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US-12625013-B2 - Method for determining the temperature in a joining zone

US12625013B2US 12625013 B2US12625013 B2US 12625013B2US-12625013-B2

Abstract

The invention relates to a method for determining the temperature in a joining zone in a vibration welding process, wherein a first joining partner ( 1 ) and a second joining partner ( 2 ) are welded together, characterised in that the first and second joining partners ( 1, 2 ) act as a thermocouple, wherein, using a first measuring element ( 5 ) contacting the first joining partner ( 1 ) at a cold site ( 3 ) and a second measuring element ( 10 ) contacting the second joining partner at a distance from a hot site ( 8 ), a potential difference (P 1 ) between the first and second joining partners ( 1, 2 ) is detected during the welding process: wherein the second measuring element ( 10 ) has a higher temperature than the temperature of the cold site ( 3 ) in the region of contact with the second joining partner ( 2 ) and has a material of the same type as the second joining partner ( 2 ): the potential difference (P 1 ) is compared with material-specific calibration data and processed using a data processing system ( 7 ) and the welding process is controlled according to the determined potential difference (P 1 ): the first joining partner ( 1 ) is in the form of a multi-wire cable: the first measuring element ( 5 ) is in the form of a measuring line, which is connected to the first joining partner ( 1 ) by its first end and connected to a data processing system ( 7 ) at a measuring point ( 6 ) by its second end: the first joining partner ( 1 ) and/or the first measuring element ( 5 ) are made from aluminium; the second joining partner ( 2 ) and/or the second measuring element ( 10 ) are made from copper; and the temperature of the cold site corresponds to the ambient temperature of approx. 20° and the contacting takes place in the region of the hot site ( 8 ) at a temperature greater than the ambient temperature.

Inventors

  • Guntram Wagner
  • Andreas Gester
  • Marco Thomä

Assignees

  • TECHNISCHE UNIVERSITÄT CHEMNITZ KÖRPERSCHAFT DES ÖFFENTLICHEN RECHTS

Dates

Publication Date
20260512
Application Date
20220610
Priority Date
20210708

Claims (3)

  1. 1 . Method for determining a temperature in a joining zone in a vibration welding process, wherein a first joining partner ( 1 ) and a second joining partner ( 2 ) are welded together, characterized in that the first and second joining partners ( 1 , 2 ) act as thermocouples, wherein a potential difference (P 1 ) between the first and second joining partners ( 1 , 2 ) is detected during the welding process by means of a first measuring element ( 5 ), which is in contact with the first joining partner ( 1 ) at a cold junction ( 3 ), and a second measuring element ( 10 ), which is in contact with the second joining partner ( 2 ) at a distance from a hot junction ( 8 ), wherein the second measuring element ( 10 ) has, in the region of contact ( 9 ) with the second joining partner ( 2 ), a temperature which is higher than the temperature of the cold junction ( 3 ) and a material of the same type as the second joining partner ( 2 ), in that the potential difference (P 1 ) is matched with material-specific calibration data and is processed by means of a data processing system ( 7 ), and in that the welding process is controlled according to the determined potential difference (P 1 ), in that the first joining partner ( 1 ) is designed in the form of a stranded cable, in that the first measuring element ( 5 ) is designed as a measuring lead which is connected at its first end to the first joining partner ( 1 ) and at its second end at a measuring point ( 6 ) to the data processing system ( 7 ), in that the second measuring element ( 1 ) is designed as a measuring lead which is connected at its first end to the second joining partner ( 2 ) and at its second end at a second measuring point ( 11 ) to the data processing system ( 7 ), in that the first joining partner ( 1 ) and the first measuring element ( 5 ) are made of aluminum, in that the second joining partner ( 2 ) and the second measuring element ( 10 ) are made of copper, in that the temperature of the cold junction corresponds to the ambient temperature of approximately 20° C. and in that the contacting in the region of the hot junction ( 8 ) takes place at a temperature higher than the ambient temperature.
  2. 2 . Method according to claim 1 , characterized in that the vibration welding process is metal ultrasonic welding.
  3. 3 . Method according to claim 1 , characterized in that the second joining partner ( 2 ) is designed in the form of a stranded cable and/or a solid body.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is the U.S. national stage of International Application No. PCT/DE2022/100436, filed on 2022 Jun. 10. The international application claims the priority of DE 102021117697.2 filed on 2021 Jul. 8; all applications are incorporated by reference herein in their entirety. BACKGROUND The invention relates to a method for determining the temperature in a joining zone in a vibration welding process and is used in particular for ultrasonic metal welding of dissimilar materials. Ultrasonic welding is a type of pressure welding process in which the joining partners are joined together by a spot temperature increase. Friction is generated by means of an ultrasonic oscillation, which is used in combination with a static pressure to increase the temperature in a controlled manner. This process has been used in microelectronics and packaging technology for decades. Another important application is the joining of stranded aluminum cables to copper conductors (terminals) in the manufacture of electric vehicles. For process control and quality assurance, it therefore makes sense to monitor the temperature in the joining zone and use this to identify good and bad welds without destructive testing methods. Thermocouples (tactile) as well as thermal imaging cameras and pyrometers (optical) are frequently used to determine the temperature in the joining zone during metal ultrasonic welding. These methods are affected by large measurement inaccuracies. Optical temperature measurement involves looking at the joining partners from the outside, so that only superficial temperature changes can be recorded. This means that hardly any conclusions can be drawn about the internal processes and the internal temperature of the joining zone, since the joining zone is covered by the welding tools and the joining partners themselves. Thus, only qualitative statements on the temperature are possible. In tactile temperature measurement, the measured temperature depends on the placement of the thermocouples. Thermocouples function according to the so-called Seebeck effect, i.e. if a temperature difference occurs along the length of an electrical conductor, a potential difference occurs between the warmer and colder ends of the conductor and a current flows. The magnitude of the potential difference is specific to each material. If two different electrical conductor materials are brought into contact and heated at their contact point, a potential difference can thus be measured between the cold ends of the two conductors due to the electromotive force. This correlates directly with the temperature at the hot junction. Typically, this effect is used in thermocouples, which often consist of pairings of NiCr/Ni, CuNi/Fe, etc. Since localized melting can occur during metal ultrasonic welding, it is hardly possible to determine the joining zone temperature reproducibly and precisely. Moreover, thermocouples must be inserted manually by the operator. The thermocouple represents a foreign body in the joining zone, which can negatively influence the welding process. In addition, the thermocouple is destroyed in the welding process. Due to these facts, the insertion of thermocouples into the joining zone is uneconomical for process monitoring. A method for temperature control during resistance welding is disclosed in the publication DD 2 52 778 A1, in which two measuring elements are used. During the welding process, the thermoelectric voltage superimposed on the welding voltage between two electrodes is measured between one of the electrodes and the materials to be joined, or direct measurement is carried out between workpieces of different materials in such a way that one measuring lead is conductively connected to one of the workpieces and a second measuring lead is brought into contact either with the lower electrode or with the upper workpiece. The publication JP 2006-159 277 A discloses an ultrasonic welding process with temperature measurement by a thermocouple, in which an aluminum cable is welded to a bronze base. However, the design of the thermocouple is not disclosed in the publication. The publication DE 22 10 855 C2 describes a method and a device for directly joining metal parts together and the application of the method. The metal parts are joined by energy pulses which are generated by vibration and are in the sonic or ultrasonic range. The method can be used, among other things, to join copper components to aluminum components. During the joining process, temperatures in excess of 1000° C. can occur, although these are narrowly localized. This prevents large-area heating of the components. The temperature is measured by means of a thermocouple. The energy in the joint, measured as thermoelectric potential, can be displayed at the interface of two layers to be joined. The publication DE 42 06 584 C2 describes a device and a method for joining two components by means of ultrasound. A