April - June 2007 - Kasetsart University

p
1,
i
*
Kasetsart J. (Nat. Sci.) 41(2) 383
q1,
i
= (1)
q
1,
i
*
q2,
i
p2,
i = (2)
q2,
i
If the manufacturer held safety stocks for every raw material, the delivery performances to
manufacture of stage-1 raw material i and stage-2 raw material j could be defined as in Equations (3)
and (4), respectively.
k
1,
i
*
1i 1,
i
1,
i
q , + x
=
q
x1,
i
= p1,
i +
q
∀ i = {, 12K , , m}
1,
i
*
q2, j + x2,
j x2,
j
k2,
j = = p2,
j +
q2,
j
q2,
j
∀ j = {, 12K , , n}
(4)
The inventory cost of the safety stock of each raw material could be computed from Equations
(5) or (6) as follows.
C1, i = c1, ix1, i = c1, iq1, i( k1, i − p1,
i)
∀ i = {, 12K , , m}
(5)
C2, j = c2, jx2, j = c2, jq2, j( k2, j − p2,
j)
∀ j = {, 12K , , n}
(6)
The manufacturing performance of stage-1 process, ps1 , was defined as the ratio between ontime
and planned production, accounting for all delays that may occur, but excluding those caused by
material stockouts. The ps1 could be found from Equation (7). The WIP delivery performance to stage-
2 manufacturing process, kw, was given in Equation (8).
p
s1
=
q
q
*
w
w
m
x
kw = ps k i + w
1∏
1,
i=
1 q
(8)
w
The inventory cost of the WIP safety stock could be calculated from Equation (9).
m
Cw = cwxw = cwqw( kw − ps ∏ k i)
1 1,
(9)
i=
1
Similarly, the manufacturing performance of stage-2 process, ps2 , the product delivery
performance, kp, and the product inventory cost could be calculated as follows.
p
s2
=
q
q
*
p
p
x
kp = ps kw k j +
2 ∏ 2
q
n
j=
1
(3)
(7)
(10)
p
,
p
(11)
C = c x = c q ( k − p k k )
p p p p p p s2w 2,
j
j=
1
n
∏
(12)