HEATING ELEMENT AND WELDING KIT FOR RESISTANCE WELDING AND METHODS OF MANUFACTURING A HEATING ELEMENT AND WELDING THERMOPLASTIC COMPONENTS

Abstract

A heating element for resistance welding of thermoplastic components includes an electrically conductive sheet with cut-outs, wherein a ratio of cut-outs to electrically conductive sheet changes at least along a transverse direction of the sheet, so that an electrical resistance of the sheet has a maximum at a center of the sheet. A welding kit includes the heating element and an electrical insulation layer. A method of manufacturing the heating element, and a method of employing the heating element for welding two thermoplastic components to one another are disclosed.

Claims

1. A heating element for resistance welding of thermoplastic components, the heating element comprising: an electrically conductive sheet comprising a plurality of cut-outs, wherein a ratio of cut-outs to electrically conductive sheet changes at least along a transverse direction of the sheet, so that an electrical resistance of the sheet has a maximum at a center of the sheet.

2. The heating element according to claim 1, wherein a ratio of cut-outs to electrically conductive sheet changes along a longitudinal direction of the sheet, wherein each end region of the sheet has a lower electrical resistance than the center of the sheet.

3. The heating element according to claim 1, wherein a first type of cut-outs is in the center of the sheet, and a second type of cut-outs is along each of longitudinally extending edges of the sheet, and/or wherein a third type of cut-outs is along each of transversely extending longitudinal end regions of the sheet, and wherein a type of the cut-outs defines a shape, an area, a longitudinal dimension, and/or a transverse dimension of the cut-out.

4. The heating element according to claim 1, wherein a distance between two adjacent cut-outs in the transverse direction is identical over an entire width of the sheet, changes gradually from the center of the sheet towards each of longitudinally extending edges of the sheet, or changes stepwise from the center of the sheet towards each of the longitudinally extending edges of the sheet, and/or wherein a distance between two adjacent cut-outs in the longitudinal direction is identical over an entire length of the sheet, changes gradually from the center of the sheet towards each of transversely extending longitudinal end regions of the sheet, or changes stepwise from the center of the sheet towards each of the longitudinal end regions of the sheet.

5. The heating element according to claim 1, wherein the sheet is made from an electrically conductive foil and/or a paper comprising carbon fibers and/or nanotubes.

6. A welding kit, comprising: a heating element according to claim 1; and at least one electrical insulation layer on a surface of the heating element, wherein the at least one electrical insulation layer comprises a layer of glass plies and/or a thermoplastic material and/or is a ceramic coating applied onto the electrically conductive sheet.

7. A method of manufacturing a heating element according to claim 1, the method comprising: providing a continuous electrically conductive sheet; and cutting a plurality of cut-outs into the sheet along a transverse direction and along a longitudinal direction.

8. The method according to claim 7, wherein cutting comprises: laser cutting the plurality of cut-outs; or rolling a roller comprising a plurality of blades over the sheet, wherein the blades are arranged and configured to cut the plurality of cut-outs.

9. The method according to claim 7, comprising: applying a tensile stress to the sheet to extend a length of the sheet and reducing a width of the sheet.

10. A method of welding thermoplastic components to one another, the method comprising: providing a heating element according to claim 1; placing a first thermoplastic component at a first side of the heating element and a second thermoplastic component at a second side of the heating element; connecting the heating element at opposite longitudinal ends of the heating element to an electric circuit; applying an electric potential to the heating element by the electric circuit; and pressing the first and second thermoplastic components together by corresponding upper and lower press elements.

11. The method according to claim 10, wherein placing the first and second thermoplastic components comprises arranging a region of the heating element having a higher electrical resistance between the first and second thermoplastic components and arranging longitudinal end portions of the heating element having a lower electrical resistance outside of the first and second thermoplastic components.

12. The method according to claim 10, wherein providing the heating element comprises providing a heating element having the plurality of cut-outs in a region having identical dimensions as a welding area of each of the first and second thermoplastic components.

13. The method according to claim 10, comprising: placing at least one electrical insulation layer on a surface of the heating element between the heating element and the first or second thermoplastic component; and/or wherein providing the heating element comprises providing a heating element, to which is attached at least one electrical insulation layer; and/or wherein placing the first and second thermoplastic components comprises providing the first and/or second thermoplastic component, to which is attached at least one electrical insulation layer.

14. The method according to claim 10, comprising cutting longitudinal end portions of the heating element protruding from the welded first and second thermoplastic components.

15. The method according to claim 10, wherein the first and second thermoplastic components are structural parts of a primary structure of an aircraft.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Preferred embodiments of the disclosure herein are now explained in greater detail with reference to the enclosed schematic drawings, in which:

[0063] FIG. 1 schematically illustrates cross sections and a plan view of an exemplary welding zone including a heating element;

[0064] FIG. 2 schematically illustrates a plan view of an exemplary heating element;

[0065] FIG. 3 schematically illustrates a plan view of another exemplary heating element;

[0066] FIG. 4 illustrates exemplary flow diagrams of methods for manufacturing a heating element and of welding thermoplastic components; and

[0067] FIG. 5 schematically illustrates a vehicle having a welding zone including a heating element.

DETAILED DESCRIPTION

[0068] FIG. 1 schematically illustrates cross sections and a plan view of an exemplary welding zone including a heating element 100 for resistance welding. Specifically, the heating element 100 comprises an electrically conductive sheet 105 that can be arranged between a first thermoplastic component 21 and a second thermoplastic component 22 that are to be welded to one another. The electrically conductive sheet 105 can be connected to an electric circuit, particularly an electrical potential illustrated as “+” and “−” in FIG. 1. Due to the electrical resistance of the sheet 105, heat will be generated when an electric current flows through the sheet 105. This heat can be used to melt at least the surfaces of the first and second thermoplastic components 21, 22, so that they can be welded to one another.

[0069] In order to facilitate the welding of the first and second thermoplastic components 21, 22, an upper press element 31 and a lower press element 32 can be provided. The upper and lower press elements 31, 32 can be configured to be moved towards one another, thereby clamping and pressing the first and second thermoplastic components 21, 22 towards one another. This allows pressing the melted surfaces of the first and second thermoplastic components 21, 22, so that they come into contact and are merged into one another. The sheet 105 of the heating element 100 will thereby be integrated into the melted thermoplastic material of the components 21, 22.

[0070] In addition, an optional electrically insulating layer 121, 122 can be placed between the sheet 105 and the corresponding first or second thermoplastic component 21, 22. Such electrical insulating layer 121, 122 can be placed on one side of the sheet 105, for example, if this side of the heating element 100 faces thermoplastic components 21, 22 subject to electrical current leakage, such as thermoplastic component 21, 22 including carbon fibers.

[0071] Moreover, the heating element 100 may be provided together with at least one electrical insulating layer 121, 122, which together form a welding kit 120. For instance, the at least one electrical insulating layer 121, 122 can be connected or attached to the sheet 105. For instance, such attaching or connecting to the sheet may be achieved by consolidating, welding or adhering the electrical insulating layer 121, 122 to the sheet 105.

[0072] As can be derived from the cross sections illustrated in FIG. 1, the electrically conductive sheet 105 extends in a longitudinal direction (Y-axis) to such an extent that it protrudes on each side from the first and second thermoplastic components 21, 22. In a transverse direction (perpendicular to the longitudinal direction; X-axis) the sheet 105 has the same size (dimension) as the overlapping area of the first and second thermoplastic components 21, 22, i.e. the welding zone or the area of the first and second thermoplastic components 21, 22 to be welded to one another.

[0073] The distances of the elements illustrated in FIG. 1 with respect to one another, particularly in a thickness direction (Z-axis) are drawn for clarity of the Figure. They shall not be understood as a required distance. Moreover, the size and thickness of the elements is not to be understood as drawn in scale, but only for illustrating purposes.

[0074] In the transverse cross-section (upper right drawing in FIG. 1) the longitudinally extending edges of the sheet 105 (left and right edges in the drawing) are disposed close to the air and next to the first and second thermoplastic components 21, 22. Thus, this region of the welding zone may be cooled by the surrounding air. This effect is referred to as the transversal edge effect.

[0075] In the longitudinal cross-section (upper left drawing in FIG. 1) the longitudinal end regions of the sheet 105 will protrude from the welding zone. In this area heat is also produced by the longitudinal end regions of the sheet 105 exposed to the outside, so that the sheet 105 as well as the first and second thermoplastic components 21, 22 next to this end region may receive additional heat. This effect is referred to as the longitudinal edge effect.

[0076] In order to reduce or avoid the transversal edge effect as well as the longitudinal edge effect and further in order to facilitate integration of the sheet 105 into the welded components 21, 22, a plurality of cut-outs is provided in the sheet 105, which will be explained with respect to FIGS. 2 and 3.

[0077] FIGS. 2 and 3 each schematically illustrate a plan view of an exemplary heating element 100. The sheet 105 of the heating element 100 of each example can be divided into two regions along the longitudinal direction. A first (center) region 110 can be dimensioned (sized) to correspond to the area of the welding zone, i.e. the welding area defined by the overlap area of first and second thermoplastic components 21, 22. This is schematically indicated by the dashed box in FIG. 2 illustrated next to heating element 100. The second region(s) are the longitudinal (exposed) ends 116 of the sheet 105 adjacent to the first region 110.

[0078] The first region 110 is provided with a plurality of cut-outs 111-113, where the sheet 105 is pierced through, i.e. the material of the sheet 105 has been removed and a plurality of through holes through the sheet 105 is present. Due to the cut-outs 111-113 in the sheet 105 the electrical conductivity of the sheet 105 is changed, particularly the electrical resistance of the first region 110 is higher than the electrical resistance of the longitudinal ends 116. Heat generated by the sheet 105, once electric current flows through the sheet 105, is higher in the first region 110 then in the longitudinal ends 116, since longitudinal ends 116 and first region 110 are electrically connected in series. This reduces or avoids the longitudinal edge effect and avoids overheating of the welding zone, particularly at the longitudinal ends of the welding zone.

[0079] A similar improvement can be achieved along the longitudinally extending edges (the lateral edges) of the sheet 105 (cf. upper and lower edges of the sheet 105 in FIGS. 2 and 3). Specifically, a plurality of cut-outs 111 can be provided along the longitudinally extending edges of the first region 110 that is of a different type than the cut-outs 113 in the center of the first region 110. The cut-outs 111, 113 define regions of the first region 110 that are electrically connected in parallel. That means that current intensity flowing through these regions will depend on the resistance of the respective region. In order to generate more heat per unit area, the resistance of the corresponding region has to be reduced. The cut-outs 111, 113 as provided in the example of FIG. 2 define a ratio of cut-outs 111-113 to electrically conductive sheet 105 that changes along a transverse direction of the sheet 105, so that an electrical resistance of the sheet 105 has a maximum at the center of the sheet 105. Due to the smaller electrical resistance along the longitudinally extending edges achieved by the cut-outs 111, the welding zone will be heated more along the longitudinally extending edges. It is to be noted that the cut-outs 111 are provided on both lateral sides of the sheet 105, i.e. of the welding zone. Thus, both regions having cut-outs 111 are generating more heat than the region having cut-outs 113 and the transversal edge effect is reduced or avoided.

[0080] FIG. 2 further illustrates an example of cut-outs 111 along one of the longitudinally extending edges as well as the cut-outs 113 in the center of the first region 110. As can be derived from this exemplary illustration, the type of the cut-outs 111, 113 changes from longitudinally extending rectangles to squares. Any other shape or form of the cut-outs 111, 113 may be employed to achieve similar effects, so that the electrical resistance of the sheet 105 can be tailored in any region as desired.

[0081] From the detailed exemplary illustration of the cut-outs 111, 113 it can further be derived that a distance between two adjacent cut-outs 111, 113 may be the same or may change in the transverse direction and/or in the longitudinal direction of the sheet 105. This distance coincides with a width and length of the electrically conductive sheet 105 in a predefined area. This influences the electrical resistance and, hence, the current intensity flowing through this predefined area of the sheet 105. Thus, heat generated by the sheet 105 in a particular region or area can also be tailored by setting the distance between two adjacent cut-outs 111, 113.

[0082] Furthermore, with respect to FIG. 3, more than one region may be provided that each have a different type of cut-out 111-113. For instance, along each of the longitudinally extending edges of the sheet 105, there is an area of a first type of cut-outs 111. Further to the center and still a long each of the longitudinally extending edges of the sheet 105, there is another area of a second type of cut-outs 112, while the center is provided with a third type of cut-outs 113.

[0083] In order to address the transversal edge effect as well as the longitudinal edge effect, the regions of different types of cut-outs 111-113 may change their form at the longitudinal ends of the first region 110. As is illustrated in FIG. 3, the extent of the area of the first type of cut-outs 111 and the second type of cut-outs 112 in the transverse direction decreases towards the longitudinal end regions 118 of the first region 110. Thus, the additional heat provided by the sheet 105 in the regions of the first and second type cut-outs 111, 112 is reduced towards the longitudinal end regions 118. The longitudinal end regions 118 form the transition of the first region 110 to the longitudinal ends 116.

[0084] It is to be understood that the longitudinal end regions 118 may be provided with another type of cut-out (not specifically illustrated) or may have no cut-out at all as the longitudinal ends 116 of the sheet 105. In addition, it is to be understood that the sheet 105 may be divided into more than three regions of different types of cut-outs 111-113. Specifically, the cut-outs 111-113 and/or the distance between two adjacent cut-outs 111-113 can gradually change in the transverse direction and/or in the longitudinal direction.

[0085] Each of the longitudinal ends 116 may be connected to an electric circuit via a respective clamp 117 or a similar measure, such as a solder spot or seam or the like.

[0086] FIG. 4 illustrates exemplary flow diagrams of methods for manufacturing a heating element 100 and of welding thermoplastic components 21, 22. The heating element 100 and thermoplastic components 21, 22 can be those illustrated in and described with respect to FIGS. 1 to 3.

[0087] Manufacturing a heating element 100 starts in step 200 with providing a continuous electrically conductive sheet 105. This sheet 105 may be provided in the form of a roll of foil and/or paper including or consisting of an electrically conductive material. Furthermore, in step 210, a plurality of cut-outs 111-113 are cut into the sheet 105 along a transverse direction as well as along longitudinal direction of the sheet 105. Optionally, the sheet 105 may be cut into longitudinal pieces, if the provided sheet 105 is longer than one heating element 100.

[0088] The design and/or layout of the cut-outs can be determined in preparation of such heating element manufacturing method. It can include finding suitable parameters for the cut-outs for the welding situation, e.g. depending on the size and shape of the join partners and/or weld zone. This determination can include, but is not limited to, a thermal-transient FEM simulation. The FEM simulation can be programmed to establish a sheet and cut-out layout and the described ration to achieve a uniform temperature distribution with respect to the circumstances given by the join partners and weld zone.

[0089] Furthermore, such heating element 100 may be provided in a step 300 of a method of welding thermoplastic components 21, 22. Alternatively, after method step 210, a first and second thermoplastic component 21, 22 may be placed at a first and second side of the heating element 100, respectively, in step 305. This placing step 305 can include arranging a first region 110 of the heating element 100 between the first and second thermoplastic components 21, 22, while longitudinal end portions 116 of the heating element 110 are arranged outside of the first and second thermoplastic components. The longitudinal end portions 116 can have a lower electrical resistance than the first region 110 of the sheet 105.

[0090] In a further method step 310, the heating element can be connected to an electric circuit. For instance, each of its opposite longitudinal ends 116 can be connected to an electric circuit at an electrical contacting point 117, such as a clamp. Thereafter, in step 312, an electric potential is applied to the heating element 100 by the electric circuit. Due to the electrical conductivity of the sheet 105, electric current flows through the heating element 100. The heating element 100 generates heat depending on its electrical resistance in the corresponding regions of the different types of cut-outs 111-113.

[0091] This heat melts the thermoplastic material of this thermoplastic components 21, 22 at least at their interfacing surfaces, so that the components 21, 22 are welded together. The welding can be facilitated by pressing, in step 320, the thermoplastic components 21, 22 together. For instance, upper and lower press elements 31, 32 can be employed for the pressing of the thermoplastic components 21, 22.

[0092] Once welded the protruding longitudinal end portions 116 of the heating element 100 can be cut along the weld seam of the first and second thermoplastic components 21, 22, in step 330. These longitudinal end portions 116 are not required after successful welding. Optionally, the remainder of the cut longitudinal end portions 116, if any, may be sealed, in order to avoid exposure to the exterior.

[0093] FIG. 5 schematically illustrates a vehicle 1 having a welding zone including a heating element 100. For instance, an aircraft 1 may comprise a plurality of structural components, such as components of a primary structure that have to be welded to one another during assembly of the aircraft 1. An exemplary primary structure component can be an outer skin, a frame, a stringer, a bar, a rib or the like that forms part of a fuselage, a wing, a tailplane or other large component of the aircraft 1. Two of these primary structure components or any other components of the aircraft can be welded to one another using a heating element 100 as described with respect to FIGS. 1 to 4.

[0094] The above description of the drawings is to be understood as providing only exemplary embodiments of the disclosure herein and shall not limit the disclosure herein to these particular embodiments.

[0095] While at least one example embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the example embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a”, “an” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.