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.