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Unformatted text preview: 1 Maintenance Models Prof. Robert C. Leachman IEOR 130, Methods of Manufacturing Improvement Spring, 2007. 1. Introduction The maintenance of complex equipment often accounts for a large portion of the costs associated with that equipment. It has been estimated, for example, that the maintenance costs in the military comprise almost one-third of all of the operating costs incurred. Alternative philosophies of equipment maintenance are as follows: 1. Breakdown maintenance . The equipment is put in service and operated until it fails. Maintenance forces then repair the equipment and attempt to restore it as closely as possible to a like-new condition, whereupon the equipment is put back in operation. Maintenance is confined to repair following failures. 2. Preventative maintenance . The equipment is periodically taken out of service for scheduled maintenance including replacement of worn components, inspection and cleaning, etc. The frequency of machine maintenance may be based on hours of usage, number of machine cycles, calendar time, etc. Repairs following failures also are performed as required on an on-call basis. (Hopefully, the preventative maintenance makes failures less likely.) 3. Predictive maintenance . The equipment is continually monitored or frequently inspected by manual or automated means. Required maintenance is identified and performed upon inspection. (This philosophy presumes a level of knowledge about the equipment sufficient to be able to detect flaws or wear in the equipment upon inspection.) As before, repairs following failures are performed as required on an on-call basis. (Hopefully, the frequent inspection or continuous monitoring makes failures unlikely.) Generally, maintenance evolves from breakdown maintenance to preventative maintenance to predictive maintenance as the manufacturing organization and systems become more sophisticated and knowledgeable about the equipment. The famous “TPM” (total productive maintenance) paradigm stresses the importance of completing the evolution to predictive maintenance in order to attain the highest productivity. Standard maintenance terminology is as follows: MBTF – Mean time between failures. This is the expected time from completion of repair following failure until the next failure. 2 MTTR – Mean time to repair. This is the expected time to repair the equipment after failure, including time waiting for parts and expertise, time to effect the repairs, and time to test and re-qualify the equipment before returning to production mode. Availability – The fraction of time the equipment is available for production operation. For the case of breakdown maintenance, the machine follows a renewal process, alternating between operating and failure states. In that case the availability may be calculated as ....
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This note was uploaded on 04/02/2008 for the course IEOR 130 taught by Professor Leachman during the Spring '07 term at Berkeley.
- Spring '07