Tel erozyon işlemine yönelik CAD-CAM-CNC integrasyonu
CAD-CAM-CNC integration for CNC wire cutting process
- Tez No: 39267
- 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: 90
Özet
ÖZET Tez çalışmasında tel erozyon işlemine yönelik CAD-CAM-CNC integrasyonunu sağlayacak yazılım geliştirilmiştir. CAD bölümünde tel erozyonu imalat yöntemiyle üretilen plastik dişli kalıplan için AutoCAD ortamında silindirik dişli tasarımı yapan parametrik tasarım programı yazılmıştır. CAM bölümünde ise, AutoCAD ortamında, çizilmiş parçanın üzerinde, teknolojik bilgiler ve yörüngeler grafik etkileşimle belirlenmekte, ve bu bilgiler son-işleyici (post-processor) tarafindan kullanılarak tezgah için NC programı oluşturulmaktadır.“Silindirik Dişli Tasannu”için evolvent profilli silindirik dişli mekanizması parametrelerinin sistemetizasyonu yapılmış bunların belirlenmesi ve aralarındaki etkileşim irdelenmiştir. Ve AutoCAD ortamında AutoLISP ve ADS kullanılarak dişli çitti tasarım programı yapılmıştır.“Tel Erozyonu İmal Usulü için Bilgisayar ile Nümerik Kontrol (CNC)”bölümünde tel erozyonu imal usulü ve pilot tezgah olarak seçilen Fanuc Cut a-OA tezgahının özellikleri incelenmiştir. Bu bilgiler ışığında AutoCAD ortamında AutoLISP kullanılarak tel erozyon teknolojik bilgilerini ve yörüngelerini belirleyen CAM programı, ayrıca Fanuc tezgahı için bir son-işleyici yapılmıştır.“Autocad'de CAD/CAM Uygulamaları Geh'ştirilmesi”bölümünde grafik etkileşim için AutoCAD ortamının nasıl kullanılacağı araştırılmıştır.“Programlama Yaklaşımı”bölümünde yapılan sayısal çözümler ve geliştirilen programlama yöntemleri (dişli veri tabanının nasıl oluşturulacağı, tablo ve diyagramlardaki bilgilerin bilgisayar veri tabanına nasıl aktarılacağı, toleransların nasıl belirleneceği, ters evolvent hesabı için sayısal çözüm, büyük dosya işleme) konuyla ilgilenen programcılara faydalı olacak noktalan içermektedir. viii
Özet (Çeviri)
CAD-CAM-CNCINTEGRATION FOR CNC WIRE CUTTING PROCESS SUMMARY Recently there has been a great increase in the number of CNC wire cutting machines in industry. Generally these CNC wire cutting machines can do only linear and circular interpolation so it is necessary to supply these machines with CAD-CAM software. in the softvvare market CAM programs for CNC wire cutting are being sold, but they are too expensive and not flexible enough to meet different user needs. The integration of computer-aided design and computer-aided manufacturing is becoming an importand need for manufacturers. Users are demanding a shorter cycle time between ideas and fînished, marketable products. CAD/CAM solutions should replace the disorderly collection of programs with integrated user-friendly systems of applications. This study has been done to produce the sofhvare which does the CAD-CAM-NC integration of the wire cutting process. The software is consist of roughly three modules. These modules, in their running, order are as follows:.Spur and helical gear design..Generic data production for CNC wire cutting machines..Post-processor. The spur and hehcal gear design is the CAD modüle of the sofhvare. Computer aided design (CAD) can be defined as the use of computer systems to assist the creation, modification, analysis ör operation of a design. The computer systems consist of the hardware and softvvare to perform the specialized design function. The CAD hardware typically includes the computer, öne ör more graphics display terminals, ixkeyboards, and other peripheral equipment. The CAD software consists of the computer programs to implement computer graphics on the system plus application programs to facilitate the engjneering functions of the user company. The result of computer aided design is a geometric data base (ör CAD model) that defînes, in numerical form, the part to be manufactured. The CAD sofhvare is then used to generate the information required to mamıfacture 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 cutter path. The CAD/CAM system then carries out the necessary mathematical calculations and translates the calculated results and the information input by designer into an NC machining program. Ali 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. înjection molds of plastic spur gears can be processed by wire cutting if the gear geometry can be transferred to tiıe CNC wire cutting machine. The spur and helical gear design modüle is a parametrical design tool which makes the graphical interface through AutoCAD and draws the involute profile of the gear. Spur gears connect parallel shafts, by teeth parallel to the axes and nominally constand in form from end to end. If accurately aligned, they produce no end thrust. The wheel may have internal teeth and is then commonly called annulus. HeUcal gears, not othenvise qualifîed, also connect parallel shafts. The tooth profile is nominally constand from end to, but the teeth are of helical form and produce end thrust under load. For external gears, the teeth of the pinion and the wheel are of opposite hand of helix, and rotate in opposite directions. A helical pinion may engage with a helical internal gear, and both members then have teeth of the same hand of helix and rotate in the same direction. The spur and helical gears held in the study has involute tooth profile. The involute profile is generally the optimum profile for gears. xThe involute profile is two dimensionally modelled by point to point representation on AutoCAD. The spur and helical gear design modüle manipulates the geometrical parameters of the gear by setting an interactive interface with the user on AutoCAD. Graphical interface is made by customizing AutoCAD package by using script utility, AutoLISP, ADS, Programmable Dialog Boxes. AutoCAD provides a script facihty that allows commands to be read from a text file. This feature lets the user execute a predetermined sequence of commands; user can invoke these commands when he start AutoCAD (using a special fonn of the acad command), ör he can run a script from within AutoCAD by using the script command. AutoLISP, a specialized implementation of the LISP programming language, is an integral part of AutoCAD. Öne can adapt AutoCAD to his work habits by using AutoLISP to automate repetitive tasks and create new AutoCAD commands. The AutoCAD Development System (ADS) programming interface lets programmer high-level programming languages like C to customize AutoCAD. Programmer can run third-party ADS application programs ör write his own. AutoLISP is generally more suitable for smaller, simple programming jobs; in addition, writing AutoLISP programs is often simpler than writing programs in higher level languages. in general, ADS is best suited to large, complex programming tasks ör compute intensitive applications. The ADS interface consists of a library of fiınctions that parallel AutoLISP functions. An ADS apphcation is not written as a stand-alone program, but as a set of external subroutine functions that are loaded by, and called from, the AutoLISP interpreter. The Programmable Dialog Box (PDB) feature lets the user design and implement his own dialog boxes, simüar to the ones employed by AutoCAD itself. Functions for displaying dialog boxes, processing input, and so forth, are provided in both AutoLISP and ADS. Generic data production for CNC wire cutting machine modüle is made by using AutoLISP programs on AutoCAD. The user defînes the technological data, and the program path interactively on the drawing of the part on AutoCAD drawing screen. xiThis module performs general translations and calculations and generates an output consisting of data regarding tool positions and machine operations. These data, known as generic (or cutter location data or cutter center line data or CLDATA for short),are then processed and translated into the format required by the NC controller by a computer program, known as postprocessor, designed specifically for the given machine. In wire cutting process, a thin running wire is used as an elecrode and this wire cuts a workpiece placed on the table with electric discharge. There are two guides - upper and lower guides which guides the motion of the wire in the workpiece. In a CNC wire cutting machine such as Fanuc Cut a-OA these guides are numerically controlled in XY axis and UV axis respectively. The wire can be in vertical or tapered position. 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 generic data produced is consist of the technological data for cutting and the geometric data of wire guide paths. Post-processor processes this data and converts it to the language that the CNC understands. 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. xnA CLFILE is transformed into NC codes through a sequence of processing operations by the postprocessor. The processing is carried out as follows (Fig. 1): When the postprocessor is first called, a record in the CLFILE is read inro the postprocessor. It is then processed by the general processing section of the postprocessor and the result is stored in a buffer array. The data are further processed, checked, and then arranged into a format that is recognizable by the NC controller. Then they are output by the postprocessor. When the postprocessor has finished processing a record, it reinitializes or updates the buffer arrays, counters, and variables in such a way that they can be used for processing the next record. Then the next record is read in. The postprocessor repeats this cycle until the FTM record is read and processed. To help CAD-CAM-NC integration in industry an academical study in general should have these targets. Introduce parametrical design abilities to improve the flexibility of big CAD packages those can be executed on workstations.. Make post-processors to integrate big CAM packages those can be executed on workstations with new CNC control systems.. Produce software for CAD-CAM-NC integration in two dimensional areas, since in two dimension it is not so much complex so that something useful can be done. The study is an example of this. In the study it is seen that customizing AutoCAD to use it as graphical interface is a very effective way. Becouse the graphical interface gained by this way is very strong, flexible and compatible to the Graphical User Interface (GUI) standarts. Wire cutting does not have the limit using standart tool that other gear cutting processes have. This property brings a different point of view to gears. The programming experience gained during producing the Post processor Fanuc Cut a-OA CNC wire cutting machine makes it easy to produce new post-processors for other CNC wire cutting machines. This is because the subroutines which manipulate big files can be used wiithout change and the knowledge base for conversion has been builded. xm
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