PROCESS CONTROL PHILOSOPHY

Japan's processes appear to be generally slower and more robust than the same operations in the United States. This is true all over Japan and even in Japanese manufacturing operations that have been opened in the United States and Canada. The Japanese are willing to sacrifice the economy of faster cycle times for reliability and repeatability.

The Japanese tend to study and thoroughly understand not only what is going on within their processes but also the external factors that affect them. They are slow to specify new substitute materials or process supplies in the interest of economy. They use the fish bone diagram effectively and determine the root causes of unwanted variation.

The following serves as an example of how the Japanese look at their processes. Engineers at one aluminum foundry, using many of the same molds, recognized that consistency of the mold coating was a key variable in producing castings with consistent microstructure properties and was a major factor influencing directional solidification. They also determined that there was little consistency between operators in the artful application of the refractory coatings. They concluded that coatings begin to wear in certain areas during the second shift of operation. Again rather than allow individual operators to touch up the worn spots, they specify complete reconditioning of the mold after two shifts.

This mold reconditioning operation is now being mechanized, with considerable difficulty, to ensure that all coating applications are identical. This deliberately structured approach requires more tooling, makes quick die changing essential, and represents a sizable investment for consistency. They are convinced it will be worth the price.

Certain aspects of liquid metal preparation have also been automated to ensure that each ladle going into a die cast machine is skimmed in the same manner. In another case, the entire degassing, filtering, and skimming operations were completely automated and engineered as a continuous process to avoid the interruptions prevalent in batch processing.

It is the norm for the Japanese to have a very detailed understanding of variation in casting operations with close attention to fewer variables than in U.S. operations. An example is tighter control of tramp elements in the raw melt materials and narrower ranges of moisture control in green sand systems.

Tooling is checked more often for dimensions with fewer dimensional checks on the end product. In general there is less leak testing of die cast automotive blocks and heads because the processes are more effective.

Many of the processes the WTEC panelists observed had been established for a few years and have been the subject of continuous improvement. In most instances, there were no control charts being used, possibly because long term process control had already been demonstrated.

Noncontact die temperature measurement devices were in use to overcome the inherent error and poor reliability of hard thermocouples.

In problem solving the panel saw examples of the Japanese attacking the root cause. As an example of the depth of understanding of costs, Hitachi Metal Ltd. has developed a flash free process to reduce the need for labor to remove fins and flash from castings. In general, Japanese foundries do very little repair and finishing work on a casting by controlling the process during molding, pouring, and core making. If finishing is required, robots are often used to avoid the difficult jobs.

Although computer integration of manufacturing processes was not observed as the norm in Japan, one application, again at Hitachi Metals Ltd., is notable. That company has installed a facility to produce 85,000 wheels each month in a variety of 16 wheel styles and sizes. This highly automated production line consists of seven special low pressure casting machines, continuous heat treat furnaces, four machining lines, and a painting facility followed by a single final inspection station. The whole line is controlled by computers. The one piece flow with this control has reduced lead time from 120 hours to 24 hours.

Two visits to ceramic producers indicate that they are hard at work looking for products that will help foundries improve process control. A few examples are as follows:

Accuracy of measurement of process variables is seen as important in Japan. There is extensive data gathering but not nearly as much closed loop control as in the United States. U.S. engineers have a tendency to want to establish controls on everything that they can measure. The Japanese tend to establish controls on what they truly understand to be necessary.

In Japan technologies for maximizing the use of natural resources while being friendly to the environment are a priority. Without exception, this is a common goal of all casting operations without pressure from the government.


Published: March 1997; WTEC Hyper-Librarian