Preventive Maintenance

Preventive maintenance is the set of steps taken to avoid breakdowns in machines. These steps may include minor activities such as topping off fluids, inspection, lubrication, filter changes, and tightening as needed. It may also include more significant actions such as overhauls, rebuilds, and component replacement.

In between those extremes are fluid changes and routine replacement of parts.

Preventive maintenance checks also look for components with a prescribed end of life. Brake pads and tires fall into this category.

Many preventive maintenance activities include prescribed, time-based maintenance. Some are minor like oil changes. Some are more significant. Your car likely has a 100,000-mile service (or thereabouts) that requires replacement of the timing belt. This is a major service but can prevent significant damage.

Checks might be done before a machine is used, or immediately after use. They might also be time based (i.e. daily, weekly, or monthly) checks. Checks might be conducted at the operator level or might have to be performed by trained maintenance technicians.

Preventive maintenance checks are typically for abnormal conditions that come with normal use. Topping off consumed fluids, tightening parts that are susceptible to vibration, checking grates for blockages, cleaning out debris, etc.

Not all checks are preventive, though.

Types of Maintenance Checks

• Checks for failures: Some checks are to catch failures as soon as possible. Leaking oil, or broken parts fall into this category.
• Preventive Maintenance Checks and Services: These are checks for abnormal conditions that are generally part of normal operation. This includes things like replacing washer fluid in your car or checking the tread life on your tires. It also includes changing components with a specified end of life, like spark plugs.
• Predictive Maintenance Checks: These look for indicators of future failures.

Some maintenance checks are not cut and dried into a category. A clogged filter, for example, could be thought of as preventive or predictive. Don’t worry too much about this. In practice, you probably won’t see predictive maintenance checks listed separately. They will be intermingled on a checklist.

The concept is more useful for the people setting up maintenance programs than for those people working off a list of checks.

Interval Based Maintenance

A big part of preventive maintenance is time-based or use-based activity. Cars provide a great example of this. You are likely told you should change your oil every 5,000 miles (sometimes 3,000) or every 6 months, whatever comes first.

One of the downsides of intervals is that they tend to be set up conservatively. The interval might be set to avoid 99.5%+ of issues. Sometimes, especially with time-based intervals, the machine might have been only lightly used. It could possibly last another 6 months before it really needed that service.

Even with use-based intervals, the type of use could make a difference in usage. 5,000 miles cruising on a highway is far different than the 5,000 miles a cab driver or police office might travel.

Preventive Maintenance and Lean

Preventive maintenance is especially critical in Lean operations. When your business is running with very little inventory, it relies more heavily on machine uptime. This issue is amplified when a machine is running near capacity with little ability to catch-up if production falls behind.

Preventive maintenance helps you avoid unexpected shutdowns that can hamper an operation. Preventive maintenance can be scheduled when the operation is not running to avoid impacting production. Preventive maintenance also tends to take less time than repair.

An important tenet of Lean is to fix underlying problems. Maintenance teams in good lean companies often head up TPM, or Total Productive Maintenance programs. This takes an overall look at how maintenance and production work together. It also involves working to make changes to machines to reduce the chance of failures. Removing or disabling unnecessary components, typically optional features, can limit the possibility of failures, for example. Some maintenance teams will even modify machines or build their own machines from scratch. They should consider the maintenance impact when doing so.

DISCLAIMER: Only qualified people should make changes, and it will probably void your warranty.

Standardizing Preventive Maintenance

Make sure you are using your set of Lean tools to make preventive maintenance go as smoothly as possible. Use 5S to organize your tools and parts. Use kanban to keep the required components on hand. Use standardization to make sure the steps are done consistently.

It is also imperative to provide time in the schedule for maintenance, if you actually want people to do it. You will have to sacrifice production time if you actually want operators to maintain their machines through preventive maintenance. If you really are pressed for time, you can get someone to do the maintenance outside of production time. The point is that the maintenance has to be accounted for in someone’s work schedule if you expect it to actually happen.

Preventive Maintenance Shortcomings

Preventive maintenance, while effective, has a few main shortcomings.

1. The PM list, due to cost, isn’t exhaustive. If manufacturers make the list too long, it can be a detriment to selling the product. Users want machines that run with minimal maintenance. The manufacturer has to be selective, so their machines don’t appear to be failure prone.
2. Preventive maintenance tends to bring systems offline. Users can’t afford to take the machine down a lot, so they might have a tendency to cut corners or extend maintenance intervals.
3. Preventive services are wasteful. The maintenance intervals are established at a point where they will prevent the majority of failures. Most of the components, when replaced, will still have substantial life left in them.
4. Preventive maintenance is often seen as secondary to production. In fairness, any form of maintenance is likely viewed like this, not just preventive maintenance.) It will take a cultural change and allocating maintenance time during the work day to convince employees that maintenance is actually important.

Types of Maintenance

Maintenance

• Fix a problem once you see the failure.

Preventive Maintenance

• Change components or do routine services at a prescribed interval (time or usage).
• Conservative approach in interval setting to avoid most failures means many services are done well before they are really needed. Wastes time and money.
• Many checks listed as preventive maintenance are actually really just maintenance (failure already occurred) or predictive (services based on observation of specific indicators.)
• Filling consumed fluids.
• Replacing components that are consumed during use (brake pads, tires.)

Predictive Maintenance

• Services done based on identifying abnormal conditions.
• Extends usage of components or time between services.
• Hard to find the proper indicators.

Preventive Maintenance vs. Preventative Maintenance

You may see this term as both “preventive” or “preventative”. Both mean virtually the same thing. Preventive is more common and is thus the form of the word we use. It is also used by the US Army. There are a lot of veterans working in manufacturing, so it is a term they are familiar with.