Patent Application
20230415265
Embodiments of the present invention relate to a laser welding apparatus suitable for welding a workpiece in a welding zone and a method of laser welding a workpiece.
Welding of thermoplastics comprises a process of uniting softened surfaces of the thermoplastics, generally with the aid of heat. The welding process conventionally includes application of heat and pressure, and cooling. The plastic foils to be welded to one another may be of single layer structure in the simplest case, or at least one of the welding components may comprise a layer structure of two or more layers laminated onto one another.
In the manufacturing of pouch cells, plastic foil welding is typically used to hermetically close and seal one or more open ends or rims of the pouch. A pouch cell is a type of battery which comprises staggered or folded active layers which are enclosed by a flexible outer pouch or bag comprising thermoplastic material. The open end or ends of the pouch is/are thermally welded while the metal electrodes protrude from the interior of the pouch to the exterior of the pouch through the welded end or ends of the pouch. Further, the pouch of a pouch cell typically comprises a layer structure of several layers of plastic foils and at least one metallic layer sandwiched between the plastic layers to provide a diffusion barrier which prevents substances from diffusing from the interior to the exterior of the pouch or vice versa.
In conventional methods of welding the open end or ends of the pouch, heated metal clamping jaws are used. In case of welding multi-layer plastic workpieces, the innermost plastic layers to be welded to one another have to be fused under pressure. If the fusion of the innermost plastic layers is performed using heated metallic clamping jaws, the required heat needs to be introduced through the outer plastic layers up to the innermost plastic layers via heat conduction. If the multi-layer structure includes a metallic intermediate layer or layers, the heat needs also to be transmitted through the intermediate metallic layer(s). The maximum allowable temperature of the outer plastic layers limits the temperature of the clamping jaws and thus the heat introduction, and thereby increases the processing time. By virtue of the comparably long processing time and different heat capacities of the layers in the layer structure, the welding may not be as uniform along the welding zone as desired.
US 2006/023740 A1 discloses a laser welding system including a free-spacing beam delivery laser head having a linear array at least two laser diodes. The laser head is arranged remote from the workpiece to be welded. A plurality of lenses are placed in predetermined distance from the laser diodes, each of the lenses adapted to focus the respective laser beam into a focus laser beam segment, thereby forming a continuous line of laser energy from a substantially serial combination of each focus laser beam segment. The workpiece to be welded has a first component and at least one other component to be welded to the first component, wherein the first component is substantially transmissive to the laser wavelength, the other component being substantially absorptive of the laser wavelength. This type of laser welding is also referred to as laser transmission welding, where the laser light is focused onto the interface between the plastic layers to be welded to one another.
Embodiments of the present invention provide a laser welding apparatus for welding a workpiece in a welding zone. The laser welding apparatus includes a first clamping jaw. The first clamping jaw includes an array of laser diodes arranged to emit laser light, and a transparent body arranged to receive and transmit the laser light into the workpiece. The array of laser diodes is arranged in proximity to the transparent body. The transparent body has a clamping surface arranged to come into contact with the workpiece.
Subject matter of the present disclosure will be described in even greater detail below based on the exemplary figures. All features described and/or illustrated herein can be used alone or combined in different combinations. The features and advantages of various embodiments will become apparent by reading the following detailed description with reference to the attached drawings, which illustrate the following:
Embodiments of the present invention provide a laser welding apparatus and a laser welding method which are suitable for welding multi-layer plastic workpieces.
Embodiments of the present invention also provide a laser welding apparatus and a laser welding method which are suitable for welding multi-layer plastic workpieces which comprise at least one intermediate layer non-transparent to the laser light which is arranged spaced apart from plastic layers to be welded to one another.
Embodiments of the present invention further provide a laser welding apparatus and a laser welding method which are suitable for welding an open end of a pouch cell through which a metal electrode protrudes. It is to be understood that the present invention is not limited to the welding of pouch cells, but can be used in many other applications in which thermoplastic workpieces have to be welded.
According to a first aspect, a laser welding apparatus for welding a workpiece in a welding zone is provided, comprising:
Instead of using heated metal clamping jaws from which heat is introduced into the workpiece to be welded, the laser welding apparatus according to embodiments of the invention uses at least one transparent clamping jaw through which laser light of a suitable wavelength is irradiated into the workpiece along the welding zone. A suitable wavelength of the laser light emitted by the laser diodes is within the infrared wavelength range, e.g. the range from 750 nm to 1,500 nm. If the workpiece to be welded has a multi-layer structure, with at least one intermediate layer which is non-transparent to the laser light, the laser light heats the intermediate layer by absorption. For example, the intermediate layer may be a metallic layer sandwiched between plastic layers which are more or less transparent to the laser light. An advantage of the laser welding apparatus according to embodiments of the invention is that the plastic layers arranged between the non-transparent intermediate layer and the transparent body will not be heated or at least not heated significantly so as to be damaged. From the non-transparent intermediate layer, the heat generated in the intermediated layer propagates by heat conduction through the subsequent plastic layers to the innermost thermoplastic layer which is to be welded with an adjacent thermoplastic layer of the same workpiece or of another workpiece.
The transparent body not only transmits the laser light into the workpiece, but is advantageously also used to provide the pressure required for pressing, in cooperation with e.g. a second clamping jaw, along the welding zone. Preferably, the transparent body is a single-piece transparent body.
If the welding zone is an elongated welding zone and defines a longitudinal axis, the transparent body preferably extends along the longitudinal axis and has an elongated shape. For example, the transparent body may be configured as an elongated transparent rod arranged along the longitudinal direction of the welding zone. The transparent body may be a solid body of transparent material, or a hollow body, e.g. filled with air. The clamping surface of the transparent body may be planar. If the welding zone is elongated and has a width perpendicular to the long dimension of the welding zone, the clamping surface may have a width which is adapted to the width of the welding zone. The latter may have a geometry of an elongated stripe.
The array of laser diodes and the transparent body are arranged in proximity to each other, i.e. with or without a gap between them, wherein a gap of several millimeters up to a few centimeters is possible. Thus, the array of laser diodes and the transparent body provide or form a very compact and integrated design of the clamping jaw.
The laser welding apparatus according to embodiments of the invention is suitable for welding the open ends of pouches of pouch cells in hermetically sealed fashion.
Preferred and advantageous embodiments are defined in the dependent claims and indicated below.
In an embodiment, the array of laser diodes may be two-dimensional, wherein sub-arrays of the laser diodes preferably are individually addressable to adjust an intensity distribution along the welding zone.
A two-dimensional array of laser diodes is advantageous, as it can provide much more laser light intensity and power density than a single row of laser diodes. The two-dimensional array of laser diodes may be a planar array. The laser diodes may be arranged in rows and columns. The transparent body may have a width at a side facing the laser diode array, which is adapted to the width of the laser diode array so as to collect as much light as possible from the laser diode array.
Preferably, sub-arrays of the laser diodes are individually addressable to adjust an intensity distribution along the welding zone. It is advantageous here that the light intensity introduced into the workpiece can be adjusted in accordance with the structure, including the material structure, of the workpiece along the welding zone. For example, in case of welding an open end of a pouch of a pouch cell through which one or more metal electrodes protrude, there might be some higher intensity advantageous in the region along the welding zone where the metal electrode(s) protrude(s) from the open end of the pouch, because the metal electrode(s) might conduct some amount of heat away from the welding zone. The two-dimensional array of laser diodes may comprise a plurality of two-dimensional sub-arrays, wherein it is also possible, that one sub-array comprises only one laser diode. The two-dimensional array of laser diodes may emit laser light with a total power density of up to several hundred W/cm2. By addressing only sub-arrays of the laser diodes, the power density can be reduced in certain regions along the welding zone where a reduced heat generation is desired. “Individually addressable” here means, that the laser diodes of the sub-arrays may be switched on or off independent of the laser diodes of other sub-arrays, and/or the intensity of the laser light emission can be increased or decreased in one or more of the sub-arrays independent of other sub-arrays by a suitable control of the laser module.
Thus, the light energy introduction into the workpiece may be profiled in time and space over the welding zone, and can be adapted to the locally distributed thermal masses and heat losses. The uniformity of the welding seam can thus be significantly improved.
Preferably, the transparent body is arranged to bundle the laser light passing through the transparent body such that a laser light bundle exiting the transparent body has a reduced area in a cross-section perpendicular to the propagation direction of the laser light, in comparison with a cross-section of the laser light bundle incident on the transparent body. This embodiment is advantageous if the array of laser diodes is two-dimensional, as the two-dimensional array of laser diodes may have a light emitting area which is larger than the area of the welding zone to be irradiated with the laser light. Thus, a higher power density in the welding zone may be achieved for a fast welding process. The transparent body may collect the laser light from the two-dimensional array of laser diodes and bundle the radiation onto the opposite surface of the transparent body, in particular the clamping surface of the transparent body. “Bundle” does not necessarily mean that the laser light is focused onto the clamping surface.
Preferably, the laser light may be transformed by the transparent body into a laser light line or stripe extending along the welding zone and may have a width perpendicular to the propagation of laser light which is adapted to the width of the welding zone.
The transparent body may be configured as a substantially cylindrical rod with a convex surface facing the array of laser diodes. Other shapes than a cylindrical surface of the transparent body are possible, for example an elliptical surface shape or the like. In further embodiments, the transparent body may be configured as a compound parabolic concentrator which may be terminated on the light entry side and on the light exit side with a planar face.
Preferably, the transparent body may comprise a projecting ridge having a front surface forming the clamping surface of the transparent body. In a further embodiment, the ridge may have a projecting elongated shape extending along the longitudinal axis.
The ridge provides a well-defined contact or clamping surface of the transparent body at its side facing the workpiece to be welded. In combination with the afore-mentioned embodiment, according to which the transparent body is configured to bundle the laser light emitted by the array of laser diodes, it is advantageous if the bundled light fills the ridge and emerges from the ridge into the workpiece. In particular, the cross-section of the laser light bundle exiting the transparent body may have a width which is equal to the width of the ridge in a direction perpendicular to the light propagation direction. The width of the ridge in turn may be adapted to the width of the welding zone.
Preferably, the transparent body may have a non-transmissive surface in regions immediately adjacent to the clamping surface. It is advantageous here that the laser light emerging from the transparent body into the workpiece is limited to the clamping surface, or, in combination with the afore-mentioned embodiment, to the ridge, and in particular to the welding zone. The area of energy supply into the workpiece is thus well-defined. The surface of the transparent body can be made non-transmissive by an absorbing, or more preferably by a reflective coating, which may be applied to the transparent body by vapor deposition, for example.
Preferably, the clamping surface of the transparent body may have a contour along its length which comprises different height levels along the length of the clamping surface. Different height levels may be realized by one or more recesses, indentations, or elevations along the clamping surface. Such a profiling of the clamping surface may be advantageous in case the workpiece to be welded has a profiled surface along the welding zone. For example, in case of use of the laser welding apparatus for welding a pouch of a pouch cell, the protruding metal electrode(s) may cause an uneven surface topology of the end of the pouch to be welded, due to the thickness and incompressibility of the metal electrode. By profiling the clamping surface, the clamping force provided by the clamping surface of the transparent body may thus be uniformly distributed along the welding zone.
In further embodiments, the clamping surface of the transparent body may be flexible or resilient so as to adapt itself to the surface topology of the workpiece surface.
Preferably, the first clamping jaw comprises a holding frame for holding the transparent body, wherein the holding body is arranged to dissipate heat from the transparent body. The laser module comprising the laser diode array may also be mounted on the holding frame. During use of the laser welding apparatus, the transparent body may be heated by the high intensity laser light transmitted through the transparent body. It is advantageous to avoid an excessive heating of the transparent body as it is in contact with the surface of the workpiece to be welded, wherein the surface of the workpiece might be sensitive to over-heating, for example if the surface is a thin plastic foil with a low melting point. In the present embodiment, the holding body of the clamping jaw advantageously serves as a heat sink for the transparent body so that the transparent body may be sufficiently cooled by the holding body of the clamping jaw. The holding body may be made of a material with high heat conducting capability, e.g. a metal.
Further heat management measures may be provided in that the transparent body is made of a heat conducting material and/or comprises interior channels for receiving a cooling fluid. These heat management measures may advantageously further reduce the heat load onto the transparent body. In case the transparent body is a solid body, the transparent body may be made of or comprise sapphire which is a good heat conductor.
Preferably, the apparatus comprises a second clamping jaw opposite to the first clamping jaw and arranged to clamp the workpiece in cooperation with the clamping surface of the preferably elongated transparent body of the first clamping jaw along the welding zone, wherein further preferably the second clamping jaw comprises a further preferably two-dimensional array of laser diodes arranged to emit laser light and a further preferably elongated transparent body arranged to receive and transmit the laser light, wherein the further array of laser diodes is arranged in proximity to the further transparent body, wherein the transparent body and the further transparent body are arranged to clamp the workpiece therebetween. This embodiment is advantageous for welding a pouch of a pouch cell, because the welding zone spans over one or more metal electrodes protruding from the open end of the pouch to be welded. If the welding zone would only be irradiated with light from one side, the heat generated in the workpiece could be insufficient for fusing the innermost plastic layers to one another, as some amount of heat may be discharged from the welding zone by the metal electrode(s). The light emitting area of the second clamping jaw may be smaller than the light emitting area of the first clamping jaw, and in particular may be limited to the region where higher energy introduction to the workpiece is required. Power consumption may be reduced in this way.
Preferably, the laser diodes are vertical cavity surface emitting lasers (VCSELs). VCSELs are cheap laser diodes with high conversion efficiency and output power. VCSELs are advantageous in providing the high intensity level of the laser light which is suitable for the welding process.
According to a further aspect, a method of laser welding a workpiece in a welding zone is provided, comprising:
The method according to the further aspect has the same or similar advantages and embodiments as the laser welding apparatus according to the first aspect. Further embodiments and advantages of the method according to the second aspect are indicated below.
Preferably, the method further comprises controlling the laser diodes to adjust an intensity distribution of the laser light along the welding zone. Controlling the laser diodes may include controlling sub-arrays of the laser diodes. Controlling the laser diodes may include switching on or switching off sub-arrays of the laser diodes and/or controlling the driving current supplied to the sub-arrays of laser diodes independently from other sub-arrays to adjust the output power to different levels among the sub-arrays.
Preferably, the workpiece to be welded comprises a layer structure of laminated layers comprising plastic layers transparent to the laser light, and one or more non-transparent layers embedded between the transparent layers. The layer structure may comprise a plurality of plastic layers of different materials, which are transparent to the laser light, and the one or more non-transparent layers embedded between the transparent layers may be light absorbing layers to generate heat, e.g. metallic layers or layers comprising an absorptive additive. In case of one or more metallic intermediate layers these may be aluminum layers. In particular the workpiece may have a layer structure typically used in the manufacturing of a pouch of a pouch cell.
Preferably, the method may further comprise transmitting the laser light from the transparent body through one or more first transparent layers to the non-transparent layer to heat the non-transparent layer and transfer the heat from the non-transparent layer to one or more underlying layers. Thus, the laser light does not directly fuse the plastic layer(s) to be welded, but the light energy is used to heat a non-transparent layer from which the heat is conducted to the plastic layer or plastic layers to be welded to one another.
Preferably, the workpiece is a pouch of a pouch cell comprising a metal electrode projecting from a part of a rim of the pouch cell, wherein the welding zone extends along the rim and over the metal electrode.
In an embodiment, the multi-layer structure of the workpiece may be provided with an additional absorbing layer at defined positions in the layer structure in order to introduce power at defined locations in the workpiece. For example, the intermediate non-transparent aluminum layer of the pouch may be provided with an additional infrared light absorbing layer which increases the absorption from about 20% to more than 50%, thus multiplying the energy efficiency of the welding process without the need for a high power laser module.
In a further embodiment, the transparent body of the first clamping jaw and/or the further transparent body of the second clamping jaw may be protected by a thin, flexible and transparent separation layer. The separation layer may be adapted to avoid that plastic parts of the workpiece stick at the first and/or second clamping jaw. For example, the separation layer may be a polyamide foil comprising a silicone-based glue for adhering the polyamide foil onto the first and/or second clamping jaw. Polyamide and silicone-based glue are transparent in the infrared wavelength range and resists power densities of several hundred W/cm2 without damage. Such an adhesive foil could be exchanged at regular intervals in an automated manner on the clamping jaw(s).
Before a laser welding apparatus according to embodiments of the present invention will be described, an example of a workpiece which can be welded with a laser welding apparatus according embodiments of the present invention is described first, with reference to
With reference to
The layer structure of the pouch 202 is a multi-layer structure, comprising a plurality of layers 220 to 232. Layers 220, 222, 224, 226, 230, 232 are plastic layers which are at least transparent at a wavelength in a wavelength range in the infrared spectrum. Layer 228 is a non-transparent layer, in particular a metal layer, e.g. an aluminum layer which serves as a diffusion barrier in the layer structure of the pouch 202. Layers 220 to 232 are laminated to one another. The layer thickness of the layers 220 to 232 is shown highly exaggerated in
With reference to
In conventional methods of welding the open end 204 along the welding zone 238 of the pouch 202, heated clamping jaws are used. This means that heat from the heated clamping jaws needs to be introduced through the outermost layers 220 and 220′ to the innermost layers 232′ and 232 and the additional layers 234. The heat needs also to be transmitted through the intermediate metallic layer 228. The maximum allowable temperature of the outermost layers 220, 220′ or the outer layers 220 to 226 and 220′ to 226′ limits the temperature of the clamping jaws and thus the heat introduction, and thereby increases the processing time. In view of the comparably long processing time and different heat capacities of the layers 220 to 232 and 220′ to 232′, the welding may not be as uniform as desired along the total length of the welding zone 238.
In the following, a laser welding apparatus will be described with reference to
The laser diodes 20 of the array 17 may be arranged in rows and columns to form a two-dimensional arrangement. The two-dimensional array 17 spans an area which may be larger than the area spanned by the welding zone 238 in
The first clamping jaw 12 further comprises a transparent body 18, which preferably is elongated if the welding zone like welding zone (238) is elongated. The transparent body 18 is mounted in a holding frame or holding body 26 of the first clamping jaw 12. The laser module 16 may also be mounted to the holding body 26 as shown in
The laser diode array 17 of the laser module 16 is arranged in proximity to the transparent body 18, while a small gap of a few millimeters up to several cm, e.g. 5 cm, is possible. The laser diode array 17 may be protected by a cover glass (not shown) on the light emission side of the laser module 16. The transparent body 18 may be protected by a thin, flexible and transparent separation layer (not shown) on its side facing the second clamping jaw 14. The separation layer may be adapted to avoid that plastic parts of the workpiece stick at the transparent body 18. For example, the separation layer may be a polyamide foil comprising a silicone-based glue for adhering the polyamide foil onto the transparent body 18 and the holding body 26.
The transparent body 18 is transparent to the laser light emitted by the laser diodes 20 of the laser diode array 17, and is arranged to receive and transmit laser light emitted by the laser diode array 17 of the laser module 16 into a workpiece along a welding zone, when the workpiece is arranged between the first and second clamping jaws 12, 14. When the workpiece is the pouch 202 shown in
The transparent body 18 may be configured as a substantially cylindrical rod as shown in
The transparent body 18 has a light entrance side 28 (
The clamping surface 30 of the transparent body 18 may have a contour along a length of the transparent body 18 which comprises different height levels along the length of the clamping surface 30. The contour of the clamping surface 30 is adapted to the surface profile of the work piece along the welding zone. An example of the contour of the clamping surface 30 is shown in the enlarged portion 34 in
In other embodiments, the ridge 32 may be made flexible or resilient so as to adapt itself to the surface contour of the workpiece to be welded.
As shown in
The holding body 26 may be configured to dissipate heat from the transparent body 18 during use of the laser welding apparatus 10. The transparent body 18 may be heated by the laser light passing through the transparent body 18. A too high temperature of the transparent body 18 may cause the surface of the workpiece to stick to the clamping surface 30 of the transparent body 18. Cooling the transparent body 18 is advantageous as it avoids that the workpiece sticks or adheres to the clamping surface 30. The holding body 26 may be made of a material with high heat conducting capability, in particular a metal. The holding body 26 contacts the transparent body 18 in an area as large as possible, except at the light entrance side 28 and the light exit side comprising the clamping surface, so as to provide a sufficient cooling effect.
As a further cooling mechanism to discharge heat from the transparent body 18, the transparent body 18 may have cooling channels (not shown) for passing a cooling fluid through the transparent body 18, wherein the cooling channels are arranged such that they do not disturb the light transmission through the transparent body.
When the laser welding apparatus 10 is used for welding workpieces which only require energy supply from one side (from an upper side or from a lower side), it is basically sufficient that one of the clamping jaws, e.g. the first clamping jaw 12, has a laser module 16 and a transparent body 18, while the second clamping jaw 14 may be configured in conventional manner, i.e. without a laser module and without a transparent body. However, in some instances, it may be advantageous to supply energy to the workpiece from both sides. For example, when the laser welding apparatus 10 is used for welding the pouch 202 of the pouch cell 200 as shown in
The second transparent body 56 may be configured in the same way as the transparent body 18. The transparent body 56 may be held in a holding body or frame 58 which is adapted to cool the transparent body 56.
The workpiece to be welded may be arranged and clamped between the clamping surface 30 of the transparent body 18 and a corresponding clamping surface 59 (
The laser welding apparatus 10 may further comprise a drive 60 to move the first clamping jaw 12 relative to the clamping jaw 14 (or vice versa or both) in order to open the clamping jaws 12, 14 as shown in
In an embodiment of a method of laser welding a workpiece, especially a pouch like pouch 202, along a welding zone like welding zone 238 in
Furthermore, the energy introduction may be profiled over welding zone 238 in time and spatially and may be adapted to the locally present thermal masses and heat losses.
The laser module 54 of the second clamping jaw 14 emits light only in the region of the electrode 212 for the reasons above, while the laser module 54 does not or substantially does not emit light in the regions outside the electrode 212. The area of the laser module 54 thus may be configured smaller, i.e. may have a lower number of laser diodes in comparison with the laser module 16.
While embodiments of the invention have been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; embodiments of the invention are not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.
In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single element or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures can be used to advantage.
Any reference signs in the claims should not be construed as limiting the scope.
While subject matter of the present disclosure has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. Any statement made herein characterizing the invention is also to be considered illustrative or exemplary and not restrictive as the invention is defined by the claims. It will be understood that changes and modifications may be made, by those of ordinary skill in the art, within the scope of the following claims, which may include any combination of features from different embodiments described above.
The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and/or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21 163 491.0 | Mar 2021 | EP | regional |
This application is a continuation of International Application No. PCT/EP2022/054709 (WO 2022/194514 A1), filed on Feb. 24, 2022, and claims benefit to European Patent Application No. EP 21163491.0, filed on Mar. 18, 2022. The aforementioned applications are hereby incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2022/054709 | Feb 2022 | US |
| Child | 18466859 | US |
