Operations Management Chapter 17 Maintenance and Reliability Power

Operations Management Chapter 17 – Maintenance and Reliability Power. Point presentation to accompany Heizer/Render Principles of Operations Management, 7 e Operations Management, 9 e © 2006 Prentice Hall, Inc. 17 –

Outline þ Global Company Profile: Orlando Utilities Commission þ The Strategic Importance of Maintenance and Reliability þ Improving Individual Components þ Providing Redundancy © 2006 Prentice Hall, Inc. 17 – 2

Outline – Continued þ Maintenance þ Implementing Preventive Maintenance þ Increasing Repair Capabilities þ Total Productive Maintenance þ Techniques for Enhancing Maintenance © 2006 Prentice Hall, Inc. 17 – 3

Learning Objectives When you complete this chapter you should be able to: 1. Describe how to improve system reliability 2. Determine system reliability 3. Determine mean time between failure (MTBF) © 2006 Prentice Hall, Inc. 17 – 4

Learning Objectives When you complete this chapter you should be able to: 3. Distinguish between preventive and breakdown maintenance 4. Describe how to improve maintenance 5. Compare preventive and breakdown maintenance costs © 2006 Prentice Hall, Inc. 17 – 5

Orlando Utilities Commission þ Maintenance of power generating plants þ Every year each plant is taken off-line for 1 -3 weeks maintenance þ Every three years each plant is taken offline for 6 -8 weeks for complete overhaul and turbine inspection þ Each overhaul has 1, 800 tasks and requires 72, 000 labor hours þ OUC performs over 12, 000 maintenance tasks each year © 2006 Prentice Hall, Inc. 17 – 6

Orlando Utilities Commission þ Every day a plant is down costs OUC $110, 000 þ Unexpected outages cost between $350, 000 and $600, 000 per day þ Preventive maintenance discovered a cracked rotor blade which could have destroyed a $27 million piece of equipment © 2006 Prentice Hall, Inc. 17 – 7

Strategic Importance of Maintenance and Reliability þ Failure has far reaching effects on a firm’s þ þ þ þ © 2006 Prentice Hall, Inc. Operation Reputation Profitability Dissatisfied customers Idle employees Profits becoming losses Reduced value of investment in plant and equipment 17 – 8

Maintenance and Reliability þ The objective of maintenance and reliability is to maintain the capability of the system while controlling costs þ Maintenance is all activities involved in keeping a system’s equipment in working order þ Reliability is the probability that a machine will function properly for a specified time © 2006 Prentice Hall, Inc. 17 – 9

Important Tactics þ Reliability 1. Improving individual components 2. Providing redundancy þ Maintenance 1. Implementing or improving preventive maintenance 2. Increasing repair capability or speed © 2006 Prentice Hall, Inc. 17 – 10

Maintenance Strategy Employee Involvement Information sharing Skill training Reward system Employee empowerment Maintenance and Reliability Procedures Clean and lubricate Monitor and adjust Make minor repair Keep computerized records © 2006 Prentice Hall, Inc. Results Reduced inventory Improved quality Improved capacity Reputation for quality Continuous improvement Reduced variability Figure 17. 1 17 – 11

Reliability Improving individual components Rs = R 1 x R 2 x R 3

Overall System Reliability n=1 80 – n=1 0 60 – 40 – n n 20 – n = 0 40 Reliability of the system (percent) 100 – 0 |– 100 | = n= 10 50 0 = 20 0 30 0 n= | 99 | | 98 | | 97 | | 96 Average reliability of each component (percent) © 2006 Prentice Hall, Inc. Figure 17. 2 17 – 13

Reliability Example R 1 R 2 R 3 . 90 . 80 . 99

Product Failure Rate (FR) Basic unit of measure for reliability Number of failures FR(%) = x 100% Number of units tested Number of failures FR(N) = Number of unit-hours of operating time Mean time between failures 1 MTBF = FR(N) © 2006 Prentice Hall, Inc. 17 – 15

Failure Rate Example 20 air conditioning units designed for use in NASA space shuttles operated for 1, 000 hours One failed after 200 hours and one after 600 hours 2 FR(%) = (100%) = 10% 20 2 FR(N) = =. 000106 failure/unit hr 20, 000 - 1, 200 1 MTBF = = 9, 434 hrs. 000106 © 2006 Prentice Hall, Inc. 17 – 16

Failure Rate Example 20 air conditioning units designed for use in NASA space shuttles operated for 1, 000 hours One failed after 200 hours and one after 600 hours 2 Failure rate per trip= 10% FR(%) = (100%) 20 FR 2= FR(N)(24 hrs)(6 days/trip) FR(N) = =. 000106 failure/unit hr FR = (. 000106)(24)(6) 20, 000 - 1, 200 FR =. 153 failures per trip 1 MTBF = = 9, 434 hr. 000106 © 2006 Prentice Hall, Inc. 17 – 17

Providing Redundancy Provide backup components to increase reliability Probability of first component + working = © 2006 Prentice Hall, Inc. Probability of second of needing component x second working component (. 8) + (. 8) x (1 -. 8) . 8 + . 16 =. 96 17 – 18

Redundancy Example A redundant process is installed to support the earlier example where Rs =. 713 R 1 R 2 0. 90 0. 80 R 3 Reliability has increased from. 713 to. 94 0. 99 = [. 9 +. 9(1 -. 9)] x [. 8 +. 8(1 -. 8)] x. 99 = [. 9 + (. 9)(. 1)] x [. 8 + (. 8)(. 2)] x. 99 =. 99 x. 96 x. 99 =. 94 © 2006 Prentice Hall, Inc. 17 – 19

Maintenance þ Two types of maintenance þ Preventive maintenance – routine inspection and servicing to keep facilities in good repair þ Breakdown maintenance – emergency or priority repairs on failed equipment © 2006 Prentice Hall, Inc. 17 – 20

Implementing Preventive Maintenance þ Need to know when a system requires service or is likely to fail þ High initial failure rates are known as infant mortality þ Once a product settles in, MTBF generally follows a normal distribution þ Good reporting and record keeping can aid the decision on when preventive maintenance should be performed © 2006 Prentice Hall, Inc. 17 – 21

Computerized Maintenance System Data Files Output Reports Equipment file with parts list Inventory and purchasing reports Equipment parts list Maintenance and work order schedule Equipment history reports Repair history file Inventory of spare parts Personnel data with skills, wages, etc. © 2006 Prentice Hall, Inc. Data entry – Work requests – Purchase requests – Time reporting – Contract work Cost analysis (Actual vs. standard) Work orders – Preventive maintenance – Scheduled downtime – Emergency maintenance Figure 17. 3 17 –

Maintenance Costs þ The traditional view attempted to balance preventive and breakdown maintenance costs þ Typically this approach failed to consider the true total cost of breakdowns þ þ þ © 2006 Prentice Hall, Inc. Inventory Employee morale Schedule unreliability 17 – 23

Maintenance Costs Total costs Costs Preventive maintenance costs Breakdown maintenance costs Optimal point (lowest cost maintenance policy) Maintenance commitment Traditional View © 2006 Prentice Hall, Inc. Figure 17. 4 (a) 17 – 24

Maintenance Costs Total costs Full cost of breakdowns Preventive maintenance costs Maintenance commitment Optimal point (lowest cost maintenance policy) Full Cost View © 2006 Prentice Hall, Inc. Figure 17. 4 (b) 17 – 25

Maintenance Cost Example Should the firm contract for maintenance on their printers? Number of Breakdowns Number of Months That Breakdowns Occurred 0 2 1 8 2 6 3 4 Total: 20 Average cost of breakdown = $300 © 2006 Prentice Hall, Inc. 17 – 26

Maintenance Cost Example 1. Compute the expected number of breakdowns Number of Breakdowns Frequency 0 2/20 =. 1 2 6/20 =. 3 1 8/20 =. 4 3 4/20 =. 2 Expected number of breakdowns = ∑ Number of breakdowns x Corresponding frequency = (0)(. 1) + (1)(. 4) + (2)(. 3) + (3)(. 2) = 1. 6 breakdowns per month © 2006 Prentice Hall, Inc. 17 – 27

Maintenance Cost Example 2. Compute the expected breakdown cost per month with no preventive maintenance Expected breakdown cost = Expected number of breakdowns Cost per x breakdown = (1. 6)($300) = $480 per month © 2006 Prentice Hall, Inc. 17 – 28

Maintenance Cost Example 3. Compute the cost of preventive maintenance = Preventive maintenance cost Cost of expected Cost of breakdowns if service + service contract signed = (1 breakdown/month)($300) + $150/month = $450 per month Hire the service firm; it is less expensive © 2006 Prentice Hall, Inc. 17 – 29

Increasing Repair Capabilities 1. Well-trained personnel 2. Adequate resources 3. Ability to establish repair plan and priorities 4. Ability and authority to do material planning 5. Ability to identify the cause of breakdowns 6. Ability to design ways to extend MTBF © 2006 Prentice Hall, Inc. 17 – 30

How Maintenance is Performed Operator Maintenance department Manufacturer’s field service Depot service (return equipment) Competence is higher as we move to the right Preventive maintenance costs less and is faster the more we move to the left Figure 17. 5 © 2006 Prentice Hall, Inc. 17 – 31

Total Productive Maintenance (TPM) þ Designing machines that are reliable, easy to operate, and easy to maintain þ Emphasizing total cost of ownership when purchasing machines, so that service and maintenance are included in the cost þ Developing preventive maintenance plans that utilize the best practices of operators, maintenance departments, and depot service þ Training workers to operate and maintain their own machines © 2006 Prentice Hall, Inc. 17 – 32

Establishing Maintenance Policies þ Simulation þ Computer analysis of complex situations þ Model maintenance programs before they are implemented þ Physical models can also be used þ Expert systems þ Computers help users identify problems and select course of action © 2006 Prentice Hall, Inc. 17 – 33