Operations Management Maintenance and Reliability 保養維護與可靠程度 Chapter 17

Outline GLOBAL COMPANY PROFILE: NASA THE STRATEGIC IMPORTANCE OF MAINTENANCE AND RELIABILITY RELIABILITY Improving Individual Components Providing Redundancy MAINTENANCE Implementing Preventive Maintenance Increasing Repair Capability TOTAL PRODUCTIVE MAINTENANCE TECHNIQUES FOR ESTABLISHING MAINTENANCE POLICIES

Learning Objectives When you complete this chapter, you should be able to : Identify or Define: Maintenance Mean time between failures Redundancy Preventive maintenance Breakdown maintenance Infant mortality

Learning Objectives - continued When you complete this chapter, you should be able to : Describe or Explain: How to measure system reliability How to improve maintenance How to evaluate maintenance performance

NASA Maintenance of space shuttles Columbia: Maintenance requires 86,000,000 miles on odometer 3 engines each the size of a VW expected to make dozens more launches Maintenance requires 600 computer generated maintenance jobs 3-month turnaround More than 100 people A point to be made here is that in order for NASA to accomplish the task it has set for itself, the shuttle must be designed for maintainability. Otherwise the problem of maintaining the shuttle would be overwhelming!

Maintenance Management All activities involved in keeping a system’s equipment working Objective: Maintain system capability & minimize total costs A major point to be emphasized here is the maintenance should attempt to minimize total cost - not just maintenance cost. A second point is that total cost should be what some call “whole body cost,” and include: - unit purchase cost - cost of training personnel to use the unit - cost of buying a replacement at the end of this unit’s lifetime - cost of disposing of the old unit - cost of maintaining the unit during its useful lifetime - cost of upgrading the unit during its lifetime - etc. © 1995 Corel Corp.

The Strategic Importance of Maintenance and Reliability Failure has far reaching effects on a firm’s operation reputation profitability customers product employees profits The effect of failure on the listed items should be discussed. A point to make is that the cost of failure implies more than simply “this unit doesn’t work.” It reduces the likelihood of return customers in many ways.

Maintenance Performance Maintenance Procedures Employee Involvement Maintenance Performance © 1995 Corel Corp. The performance of maintenance is the responsibility of whom? The worker using the unit in the performance of his/her job? Workers from the “maintenance department”? Outside contractors?

Good Maintenance & Reliability Strategy Requires: Employee involvement Maintenance and reliability procedures To yield: Reduced inventory Improved quality Improved capacity Reputation for quality Continuous improvement You might stress at this point that employee involvement is crucial.

Employee Involvement Information sharing Skill training Reward system Power sharing © 1995 Corel Corp. Employee involvement, the key to maintenance? By this time, the student should be gaining the impression that employee involvement is the key to successful OM.

Maintenance & Reliability Procedures Maintenance Procedures © 1995 Corel Corp. Clean and lubricate Monitor and adjust Minor repair Computerized records

Maintenance Benefits Lower operating costs Continuous improvement Faster, more dependable throughput Higher productivity Improved quality Improved capacity Reduced inventory Maintenance Examples demonstrating how each of the benefits is incurred would be worthwhile.

Tactics for Reliability and Maintenance Reliability Tactics improving individual components providing redundancy Maintenance Tactics implementing preventive maintenance increasing repair capabilities You might discuss the meaning of redundancy.

System Reliability - Components in Series Average Reliability of all Components (Percent) Reliability of the System (Percent) 100 80 60 40 20 100 99 98 97 96 n=1 n=10 n=50 n=100 n=200 n=300 n=400

Reliability of Components in Series R = R1 * R2 * R3 * ...

Evaluating Maintenance Reliability Probability that an item will function for a given time Mean time between failures (MTBF) Average time between failures of a repairable item Failure rate Reciprocal of MTBF

Failure Rate (%) Number of failures FR(%) = * 100% Number of units tested

Lifetime Failure Rates Infant mortality and improper use failure “normal” failure Wearout Failure rate Lifetime This is an interesting figure - but may not mean much to the students. They may be expecting a plot of mean time between failure instead of failure rate. You need to clarify this issue. It is also helpful to discuss some of the practices which stem from this curve: - computers and other electronic devices may be “burned in,” i.e., simply left running for a while to see if they will fail. (for some devices, the burn-in period is several hundred hours.) - replacement of electric motors at a point only one quarter through their estimated life span. Discuss other information we can get from plots of mean time between failures, and/or failure rates. (What does a bimodal mean time between failures plot represent?)

Failures Per Operating Hour Number of Failures FR(n) = Operating Time

Mean Time Between Failures 1 MTBF = FR(N)

Probability of first component working Providing Redundancy Probability of first component working Probability of second component working + Probability of needing second component * = P(R)

Maintenance Decisions How much preventive & breakdown maintenance Who performs maintenance Centralized, decentralized, operator etc. Contract or in-house When to replace or repair How much to replace Individual or group replacement

Types of Maintenance Preventive Breakdown Routine inspection & servicing Prevents failures Bases for doing Time: Every day Usage: Every 300 pieces Inspection: Control chart deviations Non-routine inspection & servicing Remedial Basis for doing Equipment failure Choose several items or processes, and ask students to decide upon what basis they should be maintained. Ask them also to identify some of the costs of an inappropriate maintenance schedule.

Mean Time Between Failure and Preventive Maintenance Frequency of failure Mean Time Between Failure Candidate for preventive maintenance will have distribution with low variability You might want to discuss, at least briefly, the difference in MTBF charts of mechanical versus electronic systems.

Organizing the Maintenance Function Centralized maintenance department Does all maintenance (PM & breakdown) Decentralized maintenance department Useful if different equipment used in different areas of company Contract maintenance Used if little equipment or expertise Operator ownership approach Ask students to identify some of the pros and cons of the various possibilities.

Operator-Ownership Approach Operator does preventive maintenance Equipment condition is their responsibility Learns equipment better Increases worker’s pride Reduces repair time & PM costs Maintenance department is backup Handles non-routine problems Provides maintenance training Has plant-wide responsibilities Is this an example of job enlargement or job enrichment?

A Computerized Maintenance System

Maintenance Costs Traditional View Maintenance Commitment Cost Preventive Maintenance Cost Total Maintenance Cost Breakdown Cost Optimal

Maintenance Costs Full Cost View Optimal Total costs Full cost of breakdowns Preventive maintenance costs Maintenance Commitment

Contract for Preventive Maintenance Compute the expected number of breakdowns without the service contract Compute the expected breakdown cost per month with no preventive maintenance contract Compute the cost of preventive maintenance Compare the two options

Increasing Repair Capabilities:Features of A Good Maintenance Facility Well-trained personnel Adequate resources Ability to establish a repair plan and priorities Ability and authority to do material planning Ability to identify the cause of breakdowns Ability to design ways to extend MTBF

Operations Manager Must Determine How Maintenance Will be Performed Operator Maintenance Department Manufacturer’s field service Depot Service (return equipment) Competence is higher as we more to the right Preventive maintenance costs less and is faster as we move to the left

Total Productive Maintenance Additional requirements of: Designing machines that are reliable, easy to operate and easy to maintain Emphasizing total cost of ownership when purchasing machines, so that service and maintenance are included in the cost Developing preventive maintenance plans that utilize the best practices of operators, maintenance departments, and depot services Training workers to operate and maintain their own machines Again, a multi-faceted approach!

A Key To Success High utilization of facilities, tight scheduling, low inventory and consistent quality demand reliability - total preventive maintenance is the key to reliability.

Techniques for Establishing Maintenance Policies Simulation - enables one to evaluate the impact of various maintenance policies Expert systems - can be used by staff to help diagnose faults in machinery and equipment One of the main benefits of simulation is that it helps one gain an understanding of the maintenance problem.