Environmental Engineering Reference
In-Depth Information
as a result of inverse proportionality between the
length of the sub-period of scheduling plan and the
number of machine adjustments. If longer schedul-
ing sub-periods are chosen, then the production of
setup wastes and the inventory holding costs will
be decreased but the flexibility of the scheduling
will be lost. On the other hand, if the scheduling
sub-period is shortened, then the scheduling will
be more flexible but the number of setup waste
will increase. For this reason, there is a need to
find out an optimum scheduling plan taking into
account the production of setup wastes.
When adjusting the production schedule with
the aim of minimizing setup wastes, the primary
concern of the car battery manufacturing company
is the demand level of products. Products with low
demands (products whose monthly demands are
approximately equal to the production capacity of
one shift) are produced in one or two shifts. Prod-
ucts with high demands (products whose monthly
demand highly exceeds the production capacity
of one shift) are produced on a weekly basis and
are sent to customers each week. Namely, the
monthly demand is divided to weekly demands.
Since these highly demanded products are not
produced continuously, a setup adjustment on
the closing machine is needed each time the pro-
duction of this product starts (each week). The
number of setup adjustment will be high, as well
as the setup waste generated. An alternative waste
management solution is to schedule products so
that high-demanded products are produced con-
tinuously like the low-demanded products. By
this one-month-scheduling method, the monthly
demand of high-demanded products will not be
divided by four; the monthly demand will be
produced in one batch. Namely, the production
of these products will continue until the monthly
demand is reached.
It is necessary to produce one setup waste while
making machine adjustments in the battery clos-
ing operation. This setup waste is considered as a
refurbished battery and can not be sold to custom-
considered as the on-site waste management cost
of the refurbished battery. One way to establish a
pollution prevention approach may be to change
the production scheduling policy to decrease the
number of refurbished batteries. The relation be-
tween the length of the scheduling sub-period and
setup waste amount is established to find out the
existence of an option to obtain minimum waste.
The scheduling sub-period (one week, two week,
or four week) in a month affects the number of
setup waste generated. Therefore, one of the ways
of reducing the setup waste is to determine the
sub-period with minimum inventory holding and
waste removal cost between different scheduling
sub-periods. For this reason, different scheduling
sub-periods are analysed, such as one week, two
week and four week. The company is currently
using a production scheduling based on one-week
sub-period. A binary integer programming model
is developed to determine the sub-period giving the
minimum total cost comprising inventory holding
and waste management costs. Inventory carrying
within the considered sub-period is ignored. The
model is demonstrated below.
m
3
2
∑
Minimize
WR X W R X W R X
+
+
+
h X D
+
h X D
i
i
i
i
i
i
i
1
1
2
2
4
4
1
2
i
=
1
subject to
X
+
X
+
X
=
1
1
2
4
X
k
∈
{ , }
0 1 , k
=
1,2,4
Where,
D
i
is the demand of product
i
,
W
i,k
is
setup waste of product
i
derived with alternative
k
,
R
i
is the waste management cost of product
i
, and
h
i
is weekly inventory holding cost of product
I
The
model is solved for the given data. Different types
of products with varying demands (5 of them are
low-demanded and 12 of them are high-demanded)
