levels to provide adequate heating, resulting in high losses and low efficiency. Typically, this also means that a large and cumbersome work head consisting of a transformer, resonant capacitor and copper busbars needs to be positioned nearby, which is undesirable on the end effector of a robot arm. There are other similar inductor examples, such as those combined with rollers as described in EP2801472B1 or other means of applying consolidation pressure, because the inductor itself does not usually withstand pressure well. The challenge of these designs is also to achieve the desired heating pattern.

[0005] Therefore, there is a need for an improved induction welding apparatus that can be used to better control the welding of fiber reinforced plastics while improving weld quality and reducing energy used in the process. Summary of the invention

[0006] The object of the present invention is to solve or at least alleviate the problems associated with the prior art. This object is achieved by the technology set out in the attached independent claims; preferred embodiments are defined in the related dependent claims.

[0007] According to one aspect of the present invention, there is provided an inductor unit for controlled induction welding of at least one fiber reinforced thermoplastic composite workpiece. The inductor unit comprises: at least one coil unit; at least one conductive element having a generation side and an active side, wherein the active side is configured to face at least one workpiece to be welded, wherein the cross-sectional surface area of ​​the active side of the conductive element is smaller than the generation 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 arranged on the at least one conductive element so that the induced current is guided from the generation side of the conductive element to the active side and concentrated in the active side.

[0008] An advantage of the inductor unit is that the coil unit requires a relatively low current to achieve a high current density in the active side of the inductor unit facing the workpiece to be welded and thus a high power density in the workpiece.

[0009] Another advantage of the inductor unit is that it requires less cooling, thus reducing the need for external cooling systems.

[0010] A further advantage of the inductor unit is that it can be designed to precisely match the shape of the workpiece to be welded. This also applies to complex geometries of the workpieces. The inductor unit can withstand the consolidation pressure and be used to apply the consolidation pressure in the weld area, either as a rigid structure or with a certain flexibility to adapt to the part geometry of the workpiece to be welded. The inductor unit can be used for continuous welding as well as discrete welding including spot welding. A common requirement of induction welding equipment is the flexibility to handle different geometries in a fast and cost-effective manner. The proposed inductor design can be easily and automatically adapted to handle, for example, wide and narrow welds, flat and curved geometries, different weld lengths, etc.

[0011] Unlike copper tubes, there is complete freedom of geometry and therefore fewer constraints in design optimization. The conductive and soft magnetic elements also enable the current to be directed in an optimal way to achieve the desired temperature pattern. This allows for high power density, shorter cycle times and limited heat-affected zones compared to existing technologies.

[0012] Another advantage of the inductor unit is that it can be arranged in contact with or close to the workpieces to be welded. In this way, losses can be reduced and efficiency can be increased.

[0013] The inductor unit can ensure that heating is concentrated where it is desired, reduce undesired heating of areas outside the weld area, and cool the surface to prevent remelting of undesired areas. In addition, the material of the inductor unit can provide heat loading or cooling of the weld area (also referred to as the weld area), which is tailored by the design of the inductor unit to facilitate not only a specific temperature pattern, but also a temperature distribution, thereby enhancing material properties, such as matrix crystallinity.

[0014] Additionally, a high efficiency sensor unit may be used along with a processing device to predict the temperature in the solder joint.

[0015] According to another aspect, a system for induction welding of at least one fiber reinforced thermoplastic composite workpiece is provided, the system comprising an inductor unit according to the above.

[0016] According to another aspect, a method of providing a system for induction welding of at least one fiber reinforced thermoplastic composite workpiece according to above is provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

[0018] Figure 1 is a perspective view of a portion of an induction welding system according to an embodiment,

[0019] Figure 2 yes Figure 1 A schematic block diagram of a part of the system,

[0020] Figure 3a is a perspective view of a sensor unit according to an embodiment,

[0021] Figure 3b yes Figure 3a A cross-sectional view of an embodiment of

[0022] Figure 3c is a perspective view of a portion of a sensor unit according to another embodiment,

[0023] Figure 3d yes Figure 3c A cross-sectional view of an embodiment of

[0024] Figure 3e yes Figure 3c and Figure 3d A perspective view of a portion of a sensor unit,

[0025] Figure 3f is a perspective view of a portion of a sensor unit according to yet another embodiment,

[0026] Figure 3g yes Figure 3f A cross-sectional view of a sensor unit.

[0027] Figure 3h is a perspective view of a sensor unit according to another embodiment,

[0028] Figure 3i yes Figure 3h Another perspective view of the sensor unit,

[0029] Figure 3j yes Figure 3i A cross-sectional view of a sensor unit.

[0030] Figure 3k is a perspective view of a sensor unit according to an embodiment,

[0031] Figure 4a is a perspective view of a portion of a sensor unit according to another embodiment, from a generation side.

[0032] Figure 4b yes Figure 4a A perspective view of the active side of a portion of the inductor unit,

[0033] Figure 4c yes Figure 4a to Figure 4b A schematic top view of a sensor unit of

[0034] Figure 4d is based on Figure 4a to Figure 4b A perspective view of the active side of the sensor,

[0035] Figure 4e yes Figure 4d A cross-sectional view of an embodiment of

[0036] Figure 5a is a perspective view of half of a sensor unit according to yet another embodiment,

[0037] Figure 5b yes Figure 5a A perspective view of a portion of a sensor unit,

[0038] Figure 5c yes Figure 5a A cross-sectional view of a sensor unit that is twice as large as the sensor unit shown in FIG.

[0039] Figure 6a is a perspective view of a portion of a sensor unit according to another embodiment,

[0040] Figure 6b is based on Figure 6a A perspective view of a portion of another type of sensor unit according to the embodiment shown in FIG.

[0041] Figure 6c is a cross-sectional view of a sensor unit according to an embodiment,

[0042] Figure 6d is a cross-sectional view of a sensor unit according to another embodiment,

[0043] Figure 6e is a cross-sectional view of a sensor unit according to yet another embodiment,

[0044] Figure 7a is a perspective view of a sensor unit according to another embodiment,

[0045] Figure 7b yes Figure 7a A cross-sectional view of an embodiment of

[0046] Figure 8 is a schematic block diagram showing a system for induction welding, and

[0047] Fig. 9 is a schematic block diagram of a welding method according to an embodiment. DETAILED DESCRIPTION

[0048] Embodiments of the present invention will now be described with reference to the accompanying drawings. However, the present invention can be implemented in many different ways and should not be construed as being limited to the embodiments described herein; on the contrary, these embodiments are provided so that this disclosure will be exhaustive and complete, and will fully convey the scope of the present 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 accompanying drawings, the same reference numerals represent the same elements.

[0049] Figure 1 A part of a system 1 for induction welding according to the invention is illustrated, wherein the aim is to achieve a process temperature sufficient for welding at least one workpiece 20, 21 without overheating or underheating the material or workpiece to be welded. The induction power 2 is generated by an inductor unit 100, 200, which induces a current into at least one workpiece 20, 21.

[0050] Pressure is applied to at least one of the workpieces 20, 21 to ensure proper consolidation. The pressure may be applied to the workpieces by an inductor unit, or may be applied to the workpieces by other means such as a vacuum bag or external fixture.

[0051] Before turning to a detailed description of embodiments of the disclosed sensor units 100, 200, an exemplary environment in which the sensor units may be used will now be briefly described.

[0052] Reference Figure 1, two surfaces of two workpieces 20, 21 are to be welded to each other. The workpieces 20, 21 are configured to be induction welded in a weld area A. The weld area A is defined by a first portion 20' of the first workpiece 20, which is arranged on or adjacent to a second portion 21' of the second workpiece 21 and faces the second portion 21' of the second workpiece 21. The inductor unit 100, 200 is arranged to be combined with or close to at least one of the two workpieces 20, 21. In one embodiment, the two workpieces 20, 21 are arranged in direct contact with each other in combination with the inductor unit. In another embodiment, the two workpieces 20, 21 are arranged in non-direct contact with each other in combination with the inductor unit 100, 200. Therefore, at least one workpiece 20, 21 may be in direct contact with the inductor unit 100, 200 or in non-physical contact with each other. The distance between the inductor unit 100, 200 and the workpiece is preferably less than 5 mm to have good electromagnetic coupling, but for wide welding areas the distance may be as much as between 10 mm and 15 mm.

[0053] For example, a thermally conductive material or a thermally insulating material may be placed between the inductor unit 100, 200 and at least one workpiece to control heat transfer, thereby forming an indirect contact. In one embodiment, the inductor unit 100, 200 is a predetermined distance from the at least one workpiece 20, 21, and the consolidation 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 as much as 10 mm to 15 mm. For example, after heating is completed, the consolidation pressure is also maintained by mechanical clamping outside the weld area A.

[0054] The inductor unit 100, 200 induces an electric current in at least one of the workpieces 20, 21 that is susceptible to electromagnetic heating. Alternatively, there is an embedded susceptor in or near the workpiece, typically near the weld region A. The workpieces 20, 21 are inductively heated so that the material in the weld region A is melted or fused together when it reaches a predetermined melting or processing temperature corresponding to the material properties of the workpieces 20, 21. The time required for melting the workpieces 20, 21 at the weld region A is determined by the material properties and geometry of the respective workpieces.

[0055] exist Figure 1 In the embodiment shown in , the workpieces 20, 21 are rectangular in shape. However, as will be appreciated by those skilled in the art, the workpieces 20, 21 may have any shape. For example, the workpieces 20, 21 may be beams and skins of aircraft components. The workpieces 20, 21 may also be fixing elements to be attached to an automotive component, or two similar parts to be joined, for example, see Figure 3kThe workpieces to be welded can have complex geometries and their thickness can vary from sub-millimeter to several tenths of a millimeter.

[0056] The workpieces 20, 21 are considered as susceptors, which means that they have the ability to absorb electromagnetic energy and convert it into heat. Typically, the workpieces 20, 21 are carbon fiber composites, such as carbon fiber reinforced plastics (CFRP). The fiber reinforcement material can be any type of technical fiber, such as glass fiber, flax, aramid, PET, ultra-high molecular weight polyethylene (UHMWPE). The composite material can also be a hybrid fiber reinforcement material, including more than one fiber type, such as glass carbon fiber and carbon fiber. The fibers can be continuous or chopped, unidirectional, multiaxial or woven laminates or randomly oriented fibers. Different types of fibers and laminates have their unique advantages, such as stiffness, density, cost, appearance, environmental impact, dielectric properties, etc. The susceptor material can be any conductive or magnetic material, such as carbon fiber and any type of metal. For example, steel mesh is sometimes added to enable welding of non-conductive fiber composites, as will be clear from the following description.

[0057] The workpieces 20, 21 can be made of unidirectional laminates, for example, in which each layer is arranged at a different angle relative to the adjacent layers. As a non-limiting example, each workpiece can include, for example, 10 layers of carbon fibers embedded in a thermoplastic matrix. Alternatively, the workpieces 20, 21 are made of a woven mesh of carbon fibers, such as chopped or milled, ordered or randomly oriented carbon fibers. The matrix can be an amorphous or semi-crystalline thermoplastic material, such as polyethylene terephthalate (PET), polypropylene (PP), polyamide (PA), polycarbonate (PC) or a high-end type, such as polyphenylene sulfide (PPS), polyetherimide (PEI) or polyetheretherketone (PEEK), etc. Carbon fiber composites are generally classified as semiconductors and can be directly heated throughout the thickness of the material. Due to the thermoplastic matrix, the workpieces 20, 21 can be melted, and thereby a weld is formed in the weld area A common to the two workpieces 20, 21.

[0058] The workpieces 20, 21 can also be glass fiber composites. The fibers can also be any other technical textiles, such as flax fibers, aramid, ultra-high molecular weight polyethylene, etc. As a non-limiting example, glass fibers can be used as reinforcing agents in a matrix based on polypropylene. If the workpieces 20, 21 to be welded are glass fiber composites, it may be necessary to introduce an additional layer (not shown) in the joint between the two workpieces 20, 21. This is due to the lack of electrical conductivity and magnetic permeability of glass fibers. The additional layer placed in the joint can also be called a susceptor. The susceptor can be a woven mesh of metal or carbon fibers, for example. The mesh constituting the additional layer can also be non-woven. It is possible that the additional layer is something other than a mesh. For example, the additional layer can be randomly oriented carbon fibers applied to the surface of one or both of the workpieces 20, 21 to be welded.

[0059] It should be noted that the two workpieces 20, 21 may have different materials. Thus, the first workpiece 20 may have a first material and the second workpiece 21 may have a second material. In the above embodiment, one workpiece may be made of a glass fiber composite material and one workpiece is a susceptor. Composite materials may also be constructed with mixed fiber reinforcements, such as glass fibers and carbon fibers, typically with carbon fibers at least at or near the surface of the material. The workpieces may also be welded to thermoplastic parts or metal parts, such as fixing elements.

[0060] In the above examples, welding is described as welding of two surfaces of two separate workpieces. However, as will be appreciated by those skilled in the art, two surfaces of a single workpiece may also be welded together. In other words, the two workpieces may belong to the same component, for example in the case of closed cross-section components such as open tubes that are welded together along their length.

[0061] Workpieces 20, 21 may also include non-consolidated materials, such as fabrics based on co-blended or spun carbon and thermoplastic fibers, organic sheets, other types of semi-finished products or pre-consolidated carbon fiber thermoplastic prepregs, or workpieces 20, 21 may be technical fibers with thermoplastic or heat-activated binders. Typically, in these cases, welding is used to keep the layers in place during stacking before being placed in a mold and consolidated, sometimes referred to as preforming. In addition, it should be understood that in some cases, even three or more different workpieces or more surfaces of workpieces may be welded together. Other material combinations may be reinforcement materials welded to core materials, such as metal or carbon fiber plates welded to foamed PET materials, which are commonly used in lightweight structures to increase stiffness, which is commonly referred to as sandwich structures. In another example, thermoplastic composite panels may be welded to metal frames for quick attachment.

[0062] Back to Figure 1, applying pressure to the workpieces 20, 21 to ensure good contact between the two workpieces to be joined. The pressure can be applied by an external pressure device 50 (see Figure 8 ) or may be applied by inherent characteristics of the inductor design, such as by forces generated by geometric expansion, as will be understood in conjunction with Figures 3 to 6 below. Typically, the pressure device 50 can be applied from either side of the workpieces to be welded together, preferably by a fixture (not shown) located on the opposite side relative to the inductor unit 100, 200. Depending on the setup and application, the inductor unit, pressure device and fixture may be fixed or movable. The consolidation pressure may come from any type of force generation, such as spring loading, a pressure unit, a mechanical device or an expansion component or material. The consolidation pressure may alternatively come from a vacuum bag / membrane or the like that covers the workpiece with atmospheric pressure or high pressure. For example, an autoclave or a water bath may be used to apply the consolidation pressure and, in the presence of water or other fluid, the autoclave or water bath also provides cooling of the workpieces 20, 21.

[0063] exist Figure 2 In FIG. 1 , a schematic diagram of the sensor unit 100, 200 is shown. Figure 2 The description of Figure 2 Some reference numerals are not explicitly shown in the drawings. These features will become clear when read in conjunction with the remaining drawings. The inductor unit 100, 200 includes a coil unit 110, a conductive element 120, 220 and a soft magnetic element 130, 230. In addition, the inductor unit 100, 200 is preferably in operative communication with the processing device 30. The different parts will now be described in more detail.

[0064] The inductor unit 100, 200 has 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 a conductive element 120, 220 or form a part of the conductive element 120, 220. The generating side 100a, 200a of the inductor unit 100, 200 may correspond to the generating side 120a, 220a of the conductive element 120, 220. Correspondingly, the active side 100b, 200b of the inductor unit 100, 200 may correspond to the active side 120b, 220b of the conductive element 120, 200.

[0065] In the active side 100b, 200b of the inductor unit 100, 200, the conductive element 120, 220 preferably has a smaller cross-sectional surface area than in the generating side 100a, 200a of the inductor unit 100, 200. The cross-sectional surface area is related to the area through which the current passes.

[0066] The cross-sectional surface area can be defined by the width over which current can flow multiplied by the skin depth. Since the skin depth can be assumed to be the same everywhere on the conductive element (valid if the conductive element is made of the same material everywhere, such as copper), the skin depth is the same as the cross-sectional width of the surface over which current can flow. Therefore, the surface width of at least a portion of the active side 120b, 220b can be narrower than the generating side 120a, 220a. In other words, the cross-sectional surface area can also be referred to as the cross-sectional surface width.

[0067] The conductive element 120, 220 or at least a portion thereof may be replaceable. The conductive element 120, 220 may have a curved or bent shape on the generating side 100a, 200a, thereby increasing the cross-sectional surface area on the generating side 100a, 200a compared to the surface area on the active side 100b, 200b. Conversely, the conductive element 120, 220 may have a shape that narrows toward the active side 100b, 200b of the inductor unit to form a smaller current cross section and thereby produce a more concentrated electromagnetic flux density and power density. In addition, the conductive element 120, 220 may be deformable, such as by a pressurized medium. For example, if the conductive element 120, 220 is at least partially hollow and the wall thickness on the active side 120b, 220b of the conductive element 120, 220 is small, then in the case of expansion of the hollow volume, the conductive element 120, 220 will deform and thereby exert pressure on the workpiece. This actuation is achieved if the hollow volume is pressurized, for example by air or water.

[0068] As briefly mentioned, the conductive element 120, 220 has a generation side 120a, 220a and an active side 120b, 220b. The active side 120b, 220b is configured to face at least one workpiece 20, 21 to be welded and has a smaller cross-sectional surface area than the generation side 120a, 220a at least partially. If the active side 120b, 220b of the conductive element has a varying width, the maximum power density will be generated in the narrow section, and the current density is the highest. Taking the shape of an hourglass as an example, since the distance between the active side 120b, 220b of the conductive element and the workpiece 20, 21 is the same everywhere, the central part (where the current is concentrated) will be the hottest.

[0069] The cross-sectional surface area of ​​the active side 100b, 200b may be described as the area of ​​the inductor unit 100, 200 facing the workpiece to be welded, while the cross-sectional surface area of ​​the generating side 100a, 200a may be described as the area of ​​the inductor unit 100, 200 facing away from the workpiece to be welded.

[0070] The portion of the conductive element 120, 220 that connects the generating side 120a, 121a, 220a and the active side 120b, 121b, 220b together is referred to as the transmission portion 120c, 121c, 220c, 221c, 222c. In the following, the transmission portion is also referred to as the transmission side. The transmission side 120c, 121c, 220c, 221c, 222c can have almost any shape. In some inductor designs, the transmission side can be negligible in size. Preferably, the transmission side is not covered by the soft magnetic element 130, 230.

[0071] The coil unit 110 may include one or more coils, which together form at least two turns, preferably more turns. The turns may be wound at least partially 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 is preferably made of low-loss Litz wire. The Litz wire includes a plurality of individual strands. The strands are typically composed of thin insulated wires arranged together. In one embodiment, the strands are twisted together in parallel. In an alternative embodiment, the strands are twisted together as a single bundle. In yet another embodiment, multiple strands are twisted together.

[0072] Litz wire is used to reduce the skin effect. Skin effect is the term used for the phenomenon whereby high frequency current tends to flow near the surface (or skin) of an electrical conductor. This occurs due to the high frequency alternating current inducing a magnetic field in the conductor. The magnetic field makes it difficult for the current to flow anywhere except the surface. Since the current is forced to flow in only one portion of the wire, the effective resistance of the wire is greater. The higher the frequency, the greater the losses in the wire due to this increased effective resistance. The winding pattern of Litz wire equalizes the proportion of the total length of each strand at the outside of the conductor. This has the effect of evenly distributing the current between the wire strands, thereby reducing resistance. In the same way, Litz wire also reduces the proximity effect, which forces current to concentrate in certain areas of a conventional wire due to current in adjacent wires or conductors.

[0073] 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, among commonly used metals, copper has excellent thermal and electrical conductivity. The advantage of using aluminum is that, in addition to good electrical conductivity, it is easy to apply high-temperature resistant electrical insulation in the case of aluminum oxide by anodizing, thereby allowing the inductor to be in direct contact with the workpiece surface without direct electrical contact if desired. Due to the large difference in resistivity between different materials, electrical contact between the conductive elements 120, 220 and the workpieces 20, 21 may not be a problem from a functional point of view, but this may lead to undesirable arcing. Direct electrical contact between the conductive elements 120, 220 and the workpieces 20, 21 may also provide enhanced welding results, as described below with reference to Figure 3k The conductive element 120, 220 may include multiple parts, as will be described in more detail with reference to FIGS. 3 to 7. In addition, the inductor unit 100, 200 may further include an electrical insulator and / or a thermal insulator (not shown) located between the conductive element 120, 220 and the at least one workpiece 20, 21 to be welded.

[0074] As mentioned, the inductor unit 100, 200 also includes a soft magnetic element 130, 230. The soft magnetic element 130, 230 is made of any kind of soft magnetic material with a relative magnetic permeability greater than 10. The soft magnetic material should also preferably have a high volume resistivity, thousands or even millions of times that of the conductive element. The volume resistivity is defined as the overall resistivity in the direction in which the induced current can flow, rather than a property on a microscopic level. In soft magnetic materials, a volume resistivity of at least 0.01 ohm*m is preferred.

[0075] The soft magnetic material 130, 230, also referred to as a flux concentrating element, may be a composite material or ceramic preferably having low hysteresis losses. The soft magnetic material 130, 230 may be any of a soft magnetic ferrite and / or a powder-based core, a soft magnetic composite material consisting of a bundle or stack of individually insulated soft magnetic wires, strips or laminates, including amorphous and semi-crystalline alloys. Preferably, the soft magnetic element 130, 230 is at least partially arranged on the boundary surface of the inductor unit 100, 200. More specifically, the soft magnetic element 130, 230 is preferably at least partially arranged on the surface of the conductive element 120, 220. This is to enhance the magnetic flux and to prevent current from being conducted on the area of ​​the conductive element covered by the soft magnetic element. The soft magnetic element 130, 230 arranged on the conductive element 120, 220 preferably faces the environment rather than the workpiece. The boundary surface of the inductor unit may be described as the outer surface of the inductor unit facing the environment.

[0076] The purpose of arranging the soft magnetic element above the conductive element is to guide the current induced by the coil unit 110, 210 from the generating side 120a, 220a of the conductive element 120, 220 to the active side 120b, 220b and to concentrate the current in the active side 120b, 220b. In addition, the soft magnetic element 130, 230 is provided to enhance the magnetic flux and prevent the current from being conducted on the area of ​​the conductive element 120, 220 covered by the soft magnetic element 130, 230. The soft magnetic element 130, 230 can also be arranged in the inductor unit 100, 200, with the purpose of concentrating the magnetic flux in the desired area of ​​the inductor unit and enhancing the magnetic flux, as will be clear from the following description. In addition, the soft magnetic element 130, 230 is configured to concentrate the induced current in the active side 100b, 200b of the inductor unit 100, 200 to heat the predetermined weld area A in at least one workpiece 20, 21.

[0077] In one embodiment, the soft magnetic element 130, 230 is made of soft ferrite. In an alternative embodiment, the soft magnetic element 130, 230 includes a powder-based flux material core or other similar types of soft magnetic composite materials. In another embodiment, the soft magnetic element 130, 230 includes a laminated soft magnetic structure. In general, the soft magnetic element 130, 230 is configured to concentrate the electromagnetic flux and thereby help guide the current in the desired direction. The soft magnetic element 130, 230 can be regarded as a barrier, which helps to concentrate the current.

[0078] 3 to 7. Preferably, the soft magnetic element 130, 230 surrounds at least a portion of the conductive element 120, 220. The soft magnetic element 130, 230 is configured to act as a conductor for magnetic fields rather than current.

[0079] The soft magnetic element 130, 230 can promote the concentration of current in a predetermined portion of the inductor unit 100, 200 by providing a path for magnetic flux. The induced current in the conductive element 120, 220 of the inductor unit 100, 200 is enhanced due to the flux concentration, and in particular, the current in the active side 100b, 200b of the conductive element is enhanced. This principle can be explained as follows.

[0080] The induced current in the conductive element 120, 220 is intended to minimize the stored energy of the circuit, i.e. the inductance of the circuit. Therefore, the current tends to flow on the surface not covered by the soft magnetic material 130, 230, such as the transmission side 120c, 121c, 220c, 221c, 222c, and avoids the area covered or bounded by the soft magnetic material 130, 230. The direction of the induced current is defined by the coil unit 110, 210. According to the laws of physics, the current is also forced to form a closed current loop. When the conductive element 120, 220 is in contact with at least one workpiece 20, 21 during welding, this forms a closed current loop, causing the current to flow from one area of ​​the at least one workpiece 20, 21 to another area.

[0081] In some embodiments, the conductive element 120, 220 may be formed with a surface area that tapers in a direction configured to face the workpieces 20, 21 to be welded. Alternatively or additionally, the conductive element 120, 220 may have a recess, such as a slit, extending radially outward from the central axis of the inductor unit 100, 200 in a direction configured to face the workpieces 20, 21 to be welded. In either case or in an alternative configuration, the current induced in the inductor unit via the coil unit 110, 210 may be directed through the inductor unit 100, 200 in a direction toward the workpieces 20, 21 to be welded. According to the principles described above, the presence of the soft magnetic element 130, 230 enhances the formation of such current density.

[0082] As mentioned, refer to Figure 2 The inductor unit 100 , 200 is in operative communication with a processing device 30 , such as a frequency converter. The processing device 30 is configured to generate a high frequency current in the coil unit 110 , 210 . Figure 8 The system 1 including the sensor units 100 , 200 shown in FIG. 1 further includes a processing device 30 .

[0083] Preferably, the processing device 30 is a frequency converter or includes a frequency converter. The processing device 30 is configured to generate an electromagnetic field through the inductor units 100, 200 by applying alternating current to the inductor units 100, 200 to inductively heat the workpieces 20, 21 at the weld area A, thereby welding the workpieces 20, 20 together.

[0084] The processing device 30 may also include an interface (not shown) for transmitting the data obtained by the sensor. The interface may be of any suitable type, including simple wiring, serial interfaces (such as Ethernet, RS485, USB), wireless interfaces (such as Bluetooth or WiFi), etc. The processing device 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) with appropriate software and / or firmware, and / or dedicated hardware (such as an application-specific integrated circuit (ASIC)). The processing device may be connected to a computer-readable storage medium or include a computer-readable storage medium, such as a disk or memory. The memory may be implemented using any known technology for computer-readable memory, such as ROM, RAM, SRAM, DRAM, FLASH, DDR, SDRAM, or some other storage technology.

[0085] The processing device 30 may also include a display unit to provide process information to an operator or user. Figure 8 The processing device is further described.

[0086] An advantage of the inductor unit 100, 200 of the present invention, common to all embodiments, is that the inductor unit 100, 200 can be driven with a low current due to the multi-turn structure of the coil unit 110, 210. By combining the coil unit 110, 210, the conductive element 120, 220 and the soft magnetic material 130, 230 into one unit, a relatively high power density can be achieved at the portion of the workpiece to be inductively welded.

[0087] Compared to conventional coils and work heads, the inductor unit 100, 200 is a compact, lightweight unit that can be easily mounted as an end effector of any type of robot. It can also handle long and flexible wires between the processing device and the inductor unit 100, operates stably, has no substantial losses, and has no EMC interference.

[0088] As described above, the inductor unit 100, 200 is configured to be placed near the workpieces 20, 21 to be welded, and to sense and direct the heating current to specific locations on / around the workpieces 20, 21. Depending on the thermal design, material selection, and application, the inductor unit 100, 200 may be in direct or indirect contact with the workpieces 20, 21 to be welded. The inductor unit 100, 200 may include a thermally insulating material covering the active side of the conductive element, thereby preventing excessive heat transfer into the inductor unit 110, 200. With a particular fixture, the inductor unit 100, 200 does not necessarily need to be in contact with the workpiece, but can obtain consolidation pressure by other means, which is particularly useful in the case of continuous welding.

[0089] As will now be shown and discussed with reference to FIGS. 3 to 7 , the inductor units 100, 200 can be designed to have different shapes. Therefore, the inductor units 100, 200 can be adapted to different workpiece configurations and can selectively and specifically heat the workpieces to be welded. Non-exhaustive examples of inductor configurations are shown in the accompanying drawings. It should be noted that there are other embodiments that are not presented in the accompanying drawings.

[0090] In a single embodiment, the sensor unit 100, 200 can be moved in multiple directions as long as the sensor unit 100, 200 is close to at least one workpiece 20, 21. Preferably, the translational movement of the sensor is driven by a moving device (not shown). This will be combined with Figure 8 Further Discussion Depending on its design and use, the inductor unit 100, 200 can be applied to spot welding, static line welding, segmented static line welding, or continuous or dynamic welding along a programmed trajectory.

[0091] Reference Figure 3a , shows a sensor unit 100 according to a first embodiment. Figure 3aThe inductor unit 100 in the embodiment may also be referred to as a longitudinal flux type inductor 100. In this embodiment, the inductor unit 100 has a longitudinally extended shape. The inductor unit 100 has a generating side 100a and an active side 100b, and includes three main components: a coil unit 110, a conductive element 120, and a soft magnetic element 130. The schematic illustration of the inductor unit illustrates the inventive concept in a didactic manner and can serve as a reference for other embodiments described below.

[0092] like Figure 3a As shown, the coil unit 110 is preferably a litz wire wound into a coil multiple times. The coil unit 110 extends along the longitudinal length of the inductor unit 100 .

[0093] The conductive element 120 may be formed in one piece. Figure 3a , which is more easily described as having a first part 121, a second part 122 and a third part 123. In this case, the first part 121 corresponds to the part comprising the active side 100b of the inductor unit 100, while the other parts 122, 123 serve to reduce the inductance of the circuit. Combining these three parts together may allow for a more optimized design. Typically, the different parts of the conductive element 120 are of the same material, but a combination of copper and aluminum, for example, may also be possible. The first part 121 of the conductive element 120 has a generating 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, during welding, the active side 100b of the inductor unit 100 faces the workpieces 20, 21. As Figure 3a As shown, the generating side 121a of the first portion 121 of the conductive element 120 has a larger surface area than the active side 121b. The first portion 121 of the conductive element 120 tapers from the generating side 121a to the active side 121b via the transmitting side 121c. In this embodiment, the first portion 121 of the conductive element 120 tapers from the generating side 121a to the active side 121b in a direction perpendicular to the longitudinal extension of the inductor unit 100. Therefore, with the transmitting side 121c not covered by any soft magnetic material 130, the current flowing in the generating side 121a of the conductive element 120 will be forced to flow to the active side 121b to form a closed current loop. The transmitting side 121c can be regarded as Figure 3a The end portion or gable of the inductor unit 100.

[0094] The smaller the cross-sectional surface area of ​​the active side 100b, 121b, the higher the current density and thus the higher the power density. Through the transformer action and the minimum current leakage in the conductive element 120 due to the soft magnetic element 130, the total current through the cross section of the active side 121b is almost the size of the coil current multiplied by the number of turns in the coil unit.

[0095] In addition, the first portion 121 of the conductive element 120 has a first opening 125 and a second opening 126, which can be Figure 3a 121c of the inductor in FIG. 100. These openings 125, 126 are configured to extend within the first portion 121 of the conductive element 120 along most of the length of the inductor unit 100 to form a U-shaped channel. The first opening 125 and the second opening 126 can be used for cooling of the conductive element 120. The first opening 125 and the second opening 126 can also be referred to as cooling channels. The cooling channels are configured to receive a fluid medium such as a gas or liquid medium.

[0096] It is worth noting that due to the high efficiency of heating the workpieces 20, 21 to be welded, the cooling requirements of the inductor unit 100 of the present invention are reduced. However, cooling is beneficial for repeatability and continuous operation. Although effective, due to the heat transfer from the workpieces, certain losses will be generated in the coil unit 100, the soft magnetic element 130 and the conductive element 120.

[0097] exist Figure 3a In the embodiment, the second portion 122 of the optional conductive element 120 has a generally block-like shape and is arranged within the inner portion of the coil unit 110. Figure 3b Below the second portion 122 of the conductive element 120 , ie in the direction towards the active side 100 b of the inductor unit 100 , a soft magnetic element is arranged, which will be discussed further below. Optionally, the soft magnetic element is arranged above the second portion 122 .

[0098] The third portion 123 has a similar shape to the second portion 122 of the conductive element 120 and is arranged on a side of the coil unit 110 facing the generating side 100a of the inductor unit 100. The third portion 123 is optional and is configured to reduce the inductance of the circuit, but also simplifies the pressure exerted on the inductor unit 100 (and thereby also the workpiece 20, 21 to be heated) during use and facilitates cooling of the inductor unit 100.

[0099] The soft magnetic element 130 may be disposed on one or more portions of the inductor unit 100. Figure 3a, a first portion 131, a second portion 132, a third portion 133 and a fourth portion 134 are shown. These portions are substantially rectangular in shape. The soft magnetic portions 131, 132, 133, 134 are arranged on the respective side portions of the inductor unit 100. As previously mentioned, the soft magnetic element 130 is typically a soft ferrite or powder-based flux-cored wire that is configured to conduct a magnetic field but not conduct an electric current. Therefore, the soft magnetic element 130 can be considered as a barrier to electric current. The soft magnetic element portions 131, 132, 133, 134 are arranged along the side portions of the funnel-shaped / conical conductive element 120 to help concentrate the induced current in the active side 100b of the inductor unit 100. Optionally (not shown), the soft magnetic element 130 can also be arranged on the generating side 100a of the inductor. The preferred position and geometry of the soft magnetic element 130 relative to the conductive element 120 depends on the application, geometry, material selection and design. The soft magnetic material 130 is typically made into shapes with limited dimensions, and some soft magnetic materials are difficult to process, necessitating the use of several pieces rather than one large unit. In some settings, it may be beneficial to use a one-piece soft magnetic element, or to assemble different pieces 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 flux density concentrations.

[0100] exist Figure 3b Shows Figure 3a 1 is a cross-section of the inductor unit 100 extending in the longitudinal direction. Here, it is shown that the inductor is a layered structure. Below the second portion 122 of the conductive element 120, the fifth portion 135 and the sixth portion 136 of the soft magnetic element 130 are shown. The Litz wire 110 surrounds the second portion 122 of the conductive element 120 and the fifth portion 135 and the sixth portion 136 of the soft magnetic element, and is sandwiched between the first portion 121 and the third portion 123 of the conductive element 120.

[0101] for Figure 3a and Figure 3b In the inductor unit 100 shown in FIG. 1 , the induction current flowing through the inductor unit 100 is concentrated on the active side 100 b of the inductor unit, which also corresponds to the active side 121 b of the conductive element 121 described above.

[0102] because Figure 3a and Figure 3b, a concentration of a relatively small current entering the coil unit 110 can be achieved in the active side 100b of the inductor unit 100, which is configured to be arranged near the workpieces 20, 21 to be welded. When the induced current travels through the conductive element 120 (or a portion thereof), it is forced to flow downwardly toward the tapered portion of the longitudinally extending funnel-shaped first portion 121 of the conductive element 120, i.e., the current travels from the generating side 100a via the transmitting side 121c to the active side 100b of the inductor unit 100. In other words, the current is concentrated from a relatively wide surface area (i.e., a larger cross-sectional surface area) in the generating side 121a corresponding to the space directly below the coil unit 110 to a narrower surface area in the active side 121b of the conductive element 120 corresponding to the active side 100b of the inductor unit 100.

[0103] Figure 3c The diagram shows a portion of a sensor unit 100, which is also referred to as a longitudinal flux sensor, such as Figure 3a to Figure 3b Related sensors. Figure 3c In, with Figure 3a to Figure 3b In contrast, the generating side 120a of the conductive element 120 undergoes surface expansion to form a relatively large cross-sectional surface area for current flow without consuming space in the width direction that would otherwise interfere with the workpiece or other equipment. Instead, the height of the inductor unit 100 is increased, where more available space may exist. Surface expansion can be described as Figure 3a to Figure 3b The generating side 121a of the conductive element shown is achieved by bending or corrugating.

[0104] The coil unit 110 is wound in a recess provided in the conductive element 120. Figure 3c In the figure, two coils are used. In addition, in this figure, the coil unit 110 is basically square-shaped. In practice, the corners of the square may be more rounded. Depending on the preferred inductance and / or impedance matching and setting, the coils can be connected in series or in parallel. Inside the coil unit 110, a square-shaped piece is formed, showing a piece of soft magnetic element 130 composed of several smaller pieces. The large flat side of the conductive element 120 is covered with soft magnetic material, thereby guiding the magnetic flux around the active side of the inductor unit 100. If the active side 120b of the soft magnetic element 120 is concentrated to a small tip, it can have a very high power density and work like a spot welder, for example, it can be used for preforming of carbon fiber fabrics.

[0105] Figure 3d yes Figure 3c Here, the cross-sectional view of the sensor unit 100 is shown relative to Figure 3a to Figure 3b The surface of the generating side 120a of the inductor unit is enlarged. Figure 3cThe generating side 120a in the conductive element 120 can be interpreted as being defined by two U-shaped recesses or sides in the conductive element 120. The U-shaped generating sides 120a collectively contribute to a relatively longer cross-sectional surface area, or as described above, a relatively longer cross-sectional surface width, compared to the active side 120b. The generating side 120a can also be described as an inner surface area of ​​the conductive element 120 that is greater than the cross-sectional surface area of ​​the active side 120b of the same conductive element 120. As can be seen from Figure 3c It can be clearly seen in FIG. 1 that the current flows from the generating side 120 a to the active side 120 b via the transmitting side 120 c without the soft magnetic element.

[0106] The advantages of the techniques described herein are the flexibility and opportunity to adapt the heating pattern etc. to obtain the desired heating curve. This is achieved by modifying the conductive element 120, such as making it narrower at a certain location, i.e., at the cross-sectional surface area of ​​the active side 120b, 220b, or locally removing material between the conductive material 120 and the workpiece, so that the current increases its distance to the workpiece and thereby increases its contribution to the heating.

[0107] In the case where the conductive material 120 is further away from the workpiece to be heated, a non-conductive material may be added at the interface between the conductive material and the workpiece for reasons of mechanical support and in order to cool the surface of the workpiece. The interface material may typically be a polymer, ceramic or composite material and may have any type of thermal conductivity. Another option for changing the heating pattern is a machine pocket located in the active side 120b of the conductive element 120 where material (such as a soft magnetic material) may be added with the purpose of directing the current path and thereby controlling the heating pattern. Alternatively, materials with completely different thermal properties may be beneficial in changing the heat load on the workpiece. These types of actions are Figure 3e Shown in.

[0108] The support or fixation of the workpiece on the opposite side of the inductor unit 100, 200 may also affect the heating pattern due to thermal load and material selection. A non-magnetic and non-conductive fixation device will not affect the electromagnetic field from the inductor, while a conductive material will induce a current in the opposite direction, thereby reducing the efficiency and the depth of heating, i.e., pushing the heating to the surface closest to the inductor unit 100, 200. It can also be used to reduce edge effects or reduce heating in undesired areas. Soft magnetic materials in the fixation device can be used to control the heating pattern and increase the depth of heating, i.e., extend the heat generation to a greater distance from the inductor unit 100, 200, which is useful for example for welding thick workpieces.

[0109] according to Figure 3f to Figure 3gIf space is limited in the height direction, the generating side 120a of the inductor can be bent away from the weld area. In this particular case, a slit, also called an end portion 140, is added to the conductive element to force the current from the generating side 120a to the active side 120b through the transmission surface 120c to form a closed current loop. The transmission surface 120c in this case is the wall of the slit 140 perpendicular to the active side 120b of the conductive element 120. Figure 3f In FIG. 1 , the conductive element 120 is generally L-shaped. It should be noted that the geometry of the inductor unit 100 may have a complex shape, although the illustrated geometry has straight sides and perpendicular angles. The soft magnetic element 130 may be composed of a single piece or several pieces. Figure 3g In the example of FIG. 1 , it is constructed of three pieces for manufacturability purposes. Furthermore, from a performance point of view, it may be beneficial to divide the soft magnetic element into several pieces and even introduce smaller gaps between different parts of the soft magnetic element 130, which allows for a more uniform distribution of the magnetic flux in the material, thereby reducing losses and the risk of electromagnetic saturation. Saturation is the phenomenon that causes a material to become non-magnetic when the magnetic flux density reaches a too high magnetic flux density. This limit varies with different materials and temperatures.

[0110] By completely encapsulating the coil unit 110 in the conductive element 120, efficiency is improved and the stray inductance of the circuit is reduced. In this case, the inductor unit 100 includes two different coils, which can be connected in parallel or in series for the best results in terms of impedance matching, voltage, etc.

[0111] exist Figure 3h to Figure 3j Another form is shown in FIG. , which may be referred to as an upright form of the inductor unit, wherein the coil is encapsulated inside the conductive element. This embodiment is similar to Figure 3c to Figure 3e , having a square coil unit including two coils surrounding a soft magnetic element further extending to the active side 120b of the conductive element 120. The main difference is that the conductive element 120 extends on the generating side 120a to almost completely surround the coil unit 110, with a small slit at the top, similar to Figure 3f to Figure 3g As shown, the current is forced from the generating side 120a to the active side 120b via the transmitting side 120c. In this arrangement, the transmitting side is Figure 3c to Figure 3e The setup is much longer and more similar to Figure 3f to Figure 3g It should be noted that the opening or slit can be larger, thereby forming Figure 3c to Figure 3e and Figure 3h to Figure 3j In the latter embodiment, a mechanical structure is further added in order to support and fix the inductor unit 100 in, for example, a robot actuator or a press.

[0112] exist Figure 3i to Figure 3j In the embodiment of the invention, a further conductive component 122 and two further soft magnetic elements 130 are added, wherein the new elements are positioned in a non-conductive structural support or tray 150. The added elements mean that the inductor can be adapted to different workpiece 20, 21 geometries, such as different materials, lengths, widths, thicknesses or curvatures, without changing the entire inductor unit. Typically, these settings are sensitive to the above parameters and others, and this solution creates a cost-effective way of dealing with them. For example, with regard to Figure 3e The cuts, curvatures, etc. described for the conductive element 120 in FIG. 1 may be performed in the added conductive element portion 122 .

[0113] Depending on the expected heat load on the workpieces 20, 21, the tray 150 can be made of a high thermal conductivity material or a low thermal conductivity material, such as a polymer, composite material or ceramic material. The added conductive element 122 should either be in electrical contact with the other conductive element 121, or more appropriately insulated from each other, wherein a current in a first conductive element 121 induces a corresponding current in a second conductive element 122. The component can be insulated by any ceramic or polymer material with sufficient dielectric properties, such as polyimide, aramid or sintered aluminum oxide or aluminum nitride. It may be beneficial to have good thermal contact between the two different conductive elements 121, 122 to eliminate the need to cool the second conductive element 122. The tray 150 also provides mechanical support outside the weld area, acting as a heat sink and preventing delamination in the event of excessive undesirable heat generation. The tray 150 is also adaptable to different sensor units and the size of the weld area.

[0114] exist Figure 3i to Figure 3j In the embodiment, two different conductive elements 121, 122 are mated to each other using flat surfaces, but it may be beneficial to increase the surface enlargement to reduce the resistive losses, such as two combs mating together, or male and female pieces with any geometric shape mating together. A constant gap between the two conductive elements 121, 122 is preferred because the proximity effect will distribute the current in a favorable way to minimize the losses in the two parts.

[0115] exist Figures 3a to 3kThe principle of the inductor shown and described in the drawings is to induce current in the workpiece along a straight line or open curve, where the current travels from one end to the other end. Such inductors are generally called longitudinal magnetic field inductors. As mentioned earlier, all current loops must be closed, so the current in the workpiece needs to find a return path that is not substantially part of the weld area. This is a challenge for smaller workpieces because this will cause edge effects or other undesirable heating. Since the area to be welded is subjected to thermal loading or cooling by the fixture and inductor unit, the small amount of heat generated outside the weld or clamping area may cause overheating and delamination problems. One solution to overcome this problem is to provide an easy return path for the current.

[0116] exist Figure 3k In the embodiment of the present invention, the inductor unit is provided with a conductive return portion 160. The return portion 160 is preferably made of copper. At each end of the inductor, a conductive electrode 161, 162 is mounted which is electrically insulated from the conductive element 120 of the inductor unit 100. The electrodes 161, 162 can be in contact with the surface of the workpiece, or more advantageously, the electrodes 161, 162 are connected or clamped to the side of the workpiece directly by their design or via assembly components (e.g. spring-loaded electrodes), which can ensure proper contact between the feedback loop of the current and the side of the workpiece. The shorter ends 20a, 20b and / or 21a, 21b of the workpiece are particularly suitable for transferring current from the workpiece to the electrodes, because this allows the current to flow along the entire welding length without affecting the uniformity of heating. In addition, the shorter ends are usually cut, and the cut surfaces allow good electrical contact with the carbon fibers of the different layers, while in other areas, the thin layer of plastic left by the manufacturing weakens the electrical connection. The electrodes may also be attached along the entire long edge 20c, 20d, 21c, 21d of the workpiece to reduce edge effects and enhance the path for the current by cooling the surface.The return path for the current is preferably a feature of the inductor unit, but may also be part of the fixture.

[0117] The conductive return portion 160 provides a low resistance return path for the current and is itself a passive part of the device. Figure 3k Alternatively, the conductive return portion 160 may be a portion of a conductive element 121 , 122 having a generating side 121 a , 122 a in which a voltage is induced that forces at least part of the return current to flow in the conductive return portion 160 rather than in the workpieces 20 , 21 .

[0118] Another way to mitigate the challenge of undesired heating due to return current paths is to use the induced voltage in the workpiece to control the travel of the current. In the same way as inducing current along a straight line or open curve, an inductor unit can form a closed current loop by simultaneously inducing positive and negative current directions at different locations. This type of inductor unit can be referred to as a transverse flux type inductor.

[0119] Figure 3k The inductor unit 100 includes a non-magnetic element 170 located at the end portions of the conductive element (not shown). These end portions may also be referred to as short sides. The purpose of the non-magnetic element 170 is to cool the workpiece surface closest to the inductor unit 100 during welding and to apply pressure to the workpiece materials 20, 21 at the same time. The non-magnetic element 170 may be conductive. Optionally, the non-magnetic element 170 is non-conductive. In one case, the non-magnetic element 170 is preferably electrically insulated from the conductive element 120 to prevent short circuits between the conductive elements 120 of the inductor unit 100. Preferably, the non-magnetic element 170 has a thermal conductivity of 1 W / mK or higher, such as 10 W / mK or even more preferably 100 W / mK. This is to prevent the top surface of the workpiece 21 facing the inductor 100 from undesirably melting during welding.

[0120] exist Figure 3k In the embodiment, a non-conductive structural support or tray 150 is also provided, which has the same purpose as described above with respect to Figure 3i to Figure 3j Same purpose as described.

[0121] Figures 4a to 4e is a perspective view of an inductor unit 200 according to another embodiment. In this embodiment, the inductor unit 200, also referred to as a transverse flux inductor 200, may have a substantially square shape.

[0122] Similar to Figure 3a and Figure 3b The sensor unit 100 shown, Figure 4a The inductor unit 200 has a generating side 200 a and an active side 200 b and includes three main components: a coil unit 210 , a conductive element 220 and a soft magnetic element 230 .

[0123] The coil unit 210 is preferably a Litz wire that enters the inductor unit 200 via a recess 227 in the conductive element 200. The coil unit 210 is wound in a trace or groove in the conductive element 200 in a direction around the central axis (not shown) of the inductor unit 200. The trace in the conductive element 200 encapsulates the coil unit 210 (which may also be referred to as a wire) while also forming a larger cross-sectional surface area for the induced current in the generating side 220a of the conductive element, which minimizes losses and circuit inductance. The coil unit 210 can be completely encapsulated within the conductive element, for example by adding a cover to the open surface of the trace containing the coil unit 210. Alternatively, the coil unit can be wound in a drilled or machined hole or groove in the conductive element 220.

[0124] The conductive element 220 can be formed in one piece. Usually, the conductive element 220 is made of the same material, but it can also be a combination of two or more materials. For example, the conductive element 220 can be a coated structure, such as copper-plated 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, during welding, the active side 200b of the inductor unit 200 faces the workpieces 20, 21. As shown in FIG. Figure 4a As shown, the first side 220a of the conductive element 220 has a larger cross-sectional surface area than the second side 220b. Figure 4b In FIG. 2 , a step-like shape is shown between the first side 220 a and the second side 220 b of the conductive element 220 .

[0125] It is worth noting that in all of the illustrated embodiments, the second side 200b of the sensor unit 200 appears to be generally flat and smooth. However, the surface of the active side 200b may have a degree of surface roughness, or even a pattern. Furthermore, the surface need not be limited to a square shape. For example, the cross-section may vary on the active side, and the corners may be smooth. Some of these cases may be Figure 3e Shown in.

[0126] exist Figure 4a2, on the side of the conductive element 220 shown opposite to the recess 227, a corresponding end portion or slit 240 is provided, thereby forming two transmission sides 221c, 222c, which extend between the generating side 200a and the active side 200b of the inductor unit 200 in a direction perpendicular to the active side 220b of the inductor unit 200. It should be noted that more than one slit can be provided and still provide the same functionality, thereby forming more transmission sides 221c, 222c, 223c, etc. In certain designs, several transmission sides may be convenient, which can be seen in other embodiments further below. The slits can 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.

[0127] For all embodiments described herein, the slits may also be defined as end portions, short sides or gables of the inductor unit 100, 200. The end portions 140, 240 are also part of the conductive element 120, 220. The slits 140, 240 are preferably not covered by the soft magnetic material 130, 230. Figure 3a to Figure 3b In the embodiment of the present invention, the end portion 140 or the gable can be regarded as a slit with a radius close to infinity extending longitudinally along the active side 100b of the inductor unit 100. In addition, the end portion 140, 240 extends at least partially along the active side 120b, 220b of the at least one conductive element 120, 220, and preferably extends between the generating side 120a, 220a and the active side 120b, 220b of the at least one conductive element 120, 220. The current induced by the coil unit 110, 210 is preferably guided to the active side 100b, 200b of the at least one conductive element 120, 220 facing the workpiece to be welded through the end portion 140, 240.

[0128] Return to reference Figure 4a , at least one coil unit 210 can be seen through the slit 240, i.e. in the gap (end portion) between the transmission sides or parts 221c and 222c. The current flowing in the generation side 220a of the conductive element 220 will be forced to flow to the active side 220b via the transmission sides 221c, 222c and back to form a closed current loop. It is worth noting that the total cross-sectional surface area of ​​the generation side 220a of the conductive element 220 is much larger than the total cross-sectional surface area of ​​its active side 220b. During use, the workpieces 20, 21 to be heated / welded will be arranged below the active side 200b because the current (and the heat generated thereby) is concentrated in this area of ​​the inductor unit 200.

[0129] In addition, a first opening 225 and a second opening 226 are provided on the conductive element 220. The first opening 225 and the second opening 226 may extend into the inductor device 200 and be incorporated into the structure of the conductive element 220. The first opening 225 and the second opening 226 may extend through the inductor unit 200 in the form of a channel. The first opening 225 and the second opening 226 may also be referred to as a cooling channel. The cooling channel is configured to receive a fluid medium such as a gas or liquid medium. It is noteworthy that due to the efficient heating of the workpieces 20, 21 to be welded, the cooling requirement of the inductor unit 100 of the present invention after use is reduced. Alternatively, the cooling channels 225, 226 may share space with the coil unit 220 in the inductor unit 200.

[0130] The first opening 225 and the second opening 226 are useful during cooling of the conductive element 220 and the coil unit 210, the soft magnetic material 230 and possible workpieces with a liquid or gas. The openings 225, 226 can be provided with fittings or other connection means to supply cooling fluid. There can be more than one cooling channel, and for manufacturing purposes, some openings 228 are required for drilling of the channels and can be sealed or plugged before using the inductor unit 200.

[0131] In the case of 3D-printed conductive elements, not only the electrical design can be optimized, but also the thermal and mechanical properties can be optimized, and the cooling channels and support structures can have very complex shapes, which cannot be achieved using traditional production methods. However, according to the description in this article, the coil unit and the soft magnetic element must be able to be assembled in the inductor unit.

[0132] The soft magnetic element 230 is arranged in the center of the conductive element 220. In the illustrated embodiment, the soft magnetic element 230 has a substantially square shape extending along the central axis of the inductor unit 200.

[0133] See also Figure 4d , the soft magnetic element 230 can also be arranged along the entire boundary surface of the inductor unit 200, where no current is required. In order to prevent the current in the conductive element 220 from short-circuiting through the slit 240, the soft magnetic element 230 may also need to 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 voltage across the slit depends on the size and geometry, operating frequency, current level, workpiece characteristics, etc. In order to prevent failures due to short circuits, the width of the slit and its electrical insulation properties relative to the voltage across the slit need to be considered. Similarly, the electrical insulation between the turns of the coil or between the different coils of the coil unit 210 and between the coil unit and the conductive element 220 must be sufficient.

[0134] exist Figure 4b In the Figure 4a The active side 200b of the sensor unit 200. Figure 4b It can be clearly seen 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. Figure 4b middle side facing downward) and the active side 200b (in Figure 4b The transmission side 220c between the upper and lower sides of the transmission side 220c (with the transmission side 220c facing upward) is shown as a stepped configuration. However, other transition forms are also possible. For example, the transition portion can be curved or have any other smoother shape. From the perspective of efficiency and thermal, a smooth transition is preferred, while a stepped configuration may be easier to manufacture. Figure 4a The soft magnetic element 230 shown in FIG. Figure 4b Thus, it is apparent that the soft magnetic element 230 may extend through the inductor unit 200, thereby providing a path for the electromagnetic flux to pass through.

[0135] During use, the current induced in the conductive element 220 by the coil unit 210 flows through the slit 240, or more precisely, through the Figure 4b The transmission sides 221c, 222c of the slots shown are concentrated in the active side 200b of the inductor unit 200. Figure 4a and Figure 4b It is clear that the slit 240 extends in the inner region of the inductor unit 200 and at the periphery of the inductor unit. The slit 240 creates two transmission sides 221c, 222c, which can also be referred to as walls / end parts of the slit 240. The transmission sides are not covered by the soft magnetic element 230. In addition, in the case of Figure 4a and Figure 4b Two pipe connections (not shown) may be provided in the region corresponding to the openings 225 , 226 in the housing to facilitate the connection of, for example, cooling air or water, as briefly mentioned above.

[0136] In order to better see the generating portion 200a of the inductor unit 200 and the inner portion of the inductor unit 200 arranged to be connected to the coil unit 210, Figure 4c FIG. 2 shows a top view of the sensor unit 200. Here, the sensor unit 200 is shown from different angles. Figure 4a and Figure 4b FIG. 2 shows a top view of a slit 240 disposed in a conductive element 220 .

[0137] Reference Figure 4d, showing the active side 200b of the lateral inductor unit 200, the soft magnetic element 230 now exists not only inside the inductor unit 200, but also around the entire periphery of the inductor unit 200. For example, the soft magnetic element 230 can be a soft ferrite material or a powder core, or any other suitable material mentioned above.

[0138] Figure 4d The implementation method is Figure 4e Here, the slit 240 faces the Figure 4d In the opposite direction. Figure 4e As shown, the coil unit 210 is arranged in a groove, trace or space in the conductive element 220. Here, the conductive element 220 is made as a single piece. Alternatively, the conductive element 220 can be an assembly of two or more parts. Figure 4a and Figure 4b The two openings 225, 226 are depicted extending around a central axis (not shown) of the inductor unit 200 in a direction corresponding to the shape of the conductive element 220. As briefly mentioned, the two openings 225, 226 are configured to pass a cooling medium to maintain a stable temperature throughout the inductor unit 200.

[0139] The inductor unit 200 functions in the following manner. The coil unit 210 induces a current in the generating side 220a of the conductive element 220. Since the other surfaces of the inductor unit 200 are covered by the soft magnetic element 230, when the induced current reaches the slit 240, the induced current is forced to reach the active side 220b through the transmission sides 221c, 222c to form a closed current loop. The soft magnetic material forms a variation commonly known as a pot core, which is a soft magnetic element having a central leg, a bottom and a surrounding portion. The soft magnetic element 230 forms a path for electromagnetic flux, which flows around the coil unit 210 and the conductive element 220 and induces a current in the workpieces 20, 21.

[0140] At the active side 200b of the inductor unit 200, corresponding to the second side 220b of the conductive element 220, the current density is significantly higher than at the generating side 200a of the inductor unit 200. In other words, the current is more concentrated at the active side 200b of the inductor unit 200 due to the difference in surface area between the generating side and the active side of the conductive element 220. As previously mentioned, the workpiece 20, 21 to be heated will be arranged below this active side 220b, since the current (and thus also the heat) is concentrated in this region of the inductor unit 200 during use.

[0141] The soft magnetic element 230 can be a single piece or include multiple parts. Both soft ferrites and powder cores are usually produced by pressing and have limited sizes. In addition, some soft magnetic materials are difficult to machine, which is another reason for manufacturing the soft magnetic element 230 from several parts. Dividing the soft magnetic element into several pieces can also be a way to reduce the local concentration of electromagnetic flux density to reduce losses and prevent magnetic saturation. Using materials with different properties (particularly relative permeability) is another way to control losses, prevent saturation and optimize heating patterns.

[0142] As mentioned previously, in some designs more than one slit may be beneficial. Figure 5a to Figure 5c , an inductor unit 200 is illustrated, which has two slits in the conductive element 220 and thus has four transmission sides, forming a first conductive element 221 and a second conductive element 222. Figure 4a Differently, this embodiment is constructed as Figure 5a , Figure 5b The two separate units are then assembled into two mirrored or rotated parts, see Figure 5c . In this case, the coil is limited to covering a section of each inductor unit 200, rather than having a coil unit 210 with the coil passing through a slit. More specifically, the coil covers one of the pieces of the conductive element 220. The different coils can then be operated individually or together, either sequentially or simultaneously, at different frequencies or at the same frequency. If the coils are operated at the same frequency, the current can have a phase shift between 0 and 360 degrees, or alternate between, for example, 0 and 180 degrees. The coils can, for example, be connected in parallel, in series or in anti-series, or alternate between different configurations, such as using a mechanical switch, or a network of inductors and / or capacitors.

[0143] The benefit of having the coils in each conductive element run at the same frequency and with a phase shift defined as 180 degrees is that undesirable return paths for induced currents in the workpiece associated with transverse flux type inductors are avoided, with the phase shift defined as 180 degrees creating currents of different directions in the active side 220b of the two different conductive elements 221 and 222.

[0144] By having a phase shift of 0 degrees, corresponding to having all current on the active side 220b go in the same direction, longitudinal field operation is achieved, which produces heat in the center of the inductor unit, but with the risk of undesired heating outside the weld area A. However, by alternating the phase shift during the welding operation, a uniform heating pattern can be obtained in the weld area with limited or manageable heat generation outside the weld area. By utilizing different phase shifts, the heating pattern in the weld area can be tilted in either direction. Similar to Figure 4d , Figure 4eIn the previously implemented transverse flux inductor shown in FIG, the soft magnetic element 230 covers the side and center of the conductive element 220, and the conductive element 220 can be regarded as consisting of two conductive elements 221, 222, leaving only the active side 221b, 222b, the generating side 221a, 222a and the transmitting side 221c, 222c uncovered. In longitudinal magnetic field operation, as Figures 3a to 3k As shown, almost no flux enters the central portion of the soft magnetic element, whereas in transverse flux operation, the highest flux density is usually shown in the central portion of the soft magnetic element, depending on the geometry.

[0145] exist Figure 6a Another embodiment of the concept just described is shown in FIG. 1 , in which the coil unit 210 has been more encapsulated inside the conductive element 220, similar to Figure 3h to Figure 3j , to reduce the flux density in the soft magnetic element 230, reduce inductance and improve efficiency. Figure 6a to Figure 6b In FIG. 2 , the current travels from the generating side 221a to the active side 221b via the transmitting side 221c. To further increase the flexibility in adjusting the heating mode, including the flexibility in processing workpieces of different geometries, more than two different coils and conductive elements may be used, see Figure 6b As previously described, different types of operation or alternating modes of operation, including different phase shifts between the currents in different coils, may be used to change, adjust or shift the heating pattern in the weld zone A.

[0146] like Figure 6b As shown, the conductive element 220 can be divided into a plurality of dependent or independent parts 221, 222, 223, 224. In each conductive element part 221, 222, 223, 224, the current, amplitude frequency and phase shift are controlled individually or collectively. Figure 6b In the embodiment, 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, such as Figure 3e As briefly illustrated in Figure 3e The curved, smooth surface of the active side of the inductor unit is illustrated.For example, a sawtooth pattern (not shown) of the conductive element 220 on the active side 220b may be beneficial for certain material stackups of a CFRP workpiece.

[0147] Figure 6c to Figure 6e The active side 220b of the inductor unit 200 is shown. In particular, Figure 6c The figure shows an embodiment in which the conductive element 220 has been divided into eight independent parts 221 to 228. Optionally, according to the design of the coil unit 210, the conductive element 220 can be divided into eight independent parts 221 to 228. Figure 6cThe conductive elements 221 to 228 are separated by soft magnetic elements 230 and / or non-magnetic elements 270. With this inductor design, the current direction can be selected in different ways, see e.g. Figure 6d and Figure 6e , where the direction of current is illustrated by arrows pointing in different directions.

[0148] exist Figure 6d In the embodiment, the current travels in opposite directions on the active side 220b of each adjacent conductive element portion 221, 222, 223, etc. Figure 6d As illustrated by the dashed lines in FIG. 2 , the induced current in the workpieces 20 , 21 is forced to travel in a small loop or figure 8 pattern. In this way, the temperature uniformity of certain material stacks of the CFRP workpiece can be improved.

[0149] Alternatively, if Figure 6e As shown, three Figures 6c to 6d Inductor units 200 of the type described in are arranged side by side. In this configuration, at a specific area of ​​a workpiece to be welded, different parts of the area can be heated at each point in time. Alternatively, the workpieces can be heated simultaneously using different frequencies in each of the individual inductor units 200. Alternatively, the workpieces can be heated simultaneously using the same frequency but with currents of different phase shifts. For example, the area of ​​the workpiece to be welded can be close to the edge of the workpiece.

[0150] Figure 6e The inductor arrangement shown is beneficial for both continuous or dynamic welding as well as static welding. For example, the inductor arrangement may be beneficial for static welding where the length of the weld zone varies or for generally improving the temperature uniformity of the weld zone.

[0151] exist Figure 7a to Figure 7b , another embodiment of a transverse flux inductor is shown. Figure 7a to Figure 7b The sensor unit 200 has similar features to the sensor unit 200 shown and described with respect to FIGS. 4 to 6 .

[0152] Figure 7a The coil unit 210 in the embodiment is surrounded by the soft magnetic element 230 to a greater extent than the conductive element 220. The advantage of this configuration is that the inductor unit 200 becomes more space-efficient. Figure 7a The coil unit 210 is composed of only one coil, thus representing Figures 6a to 6e A more compact version of .

[0153] Similar to Figure 3k , Figure 7aThe inductor unit 200 includes a non-magnetic element 270 located at the end portions of the conductive element 220. These end portions may also be referred to as 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 to apply pressure to the workpiece material at the same time. The non-magnetic element 270 may be electrically conductive. Optionally, the non-magnetic element 270 is non-conductive. In one case, the non-magnetic element 270 is preferably electrically insulated from the conductive element 220 to prevent short circuits 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 higher, such as 10 W / mK or even more preferably 100 W / mK. This is to prevent undesired melting of the top surface of the workpiece facing the inductor 200 during welding.

[0154] Figure 7a to Figure 7b The sensor unit 200 also includes a fixing member 250, which can be referred to as a non-conductive structural support. The purpose of the fixing member 250 can be to prevent the sensor unit 200 from contacting the workpiece to be welded. Figure 3i to Figure 3j Other examples of the purpose of a fixture 250 are described, which have similar features as referred to as tray 150 .

[0155] Figure 8 A system 1 is illustrated in which a sensor unit 100, 200 may be used. For example, the system 1 includes a moving device 40. The moving device 40 may be operatively coupled to a processing device 30 and the sensor unit 100, 200. The moving device 40 is configured to cause movement of the sensor unit 100, 200 based on process information received and / or determined by the processing device 30. In other words, the processing device 30 is configured to control the movement of the sensor unit 100, 200. Alternatively, the sensor unit 100, 200 is stationary and the moving device 40 is configured to move the workpiece 20, 21 relative to the sensor unit 100, 200.

[0156] The processing device 30 may be configured to control the applied pressure by controlling the pressure device 50. Typically, the pressure is applied in a direction substantially perpendicular to the weld area A of the at least two workpieces 20, 21 to be welded.

[0157] The moving device 40 is configured to move the inductor unit 100, 200 relative to the workpieces 20, 21 to be welded during welding or between different welds. The moving device 40 can be operatively connected to the processing device 30 and to the drive unit 70, which causes the movement of the inductor unit 100, 200. The drive unit 70 can be part of the moving device 40 or arranged outside the moving device 40. The drive unit 70 can be a motor, such as an electric motor or a pneumatic actuator or the like. Alternatively, the drive unit 70 can be a brushless DC electric motor. The brushless DC electric motor can be a stepper motor. A stepper motor divides a complete rotation into a plurality of equal steps. The advantage of a stepper motor is that it can be moved and kept in one of these steps without position sensor feedback. The drive unit 70 can also be any type of servo motor.

[0158] The processing device 30 may instruct the drive unit 70 to move the sensor unit 100, 200 along a predetermined path. The drive unit 70 may be controlled wirelessly by the processing device 30, or by wires or optical fibers. The drive unit 70 may be configured to follow a predetermined protocol stored in a memory associated with the processing device 30, and / or the drive unit 70 may be configured to follow instructions caused by a user of the processing device 30. The drive unit 70 may be arranged as part of the system 1, or as a separate external part in operative communication with the system 1.

[0159] Optionally, the mobile device 40 can be part of the processing device 30, or arranged outside the processing device 30. The mobile device 40 may include, for example, a track, a frame, a rod or a similar device that allows the movement to be controlled in a precise manner. The mobile device 40 can also be a robotic arm, a parallel kinematic robot or a gantry. The mobile device 40 can move in incremental steps to control the welding process. The mobile device 40 can also move continuously. The mobile device 40 can also be manually driven. For example, the mobile device 40 can be arranged in a housing, such as a longitudinal device, along which the mobile device 40 can move (not shown) to allow the movement of the sensor unit 100, 200. In one embodiment, the mobile device 40 may include a telescopic arm that can be extended or shortened during welding to allow different positions of the sensor unit 100, 200.

[0160] The system 1 may further comprise a cooling device 60 configured to cool the system 1 during and / or after use. The cooling device 60 is configured to cool the workpieces 20, 21 during and / or after the processing temperature has been reached and the weld has been formed. The area to be cooled may include the weld area A as well as the rest of the workpiece due to unwanted heat generation, for example along edges or crossing strands in the lamination of the workpieces 20, 21. The cooling may be controlled by the processing device 30. For example, if the welding process is continuous, the system 1 may comprise a roller or cooling cylinder configured to cool the weld area A. The roller or cooling cylinder may be arranged behind the inductor unit 100, 200 as it moves over the workpiece 20, 21. Alternatively, the cooling may come from a liquid or gaseous fluid, such as air.

[0161] Alternatively, the inductor unit 100, 200 can cool the newly welded area by thermal conduction. Unlike conventional welding inductor designs, the inductor unit 100, 200 described herein can include a solid block of thermally conductive material, i.e., an electrically conductive element 120, 220, which can be designed to provide a uniform or desired heat load to the heated area, which corresponds to the heated area. Figure 1 The weld area A in the weld seam area A. The robust design also allows it to be clamped directly or indirectly to the workpiece to form a good thermal contact. The inductor unit 100, 200 can have other non-conductive, thermally conductive materials designed to cool the workpiece, for example in areas along the edges of the conductive elements 120, 220 or in areas that are not intended to be heated. Materials with certain thermally conductive or insulating properties can be introduced between the conductive elements and the workpiece to achieve the desired thermal load of the surface. These materials can be placed there loosely or as part of the inductor unit 100, 200. The conductive elements can be equipped with cooling channels; thus, the temperature of the conductive elements can be controlled by, for example, the processing device 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.

[0162] In another embodiment, the inductor may be equipped with a vibrating device (not shown) intended to reduce friction between the inductor unit 100, 200 and the surface of the workpiece. More specifically, the inductor may include the mechanical portion of the vibrating device, or be integrally operatively connected to the vibrating device. Typically, at least the electronics or processing of the vibrating device is external and may be the same or similar to the processing of the inductor unit. The vibrating device may be piezoelectric, magnetostrictive, mechanical or electromagnetic, so as to facilitate continuous welding using pressure from the inductor unit.

[0163] For example, in the case of continuous welding, a consolidation force is always required, which may come from the inductor unit, thereby preventing it from moving. Small amplitude vibrations will reduce friction and enable it to move under high pressure. The vibrating device may include a mechanical vibrating unit (such as a motorized unbalanced rotating mass) or a piezoelectric or magnetostrictive actuator. The vibrating device is usually driven by a power electronic drive unit, for example providing a controllable DC or AC voltage or current. The vibration may also generate some heat.

[0164] In order to clamp the workpiece or apply consolidation pressure on the workpiece, one possible way is to make the active part 120b, 220b of the conductive element 120, 220 thin enough so that it can expand when pressurized. The membrane effect can be used to achieve uniform pressure distribution in the welding area, even though the surface may be uneven. The membrane effect can be defined as a flexible and deformable part or surface constrained along the outer boundary to apply force to the surface. For example, a pressurized balloon is forced to press against a surface, and even if the surface does not conform to the original shape of the balloon, it can be deformed and in some cases exert a fairly uniform pressure on a certain surface area. As another example, inflatable, expandable air bags are often used to compact composite materials, similar to the inner tube of a tire. This can be interpreted as a mechanical clamping to maintain consolidation pressure during welding.

[0165] As an alternative, the tray 150 (also called non-conductive support) can be made of a material (usually a polymer material) that can be expanded into a membrane. The expansion of this membrane (independently of being part of the conductive element 120 or the tray 150) is preferably performed by pressurization, achieved by a gas of a liquid such as air or water. Typical pressures range from less than one bar to a few tenths to several bars. In the case of higher pressures, a support is required to prevent the molten material from squeezing out during the welding process.

[0166] Another advantage of the proposed inductor concept is the opportunity to build an openable inductor unit for round objects. For example, for the joining of pipes, it would be advantageous to be able to have an inductor unit that encloses the diameter of the pipe to be welded and still be able to easily remove the inductor unit after welding. By utilizing a conductive element consisting of two or more parts, this can be achieved without disconnecting the coil unit, for example using Figure 3f to Figure 3g A variation of the illustrated inductor can be implemented.

[0167] Fig. 9A method 300 for induction welding of at least two workpieces 20, 21 using the system 1 as described above is illustrated. The method begins by first providing 310 an inductor unit 100, 200 and arranging 315 the inductor unit 100, 200 in conjunction with at least one of the workpieces 20, 21 to be welded. A processing device 30 is also provided 320. The processing device 30 applies 330 an alternating voltage V to the inductor unit 100, 200, and thereby induces a current in the conductive elements 120, 220 of the inductor unit 100, 200 via the coil units 110, 210. The current in the conductive elements further induces a current in at least a portion of the susceptible workpiece 20, 21. The purpose is to inductively heat the at least two workpieces 20, 21 so that a weld is formed in a weld region A between the two workpieces 20, 21 (see Figure 1 ). The AC voltage V is the input signal of the inductor unit 100, 200 and is applied via the processing device 30. However, the method is not limited to applying only the input voltage to the inductor. Other electromagnetic signals are also applicable, such as current I or frequency F.

[0168] More specifically, the method of induction welding is performed as follows. First, an inductor unit 100, 200 is provided 310 according to any of the above-described embodiments. The inductor unit 100, 200 is arranged 315 in conjunction with at least one workpiece 20, 21. Next, a processing device 30 is provided 320 to control the overall operation of the process and the movement of the inductor 100, 200 relative to the workpieces 20, 21 to be welded. The inductor unit 100, 200 can be positioned by a moving device 40 such as a robot arm. As described above, the robot arm can be controlled by the processing device 30. Before starting the heating process, a step 325 of applying a consolidation pressure on at least one workpiece can also be provided.

[0169] By applying 330, for example, an alternating voltage to the inductor unit 100, 200, an electromagnetic field is generated, thereby inducing a current in the conductive elements 120, 220 of the inductor unit 100, 200. The current in the conductive elements 120, 220 further generates an electromagnetic field, which induces a current in the weld region A and thereby heats the workpieces 20, 21, and after the process temperature has been reached, a weld is formed in the weld region A.

[0170] Optionally, a step 340 of providing movement means 40 configured to move the inductor unit 100, 200 and a step 350 of providing cooling means 60 configured to cool the inductor unit 100, 200 after termination of the welding process are provided.

[0171] The processing device 30 generates a current in the coil unit 110, 210. The current generates a magnetic field, which induces a current in the opposite direction in the conductive element 120, 220, which is preferably made of copper and / or aluminum or an alloy thereof, and thereby cancels the electromagnetic field, reducing the magnetic flux density of the circuit. As described, the soft magnetic element 130, 230 is arranged around the conductive element 120, 220, so as to guide the generated electromagnetic flux to the workpiece 20, 21 and force the current in the conductive element 120, 220 to flow on the desired surface, thereby improving the efficiency and generating the desired heating pattern. Because the soft magnetic element 130, 230 has a high resistivity and a small hysteresis loss, only a small amount of heat is generated in the inductor device 100, 200. Therefore, in most settings, the efficiency of heating can be improved by arranging the soft magnetic element 130, 230 around the conductive element 120, 220.

[0172] Because of the different inductor units shown in FIGS. 3 to 6 , the current induced in the conductive element 120 , 220 is directed from the generating side 100a , 200a of the inductor unit 100 , 200 to the active side 100b , 200b which is located in close proximity to the workpieces 20 , 21 to be welded.

[0173] In other words, by combining the elements of the inductor units 100 , 200 as described above, a relatively small current provided first in the coil units 110 , 210 can lead to concentrated and efficient heating of the workpieces 20 , 21 in the weld seam region A.

[0174] When the welding process is terminated, the inductor unit 100, 200 is moved away from the welding zone (also called weld zone A) by means of the moving device 40. Due to the characteristics of the inductor design, cooling is relatively easy to achieve. More specifically, the copper or aluminum (or the like) used as the conductive element 120, 220 facilitates this relatively fast and controlled cooling. Furthermore, the provision of a support or fixture positioned opposite the inductor unit 100 facilitates cooling of the workpiece. The cooling device described herein also prevents remelting of the outer surface of the workpiece.

[0175] It is noteworthy that the method of welding can be performed by a continuous process or a step-by-step static process. Optionally, before applying the electromagnetic field by the processing device 30, a load force is applied to the generating side 100a, 200a of the inductor away from the workpiece 20, 21. In addition, as long as the concentration of the current can be achieved, the bottom part of the inductor unit facing the workpiece can have different cross-sections. The cross-section can be patterned and / or have a variable cross-section over the entire bottom surface. For example, the surface can be rounded. The transmission of force from the inductor unit 100, 200 to the workpiece 20, 21 can come directly from the conductive element 120, 220, or indirectly via an electrically insulating material and / or a thermally insulating material. Alternatively, a consolidation force can be applied from the opposite side of the workpiece, while the inductor unit is fixed and a mechanical support is provided. As described, the force can also come from, for example, a vacuum bag covering the workpiece or other mechanical supports that do not act on the inductor unit. A vacuum membrane as part of the inductor unit is another alternative to achieve a clamping force, particularly suitable for welding small workpieces or attaching small workpieces to relatively large workpieces. For relatively thick workpieces, such as 10 mm or thicker, it may be beneficial to have one inductor unit 100, 200 on each side of the workpiece to more easily transfer the heat generation all the way to the weld area A.

[0176] In all embodiments of the present invention where an air gap exists in the inductor design, it may be necessary to isolate the air gap to avoid short circuits.

[0177] It is noteworthy that the soft magnetic elements are arranged and configured to concentrate the current induced in the conductive material and direct the current in a predetermined direction throughout the inductor unit. In this way, there are small self-generated losses in the inductor unit 100, 200 that heat the workpiece during use.

Claims

1. An inductor unit for controlled induction welding of at least one fiber-reinforced thermoplastic composite workpiece (20, 21), the inductor unit comprising: at least one coil unit (110, 210); at least one conductive element (120, 220), the conductive element (120, 220) having a generation 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, wherein the active side (120b, 220b) of the conductive element (120, 220) has a smaller cross-sectional surface area than the generation side (120a, 220a); and at least one soft magnetic element (130, 230); wherein the at least one coil unit (110, 210) is configured to induce a current in the conductive element (120, 220); and The at least one soft magnetic element (130, 230) is at least partially arranged on the at least one conductive element (120, 220), so that the induced current is guided from the generating side (120a, 220a) of the conductive element (120, 220) to the active side (120b, 220b) and concentrated in the active side (120b, 220b).

2. The sensor unit according to claim 1, wherein: The conductive element (120, 220) further comprises an end portion (140, 240) extending at least partially between the generating side (120a, 220a) and the active side (120b, 220b) of the at least one conductive element (120, 220), wherein the induced current is directed from the generating side (120a, 220a) of the at least one conductive element (120, 220) to the active side (100b, 200b) via the end portion (140, 240).

3. The sensor unit according to any one of claims 1 or 2, wherein: The coil unit (110, 210) includes at least one coil forming at least two turns, wherein the turns are 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).

4. An inductor unit according to any one of the preceding claims, wherein The at least one soft magnetic element (130, 230) has a relative magnetic permeability greater than 10 and preferably a high volume resistivity greater than 0.01 Ohm*m.

5. An inductor unit according to any one of the preceding claims, wherein The at least one soft magnetic element (130, 230) is at least partially arranged on a boundary surface of the inductor unit (100, 200).

6. An inductor according to any one of the preceding claims, wherein The inductor unit (100, 200) is in operative communication with a processing device (30), and the processing device (30) is configured to generate an electric current in the coil unit (110, 210).

7. An inductor unit according to any one of the preceding claims, wherein The coil unit (110, 210) includes at least one Litz wire.

8. An inductor unit according to any one of the preceding claims, wherein The conductive element (120, 220) includes copper or aluminum.

9. An inductor unit according to any one of the preceding claims, wherein: The soft magnetic element (130, 230) is selected from the group of soft magnetic ferrites, and / or powder-based cores, soft magnetic composite materials consisting of individually insulated soft magnetic wires, tapes or laminated bundles or stacks, including amorphous and semi-crystalline alloys.

10. The inductor unit according to any of the preceding claims, further comprising an electrical and / or thermal insulation between the electrically conductive element (120, 220) and the at least one workpiece (20, 21) to be welded.

11. An inductor unit according to any of the preceding claims, further comprising a cooling channel for a fluid medium.

12. An inductor unit according to any one of the preceding claims, wherein At least some of the conductive elements (120, 220) are replaceable.

13. An inductor unit according to any one of the preceding claims, wherein The conductive element (120, 220, 160) contacts the at least one workpiece (20, 21) during welding, thereby forming a closed current loop for current to flow from one area of ​​the at least one workpiece (20, 21) to another area.

14. An inductor unit according to any one of the preceding claims, wherein The sensor unit (100, 200) is deformable.

15. An inductor unit according to any one of the preceding claims, further comprising a mechanical clamp for maintaining consolidation pressure during welding.

16. An inductor unit according to any preceding claim, further comprising a vibrating device.

17. A system for induction welding at least one fiber reinforced thermoplastic composite workpiece (20, 21), the system comprising: The sensor unit (100, 200) according to any one of claims 1 to 16; at least one workpiece (20, 21) to be welded; as well as A processing device (30) is operatively connected to the sensor unit (100, 200).

18. A method of providing a system for induction welding at least one fiber reinforced thermoplastic composite workpiece (20, 21), the method comprising: providing (310) an inductor unit (100, 200) having a coil unit (110, 210) according to any of the preceding claims; Providing at least one workpiece (20, 21) to be welded; Arranging (315) the inductor unit (100, 200) in conjunction with the at least one workpiece (20, 21); and A processing device (30) is provided (320), the processing device (30) being in operative communication with the sensor unit (100, 200).

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