Design and Analysis of Integrated Manufacturing Systems (1988) / Chapter Skim
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Process and Economic Models for Manufacturing Operations
Process and Economic Models for Manufacturing Operations
Pages 92-117
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From page 92... ...
Process and economic models are essential tools in designing, developing, planning, optimizing, and controlling manufacturing operations and systems. The status of the development and application of these models is presented along with the realworld problems and challenges that influence their use.
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From page 93... ...
Imaginary objects can be represented on paper or on a computer graphic system. Although computer graphics has progressed through several stages of representations, including wire frames, polygon schemes, sculptured surfaces, and solid modeling, there are no intrinsic criteria to assure that a drawing represents a physically realizable object.
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From page 94... ...
They then proceed (a) from the goal of the specified finished object to intermediate steps by adding the necessary "stock allowance" at each preceding processing step or (b)
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From page 95... ...
In the aerospace industry, the practice of constructing life-cycle cost models to evaluate alternative conceptual designs is known to produce significant reductions in cost (Shoemaker, 1980~. This practice allows all aspects of the design to be treated as a system, including items such as product and process R&D, acquisition, support, and fuel use.
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From page 96... ...
PHYSICAL PROCESSES IN MANUFACTURING From ancient times, implements have been shaped from materials such as wood, clay, sand, fiber, and stone by using tools and processes that have been developed largely by trial and error. These shaping processes were clearly the forerunner of the historical development of manufacturing processes driven by the impetus to improve naturally occurring materials through mining and winning, refining, alloying, and other methods.
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From page 97... ...
New applications have created a demand for material processing methods that can shape objects of complex configuration, accurate dimensions, and tight tolerances. Some materials are now being processed in a fashion that leads to properties near their theoretical limits.
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From page 98... ...
Process Traditional Nontraditional Material Removal Machining Grinding Punching Material Deformation Rolling Forging Extrusion Wire drawing Forming Material Addition Plating Coating Material Joining Welding Brazing Compaction Material Transformation Solidification Heat treatment Alloying Turn, mill, drill, bore ID/OD, surface, belt Shearing, stamping Plane, rounds, tubes Open-die, closed-die Forward, backward Open-die Sheet, tube, spinning Electro, electroless Thermal spray Electrode, plasma arc Thermal Puddling Casting, lost wax Tempering, annealing EDM, ECM, laser, EBM ECG, EDG, creep-feed Laser cutting, plasma Isothermal Hydrostatic Superplastic, explosive Chemical vapor deposition, powder vapor deposition, sputtering Laser, electron, inertia Electrothermal Powder metal Directional, continuous Laser beam heat treatment Deoxidation, melt High pressure to meet special needs, traditional processes have undergone continued improvements in response to the new materials and the demand for higher performance. Thus, it is no surprise that traditional manufacturing processes continue to play a major role in manufacturing.
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From page 99... ...
Phenomenolog~cal Process Models Phenomenological models are constructed to describe the cause-effect relationships between the basic input variables and the output variables of a manufacturing process. The drive toward creating phenomenological models is a natural extension of the belief that, since we understand the basic laws of physics, it should be possible to apply these laws and define manufacturing processes mathematically.
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From page 100... ...
TIPNIS Empirical Process Models Empirical models relate process performance directly to process variables using experimental data from a real process or a closely simulated situation. As shown in Figure 4, the empirical model can be viewed to encompass one or more phenomenolog~cal models dealing with the specific cause-effect relationships.
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From page 101... ...
This approach has not yet made a significant impact on process modeling (Kapoor and Wu, 1980~. PROCESS ECONOMICS The goal of economic models is to create a tool that can be used to determine a set of operating conditions that will optimize the economic objective function within the working region of the process.
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From page 102... ...
Consequently, a trade-off function exists between the material removal rate and the tool life. Constraints on the Objective Function The range of allowable values for the variables must be constrained by the physically realizable working region.
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From page 103... ...
If the values on the R-T-F curve are beyond the working region, the optimal strategy would be to 0.010 0.008 o a so 0.006 c IL 0-004 0.002 0.10 0.20 operate at the limits of the working region closest to the R-T-F curve. Furthermore, it has been demonstrated that the minimum processing time always occurs at higher material removal rates than the minimum for cost (Ravignani et al., 1977~.
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From page 104... ...
Traditionally, most discrete parts manufacturing processes have been controlled 24.50 ~ 24.00 X , _\ 1 _ Minimum Cost I __ _ 23.00 I ~ I I 2.0 2.5 3.0 3.5 R (In.31min) FIGURE 8 Cost versus cutting rate.
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From page 105... ...
Strategic activities dominate the process design and development process in the early phases. At the top of the figure are shown the different economic models that can be used in the development of the design and manufacturing process.
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From page 106... ...
In establishing the technological feasibility, it is necessary to demonstrate that the process is feasible within the technological constraints. Establishing the economic feasibility of the process demands that the economic range of operating conditions be known and used to influence the establishment of the directions for process development.
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From page 108... ...
VIJAYA. TIPNIS PROCESS PLANNING Process planning involves the selection of a processing sequence and the operating conditions for each unit process within the sequence that will produce a given lot of parts.
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From page 109... ...
Important research areas in process planning include · Establishment of a methodology for determining processing sequence from specifications of features, dimensions, and tolerance of the part or assembly configurations; · Application of process models to determine the most economical operating conditions for each processing unit, and · Evaluation of the impact of operating conditions of each unit process on the production rate and economics of the entire sequence. Process planning can benefit greatly from a continuing feedback of data from the manufacturing floor.
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From page 110... ...
Whereas the FMS controls the actual production activities, the integrated manufacturing system (IMS) incorporates and synchronizes the preproduction activities of process planning, NC programming, and tool and material acquisition.
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From page 111... ...
As noted earlier, processing that proceeds unattended involves guarding against the risks of catastrophic failures and reduced performance. The first step in designing an FMS is to reexamine processing sequences and operating conditions of the parts in the target family of parts and to evaluate the impact of changes that the processing technology can have on the time and cost of manufacturing.
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From page 112... ...
Overall system performance must include measures of production rate, in-process buffer storage, capital investment for all processing units, and the value of work holding pallets and tools. Finally, the system performance can be improved, not by optimizing each processing unit, but by optimizing the processing rate of the bottleneck units and by relaxing the other processing units in the sequence.
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From page 113... ...
manufacturing system and then to determine the potential time and cost savings over the current manufacturing system. At this stage, the microeconomic models for each processing unit and the macroeconomic models for the entire system must be applied.
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From page 114... ...
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As was noted earlier, it is of great importance that current limitations in these theories be reduced so that they can be more broadly applied for example, to those areas in which the microstructure of the materials is treated in detail and the typical processing conditions of extreme stress, strain, strain rate, and temperature conditions can be accommodated. The state of the art of empirical process models should be advanced to develop a sound methodology for constructing models of practical use.
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From page 116... ...
1987. Computer-aided process planning: A critique of research and implementations.
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From page 117... ...
1978. Economic models for process planning.
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