In every manufacturing process, our aim is to add value to a product that the customer will pay for. While adding value to our products, there are tasks that must be done to complete the work but don’t directly add value; set-ups and inspection, to name a few. Then there are the other activities that occur during production that are waste. Waste is anything that creates no value that the customer is willing to pay for. Waste is defined in terms of value therefore we can only know the waste by first knowing the value first. Waste therefore is relative to the customers needs.
How do we begin to “See” the waste in our production systems? We begin to investigate the value adding steps and cycle times in our process, through a Value Stream Mapping process. Out of this process we now understand how long the value adding steps take and the overall lead time it takes to get a part all the way through to the customer. We realise that there is always a BIG difference between these two times. The difference between value adding time and the lead-time time provides us with oppportunity to remove the hidden wastes in the value stream. And the difference in times is where we can begin to focus on and discover where waste are hidden.
The 7 wastes (or Muda) have been defined by Taiichi Ohno, the father of the Toyota Production System, and they have become known as the 7Ws.
The orginal seven muda (Wastes) are:
- Transport (moving products that are not actually required to perform the processing)
- Inventory (all components, work in progress and finished product not being processed)
- Motion (people or equipment moving or walking more than is required to perform the processing)
- Waiting (waiting for the next production step)
- Overproduction (production ahead of demand)
- Over Processing (resulting from poor tool or product design creating activity)
- Defects (the effort involved in inspecting for and fixing defects)
Note this has now been expanded to include an eighth waste of “Non-utilized Human Resources/Talent”.
So what are the 8Ws?
- Defects – The simplest form of waste is components or products that do not meet the specification. The Toyota quality achievement came with the switch from Quality Control to Quality Assurance – efforts devoted to getting the process right, rather than inspecting the results.
- Over-Production – A key element of JIT was making only the quantity required of any component or product. This is the main challenging point to the Western premise of the Economic Order Quantity (EOQ) upon which MRP system are built on. This defines the fixed ordering costs, built around set-up times, and thus the need to spread these fixed costs over large batches. The Toyota production system moved from long set-ups to Single Minute Exchange of Die (or SMED).
- Waiting – Time that is not being used effectively can only be a waste – we are incurring the cost of wages and all the fixed costs of rent, rates, lighting and heating so we should use every minute of every day productively. The Toyota production system is focused on the reasons why machines or operators are under-utilised and set about addressing them all. Thus we have new tools for preventive maintenance, the creation of flow and the emphasis on takt time,
- Transporting – Moving items between areas, building or factories incurs a cost, in energy to initiate the movement – such as the gas absorbed by a fork lift truck. However there is much more than just the accounting costs; the movement brings another costs. Managing a factory with operations spread apart is much more difficult than when the subsequent stages are located in the same work cell adjacent to one another.
- Movement – Separate for transport of items is movement. People spending time moving around the plant or cell is equally wasteful. The time a machine operator wastes walking around in order to fine a piece of tooling or spanner could be better utilised if we improve housekeeping by locating every needed in place that is close at hand.
- Over Processing – A good example from my own experience relates to surface finishes requirements on component. The original drawing required a cyclonical grinding to improve the surface finish after turning. When a new CNC machine was installed the required surface finishes could now be achieved with a finished path of the new lathe. Thus the grinding operation was removed. A basic principle of the TPS is doing only what is needed.
- Inventory – Now everyone understands that a key element of the Totyota production system is that a JIT production system reduces the cost of inventory. By lowering the inventory we can then see the problems in resupplying the inventory in short lead times. Thus lean is a continual process of of improvement.
- The eighth waste – Non-utilized Human Resources/Talent – The waste of not using people to the best of their unique abilities. How can we involve everyone in developing ideas to generate improvements and new products?
In order to remind us on this concepts an Acronyms can be a very effective tool and here a few example,
An easy way to remember the 7 wastes is TIMWOOD.
An other easy way is NOW TIME: It’s now time to eliminate Mudas:
With the 8 wastes use the acronym DOWNTIME is a useful memory aid.
N: Non-utilized Human Resources/Talent
E: Excess Processing