Patent Application
20090283569
The invention relates generally to a technique for monitoring a weld operation, and more particularly to monitoring a quality level of a weld during the weld operation.
Various types of welding operations are known and are in use. For example, two or more metal sheets may be welded by a spot welding operation. Spot welding utilizes a spot welding machine that includes two copper electrodes held in jaws of the spot welding machine. The material to be welded is clamped between the two electrodes. Typically, a pressure may be applied to hold the electrodes together and a flow of electric current is introduced through the electrodes and the material. Further, the resistance of the material being welded is substantially higher than that of the electrodes. As a result, enough heat is being generated to melt the metal. The pressure on the electrodes forces the molten spots in the two pieces of metal to unite and this pressure is held to facilitate the solidification of the metal. It is desirable to determine the quality of the weld generated through the weld operation to ensure the structural integrity of the welded systems such as automotive frames.
Unfortunately, the present weld monitoring techniques are ineffective to determine the weld quality during the weld operation due to various reasons. One of the common reasons includes interference from electromagnetic noise. Ultrasonic signals from a weld system are typically cluttered in an electromagnetic environment (EMI) leading to unmonitorable signals and an undesirable signal-to-noise ratio.
Additionally, in certain systems, excess spot welds are installed in components to ensure the structural integrity of the welded system. Such redundant welds lead to relatively higher process time and additional costs for the manufacturers. Further, excess welds in the system also increase the possibility for corrosion zones on the final product.
In certain systems, destructive testing may be employed to determine the quality of the weld. Typically, the materials joined by the weld process are separated by a hammer and a chisel to assess the strength of the weld and of the material surrounding the weld. Moreover, such destructive testing may be performed on a periodic basis to determine the quality of the weld process. Such testing is relatively time consuming and also leads to material waste.
In certain other systems, offline ultrasonic systems have been used to provide an indication of the weld quality. However, these systems provide an inspection of the weld quality after the process is completed and the weld nugget has solidified. Such systems do not provide information about the weld quality during the weld operation. Further, the existing ultrasonic systems may require a relatively large time for inspecting the weld quality of all welds of a component.
Accordingly, it would be desirable to develop an improved technique for monitoring the weld operation.
In accordance with an embodiment of the invention, a system for monitoring a weld process is provided. The system includes an ultrasonic wave generator adapted to deliver an ultrasonic signal to a target material during a weld operation. The system also includes a pair of ultrasonic receiver elements with opposite directions of polarization relative to each other, the ultrasonic receiver elements configured to receive the ultrasonic signal propagated through the target material. The system further includes an electronic circuit coupled to the pair of ultrasonic receiver elements. The electronic circuit is configured to receive respective signals from the pair of ultrasonic receiver elements; wherein the respective signals comprise the ultrasonic signal and a noise signal. The electronic circuit is also configured to output the ultrasonic signal devoid of the noise signal. The system also includes a signal processor coupled to the electronic circuit, wherein the signal processor is configured to determine a quality level of a weld created during the weld operation by extracting data corresponding to the ultrasonic signal and comparing the data to a profile that corresponds to an acceptable quality level.
In accordance with another embodiment of the invention, a welding system is provided. The welding system includes a target material and a pair of welding shanks disposed on opposite sides of the target material, wherein the pair of welding shanks are configured to weld the target material. The system also includes an ultrasonic wave generator disposed on one of the pair of welding shanks, wherein the ultrasonic wave generator is configured to deliver an ultrasonic signal to the target material during a weld operation. The system further includes a pair of ultrasonic receiver elements disposed on another of the pair of welding shanks, wherein the pair of ultrasonic receiver elements have opposite directions of polarization relative to each other and are configured to receive the ultrasonic signal propagated through the target material. The system also includes an electronic circuit coupled to the pair of ultrasonic receiver elements. The electronic circuit is configured to receive respective signals from the pair of ultrasonic receiver elements; wherein the respective signals comprise the ultrasonic signal and a noise signal. The electronic circuit is also configured to output the ultrasonic signal devoid of the noise signal. The system further includes a signal processor configured to determine a quality level of a weld created during the weld operation by extracting data corresponding to the ultrasonic signal and comparing the data to a profile that corresponds to an acceptable quality level.
In accordance with another embodiment of the invention, a method of manufacturing a welding system is provided. The method includes providing an ultrasonic wave generator configured to deliver an ultrasonic signal to a target material during a weld operation. The method also includes providing a pair of ultrasonic receiver elements with opposite directions of polarization relative to each other, wherein the ultrasonic receiver elements are configured to receive the ultrasonic signal propagated through the target material. The method further includes providing an electronic circuit coupled to the pair of ultrasonic receiver elements. The electronic circuit is configured to receive respective signals from the pair of ultrasonic receiver elements; wherein the respective signals comprise the ultrasonic signal and a noise signal. The electronic circuit is also configured to output a desired signal devoid of the noise signal. The method also includes providing a signal processor configured to determine a quality level of a weld created during the weld operation by extracting data corresponding to the ultrasonic signal and comparing the data to a profile that corresponds to an acceptable quality level.
These and other advantages and features will be more readily understood from the following detailed description of preferred embodiments of the invention that is provided in connection with the accompanying drawings.
As discussed in detail below, embodiments of the invention include a system and method for online monitoring of a welding process such as, but not limited to, a spot welding process.
In the embodiment illustrated in
In operation, the target material 12 is clamped between the first and second electrodes 14 and 16 under relatively high pressure. In certain embodiments, the target material 12 includes two or more sheets of metal such as steel and aluminum. Further, a flow of electrical current is introduced through the first and second electrodes 14 and 16 and through the target material 12. As a result, a sufficient amount of heat is generated to melt the metal. The pressure on the first and second electrodes 14 and 16 forces molten spots in the two pieces of the target material 12 to unite and this pressure is held to facilitate the solidification of the metal and the formation of the weld between the two pieces of the target material 12. In the illustrated embodiment, the pressure and current applied to the first and second electrodes 14 and 16 is controlled via the welding controller 22. For example, a piston (not shown) may be employed to apply a desired pressure to the target material 12. Such a piston may be coupled to the first and second electrodes 14 and 16. In an alternate embodiment, a servomotor may be employed to apply a desired pressure to the target material 12. Further, a power supply (not shown) is coupled to the first and second electrodes 14 and 16. Again, the amount of current applied to the first and second electrodes 14 and 16 via the power supply is controlled through the welding controller 22.
As illustrated in
A signal processor 62 is coupled to the data acquisition unit 60 to process the data 64 acquired from the data acquisition unit 60. In a particular embodiment, the signal processor 60 extracts the data corresponding to the torsional mode from the ultrasonic signals and compares the extracted data to a profile that corresponds to an acceptable quality level. Thus, the quality of the generated weld is monitored in real-time through the torsional modes generated in the system 10 by the piezoelectric elements disposed on the welding shanks 20 and 26. As will be appreciated by one skilled in the art, other types of modes of the ultrasonic signals may be monitored to determine the weld quality during the weld operation. Examples of such modes include a longitudinal mode, a flexural mode and so forth. In another embodiment, the signal processor 62 employs digital pattern classification for determining the quality level of the weld. In yet another embodiment, the signal processor 62 employs a time-frequency filter to separate the torsional mode from the ultrasonic signal.
An electronic circuit coupled to the pair of ultrasonic receiver elements is provided in step 136. The electronic circuit receives respective signals from the pair of ultrasonic receiver elements; wherein the respective signals include the ultrasonic signal and a noise signal. The electronic circuit further outputs a desired signal devoid of the noise signal. In an exemplary embodiment, a differential amplifier is provided. Furthermore, a signal processor is provided in step 138 to determine a quality level of a weld created during the weld operation by extracting data corresponding to the ultrasonic signal and compare the data to a profile that corresponds to an acceptable quality level. In one embodiment, the signal processor employs digital pattern classification for determining the quality level of the weld. In another embodiment, the signal processor employs a time-frequency filter to separate a torsional mode from the ultrasonic signal.
The various embodiments of a system and method for monitoring welding described above thus provide a convenient and efficient means of utilizing an ultrasonic spot weld monitoring system in an electromagnetic noisy environment. Moreover, the method described herein facilitates real-time monitoring of the quality of the weld created during the weld operation process. Reducing the noise component in the signal and hence increasing the signal to noise ratio, enables utilizing advanced signal processing and pattern recognition techniques to provide quantitative measurements of the weld quality, such as the online measurement of the weld nugget diameter and thickness. Advantageously, the real-time monitoring of the weld enables real-time control of the weld quality. The technique also allows for usage of externally mounted ultrasonic transducers for weld monitoring, thus minimizing a cycle cost for probe replacement.
It is to be understood that not necessarily all such objects or advantages described above may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
Furthermore, the skilled artisan will recognize the interchangeability of various features from different embodiments. For example, the use of a capacitive micro-machined ultrasound transducer with respect to one embodiment can be adapted for use with a signal processor employing a digital pattern classification for determining quality level of a weld described with respect to another. Similarly, the various features described, as well as other known equivalents for each feature, can be mixed and matched by one of ordinary skill in this art to construct additional systems and techniques in accordance with principles of this disclosure.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
