7、Conditions for successful implementation of assembly cells

IEMS Vol. 5, No. 2, pp. 00-00, December 2006.Conditions for Successful Implementation ofAssembly CellsYu Sakazume†Graduate School of Business Administration, Keio University2-1-1 Hiyoshi-Honcho, Kohoku-ku, Yokohama, 223-8523, JAPANFax:+81-45-562-3502 , E-mail: sakazume@kbs.keio.ac.jpReceived March 2006; Accepted July 2006Abstract. Japanese electrical industries have been actively introducing assembly cells. There have, however, been no systematic discussions concerning the conditions for successful implementation of assembly cells. The purpose of this study is to examine the conditions for implementing assembly cells successfully. This study analyses two types of conditions: 1) market conditions; and 2) product and process conditions. It concludes by presenting three conditions as market conditions and eight as product and process conditions.Keywords: Assembly Cells, Conditions for Successful Implementation, Market Conditions, Product and Process Conditions, Japanese Electrical Industries.1. INTRODUCTIONSince the 1990s, Japanese electrical industries have been actively introducing cellular manufacturing systems into their final assembly processes to ride out declining local economy. Assembly cells are introduced to replace the line production system in which a large number of workers are arranged at sequent workstations. Assembly cells handle small-lot multi-kind production more effi-ciently than the line production system with the resultant advantages of a marked improvement in productivity, reduction in capital investment, shortened lead-times, saving of manufacturing work space, improvement in product quality, and so on [1-3]. However, up until now there have been no systematic discussions concerning the conditions for successful implementation of assem-bly cells.The purpose of this study is to examine the condi-tions for successful implementation of assembly cells by raising the two questions outlined below and conducting case studies of eight companies in Japan.The first question deals with the mechanisms of advantages and disadvantages of assembly cells. What kind of advantages and disadvantages occur through what mechanisms as a result of the implementation of assembly cells? This is a fundamental question regard-ing assembly cells and provides a premise for considera-tion of the second question; i.e. condition for successful implementation of assembly cells. What kind of condi-tions are needed to get effective results? In this study, two types of conditions are analyzed: 1) “market condi-tions” which promise the most effective results and 2) “product and process conditions” which may preclude disadvantages of assembly cells.First of all, this study discusses the first question as to the mechanism of how advantages and disadvantages result from introduction of assembly cells. Then, by describing the mechanisms of advantages, it provides an analysis of market environment in which these advan-tages will function effectively and elicits the market conditions. Secondly, in the same way, by describing the mechanisms of disadvantages, it provides an analysis of product and process design in which these disadvantages can be tolerated and controlled, and elicits the product and process conditions.2. PREVIOUS RESEARCH CONCERNINGASSEMBLY CELLSThe term ‘assembly cells’ refers to cellular manu-facturing implemented in an assembly process [4]. However, whereas cellular manufacturing has been in-troduced into traditional job shops in which machinery and equipment are deployed functionally, and the ad-vantages and disadvantages of this have been discussed in comparison with traditional job shops, assembly cells have been implemented in the line production system† : Corresponding Author2Yu Sakazumeand their advantages and disadvantages are discussed in comparison with the traditional line production system [5]. Thus, although assembly cells are classified as one form of cellular manufacturing, the focus of comparison when measuring their advantages and disadvantages differs from traditional cellular manufacturing, so there has been little prior research concerning the advantages of their implementation and there appear to be no exist-ing studies of their disadvantages and the conditions for their successful implementation.According to the few prior studies that have been conducted of the advantages of implementing assembly cells, the following five changes result from implement-ing assembly cells [4]: 1) U-shaped cells are introduced to replace long, straight assembly lines; 2) conveyors that prescribe the pace of work are removed; 3) the number of work stations is reduced and work stations are placed closer together; 4) the scope of the working process assigned to each worker is increased; and 5) the number of workers assigned to such manufacturing process is decreased.As a result of such changes in the manufacturing process, the following can be cited as the advantages of implementing assembly cells [4, 6]. First of all, as mul-tiple cells producing only a more limited range of simi-lar types of product than previously are established, the time for retooling and change of materials for model changeover is reduced. Secondly, as one assembly line is divided into multiple cells, even if there is a line stop-page in one cell for some reason, other cells can con-tinue production without being affected. Thirdly, the manufacturing space is reduced as a result of removing the conveyor belts. Fourthly, the number of workstations per manufacturing process is reduced and the scope of the working process assigned to each worker is in-creased, so it becomes easier to improve the efficiency of line balancing, resulting in the improved productivity and a reduction in work-in-process inventory. Fifthly, the scope of the working process assigned to each worker is increased and process ownership fostered, promoting improvements and leading to improved quality. Finally, as the scope of the working process assigned to each worker is increased, employee satis-faction is improved.3. DEFINITION OF ASSEMBLY CELLS INTHIS STUDYIn this study, the change for replacing line produc-tion systems with assembly cells is called “cell divi-sion.” This change will be focused in order to discuss the mechanisms of advantages and disadvantages of assem-bly cells.There are numerous definitions for the word “cell,” such as 1) a small room or chamber (i.e. “jail” cell); 2) each compartment of a honeycomb; 3) the smallest structural unit of living matter capable of functioning independently; 4) a memory chip or spreadsheet compo-nent; and 5) a battery. These definitions make it possible to imagine the “cell” as a basic structural unit capable of functioning independently.Figure 1 indicates typical changes brought about by implementation of assembly cells. For example, if a com-pany which has been manufacturing a certain product on a ten-worker production line implements assembly cells, it could form two assembly cells with five workers in each cell, five assembly cells with two workers in each cell, or, in an extreme case, ten assembly cells with a single worker in each cell. This is how assembly cells transform manufacturing processes. How far right a company may wish to go in this figure depends on vari-ous conditions of that company. Some companies would define assembly cells as two cells and five-workers-per-cell configuration, while others might define it as ten cells and one-person-per-cell configuration. Figure 1. Typical Changes Brought About by Implement-ing Assembly Cells.The left-to-right shift illustrated in Figure 1 indi-cates cell division. As you can see, while typical changes in production lines vary from company to com-pany, there is something common to all configurations: every cell can function independently from another. These configurations bring about two changes in the division of labor: 1) decrease in the number of workers in each cell; and 2) increase in the number of cells if the current production volumes are to be maintained (1). In this sense, cell division may also be defined as a process where 1) and 2) changes occur simultaneously.Case studies which follow describe what kind of advantages and disadvantages occur through what mechanisms with regard to each of these two changes resulting from cell division. Secondly, based on the out-comes of the descriptions of these mechanisms, market conditions as well as product and process conditions are analyzed.Conditions for Successful Implementation of Assembly Cells 34. CASE STUDY METHODOLOGYFor the purpose of this study, eight companies were selected as subjects based on two criteria: 1) the number of workers in each cell is particularly small and the number of cells is particularly large, for finding out-standing advantages and disadvantages; and 2) compa-nies operating in as diverse type of industries as possible, not just in electrical industry, where assembly cells are widely implemented and many successful cases are available, for the purpose of identifying general success conditions. Products of subject companies are: com-puters (one company), printers (three), video recorders (one), auto parts (two) and microscopes (one).Case studies began by clarifying what kind of changes occurred as a result of dividing their manufactur-ing lines into cells, then went on to study what kind of advantages and disadvantages such changes created. These causal relationships were examined, and used to analyze market conditions as well as product and process conditions.5. OUTCOMES OF THE CASE STUDIES5.1 M echanisms of Advantages andDisadvantages5.1.1 Advantages and Disadvantages of theDecrease in the Number of Workers First of all, Figure 2-1 shows that decreasing the number of workers in each cell contributes to improving the efficiency of line balancing, resulting in improved productivity. The improved efficiency of line balancing also contributes to decreasing the work-in-process in-ventory, which in turn results in shorter production lead-times and delivery times. Furthermore, decreasing the inventory for work in process shortens the product changeover times, thereby making it easier to move into small-lot multi-kind production, resulting in a decrease in finished goods inventory. Secondly, decreasing the number of workers reduces the waste of transporting items from conveyor to worktable and vice versa, result-ing in improved productivity and shorter production lead-time. Thirdly, decreasing the number of workers expands the extent of work per worker. As a result, the workers’ sense of satisfaction and accomplishment in-creases, contributing to the activation of kaizen activities, improved productivity, often a decrease in capital in-vestment because of internal production of equipment, jigs and tools, and improved product quality.On the other hand, mechanisms of disadvantages are classified into three categories. First, decreasing the number of workers expands the extent of work, thereby increasing the amount of knowledge that workers must acquire, taking time for them to acquire required skills. As a result, disadvantages arise including lower produc-tivity, increase in defective goods, maintaining the same working speed becoming difficult, and frequent model changes becoming difficult to cope with because it is more time-consuming to start the production of new products. Secondly, decreasing the number of workers in a cell expands the extent of work per worker, thereby increasing the number of parts each worker assembles, making it difficult to keep all of the necessary parts close to them. The distance workers have to cover to pick up necessary parts will increase; time lost in work-ers’ movement will not be negligible.5.1.2 Advantages and Disadvantages of theIncrease in the Number of CellsFigure 2-2 indicates that increasing the number of cells makes it possible to divide the labor by product. As a result, it becomes possible to manufacture different models simultaneously in parallel and decrease the fre-quency of product changes per cell. Moreover, because product changes and model changes can be carried out without affecting other cells, it makes it easier to cope with small-lot multi-kind production and frequent model changes. Furthermore, the division of labor by product permits the production of only similar products in each cell, reducing the diversity within each cell and making it easier to implement kaizen activities; as a result, this leads to such advantages as an improvement of produc-tivity, a decrease in capital investment, and an im-provement in product quality.Secondly, increasing the number of cells enables manufacturing the same product simultaneously in mul-tiple cells. As a result, it becomes possible to increase or decrease the number of utilized cells in accordance with the volume of the production, thereby making it possible to cope with quantitative fluctuations in demand. Thirdly, by producing the same product simultaneously in multiple cells, even if defects, equipment failure, shortages or employee absences occur in one cell, the other cells can continue production unaffected, so pro-ductivity per worker increases. Furthermore, manufac-turing the same product in multiple cells may stimulate competition among cells. As a result, kaizen activities are invigorated, thereby contributing to improved pro-ductivity, decrease in capital investment, and improved product quality.On the other hand, the mechanisms of disadvantages are as follows. First, increasing the number of cells ne-cessitates the duplication of equipment, jigs and tools, resulting in an increase in capital investment and manu-facturing work space. Secondly, increasing the number of cells makes it necessary to supply parts to multiple cells, which increases the wastefulness of parts suppli-ers’ movements.4Yu SakazumeFigure 2-1. Advantages and Disadvantages of the Decrease in the Number of Workers.Conditions for Successful Implementation of Assembly Cells 55.2 Analysis of Market ConditionsIn order to examine the market conditions for as-sembly cells, the advantageous mechanisms that emerged as a result of the case studies were analyzed.At first, an analysis was conducted to clarify the in-terrelationships among each advantage to determine what advantages turn into causes of others and what advan-tages are the main ones. As a result, six items were identi-fied as main advantages that are not followed by others: 1) higher adaptability to production volume changes; 2) higher adaptability to frequent model changes; 3) higher adaptability to small-lot multi-kind production; 4) im-provement in product quality; 5) decrease in production cost; and 6) shortened delivery time.Secondly, these six advantages were classified into two categories. The first three concern adaptability to market demand fluctuations. This adaptability refers to an ability to cope with changes speedily, with a stable production cost, when there are fluctuations in market demand. The adaptability to production volume changes refers to the stability of production costs even if the pro-duction volume of a particular product type changes, as well as the ability to respond rapidly to changes in vol-Figure 2-2. Advantages and Disadvantages of the Increase in the Number of Cells.6Yu Sakazumeume. The adaptability to frequent model changes refers to the stability of production costs even if there are fre-quent changes in the design of existing models, as well as the ability to respond rapidly to frequent changes in design. The adaptability to small-lot multi-kind produc-tion refers to the stability of production costs even when the number of models increases, as well as the ability to respond quickly to small-lot multi-kind production. The other three main advantages concern improvements in competitiveness in Q.C.D.. Improvement in product quality refers to reducing the proportion of defective goods. Decrease in production costs refers to reducing production costs through the four advantages of reduced capital investment, improved productivity per worker, lower works-in-process inventory and lower product inventory. The shorter delivery times refers to reducing production lead-times and delivery time.As shown above, an analysis of the main advan-tages of assembly cells leads us to conclude that it is a system implemented to increase the flexibility of the conventional line production system. Flexibility means increased adaptability to market demand fluctuations, and it shows the degree that competitiveness in Q.C.D. are not influenced by environmental changes or the ef-fect of diversification.Based on the foregoing analysis, assembly cells presents an effective production system for companies pursuing flexibility in production with a stable Q.C.D. competitiveness, especially under market conditions in which 1) there are drastic fluctuations in demand; 2) frequent model changes are necessary; and 3) the com-pany has been obliged to adopt small-lot multi-kind production.5.3 Analysis of Product and Process ConditionsIn order to examine the product and process condi-tions necessary for assembly cells, the disadvantageous mechanisms that emerged as a result of the case studies were analyzed. As a result, a total of eight conditions were identified to control disadvantages.First of all, there are the following three conditions controlling the disadvantage of taking time for workers to acquire the required skills. The first condition is high possibility of securing multi-skilled workers because of the low production volume. If the production volume of the product is low and it is possible to deploy existing multi-skilled workers, it will be easy to avoid the disad-vantage of taking time for workers to acquire the re-quired skills, even if the operational man-hours per worker increases. The second condition is low total as-sembly man-hours if the production volume is high but there is lack of multi-skilled workers. If the production volume of the product is high, it will not be possible to deploy existing multi-skilled workers in all cells. How-ever, if total assembly man-hours for the product are low, it will be easy to avoid the disadvantage of taking time for workers to acquire the required skills. The third condition is few difficult operations in the assembly process requiring a high level of proficiency. Where such conditions exist, it is relatively easy to avoid the disadvantage of taking time for workers to acquire the required skills.Secondly, the small number of assembly compo-nents is a condition controlling another disadvantage of the waste of workers’ movement and motion. If there are few assembly components, then even if the scope of operations carried out by each worker is expanded, it will be easy to avoid the disadvantage of the waste of workers’ movement and motion.Thirdly, there are two conditions controlling the disadvantage of increased capital investment. The first condition is that there is no need for expensive equip-ment. Although the number of units of equipment re-quired increases in accordance with increase in the number of cells, disadvantages will be minimal if each piece of equipment is not expensive. The second condi-tion is the possibility of sharing equipment. Even if each piece of equipment is expensive, there will be no major disadvantages if multiple cells are able to share the equipment.Fourthly, there are two conditions controlling the disadvantage of increase in production space. The first condition is that the product and the components are small. Even if the number of cells increases, it will not lead to an increase in production space and there will be no major disadvantages as long as the product itself and the components are small. The second condition is that the equipment is also small. Even if the number of cells increases, it will not lead to an increase in production space and there will be no major disadvantages as long as the equipment is small.Finally, the small number of assembly components is another condition controlling the disadvantage of in-crease in waste of parts suppliers’ movements. If there are few assembly components, then even if the number of cells increases, there will be no major disadvantages in waste of parts suppliers’ movements.Based on these findings, it is possible to conclude that product and process conditions are summarized as follows. First, there are three product conditions: 1) low total assembly man-hours where production volume is high; 2) small number of assembly components; and 3) small products and components. Secondly, there are five process conditions: 1) high possibility of securing multi-skilled workers because of the low production volume;2) few difficult operations requiring a high level of pro-ficiency; 3) no need for expensive equipment; 4) high possibility of sharing equipment; and 5) small equip-ment.Conditions for Successful Implementation of Assembly Cells 76. SUMMARY OF THIS STUDY ANDFUTURE ISSUESIn this study, the mechanisms of the advantages and disadvantages of assembly cells were analyzed and conditions for their successful implementation were identified. As a result, it became evident that there are three market conditions and a total of eight product and process conditions relating to assembly cells.Looking at the examples of assembly cells within Japan, there are many cases in the electrical industry. However, why assembly cells have been implemented intensively within a specific industry? Going by the knowledge obtained through this study, it is conceivable that it has continued to be implemented because the three market conditions are met in the electrical industry, and the eight product and process conditions are met in the field of such products as computers, printers and video cameras. Moreover, it seems likely that the im-plementation of assembly cells would be effective not only in the electrical industry, but also in other industrial fields, such as the automotive components and the mi-croscope, as long as the market conditions and product and process conditions identified through this study are met.Thus, this study has considered conditions for suc-cessful implementation of assembly cells. However, at the same time, there are additional issues raised in this study for further research. The main issue relates to the breadth of this study’s focus. This study examined the conditions for successful implementation of assembly cells, focusing on changes in the manufacturing process from the line production system to assembly cells. How-ever, in order to increase the flexibility of company ac-tivities in a market environment in which there are any fluctuations in demand, changing the production process alone is not sufficient: improvement that focuses on a broader sphere of activity are required, such as im-provement in distribution and in information systems. Given this situation, in order to increase their flexibility, companies should introduce assembly cells while also analyzing what kind of improvement can be imple-mented simultaneously in what other areas, and how improvement in other areas can contribute to creating the advantages of assembly cells; through this analysis, it is likely that the simultaneous achievement conditions necessary for increased flexibility will emerge. The au-thor wishes to conduct further research into such simul-taneous achievement conditions for assembly cells. ACKNOWLEDGMENTSThis study is part of the research supported by Keio Gijuku Academic Development Funds.ENDNOTES(1) In this study, of the five changes cited by Hyer andWemmerlöv (2001), a particular focus has been placed on changes in the division of labor linked to the fourth and fifth changes; changes in line configu-ration, transport method and manufacturing space, which are changes one to three, have not been taken up for discussion. This is because changes in the di-vision of labor are of particular importance in ana-lyzing the advantages and disadvantages of assem-bly cells and that, if the two changes resulting from cell division are considered, the mechanisms of ad-vantages and disadvantages can be explained. REFERENCESShinohara, T. (1995), Shocking News of the Removal of Conveyor System: Self-contained Cell Production (in Japanese), Nikkei Mechanical, (459), 20-38. 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