Principle 2: Create Continous Process Flow to Bring Problems to Surface.(Process- Eliminate Waste)

If some problems occurs in one-piece flow manufacturing then the whole production line stops. When production stops everyone is forced to solve the problem immediately. So team members have to think, and through thinking team members grow and become better team members and people.
- Teruyuki Minoura, former President Toyota Motors.


Flow is at the heart of the lean message that shortening the elapsed time from raw materials to finished goods(or services) will lead to the best quality, lowest cost and shortest delivery time.

A lean expression is that lowering the "water level" of the inventory(of materials or information) exposes problems(like rocks in the water) and you have to deal with the problems or you will sink.

Eigth non-value adding wastes that Toyota continually seeks to remove from its processes:
1. overproduction.
2. waiting.
3. unnecessary transport.
4. overprocessing.
5. excess inventory.
6. unnecessary movement.
7. defects.
8. unused employee creativity.

An example of Batch processing vs Lean Production:
Batch Production:Consider a computer monitor maker organized into 3 departments(i.e batch production). One department makes computer bases, second makes monitors and attaches the base and the third tests the equipment. In this model the material handling department decided to move a batch on 10 units to market at a time. Each department takes one minute per unit to do its work, so it takes 10 mins for a batch of computers to move between departments, it would therfore take 30 mins to make and test the first batch of 10 to be shipped to the customer.
Lean Production would take 3 mins to get the first computer ready to ship, and 12 mins to get all the 10 computers ready. In lean thinking, the ideal batch size is always one.

Benefits of One-Pience Flow
1. Builds in Quality: Each operator is an inspector and works to fix the problems in station before passing them on. There is less scope of errors as the next step in the process gets hampered and due to this the problem gets fixed in the earlier stages(vs in batch process it would get noticed only when a batch is released for next processing).
2. Creates higher productivity: The above example of computer monitor manufacturing clearly states that creating one-piece flow would increase productivity.
3. Reduces cost of Inventory: Due to one-piece flow there are less pieces waiting for the next process thus reducing the cost of inventory.