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Metal Casting Technologies : December 2006
The diagram is composed of interlocking arrows leading into a problem symbol. The main shafts to the left of the symbol represent principal causes. Smaller arrows directed toward the major shafts relate to control parameters of the cause factors. An example of a Cause-and-Effect Diagram as applied to a cast iron fracture is shown above: The procedure for making the cause-and-effect diagram is as follows: a. Identify the characteristics (major causes) to be considered and put them in the diagram as cause factors. b. Determine the factors affecting the characteristics and place them with the characteristic they affect. (Get together the personnel concerned and get their opinions regarding the factors, add some more, if there are any.) c. Determine the factors with the greatest effect on the characteristics and prioritize. (Do this by discussions among the members of the group.) d. Define and determine solutions to the wayward factors. (This is achieved by the group discussions.) Quality Control Circles In Japan a unique movement united millions of employees in a common pursuit of quality control. It is called the Quality Control Circle (QCC). The first circles were started in 1962 and they now number over 400,000 with greater than 4 million workers participating. A QCC is composed of a group of production workers and foremen who voluntarily cooperate to solve production-quality maintenance problems. No one is forced to join a circle. After one is formed, it is officially recognized and becomes part of the national organization. Though circles have a grass-roots outlook, top management provides substantial backing and encouragement. Companies help their QCC actively participate in regional and national conferences. A first-line supervisor usually leads a QCC. Meetings are typically held once or twice a month in the evening. During the meeting common problems are discussed, plans are made to solve the problems by collecting data, and recommendations based on the analyzed data are prepared for presentation to appropriate managers. Circle members use control charts, cause-and-effect diagrams, histograms and other control techniques to develop solutions. About 91 percent of the companies in Japan have QC circles. The manner of behavior of the men who are ordering the work is important in motivating the workers to contribute their originality and faculty to properly produce the products that the enterprise is producing. If the men ordering the work fully understand the requirements of each item and confront the workers, then the workers will also understand the objective of their work and tend to produce fine quality products. Work supervisors should: a. Clearly indicate to each worker the results expected of him, especially the quality required. b. Indicate the methods that will be used in checking the results of the job and the criteria to be used. c. Allow workers to work with utmost freedom and not to unreasonably force them. d. When it is inevitable to force workers to do the work in a certain manner, explain this carefully to their satisfaction. e. Teach workers how to evaluate their own work and recognize the results. f. Continually motivate the workers to give their best efforts, not only for the company, but for their own satisfaction of doing a job well. Fig. 1. A cause-and-effect (0r fish bone) diagram for cast iron fractures. METAL Casting Technologies December 2006 (CAUSE FACTOR) Pouring Temperature (CAUSE FACTOR) Mold Wash Condition of ladle Tapping temperature Amount of sea coal Amount of mold wash Pouring time Sequence of pouring Drying time Amount of slag Sequence of tapping Charge ratio of materials Hearth temperature Mold "turnover" Casting weight Mold preheating Pouring sequence Degree of cooling Metal Composition (CAUSE FACTOR) Mold Temperature (CAUSE FACTOR) (EFFECT) Fractured casting 49