May 1, 2004
By David McBride
One of the most recognizable symbols in modern manufacturing is the “TPS House” diagram as shown below. The diagram is a simple representation of the Toyota Production System (TPS) that Toyota developed to teach their supply base the principles of the TPS. The foundation of the house represents operational stability and has several components, one of which is Total Productive Maintenance.
Working with little inventory and stopping production when there is a problem causes instability and a sense of urgency among workers. In mass production, when a machine goes down, there is no sense of urgency; excess inventory will keep the operation running while maintenance fixes the problem. In Lean production, when an operator shuts down production to fix a problem, the line will soon stop producing, creating a crisis and a sense of urgency. A properly implemented and maintained Total Productive Maintenance System (TPM) will provide the needed stability for Lean production.
A little more than thirty years ago, an automotive supplier company in Japan (Nippondenso) realized that until you address and systematically eliminate the causes of poor equipment performance, you cannot deliver to your customers “just in time,” improve quality levels, lower operating costs, or improve profits. In 1969, the ideas of Total Productive Maintenance, facilitated by Seiichi Nakajima, helped take the Toyota Production System to the next level. Since the Toyota Production System was focused on the absolute elimination of waste to reduce manufacturing cost, TPM was designed to systematically identify and eliminate equipment losses (downtime, inefficiency, defects). In implementing Lean manufacturing practices, machine availability plays an important role. Preventive maintenance is a key aspect in ensuring machine availability. This practice achieves maximum efficient usage of machines through total employee involvement.
Toyota has created an organizational culture that encourages employee participation, which is essential for successful TPM. Group activities are promoted among the shop floor team members. The knowledge base of all the employees is used to improve equipment reliability and productivity thereby lowering maintenance and operating costs. Two other important aspects of TPM are training and open communication between operators and engineering. Production personnel are trained to perform routine maintenance.
The traditional approach to preventive maintenance is a clear-cut division of labor:
Machine operators perform routine maintenance functions.
Maintenance technicians are responsible for specialized maintenance and for improving maintainability.
Engineering is responsible for improving the process.
This practice is not capable of achieving the TPM targets, as there is a lack of communication between operating and maintenance teams.
Nippondenso came out with an alternative approach of appointing a machine technician (MT) that supports communication between operators and maintenance. The responsibilities of the MT were to perform minor maintenance and repair tasks. These MT’s underwent classroom training on tool finishing and fitting as well as on the job training. On the job training gave them exposure to machines and helped them gain expertise in their area.
There are two different types of philosophies of TPM. Firstly, there is the centralized maintenance approach. This requires maintenance personnel to be cross-trained, thus providing flexibility of using a number of workers for scheduling maintenance tasks. This flexibility is essential because as workers move up in seniority level there is a tendency to opt for convenient shifts instead of third shift.
The second approach is decentralization. As personnel become more experienced in one functional area, they gain more expertise. Sometimes it requires 6 months of training before a person becomes proficient in a new area. Thus frequent job rotations may result in under-utilization of skills gained through training. A good example of this type of approach is at Honda Motors for its three departments – suspension assembly, facilities and engine assembly. Each department has a separate maintenance team. The reasons for this shift were the need for 12 to 18 months of training in each area, and local regulations required maintenance to take place only on weekends and shutdowns.
Toyota has a centralized maintenance function with cross-trained employees. The benefits of decentralized maintenance are derived from the use of MT’s. These MT’s are experts in their areas. However, availability of limited maintenance personnel necessitates cross-trained employees.
Toyota also collects data for analysis and trend establishment. Sufficient data on the trend and pattern of equipment’s performance should be available for identifying and setting up standards and procedures for preventive maintenance. This data would also be useful in determining costs of preventive maintenance and repairs, run-to-failure versus preventive maintenance, and failure history.
Organizations also need to evaluate the impact of organizational structure and processes on preventive maintenance. Change in these can have an overwhelming impact on employee morale, efficiency, and effectiveness. As Toyota has shown, preventive maintenance management calls for long-term commitment to the goal and pays dividends in the long run.
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