Maintenance

Supplement 14

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Supplement 14: Learning Objectives

You should be able to:LO 14S.1 Explain the importance of maintenance in

production systemsLO 14S.2 Describe the range of maintenance activitiesLO 14S.3 Discuss preventive maintenance and the key

issues associated with itLO 14S.4 Explain breakdown maintenance and name

the key issues associated with itLO 14S.5 State how the Pareto phenomenon pertains to

maintenance decisions

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The goal of maintenance is to keep the production system in good working order at minimal cost

Reasons for wanting to keep equipment and machines in good operating condition:1. Avoid production or service disruptions2. Not add to production or service costs3. Maintain high quality4. Avoid missed delivery dates

Maintenance Goals

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1. Operations capacity is reduced, and orders are delayed

2. There is no output, but overhead continues, increasing the cost per unit

3. There are quality issues Output may be damaged

4. There are safety issues Employees or customers may be injured

Breakdown Consequences

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Reactive:Breakdown maintenance

Dealing with breakdowns or problems when they occur

Proactive:Preventive maintenance

Reducing breakdowns through a program of lubrication, adjustment, cleaning, inspection, and replacement of worn parts

Maintenance Options

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The goal of preventive maintenance is to reduce the incidence of breakdown or failures in the plant or equipment to avoid the associated costs Loss of output Idle workers Schedule disruption Injuries Damage to other equipment, products, or facilities Repairs

Inventories of spare parts Repair tools and equipment Repair specialists

Preventive Maintenance

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It is periodicIt can be scheduled according to the availability

of maintenance personnel and to avoid interference with operating schedules

Maintenance is scheduled using some combination of1. The result of planned inspections that reveal a need for

maintenance2. According to the calendar (passage of time)3. After a predetermined number of operating hours

Preventive Maintenance Schedule

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Preventive Maintenance: FrequencyThe goal is to strike a balance between the

cost of preventive maintenance and the cost of breakdown

The amount of preventive maintenance, therefore, is a function of the expected frequency of breakdown, the cost of breakdown, and the cost of preventive maintenance

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Frequency: Example 1 The frequency of breakdown of a machine per month is

$1,000 and the cost of preventive maintenance is $1,250 per month. If preventive maintenance is performed, the probability of a machine breakdown is negligible. Should the manager use preventive maintenance, or would it be cheaper to repair the machine when it breaks down?

Number of breakdowns 0 1 2 3

Frequency of occurrences .20 .30 .40 .10

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Frequency: Example 1

4.1)10(.3)40(.2)30(.1)20(.0breakdowns of

number Expected

Number of breakdowns 0 1 2 3

Frequency of occurrences .20 .30 .40 .10

$150

$1,250 - )1.4($1,000

emaintenancpreventive ofCost

breakdownofcost Expected

emaintenanc preventiveofbenefit Expected

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Suppose the average time before breakdown is normally distributed with a mean of 3 weeks and a standard deviation of .60 weeks. If breakdown cost averages $1,000 and preventive maintenance costs $250, what is the optimal maintenance interval?

Find the number of standard deviations from the mean represented by an area under the normal curve of .25

Using the standard normal table, it is -0.67Use this value to determine the maintenance interval

Frequency: Example 2

25.000,1$

250$

costBreakdown

cost Preventive

weeks2.598)(-.67)(.603deviation) (standard Mean z

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Predictive maintenance An attempt to determine when best to perform

preventive maintenance activitiesIdeally, preventive maintenance will be performed

just prior to a breakdown or failure because this will result in the longest possible use of facilities or equipment without a breakdown

Total productive maintenance JIT approach where workers perform preventive

maintenance on the machines they operate

Maintenance Approaches

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Approaches to dealing with breakdowns:Use of standby or backup equipmentInventories of spare parts are maintainedUse operators who are able to perform at least

minor repairs on the equipment they operateHave repair people who are well trained and

readily available to diagnose and correct problems

Breakdown Programs

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When breakdowns become frequent and/or costly:What is the cost of replacement compared to

continued maintenance?Issues:

Predicting breakdownsTechnological changeSystem disruptionsTraining employees on the use of new equipmentForecast of future demand

Replacement

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Breakdown programs are most effective when they take into account the degree of importance of a piece of equipment has in the operations system, and the ability of the system to do without it for a period of time.

The Pareto phenomenon exists in such situations: Few pieces of equipment will be extremely important to

the functioning of the systemThese justify considerable effort and/or expense

Some will require moderate effort and/or expense Many will justify minimal effort and/or expense

Pareto Phenomenon & Maintenance

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