Manufacturing Preventive Maintenance

An important part of proper maintenance management involves good techniques for managing material resources. Good maintenance management precipitates good MRO inventory management. As a first step, a method of determining spare parts requirements for pieces of equipment, equipment types or groups of equipment including specified quantities and usage frequencies is needed. This can be accomplished through the use of an equipment Bill of Materials (BOM) that serves as a maintenance activity parts list. BOM quantities can be determined from manufacturers' specifications and past consumption statistics. Usage frequencies can also be determined based on past consumption and an analysis of the frequency of part failures from Mean Time Between Failure (MTBF) information in equipment history.

Equipment BOMs should contain quantities of both stockable and non-stockable parts. The failure history and consumption statistics can provide information necessary to make informed decisions about what parts to stock and in what quantities. To provide for ready availability of non-stockable spares, vendor scheduling agreements with predetermined lead-times should be established. A vendor scheduling agreement will eliminate the need to stock expensive seldom used spares while at the same time provide a means of supplying spares in time to satisfy maintenance jobs.

Valid and accurate maintenance schedules are another way to achieve better MRO inventory management. Planned maintenance work orders provide a master schedule of maintenance activities over a set planning horizon. Time-phased materials requirements can be established based on that schedule. A systematic approach of determining material requirements and availability before releasing work orders to crews eliminates the need for excessive just-in-case inventories and prevents undertaking jobs that cannot be completed for lack of parts. Rather, an approach that starts with an explosion of an equipment BOM to check requirements and availability of spares, allocates or reserves on-hand quantities of stockable spares, and activates the need to order unstockable spares before launching orders ensures that schedules are met and equipment reliability is sustained.

One of the most difficult tasks of maintenance management can be that of determining which equipment to work on first when priorities shift and a methodology for addressing maintenance requirements is not in place. With a formalized planning and scheduling process that task is made more manageable and eliminates disruptions caused by shifting priorities. The absence of a methodology can result in under utilization of maintenance labor and decreased productivity.

Good MRO inventory management is based on using equipment BOMs for determining what parts are needed and the maintenance schedule for determining when parts are needed. Similarly, in manpower planning, efficient planning and allocation of resources is based on the determination of what is needed and when and matching availability to requirements. Maintenance manpower planning involves properly allocating maintenance labor hours to plans. For manpower planning the maintenance schedule provides the basis for determining when manpower is required. The type and amount of manpower is determined by a routing or job list tied to a piece of equipment or type of maintenance work.

Manpower planning begins with assessing skills by trade or craft (i.e. mechanical, electrical, etc.) in the maintenance work force. Determinations of levels within craft (master mechanic, apprentice, etc.), are also required to get a proper mix of skills to meet requirements. Crews can consist of a mix of crafts or mix of individuals of the same craft. The number of individuals in a crew and the skill mix provide a profile of maintenance capacity-the amount of labor hours and craft distribution available to perform work in the various maintenance categories. This can be broken down further by targeting crews to designated facilities, areas within facilities or to groups or pieces of equipment.

Managing the manpower involves assigning specific work to specific crews at specific times based on scheduled work orders. The ability to schedule crews to jobs requires knowing which crew (or skill requirement) is needed at what time. The process of accurately associating skill requirements to maintenance tasks is facilitated by the use of a routing or predefined task list for different maintenance jobs or equipment.

A routing is a means of tying together a sequence of steps necessary to restore or sustain equipment reliability with the necessary resources. The routing should consist of the task list for a type of maintenance activity (preventive maintenance, repair, overhaul), the craft or skill required, and the time required to complete the step. The routing could also include methods of coordinating work between different crews and production as well as the need for special licenses, permits, or tools. As with an equipment BOM, a routing may be based on manufacturers' specifications, crew knowledge, and past history. Where special skills are needed that are not available within the internal work force, the designation of a subcontracted or external crew can be designated in the routing with a purchase agreement for the service already established to avoid delaying the progress of the job.

When maintenance work orders are released an accurate match of manpower requirements to availability can be made by com­paring the craft specifications of the routing in the order to the capacity profiles for those crafts. As with the materials require­ments planning process, the manpower planning process should check the availability of the resources and allocate them to the order in the time frame needed.

To be Continued

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