ultrasonic welding device

Abstract

Ultrasonic welding device with a vibrating assembly comprising a sonotrode and a converter, where the oscillating structure can be set into a resonant oscillation by the converter, wherein the sonotrode can transmit the resonant vibration to a product to be welded in order to produce welds on or in the product, characterized in that the ultrasonic welding device is configured to produce a certain number of welds in a probing phase of an ultrasonic welding process, wherein an actual value is determined for a process parameter for each weld, wherein the ultrasonic welding device is set up to automatically determine at least one limit value for the process parameter from the actual values ​​of the welds, wherein the ultrasonic welding device is set up to produce welds in a serial phase of the ultrasonic welding process, wherein an actual value is determined for the process parameter for each weld, wherein the ultrasonic welding device is set up to automatically classify as acceptable welds in the serial phase whose actual value meets the limit value.

Description

[0001] The present invention relates to an ultrasonic welding device. Ultrasonic welding devices are known in the prior art. They are used, among other things, to join components together by means of a material bond. For this purpose, ultrasonic welding devices have a sonotrode that transmits an ultrasonic vibration to the components. The sonotrode is part of a vibrating assembly, which additionally includes a converter and optionally an amplitude transformer. The vibrating assembly is excited by piezoelectric elements in the converter at a defined frequency, causing it to vibrate at resonance (resonant vibration). Friction arises in the components or at interfaces between components due to the vibration, which ultimately leads to the melting of the components. When the ultrasonic vibration ceases, the components cool down again and the material bond is formed.

[0002] Ultrasonic welding can be a continuous or a discontinuous process. Continuous welding is used, for example, to weld webs of material together; discontinuous welding is used, for example, to seal tubes, bags, or milk cartons with a weld seam. In addition to plastics, metallic components, such as wires, can also be welded together.

[0003] Ultrasonic welding is a cost-effective and highly reproducible process, which is why it is widely used. However, as with any manufacturing process, there are negative factors that can lead to some welds not meeting quality requirements. These quality requirements can be defined in various ways. For example, even a visual irregularity in a weld seam can be unacceptable. In more serious cases, a defective weld can lead to leaks. Welds that do not meet the quality requirements are rejected.

[0004] To minimize rejects, the process parameters in ultrasonic welding are controlled, regulated, and / or measured. These process parameters include, in particular, welding time, welding path, welding energy, welding power, welding amplitude, and welding force. Often, some of these parameters are predefined (controlled), while others are determined automatically.

[0005] The parameters differ in that some parameters are very easy to control, such as welding time, whereas other parameters can only be controlled poorly or indirectly, such as welding energy.

[0006] As with many work processes, ultrasonic welding is also subject to parameter fluctuations. Even with a fixed welding time, the resulting welding path can vary from product to product. Reasons for this include, for example, tolerance-related deviations in the dimensions of the parts being joined, their positioning in the ultrasonic welding device, or the speed at which they move during the welding process.

[0007] There are various ways to reject products where the welding does not meet quality requirements. One option is to examine each individual product for compliance with quality requirements. However, this approach is extremely time-consuming and often uneconomical.

[0008] Therefore, it is common practice to define limit values ​​for individual parameters. If a product is manufactured within these limit values, the weld is assumed to meet the quality requirements. A product where a welding parameter falls outside the limit values ​​is automatically rejected, regardless of whether the weld is actually defective. In the past, these limit values ​​were often set based on experience. This approach is prone to errors, lacks transparency, and is difficult to track. In particular, it can happen that a process parameter continuously increases or decreases from weld to weld (so-called "runaway" or "drift"). In the past, this behavior was sometimes detected too late, resulting in an unnecessarily high amount of scrap.

[0009] Therefore, the object of the invention is to simplify the classification of welds in ultrasonic welding.

[0010] This task is solved by an ultrasonic welding device with a vibrating assembly comprising a sonotrode and a converter. The vibrating assembly can be set into resonant vibration by the converter. The sonotrode is configured to transmit the resonant vibration to a product to be welded in order to create welds on or within the product. The welds are formed by internal friction and / or friction at interfaces. The ultrasonic welding device is characterized in that it is configured to produce a specific number of welds during a probing phase of an ultrasonic welding process, with an actual value being determined for a process parameter for each weld. The ultrasonic welding device is further configured to automatically determine at least one limit value for the process parameter from the actual values ​​of the welds.The ultrasonic welding device is further configured to produce welds in a serial phase of the ultrasonic welding process, whereby an actual value is determined for the process parameter for each weld, and the ultrasonic welding device is configured to automatically classify welds in the serial phase whose actual value meets the limit value as acceptable. Acceptable means that the weld is not a reject.

[0011] This method allows for the automated determination of the actual process parameter values ​​that produce high-quality welds. The limit values ​​can be determined quickly, easily, and automatically. Process deviations are prevented early on. Overall scrap is reduced, and the rejection of otherwise good welds occurs less frequently. Finally, the limit values ​​are set independently of the individual employee's knowledge level, making the rejection process more objective.

[0012] Preferably, the ultrasonic welding device is configured to automatically classify welds whose actual value does not meet the limit as rejects during the serial production phase and / or to issue a message when a weld whose actual value does not meet the limit occurs. The message can be, for example, an audible or a visual signal. Based on the message, without an increasing number of messages, an operator can recognize that the process is deviating from the target.

[0013] The ultrasonic welding device is preferably configured to classify the welds produced during the probing phase as acceptable or reject by means of a quality inspection, whereby preferably only the welds classified as acceptable are used to determine the limit value. The quality inspection makes the determination of the limit value more precise. Since drift often only occurs after some time in many processes, the quality inspection of the first welds can often be omitted, with these welds then being assumed to be acceptable.

[0014] Furthermore, an ultrasonic welding process is disclosed for solving the problem, in which multiple welds are produced in one or more products. Initially, in a probing phase, a specific number of welds are produced, with an actual value determined for a process parameter for each weld. From the actual values ​​of the welds, at least one limit value for the process parameter is determined. In a subsequent serial production phase, welds are produced, with an actual value determined for the process parameter for each weld. Welds whose actual value meets the limit value are automatically classified as acceptable.

[0015] This ultrasonic welding process offers the same advantages as the ultrasonic welding device.

[0016] The ultrasonic welding process is preferably carried out by the ultrasonic welding device. The ultrasonic welding device preferably comprises a control unit, which is particularly configured to carry out the ultrasonic welding process at least partially.

[0017] In advantageous further developments of the ultrasonic welding process, it is provided that in the series production phase, welds whose actual value does not meet the limit value are automatically classified as rejects and / or that a message is issued when a weld occurs whose actual value does not meet the limit value.

[0018] In advantageous further developments of the ultrasonic welding process, it is provided that the welds produced in the probing phase are classified as acceptable or as rejects by a quality inspection, whereby preferably only the welds classified as acceptable are used to determine the limit value.

[0019] In advanced versions of the ultrasonic welding process, quality control can be automated, particularly through visual inspection using a camera or height measurement, or performed manually. Automated quality control is faster but more prone to errors.

[0020] In advantageous further developments of the ultrasonic welding process, it is provided that the quality inspection includes a leak test of the weld.

[0021] The rejection of welds can be achieved by physically removing the affected products or by storing information in a database, particularly a database of the control device or a database connected to the control device. Storing this information can, for example, associate a specific weld with the characteristic "reject," "does not meet quality requirements," or "inspect separately."

[0022] In advantageous further developments of the ultrasonic welding process, it is stipulated that the process parameter is at least one of the following: - Welding time - Sweat path - Welding energy - Welding performance - Welding amplitude - Welding force

[0023] By setting limit values ​​for several process parameters, the production of welds from different directions is limited, allowing for a very high degree of reliability in weld quality assessment. The various parameters complement each other advantageously, resulting in a high level of production reliability overall.

[0024] In advantageous further developments of the ultrasonic welding process, it is stipulated that two limit values, an upper limit and a lower limit, are determined and defined. For process parameters where the actual values ​​can deviate both upwards and downwards, the provision of two limit values ​​is advisable.

[0025] Limit values ​​can be set for one or more process parameters. It is preferred to set limit values ​​for those process parameters that are not predetermined by the process itself, but rather for those that result from other process parameters. For example, if a web of material moving at a constant speed is being welded and a specific welding time is specified, the actual welding path can then be measured and compared to the limit values. If the actual value is within the limit values, the weld is automatically classified as acceptable by the ultrasonic welding device.

[0026] In advantageous further developments of the ultrasonic welding process, it is provided that a maximum or minimum value of the actual values ​​determined during the probing phase is defined as a limit value, optionally plus or minus a tolerance value, for example 5%. However, preferably only actual values ​​at which the weld was classified as acceptable are considered.

[0027] The number of welds performed during the exploratory phase is preferably > 10, and particularly > 50. The more welds are performed and, in particular, subsequently classified with regard to their quality, the better the limit values ​​fit and the less "incorrect" rejects are produced. Conversely, if too many welds are performed, the process becomes uneconomical. The number of welds performed during the exploratory phase is therefore preferably < 1000, and particularly < 200.

Claims

[1] Ultrasonic welding device with a vibrating assembly comprising a sonotrode and a converter, where the oscillating structure can be set into a resonant oscillation by the converter, the sonotrode can transfer the resonant vibration to a product to be welded in order to create welds on or in the product, characterized by , that the ultrasonic welding device is set up to produce a certain number of welds in a probing phase of an ultrasonic welding process, whereby an actual value is determined for a process parameter for each weld, wherein the ultrasonic welding device is set up to automatically determine at least one limit value for the process parameter from the actual values ​​of the welds, wherein the ultrasonic welding device is set up to produce welds in a serial phase of the ultrasonic welding process, wherein an actual value is determined for the process parameter for each weld, wherein the ultrasonic welding device is set up to automatically classify as acceptable welds in the serial phase whose actual value meets the limit value. [2] Ultrasonic welding device according to claim 1, wherein the ultrasonic welding device is configured to automatically classify welds whose actual value does not meet the limit value as rejects during the serial production phase and / or to issue a message when a weld whose actual value does not meet the limit value occurs. [3] Ultrasonic welding device according to claim 1 or 2, wherein the ultrasonic welding device is configured to classify the welds produced in the probing phase as acceptable or as rejects by means of a quality check, preferably using only the welds classified as acceptable to determine the limit value.