Forward Scheduling

A Preactor system will NOT plan jobs in the past. So a forward schedule starts at TODAY and takes each job by priority and puts it on the planning board in the first available slot. Depending on the availability of machines due shift patterns and other more important jobs already planned on the required machine.

So a forward plan tells you:

• The earliest time that you can finish an order
• How long you can keep a machine constantly running (as long as there is feed of materials from earlier processes / purchasing)

The resulting schedule Gantt chart will show jobs bunched up to the left hand side of the timeline.

So it tends to increase WIP. And makes it difficult to get sensible promise dates for new orders because just adding them onto the schedule could result in the new order being late and an order placed weeks ago being very early. Maybe the orders have the same required date and BOTH could be on time if the whole system is re-planned!

Backward Scheduling

The Sage 1000 MRP program is a backward schedule!

It works back from the top level required date on a Sales order or forecast, calculating start / end dates for each level of BOM, using the lead times.

Often this suggests start dates that are in the past, even though the MRP program has no restriction on machine / people capacity.

With a Preactor finite capacity schedule this could be even “worse”. Preactor only lets one job be planned on each machine at a time, so if there is a long bottleneck on a resource then it too will try to plan things in the past. But Preactor deals with this in a different way to MRP, because it refuses to schedule the operations that would need to run before today on a backward schedule.

Leaving the planner to do something about them.

The resulting schedule Gantt chart will show jobs more to the right hand side of the timeline, and you will be able to see gaps in the middle where new orders can be placed without affecting the expected dates of existing orders.  

A Good Compromise

Just one idea, there are others:

• Run a FORWARD schedule
• Let Preactor highlight the EARLY operations
• Un-schedule the early orders (or those more than say 5 days early)
• Re-schedule them with a BACKWARD run

If the ops were EARLY on a FORWARD, they are bound to still FIT on a BACKWARD, without going into the past!

The end result being a plan where urgent or potentially late orders are planned to run ASAP, the rest are planned to finish when they are needed.

So they don’t start until they really need to , so WIP is reduced and MRP for purchasing can be set to only bring material in on dates where it is actually needed.

Reducing stock holding costs and freeing up cash and warehouse space!

The plan will also show gaps where new orders can be added.

Just posted this question on the Sage User Network forum, so I’ll ask it here too......

I'm trying to find some good 3rd party MPS software. Maybe it would create the sales forecast from history and sales person knowledge and promotional activity. But more importantly it needs to turn this into a MPS, taking into account the current stocks, production plans and firm sales orders. There should be an easy to use interface (we're competing with Excel here!) where the planner can modify the (system) calculated production plan as he/she sees fit. This should then be able to be published as an Available To Promise (ATP) enquiry for sales dept to use. The final MPS would also be pushed into Sage to drive MRP for the lower BOM levels. And it should be able to accept back a true forward scheduled plan (maybe from Preactor) so that the dates used in the ATP and the next MPS represent a realistic capacity constrained plan of what you will be making in the short term.
As you might imagine, this is very suitable for FMCG companies. Which reminds me - it should be able to cope with minimum stock levels expressed in terms of "days cover" rather than just a fixed stock quantity.
Anyone know of such a thing??