I am working on a job with a lot of subassemblies, and subs of those subs. So I find myself at the first grandchild assembly, looking at the operations. There are 3 operations in a row for horizontal mills. For each operation I set the send ahead offset to 1 piece, and set the operations to start-to-start.
When I unschedule the job, and then reschedule it, I expect the three operations to overlap by the amount of time it takes to run one piece. Instead, each op is still waiting until the last op finishes before starting.
In Site maintenance I have send ahead set to setup, as I want to start setting up the next operation as soon as the first piece of the first operation is done.
My guess would be that since you are using the same resource for all 3 operations it is scheduling it all on one resource. Just for S&Gs, I would change the resource on op 20 and 30 to something completely different and then reschedule.
This job does use the same resource group for three operations, but it can choose from a list of 7 different resources. We don’t normally select a specific resource at the job level, we let the scheduling engine choose the machine. When I did go in and set the specific machine resources for each operation, the first op stayed in place, but the other two ops get pushed way out. I assume they are getting pushed out past all the other jobs that are currently scheduled. They certainly did not all get run together as I expected.
I did a few more tests. I tried to add another resource to the group. But now all three ops get scheduled to that same resource. How can I tell the scheduling engine to choose three different machines for these three operations, so that they can all start after the first piece is done on the previous op?
I did that too. This does reduce the time for each op. If I give it two scheduling blocks it reduced the time by half. But it still doesn’t want to start the next op after the first op has had 1 piece finished.
Something just occurred to me. Do I have to wait until someone in the shop has documented time and quantity against the job to show that the first piece is done? I set the send ahead type to 1 piece. I know a piece takes an hour to make, so I expect the next operation to start an hour after the first operation is scheduled to start.
Yes! I forgot that too. Time/Quantity needs to be reported before the next op can start. Maybe it won’t schedule for the send ahead, just let you do it.
Thinking that I don’t want to wait for a user to enter time and qty against a job before I know the schedule. So I switched from a 1 piece send ahead to a time based send ahead. If the first op takes 5 hours to setup and 1 hour to process one piece, I set the send ahead to 6 hours. I regenerated everything, and I still get the same results. Each op is scheduled to start after the previous op completely finishes. The scheduler does not seem to care about my send ahead values.
I don’t know the answer, but my guess would be that it does not work that way because you may or may not actually do the send ahead.
This is my opinion, but I do not think you would want it to schedule the send ahead. Because if someone calls out and you cannot send ahead parts, you do not want your whole schedule blown. You would much rather have to find work instead of pushing work out.
Do you have all of the operations in the method set to finish-to-start? This will tell MRP that the next operation can’t start until the previous is completely finished. If you set them all as start-to-start, that will allow them to all run concurrently and should take that send ahead time into account.
