In my last posting I finished by saying that we would look at Lean Manufacturing’s categories of waste. Because of the lengthy discussion on waste categories, we will delay our discussion on Six Sigma’s variation reduction and control strategies until my next posting. I also said that we would look at these two subjects on how they apply to the improvement of the constraint’s capacity. So let’s first start with a review of Lean’s application, focus, major assumption and expected results. We’ll then move to Lean’s categories of waste.
The basic theory behind Lean is that waste is deadly, and that anything deadly should be removed as soon as possible. In a typical Lean implementation there are five sequential steps that should be followed with the first step being that value should be clearly defined. In Lean terms, in order for an activity to be considered as value-added, it must satisfy three basic requirements. First, the activity must move the thing through the process and change it; second, the activity must be something the customer values and has no problem paying for; and third, the activity must be done right the first time. By Lean’s definition, if even one of these requirements is missing, then the activity should be considered non-value-added and should be removed if possible. So let’s now review Lean’s categories of waste.
Eight categories of waste
When Taichi Ohno originally formulated the categories of waste, he listed only seven. But more recently, an eighth category, non- or under-utilized talent, has been added to Ohno’s original list. As a means of remembering the eight categories, acronyms have been developed such as the one you see in the table below, DOWNTIME.
In the table below I have listed each of the eight categories and their respective definitions. If we look at each category and relate it to how we can increase the capacity of a process, there are clearly examples of waste that exist within a process constraint that can be either reduced or eliminated completely. Let’s look at a few of the more common ones that we typically see within process steps; but remember, we are using this list to appraise only the constraint at this time.
Removing waste in the constraint
The first category is Defects requiring rework or scrap. No process step runs “defect free” for very long, so this is an opportunity to increase our capacity. If there is a chronic problem, meaning that if the constraint is routinely producing parts that require rework or, even worse, scraps, then we should use Six Sigma’s problem solving tools and techniques and focus on determining the root cause of the problem and correct it. Category number 2, Over-production, is probably not something we’ll find in the constraint.
The next category is Waiting and of all of the categories we should be wary of, this category takes on a special level of importance. The point is the constraint should never be forced to wait for materials to work on because any minute lost at the constraint is time that can never be retrieved. The next category, Non-utilized/under-utilized talent is my favorite because if you truly want to improve your manufacturing process, the true subject matter experts are your go-to people. The SMEs are your front line workers and believe me nobody knows their processes better than the SMEs. Go to them and explain what you’re trying to do (i.e. eliminate or reduce non-value-added activities) and I promise you they will deliver. But having said this, one of the problems I have seen throughout my career is the fear of lay-offs when processes are improved. So you must commit to not reducing headcount as a result of an improvement effort because if you do, the improvement effort will stop dead in its tracks.
The next waste category is Transport. If your constraint operator is moving materials instead of producing parts, this is an excellent opportunity to use your non-constraint operators to perform this function. As I just stated, any time lost at the constraint is irretrievable, so avoid it at all costs. Inventory is the next category and includes all forms of materials including excessive amounts of raw material, work-in-process and finished product, but can also include unused or under-utilized equipment, machines, etc. Inventory in excessive amounts ties up cash needlessly and often extends cycle times.
The next category is Motion which translates to your constraint operator having to walk around as part of his or her job or even using time-reducing hand motions. The question becomes, is there a better way to produce the product within the constraint? Study the methods and if there is an opportunity to reduce motion, act on it.
The final waste category is Excess Processing which translated means that the constraint operator is doing more than is required to produce his or her parts. This is not an uncommon thing to see as operators have a tendency to develop their “own” methods over time. My recommendation is to spend time observing the process and question in a non-threatening way why things are being done. The other part of this waste that I see many times is excessive time being spent filling out paperwork as part of the work method. This is another opportunity for the non-constraint operators to assist the constraint operator.
This completes our discussion on the eight wastes so in my next posting we’ll take a look at how we can use the tools and techniques of Six Sigma to reduce excessive variation within the constraint.
Thanks for reading. See you next time.
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