Spot Welding Equipment Calibration: the Key to Reducing Down-Time

Equipment calibration may not be the most exciting activity, but it can go a very long way in saving you both time and money by reducing plant down-time due to process control fluctuations.

Resistance weld controls, monitors, and checkers are not self-calibrating, and you must re-calibrate them periodically to maintain accuracy. Failure to do so may result in production problems that are extremely difficult to detect because the process appears to be in tolerance.

Why is calibration so important and what are the factors that may lead to inaccuracy?

Today’s manufacturing environment calls for tighter and tighter engineering tolerances (defined as specifications which allow reasonable leeway for imperfections and variability without affecting or compromising performance), and the elimination of errors. This makes accurate calibration and maintenance of weld controls, monitors and checkers more essential than ever before. Calibration verifies that the equipment’s current, voltage, and other measurement capabilities are within a stated specification, and confirms that the instrument performs as specified when compared to a standard of known precision.

Unfortunately, there are many factors on a manufacturing floor that might contribute to inaccurate measurements or readings, and this increases the level of process uncertainty – not a good situation to be in. Some of the more important ones I can think of include product damage or abuse, aging electronic components (component drift) and, the one I consider the real kicker, human intervention.

How often should you recalibrate?

I get asked this question a lot, and am hesitant to put a stock answer out there. I do feel confident in recommending that calibration be performed – at minimum – every twelve months. That said, some companies choose to put their equipment on a six month calibration schedule. Calibration frequency can be based on a number of factors, including internal quality standards, obvious damage to the instruments, and perhaps most importantly, whether any manufacturing descrepancies have been attributed to equipment inaccuracy in the past.

It is important to point out that when the time to recalibrate comes around, you need to be sure to check the equipment and take readings before making any adjustments. If all of the readings are well within specifications, the unit does not need to be adjusted. If the readings are out of tolerance, according to your own internal quality procedures, you may need to review any product that was manufactured using the equipment to verify whether the product needs to be reworked.

Should we send the equipment back to the factory for calibration, or do it ourselves?

Some companies choose to calibrate all of their manufacturing equipment in-house, while others prefer to send it back to the manufacturer. If you decide to invest in calibration equipment and training to perform calibration in house, keep in mind these key concepts that we follow for calibrating Miyachi Unitek products at the factory:

• Calibration equipment is traceable to NIST standards
• Personnel are trained in both calibration and repair of products
• Calibration is done using specific written procedures designed for a particular piece of equipment
• Repair materials are kept in stock for quick delivery
• Service is guaranteed

If you choose to send the equipment to the factory for calibration, I recommend that you send in all of the accessories as well (toroidal coils, displacement sensors) so a complete system calibration can be done; this really is the only way to give you the highest degree of accuracy. Finally, be sure to ask for a calibration certificate and a sticker that identifies the calibration date, who performed the calibration, and the date calibration will again be required.

Proper calibration of resistance weld controls, monitors, and checkers minimizes measurement uncertainty and establishes standards that will give you the quality you are looking for. For information about Miyachi Unitek’s calibration and other services, visit us here.