In the Lean philosophy the activities in a value stream are typically divided into “value-added” and “non-value added”. Value-added activities are defined as those for which the customer is willing to pay. These include those operations to transform the raw material at each stage of production into a finished good that meets the customer’s requirements. Non-value-added activities are those for which the customer is not interested in paying for. Typical non-value added activities are wait time, inventory time, transportation time (between work centers), set up time, lot sizes, rework and over-production. Remember, a customer can be either an external customer (who is paying for a product); or an internal customer (who is the next work center).
There is a third category of activity that falls in between the first two: Non-value-added but Necessary. These are activities that the customer doesn’t ask for and doesn’t want to pay for; however, they are necessary to satisfy government regulations or quality parameters. If you agree that rework is a waste and is a non-value added activity, then you have to agree that we need to inspect the production results to make sure we are producing to our specifications. Not to inspect opens us to the risk of finding defects further down the production stream where the cost of correcting the defect may increase exponentially. It makes sense to perform inspections close to the critical operation to avoid adding more labor to a defect and wasting productive capacity.
If we agree with this common sense thinking, then how do we reduce the negative impact of quality or government inspections? The best way to address these activities is not to pretend they can’t be improved, but to find a way to perform them in a more efficient manner.
When you add inspection points to the value stream flow, you have two opportunities to improve efficiency. First, ask yourself: are we performing these activities at the proper place in the value stream? It doesn’t serve any good purpose to delay the inspection or measurement until all the labor and material has been added to the product. Look at the defects and where they occur and decide if a quick inspection step will reveal defects more quickly.
One advantage to a manufacturing cell is that if a defect is made at the first step in the process, it may be detected at the very next step. Thus, you haven’t built up an inventory of defective parts before you find the defect. The second step can be almost the same as an inspection point if the part won’t fit the set-up fixture for the second step. Immediate identification can be a key; not only to catching the defect, but to show what is causing the defect in the first place.
The second opportunity to improve the value stream flow is the use of simple “go-no go” gauges to measure critical dimensions on a part. By having these gauges ready at the work station, the operator can determine quickly whether the part he just made is accurate.
These inspection steps must come with the ability to stop production when an out-of-spec part is identified by the operator. Operators must be trained to understand that a defect is not something to hide, but a cause to raise the alarm and call in resources to fix the problem. This last issue is a training issue. If you are taking time to measure a part for compliance to specs or regulations, you are wasting your time if you try to hide the problems. Remember the “Rule of Decades”: It costs ten times more to repair a defect for each stage of production it goes through before discovery. What could be fixed with a $.10 change at stage one, will cost $1.00 to fix when discovered at stage two. It will cost $10.00 to fix when discovered at stage three. If you haven’t heard this rule or don’t believe it, try calculating the costs. Then think about the cost of a defect when discovered by the customer at his site!
Quality control has a role to play in Lean Manufacturing. Don’t fool yourself by ignoring it. Defects don’t go away by hiding them. They go away when you apply time and resources to make sure they are minimized or eliminated entirely!
Maybe we should reclassify quality and regulatory measurements as value-added in that they reduce waste?
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