Supplement 15 Maintenance McGraw-Hill/Irwin Copyright © 2009 by The McGraw-Hill Companies, Inc All Rights Reserved Supplement 15: Learning Objectives • You should be able to: – Explain the importance of maintenance in production systems – Describe the range of maintenance activities – Discuss preventive maintenance and the key issues associated with it – Discuss breakdown maintenance and the key issues associated with it – State how the Pareto phenomenon pertains to maintenance decisions 15S-2 Maintenance • Maintenance – All activities that maintain facilities and equipment in good working order so that a system can perform as intended – Maintenance activity categories: • Buildings and grounds • Equipment maintenance 15S-3 Maintenance Goals • 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: – – – – Avoid production or service disruptions Not add to production or service costs Maintain high quality Avoid missed delivery dates 15S-4 Breakdown Consequences • Operations capacity is reduced, and orders are delayed • There is no output, but overhead continues, increasing the cost per unit • There are quality issues – output may be damaged • There are safety issues – employees or customers may be injured 15S-5 Maintenance Options • 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 15S-6 Total Maintenance Cost 15S-7 Preventive Maintenance • 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 Damange to other equipment, products, or facilities Repairs 15S-8 Preventive Maintenance Schedule • It is periodic • It is scheduled according to the availability of maintenance personnel and to avoid interference with operating schedules • Maintenance is scheduled using some combination of – The result of planned inspections that reveal a need for maintenance – According to the calendar (passage of time) – After a predetermined number of operating hours 15S-9 Preventive Maintenance: Frequency • The 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 15S-10 Frequency: Example • 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 Frequency of occurrences 20 30 40 10 15S-11 Frequency: Example Number of breakdowns Frequency of occurrences 20 30 40 10 Expected number = 0(.20) + 1(.30) + 2(.40) + 3(.10) = 1.4 of breakdowns Expected benefit of Expected cost of Cost of preventive = − preventive maintenance breakdown maintenance = 1.4($1,000) - $1,250 = $150 15S-12 Frequency: Example • Suppose the average time before breakdown is normally distributed with a mean of weeks and a standard deviation of 60 weeks If breakdown cost average $1,000 and preventive maintenance costs $250, what is the optimal maintenance interval? Preventive cost $250 = = 25 Breakdown cost $1,000 • 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 -0.67 • Use this value to determine the maintenance interval Mean + z (standard deviation) = + (-.67)(.60) = 2.598 weeks 15S-13 Maintenance Approaches • Predictive maintenance – An attempt to determine when best to perform preventive maintenance activities • Ideally, 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 15S-14 Maintenance Problems • Maintenance problems are sometimes designed into products: – Poor design – Designer have accorded other aspects of design greater importance • Cost • Appearance is more important than maintenance activities 15S-15 .. .Supplement 15: Learning Objectives • You should be able to: – Explain the importance of maintenance in... to production or service costs Maintain high quality Avoid missed delivery dates 15S-4 Breakdown Consequences • Operations capacity is reduced, and orders are delayed • There is no output, but... program of lubrication, adjustment, cleaning, inspection, and replacement of worn parts 15S-6 Total Maintenance Cost 15S-7 Preventive Maintenance • The goal of preventive maintenance is to reduce the