The Toyota Production System (TPS) describes seven different categories of waste (or muda) in the production process. The elimination of these wastes is the most important step in creating a lean production process. (Lean=No Waste.) This is the second in a series of posts describing each form of waste and where it can be found in everyday life processes.
The seven muda are Defects, Inventory, Motion, Overprocessing, Overproduction, Transportation and Waiting. This time we’ll talk about Defects.
There are a number of ways that defective elements can come into a production process:
- Materials – Sometimes the raw materials used in a process are contaminated or of too low a quality, and using these materials leads to some of the products being defective. (Getting bad parts from vendors is an example of this as well.)
- Tools – Tools that are poor quality, poorly understood, poorly maintained, or not suited to a task can create defective products.
- Training– When people do not understand a step in a process (or the process as a whole), they can easily make mistakes in their performance that will cause some of the products to be defective.
- Design– Products that are poorly designed can include pieces that fit together incorrectly, movements that do not work smoothly, etc.
- Pacing – When demand is not level, production can start to move too quickly (rushing), which leads to mistakes and thus defects. Demand being too low can cause similar problems as the pace begins to drag.
Defects are a major production problem because there are only three ways of dealing with them, all bad:
- Overlook them. Go ahead and bolt that flawed windshield on the car and hope for the best. This can work for a while, but inevitably leads to a decline in the reputation and desirability of the product or outcome you are producing. Many argue that this approach is one of the things that led American car companies to decline at the end of the 20th century.
- Reject them. Tossing out the flawed windshield rather than bolting it into a car protects your reputation, but it has a huge cost. The materials, labor, training, etc., that went into producing the windshield are lost. Too much of this, and your profitability goes out the window. Piles of rejected parts also add to inventory issues.
- Rework them. Putting the flawed windshield on a pile until some guys with tongs and glue can come around and bang it back into shape saves some of the investment you have in it, and the reworked product may be reliable enough to save your reputation. But it also has costs, eating up precious time, labor, storage space, tool use, and other resources that wouldn’t have been necessary if the product had been defect-free to begin with.
In the old-style automobile companies before lean production came along, defects were seen as acceptable and unavoidable. Cars would come down the line with parts bolted on incorrectly, glue that wouldn’t hold, paint that wouldn’t dry smooth, and a myriad of other problems. Instead of stopping the process to find out why each of these defects was happening (a big no-no), the defects would either be ignored or put aside for reworking. Entire lots behind car factories were filled with completed vehicles needing substantial fixes before they could be shipped out.
Lean automobile factories treat defects as a much more serious issue than did traditional factories. Workers are given permission to stop the production line any time a defect appears and use a problem-solving technique, such as the Five Whys, to locate the root cause of problems at their source. The assumption is that defects are not random occurrences, but are symptoms of systematic problems that will simply recur if not dealt with.
The reduction of defects is a difficult task, but it has many rewards. Fewer defects means less wasted materials, less inventory space for defective products, lower labor costs for rework, higher reliability and customer satisfaction, and higher worker satisfaction due to the increased personal responsibility.
Reducing defects is so important to lean production that a whole variant system, Six-Sigma, was created at Motorola to deal with defects. (More on Six-Sigma in a later post.) However, defects are just one source of waste in production, and reduced defects are just one of the positive results of a continuously-improving lean process.
Bringing lean concepts back into everyday life, it is often not hard to see where defects begin to crop up in day to day processes. Burnt toast leads to waste as we either have to choke down the char (ignore it), throw away the piece entirely (reject it), or scrape off the char with a knife (rework it). Failing to figure out why the dryer is staining clothes leads to some shirts being relegated to rag duty or being worn under sweaters. Using bad running form leads to calf and shin injuries.
And in our case, the dishwasher that doesn’t get dishes properly clean leads to waste as some dishes end up being rewashed, sometimes multiple times. The lean approach to this issue is to stop using the dishwasher entirely, trace the problem back to its root cause, and deal with it before moving on and creating more defects. Unfortunately, two visits from the repairman haven’t divulged the root cause, so the defects, and waste, continue. It’s a target for continuous improvement efforts in the future.
Defects can be found as an input, a transitional state, or an output of production processes, and must be stamped out at each point for the process to be truly lean.