Preventative Maintenance (PM) is a more proactive approach, allowing organizations to schedule planned maintenance activities.
Activities are either planned on a Mean Time Between Failure (MTBF) estimate - a number given by the manufacturer that estimates the average length of time between failures of a machine and its components, which can be used to dictate an optimized service interval. Or an in-service derived optimum service interval based upon historic maintenance data, which may include information from Reliability Centered Maintenance (RCM) records and/or a Failure Mode Effects and Criticality Analysis (FMECA). This is effectively an MTBF based on more local knowledge.
Machinery is then inspected/serviced on that interval, and assets are repaired, restored, or replaced accordingly.
When would you use preventative maintenance?
For organizations looking to be more proactive and aiming to reduce the risk of machinery experiencing unplanned failures, preventative maintenance activities are scheduled for when the MTBF number is approaching or has been exceeded (in terms of machine running time). In some instances, preventative maintenance is also calculated on a usage-based trigger, for example, the number of production cycles, or a machine load-based calculation. Time-based triggers are more commonly used, but both are assumptive measures on when to schedule your planned maintenance.
Preventative maintenance in theory
Planning PM based on time or usage triggers means, in theory, that organizations can efficiently plan maintenance operations between operating phases based on certain time or usage periods. Scheduling maintenance during planned downtime can offer significant efficiency savings. In theory, the organization can operate normally and proactively plan maintenance when appropriate to increase machine uptime, boost throughput and maintain quality standards.
Preventative maintenance in reality
PM cannot indicate potential failure points and is not based on the actual condition of machinery. It cannot solve unplanned breakdowns which result in additional downtime, though it may reduce the risk of such failures occurring. It is complex to find the right frequency of doing PM activities and many companies find themselves either wasting money by replacing good parts (over-maintenance) or experiencing unplanned downtime (under-maintenance). Both are costly and risky to business sustainability.
Important considerations with preventative maintenance
PM can achieve from 12% to 18% cost savings over reactive maintenance. It is more efficient than reactive maintenance and so should make up a more significant part of an organization’s maintenance strategy. In preventative maintenance the key is planning and ensuring that labor is available when needed and that not all machines need to be maintained at the same time. The efficient usage of machines to stagger their maintenance intervals requires a skilled operations plan and this often gets forgotten when customer production schedules demand high utilization.
Advantages of preventative maintenance
Compared to corrective (reactive) maintenance, preventative maintenance allows for better planning, and can offer significant reductions in the cost of emergency maintenance.
Better understanding of risk
As the maintenance is planned using manufacturer failure statistics or historic maintenance knowledge, in theory it should allow for a better understanding of production risk and capabilities.
Clearer understanding of upcoming component usage for budgeting
Preventative maintenance schedules will describe which components need inspecting or replacing and at what intervals. This allows for more precise budgeting of required inventory.
Disadvantages of preventative maintenance
Over and under scheduling
Organizations run the risk of over and/or under scheduling maintenance activities, without the use of condition data to optimize PM schedules. Resulting in resource waste (labor and parts) or unplanned downtime.
Not based on actual condition
As maintenance is performed on a time basis, machines driven lightly might end up with perfectly good components being replaced or machines driven hard failing before their planned maintenance interval.
Complex to manage for large numbers of assets
Managing more than a few tens of assets on a time-based preventative schedule provides some significant challenges to guard against many machines needing maintenance at the same time.