Dönel simetrik elemanların modüler tasarımı CAM-CNC integrasyonu ve simülasyonu
Modular design, CAM-CNC integration and simulation of rotational parts
- Tez No: 39265
- Danışmanlar: PROF.DR. MUSTAFA AKKURT
- Tez Türü: Doktora
- Konular: Makine Mühendisliği, Mechanical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1994
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 86
Özet
ÖZET Günümüzde imalat uygulamalarında takım yörüngelerini oluşturan NC program dosyalarının direkt olarak tasarım geometrisinden elde edilmesi konusuna ağırlık verilmektedir. Üretim verilerinin oluşturulması sırasında normal olarak bulunan bir çok zaman alıcı işlemi kısaltmak ve böylece tasarım ile imalat arasıdaki boşluğa bir köprü kurmak için, mühendisler gerekli bilgileri tasarım verilerinden elde edebilmelidirler. Bu sebepten, CNC torna tezgahlarında işlenebilecek dönel simetrik parçalar için bir bilgisayar destekli tasarım ve imalat (CAD/CAM) paket programı geliştirilmiştir. Borland C++ 3. l'de 'expert sistem' yaklaşımı ile hazırlanan ve VGA grafik kartına sahip PC bazında bir bilgisayarda DOS ortamında çalıştırılabilen program üç ana modülden oluşmaktadır. Bu modüller sırasıyla CAD modülü, CAM modülü ve simülasyon modülüdür. Programın CAD modülü yardımıyla dönel simetriye sahip hemen hemen bütün parçalar tasarlanabilmekte ve elde edilen geometrik veriler sonradan tekrar kullanılabilecek şekilde sabit diskte veya disketlerde çok küçük alanlarda 'ski' uzantısıyla saklanabilmektedir. Parça geometrisi silindir, koni, küre parçası gibi dönel simetrik elemanların modüler olarak sıralanması ile oluşturulmaktadır. CNC tezgahta hammaddeden istenen parçanın elde edilmesi için gerekli olan teknolojik ve geometrik verilerin tezgahın algılayacağı formatta G-kodları ile yer aldığı NC programının hazırlanması işlemi programın CAM modülünde yer alamaktadır. Bu modülde öncelikle hammadde boyutları ve malzemesi verilmekte ve daha sonra parçanın teknolojik planı program tarafından otomatik olarak yapılmaktadır. Bununla birlikte paso kalınlığı, kesme hızı, ilerleme gibi kesme faktörleri ve işlemler için kullanılacak takımlar istendiği taktirde kullanıcı tarafından değiştirilebilmektedir. Programın simülasyon modülü yardımıyla CAM modülünce hazırlanan NC programının simülasyonu yapılmakta ve mevcut hataların imalat öncesi düzeltilebilmesi imkanı sağlanmaktadır.
Özet (Çeviri)
MODULAR DESIGN, CAM-CNC INTEGRATION AND SIMULATION OF ROTATIONAL PARTS SUMMARY The rapid devolopment of computer-aided design (CAD) technology in the 1960s made it possible for designers to construct engineering drawings on a cathode ray tube (CRT) screen and to create a geometric model within the computer. A geometric entity defined by a CAD system within a computer is represented by a group of data, the parameters of the mathematical functions or equations describing the geometric entity. In other words, such data are representation of a part within the computer and are called the CAD model of the part. The data of a CAD model can be further used to define an NC cutter path with the aid of certain NC programming software. Thus if a CAD system is provided with the necessary function to define an NC cutter path based on the CAD model, one can also define an NC machining process directly on the drawing displayed on the CRT screen. Such a system is usually called a computer-aided design/computer-aided manufacturing (CAD/CAM) system. CAD/CAM systems were not widely used before 1980 because of their high cost and the unreliability of the CAD/CAM software. Computer-aided desing (CAD) systems have been widely used in industry for over 20 years to design parts and to draw, store, and modify them. A part is represented in a CAD system by a set of data. If an NC function is incorporated into the system, the very data stored in the memory unit of a CAD system to define a part can also be used to generate the NC machining program. All computer-aided design/computer-aided manufacturing (CAD/CAM) systems are based on a technique, called computer graphics, that allows the creation and display of an object in graphic form on a cathode-ray tube (CRT) screen through the use of the computer. The object is stored in the computer in the form of mathematical or geometric data, called the mathematical or CAD model of the object. By taking advantage of the processing speed of the computer, one can men VImanipulate the model interactively to obtain a more desirable representation of the object and can further process, analyze, and evaluate the model. Additional information and functions, other than those needed for representing the object grabhically, can also be added into the computer graphics system so that the object can be defined in a manner that can meet not only the requirements of design but also those of testing, manufacturing, and management. A CAD system can be further upgraded by incorporating software that performs the numerical control function and permits a user to define, on the screen, a cutter path based on part profile and machine operations. A part machining program, in APT or other higher-level NC programming languages, defining the sequence of machine operations and the cutter motion can then be generated automatically. There are also upgraded CAD systems that include software for facilitating the manufacturing process planning and production simulation. Based on geometric models and an extensive data base, including the necessary data for part classification, process planning, and so forth, these CAD systems can assist the manufacturing engineer in planning and simulating manufacturing processes. Some of the NC-oriented, upgraded CAD systems also include programs that assist the user in generating a customized postprocessor. Such upgraded systems, which support bom design and manufacturing, are called CAD/CAM systems. Despite their power and versatility, CAD or CAD/CAM systems cannot, of course, carry out automatically a complete job of design and analysis. Their role is to assist the human engineer during the highly complex design process. Thus the designer and the CAD system work as a team, combining the best characteristics of each. The person conceives a design, inputs it into the system, examines it, modifies it, edits the information, and makes decisions, whereas the CAD system carries out the necessary numerical analyses and organizes, stores, transmits, and accesses the information. Each partner does only the work that he (it) can do best. The result of computer-aided design is a geometric data base (or CAD model) that defines, in numerical form, the part to be manufactured. The CAM software is then used to generate the information required to manufacture the part on the basis of the geometric data base. During this process, the human being again plays the same role as in CAD. For example, when working on an NC program, the designer must determine the starting point, the sequence of machine operations, the machining specifications, and the cutter path. The CAD/CAM system then carries out the necessary mathematical calculations and translates the calculated vnresults and the information input by the designer into an NC machining program. NC is a manufacturing method that makes it possible, for the first time, to fabricate a mechanical part of arbitrary form without relying on the operational skill of a human being. Designers can specify, in their design, the forms, surfaces, or profiles that were previouslyconsidered economically unjustified or not manufacturable. Because of the high positioning accuracy, multiaxial motions, and multiple functions of modern NC machines, it is also possible to cut easily the parts that have a combination of geometric elements with strict requirements for their relative positions and orientations. The operation of an NC machine tool is controlled by a program written in NC code, called NC program, which consists of a series of statements, or blocks, specifying the operations to be executed and the cutter motion to be realized by the NC machine in order to machine a specific part. On classic metal-cutting machine tools, a machining process plan is usually provided and should be followed by the operator in order to make the part to the required dimensions and tolerances. Correspondingly, an NC program is the translation of a machining process plan into NC codes that are understandable to the NC machine controller. The program is read and than executed by the NC machine controller system. What is normally called NC programming consist in writing down the machining operations step by step in terms of NC codes. In fact, it is the process of translating a machining process plan into NC codes. Depending on experience and knowlage of NC programmers, programs written by different programmers for the same part might differ. The criteria for evaluating an NC program are correctness, accurasy, and the memory space needed for storing the program in the CNC controller. With the increasing use of all kinds of programmable devices and systems, including CNC machines, robots, computers, CAD/CAM systems, flexible manufacturing system (FMS), and computer-integrated manufacturing system (CIMS), manufacturing has been completely revolutionized. Computer-aided manufacturing (CAM) requires that a process be planed in every detail and that every step in the operation be clearly defined before a part is manufactured. This means that a manufacturing process cannot be loosely defined, as had been done for many years in a process router or general process plan wherein many vm p^sadetails were left to machinists or operators. In other words, manufacturing can no longer be treated simply as practice-related knowlage in the modern CAD/CAM environment. Much research work is needed in the field of manufacturing management, process planing, parts classification, automatic parts and metarials handling, automatic inspection, automatic monitoring of machine tool status, integration of computer with production equipment, manufacturing data base, manufacturing application software design, and even manufacturing processes. The achievement attained by NC technology today would not be possible if the software necessary to facilitate NC programming had not been developed. As can be seen from the above description, precise data regarding consecutive tool positions in a machining operation should be given in the NC program. For parts of complicated shapes, it is not possible to calculatethe tool position data manually. Even for those parts whose NC cutter paths can be calculated manually, the time required for such programming is considerable. The difficulty in programming arises also from the need for translating the data into the codes required by different NC controlers. The integration of computer-aided design and computer-aided manufacturing is becoming a pressing need for manufacturers. Users are demanding a shorter cycle time between ideas and finished, marketable products. Future CAD/CAM solutions should replace the disorderly collection of programs with integrated user-friendly systems of applications. Manufacturing applications today primarily concern the ability of the system to generate NC cuter path files directly from the design geometry. To shorten many of the time-consuming processes normally involved in creating production data, engineers should be able to generate the required information interactively from design data, thus bridging the gap between design and manufacturing. For this reason, a computer integrated design and manufacturing program has been developed for rotational symmetric parts that can be machined in CNC lathes. The program, which should be run on a PC with VGA card, consists of three main modules; CAD module, CAM module and simulation module. Mechanical engineers usually enter the CAD/CAM process at its earliest stage, when the design is being conceived. To assist the designer, CAD module of the integrated system has modeling functions that provide comlete geometric representation, visualization and data generation. IXUsing simple, interactive commands, the design engineer can create models of products. The constructive geometry approach combines placement of different geometric primitives such as spheres and cones which can form almost any rotational symmetric object. CAD module of the program allows the user to generate, display, manipulate, and modify the graphic object. Drawings which are produced can be stored in a much more compact form (on hard disk or floppy disk) with the extention of 'ski', and user can retrieve and modify a drawing quickly at any time. In the CAM module of the program, the CAM procedure for NC programing begins with the geometric defination and selection of material of the unmachined part. A significant benefit of using a CAD/CAM system is realized when this geometric data have already been created during design. If the geometric model of the part has not been previously created, it must be constructed on the graphics terminal with the aid of the CAD molule. Tool selection is the next step in the procedure. The CAM module have a tool library with the various tools used in the shop catalogued according to the type and either the programmer or the program itself could select one of these tools. After mat optimum cutting parameters such as cutting speed, feed, depth of cut and tool life are calculated by program or selected by user and process plan of the part is prepared. The language through which human beings communicate with CNC machines consists of NC codes in word address format. It is clear that precise coordinates of tool positions are needed to write an NC program. There are two disadvantages of programming in NC codes. First, tool position coordinates are not easy to calculate for many parts, indeed, manual calculation is time consuming and error prone. Second, an NC program written manually in NC codes has to be input manually into the NC machine or a tape-preparing device, or it has to be manually keyed into a computer and then sent to the NC controller. Since NC programs of hundreds or even thousands of statements are common, manual input takes excessive time and generates typing errors that are difficult to detect. At last step CAM module of the program automatically prepares NC program with using standart G-codes to generate desired part geometry. **^Testing of CNC part programs can be expensive and hazardous. Usually testing is done directly on a CNC machine tool which, if there are errors in the G-code program, can be dangerous to the operator as well as to the machine tool. This approach is also an inefficient use of the machine tool when it could be otherwise producing parts. Simulation module of the program can be used to test part programs and to produce a graphic display of the tool path. The objective of the simulation module is to provide an error check on the accuracy of all G-code statements. The program allows the user to read, check and correct a G-code file, and to display the tool and tool path on the screen. XI
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