Scheduling - Problem With Backward Scheduling

Can anyone help?

We are running our machine shop using backward scheduling but it is not working well for us. We have orders due in October which are ten days late but the schedulie has allowed a 10 day gap to open at the beginning of September (presumably because the orders wanted at the end of September are on time). Why doesn't the schedule move everything backwards until the October orders are on time? There are no other operations affecting this.

Is there anything I can do to put this right or am I going to have to buy some 3rd party scheduling software?

Thanks

Elaine Slater

Hydraulic Projects Ltd

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Richard Lagoy

Have you looked at the scheduling audit to determine the contention?

unknown

Hi Richard

Thanks for the reply. I'm don't really know where to start in analysing the scheduling audit. The thing is I'm not looking at one job, I'm looking at a series of jobs. There is a long gap at the beginning of September on a particular machine, the second half of September is all blue (ie everything is on time) and then there is a job due for mid October which is going to be very late. I'm not sure what I should be looking for.

Thanks

Elaine

unknown

A couple of questions;

How long is the operation in question?

Is the resource scheduled normally or discontinuous?

What settings do you have in the concurrent scheduler (Options-Preferences-After forward pass)?

regards.

unknown

Hi Elaine,

We often have the same problem with finite resource. We start by looking at one work order with the problem, most of the time, we have the answer with one or two examples. Open the work order in manufacturing window, Info, show work order audit detail. Selected the production schedule. Export the result in Excel, it’s easier to understand.You probably have the same contention issue on all work order.

We are able to explain the gap we see in the scheduling with the work order audit.

Nancy

unknown

This resource is scheduled normally

The sort date is by want date.

After forward pass we have 'backward schedule if on time' in all cases

Preserve determinate path is ticked.

Materials are not checked but services are.

The operation is 6 days in duration. This is followed by 7 days at outside services.

todd-vigorito

We find it more efficient to forward schedule everything. You end up with less gaps in the schedule because everything drops in at the soonest available time. You need to make sure you set a release date not sooner than you would be able to or want to start. We usually have a 6 to 10 week lead time for our products, and set the release date based on when we should be able to have most of the parts available, but not more than 4 weeks before the ship date.

unknown

Nancy

I have printed off the audit schedule on the late order but I'm not really sure what I am looking for. I think it's just saying that load exists until 30th September and perhaps the gap it is seeing isn't quite big enough. The thing is, I don't want this order stuck in the gap (that would put it ahead of items which are more urgent), I want all the orders to shuffle backwards if the one on the end is late.

We have tried forward scheduling. That works when you are not busy and you just want to close up gaps to make sure the raw material is here and the job can be started. However, when you are really very busy, it's very hard to determine a sensible release date to make sure that your requirements come out in the right order. Unless I am much mistaken, there are serious problems with the program.

Elaine

d-catalano

In response to: "I want all the orders to shuffle backwards if the one on the end is late."

In my experience, this is not how the schedule works. If you want this, I think you would need to forward schedule all of your orders. If the one on the end is late, and your other orders are backward scheduled (and therefore still on time), the one on the end will forward schedule, but will not jump in front of the other orders unless there is free space in the schedule, which is part of the point of backward scheduling.

unknown

Just curious, is changing the schedule priority for that work order not an option you are willing to employ? If you change the schedule priority of that work order to a lower number than 50, it will schedule on time.

unknown

I have considered using 'priority' but I don't really understand how to make it work with my want dates. If I put a lower number on the late job, won't it just push ahead of something else and make that late instead? I want the system to schedule by want date (to tie up with my assembly shop) but I want gaps to be filled where any orders in the schedule finish up overdue. This should be an additional pass to close up gaps where anything is overdue.

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