Makespan - Production Planning & Scheduling Solutions Ltd.
Production
Planning and Scheduling
in a CASTING PLANT
In this example the planning quality of EFA is demonstrated by comparing its results to those obtained by the Earliest Due Date (EDD) rule and partially to those obtained by the Bottleneck Approach. The comparison is made in a Casting Plant which produces a large number of different products in a serial production process consisting of seven work centers [M] as described in Fig-1.
The planning results are compared in two situations:
1)
The
manufacturing jobs have different Due Dates,
2)
All
manufacturing jobs have the same Due Date.
In order to simplify the example some assumptions are made:
-
Each work center consists of one machine.
-
The process batch of each product is the full
ordered quantity.
-
The transfer batch
from a work center to the next one
is of one unit.
-
Additional times are neglected (for example waiting
time for material to cool after tempering).
-
Production starts from an "empty floor".
-
The plant works 5 days a week (Monday-Friday) using
one shift of 8 hours
(07:00 - 15:00 without break), no overtime.
The manufacturing order list for approximately one month is given in TABLE 1.
The starting date for planning is
Remark: the dates are
written in MM/DD/YY format.
The process route and data are given in
Workload:
The total workload in each work center is seen in Fig 2. The maximum workload is 18.96 working days (151.7 hours) in work center M5. This is the minimum theoretical total lead time. Converting it to calendar dates shows that the earliest date that production could be finished would be on
Planning Results:
Remarks:
1) The planning results are presented in summary tables.
2)
Calculating the sequencing order as described in the summary table is
the first step in the planning process. The next step is the detailed planning
for each machine. The total lead-time achieved by the detailed planning is usually slightly longer than the one
achieved in the first step.
1) Different Due Dates (as shown in TABLE-1 above)
The EDD schedule is described in TABLE-3 at the bottom of
this page.
The EFA schedule is described in TABLE-4 at
the bottom of this page.
The
different results obtained by the two schedules are described in the table
below.
|
|
EFA |
EDD |
|
Finishing Date |
03/29/10 |
04/02/10 |
|
Duration (hours= days * 8) |
160.6 |
194.5 |
|
Delay
(days) |
0 |
4 |
|
Delta Time (hours) |
0 |
33.9 |
|
Increasing rate (%) |
0 |
21% |
Note, Running EFA scheduling during a period similar to that of EDD, that is 194.5 hours, enables to add an identical composition of product basket in which the quantity of each product is 25% of the original quantity.
2) Same Due Dates (
The EDD schedule is the same as above.
The EFA schedule is described in
TABLE-5 at
the bottom of this page.
Two planning reports that were derived from the EFA detailed schedule are presented here:
a)
WORKPLN,
it shows the detailed planning for each machine.
b)
LOADCHART,
it shows the detailed distribution workload in each machine.
An interesting schedule is achieved by applying the
Bottleneck (BN) Approach.
That is keeping the
Bottleneck
busy from the
beginning. As can be seen in the
WORKLOAD
Chart above, the
Bottleneck
is
M5 - the
GRINDING MACHINE. In order to assure continuous
work of the bottleneck from the beginning the first products to be
scheduled are
B, D, G, H, Q, S, T
in these products the grinding
process takes place (see
TABLE2).
The BN
schedule is described in
TABLE-6.
The
different results obtained by the three schedules are described in the table
below.
|
|
EFA |
EDD |
BN |
|
Finishing Date |
03/25/10 |
04/02/10 |
04/07/10 |
|
Duration (hours= days * 8) |
152.0 |
194.5 |
218.2 |
|
Delay
(days) |
0 |
5 |
8 |
|
Delta Time
(hours) |
0 |
42.5 |
66.2 |
|
Increasing
rate (%) |
0 |
27.9 |
43.5 |
Notes:
1) The total lead time achieved by EFA is 152.0 hours, which is identical
to the
minimum theoretical total lead time.
2)
Running EFA
scheduling during a period similar to that of EDD, that is 194.5 hours, enables to
add an identical composition of product basket in which the quantity of
each product is 28% of the original quantity.
Summary
In both situations the total lead time achieved by EFA is shorter than the one
achieved by EDD. Shortening lead time improves the ability to deliver all jobs
on time and reduces work in process (WIP) expenses. The time saved enables the
acceptance of more customer orders at almost no additional cost (except for raw
materials).
Note, the difference between the total lead
time achieved by EFA in situations 1 and 2, 160.6 and 152.0 hours respectively
shows that less due date constraints,
usually
enable
better planning results. It should be considered when accepting customer
orders.
Reports (example)
TABLE2 Process Data
The process times in TABLE-2 are given in minutes.
The Setup times for manufacturing jobs in machines M1, M2 is 20 minutes, and in
M6 30 minutes.
There are no setups in other machines.
TABLE3
EDD schedule for different due dates.
Note: If several jobs have the same Due Date, the sequencing order is the same
as in the Order List.
TABLE4
EFA schedule for different due dates
TABLE5 EFA
schedule for the same due dates
TABLE6
Bottle-neck
schedule for the same due dates
