How Preventive Maintenance affect your Production Floor – machine | factory | schedule
How Preventive Maintenance affect your Production Floor
Machines break, and when they break it’s usually at the worst possible time. Your car breaks down on the way to work. A factory machine stops running in the middle of an order for your most important customer. You try to prevent these problems by taking care of your car and your machines. You change the oil in your car so it will not break down on the way to work. Likewise, you perform preventive maintenance on your factory machines to ensure those important jobs aren’t interrupted. So preventive maintenance is a good thing. But at the same time, it’s a bad thing. Because each time you stop a machine, you disrupt the smooth flow of production through your factory.
For that period of time, the machine has no output. Rather quickly, the downstream machines have no material to process. Production abruptly stops. So, the longer a machine is down for preventive maintenance, the more this disrupts heijunka, the lean concept of having a level and smooth flow of output.
Here’s an example. A machine in your factory is scheduled for preventive maintenance each day. This is usually just a few routine checks, and it takes about five minutes. This is not really a concern. Every week some additional maintenance is done, and this takes about one hour. This is also okay. But every month, preventive maintenance is scheduled for one shift, and every year the machine is taken down for one full day.
These maintenance downtimes are clearly a concern because they will create major disruptions to the production flow. Now by the way, I’m using time periods in this example, but you can just as easily schedule preventive maintenance based on the number of units processed. The traditional solution is to buy equipment that can produce more than is needed and then simply overproduce before each scheduled downtime.
The other work stations have material to process until maintenance is finished and the machine is operational again. The problem with this approach is that it builds small batches of inventory throughout the factory. Material moves through the system in these small lumps, which certainly is not the definition of smooth production flow.
Because of these small batches, the overall inventory level is higher than needed to meet customer orders. This unneeded inventory is a waste. The solution is to level the preventive maintenance schedule so that you support level production flow. Maintenance is done more often but in shorter periods. You want to avoid those long periods of maintenance downtime.
Here’s how it’s done. Instead of having an annual downtime of one day, divide those maintenance tasks into four equal amounts and do one portion each quarter. Each task is still done annually, they are just spread out. The machine is now only down for six hours rather than 24. This is less disruptive to the factory. But don’t stop there. Perhaps the six hours could be further reduced by doing some of those tasks monthly. You can divide the monthly maintenance into biweekly periods. Maybe some monthly tasks can be distributed throughout the weekly schedules, and some once a week repairs can be done throughout the week.
Your new schedule might have periods of downtime that range from 15 minutes per day to three hours per quarter. The smaller, incremental downtimes make it much easier to manage a smooth, continuous flow of inventory throughout the system. And, you eliminate those small batches that are aren’t really needed. It takes time to implement this lean approach to preventive maintenance, and it must be done carefully to avoid disrupting the factory. What’s the best way to start? One work station at a time.