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Point welding is a common technique for joining two pieces of metal between them. This process is often used in the automotive industry for body parts and chassis parts.
These welds are made using two electrodes in contact with the parts to be joined. They are traversed by a powerful electrical signal that will melt the metal. It will then solidify in the form of a round joint resembling a doughnut.
If the welding is not well done, there may be a lack of fusion between the two parts or the welding surface may be too small. In these cases, it will not be mechanically resistant enough. It is therefore important to monitor the integrity of the welds by point.
These types of indications are not detectable by optical control and destructive controls are ineffective and limited to a few parts. However, with the right equipment and technique, non-destructive ultrasonic control is fast and effective.
Olympus recommends using a EPOCH650 and a high-frequency probe.
The EPOCH650 is designed to meet the requirements of EN12668-1 and offers a full range of defect search features as standard and optional. A large number of integrated reporting tools and a comprehensive data filing system make it easy to collect inspection data and generate reports. Robust and ergonomic, this device can be used in almost any inspection environment. In addition, the capabilities of its PerfectSquare transmitter™ and digital filters improve the signal-to-noise ratio and enable it to respond to a large number of applications.
Olympus offers a set of probes adapted to this application whose frequency varies from 10 to 20 MHz. Olympus probes with a delay line use a plastic waveguide to improve coupling with the part. Localized immersion probes, or water column probes, are composed of a rubber membrane that adapts to the shape of the weld, which also improves coupling and near-surface resolution. The diameter of the sensitive element of the probe should correspond to the diameter of the weld.
This material generates multiple repetitions of background echoes. With a healthy weld, the spacing between the echoes is proportional to the thickness of the weld and the decrease in the amplitude of the echoes is related to the mitigation of the weld.
A series of standard echo mitigation should be used for a healthy weld. It is useful to make a DAC curve in order to use it as a reference.
If there is no fusion or lack of fusion between the two pieces, then the successive echoes will be close together and will have greater amplitudes.
In the case of a weld with a diameter that is too small, some of the ultrasound will be reflected by the total thickness of the two parts and some will be reflected by the weld. There are then small echoes between the echoes related to the weld.
Finally, if the welding temperature is not high enough, the weld is not fully formed and the background echoes will be less attenuated. This indication will be noticeable by the fact that the multiple echoes will have an amplitude greater than the DAC curve. Indeed, if the weld is fully formed, the structure of its grains will diffuse the ultrasonic signal and the reflected echoes will be weaker.
Thus, using an EPOCH650 and adequate sensors, Olympus offers a simple, reliable and portable solution for point welding control.
Find out more: www.olympus-ims.com
