Job Shop Scheduling Problems and Challenges

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Job Shop Scheduling – High mix low volume job shops and machine shops can be quite a challenge to schedule.

 

Why?  Here are just a few of the complex problems and challenges that plague the environment:Job Shop Scheduling

  • Bottlenecks or constraints in job shops can move based on the volume and type of work.
  • Work is diverse — typically low volume high mix but a production job may be run on occasion, or prototypes will be in the mix.
  • Jobs are typically made to order, but there are some job shops that may make a stock part, in addition to, custom parts.
  • While producing new custom jobs are the norm, some job shops and machine shop will do repair work.
  • Shops may do some amount of on-site new work or on-site repairs.
  • Emergencies can be fairly common and can take a fair amount of capacity (2% to 30%) and be very disruptive.
  • For some shops, customers call and make changes (frequently) – dates, quantity, or change their order completely.
  • It’s common place to have employees which are not cross trained at all or cross trained very little so the skill needed isn’t always available.
  • Shop employees don not always show up for work or on they may not show up on time.
  • Set-up times can vary and some set-ups can take a substantial amount of time, while others take very little time. And, what’s worse, is that both scenarios can occur in the same shop and at the same time.
  • The high mix low volume nature of custom job shops leads to a mix of jobs with all different quoted leadtimes.
  • The touch time to complete a job can also vary wildly. The same shop can have very short touch time jobs and at the same time have very long touch time jobs and everything in between.
  • Due to precision and/or tolerances, certain jobs have to run on particular machines, making scheduling a problem.
  • And if those weren’t problem enough, some jobs have outside processing to be done and some don’t. Some have more than one outside process to be and some have none.
  • The leadtime on necessary outside processes will vary by the process and the vendors do not always deliver when they promised.
  • Yield rates are not perfect — they may not be 100% or quality issues can play a role depending on the precision and type of work.

And, regardless of all these problems that can occur in scheduling a job shop and often do, customers still want their job done on time.

Now you know why it’s so difficult to schedule a custom job shop.  It is the nature of the beast.

There is a solution — it is called the Velocity Scheduling System. It was developed for highly custom job shops and machine shops where these problems and Murphy not only exist, but thrive.

Velocity Scheduling is NOT software but a visual scheduling system. It is a manual system that includes a visual planning board, as well as, a visual scheduling board. These boards are customized for your specific situation. Given all the complex challenges discussed above, you can imagine how important it is to customize any solution for your particular environment.

To learn more, check out the ebook tab and the webinar tab. The ebook provides more information on the scheduling challenges and the traditional solutions while the 47 minute webinar provides the VSS solution.

Best Wishes,

Dr Lisa

By Dr Lisa Lang

This article is copyrighted by Science of Business, Inc.

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{ 2 comments… read them below or add one }

Steve Arnold

Dr. Lang,
Please explain your definition of “touch time.”
Thank you,

Reply

Dr Lisa Lang

Hi Steve,
In this context I’m referring to the estimated time to do the actual work. So if you added up the time estimates for each step in the routing, you’d get the total estimated touch time.
The other variable to consider, in addition to outside process time, is any cooling time, drying time or other time like that where there is a required wait time due to the nature of the process. For example, after heat treat (an internal process) there could be a required 24 hour cooling period before additional machining could be done.
Dr Lisa

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