No-leak demand prompts 100 percent inspection

How do you satisfy a customer that wants a reject rate on deliverables of zero ppm for a program that produces three million parts per month? Easy. You test every part before it goes out the door. That’s what Omni Plastics does for its dispensers, and in more than two years, the molder has never had a product failure.

The dispenser consists of a body and spout, molded of polyethylene and used as a closure on a blowmolded bottle that dispenses a food product. There is one simple requirement of the dispenser. It cannot leak. If it does not seal properly—particularly during shipping—and leaks the contents of the bottle, the manufacturer is responsible and liable for all damage and associated costs.

Steven Young, manufacturing engineering manager at Omni, says that, considering the volumes his customer produces, even a leakage rate as low as 1 percent is an unacceptable liability. “Previous valves have had leakage,” he says. “Not too bad, say six out of a million, but that was enough for the manufacturer to demand a change.”

The dispenser’s base and spout are molded separately, assembled, and then tested to verify that a seal has been established between the mated parts. In order to test every dispenser, Young says Omni needed something fast (one dispenser per second) that could test multiple parts simultaneously. The company had considerable experience with testing methods, but had yet to find anything that could meet the requirements.

A positive air flow test Omni had used in the past was fairly effective, but took up to 8 seconds per dispenser. A system that tested up to four dispensers at once was faster, but rejected all four caps if one failed the test.

For help, Omni turned to a relatively unknown company in Salt Lake City, UT called Uson Inc., which said it could provide multiple-dispenser testing on independent circuits, which means that only failed parts are rejected.

The system is called the Sprint LC-4PC, and it works like this:

1. Molded bases and spouts are delivered to a vibrator/separator, from which a pick-and-place robot pulls parts and assembles dispensers.

2. Another robot picks up the assembled dispensers and mounts them, four at a time, on fixtures at the testing station. Each fixture has an opening shaped like the one on the blowmolded bottle.

3. In less than a second each dispenser is filled with pressurized air, and in another half second the air is stabilized.

4. During the next 2 seconds the Sprint system measures pressure decay over a set period of time. Each dispenser’s decay is measured and displayed independently on the device’s control screen.

5. Dispensers with pressure decay that exceeds the threshold are deemed failures, flagged by the system, and removed by the robot for recycling. Dispensers that pass the test have a tamper-evident tag attached and are used on the bottle.

All of this happens in less than 4 seconds, says Young. That’s nearly one dispenser a second, 3000 every hour. The company molds three million dispensers a month. Data for every test is saved by the Sprint system and output to Omni’s PLC. The unit meets ISO 9000 and FDA GMP requirements and is calibrated by Omni to maintain consistent quality. “We have produced millions of parts a month,” Young says, “we’ve been in this third-generation product for two years, and we’ve had zero parts come back for leakage.” The molder has instilled such confidence in the customer that dispensers are shipped directly to the facility where bottle and food product meet.

The Sprint LC-4PC four-channel concurrent testing system costs about $20,000. A standard one-channel tester starts at $9000. A base system can provide air pressure ranging from 3 to 150 psi; for a little more money the unit can go up to 500 psi. The system will store up to 99 programs.

A PLC interface must be purchased separately.