Bilgisayar destekli konstrüksiyon ve imalatta modelleme teknikleri
Başlık çevirisi mevcut değil.
- Tez No: 55528
- Danışmanlar: PROF.DR. TEOMAN KUTAY
- Tez Türü: Yüksek Lisans
- Konular: Makine Mühendisliği, Mechanical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1996
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 122
Özet
ÖZET BİLGİSAYAR DESTEKLİ KONSTRÜKSİYON ve İMALATTA MODELLEME TEKNİKLERİ Bilgisayar Destekli Mühendislik uygulamaları özellikle Bilgisayar Destekli Konstrüksiyon, İmalat (BDK/BDİ-CAD/CAM) ve Bilgisayar Destekli Mühendislik (BDM-CAE) uygulamaları günümüzde yaygın şekilde kullanılmaktadır. Mühendislik uygulamaları ve bilgisayarların bütünleşmesi aşamasında kullanılan sistemlerin anlaşılması çok önemlidir. BDİ / BDK uygulamalarında kullanılacak bir yazılım gerçekleştirilmek istenirse bu sistemlerin temellerini oluşturan kavramların daha açık bir şekilde irdelenmesi gerekir. Bu çalışmada da halen kullanılmakta olan yazılımlardaki çeşitli elemanlar matematiksel olarak irdelenmiştir.. Eğri, yüzey ve katı gösterimleri incelenerek bunların kullanım alanları belirlenmiştir. BDK' dan BDİ' a geçişte gerekli olabilecek veri dönüşümleri gibi ara çözümlerde incelenmiştir. İmkanlar dahilinde, yazılımlar incelenerek, uygulamalar verilerek örnek bir varil pompası gövdesine ait katı model AutoCAD Release 12 programında yapılmıştır. Ayrıca Mastercam Demo programından faydalanarak modelleme elemanlarına ait basit eğri ve yüzey örnekleri verilmiştir. Katı modelleme uygulamasında katı modellemeye ait temel kavramların uygulaması gösterilmiştir.
Özet (Çeviri)
SUMMARY GEOMETRIC MODELLING IN CAD/CAM In engineering practice, CAD/CAM has been utilized in different ways by different people. Some utilize it to produce drawings and document design. Others may employ it as a visual tool by generating shaded images and animated displays. A third group of perform engineering analysis of some sort on geometric models such as finite element analysis. A fourth group may use it to perform process planning and generate NC part programs. In order to establish the scope and definition of CAD/CAM in engineering environment and identify existing and future related tools, a study of a typical product cycle is necessary. Figure 1 shows a flowchart of such a cycle. [9] THE DESIGN PROCESS iiz~ l Synthesis“' Design need Design definitions, specifications. and requirements Collecting relevant design information and feasibility stud\ Analvsis ”1 i THE CAD PROCESS Design ?] communication and documentation {Design evaluation Design optimization H Design analysis Ü i i Design modeling and simulation H Design conceptual ization THE MANUFACTURING PROCESS Process planning Production planning Design and procurement of new tools Order material 4 NC. CNC. DNC programming Production K Qualm control Packaging Shipping THE CAM PROCESS Marketing * FIGURE 1. Typical product cycle The product begins with a need which is identified based on customers' and markets' demands. The product goes through two main processes from the idea conceptualization to the finished product: the design process and the manufacturing process. Synthesis and analysis are the main subprocesses that constitute the design process. Synthesis is as crucial to design as analysis. The philosophy, functionality, and uniqueness of the product are all determined during synthesis. The major financial commitments to turn the conceived product idea into reality are also made. Most of the information generated during the synthesis subprocess is qualitative and consequently is hard to capture in a computer system. The end goal of the synthesis subprocess is a conceptual design of the prospective product. Typically, this design takes the form of a sketch or a layout drawing that shows the relationships among the form of a sketch or a layout drawing that shows the relationships among the various product parts, as well as any surrounding constraints. It is also employed during brainstorming discussions among various design teams and for presentation purposes. The analysis subprocess begins with an attempt to put the conceptual design in the context of the abstracted engineering sciences to evaluate the performance of the expected product. This constitutes design modeling and simulation. The quality of the results and decisions involved in the activities to follow such as design analysis, optimization, and XIevaluation is directly related to and limited by the quality of the chosen design model. It is the responsibility of the designer to ensure the adequacy of a chosen model to a particular design. An important characteristic of the analysis subprocess is the“ what if ”scenario, which is usually valuable in design situations where analytical solutions do not exist. A computer environment where various design alternatives can be investigated is ideal to make better design decisions in shorter periods of time. Algorithms for both design analysis and optimization can be implemented and utilized. While design optimization may be embedded in design analysis, it is identified as a separate phase in Figure 1 to emphasize its significance to the design process as a whole. Once the major elements of the design have been analyzed and their nominal dimensions determined, the design evaluation phase starts. Prototypes can be built in a laboratory or a computer to test the design. More often computer prototypes are utilized because they are less expensive and faster to generate. They also help the designer determine other dimensions of the product that are not analyzed, as well as finalize those that result from analysis by employing commonsense design rules. The designer can also generate bills of materials, specify tolerances, and perform cost analysis. The last phase of the analysis subprocess is the design communication and documentation which involves preparations of drawings reports, and presentations. Drawings are utilized to produce blueprints to be the passed to the manufacturing process. The main phases of the manufacturing process are shown in Figure 1. It begins with the process planning and ends with the actual product. Process planning is considered the backbone of the manufacturing process since it attempts to determine the most efficient sequence to produce the product. A process planner must be aware of the various aspects of manufacturing to plan properly. The planner works typically with blueprints and may have the communicate with the design department of the company to clarify or request changes in the final design to fit manufacturing requirements. The outcome of process planning is a production plan, tools procurement material order, and machine programming. Other special manufacturing needs such as design of jigs and fixtures are planned. Process planning to the manufacturing process is analogous to synthesis to the design process; it involves considerable human experience and qualitative decisions. This makes it difficult to computerize. However, CAPP (computer aided process planning) has progressed significantly. In addition to a centralized CAD/CAM database for CAPP, geometric models that are accessed must be in CAPP development. Once the process planning phase is complete, the actual production of the product begins. The produced parts are inspected and usually must pass certain standard quality control (assurance) requirements. Parts that survive inspection are assembled, packaged, labeled, and shipped to costumers. Market feedback's are usually valuable in enhancing the products. These feedback's are usually incorporated into the design process. With the market feedback, a closed-loop product cycle results, as shown in Figure 1. The phases of the design and manufacturing processes shown in Figure 1 serve as the basis to define the design and manufacturing contents and consequently the tools properly, a CAD/CAM system must provide for engineers. To identify these tools properly, a CAD process and a CAM process have been defined in relation to the other processes. The CAD process and a CAM process is a subset of the design process. Similarly, the CAM process is a subset of the manufacturing process. The implementation of the CAD process on current systems takes the generic flow presented in Figure 2. Once a conceptual design materializes in the designer's mind, the definition of a geometric model starts via the user interface provided by the relevant software. The choice of a geometric model to CAD is analogous to the choice of a mathematical model to engineering analysis. It depends directly on the type of analysis to be performed. For example, finite element analysis might require a different model than kinematic analysis. A valid geometric model is created by the CAD/CAM system through its definition translator which converts the designer input into the proper database format. In order to apply engineering analysis to the geometric model, interface algorithms are provided by the system to extract the required data from the model database to perform the analysis. In the xiicase of finite element analysis, these algorithms form the finite element modeling package of the system. Design testing and evaluation may require changing the geometric model before finalizing it. When the final design is achieved the drafting and detailing of the models starts, followed by documentation and production of final drawings. FIGURE 2 Implementation of a typical CAD process on a CAD/CAM system. The core of the CAD tools are geometric modeling and graphic modeling and graphics applications. Aids such as color, grids, geometric modifiers, and group facilitate structuring geometric models. Manipulations include transformation of the model in space so it can be viewed properly. Visualization is achieved via shaded images and animation procedures which help design conceptualization, communication, and interference detection's in some cases. The tools for design modeling and simulation are well diversified and are closely related to the available analysis packages. Optimization CAD tools are also available. Some FEM (finite element modeling) packages provide some form of shape and structural optimization. Even though CAD tools for design evaluations are hard to identify, they may include the proper sizing of the model after the analysis is performed to ensure engineering practices such as gradual change in dimensioning and avoidance of stress concentrations. Adding tolerances, performing tolerance analysis, generating a bill of materials, and investigating the effect of manufacturing on the design by utilizing NC packages are also valuable tools that are available to designers. These are the most important concepts in industry, product determined by these stages. Because the quality of the xmTABLE 1 1 CAD tools required to support the design process. Design phase Required CAD tool(s) Design conceptualization Design modeling and simulation Design analysis Design optimization Design evaluation Design communication and documentation Geometric modeling techniques; graphics aids, manipulations, and visualization Same as above; animation; assemblies; special modeling packages Analysis packages; customized programs and packages Customized applications; structural optimization Dimensioning; tolerances; bill of materials; NC Drafting and detailing; shaded images The implementation of the CAM process on CAD/CAM systems is shown in Figure 3. The geometric model developed during the CAD process forms the basis of the CAM activities. Various CAM activities may require various CAD information. Interface algorithms are usually utilized to extract such information manufacturing (e.g., holes, slots, etc. ) must be recognized to enable efficient planning manufacturing. NC programs, along with ordering tools and fixtures, result from process planning. Once parts are produced, CAD software can be used to inspect them. This is achieved by superposing an image of the real part with a master image stored in its model database. After passing inspection, CAM software can be utilized to instruct robot systems to assemble the parts to produce the final product. [5] TABLE 2 CAM tools required to support the design process. Manufacturing phase Required CAM tool(s) Process planning Part programming Inspection Assembly CAPP techniques; cost analysis, material and tooling specification NC programming Inspection software Robotics simulation and programming Table 2 relates the CAM tools to provide phases of the manufacturing process. CAPP techniques include variant, generative, and hybrid approaches. Various part XIVprogramming languages are supported by most CAM software. These include APT, COMPACT II, SPLIT, etc. Inspection software utilizes CMMs ( coordinate measuring machines) which compares the coordinates of the actual parts with those of the master database. The robotics software supports robot simulation, off-line programming, and image processing, and vision applications. Geometric model Interface algorithms Process planning NC programs Inspection Assembly Packaging T To shipping and marketing FIGURE 3 Implementation of a typical CAM process on a CAD/CAM system. CAD/CAM applications are very important in manufacturing. Time consuming works can be reduced. Especially concurrent engineering applications needs that system to be more successful. Changes m the design can be done as soon as the problems occurred. And this gives company competitive advantage in the market. And also manufacturing department in the factory can modify the design by network. And by that way the product can be produced faster. It is very important in our century to be more sensitive to the consumer needs. And in our daily life consumer needs change so fast and companies must adopt themselves to that changes faster than competitors. In this study a practical model designed in the computer. AUTOCAD Release 12 program used for modeling, ft is not good enough for solid modeling but it is used for giving the principles of solid modeling. All the stages in modeling can give an idea what can be done by solid modeling. xv
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