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A computer simulation study of manual flow lines
EDITORIAL REVIEWS
"The Effect of Part Assembly on Manual Assembly Times" by Z. Yoosufani, M. Ruddy and G. Boothroyd
leads to the machining center conceptualization rather than the flexible manufacturing system approach. This is probably intrinsically right, but leaves unaltered the constitutional design and role of the process.
In this paper, Professor Boothroyd and his colleagues have described a very useful study that quantizes the effect of part symmetry on manual assembly handling times. Previous work by others in this field has been largely empirical; this study approaches the problem from a more rational approach. The analytical basis for the research is simple and straightforward and the experimental tasks, although somewhat simplistic, correlate well with the theory. Much more work remains to be done in this area and the authors should be encouraged to conduct further research in the design of parts for economical assembly.
A third influence of adaptive control per SE results from its dedicated and embedded nature. By contrast, computer aided manufacture reaches outwards and offers integration within the overall manufacturing system. This has been achieved in the numerically controlled wire cutting machine type. This now offers CAD]CAM possibilities whereby very considerable reductions in overall time span from des!gn and programming through to cutting to finished profile, accuracy and finish can be achieved-this within a unified span of technological capability and practical use. Obviously this has come about through its foundation upon NC technology, plus the accepted and expected utilization of it in a CAD]CAM mode arising from general practice and experience.
Marvin F. DeVries Professor, Dept. of Mechanical Engineering University of Wisconsin-Madison
Nevertheless some advances have been made in the integration of cavity forming EDM within the CAD] CAM philosophy, and it is believed that this will represent yet a further step in the evolving technological maturity of EDM. John R. Crookall Professor of Manufacturing Systems Cranfield Institute of Technology
"Survey of Adaptive Control in Electro Discharge Machining" by R. Snoeys, D. Dauw and J.P. Kruth This is a useful critical survey of approaches to adaptive control of EDM which have been made by a number of investigating centers within the industry. In terms of adaptive control per SE, the EDM process is well up to the state-of-the-art within both conventional and nonconventional machining processes. The extensive range of parameters referred to by the authors, for instance in their Tables 2 to 4, illustrates the technological detail involved in controlling and optimizing the process.
"A Computer Simulation Study of Manual Flow Lines" by D.S. Hira and P.C. Pandey In 1966 Dr. Redford of the University of Salford and I published an analytical method to determine the performance of automatic assembly machines of the freetransfer type ("Free-transfer Can Improve Assembly Machine Economics", Metalworking Production, June 1966, pp. 67-70). This work is now reproduced in a textbook on automatic assembly (G. Boothroyd, C. Poll and L. E. Murch, Automatic Assembly, Marcel Dekker, 1982). A free-transfer automatic assembly machine is one particular type of the flow line production system studied by the authors, and an empirical solution to the problem is most welcome. There are several results of the work in this paper that could have been deduced.
And yet the case could be argued that in terms of practical use in industry, this has not so far resulted in a significant increase in total automation of the EDM operation on the shop floor. The exception is in production hole drilling by EDM which is now extensively automated, and yet paradoxically, has little of the scale or sophistication of adaptive control already available for the cavity forming variety referred to by the authors. Without entering into the detailed reasons, the main influence here is that it is a production operation of holes often required in considerable numbers. Thus, 'scale has forced considerable economics'.
In the ease of an assembly machine, the variability in operating time arises from stoppage ofworkheads due to faulty parts. When such a stoppage occurs, the workhead is "down" for a few cycles and the preceding workheads will have to stop when their buffers fill up. The workheads
A second factor lies in the continuing conception of EDM as a stand alone operation, where electrode changing rather than work movement is employed. This
conthnwd vii
editorial reviews
" C A M for Developing Nations" by Bolek Brunak (Volume 2/No. I)
following the stopped workhead will stop when the supply of assemblies in the previous workhead's buffers is exhausted. Thus, in the long run, spaces in the buffers at t h e beginning of a line are equivalent to assemblies stored in the buffers at the end of the line and would have the same effect on performance. Thus, if the n 'h buffer from the beginning of the line runs on an average of two-thirds capacity, then the n th buffer from the end of the line must run at one-third capacity. This behavior is clearly depicted in the authors" results as shown in Figure 9. Also, it is therefore not surprising that the average utilization of buffers is found to be 50%.
This paper clearly demonstrates the presently emerging possibilities for computer aided and integrated manufacturing to be extended to developing countries as a direct extension of the current manufacturing systems of industrialized countries. It is therefore, in a way, a significant extension and broadening of concepts developed earlier by Professor O. Bjorke of the Technical University of Norway, for decentralizing manufacturing within a given country by making use of the inherent potential of CAM for ready transfer of manufacturing information and skills.
It is interesting to note that a workhead breakdown will equally affect the workheads positioned before and after on the line--the closer the workhead, the greater the effect. Thus, the effect of stoppages of workheads at the beginning and end Of the line will be less than the effect of stoppages of workheads near the middle of the line. For this reason, the larger buffers are required near the m i d d l e o f the line in o r d e r to o b t a i n m a x i m u m performance.
Bolek Brunak clearly outlines how it is now becoming possible to do this on a global scale by making use of telecommunications, for example. He describes not only how this can be accomplished, but also the benefits which can be expected to accrue for both developing and industrialized countries by so doing. Brunak's recommendation that the feasibility of currently putting these possibilities to work by implementing a pilot project in Mexico, is an excellent and practical proposal, and one which should be seriously considered and explored by advanced American manufacturing companies.
Finally, if .workcarriers or platens are involved, these must be circulated around the machine. In this case, the line becomes a closed loop system rather than an open loop system as in the authors' model. Using the same arguments as above, the utilization of all buffers would then be 50% if the buffers were of equal size, and there would be no point in varying buffer size unless one workhead or station were more prone to stoppage than the others.
M. Eugene Merchant Director, Advanced Manufacturing Research Metcut Research Associates Inc.
Geoffrey Boothroyd Professor of Mechanical Engineering University of Massachusetts
VUl
"The Effect of Part Assembly on Manual Assembly Times" by Z. Yoosufani, M. Ruddy and G. Boothroyd
leads to the machining center conceptualization rather than the flexible manufacturing system approach. This is probably intrinsically right, but leaves unaltered the constitutional design and role of the process.
In this paper, Professor Boothroyd and his colleagues have described a very useful study that quantizes the effect of part symmetry on manual assembly handling times. Previous work by others in this field has been largely empirical; this study approaches the problem from a more rational approach. The analytical basis for the research is simple and straightforward and the experimental tasks, although somewhat simplistic, correlate well with the theory. Much more work remains to be done in this area and the authors should be encouraged to conduct further research in the design of parts for economical assembly.
A third influence of adaptive control per SE results from its dedicated and embedded nature. By contrast, computer aided manufacture reaches outwards and offers integration within the overall manufacturing system. This has been achieved in the numerically controlled wire cutting machine type. This now offers CAD]CAM possibilities whereby very considerable reductions in overall time span from des!gn and programming through to cutting to finished profile, accuracy and finish can be achieved-this within a unified span of technological capability and practical use. Obviously this has come about through its foundation upon NC technology, plus the accepted and expected utilization of it in a CAD]CAM mode arising from general practice and experience.
Marvin F. DeVries Professor, Dept. of Mechanical Engineering University of Wisconsin-Madison
Nevertheless some advances have been made in the integration of cavity forming EDM within the CAD] CAM philosophy, and it is believed that this will represent yet a further step in the evolving technological maturity of EDM. John R. Crookall Professor of Manufacturing Systems Cranfield Institute of Technology
"Survey of Adaptive Control in Electro Discharge Machining" by R. Snoeys, D. Dauw and J.P. Kruth This is a useful critical survey of approaches to adaptive control of EDM which have been made by a number of investigating centers within the industry. In terms of adaptive control per SE, the EDM process is well up to the state-of-the-art within both conventional and nonconventional machining processes. The extensive range of parameters referred to by the authors, for instance in their Tables 2 to 4, illustrates the technological detail involved in controlling and optimizing the process.
"A Computer Simulation Study of Manual Flow Lines" by D.S. Hira and P.C. Pandey In 1966 Dr. Redford of the University of Salford and I published an analytical method to determine the performance of automatic assembly machines of the freetransfer type ("Free-transfer Can Improve Assembly Machine Economics", Metalworking Production, June 1966, pp. 67-70). This work is now reproduced in a textbook on automatic assembly (G. Boothroyd, C. Poll and L. E. Murch, Automatic Assembly, Marcel Dekker, 1982). A free-transfer automatic assembly machine is one particular type of the flow line production system studied by the authors, and an empirical solution to the problem is most welcome. There are several results of the work in this paper that could have been deduced.
And yet the case could be argued that in terms of practical use in industry, this has not so far resulted in a significant increase in total automation of the EDM operation on the shop floor. The exception is in production hole drilling by EDM which is now extensively automated, and yet paradoxically, has little of the scale or sophistication of adaptive control already available for the cavity forming variety referred to by the authors. Without entering into the detailed reasons, the main influence here is that it is a production operation of holes often required in considerable numbers. Thus, 'scale has forced considerable economics'.
In the ease of an assembly machine, the variability in operating time arises from stoppage ofworkheads due to faulty parts. When such a stoppage occurs, the workhead is "down" for a few cycles and the preceding workheads will have to stop when their buffers fill up. The workheads
A second factor lies in the continuing conception of EDM as a stand alone operation, where electrode changing rather than work movement is employed. This
conthnwd vii
editorial reviews
" C A M for Developing Nations" by Bolek Brunak (Volume 2/No. I)
following the stopped workhead will stop when the supply of assemblies in the previous workhead's buffers is exhausted. Thus, in the long run, spaces in the buffers at t h e beginning of a line are equivalent to assemblies stored in the buffers at the end of the line and would have the same effect on performance. Thus, if the n 'h buffer from the beginning of the line runs on an average of two-thirds capacity, then the n th buffer from the end of the line must run at one-third capacity. This behavior is clearly depicted in the authors" results as shown in Figure 9. Also, it is therefore not surprising that the average utilization of buffers is found to be 50%.
This paper clearly demonstrates the presently emerging possibilities for computer aided and integrated manufacturing to be extended to developing countries as a direct extension of the current manufacturing systems of industrialized countries. It is therefore, in a way, a significant extension and broadening of concepts developed earlier by Professor O. Bjorke of the Technical University of Norway, for decentralizing manufacturing within a given country by making use of the inherent potential of CAM for ready transfer of manufacturing information and skills.
It is interesting to note that a workhead breakdown will equally affect the workheads positioned before and after on the line--the closer the workhead, the greater the effect. Thus, the effect of stoppages of workheads at the beginning and end Of the line will be less than the effect of stoppages of workheads near the middle of the line. For this reason, the larger buffers are required near the m i d d l e o f the line in o r d e r to o b t a i n m a x i m u m performance.
Bolek Brunak clearly outlines how it is now becoming possible to do this on a global scale by making use of telecommunications, for example. He describes not only how this can be accomplished, but also the benefits which can be expected to accrue for both developing and industrialized countries by so doing. Brunak's recommendation that the feasibility of currently putting these possibilities to work by implementing a pilot project in Mexico, is an excellent and practical proposal, and one which should be seriously considered and explored by advanced American manufacturing companies.
Finally, if .workcarriers or platens are involved, these must be circulated around the machine. In this case, the line becomes a closed loop system rather than an open loop system as in the authors' model. Using the same arguments as above, the utilization of all buffers would then be 50% if the buffers were of equal size, and there would be no point in varying buffer size unless one workhead or station were more prone to stoppage than the others.
M. Eugene Merchant Director, Advanced Manufacturing Research Metcut Research Associates Inc.
Geoffrey Boothroyd Professor of Mechanical Engineering University of Massachusetts
VUl