Design for Manufacturability and Design for âXâ: Concepts, Applications, and Perspectives. T. C. Kuo and Hong-Chao Zhang. Department of Industrial ...
Design for Manufacturability and Design for “X”: Concepts, Applications, and Perspectives T. C. Kuo and Hong-Chao Zhang Department of Industrial Engineering Texas Tech University Lubbock, Texas 79409-3061 Abstract: Design for Manufacturability (DFM) is a system approach that simultaneously considers all of the design goals and constraints for products that will be manufactured. Sometimes DFM is confused with Design for Assembly (DFA), which is only one aspect of design for Manufacturability. Other aspects include all the “design for’s’’ or “-abilities;” design for Quality, design for Maintainability, etc. They are sometimes referred to as “design for X” (DFX). This paper presents the concepts, applications, and perspectives of DFX, thus, providing some guidelines and references for the future researches and implementations.
Environment (Leonard 199l), Design for Recyclability (Henstock 1988) and Design for Life Cycle (Ishii and Eubanks 1993). These are sometimes referred to as Design for X (DFX). Since the late 1980s, hundreds of papers have been published pertaining the DFX applications in manufacturing. Most of them arc widely scattered over many different disciplines and publications. This makes it very difficult for one to locate all the information necessary for using DFX in manufacturing. A paper that can help researchers and practitioners in applying this emerging technology is highly desired. The objective of this paper is to present the concepts, applications, and perspectives of “DFX” in manufacturing, thus providing some guidelines and references for the future researches and implementations.
1. Introduction It has been recognized that the final cost of a product is largely determined during its design, therefore, designer must take manufacturing into account from the outset. This phenomenon reveals the need for a well-thought out design and for considering manufacturing issues at the early design stages. As early as the 1960’s, several companies developed guidelines for use during product design. One of the best known examples is the manufacturing Producibility Handbook published for internal use by General Electric in the USA (MPH 1960). The manufacturing data was accumulated into one large reference volumes with the idea that designers could have the manufacturing knowledge for efficient design. However, the emphasis was on the “Producibility” and very little attention was given to the manufacturing and assembly process. An outstanding analysis of the potential of Design for Assembly (DFA) was provided by Boothroyd and Dewhurst (1983). DFA was defined by Boothroyd and Alting (1992) as “design of the product for ease of assembly.” Expanded from DFA, Stoll (1988) developed the concept of Design for Manufacturability (DFM) to simultaneously consider all of the design goals and constraints for the products that will be manufactured. Several papers about DFA and DFM can be found in the litcrature (Andreasen and Kahlcr 1983, Waterbury 1985, Scarr 1986, Kobe 1990). DFA and DFM have generated a revolution in design practices including simplification of products, lower assembly and manufacturing costs, rcduction of overheads, improvement of quality, and reduction of time to market. More recently, environmental concerns are requiring that disassembling and recycling need to be considered during product design. Studies have been started on Design for Quality (Unal and Lance 1992), Design for Reliability (Anderson 1990), Design for Disassembly (Boothroyd and Alting 1992 ), Design for 0-7803-2037-9195 $4.00 01995 IEEE
2.1. Design for Manufacturability It has been identified that 75% to 90% of total product cost is determined when a design is released to production (Fabrycky 1987, Daetz 1987). DFM was defined by Stoll (1990) as “the full range of policies, techniques, practices, and attitudes that cause a product to be designed for the optimum manufacturing cost, the optimum achievement of manufactured quality, and the optimum achievement of life-cycle support, serviceability, reliability, and recyclability.” The objectives of DFM approach are to: (1) identify product concepts that are inherently easy to manufacture, (2) focus on component design for ease of manufacture and assembly, and (3) integrate manufacturing process design and product design to ensure the best matching of needs and requirements (Stoll 1988). DFM seeks to identify the appropriate materials and manufacturing processes for component parts being considered in a product’s design based on the combination of various capabilities and limitation of products (Kirkland 1988). Typically, DFM focuses on a particular manufacturing process, e.g., machining, stamping, injection molding, assembly, etc., and seeks to incorporate into the early product design measurements that can prevent manufacturing problems and significantly simplify the production process (Yu 1993). DFM can be modeled as a single process, divided into three stages: design, transition from design to production, and the production operation. Each stage contains a Plan-Do-S tudy-Act (PDSA) with unique tasks performed during the four step (Ehresman 1992). For more details about PDSA, see Ehresman (1992). Two consideration associated with DFM approach are DFM process and DFM methodologies and toolkits. In 446
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discussing the DFM approach to product design, it is necessary to develop a structured DFM process to help guiding the design team toward its goal of a product design for ease of manufacturing (Stoll 1988). The DFM process, shown in Figure 1, begins with a pralposed product concept, a proposed process concept, and a set of design goals. The four activities comprising this process are arranged in a circular fashion to emphasize the iterative nature of the process. Each activity of DFM process addresses a particular aspect of the design. Optimization of the product/process concept is concerned with integrating the proposed product and process plan to ensure inherent ease of manufacture. The next activities is to focus on the component design for ease of assembliy and handling and on the simplification of components to further promote ease of manufacture, improve quality and reduce manufacturing cost. The third activity is to aim at ensuring conformance of the design to processing meeds. The last activity is to ensure that all of the design conslraints, including assembly, proccssing, and material handling requirements, are known before the optimization is attempted (Stoll 1990).
feature or componcnt within the design. It is also useful in this step to build the FRs in a hierarchical structure, starting with I.he primary FRs and proceeding to the FRs of least importance. The second step is to proceed with the design, applying the axioms to each individual design decisions. Albano (1994) et al. presented the concept of axiomatic design as a framework for concurrent engineering. It is based on the design that provide basic principles. The author provides a theoretical framework for introducing the computer as a design assistant and an architecture for a computational design environment. These concepts have been formalized as the following design axioms (Yasuhara and Suh 1980): Axiom 1: In good design, the independence of functional requirements is maintained. Axiom 2: Among the design that satisfy Axiom 1, the best design is the one that has minimum information content. DFM Guidphdi The application of the DFM guidelines is not always easy or straightforward. Stoll (1988) cited a check-off list of DFM guidelines which represent a systematic and identified list of statements of good design practice.
Design Axioms Many research efforts have been dedicated to the DFM
E:ngineering Release Package: .Part Drawings .Part List .Assembly Drawings
Proposed Product Concept Proposed Process Design
\
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Optimize Concept
Simplify Product Design
0p t i mi ze Product Function
.Least
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ProductlProcess
L L Conformance
Figure 1: Continuous Optimization of Product arid Process (Stoll, 1990) Typically, the design guidelines are stated as directive that act to both stimulate creativity and show the way to good design for manufacture. A simple summaries is as follows:
methodologies and tools of DFM. Suh et al. (1978) use the fundamental principles of design axioms to guide and to evaluate design decision. Stoll (1990) discussed tlhe use of axioms design in DFM should includes two step processes. The first step is that each functional requirement (FRs) and constraints of a product, device, or system should be satisfied independently by some aspect,
1) Design for a minimum number of parts 2) Develop a modular design 3 ) Minimize part variations 447
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Moldflow Australia (PTY) Ltd. Moldflow is a computer simulation of molten plastic moving through the gates, runners and cavity of an injection mold (Kuttner 1985).
4) Design parts to be multifunctional 5 ) Design parts for multiuse 6) Design parts for ease of fabrication 7) Avoid separate fasteners 8) Minimize assembly defections; design for topdown assembly 9) Maximize compliance; design for ease of assembly 10) Minimize handling; design for handling and presentation 11) Evaluate assembly methods 12) Eliminate or simplify adjustments 13) Avoid flexible components
Group Technology Group Technology (GT) is a method that exploits similarities among parts through classification into part families on the basis of some common characteristics. Each family is identified by a multiple digit alphanumeric code which signifies those characteristics of the family that influence the application for which the GT scheme was developed (Shah and Bhatenagar 1989). As a DFM tool, group technology can be used in a variety of ways to predict significantly design efficiency, product performance, and quality improvement. The earliest work using features for GT coding was done by Kyprianou (1980). The author proposed a method for feature recognition based on the classification of edges and faces. Okino (1984) developed a system to generate GT code automatically for axis symmetric parts from boundary representation models. Bond and Jain (1988) used wire frame models from a drafting system to generate Lockheed sheet metal code. The typical utilization of GT is in the discrete parts of manufacturing enterprise where the parts are grouped into part families by means of coding and classification. There are five methods used to form part families: manual/visual search, nomenclatures/ functions, production flow analysis, classification and coding, and mathematical programming/expert systems (Zhang and Alting 1994).
Taguchi Engineering Variability is the enemy of manufacturing. A key factor in minimizing variability in a product's functional characteristics is to systematically select controllable factors which are minimized. The controllable factors include product design parameters, part geometry, design configuration, process design parameters, and process setting parameters. Taguchi emphasizes pushing quality back to the design stage and lists three steps for quality by design: (1) system design, (2) parameter design, and ( 3 ) tolerance design (Taguchi 1986). 1) System design is the process of applying scientific and engineering knowledge to produce a basic functional prototype design (Kackar 1985, Phadke 1989). 2) Parameter design is to identify the settings of design parameters that optimize their performance characteristic and reduce the sensitivity of engineering designs to the sources of variation (Kackar 1985, Phadke 1989). 3) Tolerance design is the process of determining tolerances around the nominal settings identified in the parameter design process (Kackar 1985, Phadke 1989).
from variation simulation analysis to solid modeling and
Failure Mode and Effect Analvsis Failure mode and effect analysis (FMEA) is an important design and manufacturing engineering tool. FMEA seeks to prevent failures and defects from occurring and reaching the customer. Failure is defined as the inability of a component/ subsystem/system to perform the intended function. For each failure mode, there are possible mechanisms and/or cause of failure. Hunt et al. (1992) provided a program which automates the generation of the effects of failure modes for automotive electrical systems. The author used the program to illustrate the context of a cruise control system. Weibenburg (1993) used computer aided FMEA in injection molding shops. Lehtela (1990) presented a computer-aided tool for FMEA of electronic circuits. The FMEA program was used to estimate the existing circuit analysis.
design with feature techniques (Stoll, 1990). The implementation of a full and robust computer-aided DFM environment is almost exclusively dependent on threedimensional CAD/CAM modeling, design and manufacturing technique. A major advantage provided by most three-dimensional computer-aided design systems is to rapidly evaluate a number of alternatives, in terms of form, fit, and function, early in the design process before committing to a final design (Baumgardner 1992). Onc commercial software is Moldflow, which is produced of
Value Engineering Value engineering provides a systematic approach to evaluate design alternatives that is often very useful and may even point out the way to innovative design approaches or ideas. It also go by many names such as value control, value engineering, or value management to analyze the functions provided by the product and the cost of each function. In value analysis, value is defined as a numerical ratio, the ratio of function or performance to the
DFM Toolkits The design toolkits could ensure the product/process conformance and enable process driven design. It can generally be classified as either process specific or facility specific. Computer-based tools which help integrate product and process includes a variety of tools ranging
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cost. The value index is represented as follows (Miles 1972, Mudge - 1971). Worth utility Value index = -- Cost cost
effectiveness (DAC) (Yamigiwa 1988). Scarr (1986) emphasized the need to provide the information on a CAD-based workstation. He has concentrated on developing guidelines in the form of design rules for the design of products for which automated assembly and robotics assembly techniques are appropriate and then establishing ithe relationship between design and the manufacturing tolerance assigned to the product. General Electric’s Cooperate Engineering and Manufacturing staff has conducted a total of 42 Design-for-Assembly workshops through the company, with the goal of redesigning products for ease assembly, both manual and automatic (Pvlilczka 1984). Other companies also began to use DFMA ispiproach to reduce the assemble parts and cost (Kobe 1990:). Since 1980, the DFM approach was developed to obtain cost estimation for parts and tooling during the early design stage, a lot of researches have been completed for machining parts (Boothroyd 1989), injection molding (Dewhurst 1987), sheet metal stamping (Zenger and Dewhurst 1988), die cast parts (Dewhurst and Blum 1989) and powder parts (Knight 1991). Also, Zenger and Dewhurst (1988) proposed a model of the interaction of CAD system and DFA sheet metal stamping, especially extracting feature information from CAD system database is studied (Eversheim and Baumann 1991).
In DFM approach, a value analysis is carried out in two phases, the analytical phase and the creative phase. In analytical phase, the functional value and prestige value offered by the product are systematically investigatedl by a team made up of experts representing all relevant components of the manufacturing system. Finding generated in the analytical phase are then used by the team in the creative phase to define innovative design solutions that maintain the desired balance between use and esteem value, maximize these values by providing required functions for the lowest cost, and eliminate identified waste (Stoll 1988). 2.2. Design for Assembly The benefit of DFA method was not realized until thie late 1970’s. Hitachi (1980) developed a system that using the Assembly Evaluation Method (AEM) in 1980. This method is based on the principle of “one motion for one part.” For more complicated motions, a point-loss standard is used and the assemblability of the whole product is evaluated by subtracting points lost (Boothroyd and Alting 1992). Boothroyd and Dewhurst, two of the pioneers performed the research on the knowledlge of handling and assembling directly related to design. Their handbook provided some guidelines for ease of assembled parts (Boothroyd and Dewhurst 1990). The concept of designing for assembly consists of three basic processes: (1) manual assembly, (2) special-purpose automated assernbly, and ( 3 ) flexible assembly. The prediction of handling and assembly times can b’eused. to point out the need of design changes from the viewpoint. of assembly (Waterbury 1985, Elmaraghy et al. 1988). DFA use the database to estimate assembly time together with companion techniques for estimating part costs at the designer to make trade off decisions before final design is determined. Eversheim and Bradyhouse (1984) combined the DFA method and value engineering to reduce the assembly cost. Elmaraghy and Knoll (1989) used the DFA method to analyze a family of D. C. motors amd to redesign them with emphasis on meeting the criteria of the market. Other design for assembly researcher, Bootiroyd et d.(1980) developed a spread sheet approach 1.0 rate design on the basis of their ease of automatic assembly. Cont.inued from the AEM and Boothroyd and Dewlhurst‘s DFA approaches, a lot of DFA methods are developed from the other viewpoints. Lucus Method is developed by Miles and Swift (1992). They began to summarize the reasons why the traditional and functional organized product introduction process is incapable of meeting modern requirement. Sony Cooperation claimed to have developed a unique set of rules for increasing productivity in the 1980, involving design for assembly cost
2.3. Design for Quality Quality is ]used to refer to quality problems within the factory or at customer acceptance whereas the word “reliability” is used to refer to quality problems that develop in u:je (Anderson 1990). Since 1960s, Genichi Taguchi, a Japanese engineer, has introduced several statistical tools and concepts of quality improvement that depend heavily on design of experiments theory (Gunter 1987, Tagixhii 1987, Phadke 1989, Una1 1992). From that time, people understand that “Quality must design in product”, because inspection and statistical quality control can never fully compensate poor design (Bendell 1988). Ilubka (1989) discussed design for quality and examined designer’s contributions to product quality in the context of models both of the design process and of technical system. Hiis analysis, while containing valuable pointers for design managers, is intentionally at a general level. Hales (19119) and Castelli (1989) provided specific examples of the application of systematic design methods to the assessment of the quality of product design. Crow (1992) reported the overall objective of Design for Quality are: 1) Dcsign of a product to meet customer requirements, both the spoken as well as unspoken needs. 2) Desiign of a robust product that can counter or miniimize the effects of potential variation in manufacture of the product, the product’s
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scheduled to replace parts before they are expected to fail. Priet (1974) defined four distinct ways of maintenance according to the overall performance: (1) breakdown, (2) routine, ( 3 ) planned, and (4) preventive maintenance. Routine schedules are characterized by a regular cycle. The rate of maintenance can be scheduled by the amount of time spent per day, per week or per month. Two engineering problem associated with implementing design for maintainability are how to minimize maintenance cost and how to measure the maintainability. As mass-production techniques became commonplace, designer tended to more and more stress producibility over maintainability, but it appears that some of the design practices that facilitate manufacturing also favor Moss (1985) developed some maintainability. fundamental principles of maintainability to obtain the objective of design for maintainability, such as standardization , interchangeability etc. Unger (1980) modeled a system analysis to superimpose control sector for total maintenance and minimize the maintenance cost. This system classified the maintenance cost into four categories: (1) total costs of failure-related repairs, (2) total costs for condition-monitoring maintenance, ( 3 ) permanent costs for safety-related maintenance to meet legal criteria and (4) special maintenance. The achievement of optimal maintainability requires that the design demonstrate maximum compatibility with the user’s maintenance capabilities and procedures. The calculation of Measuring Mean-Time-To-Repair (MTTR) is usually the common performance measurement of maintenance (Kolarik 1995). Nippon and Denso (1977) developed an evaluation scale for preventive maintenance (PM) performance. These measurement values are put into a graph so that long term maintenance performance can be studied. The most important feature that distinguishes the Hibi maintenance system from the other maintenance measurement is that it provide fragmentary and quantitative measurements. This system is also unique in that its computation formulas employ latestpoint-in-time benchmarks, so achievements can always be assessed in the most recent frame of reference, thus enabling results to be utilized (Hibi, 1977). Douglas Aircraft company merged the computer -drawn anthropomorphic model (human models) with computeraided-design (CAD) vehicles to simulate engineer design, maintainability and human factor with the process of design for maintainability (Majoros, 1991).
environment, and the use or misuse of the product. 3) Continuously improve product reliability, performance, and technology to exceed customer expectations and offer superior value. There are three different techniques/ concepts that can help achieve these design for quality objectives: quality function deployment (QFD), Taguchi quality engineering, and benchmarking. Since Taguchi quality engineering is already discussed in the DFM approach, this section will only discuss QFD and Benchmarking. QFD begins with market research to obtain consumers feedback on product features, performances, and services (Sullivan 1986). This feedback, referred as “the voice of the customer,” is then input into part specification and manufacturing parameters upon which an engineer can act (Berger 1988). QFD sometimes called “The house of Quality”, because of the distinctive matrix diagram that appears as the roof of a house (Berger 1988, Havener 1993). Madu and Kuei (1993) defined benchmarking as “the process of learning from the best in terms of business strategies, business operations, and business processes.” Zairi (1992) pointed out that there are three types of benchmarking: internal, external and generic. Internal benchmarking studies the best performance in an organization; external benchmarking deals with the best competitors in an industry; and generic benchmarking studies the best business practices in the world. Many American industries view benchmarking as a powerful tool for the purpose of competitive analysis and continuous improvement (Bemowski 1991, Biesada 1991, Geber 1990).
2.4. Design for Maintainability The basic objective of design for maintainability is to assure that the product could be maintained throughout its useful life cycle at reasonable expense without any difficulty. Maintainability was defined by Moss (1985) as “an element of product design concerned with assuring the ability of the product to perform satisfactorily can be sustained throughout its intended useful life span with minimum expenditure of money and effort”. Traditionally, Gantt Chart was used in the maintenance scheduling. This chart was developed by Henry L. Gantt during World War I for use in production scheduling. Later it became known as a bar graph and became a standard tools in maintenance, project, and product scheduling. Anderson (1990) pointed out the maintenance can either be performed after something fails (unscheduled maintenance) or at scheduled intervals to replace parts before they are likely to fail (preventive maintenance). Unscheduled maintenance restoring operation after a failure. Design for ease of repair will greatly improve the ease of maintenance in general. If the system is important to avoid downtime, then preventative maintenance can be
2.5. Design for Reliability The great breakthrough in applying reliability theory came in the latter 1950s, in the form of specific requirements by military contracts for major missile weapon system. Reliability was defined by Smith (1993) as “the probability that a device will satisfactorily perform a specified function for a specified period o time under given operation conditions.” Another definition by Moss (1985) was “the probability that a product manufactured to a 450
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given design will operate throughout a specific period without experiencing a chargeable failure.” Reliability studies predict part failure frequencies and are the criterion for part selection. Anderson (1990) indicated the element of reliability includes probability, performance, time, and usage. Four measurements of reliability analysis are used: measurement of reliable life, mean time to failure (MTTF), mean time between failures (MTBF), and failure rate. Reliable life is a measurement of how long an item (can be expected to perform satisfactorily and is often expressed in units of time as years. Mean time to failure is a common reliability parameter for items that are irreparable or are subject to mechanical wear out. Mean time between failures is the product that are expected to fail arid be repaired prior to wearing out. Failure rate is the average number of failures from a group of items expected in a given period of time (Priest 1988). The reliability of a product can be expressed as follows (Anderson 1990, Moss 1985, Kivenson 1971): R ( t ) =e-
joining methods are well-suited for assembly, but are difficult to remove (rivets, snap-fits, spot welds). The main pnnciple of Design for Disassemble (DFD) is the same as Design for Assemble: to reduce the number of parts in a product (Welter, 1991). The fewer parts, the faster the disassembly. Material-selection strategy is another arleal in product development of design for disassembly, according to Rick Noller, director of Polymer Solutions (I,eonard, 1991). In choosing materials with a view of disassembling it is the subsequent manipulation of the disassembled parts and their environment effects (Wittenburg 1992). The third strategy, also the heart of DFD, is fastening. Two basic methods of disassembly was used: reverse assembly and brute force reported (Leonard 1991). For reverse-assembly, if a fastener is screwed in, it is screwed out; if two parts are snap fit together, they are snap apart, while, for the brute force, parts are just pulled or cut apart. Seliger er al. (1993) pointed out that it is difficult to gain all the information necessary to plan the disassembly. Parts of the product might have been modified during repair, and wear can make joining elements difficult to remove. Another problem is most consumer products are not designed for ease of disassembly, particular in (Milberg et al. 1992):
ht
Where e is the Napierian (natural logarithmic base); h is the failure rate of the item throughout the period; t is the duration of mission
1) product structure is optimized on the basis of functional and assembly requirements, resulting in a lot of unwanted disassembly steps, 2) joining methods are chosen for simple assembly and safe joining, 3) materials are chosen so as to be economical and off alptimum performance; this means a lot of different, often recyclable, materials, with high disassembly and sorting costs.
Use of computer-aided engineering (CAE) analysis and simulation tools at an early design stage can improve product reliability more inexpensively and in a short time than building and testing physical prototypes. Tools such as Finite Element Analysis (FEA), fluid flow, thermal analysis, and integrated reliability prediction models are becoming more widely used, and less expensively. Taguchi quality engineering technique can also provide a structured, pro-active approach to improving reliability and robustness as compared to unstructured, reactive design/build/test structure (Crow 1992). As reported by Wheeler (1986), Hp developed a farnily of oxdilloscopes with increasing capability and reliability three times greater than existing models. Another successful design for reliability effort by Texas Instrument was to develop a family of forward-looking infrared raiders (FLIR). One of the first step of this model is improve the design’s reliability and productivity was to modularize the system by designing common models.
Disassembly sequence is another problem encountered in design for disassembly. Subramani et al. (1991) presented an approach to determine disassembling sequence. In their approach, the authors proposed local disassembly refers to the ]process of removing a part with respect to its local constraiints. This information is represented in terms of dlsassenibly directions of parts with respect to their contacts or obstructions. The problem associated with disassembly sequence is (1) freeing the part of all attachments, (2) finding the succeeding part in the disassembl!r sequence and (3) disassembling of the succeeding part. Beasley et al. (1993) reported to ensure properly dksassembly motion, both local and global geometric information must be considered. The local geometric information feasibility of a motion relates to whether an infinitesimal motion can be made. It is determined by the surface contacts between a part and other part. ‘The global geometric feasibility of a motion relates to whether a finite motion can be made in a particular direction. It depends not only on the
2.6. Design for Disassembly The rapidly growing concern for environmental protection and resource protection has stimulated many new activities in industry to solve the disposal of used product. Even though recycling is increasing, a large amounts of solid waste are disposed of in landfills creating serious pollution. Early studies have pointed out the differences between design for assembly and design for dlsassembly (Boothroyd and Alting 1992). For example, some kinds of
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disruption to service. Lee and Tapiero (1987) developed a framework to identify the interaction between quality control parameters and product servicing. Assuming a linear cost structure, Hegde and Karmarkar (1993) derived an economic structure to be observed in the market for product support. The author incorporates the discounting issues and the nonlinear cost structure of the product failure cost and establishes altogether a different relationship between design parameters and customer costs experience. Hegde (1994) modeled failure costs as four categories (1) failure cost to customer as the sum of fixed costs of failure and variable costs of failures, (2) the failure cost of downtime is proportional to a power of the length of downtime, (3) failure cost is a storage device fits this category, and (4) failure cost is almost zero to calculate the total discount cost.
relationship between thc part to be moved but also on its relationship with all the other parts in the assembly. Many companies and laboratories modeled the disassembly process in the manual or automated dsassembly of existing products. Some European automobile manufacturers have set up dismantling center where they analyze disassembly times in order to find the best methods for dismantling cars (Weule 1993, Siuru 1990, Sprow 1992). Tokyu Corp. introduced robots for industrial in the field of maintenance work (Miyata 1992). Adopting electronic technology and computer control, this system automates disassembling and assembling work of parts through a combination of an industrial robot of standard type with tools and software programs.
2.7. Design for Life Cycle Traditionally, development of new products starts on the basis of a set of specifications and based on the assessment of customer’s need. Then the selection of technical solutions is based on company policy, product and manufacturing properties and cost. Rarely environmental impact are discussed during the process. For example, the disposal costs and the maintenance costs are hidden which is paid from customers (Alting 1991). Design for lifecycle, also called System Life-Cycle Engineering (Fabrycky 1985), considered from the early product concept including the product/market research, design phases, manufacturing process, qualification, reliability issues, and customer service/ maintainability/supportability issues. Boothroyd et al. (1992) distinguishes six phases in product life cycle: need recognition, design development, production, distribution, use and disposal. Similarly, Zust and Wagner (1992) confined four phases of the product life cycle: (1) Product definition, (2) Product development ( 3 ) product marketing and manufacturing, and (4) product usage. At each one of these phases there exists a definition of objectives, activities, and deliverables for next phase. Keys (1988) described during the conceptual model phase, various paper and/or simulation models of the product are generated. Various ways of partitioning and fabricating these models will be considered consistent with the possible manufacturing, quality, reliability objectives, and customer service/support objectives. From these conceptual models, requirements, specification, and analyses will evolve decisions for breadboard/ brassbound models. Hewlett-Packard company addressed the life-cycle issue by prototyping software, defining development, and phases, standardizing modules/ packages (TP 1982). The concept of life cycle cost-purchase and maintenance outflows less the salvage value inflows- is another approach in life cycle design. Several papers about life cycle cost in life cycle design can be found in the literature (Frees and Nam, Chikte and Deshmukh 1981, Berg 1980). Lele and Larmarkar (1983) identified the product failure causes customers certain other costs in addition to the cost of the repair bill. These cost are opportunity cost, the cost of keeping the related system idle, and the cost of
2.8. Design for ServiceabilitylRecyclability Serviceability is determined during the design phase, however, the traditional design methodology scarcely considers the service. A design without serviceability could lead to an unexpected increasing in servicing and warranty cost. Also, a significant downtime could hurt the customers. Eubanks et al. (1992) addressed that DFA methodology covered serviceability to a certain extent. However, serviceability concerns are broader than those of DFA. A product may go through the production assembly once under a controlled environment, while the service operations may take various forms. Each service operation may require different tools and techniques. Hence, there is a need to consider serviceability during the design phases. Many research efforts have been dedicated to the application of design for serviceability. Bancroft (1988) indicated that the best way to reduce the service cost is to increase the reliability of the product. This will not only lower warranty costs, but also reduce the size of service department and all of the costs associated with it. Makino et at. (1989) provided the initial work in the creation of serviceability design expert systems. The author defined the elements in a design €or serviceability expert system and the economic benefits. Murakami and Nakajima (1988) proposed a thoroughly consideration of diagnostics in electronic circuit design. The consideration during the design phase has also been used widely in the heavy machinery and farm equipment industries (Parks 1986, Barquist and Malcolm 1989). These industries focus on decreasing service time and utilizing only standard tools. Eubanks et al. (1992) developed an interactive computer program that assists engineers to incorporate serviceability into product design. Bryan et al. (1992) developed a Service Model Analysis (SMA) to estimate the service costs. For environmental problems and pollution, the recycling of product is important in industry. “Recycling means recovering materials or components of a used product in order to make them available for new products” ( Jovane et 452
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ut. 1992). Wolf (1991) reported that the paper industry is recycling as much as 50% of its output. However, in plastics industry, only a little are recycled such as Polyethylene Terephathalatc (PET) bottles, and Styrofoam cups, plates, and tray. The author further reported there were ’$8 billion pounds of plastic resin sold in the United States and less than 1% of this was recycled. Ishii (1994) proposed a design for product retirement model to recycle the end-of-life products, see Figure 2. The author use the concept of clump which is a collection of components and/or subassemblies that share a common characteristic based on the designer’s intent. Recycling requires materials and fastening method in the clump to be compatible with existing expressing technologies. Two engineering problem associated with design for recyclability are dismantling and recycling cost. Simon (1991) pointed out that dismantling required the knowledge of the destination or recycling possibility of the component parts of disassembling part. Here lies a difficulty because between the design of a product anjd the time it reaches the end of its life, there will have advamced techniques in recycling and re-engineering. The author proposed two guiding strategies in dealing with this problem: (1) remove the most valuable parts first, (2) Maximize the ‘yield’ of each dismantling operation1 (for more detail, see Simon 1991).
single chips and transformers are on single circuit board. Wittenburg (1992) proposed a concept of the recycling path of compolnents and materials, as envisaged by BMW. It entails a “cascade model” of decreasing values, in which attention is fiirst focused on disassembled parts suitable for re-use and thus having the highest value. The Decree on Electronic Waste (Ertel 1993) and the Decree on Used car (Rummler 1993) forced manufacturers to reclaim waste, to reuse the recyclable fraction and to dispose of the residue. In automobile industries, BMW is the leader in design for disassembly. The Z1 is a two-seat automobile with an all plastic skin that can be removed from the metal chassis in 20 minutes (Burke 1992). The doors, bumpers, and front, rear and side panels that are made of recyclable thermoplastics produced by GE. The other model 325 1 of BMW is also used recyclable plastic parts and targeting the environmental conscious customers (Braunstein 1991). Through these efforts, BMW has identified some guidelines that make disassembly easier. Seegers (1993) reported GE plastics offered several recycled grades, which can continue the material flow scheme in basically two ways: - More generations of materiel in the same field of applications: e.g. from a car grille to a car grille, The recycle material is used in a today different application (often with somewhat lowler property demands). Several researchers have addressed the issue of design for manufacturing of plastics, particular in injection molding. Ishii and Hoirnberger (1989) focused on designs for tooling and created a training tool based on design compatibility analysis. Rosen et a1.(1991) have been constructing a manufacturalbility assessment system based on feature-base design. Beiter et al. (1991) proposed their approach to compiling glerreric manufacturability guidelines based on geometry chmacteristics of plastic parts. Navichandra (1991) conducted an extensive survey of the implications of design for environmental compatibility. The author not only address recycling, but also the inevitable disposal costs. He also clarify costs associated with the overall product and material recycling loop. Shergold (1’994) indicated that, in automotive industry, disposal has resulted in about 75% by weight of each vehicle being recovery for recycling. The author further explained that parts removed by a dismantler are defincd by market dernand and will generally include items such as engine, gearbox and other mechanical parts, electronic components. Scegers (1993) reported, in automotive industries, there are two phases in which the material can be severcly damaged:
Figure 2: Product Life Cycle (Ishii 1994) One intangible benefit arising from recycling is “green image”. Navinchandra (199 1) proposed “Green Engineering Design,” which aimed to identify, develop, and exploit new technologies that can bolster productivity without costing the environment. The author exp1,ained that green engineering design includes two parts: (1) the development of special green indicator-measures of environmental compatibility, and (2) tools that usie the green indicators to help designers assess, compare, and make design decisions. Roy (1991) reported the recycle considerations: 1) use of the same plastics as far as possible. 2) mechanical fixing techniques to enable quick disassembly. 3) cables for internal connections from same plastics design for electronics should be modified so that
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product design, process design, and the product development. Life-Cycle design addresses not only the functional requirements of a product, but also its life-cycle values such as disassemblability, serviceability, maintainability, reliability, and recyclability. Design for Life Cycle is try to establish a methodology to maximize the users’ life-cycle values and minimize cost at the early stages of design. The basic ideas, perspectives, and overview of life cycle design are presented. These include design for disassembly, design for maintainability, design for reliability, design for serviceability and design for recyclability. The Technical University of Denmark was approached by five major Danish companies (DANFOSS A/S , B&O A/S, GRUNDFOS A/S, KEW INDUSTRI A/S, AND BRDR, GRAM) concerning initiating a research/development program within life-cycle design of products (Alting, 1993). The next few years will show very exciting developments, maturing and the presented sketch of life-cycle design of products. The principle of considering all goals and constraints early can produce a better product. Furthermore, the product will enter the marketplace earlier because an inherently simpler product is designed right the first time without introducing problems, delays and orders change. Quality and reliability also can be assured by design and process controls rather than expensive testing, diagnostics, and rework. Design for life-cycle makes the designer plan ahead for product processing after its useful life. There is no doubt that DFX will play an important role in the current manufacturing industries, and it is expected that in the future DFX will become the cutting edge of the technology.
Damage during initial processing, such as faults in pre-drying, overheating, or excessive shear during plasticising. Damage through uncontrolled use of engineering thermoplastics, such as UV attack, humidity, high temperatures, a aggressive media and conjunction with other incompatible polymers such as PU foam, paint or adhesives.
Material recognition is another interesting approach of recycling. This needs some technology that is able to identify materials, including proportion and type of filler material used. Ideally, it should be cheap, hand-held for use on different components and significantly rugged to be used in a workshop-type environment. A number of researcher have been working in this area with various levels of success. Shergold (1994) indicated that Fourier transform infra-red (FT1R)-based equipment that Rover and Bird developed is good at identifying plastics and some filler materials. 3. Summary
Design for Manufacturability and Design for Assembly are becoming the way of life in many industries. The DFM approach is to idcntify product concepts that are inherently easy to be manufactured, to focus on component design for ease of manufacture and assembly, and to integrate manufacturing process design and product to ensure the best matching of needs and requirements. Thus, cost and time to markct are often cut in half by using the DFM approach. However, DFM caused some disruptions. Constance (1992) pointed out, ‘Under DFMA, engineers and designers are forced to work in teams rather than individually, and this occasionally creates piction. Additionally, their work is more closely scrutinized, as DFMA often reveals that their initial ideas may not be the most effective.’ Therefore, the justification for adopting DFM is a strategic issue for a company. Winchell (1988) reported many companies are currently using portions of DFM, particularly in designing parts. One of the principles of total quality management is that quality must bc designed into product, because inspection and statistical quality control can never fully compensate poor dcsign. Design for Quality is pushing quality back to the design stage. The concepts and tools of Design for Quality are discussed. These include Quality Function Deployment (QFD), Taguchi Engineering, and Benchmarking. These three quality techniques address different aspects of designing quality into the product at the early stagcs. QFD can effective translate these requirements into specific product and process designs. Taguchi quality cngineering techniques aid in the development of a robust product and process design in the face of difficult to control. Benchmarking provides a mechanism to look externally at opportunities to improve
4. Feature trend Concurrent engineering has been recognized to have a dominant impact on subsequent manufacturing processes of part production. Design for Manufacturability has provided engineers with a systematic methodology to reduce development time, cut production cost, improve quality and reduce defects. Typically, DFM focus on a particular manufacturing process, e.g. machining, stamping, injection molding, assembly, etc., and seeks to incorporate into the early product design measures that can prevent manufacturing problems and significantly simplify the production process. Thus, engineers can greatly benefit from a design tools that allow them to compare different processes in a more rational, systematic manner, utilizing as much quantitative information as possible. The life-cycle design principle should not be considered as an obstacle but as a new and challenging opportunity. The opportunity is that life-cycle will bring new and more competitive products to the market, fulfilling their requirements of customers and society. The future trend will be Alting (1993):
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1. Lite-cycle design principles ensuring “green” products fulfilling the demands from1 the customers and the society; 2. Human beings as decision-makers supported by computer: 3. Concurrent engineering approaches 4.. Dynamic organizations 5. Computer-integrated manufacturing, including detailed monitoring and control 6. “Visible” policies for life-cycle design1 of products, technologies, environmental issues, occupational health issues, and disposal recycling.
Baumgxdncr, O., “Computer-Aided Technology, “in Tools and Monufacturing Engineers Handbook Design for Manyfacturing, vol. 6, R. Bakerjian edit, 1992, pp. 7-1-7-37. Bazovsky, 1 ., Reliability Theory and Practice, PrenticeWall, Inc..,Englewood Cliffs, 1972. Weasley, D. and Martin, R. R., “Disassembly Sequences for Object Built from Unit Cubes,” Computer-Aided Design, vol. 25, no. 12, Dec., 1993, pp. 751-761. Beiter, K., Ishii, K., and Hornberger, L., “Design for Injection Molding: Geometry-Based Indices for Plastic Part Quahty,” Proc. of the ASME Design Theory and Methodo1oj:y Conference, Miami, FL, 1991, pp. 111118. Bemowski, K., “The Benchmarking Bandwagon,” Quality Progress, Jan., 1991, pp. 19-24. Bendeli, A . “Introduction to Taguchi Methodology”, Taguchi Methods: Proceedings of the 1988 European Conference, London: Elsevier Applied Science, 1988, pp. 1-14. Berg, M., “,4Marginal Cost Analysis for Preventive Replacement Policies,” European Journal of Operational Research, vol. 4, 1980, pp. 136-142. Berger, R. W., “Achieving Quality,” Tools and Manufacturing Engineers Handbook: Manufacturing Managemeilzt, vol. 5 , 1988, pp. 23-1-23-19. Rhadra, A. and Fischer, G., “A New GT Classification Approachl: a Database with Graphical Dimensions,“ Manufacturing Review, vol. 1, Mar., 1988. Biesada A., “Benchmarking,” Financial World, Sep. 17, 1991, pp. 28-32. Bond, A. €I. and Jain, R., “The Formal Definition and Automatilc Extraction of Group Technology Codes,” Proceedings I988 ASME Computers in Engineering Conferenice,San Francisco, August, 1988. Boothroyd, G. and Alting, L., “Design for Assembly and Disassembly,” Keynote paper, Annals of the CIRP, vol. 41, no. 2, 1992, pp. 625-636. Boothroyd, G. and Dewhurst. P., Product Design for Assembly. I3oothroyd Dewhurst, Inc., Wakefield, 1990. Boothroyd, Gr. and Poli, C. and March, L., Handbook of Feeding (arid Operating and Orienting Techniques ,for Small P a m , Technical Report, Mechanical Engineering Departmenit, University of Massachusetts, 1978. Boothroyd, G. and Radovanovic, P., “Estimating the Cost of Machined Components During the Conceptual Design of ia Product”, Annals of CIRP, vol. 38, no. 1, 1989, pp. 157. Boothroyd, G., Dewhurst, P. and Knight, W., Product Design for Manufacture and Assembly, New York: Marcel Dekker, 1994. Boothroyd, G., Poli, C. and March, L., Automatic Assembly, Marcel Dekker, New York, 1980. Boothroyd, (3. and Dewhurst, P., Design for Assembly4 Designers Handbook, Technique Report, Department of MechanicaI Engineering, University of Massachusetts, 1983.
There are several successful examples in industrial that exemplify the DFM and DFX approach in manufacturing environment (Hashizume 1980, Kroll 1988, Rosario 1989, Kobe 1990). DFM and DFX may require additional effort early in the design process. However, the integration of product and process design through business practices, management philosophies and technology tools will result in a more predicable product to better meet customer needs, a quicker and smoother transition to manufacturing, and a lower total life cycle cost. The greatest challenge exist not in implementing new techniques, but in overcoming the organizational barriers and the resistance to changing the way things are done. As new products and time to market become crucial in achieving competitive advantage, thc use of DFM and DFX approaches as a basis for new product development will become essential.
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