Lean Manufacturing in Simple Terms: Error Proofing

Whenever I think of manufactured items coming down a production line, I always recall the old episode of I Love Lucy, where Lucy and Ethel are responsible for wrapping individual chocolates as they pass along the conveyor. Everything is fine at first, but soon the line gets faster and faster, and the girls are forced to eat or hide most of the candy in the clothing so that their supervisor doesn't find unwrapped chocolates farther down the way. Lucy and Ethel weren't performing quality inspections, but many companies examine their finished product in a similar fashion, and when the process speeds up, the inspection starts to miss articles that may be defective. The result is that the customer could end up with a non-compliant product, become dissatisfied, and take his business elsewhere.

In the world of lean manufacturing, where the objective is to reduce waste at all costs, post-production quality inspections can be very ineffective. After all, what can be done with substandard parts after they are already built? Chances are that they are either discarded, or returned back to the process for re-work. Both options cost money.

Lean manufacturing methods focus more on error proofing than on defect detection. Locating the problem within the system that allows for even a small percentage of products to be defective is more effective than discarding the bad pieces. Eliminating the cause of the problem before it creates defective items reduces material costs, labor performed for repair or rework, and increases customer satisfaction since he will be getting exactly what he ordered.

Obviously, lean manufacturing methods are different for each different type of business. However, error proofing in any manufacturing system should focus on three specific areas.

a) Error Proofing Your Equipment. Lean manufacturing methods that reduce the variation in the way your product is fabricated must include the error proofing of your equipment or work stations. Automatic aborts or audible alarms that warn the operator when a condition has become outside set control levels are excellent lean manufacturing additions. Installation of hard-mounted guide rails that allow only the right size article to pass a particular point is another good example. You get the idea...anything that automatically maintains the limits established for a controlled process should be considered when designing your production equipment and fixtures.

b) Error Proofing Your Operators. Everyone knows that to err is human, but too many botched attempts when manufacturing a product, and your profits start sailing south. Lean manufacturing methods must include the special training of operators. Error proofing the worker includes the process of making sure he has the proper knowledge to do his job, the absence of distraction in his work area, and making sure he understands the importance of constant focus. Unlike machinery, the human worker requires reasonable rest periods and ways to combat the dangers of boredom on the job. (When an operator is ink stamping 500 parts every single day, sooner or later he is going to stamp one upside down.) In today's world when so many of your competitors are practicing lean manufacturing methods, your workers need to be trained to understand that even one mistake can be costly to customer satisfaction and the company's bottom line.

c) Error Proofing Your Processes. Error proofing your written instructions or processes is another way to practice good lean manufacturing. The workers on the plant floor should have no questions about the written instructions they are asked to follow. This means that the language should be clear and precise, and should include visual aids, where necessary. Error proofing can be accomplished as easily as having a number of different people read and comment on written instructions before they are taken to the floor for use. One person may catch an error that the previous proof reader did not, or another worker may have a better method of describing the right process, and then suggest improved wording.

Error proofing obviously takes extra time. You will be looking at parts of your manufacturing system inside and out, even before the fabrication begins. But the benefit of getting more profit because of reduced waste will make the effort well worth the trouble.