Spot welding is one of the resistance welding processes and is a common technique for firmly joining two or three metal parts, usually sheets or plates of steel or aluminium. It is the most important joining method, especially in the large-scale production of car bodies, but is also used in other areas of sheet metal processing. Every day we rely on the quality of these spot welds, whether in our car or in our environment. The demands on the quality assurance of these weldings are correspondingly high and have been continuously further developed in recent years.

For a more user-friendly and faster spot weld inspection

The foundations for today’s innovative and reliable spot weld testing were laid well before the millennium. This is because at that time Göran Vogt, Managing Director of VOGT Ultrasonics, visited a customer from the steel processing industry with an innovation for the German market in his pocket: The first portable, digital ultrasonic testing device with integrated PC – the UPI 50, a product of ScanMaster. However, this customer also had a completely different inspection problem and showed Göran Vogt the application and challenges of spot weld testing. The customer used a new digital testing device for this purpose, but the application was unsatisfactory and time consuming. On the basis of the A-scans visualised on a screen, the spot weld was evaluated by the inspector. This procedure requires a lot of experience, a deep knowledge of ultrasonics and a meticulous manual documentation by the test engineer.

Göran Vogt identified the need for a new type of ultrasonic device that would optimize the inspection process, make it faster and safer. Already at that time he had acquired profound ultrasonic know-how through decades of experience in the use of manual testing devices and his engineering education. With this background, he designed the corresponding inspection software and workflow to revolutionize the market.

Shortly afterwards he used the UPI50 digital testing device as the inspection system basis and implemented his idea with the programmers from ScanMaster. The developed digital spot weld inspection device supported the operator in the evaluation of the spot weld quality (good spot, small lens, adhesive, burnt spot) and at the same time ensured an automatic and complete documentation of the test results including storage of the corresponding A-scans. For the first time, the test result could be classified and visualized accordingly and documented reliably and digitally. Due to the first integration of the MS-DOS based database into an ultrasonic device, it was now also possible to create inspection plans and to organize the processing of the welded spots to be inspected. The network connection and the central administration of the inspection data and inspection plans were also implemented shortly afterwards.

Spot weld inspection becomes smart – inspection software makes spot weld quality visible

With the product line PHAsis spot weld inspection systems VOGT Ultrasonics has now taken up another innovation and developed it further for the application in spot weld inspection: the Phased Array Ultrasonic Technology. It has been successfully used in other areas of non-destructive testing technology for years and when this technology finally became affordable for use in spot weld spection, with PHAsis began the implementation of another vision of Göran Vogt – the imaging of the spot weld quality and its lens diameter.

Fig. Phased array ultrasonic inspection systems of the PHAsis family

Phased array ultrasonic inspection technology with PHAsis is characterized by a very high inspection resolution, short inspection times and extremely user-friendly evaluation. In contrast to conventional ultrasonic technology with one oscillating element, a probe with up to 121 individual oscillating elements is used. Each of these elements can be activated individually or activated in groups. The simultaneous or delayed activation of the elements generates a steerable and focusable ultrasonic field. This field can be digitally manipulated in diameter, angle and focus point, thus allowing the operator a flexible insight into the spot weld.

Each ultrasonic wave of the ultrasonic field generates an A-scan. On the basis of these A-scans, the inspection device generates an image of the spot weld, which allows possible defects to be reliably detected (D-scan). In this case green means welded, red means not welded. A dotted circle around the welded spot shows the minimum diameter of the welding lens previously determined by the user. Other key figures which PHAsis automatically calculates are the lens diameter, residual wall thickness and sound attenuation as possible supporting evaluation criteria for zinc bonded joints.

Phased array ultrasonic testing of spot welds with PHAsis has several advantages over conventional ultrasonic testing. The imaging representation (D-scan) makes the spot weld “visible” and makes it easier to evaluate the spot weld quality. The simultaneous recording of more than 700 measuring points results in a much higher resolution for the welding lens diameter compared to conventional ultrasonic testing. The pure physical resolution is more precise than 0.35 mm. The computer-controlled manipulation of the sound field eliminates the need to convert the probe to the expected lens size.

Another special feature of PHAsis is the support of the operator with an automatic and imaging evaluation proposal based on stored parameter sets. This function now also allows the use of test personnel without in-depth ultrasound expertise.

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