Method and device for welding a separated, multi-layer product

Abstract

Method and device for welding a separated, multi-layer product.

Description

The present invention relates to a method and an apparatus for welding a singulated multi-layer product.Ultrasonic welding has been found to be a very advantageous method in many areas of product manufacture. Two centroids of ultrasonic welding are continuous methods in which, for example, multi-ply material webs are continuously welded, and discontinuous methods in which, for example, two components of an assembly are joined together repeatedly by a person in chordwise work. A continuous process is known from DE 10 2014 110 634 A1.In the field of production technology, there are still joining processes which hitherto cannot be implemented by means of ultrasonic welding, for example the continuous sealing welding of individual containers, in particular bags. During the sealing welding, a single, still open container is sealed by means of a weld seam. The container has usually been filled beforehand, for example with foods, animal feed or care products. By means of the weld seam, several layers of the container, usually two walls delimiting the container, are welded together. In seal welding, it is of considerable importance that the weld seam seals the container airtight to protect the contents from the ambient air.The ultrasonic welding methods known from the prior art are not satisfactorily suited for the continuous sealing welding of single containers / packages. In previous attempts with continuous ultrasonic welding methods, the container has been damaged, especially at its edges, or the weld has not become tight by the welding process, which is unacceptable.Discontinuous methods are suitable for the seal welding of individual bags. However, they often take longer and can only be incorporated into production sequences of flow production by considerable effort.It was therefore an object of the invention to provide a possibility for rapidly and reliably continuously welding individual products.This object is achieved by the method according to the invention and the device according to the invention.In the method for welding a single, multi-layer product by means of an ultrasonic tool, which comprises a generator, an anvil and a vibrating structure with a converter, a sonotrode and optionally a transformation piece (amplitude amplifier), the product is moved through a gap formed between sonotrode and anvil with a gap width S. The (singled out) product is welded during its movement along a welding path by the ultrasonic tool in that sonotrode and / or anvil are pressed with a force against the product and the sonotrode is excited by the generator in such a way that it oscillates with a predetermined amplitude and transmits the oscillation to the product. At least one welding parameter, preferably the amplitude and / or the force and / or the gap width, is controlled and varied during the movement of the product.Other welding parameters can also only be controlled without being varied. They can then be set, for example, to a constant setpoint value.When welding individual products, the situation in the gap is not always the same, as is the case, for example, with continuous welding methods of material webs. At some times, one product is in the nip, but not others. A particular challenge is the edge regions of the individual products, i.e. the transition between the situations with product in the gap and without. By varying one of the welding parameters, the welding can be adapted to the situation currently present in the gap and the transition can be bridged. Thus, for example, due to a reduced amplitude, less welding energy can be introduced in edge regions of the product, whereby the edges are not damaged. Advantageously, the welding path therefore starts in a first edge region of the product and / or ends in a second edge region of the product. Damage to the edges is thereby avoided.The amplitude is a usual process variable. A predefined amplitude is understood to mean a setpoint value which can be input, for example, at the ultrasonic tool.The method according to the invention is in particular a method for welding a plurality of individual, multi-layer products. In this case, a plurality of products are moved successively through the gap and each product is welded during its movement by the ultrasonic tool along a welding path, wherein the products are in particular spaced apart from one another.One application for the method is the seal welding of bags or similar packages. Bags of this type generally consist of at least two layers of a material which are generally of the same size and are placed one above the other. The plies are then bonded together at three edges (left, right and bottom), often by heat sealing. Other types of connections, for example ultrasonic welding, are also possible. The open bag thus produced can then be filled with contents. The opening of the bag must then be closed in order to protect the contents from environmental influences. The heat-sealed edge regions represent a hard edge. Ultrasonic tools experience a strong impulse at this edge, which has lead to damage in the edge regions during tests with constant welding parameters. The method according to the invention is particularly suitable for closure welding, since by varying the welding parameters an adaptation to the layers previously bonded together is also possible. In advantageous refinements, the products are accordingly closed in a materially integral manner in at least one of the edge regions before they are moved through the gap. The width of the edge regions is preferably 5-8 mm. The product of the method is accordingly preferably a bag, in particular a bag open at the top and / or a bag filled with content.The welding energy introduced into the product is significantly influenced by the amplitude. It has therefore proved to be particularly advantageous to vary the amplitude. Advantageously, therefore, for welding the product, the sonotrode is excited to oscillate with an amplitude A high where A high is preferably between 20 μm and 40 μm, and the sonotrode is excited at other times to oscillate with an amplitude A low, which is less than A high where the following applies preferably: 0<A low and / or A low< 0,5 * A high. The low amplitude A low is used especially when no product is placed in the gap. The reduction in amplitude reduces the momentum experienced by the ultrasonic tool as the edge of the products is moved into the nip. As a result, the edge region suffers less damage. Below 0.5*A high virtually no welding effect is achieved, which is also not necessary in the edge region, however, since the layers are already bonded to one another there. The amplitude is preferably not lowered to 0 so that the increase to A high takes less time. As a result, the speed at which the products are moved through the gap can be increased and / or the distance between the products can be reduced. The production is thus accelerated overall. Below 20 μm, sufficient welding is not achieved; above 40 μm, the welding can be damaged and leak. The distance between the products is preferably 10 mm to 250 mm, in particular 30° mm to 180° mm.The welding parameter of the ultrasonic tool is preferably regulated depending on the movement or the position of the product. In particular, the amplitude is set to A high when the product arrives at or before the gap and / or the amplitude is set to A low when the product leaves the gap. This ensures that the actual welding process takes place via the desired welding path. In the case of seal-welding bags, a tight and firm weld could thus be achieved without the edges being damaged.The variation of the welding parameter can take place depending on different mechanisms. Thus, the variation can take place as a function of time, i.e. in a time-controlled manner. In this case, a program can be stored in a controller of the generator, which program varies the welding parameter over time. If the speed of the products is known, then such control may suffice. The speed of the products can also be an input variable for varying the welding parameters. In order to achieve a more precise adaptation of the welding parameter, it is provided in advantageous refinements that the position of the product to be welded is detected at least once. It can thus be detected by means of a sensor unit whether the product arrives at the gap or the product leaves the gap. Subsequently, the welding parameter can be adjusted. Particularly preferably, the sensor unit sends a signal directly to the generator and the generator sets the amplitude to A high or A low optionally with a time delay. The direct connection of sensor unit and generator prevents a loss of time due to the signal processing in a controller. The signal is preferably a binary signal, as a result of which time is saved during the processing by the generator. If the sensor unit or the location of the detection of the product is spaced apart from the gap, the time which the product still takes to arrive at the gap can be compensated for by the time delay.In order to avoid damage to the product and the ultrasonic tool, a transition from a current amplitude A now to a target amplitude, in particular A high or A low, is preferably effected by a continuous adaptation (ramp) of the amplitude, wherein a slope of the ramp is preferably continuously regulated and / or wherein the ramp lies within one of the edge regions or overlaps with one of the edge regions. The same also applies preferably to other welding parameters.At different times during the course of the method according to the invention, a product may be located in the gap or the gap may be free. In order that in the last case the next arriving product can reach the gap and at the same time immediate processing of the product is possible, the gap width S of the gap is preferably set continuously by moving sonotrode and / or anvil relative to one another, wherein preferably a metal contact detection and / or a distance measurement is used as input variable for a regulation of the size of the gap and / or a setpoint variable for the gap is fixed and used as input variable for the regulation of the gap width S. In continuous welding methods, for example of material webs, it is not expedient to regulate the gap width, since material is always located between sonotrode and anvil in any case. The gap width S is preferably the shortest distance between anvil and sonotrode.As mentioned above, the product is preferably filled with contents before it is moved through the gap and welded. As a result, subsequent working steps are avoided and the method according to the invention can represent the last working step in the production of a filled product.The economics of the process are critically dependent on the speed of the products. The speed may also have an influence on the quality of the weld. At the same time, it must be ensured that the products are welded evenly and securely. Preferably, the product is moved through the nip at a rate of from 5 m / min to 100 m / min. Below 5 m / min, not enough products are produced per unit time; above 100 m / min, defects can occur during the welding.In addition to speed, the number and thickness of the layers of the product also influence the quality of the weld. The product preferably comprises at least two layers, preferably having a layer thickness of in each case between 50 μm and 300 μm. With layer thicknesses below 50 μm, the welding energy introduced can be too great and damage to the layers occurs, leading to a leaky weld. Above 300 μm, the welding energy introduced can be too low and a dense welding is likewise not achieved.The device according to the invention for welding a single, multi-layer product has an ultrasonic tool and a conveying device. The ultrasonic tool comprises a generator, a converter, a sonotrode and an anvil, wherein a gap having a gap width S is formed between sonotrode and anvil, wherein the generator is configured to excite the sonotrode in such a way that it oscillates with an amplitude and wherein the ultrasonic tool is configured to press sonotrode and / or anvil against the product with a force. At least one welding parameter of the ultrasonic tool, preferably the amplitude and / or the force and / or the gap width, can be regulated and varied. The conveying device is configured to move the separated product through the gap, preferably to move it in such a way that the product is welded during its movement by the ultrasonic tool along a welding path by the sonotrode being excited by the generator in such a way that it oscillates with a predetermined amplitude and transmits the oscillation to the product.The converter and sonotrode form an oscillating unit of the ultrasonic tool. The oscillation unit can also comprise an amplitude amplifier.The ultrasonic tool, in particular the generator, and the conveying device are preferably connected to a common control device.As described above, detection of the product is advantageous for the welding. The device therefore preferably further comprises a sensor unit which is configured to detect whether the product arrives at or in front of the gap or whether the product leaves the gap. Depending on the sensor signal, the desired welding parameter can then be varied. The sensor unit is particularly preferably connected directly to the generator. This prevents a time delay through an interposed control. In this case, the generator is configured to vary the welding parameter, in particular the amplitude, in response to a signal from the sensor unit. The amplitude can be effected, for example, by changing the frequency at which the generator excites the converter.In advantageous refinements, the sensor unit comprises at least one sensor, preferably an optical sensor and / or a capacitive sensor, which is oriented in such a way that the product is moved into a detection region of the sensor and / or out of a detection region of the sensor when it arrives at or in front of the gap and / or when it leaves the gap. In this way, the arrival at the gap or the leaving of the gap can be detected reliably. The sensor can be, for example, an optical reflection switch.The conveying device preferably comprises movable grippers which are configured to grip one or more products in each case. Furthermore, the conveying device preferably comprises a continuous conveyor, in particular a conveyor belt, by means of which the grippers can be moved. Particularly preferably, the conveying device is a linear axis system with grippers.In advantageous refinements, the sonotrode and / or the anvil have an at least partially circular outer contour and are rotatably mounted. The circular outer contour represents a physical ramp for a product arriving at the gap. This attenuates the impulse which arises when the product arrives in the gap. The rotation also reduces the impulse, since the sonotrode or the anvil can follow the product. Particularly preferably, the rotating part is even actively rotated, in particular in such a way that it is entrained with the product.As described above, the gap width S is preferably controlled. In the device, the sonotrode and / or the anvil are therefore preferably displaceable relative to one another. Preferably, a gap control device is electrically connected between sonotrode and anvil to a metal contact detection device. Alternatively or additionally, a sensor for detecting a distance between sonotrode and anvil is possible. The displaceability allows the gap width S to be adjusted. The distance sensor provides an input signal for regulating the gap width S. Alternatively, the gap width S can be fixedly set. The device is then less complex overall.The invention is illustrated and explained by way of example with reference to the drawings. It shows FIG. 1 shows an embodiment of a device for welding a single-layered, multi-layered product in a front view, FIG. 1 xthe detail X of FIG. 1, FIG. 2 shows the device according to FIG. 1 in a plan view, and FIG. 3 schematically shows the welding of a product.The apparatus 10 shown in FIG. 1 has a conveying device 20 and an ultrasonic tool 30. In this embodiment, the conveying device 20 comprises a conveyor belt 22 with gripping elements 24. the gripping elements 24 can be moved by means of the conveyor belt 22 in a conveying direction R. The conveyor belt 22 moves at a constant speed. The gripping elements 24 are configured to grip individual products 100, here bags. In this way, the products 100 are moved continuously and at the same speed in the conveying direction R. The gripping elements 24 are spaced apart from one another, so that the products 100 are also transported spaced apart from one another.The products 100 in the embodiment shown here are multi-ply bags which are open at the top and are filled with contents. The bags are only schematically shown.The ultrasonic tool 30 is shown in more detail in FIGS. 1 xand 2. It comprises a generator 36, an anvil 32 and a vibration unit 40 with a sonotrode 42, an amplitude amplifier 44 and a converter 46. The converter 46 is supplied with a voltage from the generator 36. The oscillation unit 40 is configured to resonate when the converter 46 is excited by the generator 36 with voltage of a predetermined frequency. The sonotrode 42 oscillates with an amplitude which depends, inter alia, on the excitation frequency. The amplitude is measured in particular along the main axis of the oscillation unit 40. The generator 36 is configured to excite the sonotrode 42 or the oscillation unit 40 with different amplitudes, in particular a high amplitude A high and a low amplitude A low,Sonotrode 42 and anvil 32 form between them a gap 34 which has a gap width S. The gap width S is preferably the shortest distance between anvil 32 and sonotrode 42. The low amplitude A low is 30% of the high amplitude A high( A low= 0,3 · A high). in the embodiment shown. With the low amplitude A low no or almost no welding occurs when a bag is in the gap 34. The high amplitude A high on the other hand, causes the layers of the bag to be welded together at the locations where the bag is located between anvil 32 and sonotrode 42.The gap control device between sonotrode 42 and anvil 32 is connected to a metal contact detection device. A control which can be used for this purpose is known, for example, from EP 0 790 888 B1. The gap width S is continuously regulated by the metal contact detection. Simultaneously, sonotrode 42 and anvil 32 are subjected to a force, whereby a force is exerted on the products 100 when they are located in the gap 34.The products 100 are moved in the conveying direction R by the conveying device 20 (not shown in FIG. 2 ) as described above. As a result, the products 100 pass, one after the other, into the gap 34, pass through the gap and subsequently leave the gap 34 again. If the oscillation unit 40 is excited during the movement, the layers of the respective product 100 are welded to one another when it is located in the gap 34. The bags are closed at the top in this way.The device 10 further comprises a sensor unit 60 with a sensor 62, The sensor 62 has a detection region into which the products 100 are moved when they arrive in front of the gap 34, i.e. before the respective product 100 is located in the gap 34. This state is shown in FIG. 2. When no product 100 is in the gap, the generator excites the vibration unit 40 such that the sonotrode 42 vibrates with the low amplitude A low.The sensor 62 is spaced from the gap 34, the distance being known. Since the speed of the bags is also known, the time that passes between detection and entry of the bag into the gap (time=space / speed) can be calculated therefrom. The sensor 62 directly transmits a detection signal to the generator 36 of the ultrasonic tool 30. after a preset time delay, the generator 36 excites the vibrating unit 40 to vibrate the sonotrode 42 to the high amplitude A high. The time delay is selected depending on the distance of the sensor 62 from the gap 34 and the speed of the bags (see above).The distance between the sensor 62 and the end of the gap 34 is also known. In combination with the speed of the products 100, it is accordingly also possible to determine when a detected product 100 leaves the gap 34. The generator 36 therefore excites the oscillation unit 40 again after a further time delay in such a way that it oscillates with the low amplitude A low. Alternatively, the changeover to A low can also be triggered by the sensor 62 no longer detecting the product 100. Here too, a predetermined time delay can be provided.The transition from A high to A low and vice versa does not take place abruptly, but continuously and uniformly. This transition is schematically shown in FIG. 3. The product 100 to be welded is, as mentioned above, a bag which is open at the top 108. In its edge regions 102, 104 and at the base 106, the bag is already closed by material bonding. Therefore, the bag can be filled with contents before being sealed. The conveying direction R is also shown here.Also schematically shown in FIG. 3 is the change in the amplitude of the sonotrode 42 during the movement of the bag. In the initial state, the sonotrode 42 oscillates with the low amplitude A low, The edge region 102 of the bag first strikes the ultrasonic tool 30, and the sensor 62 previously detects, as described above, that the product 100 reaches the vicinity of the gap 34. Then, the amplitude of the horn 42 is set to the high amplitude A high. The transition from A low to A high takes place along a ramp, i.e. continuously and uniformly. The increase in amplitude begins shortly before the edge region 102 enters the gap 34. The high amplitude A high is reached even before the edge region 102 is arranged completely in the gap 34. The ramp thus overlaps with the edge region 102.If the second edge region 104 leaves the gap 34, the amplitude of the sonotrode 42 is reduced along a ramp down to the low amplitude A low, The beginning of the reduction takes place shortly after the edge region 104 has left the gap 34. The reduction ends shortly after the edge region 104 has completely left the gap 34.The targeted increase and decrease of the amplitude ensures that the desired welding takes place completely in high with the high amplitude A. The path along which the bag was welded is referred to as a welding path. In the embodiment shown, the welding path thus begins in the edge region 102 and ends in the edge region 104. This procedure has proven its worth with regard to the quality of the processing, in particular at the edges of the bag. The welding begins and ends to a certain extent in the edge regions 102, 104, whereby the edges of the bag remain largely in their previous state. The previously open region of the bag is securely closed in this way and the edges remain largely unaffected.List of reference characters10 Device 20 Conveying device 22 Conveyor belt 24 Gripping elements 30 Ultrasonic tool 32 Anvil 34 Gap 36 Generator 40 Vibrating unit 42 Sonotrode 44 Amplitude amplifier 46 Converter 60 Sensor unit 62 Sensor 100 Product 102 Edge region 104 Edge region 106 Base 108 Upper end R Conveying direction S Gap widthReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2014 110 634 A1

[0002] EP 0 790 888 B1

[0035]

Claims

Method for welding a single, multi-layer product by means of an ultrasonic tool, which comprises a generator, a sonotrode and an anvil, wherein the product is moved through a gap formed between sonotrode and anvil with a gap width S, wherein the product is welded during its movement by the ultrasonic tool along a welding path by pressing sonotrode and / or anvil against the product with a force and by exciting the sonotrode by the generator in such a way that it oscillates with a predetermined amplitude and transmits the oscillation to the product, wherein at least one welding parameter, preferably the amplitude and / or the force and / or the gap width, is regulated and varied during the movement of the product.Method according to claim 1, wherein the welding path begins in a first edge region of the product and / or ends in a second edge region of the product, wherein the products are preferably closed in a materially bonded manner in at least one of the edge regions before they are moved through the gap.Method according to any one of the preceding claims, wherein the sonotrode is excited to oscillate with an amplitude A high for welding the product, A high preferably being between 20 μm and 40 μm, and the sonotrode is excited at other times to oscillate with an amplitude A low, which is less than A high preferably the following applies: 0 < A low< 0,5 * A high.The method of claim 3, wherein the amplitude is set to A high when the product arrives at or before the gap and / or wherein the amplitude is set to A low when the product leaves the gap.Method according to claim 3 or 4, wherein a sensor unit is used to detect whether the product arrives at the gap or the product leaves the gap, and the sensor unit sends a signal directly to the generator and the generator, optionally with a time delay, sets the amplitude to A high or A low.Method according to one of Claims 3 to 5, wherein a transition from a current amplitude A now to a target amplitude, in particular A high or A low, takes place by means of a continuous adaptation (ramp) of the amplitude, wherein a slope of the ramp is preferably continuously regulated and / or wherein the ramp lies within one of the edge regions or overlaps with one of the edge regions.Method according to one of the preceding claims, wherein the gap width S of the gap is continuously adjusted by moving the sonotrode and / or anvil relative to one another, wherein preferably a metal contact detection and / or a distance measurement is used as input variable for a regulation of the size of the gap and / or a setpoint variable for the gap is fixed and used as input variable for the regulation of the gap width S.The method of any preceding claim, wherein a plurality of products are successively moved through the gap and are each welded along a welding path.Method according to any one of the preceding claims, wherein the product is filled with content before it is moved through the gap and welded, and / or the product is moved through the gap at a speed of 5 m / min to 100 m / min, and / or the product comprises at least two layers, preferably with a layer thickness of between 50 μm and 300 μm each.Device for welding a singled, multi-layer product, comprising: - an ultrasonic tool which comprises a generator, a converter, a sonotrode and an anvil, wherein a gap having a gap width S is formed between sonotrode and anvil, wherein the generator is configured to excite the sonotrode in such a way that it oscillates with an amplitude and wherein the ultrasonic tool is configured to press the sonotrode and / or anvil against the product with a force, wherein at least one welding parameter of the ultrasonic tool, preferably the amplitude and / or the force and / or the gap width, can be regulated and varied, and - a conveying device which is configured to move the singled product through the gap, preferably in such a way that the product is welded during its movement by the ultrasonic tool along a welding path in that the sonotrode is excited by the generator in such a way, oscillating at a predetermined amplitude and transmitting the oscillation to the product.The device according to claim 10, wherein a sensor unit is further provided, which is configured to detect whether the product arrives at or in front of the gap or whether the product leaves the gap, wherein the sensor unit is preferably directly connected to the generator.The device according to claim 11, wherein the sensor unit comprises at least one sensor, preferably an optical sensor and / or a capacitive sensor, which is oriented such that the product is moved into a detection area of the sensor and / or out of a detection area of the sensor when it arrives at or in front of the gap and / or when it leaves the gap.Apparatus according to any one of claims 10 to 12, wherein the conveyor comprises movable grippers configured to grip one or more products each.The device according to any one of claims 10 to 13, wherein the sonotrode and / or the anvil has an at least partially circular outer contour and is rotatably mounted.Device according to one of claims 10 to 14, wherein the sonotrode and / or the anvil are displaceable relative to one another, wherein preferably a gap regulating device is electrically connected to a metal contact detection device and / or a sensor is provided for detecting a distance between sonotrode and anvil.

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