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Tsurube System ( よくバケツ ) – Pull System (JIT)
Many people call Tsurube as system, however, from my point of view and based on my experience in Japanese companies, is a Method into the Pull System (JIT). Tsurube combines FIFO (First In First Out) with Kanban, promoting, sequencing and the correct leveling of inventories at the same time.
Tsurube is the Japanese word for “well bucket”. As I have commented, it is a method of the pull system, a material replenishment method used when there is the middle process step is physically separated from the upstream and downstream processes by lead-time due to distance and/or batch processing. A “bucket” (container of unprocessed material) is sent down the “well” (the remote process) and at the same time a full “bucket” (processed parts) is returned up from the well.
Tsurube is not easy to implement because it requires a very good quality in processes and a good up time of the machine, since any interruption or variation breaks the FIFO sequencing.
However many companies require this method or in other words must implement immediately, hence the importance of having someone with extensive experience in the implementation.
This Tsurube method, is used to maintain a continuous flow when there are interruptions such as process off-line or off-site and must have a batch system.
Used when the product leaves the production cell lines or because the process, can not, be in the cell (Kilns, painting, heat treatments, anodizing, plating, ect) and operates as follows.
A supermarket finished products located at the end of the line, which has predetermined quantity of material, usually a PITCH, in this example it will be 30 minutes.
Once the amount is removed; then a kanban signal its send to the process A, which can be the pacemaker; which prompts you to start producing parts (quantity = pitch) is sent.
Usually the FIFO system is used to move the product to process B. Process B also, have and process the same quantity and this is passed to the process that we have offline. (Process C)
And this last process the same amount to the process C is passed to end the cycle Process D and then to SMKT Finish Goods; ant his process is repeated as often as needed.
It is very important to consider the SWIP (Standard Work In Process) the usual way to calculate is the following.
SWIP = [Total Lead Time =(Transportation Lead Time + Manufacturing Lean Time)] / Takt Time.
The SWIP (two buckets) maintains continuous flow through a batch or outside process. Transportation of materials is never empty in either direction and the arrival of the bucket to the well process is a signal to produce. It is in effect an instance of a non-card type production instruction kanban ; it is a FIFO process sequencing.
There are three golden rules for this Tsurube method:
1.- Respect the FIFO sequence
2.- Quantity shipped must equal amount received
3.- Do not send more parts if those sent were not received.
Zero Defects and TPM must be implemented before or at same time (in parallel).
I hope this information will be helpful in your next kaizen event.