Assembly tools need periodic calibration because readings can drift over time. But how often should you be doing this?

Unfortunately, there is no simple answer. The real question is: What risks follow if your tool’s measurement values are outside of acceptable tolerance? For assembly lines, this means over- or under-tightening, both of which result in costly rework and, in worst-case scenarios, warranty and/or liability claims.

The Standard Recommendation

Quality system standards, including ISO 9001, say that a calibration frequency should be set, but don’t dictate what it ought to be. Most authorities consider 12 months to be the default period.

However, this should be adjusted as needed to reduce risk. Since every plant (and tool) is different, we recommend calculating the ideal calibration frequency for your tools based on:

Factors Influencing Calibration Frequency

Tool’s Age & History

Older tools tend to suffer more drift, usually due to mechanical wear, hardening of plastics and adhesives, resistor drift, and creep in sensors like strain gauges. As equipment ages, it’s best practice to address this drift by increasing calibration frequency.

Calibration should also be reviewed periodically, especially when a tool is found to be outside of acceptable limits, to identify any trends. An increase in drift seen over several periods should prompt a step up in frequency, perhaps moving from 12 to 6-month periods.

Physical Condition & Damaging Events

Assembly tools are engineered for life in industrial environments, but they contain sensitive components. Knocks and drops are common, and electrical shocks can occur on occasion, all of which will affect measurement accuracy. Any time an incident takes place, send a tool for calibration, even if there is no obvious damage.

Nature of Measurements

When assembly tools are used on safety-critical products, like those used in aerospace, it’s advisable to reduce the period between calibrations. In fact, some customers may even request this.

In some situations, calibration is required both before and after use to verify that the fasteners were tightened to the specified torque and angle.

Manufacturer Recommendations

Assembly tool manufacturers recommend calibration periods in terms of both calendar time and number of cycles performed. These typically suggest that a tool be calibrated after 12 months or 100,000 cycles, whichever comes first. Note that this requires counting the number of cycles (rundowns) while the tool is in use. Most modern DC torque tools have this ability.

In some cases, a manufacturer may recommend calibration after a smaller number of cycles, such as 50,000 rundowns. Always follow their advice.

Production Volume

As there are just over 500,000 minutes in a year, it’s easy to see how high-volume work could quickly hit the 100,000 cycle mark. For tools used in such environments, your tool maintenance program should be set up to initiate calibration at a frequency that hits manufacturer recommendations and reduces the risk of fastening errors.

Harsh Environments

Temperature variations, high humidity, dust and contaminants, and excessive vibration can all affect the precision of torque and angle measurements. Casting and grinding operations, fabrication shops, and plants that require washdowns are all great examples of such environments.

If any of these environmental factors are present, the calibration frequency should be increased to mitigate the risk of drift and reading errors.

Get Help Managing Your Calibration Schedules

Encore Systems can help you reduce downtime and manage risks by offering on-site tool management expertise. Our tool management program includes custom-tailored software for managing online and offline tools, online and in-lab calibration (and verification) performed by an ANSI-accredited lab in accordance with ISO 17025 standards, fast assembly tool repairs, and line calls as needed for troubleshooting and tool swaps.

Visit our website to learn more, or contact us today to request a quote.