Scheduling
The scheduling menu maintains the Firm Work orders, which were created
from the conversion of planned Work orders.
Finite capacity scheduling, an option in the scheduling menu, schedules
precisely the firm and open orders.
When the schedule is acceptable, you can call the Release function that
converts firm orders into open orders.
Firm Work Orders
A Firm Work order originates from the individual conversion of planned
orders into firm orders (Firm WO button in the planned WO window), or
from an automatic transformation (Planning menu, option Planned to firm
WO conversion) or from the manual creation of a firm order using the
New button.
When a firm order is opened clicked on, the part requirements list and
available inventories are shown in the table.
Firm Work Order Maintenance Window
A Firm Work order can be modified or deleted as long as it has not been
released. In particular the quantity, release dates or due dates can be
changed. The resulting component requirements are updated.
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Fields
Quantity
Release date
Due date
Priority
Transfer batch
quantity released
planned release date
calculated required date
priority index which can be used with finite capacity scheduling
transfer lot size for a WO which is used for overlapping
Buttons
Apart from the standard buttons, this window has seven buttons:
Lets you create a new Work order. It assigns a number. All fields must be
filled.
Release routings can be found in the list of routings attached to the item.
The routing revision is automatically chosen according to the release date
of the Work order.
Calls the release procedure by reserving components in inventory. If a
inventory is too low or the routing is absent, the release is impossible and
the button is inactive. See further on for the detail of the release procedure.
At the time of release, the total order quantity is placed waiting at the first
operation.
Opens the window which manages the operations of a Work order.
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This buttons performs an infinite capacity schedule then either a forward
or backward finite capacity schedule for a Work order within the existing
machine schedule. If the Work order is already scheduled (the planned start
and finish dates are reminded), a de-scheduling is proposed. Overlapping of
the Work order is done before scheduling.
If the Work order has been scheduled, this button shows the list of relevant
workshop events.
This shows the Gantt chart for the Work order, in other words the earliest
and the latest schedule, and the schedule according to the scheduling
release dates.
The operations are created in the WIP when a planned order is converted or
when a firm order is directly created. Information featured in the relevant
manufacturing routing is stated there.
The transaction number is marked next to the order number, for the Work
order involved in a transaction.
This window has three panels:
•
the first presents the manufacturing operations; when an operation is
clicked on it is shown,
•
the second shows the part requirements list; when a part in the list is
clicked on, its production schedule is shown.
The Available column shows the current inventory of a part, whereas the
Available/ Rel shows the forecasted available inventory on the release
date.
•
the third shows the scheduling dates that were calculated by the
Infinite capacity loading function or by the button Scheduling, it also
shows the finite capacity scheduling dates.
Slack is expressed by the number of hours between the earliest and latest
end dates.
The infinite capacity ratio is equal to the relationship of the work hours to
the throughput time ( that includes the transfer time).
The finite capacity ratio is equal to the relationship of work hours to the
throughput time increased by the buffer inventories in front of each
operation (that can be seen on each of the operations sheets).
Direct creation of Work Order
Having examined the finished parts requirements, you can create the Work
order entering a different quantity than that suggested. By manually
creating a Work order, a resource (of positive quantity) is introduced into
the projected profile of the item inventory; this will be taken into account,
but not checked, by the MRP calculation.
If you want to create buffer stocks, for example to regulate the shop floor
work load, you must create a Work order manually.
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To create a Work order, the “Firm Work order” option must be selected
from the Scheduling menu, then click on the New button. A number is
automatically allocated. Enter the relevant item code here. The release
routing code is displayed.
Next you should enter the order release date, the quantity released and the
required date, in other words the date on which the products should be
available. The release routing revision that will be used is displayed.
When you create a Work order by pressing on the OK button. This causes
the creation of requirements for each component of the item and the
creation of operations from the release routing.
The new order can be immediately scheduled (If the machines schedule
exists) using the Sched. button. It can be immediately started if the parts
have sufficient quantity in stock.
WO Operations Maintenance Window
The operations that already exist can be deleted, canceled or modified,
that’s to say those which do not have a quantity waiting or being processed.
To create a new operation not mentioned in the manufacturing routing,
enter an operation number that places the operation correctly in the
operation sequence and fill all the fields.
Fields
Operation #
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All these come from the routing operation that was used for the release.
mandatory (three digits). If the number exists, the operation is shown.
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Work center #
Description
Set-up time
Preparation labor time
Machine Run Time
Labor Run Time
Quantity per time
Quantity per cycle
Move time
Fixed scrap
Proportional scrap
Count point
Machine number
refer to the description of the Routing Operation window for the meaning
of the many different fields of this window.
The last operation must be a count point.
If a machine code has been assigned in the manufacturing routing, the code
is shown in this field and is not modifiable. The box Imposed is filled.
If the Work order has been scheduled, this field contains the machine code
to which the operation had been allocated.
If you want to set the operation in motion on a specific machine in a work
center, you can type in the machine code and then mark the box Imposed.
Buttons
Cancel the operation without deleting it from the file. It will not disappear
as its status is changed to Canceled. The operation will be ignored in
scheduling and in control.
Clicking again on the Cancellation button could reactivate a canceled
operation.
If the Work order has been scheduled, this button shows the events list of
the workshop concerning the operation: an arrival in the queue, start and
end of work.
This window has three panels:
•
the first allows the modification or entry of the manufacture times,
•
the second shows the state of advancement and the allocated times,
The labor allocated time is equal to the labor set-up time plus the product
of the order quantity by the labor run time divided by the units of time and
the cycle time units.
The allocated machine time is equal to the set-up time plus the product of
the order quantity multiplied by the machine time divided by the units of
time and the throughput time units.
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The third shows the scheduled dates, which are calculated by the
Material Requirements Planning function or by the button
Scheduling, as well as the dates scheduled by finite capacity
scheduling. The Wait field contains the number of hours the batch
must wait before being processed on the planned start date.
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WO Gantt chart
By clicking on an operation scheduled WO, a window appears where you
can see the sequence of each operation.
In blue shows the earliest sequence by infinite capacity planning.
In red shows the latest sequence by infinite capacity planning.
In green shows the sequence given by the schedule using finite capacity
planning.
Scheduling WO by WO
When the Scheduling button is pressed and the WO has not been
scheduled, it can be scheduled forwards or backwards, with or without
overlapping.
In order that the WO scheduling takes place, the machine schedule must be
created, either by a previous schedule, or by selecting the option Create
Schedule in the finite capacity-scheduling window.
If the WO could be scheduled, its scheduled start and finish dates and times
are shown.
Firm Work Order List
The Firm WO list function show the firm orders list, which can be sorted
by WO number, by item code, or by due date.
If you select an order and click on OK, the order’s window appears.
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Not Scheduled Firm Order List
This list displays the firm work orders which could not be scheduled by the
Finite Capacity Scheduling function. The scheduling failure may have
been caused by a WO due date being later than the finish date of schedule,
which was specified when the function was first entered or at the start of a
manufacture cycle that overshoots the scheduling horizon.
Firm Order Slacks
This function shows the list of firm orders sorted by increasing slack,
calculated by infinite capacity scheduling.
If you select an order and click on OK, the order’s window appears.
Machine Downtime
It is possible to define time brackets in which a machine is not available
and for which it will not be able to schedule manufacturing operations.
Such time brackets could be defined for maintenance or breakdown.
When Machine Downtime is selected, the system shows the list of all
downtimes already recorded that could be sorted by date or by Wk
Ct/machine.
To deleted or modify a downtime, select an item in the list and then click on
the Change button.
To enter a new downtime, click on the New button.
A limit of 99 machine downtimes can be entered at one time. Those that are
out of date must be deleted.
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Machine Downtime Maintenance Window
Fields
Work Center #
Machine
Start date/ start time
End date/ End time
Reason
Mandatory. The work center must exist.
Mandatory. The machine must exist in the work center.
Start date and time of the Downtime of the machine.
End date and time of the Downtime of the machine. This must be later than
the start date and time.
Note: It is not possible to have two downtimes that overlap on the same
machine.
Comment indicating the cause of the unavailability.
Buttons
Apart from the standard buttons, this window has only one other:
This shows a start hour 00:00 and a finish hour 23:59
Finite Capacity Scheduling
Finite capacity scheduling places operations on machines to produce a job
schedule for each machine.
Several scheduling methods are proposed: forward or backward scheduling,
or priority rules.
Before starting the scheduling procedure, you must make sure that the
machine calendars are up to date and must enter the possible downtime of
the machines that need maintenance or could break down.
Procedures for Finite Capacity Scheduling
The scheduling procedures can be called by the Finite Capacity
Scheduling option from the Scheduling menu. Their purpose is to produce
a detailed work schedule for the machines or work stations. They take into
account the released WO’s and the firm WO’s.
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First the scheduling end date must be specified. Finite capacity scheduling
is usually based on a short planning horizon, one to two weeks. Beyond
that, it would be impossible to plan the production due to the unknown
production factors.
Preparation for machine scheduling
The system starts by creating time slots, concerning a specific machine,
that are found in its calendar. The slot starts at the indicated start time. Its
length is equal to the length of the slot multiplied by the yield of the
machine. For example, if a slot is 8 hours long and the machine has a yield
coefficient of 85%, the length of the slot will be 6.8 hours.
For the type M work centers, the number of work stations created equals
the value in the Capacity coefficient field.
If a work center is not allocated a machine, the type (F or M) is
nevertheless recorded as a single machine.
If the Prepare schedule option is selected, the time slots are created but the
automatic scheduling is not started. However, each WO can be scheduled
using the existing schedule, by clicking on the Schedule button from the
firm/open orders window.
Next select the scheduling method.
There are two major types of scheduling:
•
scheduling WO by WO, either forward or backward,
•
scheduling by simulation of the workshop activity with priority rules
for each operation in a work center.
Scheduling by WO
For this type of scheduling, all the operations of a WO are sequenced
before moving to the next WO.
The scheduling can be done as follows
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•
either by forward scheduling, sequencing the operations as soon as an
available slot is found that is large enough to place the operation from
the current time,
•
or by backward scheduling, using the WO due date, the operations
are sequenced in reverse order.
In both cases, the order in which each WO is executed must be determined.
The released WO’s always have a higher priority than the firm WO’s and
are sequenced into the earliest available slot. The priority is a major sorting
criterion when compared with the WO sorting criteria.
This program offers nine sorting criteria:
•
Order number: the WO’s are processed by number
•
Release date: the WO’s are sorted by increasing release date then are
loaded
•
Due date: the WO’s are sorted by increasing requirement date then are
loaded
•
Lowest number of operations: the WO’s are sorted by increasing
number of operations then are loaded
•
Greatest number of operations: the WO’s are sorted by decreasing
number of operations then are loaded
•
Greatest total load: the WO’s are sorted by total decreasing load
(sum of the machine time allocated to machines) then are loaded
•
Least total load: the WO’s are sorted by total increasing load (sum of
the machine time allocated to machines) then are loaded
•
Slack: the WO’s are sorted by increasing slack then are loaded
•
Random: the operations are sequenced randomly.
One of the sorting criteria is selected from the pull-down list.
A forward schedule is always performed on a released WO.
When a backward schedule is requested and it is not possible to sequence
all the WO operations, the program tries a forward schedule.
The WO’s that cannot be totally sequenced before the due date are descheduled and appear in the Not Scheduled WO List.
Priority Scheduling
Here, the processing of operations is simulated starting with a time on the
“clock” and incrementing the “clock” following the forecasted events that
affect the workshop.
When, on a given date, several jobs are waiting in front of the work centers
and only one machine is available, the priority rule is applied to determine
which to sequence on the machine.
The system proposes twelve priority rules:
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1- FIFO: First come, first served
2- LIFO: Last come, first served
3- Shortest Operating time: Amongst all the waiting operations, the
operation that has the shortest total time (set-up time plus processing
time) is sequenced.
4- Longest Operating time: Amongst all the waiting operations, the
operation with the shortest completion time (set-up plus processing
time) is sequenced first.
5- Minimum remaining operations: The WO with the fewest remaining
operations to process is selected.
6- Minimum remaining work hours: The WO with the least amount of
remaining total work time is selected.
7- Minimum Slack: The WO with the least Slack (number of hours
available until the due date minus the remaining processing time) is
selected.
8- Minimum Slack / number of remaining of operations: The WO that
has the lowest ratio of slack to remaining number of operations is
selected.
9- Minimum Slack / remaining work hours: The WO that has the lowest
ratio of slack to process time is selected.
10-Shortest next queue: The WO that must be sequenced on the work
center with the shortest queue is selected.
11-Least loaded Next work center: The WO that must be sequenced onto
the work center with the lightest waiting load is selected.
12-Random: A WO is selected from the queue randomly.
A priority rule must be chosen from the pull-down list.
To start the scheduling procedure, click on OK.
During the scheduling procedure, the released operations are sequenced in
priority on the machine in hand.
When the scheduling is finished, the machine schedule is displayed, as well
as the results sorted by WO and the evolution of the queues in front of the
work centers.
Overlapping
Scheduling method where the next operation is started on the first part of a
batch without waiting for the preceding operation to finish.
In order that the overlapping can play its part, three pieces of information
must be entered:
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A transfer lot has been entered into the routings, or on the WO. If the
transfer lot is nothing, then there can be no overlapping; also, there is a
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maximum of 100 lots, the size of the transfer lot must be at least a
hundredth of the size of the manufacture lot,
•
The type of overlapping has been specified on successive operations.
For a particular operation, the overlap is specified relative to the
previous operation, it is without sense therefore to give the overlap for
the first operation of the WO.
•
If you want to use overlapping then check on the Overlapping box in
the finite capacity scheduling window.
Types of Overlap
There are three possible types of overlap:
1- '01' Early Set-up: The set-up is started before the part arrives at the
machine.
2- '10' Simple overlap: The set-up is started when the first lot arrives at
the machine.
3- '11' Set-up and overlap: The set-up is started in such a way that
production can start when the first lot arrives at the machine.
Prelude determines the possible start date for the second operation
according to the first, according to whether the second operation is longer
or shorter than the first: the first transfer batch must be available, but also
the previous lot must have already arrived.
List of Non-scheduled WO’s
The option Non-scheduled WO list shows the list of released or firm
WO’s that have not been scheduled. A schedule may fail due to a due date
being to long or the congestion the part flow that prevents the loading of
certain operations.
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Shop event history
The option Shop event history lets you see the progress of an operation
through the workshop. By clicking on the corresponding button, the list can
be sorted by date, by WO or by work center.
The event codes are explained below:
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AQ: arrival in queue
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•
SW: start of work
•
EW: end of work
•
SB: start of machine blockage (unavailability)
•
EB: end of machine blockage
•
SA: start of available slot
•
ES: end of simulation
Machine Schedule
In this schedule, WO’s are show with their numbers (as long as the
operation length allowed each operation to be sequenced). The black slots
represent the Downtime of machines. The white slots represent the unused
time slots.
The number of days to shown can be changed by clicking on the
corresponding buttons. The buttons >> and << allow the display to scroll.
The Calendar button makes it easy for you to get to the desired date. The
Print button prints the current page.
By clicking on a scheduled operation of a WO, the WO window appears.
By clicking on a downtime, its properties are made to appear.
By clicking on a free slot, its length, start and finish dates or times appear.
By clicking on a machine label, the Prelude displays what the machine is
currently doing.
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Utilization of Machine...
The machine occupation list displays each time slot, which WO operation
is scheduled for it, as well as the time slots not used. In the ‘type’ column,
S signifies set-up, R run and D downtime. The labor loading figures are
displayed in the last column.
Work Order schedule
The Work Order Schedule option shows, one order per line, the time slots
used by each scheduled WO. The number of days displayed can be changed
by clicking on the relevant buttons. The buttons >> and << allow the
display to scroll. The Calendar button makes it easy to get to the desired
date. The Print button starts printing the current page.
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By clicking on a WO, the corresponding WO window appears.
By clicking on a scheduled operation, the operation window appears.
By clicking on a free time slot, the planned works list for the WO is shown.
Schedule of a WO
The window ‘Schedule of WO xxx’ shows the start and finish dates and
times of operations; it also shows set-up times and operating times.
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W.O. Release and Due Date Analysis
This option shows the list of WO’s sorted by slack between the expected
finish date (scheduled date) and the specified due date for the WO (latest
possible date).
If the WO’s have negative slack times, that means that they will finish late
in relation with the due date.
Work Load profile
This graph shows the Machine or labor loads that come from the finite
capacity scheduling.
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Firstly, select a work center or department.
Then the type of load, to view and analyze, should be selected:
•
Loading that shows the loads of set-up and processing,
•
Capacity Utilization,
•
Capacity that shows the daily capacities and the downtime of
machines.
The number of weeks to display can also be chosen (between one and five).
The Capacity utilization, by definition, is always less than or equal to one
for the machine loading.
Queue Profile
This option shows the evolution, through time, of the waiting in queues,
calculated by work center. It is shown at the top. The description of the
work center is shown at the bottom.
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Firstly, a work center must be selected from the work center list.
Then, the units and number of units of time to display can be chosen. All
shows the queuing for the whole scheduling time horizon.
The buttons >> and << allow the display to scroll. The Calendar button
makes it easy to get to the desired date. The Print button starts printing the
current page.
The button Events shows the chronological list of events that make up the
work center. See the shop event history for the meaning of the codes.
The button ‘Utilization’ shows the detail of the machine utilization for the
work center.
Work Center Utilization
This function displays for all of the work centers, the summary of loads for
the scheduling horizon.
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Work Order Release
A WO should only be released when it is certain that the slacks are not
negative and the work loads are compatible with the capacities.
The release routing must be well put together.
The release function performs, on each WO, a verification of the
availability of the parts by looking at the total available (status AVAIL). If
the available quantity of one of the components is insufficient, the release is
impossible.
To release a WO, click on the Release button from the firm WO
maintenance window.
To release a group of WO’s, use the mass work order release function.
Shortage analysis
This can be reached from the Scheduling menu. It looks at all the WO’s
and sees if the available inventory for each of the required parts is enough
to allocate the reservations. It shows for each WO, the list of the shortage
items.
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By selecting a WO and by clicking on OK, the window of the WO is
shown.
When you look at a firm order, the system shows the part requirement
table, as well as the available inventories, for the WO. If one of the parts is
found to have a shortage, manual release cannot be done.
However, if several firm WO’s require the same parts and the total
requirement for a part is more than the available inventory, the release of
some orders will be refused at the time of an automatic release. This is due
to the inventory having been calculated according to the order for which the
releases are allocated.
If the part levels are sufficient, the release function performs a transfer of
parts from the AVAIL status to the RESV (reserved for manufacture)
status, staying within the same warehouse.
The status of the order changes to Open. They are called Open Orders.
They are therefore accessible from the Control menu.
Mass Work Order Release
Once assured of the coherence of the firm orders, they can be released
automatically. You can do this using the Mass W.O. Release function,
from the Scheduling menu. It avoids repetitive work.
The release end date must be entered. All the orders whose date is before or
on the end date are examined. They are sorted by increasing release date,
then Prelude tries to release them. It is possible that the last orders might
not be able to be released if their components were reserved by previous
WO’s.
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