Life is often not as difficult as it seems, and it is a good idea to ratchet back on complexity, keep things simple, and stick to what is important.
The input/process/output diagram above helps us do exactly that, and it can improve the way we measure and manage maintenance effectiveness.
The box on the left shows the inputs, or resources, we use to maintain our equipment. These include the hard resources such as the labor, filters, fluids, parts, supplies, and consumables required as well as the soft resources such as time, space, training, and skill. We spend time and money on resources, and in the vast majority of cases we are good at measuring the cost of what we use. We have good estimates for the cost of a 500-hour service, and we will certainly know what we spent once the job is done.
The middle box shows the processes we use to do our maintenance efficiently and effectively. Three things are important.
First, the processes must be disciplined. Maintenance cannot happen on a whim. It must be planned, scheduled, and performed as required—on time, every time.
Second, the processes must be systematic. There must be a system to trigger a maintenance action and call attention to the fact that work is due. Checklists, procedures, and protocols must be in place to define the required work, and technicians must have the training needed to perform the work.
Third, the processes must be thorough. There must be a way to verify that the maintenance action has been performed according to the checklists, procedures, and protocols, and that any follow up work will be scheduled and performed as needed.
This all sounds like common sense. There are, however, some issues, and many preventive maintenance programs do not function as well as they should. The first snag is the fact that maintenance actions do not enjoy the same sense of urgency as that enjoyed by repair actions. There is no doubt that when a machine is down, resources needed to repair a machine and return it to service receive priority. The urgent takes precedence over the important. The second snag is the fact that we really do not know why we do preventive maintenance. We know that preventive maintenance is a good thing to do. We know that we must look after our assets and that it is better to prevent an on-shift failure than repair a machine that has broken down and disrupted production. We do not really know what results we want to achieve, and above all, we do not really know how to measure success.
This is where the input/process/output diagram helps. Companies absolutely know the input resources used and know how much it costs to provide these inputs. Their preventive maintenance processes are frequently in place and functioning, and are thought to be disciplined, systematic, and thorough. Their maintenance-management software tracks maintenance due dates and issues preventive maintenance work orders and/or checklists as and when due. These are filled in and returned, the clock is reset, and the cycle continues.
The question is, what output do they seek to achieve from the maintenance process? What results do they hope to produce? How do they measure success?
As with most processes, outputs can be defined in two dimensions: efficiency and effectiveness. Efficiency—doing the thing right—means that the checklists and protocols needed to perform the work are in place and that the required work is performed on time and on budget. Checklists are filled in and returned when due, and the whole process is verifiable. Success is defined as completing a high percentage of preventive maintenance actions within a short period of due date.
Efficiency and timeliness are important, but success is measured by the time between a PM action and the next action of any kind.
An effective preventive maintenance operation is similar but different. Checklists and predefined protocols are used as needed, but the focus is on inspection and doing all the work required to ensure safe and reliable operation for at least the time to the next preventive maintenance action. The predefined checklist is seen as a starting point, not as an end in itself. Technicians are trained, encouraged, and required to go beyond the minimum and do what is needed. Efficiency and timeliness are important, but success is defined and measured in terms of the time between a given preventive maintenance action and the next action of any kind performed on the machine. If the preventive maintenance interval is 250 hours and an effective action was performed at 9,750 hours, then you really should not expect to visit the machine again until it reaches 10,000 hours.
Measuring the effectiveness of the preventive maintenance program is not complex. We have argued strongly for the need to use part of the work order coding system to identify work orders that are written because of (i) a reported emergency down event, (ii) an inspection or condition assessment that identifies a pending failure, and (iii) a regularly scheduled preventive maintenance event (see “Three Masters to Serve,” February 2017, and “Codes Drive Data,” August 2017). If this is done, then it is relatively simple to determine the interval between each regularly scheduled PM event and the next work order of any type written against the machine.
For example, if the period between the regular PM and the next work order is 150 hours and if the predetermined service interval is 250 hours, then the effectiveness of the preventive maintenance program is 60 percent (150 hours divided by 250 hours).
Five common maintenance practices
These are the top five things I see in practice.
- The vast majority of companies have a preventive maintenance program in place. Most do at least the minimum because the down side of not doing it is just too big.
- We focus too much on inputs. We know what we spend because preventive maintenance is seen as a good thing to do.
- Many companies have first-class preventive maintenance processes. Preventive maintenance checklists and work orders are frequently auto-generated by computerized maintenance-management software that tracks due dates and manages the maintenance cycle. The process functions.
- These companies almost universally define success in terms of timeliness. Two metrics are used: the number of preventive maintenance work orders outstanding, and the percentage of preventive maintenance work orders performed within 40 hours of due. The focus is on efficiency—doing the thing right.
- Few companies focus on the effectiveness of their preventive maintenance program in reducing the number of breakdowns, repairs, and other expensive events from occurring between preventive maintenance actions. Few calculate and use the maintenance effectiveness metric defined above. They do not know what they receive from their spending on preventive maintenance.
We have seen how the input, process, output diagram provides a framework that can be used to measure the effectiveness of a preventive maintenance program. It has many other uses and helps to steer you away from a tendency to focus too much on what we spend and too little on what we produce. Ordinary repair decisions are another good example. We seek to reduce cost and return the machine to use as soon as possible, but lose sight of the fact that we may be setting ourselves up for another repair action in the next short while.
Success is about maximizing the relationship between outputs and inputs. Complex problems are frequently solved by focusing on the efficiency and effectiveness in the processes we use.
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