Robotic leak testing in the automotive industry is growing with increases expected throughout the next 5 years, thanks to increased production throughput and inspection reliability, and improved product quality. Only 5% of automotive plants currently have robotic leak-detection systems, but that number will climb to 20% or more by 2024.
How companies leak test is as important as the equipment used. A properly installed robotic station can make the difference between stellar product quality and an expensive exercise in futility. To set up robotic testing that eliminates costly human error for repetitive tests, attention to detail is critical. Five tips could help companies avoid pitfalls.
1. Meet requirements
When leak testing, have the equipment, including a high-flow leak detector and a robotic arm (properly programmed with the right instructions) working at an appropriate scanning speed. Determining whether a process will be static or dynamic dictates the exact equipment needed.
Static testing is suitable if you know where leaks typically occur on a part or assembly, for example, at certain joints. In this case, the robot arm may move at high speed before and after the measuring process but stay static during measurement. A dynamic robotic sniffer test operating at an appropriate speed is best when checking a larger surface of a component for leaks. Dynamic sniffing saves time when physically handling the part rather than during sniffing.
With dynamic robotic sniffer leak detection, the sniffer probe should move over the test piece as slowly as the cycle time of the production line will allow to provide the best test reliability, since reliability of tests increase as the probe’s speed falls. More important than speed is the distance between the probe and the surface of the part being inspected. Shorter test distances produce more accurate results.
2. Avoid crosswinds
This warning applies to robotic leak testing or driving a panel truck. Poorly timed crosswinds can make driving erratic, and similarly, a draft of air during sniffer leak detection, even from a distance, can mar results.
For best results, enclose the test area. Typically, robotic stations are enclosed in cages to ensure worker safety, so substituting acrylic glass for mesh cages would protect employees and shield the test area from air movement caused by heating, ventilation, and air conditioning (HVAC) systems or passing forklifts. In static testing, working with clam shells at the tip of the robotic arm can protect joints being tested from drafts.
3. Calibrate carefully, regularly
Calibrate systems and check frequently – typically once per shift. Guide the sniffer tip to a reference leak of a defined size, which will always cause the same leakage rate. If the system fails to determine the exact reference leakage rate, its calibration is no longer precise, and a new calibration factor must be used. The external calibration function of the sniffer leak detector can automatically determine this using the reference leak. The new calibration factor usually will differ from the old one only by a few percentage points.
4. Watch your back(ground)
The most common cause of false positive test readings for leak testing is high background concentrations of test gas. Avoid false positives by reducing background sources:
- Evacuate test parts before, after each test
- Monitor tracer-gas fill processes to ensure correct part connection
- Locate test gas supply cylinders away from test station, avoiding cylinder-change mishaps that could affect the entire station
- Thoroughly inspect gas supply lines for leaks, an obvious source of excessive underground concentration
- Prevent test-gas accumulation to ensure gradual, even test enclosure air exchange; consider replacing enclosed volume with fresh air once a minute
- Locate enclosure fresh air supply away from test gas exhaust
5. Avoid forming gas cross contamination
Forming gas (95% nitrogen/5% hydrogen) often is used as an inexpensive test gas. Industrial environments often contain other sources of hydrogen not always obvious to testers – lead-acid battery charging stations where hydrogen is a byproduct and forklift truck exhaust gases.
About the author: Thomas Parker is North American automotive sales manager for Inficon. He can be reached at firstname.lastname@example.org.