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x
x
Let k =
max
min
, where max = maximum and min = minimum, then the
3
intervals are obtained as:
Highfrequency
= [
xx
)
(1)
max
max
Mediumfrequency
= [
x
k x
,
2
k
)
(2)
max
max
Mediumfrequency
= [
x
2,
k x
]
(3)
max
min
y
y
max
min
Similarly, let y be the downtime of the machines. Let l =
, then the
3
intervals are obtained as:
Highdowntime
= [
y
,
y
)
(4)
max
max
Mediumdowntime
= [
y
ly
,
)
2
l
(5)
max
max
Mediumdowntime
= [
y
2,
ly
]
(6)
max
min
Using the above formulae, machines are mapped into a two-dimensional matrix
based on their respective intervals on frequency of failures and downtime. Next,
decision strategies for machines such as OTF, FTM, SLU, CBM, DOM, RCM or TPM
can be implemented (Labib (1998b)).
Step 2.
Decision Mapping: Those machines that meet both criteria and are ranked in Step 1,
are then mapped on the grid as shown in Table 1.
Downtime
Frequency
Low
Medium
High
Low
OTF
FTM1
CBM
FTM2
FTM4
Medium
FTM3
High
SLU
FTM5
DOM
Table 1. Decision-Making Grid (Labib, 1998b)
In this phase the decision is developed by comparing two-dimensional matrices.
The objective of this exercise is to implement appropriate actions that will lead to
the movement of machines towards improved machine maintenance strategies,
complying with Labib (1998b) in respect of the multiple criterions as follows:
a.
Operate to failure (OTF): Machines that are very seldom failed (low frequency).
Once failed, the downtime is short (low downtime). The machines in this region are
performing well and are easy to repair
b.
Skill levels upgrade (SLU): Machines that always fail (high frequency), but can be
fixed quickly (low downtime). Basically, the problems faced by the machines in this
grid are relatively easy to fix. Upgrading operators' skill levels in fixing the
problem will help to reduce response time;
c.
Condition-based maintenance (CBM): Machines that seldom fail (low frequency).
However, this is a killer machine, as it takes a long time to bring it back to normal
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