Grup teknolojisi kümelerinde yöntemleri ve atama yönteminin bilgisayar destekli uygulaması

Abstract

Son yıllarda miktarca azalan ve çeşitlenen müşteri istekleri, büyük partiler halinde çok sayıda mamul üreten atölye tipi işletmelerin tasarım, planlama ve üretim sorunlarının önemli boyutlara ulaşmasına yol açmıştır. Bu sorunlara köklü çözümler öneren "Grup Teknolojisi" makina imalat sanayiinde her geçen gün önem kazanmakta ve geniş uygulama alanları bulmaktadır. Üretimde ise, grup teknolojisi (GT), üretilecek iş parçalarını ve bunlar için gerekli makinaları ortak özelliklerine göre gruplandırarak maliyetleri düşürmeyi ve aynı zamanda esnek bir üretimi amaçlar. GT bir üretim felsefesidir ve birçok problemin temelde birbirine benzer olduğunu kabul eder ve benzer problemleri bir araya toplayıp tek çözüm aramayı amaçlar. Bu suretle zaman ve çabalardan tasarruf sağlanır. Bu çalışmanın ilk bölümünde GT hakkında genel bilgiler verilmekte ve GT üretim sisteminin, diğer üretim sistemleri arasındaki yeri belirtilmektedir. Ayrıca üre timde, bu sistemi uygulamanın faydaları ve sakıncaları sıralanmaktadır, ikinci bölümde, GT'nin elemanları hakkında bilgi verilip GT'ndeki yaklaşımlar sıralandıktan sonra hücrelerin çalışma düzenleri açıklanmaktadır, üçüncü bölümde, GT üretim sistemi tasarımı için gerekli model ve algoritmalar tanıtılmaktadır. GT'nde hücre oluşturma yön temlerinden hiyerarşik ve hiyerarşik olmayan kümelendirme yöntemlerinin karşılaştırılması yapılmakta, daha sonra kümelendirme yöntemlerindeki performans ölçüleri hakkında bilgi verilmektedir. Son bölümde ise kümelendirme yöntemleri arasında önemli yer tutan atama yöntemi analiz edilip bu yöntem, BASIC dilinde programı yapılarak çeşitli atölye verilerine uygulanmaktadır.

Recently, the market demands show a clear inclination towards producing goods in smaller lots and increased varieties. For these reasons, many companies which manufacture variety of products with large lots suffer from many problems in the designing, planning and production stages for the the products manufactured. Group tehnology (GT) production systems suggest radical solutions for these problems. GT production systems have been increasingly attracted in many countries and wide variety and successful applications are especially known in Japan and U.S.A. GT or ceilular manufacturing is an accepted solution to the problem of productivity in batch-production systems. Parts are classified into part families and machines into machine cells, based on the "sameness" or similarity of operations. This is the first step towards the implementation of a GT system. Many heuristic and non-heuristic methods are in vogue for such concurrent classification of parts and machines. In most of such approaches, the primary input data is the machine-component incidence matrix (aij) in which the columns and rows represent the parts and machines respectively. The (i,j) th element of (aij) is 1 if the j th part visits the i th machine; otherwise it is 0. GT is a manufacturing philosophy. It emphasizes -v- that many problems are mainly similar and collecting the similar problems in a group and finding just one solution for them provide us time and efforts savings. In the first chapter of thesis, GT is introduced. After the efficiency factors of a manufacturing system explained, the applications of GT manufacturing systems among the other manufacturing systems are discussed. Besides these, the advantages and disadvantages of GT are explained. In the second chapter, the elements of GT are introduced and the one that simplifies the material flow system is widely examined. This is the layout of the production systems The layout of the production systems is classified into three main types. They are firstly examined individually and then compared with each other by determining the similarities and differences among them. These layouts are: * Functional layout * Group layout * Line layout In a functional layout, factory is divided into departments in where there are machines grouped for only one process. For example, a department for turning, a department for milling, etc.. In a group layout, factory is divided into departments in where similar parts are operated. In a line layout, factory is divided into departments in where there are machines used for just one part type. In this chapter, the savings provided by GT are also explained. After the GT approaches are described, the production flow analysis is explained in detail, and ?vi- then the cellular manufacturing system is introduced and discussed through an example. In the third chapter, the following two methods of solving the GT design problem are discussed. * Classification * Cluster analysis The classification method is used to group parts into part families based on their design features. Two variations of the classification method are autlined. * Visual method * Coding method The visual method is applicable in a case when the number of parts is rather limited. Therefore, the coding methods, which are more commonly used, are discussed. There are three basic types of coding system. * Monocode * Polycode * Hybrid In a monocode system, features of each part are mached with list of features corresponding to each node of the tree, and a part code is generated. Since a monocode system has a tree structure, a digit selected at a particular node depends on the digit selected at the preceding node. To understand fully the representation of a part monocode, all its digits are required. For a given part, the length of its monocode is rather short compared to other coding systems. In the coding methods, parts can be classified on the basis of the following features. -vii- * Geometric shape and complexity * Dimentions * Material features * Geometric shape of row material * Required accuracy of the finished part The cluster analysis approach is used to group machines into machine cells and parts into part families based on the similarity of operations. Three cluster formulations are introduced in GT. * Matrix formulation * Mathematical programming formulation * Graph theoretical formulation Since the GT problem is NP complete, heuristic algorithms are most likely to be used for solving large- scale industrial problems. The results grouping lead to the physical machine layout or logical machine layout. The latter is used in case when the production content changes rather frequently. In this case GT makes the tool management and part scheduling easier and this improves the efficiency of production planning and control. In the fourth chapter, the computer application of the assignment method is introduced. The assignment method is also mentioned in the third chapter, but there are not any examples. Here five different examples are chosen and GT cluster problems are solved by using this method. The clustering criteria is based on similarity coefficients. A similarity coefficient is defined between two machines. After all similarity coefficients are computed, these are gathered in a matrix. The obtained matrix is the starting point of this method. The assignment method problem uses the branch and bond algorithm. The computer program written in BASIC is introduced -viii- into seven stages. * Running the program * Entering the data * Computing the similarity coefficients * Solving the assignment problem by branch and bond algorithm * Determining the machine cells * Determining the part families * Determining the performace of cellular systems * Reporting all of them mentioned before These all stages are discussed briefly through an example and finaly the procedure of the assignment is evaluated