Chapter 14S – Maintenance
CHAPTER 14S
MAINTENANCE
Teaching Notes:
Maintenance is critical with JIT and TQM implementation. Poor maintenance leads to direct repair
expenses and other expenses resulting from lost production. The production line disruptions are
particularly important in JIT environments. An effective maintenance program ensures that machines
Answers to Discussion and Review Questions
2. Breakdown costs would include such items as repair of equipment (perhaps on an emergency
3. Preventive maintenance may result from inspections that reveal the need for preventive
maintenance, according to calendar (passage of time), or after a set number of operations.
4. Predictive maintenance is an attempt to predict when breakdowns are likely and schedule
5. Organizations use some combination of these approaches to deal with breakdowns: Standby or
6. The Pareto concept is that in any list of factors known to contribute to a certain result or
outcome (accident, injury, equipment breakdown or whatever), a relatively few factors will
7. The key points should involve these concepts:
a. The need for maintenance
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14S-2
8. As the Preventive Maintenance increases, the probability of breakdown and the associated
repairs decrease. When a machine fails, the following related costs must be considered.
a. Cost of lost production capacity (when machines are down, production capacity is reduced
9. When implementing a JIT system, there is very little, if any, work-in-process inventory.
Therefore, the machines (operations) depend on each other for incoming materials and parts.
10. As the level of investment in Preventive Maintenance increases, the likelihood of machine/
equipment breakdowns decrease if the machine is well maintained. Properly maintained
machines will produce less defects, which will result in higher quality products.
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Solutions
1.
Number of
recalibrations
Probability of
occurrence
Expected number of
recalibrations
0
.15
0
1
.25
.25
Expected cost of recalibration: 1.85/month x $500 = $925/month.
Service contract = $650. This is $275 less than a month.
2.
Number of
breakdowns
Probability of
occurrence
Expected number of
breakdowns
0
.10
0
1
.30
.30
2
.30
.60
3
.20
.60
4
Repair approach would have an expected cost of:
1.90 breakdown/month x $240/breakdown = $456/month
A service contract with a single fee and all repairs covered would cost $500
3. Using the formula:
Preventive cost
Breakdown cost
= Probability
Equipment Probability Z Maintenance Interval
A201:
$300_
$2,300
= .1304
–1.12
20 –1.12(2) = 17.76 days
$200_
= .0571
–1.58
30 –1.58(3) = 25.26 days
C850:
$530_
$4,800
= .1104
–1.22
40 –1.22(4) = 35.12 days
2
.30
.60
3
.20
.60
4
Chapter 14S – Maintenance
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Enrichment Module: Maintenance Problems
The purpose of this enrichment module is to further demonstrate the various trade-offs in maintenance
management by using realistic problems. In addition, these problems are designed to add richness, and
1. ITL Inc. has been keeping track of breakdowns per month of their automated assembly line,
over the past three years.
# of Breakdowns
# of months this occurred
0
3
1
10
2
9
3
4
8
5
2
Each failure (breakdown) of the assembly line will cost the company $350 to repair and the
associated average downtime cost is $300. ITL Inc. is considering to purchase a preventive
maintenance (PM) service contract.
▪ The monthly cost of this maintenance contract is $600.
It appears that ITC Inc. has two options:
2. A local cutlery manufacturing company has been analyzing the breakdown/failure records of a
certain type of a cutting machine. This particular type of cutting machine had the following
breakdown record.
# of breakdowns per day
Frequency
0
72
1
135
2
3
45
4
18
Cost of repair for this type of machine is $80 per breakdown. The preventive maintenance
program would cost the company $30/day and would repair the machine free of charge after
the first breakdown.
a. Determine the total daily cost of repairs if the company does not implement the preventive
maintenance program.
3. Use the information given in Problem 1 and determine the maximum amount that ITL Inc.
would be willing to pay for the preventive maintenance service contract (Breakeven point).
4. Use the information given in Problem 1 to solve this problem.
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Solution to Problem 1
Option 1:
X
F(x)
P(x)
X*P(x)
# of breakdowns
# of months this
occurred
Probability of # of
breakdowns/months
0
3
.0833
0
1
10
.2778
.2778
▪ E[X] = 2.2775 Expected # of breakdowns per month
▪ The total cost of implementing the repair program without purchasing the maintenance contract is:
E[X] * [Cost of repairs]
(2.2775) * ($650) = $1,480.37
▪ The total cost associated with the maintenance service contract can be determined as follows:
X
# of breakdowns
Cumulative prob. of months with X breakdowns
0
.0833
1
.3611
2
.6111
3
.7222
4
.9444
5
▪ P (X 1) = 1–.0833
P (X 1) = .9167 (Probability of at least one breakdown)
2
9
.25
3
.1111
.3333
4
.2222
.8889
5
36
Solution to Problem 2
(x) – # of
breakdowns/day
Frequency
P(x)
x * P(x)
0
72
.20
0
1
135
.375
.375
2
90
.25
.50
3
45
.125
.375
4
18
.05
.20
360 days
1.0
1.45
▪ E [x] = 1.45 breakdowns/day
a. Total cost if the preventive maintenance program is not purchased:
▪ Since 94 < 116, purchase the service contract.
Solution to Problem 3
▪ E [x] = Expected # of repairs/month
▪ RC = Repair cost/breakdown
▪ y = # of breakdowns not covered by the service contract
Chapter 14S – Maintenance
Solution to Problem 4
▪ E [x] = 2.2775 breakdown/month (from problem 1)
▪ Since the first breakdown is covered by the service contract