TPM at the Heart of Lean
Total Productive Maintenance (TPM) has been a very important tool for equipment-intensive manufacturing sectors. It is a fundamental factor in increasing machine availability, and a vital step in connecting machines to create better flow. Many plants, however, have not been able to achieve the full potential of this tool and have instead captured only part of the benefits. Toyota Motor Corporation has developed its own unique style of TPM actions over the last thirty years, which are critical both in supporting the lean production system and in achieving exceptional industrial maintenance results.
The essence of TPM was developed at Denso, a tier-one automotive supplier in Toyota's supplier group, during the 1960s and 1970s in Japan. The core idea of the program is the complete elimination of everything that is part of the so-called "six major machine losses": breakdowns, setup times, cycle losses, minor stoppages, scrap and rework, and losses due to instability at the start of the shift. While lean thinking tries to eliminate waste related to manpower, machines, materials and methods, TPM dives deep into the specific area of production losses related to the 'machine' component.
Each letter of the acronym TPM has a meaning that is not obvious, but very important. "Total" implies a comprehensive view of all activities related to equipment maintenance and of the impact each one has on availability. "Productive" relates to the ultimate goal of an efficient production system, and not merely of efficient maintenance, as is often mistakenly assumed. "Maintenance" means the idea that drives the program to ensure reliable processes and continuous production.
Operational availability has long been recognized as paramount in many process-intensive industries. For example, oil extraction companies, airlines, chemical process plants and many other asset-intensive companies simply cannot afford to stop their processes. Every minute an oil well is down represents an enormous loss of barrel production and a large loss of revenue for the company. Airlines also cannot have any unavailability, for obvious reasons of passenger safety and lost revenue. It is not surprising that these companies are usually the benchmarks in terms of operational availability, although this is often achieved through the use of redundant systems, as well as through excellence in maintenance methods.
However, other companies should also evaluate the benefits of TPM for several reasons. First, TPM is a basic precondition for many elements of lean production to thrive, and second, there are also the financial benefits.
The best-known elements of lean production tend to be the flow concepts: takt time, standardized work and pull production. However, a simple examination of all these methods shows that they all assume, first of all, that there is sufficient machine availability. For many industries pursuing a lean transformation, this assumption is not a reality. Many of the plants I visit struggle to achieve sufficient availability, averaging 60% to 70% at best during a normal production shift. It is important to note that, from a historical perspective, during the 1960s and 1970s, while lean production was being perfected at Toyota, significant time and attention were devoted to developing both robust quality processes and maintenance systems. In most of Toyota's current literature, these items are commonly listed among the preconditions for lean elements such as flow or standardized work. Simply put, those who are having difficulty carrying out the lean transformation should take a step back and notice that the root cause of the inability to flow or to produce 100% of the time based on takt time stems from problems related to these non-trivial preconditions.
In addition, there is a significant financial as well as operational benefit for a company that successfully implements TPM. Let us consider the simple case of two companies making a similar product. One plant has problems with a lack of machine availability and the other produces without significant breakdown problems. The company with lower machine availability will face the following disadvantages: a higher number of defects will be common, more overtime and expedited shipments to the customer will occur, more manpower will be needed to produce and maintain the machines, and consequently a larger amount of capital will be required to support production (to cover the losses). Clearly, the plant with fewer equipment problems will, in the long run, bring more satisfaction to customers, employees and shareholders.
There are four key points that Toyota has emphasized in implementing TPM over recent decades. These points are essential to the long-term success of the program:
"A total life-cycle approach" recognizes that, just as with people, equipment needs different levels of resources and types of attention during its life cycle. Start of production is when problems occur most frequently, and significant time is spent trying to solve machine problems and learning how to fix and maintain the processes. Toyota begins this learning process even before the equipment arrives on the shop floor, through extensive prior process development, keeping what works well and improving the weak points in the machine's design.
After the machines have been installed and production has started, Toyota employs different maintenance techniques to maintain production efficiency. As a last resort, breakdown maintenance is used on what is failing, until the root cause is fully identified and the problem can be prevented from recurring. For most of the equipment's life cycle, condition-based preventive maintenance frequencies or methods are used to prevent problems before they occur. Preventive maintenance intervals and their content are adjusted as experience of the equipment's behavior over its life cycle increases. Daily maintenance is practiced by the equipment operator and involves tasks such as checking the lubrication level, cleaning the machine daily, observing the condition of the tools and reporting any abnormal machine conditions detected. Generally, this last action provides vital information for the preventive maintenance system.
Occasionally, equipment reliability problems arise that require the time and attention of the equipment manufacturer or specialists to be solved. In these cases, corrective maintenance is used and fundamental improvements to the process design are implemented. Toyota calls this "machine kaizen" (as opposed to motion or work-method kaizen) and considers it an important process improvement activity. Finally, all processes are studied throughout the entire life cycle so that it is possible to see where time, spare parts and money are being consumed. When new equipment is requested, a list of necessary improvements is drawn up for the supplier to be analyzed jointly in accordance with the preventive maintenance activities.
"The total pursuit of production efficiency" relates to the goal of eliminating all production losses associated with any piece of equipment. Different situations and types of equipment require different improvement activities. For example, during the 1950s, the main source of production losses in the stamping department was the process of changing from one die to another. This die change often took one to two shifts to perform. Over a period of approximately 10 years, by studying the tool changeover process and identifying the waste in the process, the teams were able to reduce all the time lost in changeover to just a few minutes. In some cases, tool changeovers can now be performed in seconds.
Today, in other processes, such as machining lines, equipment loss is predominantly caused by time lost to machine breakdowns or minor stoppages, which are often difficult to identify. Analyzing the data collected over years at Toyota, the simple fact becomes evident that up to a third of equipment downtime is caused by failures in a simple limit switch or proximity sensor. Of course, the emphasis of the program is on eliminating the cause of the problem; however, in some cases, the roots of the problems have not been completely eradicated. To end this loss of production time, the quick repair of this type of problem is prioritized and "one-minute maintenance" (less than 10 minutes of lost production) is put into practice. Similarly, the type of production environment you work in and the type of loss you have been facing should guide your improvement actions.
The "total participation" aspect of TPM is often presented by consultants and described in articles as a group action, in which a single piece of equipment is cleaned and inspected from top to bottom to increase its available uptime. These projects are noble and are excellent learning activities. However, they should not be mistaken for the fundamental way of implementing participation.
The Toyota style of participation is based on everyone knowing exactly their roles and responsibilities and carrying them out day to day. For example, with respect to equipment-intensive areas, operators have a well-defined checklist and a set of simple maintenance activities that can be monitored or performed during the shift. Abnormalities are recorded and communicated to maintenance to be repaired. Maintenance technicians attend to breakdown problems when necessary and constantly look for ways in which they can either use preventive measures to keep problems from occurring or establish some kind of preventive maintenance activity. Engineering assists maintenance in the area of equipment improvement when special analysis or coordination with equipment suppliers is needed. Managers ensure discipline in the system by making sure that the important indicators are collected, that the biggest problems on the Pareto chart are identified and that the corrective actions for the problems are being followed up within a set time.
Lastly, what is important to Toyota's success in maintenance is the notion of a "total systems approach." Like a chain made up of multiple links, the system will only be as strong as the weakest link in the chain. Constant commitment and attention from management are needed to improve the aspects described in the equipment life cycle, in the pursuit of efficiency and in the participation of everyone according to their respective responsibilities. A total systems approach also means efficiently linking and improving all support activities, such as employee training and development, management of documents and spare parts, collection and analysis of maintenance data, and feedback to equipment suppliers.
