Esnek üretim sistemleri
Flexible manufacturing systems
- Tez No: 39853
- Danışmanlar: PROF.DR. GÖNÜL YENERSOY
- Tez Türü: Yüksek Lisans
- Konular: Endüstri ve Endüstri Mühendisliği, Industrial and Industrial Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1993
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 243
Özet
ÖZET Firmaların, kaliteli ürünleri kısa bir zaman içinde, en ekonomik ve etkin bir şekilde üretebilmeleri, yoğun ve ezici rekabet koşullarında ayakta kalabilmeleri ve kar edebilmeleri için, gelen taleplere en etkin ve en az maliyetli bir biçimde cevap verebilme yeteneğinde olan sistemlere olan ilgileri oldukça artmış bulunmaktadır. Sözü edilen sistemler, çok hassas toleranslarda imalat yapabilme, gelişen teknolojilere paralel hareket edebilme ve pazar yapısında ortaya çıkabilmesi muhtemel değişikliklere uzun hazırlık zamanları gerektirmeksizin cevap verebilme özelliklerine haizdirler. Bu bakımdan esnek üretim sistemleri, üretim endüstrisinin günümüzde ulaştığı son nokta olarak nitelendirilebilir. Otomasyon kavramı ve yüksek teknolojiyi tek bir üre tim sisteminde birleştiren esnek üretim sistemleri, nümerik kontrollü tezgahları, otomatik malzeme taşıma ve depolama ünitelerini, robot sistemlerini ve hiyerarşik bir düzende işleyiş gösteren bilgisayar kontrol sistemlerini ihtiva etmektedir. Zira esnek üretim sistemle rinde genel amaç üretilecek parçaların sistem içinde yer alan hareketlerinin otomatik malzeme taşıma sistemleri, parçalar üzerinde yapılacak işlemlerin ise çok yetenekli sayısal kontrollü tezgahlar ile otomatik olarak gerçekleştirilmesidir. Özet itibarı ile esnek üretim sistemleri esnek otomasyonu mümkün kılan kombine imalat sistemleridir. Bu açıdan, bilgisayar bütünleşik imalat kavramı ile beraber çalışan, değişken talep ve rekabet koşullarına büyük bir esneklik ile cevap verebilen bu sistemler ile kuruluşlar dünya pazarlarındaki yerlerini almaya çalışmaktadırlar. xii
Özet (Çeviri)
In the present competitive market environment, the industrial processes are automated to the higher degree in order to perform the production efficiently. In the case of manufacturing systems, the automation requires a greater flexibility in a way that one can change ra pidly a production type to another. But the greater flexibility implies a greater complexity of the process control. The flexible manufacturing systems control specification requires consequently more complex tools but the classical methods for specification such as spe cification languages, network queue models cannot be u- sed for the FMS problems which require simultaneous evo lution and a high degree of parallelism and synchronisa tion. The recent advances in manufacturing processes, inc luding the generation of cheap and powerful computers, permit the integration of many previously distinct man ufacturing concepts. Today the highest hierarchical le vel in computer control of a manufacturing plant conta ins flexible manufacturing systems. FMS is an integra ted, computer-controlled complex of automated material handling devices and numerically controlled machine to ols that can simultaneously process medium sized volumes of a variety of part types. Through extensive computer control in an FMS it is possible to achieve the effici ency of well-balanced transfer lines and retain flexibi lity of a job shop simultaneously machine multiple part types. xiiiIn another words, a flexible manufacturing system is a fully automated, computer controlled production system that may offer substantial advantages in comparison to the conventional job shop. While FMS has been given a variety of names -e.g., computerized manufacturing sys tem (CMS), and variable manufacturing system (VMS) the fundamental definition of a 3?MS is, in the words of Bu- zacott,“ a set of machines... linked by a materials handling system and all under central computer control.”This definition is rather broad and may encompass a va riety of machine configurations in diverse applications. However, it emphasizes hardware and neglects important aspects of managing and controlling such a system. The ability to manage and control an 3PMS is essential to ac hieving the potential which such a system promises. Yet many problems in this area remain unsolved. Flexible manufacturing systems are a promising new development in the field of automated manufacturing and are being developed in many different countries and in dustries. In the lifetime of the FMS, an organization goes through many phases of decision making, initial de sign, detailed design, installation, operation and ongo ing modifications and improvements. The outcome of a FMS's performance depends on many things : type of mac hines purchased, number of transportation vehicles or pallets installed, differet ways of machine grouping, re liability of the machines and future demands. In the i- nitial design and operation of such a system, it is use ful to have tools that can predict system performance for different operational conditions to see how these factors contribute to system performance, FMS's are designed for production of small and medi um-sized batches comprising several different part types with the efficiencyof automated mass production and the flexibility of the job shop. However there is a great xivdeal of confusion and uncertainty as to what constitutes an FMS. Herroelen has calculated that by 1983 there we re 120 FMS's in existence around the world. The clas - sification of a manufacturing system depends on the ex tent of automation and the diversity of the parts to be machined. On this basis Browne define four types of PMS The first one is flexible manufacturing cell. This is the simplest type of FMS and it consist of one special purpose CNC machine tool, interfaced with automated ma terial handling which prowides raw castings or semi- fi nished parts from an input buffer for machining, loads and unloads the machine tool, and transports the finis hed workpiece to an output buffer for eventual removal to its next destination. The other type is flexible machining system. This generally has real time, on-line control of part produc tion. There are several routes for parts, with small volume production of each and it consists of FMCs of different types of general purpose, metal-removing mac hine tools. Real time control capabilities can automa tically allow multiple routes for parts. The third one is flexible transfer line. For all part types each operation is assigned to, and performed on, only a machine. This results in a fixed route for each part through the system. The layout is process - driven and hence ordered. The material handling system is usually a carousel or conveyor. The storage area is local, usually between each machine. In addition to ge neral purpose machines, it can contain special - purpose machines, robots and some dedicated equipment. The fourth and the last type is flexible transfer multi line. This type consists of multiple type III FMSs that are interconnected. xvA consequence of this automation lias been the diver se types of flexibility that can be attained by the use of a FMS. Browne have described in detail eight diffe rent types of flexibility. Various levels of flexibi - lity enables an FMS to produce different sets of part types economically, quickl, in several different ways and at different production levels. It is this ability of an FMS that is in sharp contrast to the limited flex ibility in a job shop or to the rigidity of automatic transfer lines. The flexibility in an FMS has provided new and uni que problems in the areas of design, planning, schedu - ling and control of a FMS. Once the system has been set up during the planning stage, the FMS scheduling problem deals with the real time control of the running of an FMS. Stecke has indi cated the inadequacy of conventional schduling methods which do not distinguish the loading problem from the scheduling problem. She has clearly distinguished bet ween the two in the context of an FMS and has provided guide-lines for the loading problem. She has also indi cated the potential advantages from using a real time on line control policy for the scheduling problem in an FMS Unfortunately, the complexity of the on-line scheduling problem makes it intractable to any known mathematical programming techniques. Flexibility gives rise to many of the relative ad vantages of an FMS. Since machine tools are computer controlled, the system is flexible to produce a variety of parts by a simple change of software. During opera tions, the system can respond flexibly to unforseen e- vents, such as machine breakdown and temporary overloads by rerouting workpieces to alleviate potential bottle necks. Flexible machining centers in a system allow xvimultiple operations to be performed on a workpiece. Furthermore, with automatic tool interchange capabili ty, setup time is eliminated, improving machine pro ductivity and workflow characteristics. These flex ibilities, along with others, promise productivity imp rovements through increasing machine utilization and, at the same time, reducing levels of work-in - process and production cycle time. The scheduling of flexible of FMS is critical to the effective use of this capital intensive process. FMS is advantageous when production volume is not suffici ent to justify the capital expense and risk associated with specialized production lines, but when sufficient volume is available within a family of similar parts to substantiate the purchase of computer- controlled flex ible machines. An FMS incorporates many of the advan tages of high speed transfer lines and the flexible job shop. The scheduling of FMS requires the use of both traditional job shop scheduling concepts and the consi deration of the special system characteristics of al ternative routings and sequence of operations. When an investment of several million dollars is being considered the expenditure of some tens of thou sands is a small insurance premium to avoid major un- forseen problems. It is now generally accepted that simulation has an important role to play in the plan ning of FMS. The main uses are in evaluating proposed designs and in developing management tools such as sch eduling priority rules. Although it may be suggested that FMS simulation is just another application of simulation, there is one very important difference between the simulation of an FMS and that of any other manufacturing facility, such as a job shop. Since FMS are computer controlled many xviiof the sources of random disturbances have been elimina ted. There can therefore be much greater confidence in simulation results. Unfortunately the use of simulation is not necessa rily straight forward, and the majority of companies considering installing FMS have only very limited exper tise, if any, to carry out simulation studies. Conse quently, many companies rely on the suppliers to present sound proposals, or on outside consultants to assess the proposals for them. Even when expertise is available or is commissioned there are major stumbling blocks. As we shall see, simulation needs data to work on, and that is usually in short supply until well on into a project. Under all those circumstances, while changing from conventionel manufacturing systems to“Future's Factory”concept, since there are lots of problems awaiting to be solved such as probable improvements in the machine to ols and material handling systems, major changes in the production philosophy, computer and numerical control technology, the reaction of people's attitudes towards a factory that might need less employees, reseachers and engineers have the greatest responsibility to access so lutions to many of the above mentioned problems. Since flexible manufacturing systems are essential for the near future and in time the necessity for those kinds of systems arises engineers and competitors invol ved in todays rapidly changing demand market have to get into corporation to achieve a position in the ever- imp roving technology and have the chance to get benefit of those technologies. xviii
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