Optimizing the Stabilization Phase to Reduce Leak Test Cycle Time

An unnecessarily long test cycle has a direct production cost. If a leak test cannot meet required throughput goals, manufacturers often add test stations. This increases capital costs, floor space, and maintenance requirements.

Attempting to reduce cycle time is one strategy used to boost throughput without adding stations, but this must be done carefully and with validation. Failure to ensure sufficient time for each stage of a leak test process can cause false rejects, increasing scrap and rework, or false accepts, which become a problem in the field.

Balancing leak test cycle time and measurement accuracy can be challenging. The goal is the shortest cycle that produces repeatable, reliable results. Optimizing the stabilization phase can be used to reduce leak test cycle time without compromising measurement accuracy.

The Role of the Leak Test Stabilization Phase

Filling or evacuating a test part changes the temperature of the air inside it. If the part has not returned sufficiently toward ambient temperature before measurement during the stabilization phase, the resulting pressure change can appear as a leak.

Flexible parts introduce another effect: expansion or mechanical settling under pressure. This can produce a similar measurement signature.

These effects can be significant compared with the actual leak signal. A temperature change of approximately 1 Kelvin can produce a pressure shift of hundreds of Pascals at near-constant volume, while a typical limit leak may produce only a few Pascals.

Stabilization time allows these thermal and mechanical effects to settle before measurement. It is therefore important that reducing stabilization time be approached with a careful framework to ensure sufficient time for a reliable, repeatable measurement.

How to Determine the Minimum Stabilization Time

A systematic study can identify the shortest acceptable stabilization period:

1. Establish a baseline. Run the test with generous fill, stabilization, and measurement times. Confirm that the fixturing, tubing, and connections are sufficiently leak-tight.
2. Measure current repeatability. At the existing stabilization time, test a known-good part and a part at the reject limit. Use these results as the baseline for comparison.
3. Reduce stabilization time incrementally. Repeat the study at each shorter setting. Look for increased variation or a plateau pattern in which early measurements differ from later cycles.
4. Confirm separation from the reject limit. Repeatability alone is not sufficient. The test result must remain clearly separated from the acceptance threshold.
5. Select the shortest time with adequate margin. Do not select the shortest setting that barely passes. Select a setting where variation remains comfortably below the measurement signal. As a general guideline, variation should be well below 10% of the measurement signal.

The study should be repeated for each different part design. Note: Rigid parts typically stabilize faster than plastic or elastomeric components.

What Happens When the Stabilization Phase Is Too Short

Insufficient stabilization can produce several recognizable symptoms:

• False rejects: Residual thermal effects are interpreted as leakage.
• Systematic measurement error: Results may be repeatable but consistently offset from the true stabilized value.
• Greater sensitivity to ambient conditions: Changes in shop-floor temperature or airflow have a greater effect on results.

Stabilization time should also be reviewed when process conditions change. A tighter leak-rate specification or higher variation in incoming part temperature may require additional stabilization time.

Offset vs. Volume Adjustment

After establishing stabilization time, consider how the instrument converts the measured pressure or flow signal into the displayed leak rate.

Volume adjustment calibrates the displayed leak rate against a calibrated standard leak. It provides greater traceability and is generally preferred in documented quality systems.

Offset calibration zeros the test against a known-good master part. This compensates for predictable non-leak behavior, such as expansion or creep, rather than waiting for those effects to subside. It can reduce cycle time, but its accuracy depends on the master part remaining representative. The master should therefore be re-verified regularly.

Using the above frameworks to validate your new leak test parameters, manufacturers can confidently optimize the stabilization phase to reduce the overall leak test cycle time, boosting throughput and production line efficiency.

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With more than 40 years of experience in leak testing, innomatec supports manufacturers worldwide with the design, validation, and optimization of leak testing processes.

Do you want help to determine the efficiency of your leak test process? Contact innomatec to discuss your application.