identification and elimination of waste through continuous improvement. The problem of under-maintaining assets is often addressed through loss elimination and continuous improvement programs. The problem of over-maintaining by comparison receives little attention. Left unattended the over-maintaining of assets silently and continuously squanders precious maintenance resources.
Industry has been conservative in its approach to setting preventive maintenance intervals. On some sites:
- 80 % of Preventive Maintenance costs are spent on activities with a frequency 30 days or less.
- 30 to 40% of Preventive Maintenance costs are spent on assets with negligible failure impact.
We now explore the impact of frequency on the over maintaining problem and proposes, with the use of a case study, low risk methods for reducing Preventive Maintenance costs. Keywords: Preventive Maintenance, Waste Elimination, Activities, Frequency, Analysis, Cost Reduction.
Buell and Smedley define Lean Manufacturing as “a systematic approach to identifying and eliminating waste through continuous improvement”. Waste is further defined as “anything that adds no value to the manufacturing process. Common sources of waste in manufacturing are identified (2) as:
- Overproduction – Producing product quantity in excess of requirement or demand.
- Inventory – Producing levels of end product or work in progress above the optimum.
- Waiting – Delays in the production process.
- Transportation – Transporting end product or work in progress unnecessarily.
- Motion – Unnecessary motion of workers, assets or materials associated with production.
- Processing – Redundant steps or activities in the production process.
Reducing the Cost of Preventive Maintenance
The application of the term “Lean” to maintenance similarly aims to target waste. Bever estimates that between 18% and 30% of every dollar spent on maintenance is wasted. Greg is reported as observing that maintenance operations may be wasting up to 25 percent of available labour and that up to 60 percent of this waste results from activities that add no value to the performance of the plant. Similar categories of maxpanda for Lean Manufacturing can be applied to the exploration of Lean Maintenance. Building on a list developed by O’Hanlon, seven categories of waste in maintenance are summarised as follows:
- Overproduction – Performing preventive and predictive maintenance activities at intervals more often than optimal
- Inventory – Overstocking maintenance spares with slow moving parts and secret inventories.
- Waiting – Waiting for tools, parts documentation, transportation, etc.
- Transportation – Time spent walking, running, driving, and flying associated with maintenance work
- Motion –PM performed that adds no value to the prevention of downtime.
- Processing– Opportunity to improve the quality of repairs in reactive or breakdown maintenance.
- Defects – Asset failure caused by under-maintaining assets or maintenance rework.
Waste in maintenance can be considered as a problem of strategy, planning and control. This paper is specifically concerned with waste arising from strategic decision making. This particularly targets maintenance waste associated with “overproduction”, “inventory” and “motion” from the above list. These three topics are referred to specifically as over-maintaining.