Makespan - Production Planning & Scheduling Solutions Ltd.
Production Planning and Scheduling
in a Printed Circuit Board (PCB) 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 . The comparison is
made in a
Printed Circuit Board (PCB)
Plant which
produces a large number of different PCBs. The PCBs are divided into two
main types:
1- Double Sided (DS), these are PCBs with two layers (LAY), they have no
subassemblies.
2-
Multi layers (ML), these are PCBs with four, six, eight
and more subassemblies. (A subassembly consists of two layers).
The production line which consists of 14 work centers [M] and
the process flow of DS, ML and LAY are described in FIG-1
The product structure of multi layers is described below
(six layers)
In this example
the planning results of one planning situation are compared:
- The
manufacturing jobs have different Due Dates.
(unlike in the CASTING PLANT example, in this case the planning results
are the same, both in case the due dates are different or similar)
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
one work center to the next one
is of one unit.
- 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 route and process data for every product are given in TABLE2 at the bottom of this article.
Workload:
The total workload in each
w
The maximum workload is 15.09 working days (120.7 hours) in work center M5-1. This is the minimum
theoretical total lead time. Converting it to calendar dates shows that the earliest
date that production could be finished is
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
real total lead time
achieved by the detailed planning
is usually slightly longer than
the
one achieved in the first step, especially in complicated production lines.
This production line is more complicated than the CASTING one because there are two generations (father-son) in the product structure of some of the jobs and both are
manufactured in the same production line.
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.
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.
The different results obtained by the two schedules are described in the table
below.
|
|
EFA |
EDD |
|
Finishing Date |
|
|
|
Duration (hours= days * 8) |
139.0 |
182.3 |
|
T.Delay
(Calendar
days) |
0 |
20 |
|
Delta Time (hours) |
0 |
43 |
|
Increasing rate (%) |
0 |
30 |
Note, Running EFA scheduling during a period similar to that of EDD, that is 182.0 hours, enables to add an identical composition of product basket in which the quantity of each product is 25% of the original quantity.
Summary
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 and production of
more customer orders at almost no additional cost (except for raw materials).
Reports (example)
TABLE-2
Process Data:
The process times in TABLE-2 are given in minutes. The sign “–“means no process.
The first and second lines of each product are the setup and process time
respectively.
M8-X, M9-X denotes
M8-1, M9-1
for
ML or DS
and
M8-2
or M9-2
for
LAY.
TABLE-3 EDD schedule
Notes:
1) If several jobs have the same Due Date, the sequencing order is the same
as in the Order List.
2) If any part can not be processed for whatever reason, in this case a father
that his sons are still in process, the system schedules the next part(s) in the sequencing queue, for example part ML-A in line 33.
