CAM sistemlerinin, CNC takım tezgahlarına uygulanması ve postprocessor hazırlanması

Abstract

ÖZET Bilgisayar Yardımı ile İmalat ( Computer Aided Manufacturing - CAM ) konusu, Bir parça veya kalıbın Bilgisayar yardımı ile tasarlanıp, bilgisayar kumandalı sayısal kontrollü (NC veya CNC) takım tezgahlarında işlenmesini içerir. CAM yazılımları, parça geometrik bilgilerini kullanarak ve imalat yöntemi ile ilgili teknolojik bilgi ve verilere dayanarak, parçaların işlem sıra ve verilerini üretir. Yani kullanılacak olan sayısal tezgahın anlayacağı makina dilinde NC programını hazırlar. Sayısal Kontrollü (NC/CNC) tezgahlarda imal edilen parçaların birçoğu oldukça karmaşık şekilli parçalardır. Parçanın karmaşıklığı arttıkça elle programlama işlemi daha içinden çıkılmaz bir hal almakta ve hata yapma olasılığı artmaktadır. Bu gibi durumlarda programlama işlemine yardımcı olmak üzere bir bilgisayar kullanılması ve programcının yapması gereken bazı tekrarlı hesaplamaların bir programlama dilinin yardımı ile yapılması gerek zamandan büyük bir tasarruf sağlayacak ve gerekse programlama işleminin çok daha hassas ve verimli olmasını sağlayacaktır. Sayısal denetimli NC veya CNC Torna, Freze, Telerozyon vb. takım tezgahlarında işlenmesi düşünülen parçaların (NC) programlarının hazırlanmasına büyük ölçüde kolaylık getiren ` QuickBASIC ` Programlama dilini kullanarak bir bilgisayar programı; `CAM ve POSTPROCESSOR` aşağıdaki kotrol sistemlerine uygun olarak hazırlanmıştır. 1- CNC Freze tezgahı (Maho 432, Deckel ve Fanuc) 2- CNC torna tezgahı (Fanuc, Siemens, GE) 3- CNC tel erozyon tezgahı (Fanuc) Bu program sayesinde, herhangibir CAD sisteminde sadece teknik resmi çizilmiş olan parçanın `DXF` çıkışını programa okutmak kaydı ile NC programının ` G ve M Fonksiyonları ` kolayca ve süratli bir şekilde elde edilmesi mümkündür. Bu tezde, Ülkemizde yeni yeni kullanılmaya başlanılan CAM sistemlerine benzer Quikbasic programlama dilinde basit bir CAM programı hazırlanmıştır. Bu program, CNC takım tezgahlarının programlanması için yeterli temel bilgiye sahip olmayan, sadece talaş kaldırma teknolojisini bilen elemanlar tarafından parça resmi çizilmek kaydı ile NC parça programının istenilen tezgaha uygun olarak kolayca elde edilmesini sağlayacaktır.

SUMMARY APPLICATIONS OF CAM (COMPUTER AIDED MANUFACTURING) SYSTEMS FOR CMC MACHINING TOOLS AND DEVELOPING OF POSTPROCESSOR. In this thesis, I studied `applications of CAM (Computer Aided Manufacturing) systems for CNC machining tools and developing of postprocessor`. CAD/ CAM is a term which means computer-aided design and computer-aided manufacturing. It has the technology concerned with the use of digital computers to perform certain functions in design and production. This technology is moving in the direction of greater integration of design and manufacturing. Two activities which have traditionally been treated as distinct and seperate functions in a production firm. ultimately, CAD /CAM will provide the technology base for the computer- integrated factory of the future. Computer-aided design (CAD) can be defined as the use of computer systems to assist in the creation, modification, analysis or optimization of a design. The computer systems consist of the hardware and software to perform the specialized design functions required by the particular user firm. The CAD hardware typically includes the computer, one or more graphics display terminals, keyboards 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 engineering functions of the user company. Examples of these application programs include stress- strain analysis of components, dynamic response of mechanisms, heat transfer calculations and numerical control part programming. The collections of application programs will vary from one user firm to the next because their product lines, manufacturing processes, and customer markets are different. These factors give rise to differences in CAD system requirements. VIIComputer-aided manufacturing (CAM) can be defined as the use of computer systems to plan, manage and control the operations of a manufacturing plant through either direct or indirect computer interface with the plant's production recources. The CAD/CAM procedure for NC programing begins with the geometric defination of the 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 part displayed on the CRT screen, the programmer would proceed to label the various surface and elements of the geometry. The CAD/CAM system would accomplish the labeling in response to a few simple commands by the programmer. After labeling is completed, the APT ( Automatically Programmed Tools ) geometry statements can be generated automatically by the system. In addition to the ease with which the APT geometry has been defined using the CAD/CAM system, there are several other benefits afforded the user of a graphics system for NC part programming. The part can be displayed at various angles, magnifications, and cross sections to examine potential problem areas in machining. This capability to manupulate the part image on the CRT screen is helpful to the programmer in visualizing the design of the part. Tool selection is the next step in the procedure. The CAD/CAM system would typically have a tool library with the various tools used in the shop catalogued according to the type. The programmer could either select one of these tools or create a new tool design by specifying the parameters and dimentions of the new tool (diameter, corner radius, cutter length, etc.) Generation of the tool path At this point in this thesis, the programmer has a geometric model of the work-part and the tools needed to VIIImachine the part. The next step is to create the cutter path. The method of accomplishing this using interactive graphics depends on the type of operation (e.g., profile milling, turning, sheet metal working) and the complexity of the part. The currently available commercial CAD/CAM systems use an interactive approach, with certain common machining routines being done automatically by the system. These automatic routines might include profile milling arround a part outline, end milling a pocket, point-to- point, PTP presswork hole piercing, and surface contouring. The interactive approach permits the programmer to generate the tool path in a step-by-step manner with visual verification on the graphics display. The procedure begins by defining a starting position for the cutter. The programmer would then command the tool to move along the defined geometric surface of the part. As the tool is being moved on the CRT screen, the corresponding APT motion comments automatically prepared by the CAD/CAM system. The interactive mode provides the user with the opportunity to insert postprocessor statements would consist of machine tools instructions such as feed rate, speed and control of the cutting fluid The automatic machine routines are called into operation for frequently encountered part programming situations. These routines are analogues to high level MACRO subroutineswhich have been developed as part of the CAD/CAM system software. The part geometry data represent the set of the parameter definitions or the arguments for the MACRO. Accordingly, these automatic routines can be called with a minimum of the user interaction. Profiling and pocketing are two common examples of automatic machining routines that are available on most CAD/CAM systems. The profiling routine is used the generate the sequence of cutter paths for machining around a series of element which have been identified by the user. These geometry elements would Typically define the outline of the workpart. In generating the tool path on a CAD/CAM system the use of color graphics is very helpful to the programmer. The part can be display in one color, while the tool path would be shown in a different color. This permits easy visual differentiation of the tool path from the part IXoutline. Another feature which aids visualization of the machine sequence is dynamic tool path simulation on the graphics screen. Advantages of CAD/ CAM in MC programming Many of the achievements in computer-aided design and manufacturing have a common origin in numerical control. The CAD/ CAM approach offers several very significant advantages in numarical control part programming. Among these advantages are the following: * Savings in geometry defination: Since the part geometry have already been created during design using the CAD/CAM graphics ssytem, the part programmer is not required to redefine teh geometry of the part. This can be a time consuming procedure in conventional APT programming. * Immediate visual verification: The graphics terminal provides a display of the tool path for immediate verification by the part programmer. Most programming errors can be detected by the user and corrected at the time error is made. When conventional APT or other NC language, there is delay between writing the program and the verification/ correction process. * use of automatic programming routines: For common part programming situations such as profiling and pocketing, the use of automatic Macro type routines yields significant raduction in part programming time. * One-of-a-kind jobs: Because the part programming time is significantly reduced when using a CAD/ CAM system. Numerical control becomes an economically attractive method for producing one-of-a-kind jobs. Without CAD/CAM, the time required for prepare the part program represents a significant obstacle which often precludes the use of the NC for one/ off production. * Integrated with other related functions: There is the obvious opportunity to integrate the product design function part programming. Other oppurtinities for functional inntegration within manufacturing also exist.These include tool design, process planning, preperation of operator and setup instructions, grouping of parts into families for programming convenience, and so on. With the tremendeous advances made in NC programming over the last thre decades, it is not diffucult the imagine that the entire logic of the part programming process will be captured and put onthe the computer. This would permit NC programming to be accomplished completely and automatically by the computer without human assistance. XI