In-Process Monitoring Works
by Denise Robitaille
Despite the adage that says, “You can’t inspect quality into the product,” sometimes more aggressive in-process inspections actually are the answer to elusive problems.
A manufacturer of materials used for packing and shipping was having repeated product failures in the field. Unfortunately, when the product failed, it often contaminated material that wasn’t defective, or sometimes the customer’s goods. This made it impossible to identify and sort the good units, resulting in an entire lot being rejected. Because one lot could easily constitute a truckload, returning material was not cost-effective, so customers were routinely told to return samples only for analysis and scrap the rest.
There are generally three direct costs associated with product fabrication: raw materials, equipment and labor. With this particular product line, the raw materials are the least costly of the three. The real loss to the company came in the disruption to the production schedule for the no-charge replacements and the cost associated with running the machines. This spate of problem shipments arose at the onset of the company’s busiest season. The situation needed to be addressed immediately.
A preliminary evaluation yielded the realization that there was no easily discernible cause to the problem. It could have been related to production equipment, process speeds, the operators, raw materials, ambient temperatures or packaging material--a near-perfect fishbone with the classic machine, method, manpower, measurement, material and environment.
These were the constraints facing the company:
 Its equipment is older, making it capricious and in need of constant monitoring
Extensive diagnostics require the machines to be shut down for two days
The process is affected by changes in room temperature and humidity
Analysis of the raw material would take weeks
The staff is comprised of individuals representing countries on five continents--and at least as many languages--making it difficult to recruit people who understand the process and could also work on the root cause analysis.
Subclause 8.5.2 of ISO 9001 relates to this situation. It states: “Corrective actions shall be appropriate to the effects of the nonconformities encountered.” Basically, the price tag to fix the problem should not exceed the costs generated by the effects of the problem. In this case, the expense to begin investigating all the probable causes (a necessary step in the corrective action process) was cost-prohibitive.
The company determined that it would be easier to establish more aggressive monitoring of the product in process. It devised a simple test that would indicate the probability of failure, regardless of cause. Tests are done every half-hour. Results are recorded and trended. If a sample fails the test, the machine from which it had come is immediately halted, and all product that had been manufactured since the last successful test is quarantined.
A second test level was also established. If three consecutive tests show that product is within 15 percent of the failure point, the machine operator is alerted and the line stopped. In that case, the material from the most recent lot is segregated; if a problem is detected, materials from previous lots are retrieved before shipment. Quarantine materials have bright orange stickers; accepted materials have green stickers.
The machine operator has four possible actions:
Check/adjust machine settings
Clean jigs/guides of gummy build-up
Check for tears in packaging material
Verify the consistency and thickness of the batch of raw material
If it’s obvious that purchased material is defective, a supplier corrective action is issued. If, after restarting, the next test shows the continuation of the problem, the production manager is notified for further action. To date, this has not occurred. One of the four actions has always worked.
While the operator works on the machine, the line supervisor and her staff inspect the most recently manufactured batch. A simple illustration was developed demonstrating how to quickly and efficiently check an entire pallet.
After 90 days the program was evaluated, with the following results:
The line had been stopped 13 times.
In five instances, no defects were found.
For the remaining incidents, a total of 81 cases of defective material were discarded, representing a fraction of one percent of total production--0.02 percent.
Total downtime was 185 minutes.
Number of customer complaints: zero
Ninety days later, the program continues with the same success. There has been only one customer complaint, and it was caused by a separate (and easily identified) factor.
With that kind of success rate, any justification for delving into the root cause of this problem is close to nonexistent… for now.
Denise Robitaille is a consultant, writer, trainer, lead assessor and certified quality auditor. She’s the author of The Corrective Action Handbook, The Preventive Action Handbook and Root Cause Analysis: Basic Tools & Techniques, each of which is available from Paton Press ( www.patonpress.com).
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