Lean manufacturing including lean maintenance has long been a concept both in the United States and in Europe.
Lean Maintenance in Manufacturing & Delivery of Raw Material
- Loss in quality.
- Stop times.
- Loss in speed.
Partnership between Operations – Maintenance – Engineering
- Reliability and maintenance related design.
- Operator based maintenance.
Elimination of root cause of the problem
- Choose problem to eliminate.
- Eliminate problems.
- Educate and teach.
- Reduce the store value at the same time as you preserve service level to maintenance.
Integration and application of increased knowledge and skills
- Education and training of crafts people to enable multi craft or multi skills.
- Implementation of flexible work systems.
- Make more than what has been sold.
- Manufacture too early.
- Perform too much and wrong preventive maintenance.
- Perform preventive maintenance before it is needed.
- Do corrective maintenance with higher priority than needed.
Use of new technology
- Less need for maintenance.
- Better maintainability.
- Smart tools and methods.
In the following text I will discuss the aforementioned areas more in detail. I will start with some fundamental concepts within manufacturing reliability.
Image 1. Basic Reliability mathematics. It isn’t always obvious where improvements in the manufacturing chain are the most cost effective to implement. Flow of a product is the result of Capacity x Reliability.
At first glance you could believe that C is the bottleneck in the production chain since capacity there is 316 pieces per hour compared to the higher capacity in A (356) and B (333). If you calculate the flow you will find that the bottleneck is at manufacturing stage B. this is compensated and hidden by increasing storage of Work In Progress (WIP) so that it can sometimes seem that throughput is not a problem. WIP is a big hidden cost for a lot of companies.
Image 2. Reliability Mathematics.By raising the reliability in step C to 83% the increased throughput is 260 per hour. The WIP is reduced since the manufacturing steps are now balanced.
Lean manufacturing’s sub-target is to reduce WIP and speed up the throughput in the manufacturing chain. Reliability includes quality, time and speed. Lean maintenance has a crucial key role in raising the part of reliability that is affected by the manufacturing equipment.
Since the manufacturing process is more and more dependent on automation, good maintenance becomes more and more important.
Availability or reliability?
Many organizations use availability as a key measurement for manufacturing efficiency, but availability encompasses only the percent of planned time, or available time, that a production process produces.
Availability excludes the quality of that which is produced. To produce something that isn’t up to quality standards are often more expensive then to not produce at all.
To slow down a process because, for example, a part of the production process can’t operate at full speed is also expensive. So we must focus the improvement initiative on all elements of what we call manufacturing reliability. They are quality, time and speed.
Manufacturing reliability can be measured in various ways and, simply put; it is about how much is manufactured at the right quality divided by how much could have been manufactured at the right quality. Or, % Quality x % Time x % Speed. Overall nothing should be manufactured before it has been sold and is to be delivered.
In many heavy process industries people are still living with the thought process to always produce as much as possible. In”lean thinking” nothing is produced until it needs to be delivered because it has been sold.
A good example is computer companies. When you order a computer from, for example, Dell, the order is sent to production planning that begins to assemble the computer in order to deliver it within a few days to you. Instead of having all types of computers in storage, the whole company’s economy including cash flow, liquidity, costs for materials and material storage and capital costs are affected.
To have a lean production process and be able to produce things”just in time” is possible if the production reliability is very high.
With a raised automation level the company becomes more and more dependant on reliable equipment, in other words maintenance.
Reliable production equipment is the most important result a maintenance organization generates and it can be seen as the maintenance department’s income generating section.
To become lean it is important that you know where the greatest benefits are. What is the worth of reducing the difference between how good you are and how good you could be? In a market situation where you can sell everything you can produce the equation is simple.
In certain industries the sales price of what you are selling can drastically fluctuate. Then you can base your calculations on the average sales price and variable cost over, for example, five years.
|Average sales price five years||Euro 510/unit|
|Average variable cost five years||Euro 340/unit|
|Benefit per produced, sold and delivered unit||Euro 170/unit|
The value of producing and delivering a sold unit is Euro 170. If you currently produce and deliver 25,000 units per year and your production reliability is 88% but it is possible to reach 94% then the value of increasing manufacturing reliability is 6%.
1500 units x Euro 170 = 255,000 Euro per year.
The next question you should ask is if you can reach even better results through focusing on lowering maintenance costs.
Could it be more beneficial to lower maintenance costs if you can maintain manufacturing reliability at 88%?
The answer seems to be obvious but it isn’t that unusual that those economists are so focused on lowering visible costs that they don’t see the invisible, large opportunities that are concealed in increased production or faster throughput of product.
A concept worth repeating many times is that if you increase manufacturing reliability then manufacturing costs, including maintenance costs, will decrease.
If you can’t sell the increased volume that you can reach with the higher manufacturing reliability, then the savings most often lie in more reliable and faster delivery of goods sold, less energy expenditure, much better safety and less overtime.
I like to give an example on the impact of reliability in a situation where you can not sell everything you manufacture as a result of increased reliability. The example also shows the importance of including the quality component of the reliability formula.
In a pharmaceutical industry there was a lot of over capacity and it was thought that manufacturing reliability wasn’t that important, after all they could catch up losses with the extra capacity they had and they could use overtime to compensate for any production losses.
Management viewed that it was much was more important to have lower maintenance costs.
When manufacturing efficiency was measured the only thing considered was availability. One day a tumbler broke in the end stage of the manufacturing of tablets. In the tumbler the tablets were covered with a coating before packaging and delivery.
The break down was caused by a burnt and worn out v-belt.
The shut down, which only lasted for 45 minutes, resulted in that lots of expensive medicine had to be scrapped at the cost of Euro 49 000. Since this had happened one time before, two years prior, it was decided that quality must be included in how you measured manufacturing reliability.
Instead of talking in terms of availability this plant now include quality performance when they identify losses and measure manufacturing reliability.
Increased manufacturing reliability will increase product throughput and reduce the time between incoming raw materials to the finished product. Better reliability is the foundation to a faster and safer manufacturing flow.
This will result in lowered losses in delayed deliveries, over production, work in progress and energy expenditure. Here lie the biggest gains if you can’t sell everything you produce. This cannot materialize if you don’t have equipment with very high reliability. If you do have it then you can, with prosperity, apply the “Dell model” or “Just- In- Time” manufacturing principles very successfully.
In addition work related injuries and energy costs are always positively affected by high reliability.
I often get the question, ”What is good manufacturing reliability?”
It obviously has to do with your process and equipment quality. Also pay attention that we aren’t only talking about equipment efficiency.
It is common to use the concept OEE – Overall Equipment Efficiency when measuring manufacturing reliability, but that is only a part of the reliability concept, the other part is Overall Process Efficiency which is the manufacturing process, or the chemistry of making your product such as raw materials, pressures, temperatures, chemical mixtures, packaging material, operating practices etc.
In this concept we are discussing OMR – Overall Manufacturing Reliability.
From the maintenance point of view there are three elements that we have seen that affect how good OMR can be.
- Equipment quality.
- The number of components that can cause a problem.
- The maintenance organization’s efficiency.
Equipment quality including maintainability and reliability design which will require an article by itself.
The number of components that can cause a problem.
I often use paper machines as a guideline when I judge possible reliability in different processes that I don’t have data on. The most reliable paper machines are machines that produce, for example, towel and tissue paper. Such machines often have one or two driers, so called yankee cylinders or driers, each with one drive unit.
A paper machine with several layers and surface coatings has many more components that can cause problems.
Such a machine can have over 100 drier cylinders. Thus OMR differs between 96 % for a tissue/towel machine and 82 % for the more complicated machine. A package line with good OME can reach 85 – 90 %. All of these calculations are based on 8760 hours per year.
The maintenance organization’s efficiency.
One of the best indicators of effective maintenance is still the degree of planned and scheduled maintenance. This is because it affects both manufacturing reliability and maintenance efficiency to a very high degree.
Furthermore, a high level of planning and scheduling cannot be reached without the support of all of the other elements of good maintenance including maintenance prevention, preventive maintenance, store room support, root cause problem elimination etc.
In studies that we have established a strong correlation between high manufacturing reliability and a high degree of planning and scheduling of all maintenance and operations work.
In this study we evaluated the Manufacturing Reliability of 38 very similar process lines. The blue line shows the lowest to the highest manufacturing reliability. The only thing we could correlate to higher manufacturing reliability was the level of professional planning and scheduling.
Depending on what different plants included in their maintenance costs, this cost was lower the higher the level of manufacturing reliability and level of planning and scheduling was.
Over manufacturing and over maintenance
Over manufacturing is to make more than what has been sold and before it needs to be delivered. This is one of the biggest sins in lean manufacturing. The same view should be taken when it comes to maintenance.
To perform more maintenance than is needed or to perform maintenance before it is needed should be considered a waste or an opportunity to improve.
The biggest improvement opportunities lie in:
- Optimizing old preventive maintenance systems.
- Decide if work that is performed during scheduled downtime actually needs to be done.
- Prioritize, plan and schedule work in a disciplined way.
Optimize Preventive Maintenance (PM)
Optimization of preventive maintenance also requires an article by itself. Here I like to add more information as it relates to lean maintenance.
To optimize your PM is one of the efforts that can give the fastest return on investment. If you have a PM system that has all PM activities documented under each equipment identification number, optimization can be done relatively quickly. If you have a system where all PM inspections and other PM activities are documented in a work order, then the work becomes much more extensive, if not impossible.
If you want to optimize your PM then you must have a system that can collect all PM efforts in a lucid way under respective identities on the maintenance object. This is important because more than 95% of all PM activities are performed as route based activities while the manufacturing process is operating.
Through more and more integration between what lubricators, mechanics, electricians and operators do, the system must always change and it has to be able to change in a very simple way. It can be easier to start from the beginning with a route based system if your existing system is based on work orders. A route based system can be set up at a very low cost.
During the 1970’s I myself led the implementation of many PM systems in industry. Thirty years later I have visited many of those plants and I am surprised to see that many of these systems still looked like they did thirty years ago. The distribution between what is done by different work groups is still the same as back then.
In many of these companies the operators are now involved in the preventive maintenance but their efforts are added to all the other PM measures. Here lies a big opportunity to optimize PM inspections, lubrication, etc.
As an example. In a chemical plant most pump units had the following PM measures done on most of their pumps.
- Lubricators lubricate everything, except for electric motors.
- Electric motors are lubricated by electricians. (Believe me, even if it is old-school and a waste of the electricians skills, it still happens today when you come across old work systems that should have been changed forty years ago)
- A mechanical PM inspector performs mechanical inspections.
- Gear couplings are overhauled during a scheduled shut down each year. (This can easily be moved to inspections while equipment is running and repairs are done when needed)
- Electricians and instrument technicians inspect electrical components and sensors.
- Vibration analysis is done by a technician.
- Operators do general inspections of unit.
After optimizing this PM system, PM activities were reduced by 50% and the new PM activities were better than before.
It can be a good idea to take photos of several pieces of the equipment and then show which PM is performed and by whom. Then show how you can integrate and optimize all PM. After that you can determine costs and savings.
Shut Down Management in Lean Maintenance
Depending on the industry a shut down can be different in scale, for example:
- Several weeks for a stop in an oil refinery.
- Days for a longer shut down in a chemical plant.
- Hours for a recurring shut down in many process industries.
- Minutes for adjustments and tool changes in manufacturing industries.
- Seconds for a Formula 1 or NASCAR pit stop.
NASCAR is a good example of what can be accomplished through precision planning and scheduling and execution.
Major contributors to their pit stop, or shut down performance, include operations and maintenance communication and continuously working on improving the basics of Planning and Scheduling, Execution and Root Cause Problem Elimination. In the nineteen fifty’s a good pit stop lasted around 240 seconds.
If nothing had been done because everyone thought this is very good, then we would still have four minutes pit stops, but the crew that could bring it down to where it is today, at a record 12,6 seconds, would win the race.
The driver of the car is in constant contact with the pit stop crew, they do not show up suddenly telling the pit crew “I think I have a problem with the right front tire” and the crew answers “We will go to the store and check if we have any replacement tire”. But this happens daily in most plants. In a NASCAR race there is a strong motivation to win the race, in a plant there might be completely other factors driving motivation.
In addition to driving Planning and Scheduling to precision and excellence NASCAR pit crews are continuously working on improving the basics.
- Lug nut tool is turning at 24000 rpm.
- All parts sorted and placed on where they are used.
- Steering wheel straight position is marked.
- Wheel bolts rounded tops.
- Wheel nuts glued to wheel.
- IR measurement of tire temperature.
- Measurement of tire wear.
- Marked wheel position to speed up wheel change.
- Wheel nuts painted yellow for visibility.
- Analysis of problems and successes.
- Training 20 hours per week for 20 seconds of work on Sunday.
- Always do work right before fast.
Regardless of the length of the shut down, the same principles apply to make the shut down more effective or what we like to call lean.
- First and foremost we should be able to manufacture without any problems between scheduled shut downs. Mean Time Between Production Losses (MTBPL) including Quality, Time and Speed) should be as long as possible.
- When we have a shut down we want to perform it with the right quality on all of the jobs and as quickly as possible.
The combination of how many shut downs you have and how long they are affects your manufacturing volume and your ability to deliver products on time.
It is a given that the shut down must be scheduled (when and who executes what) and that all the jobs must be planned (what, how, all the tools, spare parts and materials, lock out tag out etc. identified) before the shut down begins.
All shut downs should also have a set time for freezing the schedule. After the freezing point no new jobs will be accepted without harsh criticism. Two measurements can be used to challenge your organization and to measure and show improvements.
Number of added on jobs and changed jobs.
Define a scheduled shut down as a scheduled shut down if it is done within the agreed upon time-frame. For example, 44 hours before a shut down for an eight hour shut down on a larger process line, four weeks before for a three week long shut down in an oil refinery and four hours for tool changes that has been scheduled to take approximately forty minutes.
Then measure how many jobs that are added or changed after the freezing point and during the shut down. Scrutinize all the added or changed jobs at the latest, three days after the shut down. Have them explained and learn how they can be avoided next time you have a shut down.
The relationship between scheduled and unscheduled shut downs
With the same definition as in the previous paragraph, we can measure the relationship between scheduled and unscheduled shut downs. For many process industries the quota of the equation is over 1 and should steadily increase.
This is on the condition that scheduled shut downs are not programmed and based on old habits but based on market and condition monitoring of process and equipment.
Do all jobs need to be done during a shut down?
It is not at all unusual that many of the jobs that are performed during a Shut down are only done because they have always been done and no one has ever questioned if they actually need to be done or not.
To know if what you are doing is right you must have a good understanding of the expected life for each respective component. To, for example, regularly change a roller bearing after 8000 – 10000 hours of operation time cannot be right. Still, it is a common preventive recommendation from manufacturers.
Recently I discussed the recommendation to change the bearing of a centrifuge once per year. “The centrifuge rotates with a high r.p.m. and if a bearing breaks the rotating unit can cause severe damage, including bodily injury,” was the answer.
According to the bearing manufacturers’ calculations the life for a bearing is between 1 to 15 years. (L10 – L90 life span) It is calculated that ten percent break before one year of operation and ten percent are calculated to last longer than 15 years, in this application. It is just that fact that indicates that it is wrong to change the bearings once per year. T
he bearing that is changed could potentially last for more than ten years whereas the new bearing might not last more than three years.
Moreover you are always risking that a problem will be induced when you change a component. Within reliability theory bearing failures are defined as random failures, you don’t know when failures will occur.
So that means you can’t know when it needs to be changed either. ”Even though I know that it isn’t right to change the bearings, I still do it,” the maintenance manager said to me. ”
What do you think would happen if I didn’t change the bearings one year because I mounted a vibration sensor in the bearings and then measured the condition continuously, so I know when the bearings should be changed and we had a breakdown?”
He continued. ”I can always try to explain to the plant manager, who is an economist, that based on reliability theory it isn’t right to change the bearings once a year, it would instead be correct to base the change on the bearings’ condition.”
”We have, through the years, had several breakdowns, but we always came away without all too harsh words, if we had changed the bearings according to our existing preventive maintenance plan.”
The maintenance manager ended with, ”So it isn’t always that easy to become lean even if our plant manager pushes lean manufacturing hard.”
You should also always ask if the jobs that are done during the shut down could be done during production. One good example of innovation and new thinking is to change the joints of electric power high voltage lines.
With the help of a helicopter and dynamite the old joints are improved without disruptions in power supply. Click on www.idcon.com “Reliability Tips / March 2008 / Power line workers” in the middle of the home page and you can see a movie that shows how it works.
Basics of Lean and Reliability Based Spare Parts and Materials Management.
In about 50% of organizations spare parts and materials stores reports to the maintenance organization. In about 50 % of organizations spare parts and materials stores is part of the purchasing function.
One of the areas that are first attacked when an organization wants to become lean is the materials and spare parts areas.
Through reducing the value of spare parts and material kept in storage you can of course reduce costs. It is true that there are often big opportunities to lower the value in many stores, but it can also become very expensive if it is not done correctly.
One of the most common mistakes is to discard parts that haven’t been used in, for example, the past five years or more. To discard these parts based on the fact that they have not been used for a long time is way too simplified and risky and I am surprised every time I see that this tactic is still being used in many plants.
That these incorrect and expensive cutbacks happen is a result of that the people in charge of the stores often having the goal of reducing the store value, while the consequences of not having the right part in storage when the parts are needed, is a problem for those responsible for operations and maintenance.
Most stores, especially in plants that are ten or more years old, can reduce their value by 10 to 20% without negatively affecting production reliability.
To successfully, and sustainably, reduce the value of parts and material kept in stores you must focus on measures that drives down the cost, not only on reducing the store value. You should also set up a measurable goal for this effort.
The goal could for example be “With a service factor maintained at 97 % we will reduce value of inventory kept in stores”. In this case the service factor is percent of occasions the right parts/material have been available when needed for a maintenance job.
First you need to know what parts and material you have in your stores.
First do a quick evaluation of how accurate the inventory list is. Randomly choose 300 to 500 articles and compare how correct the balance is, the location in the stores is etc.
We have often found that the inventory catalogue is 70% accurate while a good value would be 98%+. Even if this accuracy value is 100% it does not mean that the stores are cost effective. Do we have the right articles? Do we have too many?
Find out how many articles exist in undocumented storages.
If the inventory catalogue and/or the plant register, including component record and spare parts documented for each piece of equipment, are not accurate and reliable, then the users will not trust that the articles they need are going to be available in the store when they need them.
This one of the reasons why people start building up their own stores.
These stores can become extensive and very expensive to have. The costs are invisible. More articles are purchased before they are needed and often in greater quantities than necessary.
Moreover the articles are often stored in a bad environment where they can be damaged by corrosion, dirt, vibrations, etc. It is imperative to clean up, sort, organize and document all the articles in all these storages.
The store manager will most likely not want to take all these items back in the central stores, because this would increase stores value and take up costly space.
I sometimes call these undocumented stores emotional stores. If you have made efforts to document all these stores and then take away all parts in these stores from the people who have them, and put the parts in central stores, then you will understand why I call them emotional stores.
Decide what you are going to have in storage.
In addition to known and traditional methods and data used to decide what should be kept in storage such as delivery times, economic purchasing quantities, consumption statistics etc. it is not uncommon that information such as; risk for breakdown of a component, cost if an article is not in storage when it is needed, condition monitoring based storage, number of identical parts used in the plant equipment etc. are missing.
Then only guesses are made as to what should and should not be kept in storage.
It is important that an analysis has been done on what production equipment is critical and which components within each piece of critical equipment could cause a breakdown.
The breakdown cost compared to the cost of keeping parts in store is an important piece of information that should be taken into consideration when storage levels are decided.
With good condition monitoring you can often avoid keeping parts in storage if the so-called failure developing period is longer than the delivery time of the parts you are monitoring. A practical example is chains and sprockets made of steel. They wear down over a longer time period, they are easy to inspect with objective methods and the delivery time of replacement sprockets and chains are often short. If you monitor wear of sprockets and chains you can order them when you need them instead of keeping them in store.
With an accurate inventory catalogue and/or the plant register, including component record and spare parts documented for each piece of equipment you will know how many identical articles are included in the production equipment.
This is necessary and important information to have when doing evaluations of suppliers’ recommendations and decisions on what to keep in stores. The absence of this documentation will lead to that you keep wrong parts and in the wrong quantities in your stores.
Standardization can also reduce storage substantially.
If you have a production line with 22 or so different and critical, electrical motors you might decide to keep one of each of the 22 motors in the storage.
You can often standardize by about five different motors or even just one type. Then only five or maybe just one motor is kept in storage.
What good looks like
A good storage does not only have a cost effective store volume. The store is closed and delivers parts where and when they are needed. The picture shows the delivery of parts and special tools for a shut down that is going to start in three days. In the worst organizations there is a line outside the store in the morning of the shut down.
Store item maintenance.
You need to keep parts you store in the right environment, free of dust, other contaminations and vibrations.
Shafts of rotating items such as electric motors and pumps shall have their shafts oriented towards the isles in the store so they can easily be rotated to avoid sagging of shafts and damages of bearings. V-belts and other belts made of rubber and similar material shall be kept away from day light, preferably in a dark location.
Bearings should be stored laying flat and turned on a regular basis.