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From good to great with lean maintenance

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From good to great with lean maintenance

February 20, 2011 - 14:00

USA, Feb. 21, 2011 (RISI) -Long a guiding principle in the US and European industries, the concept of "lean" (manufacturing and maintenance) seems to have vastly increased in popularity over the past five years. Simply put, the idea behind lean is that those things that need to be delivered are to be produced on time with fewer resources. In other words, you need to be eliminating waste wherever you can. In the area of lean maintenance, cutting out waste is all about executing the basic elements of good maintenance management better.

To become lean, all losses in the processing of raw material and subsequent delivery of products to customers must be eliminated. For readers of this magazine, that means preventing maintenance needs and performing remaining maintenance more effectively. What is the payoff from all this? Manufacturing reliability will increase and production costs - including those for maintenance and storage - will decrease. The biggest improvement opportunities include:

- Manufacturing reliability

  • Loss in quality.
  • Stop times.
  • Loss in speed.

- Partnership between operations/maintenance/engineering

  • Reliability- and maintenance-related design.
  • Operator-based maintenance.

- Root cause problem elimination

  • Choose problem to eliminate.
  • Eliminate problem.
  • Educate and teach.

- Storage

  • Reduce store value while preserving service level to maintenance.

- Skills and flexible work systems

  • Education and training of crafts people to enable multi craft or multi skills.
  • Implementation of flexible work systems.

- Over-manufacturing

  • Make more than what has been sold.
  • Manufacture too early.

- Over-maintenance

  • 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.

Before exploring these points in more detail, it's important to review some fundamental concepts of manufacturing reliability, Fig. 1, 2.

Figure 1 shows 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 finishing/converting is the bottleneck in the production chain since capacity there is 32 tons/hr compared with the higher capacity in the pulp mill of 35 tons/hr and the paper machines at 33 tons/hr. If you calculate the flow you will find that the bottleneck is at the paper machines. 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. With low reliability throughput of product in the manufacturing chain it takes a longer time and the costs are increased for the WIP.

Figure 2 show additional basic reliability mathematics. By raising the reliability in finishing/converting to 83%, the increased throughput there is 26.56 tons/hr. Increased reliability in the pulp mill and paper machines to 78% and 82% respectively will increase total throughput to 26.56 tons/hr. The WIP is reduced since the manufacturing steps are now more balanced. Other solutions include procurement of increased capacity through investing in a parallel machine for finishing/converting. This would lead to unnecessary high capacity in this section. Moreover the cost of buying more capacity is at least ten times higher than investing in measures that will increase reliability.

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.

Figure 1 - Throughput and reliability

Availability or reliability?

Many organizations use availability as a key measurement for manufacturing efficiency, but availability encompasses only the percent of scheduled 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 is often more expensive than to not produce at all. To slow down a process because, for example, a part of the 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: quality, time and speed.

Manufacturing reliability can be measured in various ways. The most simple way is to calculate how much is manufactured at the right quality, divided by how much could have been manufactured at the right quality (% Quality x % Time x % Speed). Overall, nothing should be manufactured before it has been sold and is to be delivered.

In many mills, people are still living with the idea to always produce as much as possible. That's not "lean thinking," which says nothing is produced until it needs to be delivered because it has been sold. However, having a lean production process and being able to produce things "just in time" is possible only if the production reliability is very high. With a raised automation level, a company becomes more and more dependent on reliable equipment and the maintenance that ensures the reliability of that equipment. Reliable production equipment is the most important result a maintenance organization generates. It can be seen as the maintenance department's income-generating section.

For an organization striving to be lean, it is important to 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. Consider the following:

In the pulp and paper industry, the sales price of what you are making can fluctuate. Thus, let's base our hypothetical manufacturing example on the average sales price and variable cost of a product over, five years.

Average sales price five years $510/ton

Average variable cost five years $340/ton

Benefit per produced, sold and delivered unit $170/ton

The financial contribution of producing and delivering a sold ton is $170. If you currently produce and deliver 250,000 tons per year and your production reliability is 88%, but it is possible to reach 94%, then the value of increasing manufacturing reliability is 6%: 15,000 tons x $170 = $2,550,000/yr.

The next questions you should ask are these: Can you achieve even better results by lowering maintenance costs? Would it be beneficial to lower maintenance costs if you can maintain manufacturing reliability at 88% without lowering them? The answer seems to be obvious, but it isn't that unusual that some 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. An idea worth repeating - as we are doing here - is that when you increase manufacturing reliability, production costs, including maintenance and storage costs, will decrease.

If you can't sell the increased volume that you reach via higher manufacturing reliability, then the savings most often lie in more reliable and faster delivery of goods sold, less energy expenditure, improved safety and less overtime. Consider the following example from the pharmaceutical sector, which also shows the importance of including the quality component of the reliability formula:

There was a lot of over-capacity at a pharmaceutical company. Consequently, manufacturing reliability wasn't considered to be "that important." After all, it was assumed that the plant could catch up losses with the extra capacity and turn to overtime to compensate for any production losses. Management reasoned that it was much more important to have lower maintenance costs. When manufacturing efficiency was measured, the only thing really taken into account was availability.

One day a tumbler broke in the end-stage of a tablet manufacturing process. (Tablets in the tumbler were covered with a coating before packaging and delivery). The breakdown of the tumbler was caused by a burned, worn-out V-belt. Although the resulting shutdown lasted only 45 minutes, plenty of expensive medicine had to be scrapped, to the tune of more than $62,000. Since a similar costly incident had occurred two years before, management realized it needed to change the way it thought about some things. That's why instead of talking only in terms of availability, this plant now also considers the aspect of quality performance when it identifies losses and measures manufacturing reliability.

Figure 2 - Throughput and reliability

What is good manufacturing reliability?

Increased manufacturing reliability will increase product throughput and reduce the time between incoming raw materials to the finished product.

As to the question of what constitutes "good manufacturing reliability," the answer has a lot to do with your process and equipment quality. Note that we aren't only talking about equipment efficiency here. It is common to use the concept Overall Equipment Efficiency (OEE) 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 that goes into making your product, such as raw materials, pressures, temperatures, chemical mixtures, packaging material, operating practices etc. What this all boils down to is Overall Manufacturing Reliability (OMR).

From the maintenance point of view, there are three major elements that affect how good OMR can be:

1. Equipment quality

2. The number of components that can cause a problem

3. The efficiency of the maintenance organization

Equipment quality:Equipment quality, including issues associated with designing for maintainability and reliability, is beyond the scope of this article. This element affecting OMR is such a complex (and crucial) topic that it requires an entire article unto itself.

The number of components that can cause a problem:As a consultant, I often use paper machines as a guideline when projecting reliability in processes for which I don't have data. The most reliable paper machines produce, for example, towel and tissue paper. They often incorporate one or two dryers - so-called "Yankee" cylinders or dryers - each with a drive unit. A paper machine with several layers and surface coatings, however, has many more components that can cause problems. Such a machine can incorporate 100 dryer cylinders. Thus, good OMR differs between 96 % for a tissue/towel machine and 82 % for the more complicated units. A package line, or converting line with good OME can reach 85 - 90 %. (All of these calculations are based on 8,760 scheduled production hours per year.)

The efficiency of the maintenance organization:One of the best indicators of effective maintenance is still the degree of planned and scheduled maintenance work. This is because it greatly affects both manufacturing reliability and maintenance efficiency. 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, storeroom support, root-cause problem elimination etc.

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.
  • Deciding if work that is performed during scheduled downtime actually needs to be done.
  • Prioritizing, planning and scheduling work in a disciplined way.

Reliability and maintenance-management expert Christer Idhammar is the founder and executive vice president of IDCON, based in Raleigh, NC. For more information,