In a previous blog, we wrote about the best way to get your manufacturing automation timeline right. And one conclusion was that a factory should develop its maintenance capabilities before entering complete automation. This blog discusses the definition of preventive maintenance, creating a preventive maintenance plan, and three preventive maintenance examples that will help you develop a sustainable factory.
What is Preventive Maintenance?
Preventive maintenance consists of regular cleaning, lubrication, and adjusting your processes to produce consistently within specifications – in other words, with higher quality. For most production equipment installed in a typical factory, it makes sense not to wait for that equipment to break down.
Preventive maintenance also leads to lower costs. Here are the numbers:
- Unplanned repair (once the machine is down because, for example, a cutting tool is broken): 150 hours of downtime, 130,000 RMB of parts, labor, and expedited shipping (the tool might have broken another component because it created quality issues before it broke, and so on).
- Planned repair: 10 hours downtime, 20,000 RMB of parts and labor.
How To Create a Preventive Maintenance Plan
Let’s say your factory has 20 pieces of equipment – for example, CNC milling machines or plastic injection presses. Where should you start? Here is a set of rules for you to follow for an effective preventive maintenance plan.
Source: Maintenance, Replacement and Reliability: Theory & Applications, 2nd edition, by Jardine and Tsang, CRC Press.
3 Preventive Maintenance Approaches to Increase Factory Efficiency
By gathering past breakdown data and running a statistical analysis, it is possible to predict the risk of failure for each piece of equipment at different times in the future. Let’s look at the three most common approaches.
1. Preventive Planning & Condition Monitoring
This approach entails:
- Setting an inspection schedule (e.g. recording the temperature, vibrations, and noise or a bearing);
- Planning for specific actions if the findings are beyond a certain threshold;
- Using the results from those inspections to predict the timing of the following assessment.
The great thing about this approach is that it gives very granular directives (at the level of each piece of equipment). Why is this important? You might have 20 machines, but do they all have the same hazard rate? Maybe not. They don’t process the same parts and are set at different speeds. They had various incidents in the past, and so forth. Making predictions as if they were a homogeneous group might not make sense.
2. Scheduled Preventive Maintenance
Scheduled preventive maintenance is a scheduled service visit or inspection carried out by a qualified technician or engineer to detect and correct any potential problems before they become major issues. It is designed to keep machines and equipment running smoothly, reduce the likelihood of breakdowns and extend the life of the equipment. Preventive maintenance usually takes the form of time-based maintenance (e.g. “lubricate every 30 hours of operation”), but it is often based on guesswork. Injecting some predictive power will improve the choice of time intervals.
Let’s take an example. Let’s say there is a 15% chance of failure on the CNC milling machines 20 days after last maintaining them. If you are aware of this, you can take the right actions – each machine can be stopped for inspection when they reach that milestone, and you can order spare parts a little in advance, etc.
Statisticians have done a fantastic job developing formulas that account for incomplete data (as is often the case in Chinese factories). Even if you only have past failure incidents data on 5 or 6 of these 20 machines, you can still rank them and run a Weibull analysis.
3. Time-Based Maintenance for Individual Machines
Yes. And this is often a welcome refinement.
You can run a Weibull analysis based on the past failure data of each piece of equipment. This data about some of your machines will better equip you to forecast each machine’s mean time to failure and other valuable statistics. I hope these rules of thumb about setting up a preventive and predictive maintenance system have been helpful. Let's recap:
- Predictive maintenance can make your preventive efforts much more time- and cost-efficient using a statistical software package such as Minitab.
- Before analyzing data about all your machines as a homogeneous group, check if condition monitoring is feasible.
- If it is not, set the correct time intervals for time-based interventions.
Could a robust preventive maintenance system help you cut costs and increase quality? Download the guide below to find out.