How to Operate an Ultrasonic Welding Machine

Abstract

The invention relates to a method for operating an ultrasonic welding machine, in which during the welding process a planar workpiece is moved continuously at a welding speed through a gap formed between a sonotrode 1 excited with a welding amplitude at ultrasonic frequencies and an anvil 2, while a welding force is applied to the planar workpiece by the anvil 2 and / or by the sonotrode 1, characterized in that during the welding stage the actual temperature of the planar workpiece is measured after it has passed through the gap, the actual temperature is compared with a defined target temperature, and the welding amplitude is varied depending on the comparison result.

Description

[Technical Field]

[0001] The present invention relates to a method of operating an ultrasonic welding machine in which a planar workpiece is continuously moved at a welding speed through a gap formed between a sonotrode and an anvil during a welding process. The sonotrode is excited at an ultrasonic frequency with a welding amplitude. As the planar workpiece, which may comprise, for example, multiple sheets to be welded together, moves, a welding force is applied to the planar workpiece by the anvil and / or the sonotrode. In most cases, the sonotrode applies the force to a stationary anvil through the workpiece. However, it is also possible for the force to be applied to the planar workpiece by the anvil. [Background technology]

[0002] When welding sheets made of various layers, it is often desired that only the sheet layers facing each other in the welding process are melted by ultrasonic incorporation, while the other sheet layers are not melted. This can be achieved by appropriately selecting the melting points of the individual layers of one sheet.

[0003] However, monolithic sheets are increasingly being used. In monolithic sheets, the individual layers are made of the same material but undergo different physical processes. For example, one layer may be uniaxially or biaxially oriented, while another layer is not. However, because these different layers are made of the same material, they have very similar melting temperatures. Therefore, when welding such sheets, the process window, i.e., the temperature range that can and must be reached between the sheets to be welded during ultrasonic processing, is very narrow.

[0004] This is especially problematic at the start of ultrasonic welding machines, because such machines heat up slowly during operation. Additionally, variations in welding speed, material thickness, and other changes in the system can occur. This can result in the process window being exceeded, causing the planar material to be welded too strongly, damaging other layers, or too weakly, causing the weld to loosen again during later use, resulting in a less-than-tight weld joint.

[0005] Furthermore, it may be necessary to intentionally change the welding speed. However, at higher welding speeds, the temperatures reached by the joined sheet layers will be lower than at lower welding speeds, under otherwise identical conditions. Therefore, with any change in the process, the ideal process parameters must again be found to ensure a reliable weld. Due to the narrow process window, this can only be achieved by highly skilled personnel. Furthermore, this can be very time-consuming. Summary of the Invention [Problem to be solved by the invention]

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method by which an ultrasonic welding machine can be operated easily and particularly reliably. [Means for solving the problem]

[0007] According to the present invention, this problem is solved by measuring the actual temperature of the planar material after it passes through the gap during the welding step, comparing the actual temperature with a specified target temperature, and varying the welding amplitude depending on the comparison result.

[0008] Therefore, if a change in the welding speed occurs during operation, this directly affects the temperature of the planar material after it passes through the gap. Such temperature deviations are determined in accordance with the present invention, and the welding amplitude is changed accordingly. For example, if the measured actual temperature is below the specified target temperature, the welding amplitude is increased in accordance with the present invention. Conversely, if the actual temperature is above the specified target temperature, the welding amplitude is reduced in accordance with the present invention.

[0009] In an advantageous embodiment, the method according to the invention is implemented within the framework of continuous adjustment within the welding interval.

[0010] The temperature changes mentioned above can occur not only due to changes in the welding speed. The material to be welded may also have thickness variations, which are also manifested in temperature fluctuations. Furthermore, the welding process is particularly initiated after a longer pause due to temperature changes, since initially cooled components, such as the sonotrode and the corresponding tool, are slowly heated up after the start of the welding process.

[0011] The method according to the invention makes it possible to significantly reduce the waste that is inevitably generated at the start of a welding process.

[0012] In a further advantageous embodiment, the welding speed and / or welding force are held constant during the welding phase. In particular, if the welding speed is varied by the user and not only by the tension in the material, the welding force is set in an advantageous embodiment depending on the welding speed. Furthermore, for example, a table can be recorded. It can be determined in the table which welding force is advantageous at which welding speed. This ensures that the welding process is at least very close to the desired process window. Fine adjustments are then made in accordance with the present invention by adjusting the welding amplitude.

[0013] In a further advantageous embodiment, during a start-up phase before the welding phase, the welding speed is increased from 0 to a defined welding speed value.

[0014] In other words, the welding phase in which the adjustment according to the invention is carried out is preceded by a start phase in which the welding parameters, i.e. in particular the welding speed, welding amplitude and welding force, are set to defined values.

[0015] Advantageously, during the start-up phase the welding amplitude is not changed depending on the comparison result.

[0016] The purpose of the start-up phase is therefore to set the welding parameters to specified values that are as close as possible to the optimum. In an ideal case, this would already result in the welding process occurring within the desired process window. However, even if the welding process does not occur immediately within the desired process window, adjusting the welding amplitude according to the present invention can still allow the welding process to occur very quickly within the desired process window. This is because the welding phase begins after the start-up phase, and during this welding phase the welding parameters are finely optimized by varying the welding amplitude depending on the measured temperature.

[0017] In a further advantageous embodiment, the start-up phase ends after a defined time and the welding phase begins, whereby, for example, the typical time required to bring the system into a quasi-continuous steady state can be used as the defined time.

[0018] Alternatively, the transition from the initiation phase to the welding phase can occur as soon as the welding amplitude reaches the predetermined welding amplitude value and / or the welding force is increased to the predetermined welding force. The transition from the initiation phase to the welding phase can also occur when the actual temperature reaches or exceeds the target temperature.

[0019] In a further advantageous embodiment, the start phase is still preceded by a standby phase, in which the welding speed is zero and the welding amplitude and / or welding pressure are held at a defined reduced welding amplitude value or a defined reduced welding pressure value, which in an advantageous embodiment is 40-60% of the value to be obtained during the start phase.

[0020] In the event of an interruption of the welding process due to a malfunction or a shortage of product, the system is not switched off completely but is shifted into a standby phase, in which the welding amplitude and / or welding force are set to a defined reduced value in order to be able to resume use as quickly as possible.

[0021] Further advantages, features and possibilities for use of the invention will become apparent from the following description of advantageous embodiments and the accompanying drawings. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a schematic diagram showing a welding machine. [Figure 2] FIG. 2 shows the time dependence of individual ultrasound parameters. DETAILED DESCRIPTION OF THE INVENTION

[0023] 1 shows a schematic representation of an ultrasonic welding installation. It comprises a sonotrode 1 and a mating tool 2. Two material webs 4, 5 are guided between the sonotrode 1 and the mating tool 2 and are welded to one another within the welding installation. Furthermore, the sonotrode 1 is excited with ultrasonic vibrations at a welding amplitude. During the ultrasonic treatment, at least the opposing regions of the material webs 4, 5 are melted, so that the two material webs 4, 5 are joined to one another, resulting in a sandwich structure 6.

[0024] The process is usually continuous: during welding, the material webs 4, 5 or the sandwich structure 6 are moved through the gap in the direction of the arrows at the welding speed. According to the invention, the temperature sensor 3 now measures the temperature of the welded material webs, i.e., the sandwich structure 6, preferably immediately after the welding has taken place.

[0025] To obtain particularly reliable welding results, it is necessary that the desired melting temperature be reached in the facing layers of the material webs 4 and 5 during welding. Even if the temperature cannot be measured at the welding point because it is covered by the sonotrode 1 or the corresponding tool 2, the temperature sensor 3 is arranged to detect the temperature as soon as the welded sheet web 6 leaves contact with the sonotrode 1. Even if the detected temperature is not the melting temperature, it is still a measure for the welding temperature that has been reached.

[0026] The melting temperature depends on many factors. These factors can change intentionally or unintentionally during continuous operation. For example, the target welding temperature can change with changes in the welding speed. Variations in the material thickness of the material webs 4, 5 also change the achieved welding temperature. Finally, the temperature is also affected by the applied welding force, welding amplitude, and the surface temperatures of the sonotrode 1 and the corresponding tool 2.

[0027] This means that at the start of the welding process the sonotrode 1 and the corresponding tool 2 are cooled and therefore the welding temperature achieved is lower than that which applies later when the sonotrode 1 and the corresponding tool 2 are at their working temperature.

[0028] According to the invention, therefore, the welding amplitude is adjusted, which in turn is adjusted depending on the result of the comparison of the measured actual temperature with a defined target temperature.

[0029] This means that the welding process can be carried out with a somewhat increased welding amplitude, as long as the involved welding tools, i.e., sonotrode 1 and counter tool 2, have not yet reached their working temperature. Speed variations can also be accommodated by adjusting the welding amplitude without deteriorating the welding result.

[0030] For illustrative purposes, seven welding parameters, a) welding speed, b) adjustment status, c) ultrasonic excitation state, d) welding amplitude, e) welding pressure, and f) actual temperature and g) target temperature, are plotted one above the other as a function of time (t) in arbitrary units in Figure 2. The following discussion concerns only the qualitative characteristic curves of the parameters, not their actual values. Because welding pressure can be calculated from welding force and the area over which the welding force is applied, welding pressure and welding force can be easily converted to each other.

[0031] The process is carried out in six stages I to VI.

[0032] Phase I is when the welding equipment is switched off. The welding speed (a), welding amplitude (d) and welding pressure (e) are zero. There is no ultrasonic excitation or adjustment. The actual temperature (g) is at its minimum.

[0033] Phase II is the standby phase. In the standby phase, the welding speed (a) is zero, but the ultrasonic excitation (c) is activated, and a reduced ultrasonic amplitude (d) and a reduced welding pressure (e) are set. In this state, a steady state already exists. Furthermore, the sonotrode and the corresponding tool are already lightly heated.

[0034] The standby phase II is followed by a start-up phase III. Within such a start-up phase, the welding speed (a) is increased from zero to a specified value. The point in time at which the welding speed is increased from zero is specifically marked in the figure.

[0035] At the same time, the welding amplitude (d) is increased to a specified value, and the same applies to the welding pressure (e). A significant temperature increase already occurs here (see FIG. 2, g). As soon as the actual temperature reaches the target temperature, a transition to welding phase IV occurs. This transition is specifically illustrated in the graph. Only in the welding phase are the welding amplitude (d) and thus the welding pressure (e) changed, which is also changed according to the difference between the measured actual temperature (g) and the specified target temperature (f). As soon as the welding process is finished, a transition to phase V occurs. Phase V is again a standby phase. This can optionally be followed by phase VI, which is a shutdown phase and essentially corresponds to phase I. However, standby phase V can alternatively again enter start phase III, which is then followed by welding phase IV.

[0036] The actual adjustment (b) only takes place during welding phase IV. The preceding standby phase II shortens the start-up time of the system. Waste can only be produced during start-up phase III, when no adjustment has yet taken place. Phase III can therefore be made as short as possible. The present disclosure also includes the following inventions. The first aspect is 1. A method of operating an ultrasonic welding machine, wherein during a welding process, a planar workpiece is continuously moved at a welding speed through a gap formed between a sonotrode excited at an ultrasonic frequency with a welding amplitude and an anvil, while a welding force is applied to the planar workpiece by the anvil and / or the sonotrode, A method of operating an ultrasonic welder, comprising: measuring an actual temperature of the planar material after it passes through the gap during a welding step; comparing the actual temperature with a predetermined target temperature; and varying the welding amplitude in response to the comparison. The second aspect is The method of a first aspect, further comprising continuously adjusting the actual temperature during a welding interval by varying the welding amplitude in response to the comparison. The third aspect is The method of the first or second aspect, wherein the welding speed and / or the welding force are held constant during the welding step. The fourth aspect is The method of any one of the first to third aspects, characterized in that during an initiation stage prior to the welding stage, the welding speed is increased from 0 to a predetermined welding speed value. The fifth aspect is A method according to a fourth aspect, characterized in that during the initiation stage, the welding amplitude is not changed in response to the comparison result. The sixth aspect is The method of the fourth or fifth aspect, wherein during the starting stage, the welding amplitude and / or the welding force is increased to a predetermined welding amplitude value or predetermined welding force. A seventh aspect is The method of any one of the fourth to sixth aspects, wherein the initiation step ends after a predetermined time and the welding step begins. The eighth aspect is A method according to a sixth aspect, characterized in that the initiation stage is terminated and the welding stage is initiated as soon as the welding amplitude reaches the specified welding amplitude value or as soon as the welding force is increased to the specified welding force. A ninth aspect is The method of any one of the fourth to eighth aspects, wherein the welding amplitude and / or welding force is maintained at a specified reduced welding amplitude value or a specified reduced welding force value during a standby stage before the starting stage. [Explanation of symbols]

[0037] 1 Sonotrode 2. Compatible tools 3 Temperature Sensor 4. Material Web 5. Material Web 6 Sandwich structure / sandwich web

Claims

1. A method of operating an ultrasonic welding machine, wherein during a welding process, a planar workpiece is continuously moved at a welding speed through a gap formed between a sonotrode excited at an ultrasonic frequency with a welding amplitude and an anvil, while a welding force is applied to the planar workpiece by the anvil and / or the sonotrode; During the welding step, measuring an actual temperature of the planar material after the planar material passes through the gap, comparing the actual temperature with a predetermined target temperature, and varying the welding amplitude in response to the comparison; 1. A method of operating an ultrasonic welder, comprising: increasing the welding speed from 0 to a predetermined welding speed value during a start-up phase prior to the welding phase; During the initiation stage, the welding amplitude is not changed in response to the comparison result; 10. A method of operating an ultrasonic welder, wherein the initiation step ends after a predetermined time and the welding step begins.

2. 2. The method of claim 1, wherein the actual temperature is continuously adjusted during the welding interval by varying the welding amplitude in response to the comparison.

3. 3. A method according to claim 1 or 2, characterized in that the welding speed and / or the welding force are kept constant during the welding step.

4. 4. The method according to claim 1, wherein during the starting phase the welding amplitude and / or the welding force is increased to a defined welding amplitude value or a defined welding force.

5. 5. The method of claim 4, wherein the initiation stage is terminated and the welding stage is initiated as soon as the welding amplitude reaches the specified welding amplitude value or as soon as the welding force is increased to the specified welding force.

6. 6. The method according to claim 1, wherein during a standby phase before the starting phase, the welding amplitude and / or welding force is held at a defined reduced welding amplitude value or a defined reduced welding force value.

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