Job Shop Scheduling – a high mix low volume job shop can be a challenge.
The complexities and problems in the job shop environment are numerous, just check out this list.
Given the long list of challenges, it would seem almost impossible to improve flow in a job shop. However, it IS quite possible. BUT you do have to go about it differently than regular production manufacturing environments. Production manufacturing commonly uses takt times to improve flow.
“Takt time helps you to achieve a consistent continuous flow of production.” wikihow.com
BUT, you can’t really collect takt times in custom job shops. See pic below with some information about takt times. From the pic you can see that the emphasis is put on balancing capacity to your customers’ demand.
Can you imagine trying to calculate takt time in a job shop where:
- mix is constantly changing
- work is diverse
- some jobs won’t repeat
- work is mostly make to order
- customers change orders
- work consists of repairs and new products
- some work is done on-site
- and more, see full list here
And many job shops are MUCH more complicated than what I listed above. Both available time (capacity) and customer demand can fluctuate.
So if typical lean approaches and takt time DON’T work, what does?
You have to balance FLOW not CAPACITY!
I have outlined the evils of balanced capacity before. Flow-based scheduling and flow manufacturing are key.
To balance flow, you have to take into account your constraint (which can move) and release work at the rate the constraint can consume it. Releasing it faster than that results in too much WIP and high queue times. With high queue time, you get a bunch of accompanying negatives. (See my scheduling report that covers Little’s Law.)
If you release work slower than the constraint’s rate of work, you will starve the constraint and an hour lost on the constraint is an hour lost to the output of the entire company and that company’s profits.
Job Shop Scheduling
Balancing flow in a CUSTOM complex job shop is what we do in Velocity Scheduling System. VSS is NOT software but a visual manual system that works with your existing ERP software. As you can image job shop scheduling software really doesn’t work in this environment. (Dah – That’s probably why you’re here!)
How do you approach flow in your job shop? Leave me a comment.
By Dr Lisa Lang
This article is copyrighted by Science of Business, Inc.