Help me with this Kanban/CONWIP case!

[pabloquintana]

Hello, I have one four assembly lines doing different products from a same family. The assembly line approx cycle time is 30 sec and each line has 10 operations.

Right now each operator has the instruction to move in batches of six units max when an audible alarm sounds.

The process supplying these lines is a four welding workstations that can cycle the majority of the products below 30 sec, but some more complicated ones will take as much as twice that time, making it impossible to flow into the assembly line.

My idea is to use kanban at the end of the assembly line to send production instructions to the welding workstations, and a FIFO lane with some max quantity per line between the assembly lines and the welding workstation.

The requirement of units per day is around 1000.

Any idea on how many cards will I need and how to implement this kanban?

Thanks

Pablo.

[wmarhel]

Originally Posted by pabloquintana

Hello, I have one four assembly lines doing different products from a same family. The assembly line approx cycle time is 30 sec and each line has 10 operations.

Right now each operator has the instruction to move in batches of six units max when an audible alarm sounds.

The process supplying these lines is a four welding workstations that can cycle the majority of the products below 30 sec, but some more complicated ones will take as much as twice that time, making it impossible to flow into the assembly line.

My idea is to use kanban at the end of the assembly line to send production instructions to the welding workstations, and a FIFO lane with some max quantity per line between the assembly lines and the welding workstation.

The requirement of units per day is around 1000.

Any idea on how many cards will I need and how to implement this kanban?

Thanks

Pablo.

The formula for calculating the number of kanban cards in a system for a particular product is:

(Daily Demand x (Run Frequency + Lead Time + Safety Time)) / Container Capacity

Where:

Daily Demand = Customer Consumption expressed as # of units

Run Frequency = Frequency which you decide to set-up and produce that item. This is expressed as a unit of time. For a five day work week, running the product every day would equal (1), every third day would equal (3), etc.

Lead Time = Manufacturing lead time (processing time + Set-up time + queue time) + lead time for kanban retrieval expressed as a unit of time.

Safety Time = Allowance for variations in demand and supply, also expressed as a unit of time. Keep as low as possible.

Container Capacity = Number of units per container (# of units in a container is always the same number).

There are some assumptions you'll need to make regarding the above variables.

Another way to go through this is to first make kanban cards for your present finished good level. Then take away a card or two. If nothing happens and there are no problems take away a few more and so on and so on. When you do run into a problem, fix the problem and continue removing cards. Less scientific, but it may do the trick.

On another note, I'm willing to bet you can flow your product. You'll just need to assess your current layout/set-up and make changes. But there are always improvements to be made.

Wayne