Lean Manufacturing Principles Improve Production

The principles of lean manufacturing developed by the Japanese are at work in Smyrna, TN, at the North American home of Nissan Motor Manufacturing Corporation

Redwolf Industries, Inc., Mason, OH, has installed monitoring systems on eleven 1200-metric ton presses in the stamping department of Nissan's Smyrna, TN plant. Data is updated continuously so that the press operator can determine actual performance compared to target values.

The term "lean manufacturing" was coined from an MIT study of Japanese manufacturing methods published in the book, "The Machine that Changed the World" by J. P. Womack, et al. A key benefit of lean manufacturing is having a system in place to quickly detect problems and inefficiencies. Continuously solving these problems steadily improves the process.

Nissan's Smyrna plant recently was named North America's most productive auto plant by Harbour and Associates. Employing more than 5900 persons, with a production capacity of 450,000 vehicles per year, Nissan knows the importance of synchronizing flow, JIT manufacturing and optimizing production processes. In 1993, the Nissan Smyrna plant produced one truck per shift for every 2.3 workers and one car per shift for every 2.32 workers.

Sometime ago, Nissan contracted with Redwolf Industries, Inc., Mason, OH, a domestic specialist in turnkey productivity systems, to implement a productivity monitoring and feedback system. A monitoring and feedback system is a cost-effective method to implement features of lean manufacturing as well as a way to quantify and coordinate the production process. The system is designed to synchronize output, establish a standardized work pace and monitor equipment conditions -- all while continuously storing production data. In addition, these data are displayed in real time on large "Andon" boards so that everyone understands the current plant situation.

A standard component at Japanese auto plants is the continuous display of production information on lighted electronic displays known as "Andon" boards. These large displays keep score by showing the progress of production to the desired output. Displays indicate the desired shift schedule, the target quantity (the quantity the worker should have produced at a given, point in the day), the actual quantity and the variance between the actual and target values.

The system shows individual progress compared with the flow at any instant in the day. In addition, equipment status is displayed to immediately alert maintenance personnel of equipment downtime and other potential problems. Systems like this have increased productivity and reduced downtime in many Japanese North American facilities.

The Japanese have found that by reducing and dividing the manufacturing flow into distinct processes and procedures (work cells), each station in the flow can be more closely examined. The "tact time" (time allotted an individual work cell to complete its task) and the synchronization between work cells translates into the time finished products are produced. Therefore, close observation to fine tune each cell becomes critical to keep the process steady and improve overall production time. Identification of a process as the weak link in the chain soon becomes apparent when the tact time at a particular station becomes out of balance compared to the rest of the process.

The importance of maximizing productivity was illustrated in the book, "New Shop Floor Management," by K. Suzaki. It is evident from Table I that even small increases in productivity can greatly affect the overall process.

Table 1

Increased output is one of many benefits derived from production monitoring. Providing real time visual information allows workers and management instant feedback concerning daily production targets and downtime. Monitors, visible to the worker provide goals and incentives to improve continuously. The stamping department needed a way to efficiently coordinate its output with the remaining assembly operation. Since various models share the same assembly line, coordination is vital to assure proper assembly setup and to synchronize stamping output with assembly output. This reduces work-in-progress and minimizes overall assembly changeover time.

The stamping process is the first link in a long and sophisticated manufacturing chain. Its impact greatly affects the remaining assembly process. In the stamping process, several presses are used with various dies to produce the many components of the vehicle. Dies must be changed repeatedly to produce each separate part. Coordinating the schedule of the correct die in the proper quantity is vital to smooth production flow. Accurate data of when a particular part should be produced and its proper quantity is needed to avoid errors what can lead to disastrous delays in subsequent production processes. In addition, the stamping process must accurately predict this information to minimize the number of die changes and the die changeover period. The system tracks die change downtime occurrences and duration. Efficiently changing dies in the stamping process is a key factor in overall productivity since a single press is used with various dies to produce numerous parts used in assembly. Both of these factors deplete the actual window of time the press is in operation, which can impact the assembly operation that is solely dependent upon stamping output.

Monitoring systems provide a way for manufacturers to get quantifiable results. Data are processed into reports that aid in evaluating worker performance, as well as provide trend analysis and indentification of process inefficiencies.

Synchronized production also is a vital concern. To properly complete assemblies, the correct ratio of component parts is essential. Monitors instantly indicate both target and actual quantities produced so that potential problems in work delays or excessive work in process (WIP) can be avoided. Analyzation of past production data allows Nissan to identify weak areas in the scheduling procedure and its impact on finished production output.

Based upon the total number of minutes in the shift (not including breaks), the system will calculate a running target. This target is synchronized with the tact time of the assembly operation. This means that at any point in time during the shift workers knows exactly where they are compared to where they should be in order to achieve the output goal. At the end of a shift, if the actual parts equal the target parts, the goal is achieved. If actual parts and target parts are not equal, then the scoreboard displays the production variance.

The system tracks die changeover and downtime occurrences and duration. Efficiently changing dies in the stamping process is a key factor in overall productivity since a single press is used with various dies to produce numerous parts. The change activates a display timer on the production scoreboard. After the die has been changed, the timer is locked and the total elapsed time is displayed on the production scoreboard. The time remains displayed until the next downtime occurrence. Downtime is recorded automatically, according to category. This information is stored and reviewed for immediate analysis.

Each station is linked via RS-485 port to a central PC to store and evaluate pertinent production data. Reports compile this data for use in process management. These reports aid in evaluating worker-to-worker performance, trend analysis and identification of inefficiencies. Analysis of these parameters indicates areas for improvement. This cycle is continuously repeated to optimize production.

Each monitoring system communicates with a PC via its RS-485 port. Accumulated downtime for maintenance and tool changes can be displayed as well as recorded.

Improvements come by refining the overall process. Knowing the condition of the process will come only by observing and recording production data. Monitoring systems provide a way for manufacturers to get quantifiable results. Analysis of past trends points the way to future improvement.

With more than seven auto plants operating in the United States, the Japanese are spreading the lean manufacturing philosophy to U.S. companies. Through interface with U.S. suppliers, local content requirements and the new sticker disclosure law, the Japanese are converting U.S. suppliers to these methods. Continuous improvement (Kaisen), just-in-time (JIT) delivery and inventory management are all catch phrases describing key elements of the lean manufacturing philosophy. MF