Resistance Testing Welds

During a production process that includes welding operations, the finished welds must remain consistent. Weld quality proves critical in end-product implementations such as in the automotive, aerospace, or medical device industries. Operational performance of the finished product is critical in these and similar applications. Fortunately, the quality of parts produced during production can reliably be tested by recording electrical resistance of the finished weld. Therefore, QA/QC technicians must periodically test and record the resistance of finished welds with a micro-ohmmeter. This article discusses the importance of this inspection and the kinds of problems it can detect.

What is a Micro-Ohmmeter?

A micro-ohmmeter, also known as a low resistance ohmmeter, is an instrument used to measure the resistance of an electrical circuit with very low values. It is widely used to test electrical contacts, cables, and switches. Production facilities that involve welding stations also use a micro-ohmmeter to check the resistance of finished welds. Micro-ohmmeters have a high degree of accuracy and sensitivity, making them ideal for detecting small changes in resistance that may indicate a problem with the weld.

Conducting Periodic Resistance Tests of Finished Welds

Poor or failed welds can have serious consequences. Poor quality welds may result in structural weaknesses, which can lead to catastrophic failure. In high-risk applications such as aerospace and transportation, such a failure could well lead to major liability for the part maker shipping parts to the OEM. The electrical resistance of the weld provides an accurate and repeatable measure of its quality. If the resistance is too high, it can indicate a lack of fusion or penetration, which can lead to weak welds that are susceptible to cracking or breaking. On the other hand, if the resistance is too low, it can indicate a short circuit or a lack of insulation, which can cause electrical hazards.

Periodic checks of the resistance of finished welds allow product manufacturers to identify problems early on and take corrective action. Regular resistance checks verify and provide a record that the welds are of good quality and meet the required specifications. Such checks reduce the risk of failure and increase the overall safety of the structure.

Welding Problems Detected with a Micro-Ohmmeter

The results from a micro-ohmmeter weld test provide clues to a range of problems that may affect the quality of a weld. Following are some of the most common issues this inspection can detect:

1. Overly high resistance may indicate that the weld did not achieve full fusion or penetration, which can result in a weak bond.
2. High resistance can also be an indicator of cracks or porosity in the weld, which can cause the weld to fail under stress.
3. If the resistance is higher than expected, it may indicate contamination in the weld, such as dirt, oil, or rust. This can weaken the bond and reduce the strength of the weld. Destructive testing may be necessary if the contaminant is not readily identifiable.
4. An extremely low resistance reading can indicate the potential for an electrical hazard, such as a short circuit or electrical fire.
5. If the resistance readings of the weld are inconsistent, they may indicate that the welding technique is incorrect or that the equipment was not set up correctly.

Conclusion

In production environments, it’s critical to measure the resistance of finished welds to assure ongoing quality and safety of the structure. This inspection can detect a full range of problems as noted above. Periodic inspections with a micro-ohmmeter will identify such problems so that corrective action can be taken. This reduces the risk of failure and increases the overall safety of the structure. Therefore, it is crucial to include this periodic micro-ohmmeter inspection as part of the quality control process for all welding applications.

The Advanced Energy's TEGAM 1750 micro-ohmmeter, recognized as the fastest precision micro-ohmmeter in the industry, now ranks as the number one choice in manufacturing environments. The instrument applies multiple techniques to achieve its impressive accuracy of up to 0.05%. The 1750 can set-up, zero-out thermal error, acquire data and make its first reading in less than 12 milliseconds. The instrument is the premium programmable micro-ohmmeter. It operates via either the front control panel or over the bus via multiple interfaces including IEEE-488, RS-232C, and RS-422 to maximize programming efficiency. The same programming command set is used for each interface. Front panel indicators provide continuous status of all monitored operations.

High Speed Micro-ohmmeter 1750