Montaj hattı dengeleme
Assembly line balancing
Yazar: MURAT UZMEN
Danışman: PROF. DR. GÖNÜL YENERSOY
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü
Derece: Yüksek Lisans, 1990
Konu: Endüstri ve Endüstri Mühendisliği = Industrial and Industrial Engineering
Dizin: Benzetim = Simulation ; Montaj hattı dengeleme = Assembly line balancing

Özet:
Montaj hatlarının dengelenmesi, talebi yüksek olan mamullerin verimli, seri ve istenen şekilde üreti mini sağlamak amacıyla yapılır. Bu nedenle birçok yön temler geliştirilmiştir. Ancak bu yöntemlerin direkt olarak incelenen sisteme uygulanması bazı sorunlar yara tır. Günümüzde bir mamulün benzer modellerine olan talep detayına göre çok modelli veya karmaşık modelli montaj hatları geliştirme ve dengeleme konusunda akade mik ve fiili çalışmalar yoğunlaşmaktadır. Ancak bu tür montaj hatlarının tercih edilmesi için maliyet faktörle ri ve uygulanabilirliğin çok iyi incelenmesi gerekir. Simülasyon yaklaşımı montaj hattı dengeleme problemine yeni boyutlar kazandırmıştır. Bu sayede ge liştirilen yöntemlerin perf ormansı, uygulanabilirliği ko layca incelenebilmekte yeni çözüm yaklaşımları edinile bilmektedir. Bunun yanında çeşitli yöntemlerle elde edilen hat dengeleme çözümleri mukayese edilebilmekte dir. Yukarıda değinilen üç sorun veya yaklaşımla hat dengeleme problemine yeni bir boyut getirmek mümkündür. Mevcut yöntemlerin montaj hatlarına uygulanabilirliğini incelemek, değişik montaj hattı yaklaşımları kullanmanın getireceği sonuçları irdelemek ve bunda simülasyon yak laşımının getirdiği avantajlardan yararlanmak karşımıza önemli sonuçlar çıkartabilir. Bu tür çalışmalarda elde edilecek sonuçlar, bize en iyi tercih yollarını seçtire- cektir. vıı

Abstract:
Humankind must obtain all the needs he has for remainance. But these needs are endless and the sources are limited. So production is the facility, created by humankind, to get the products that they can not get from the nature. Economists call the production as creating profits, and engineers define it as creating a difference on a physical body that increases its value, or changing a semi-product or a source to a useful product. So, the main aim of the production is, creating a profit or a product. For doing a production, production factors and sources must get together under certain conditions and by certain methods. During the production using these factors and sources, economically and more efficient is the most important problem. Nature of this problem widely belongs to the construction of the product. Production can be called in two groups, called continious and discontinuous production. In the first group, the demand must be too much for the product and there is a non-stop production. In the second group, different kinds of products are on line and they have not much demand. Mass production is a branch of continuous production. Flow shop also have the facilities of mass production. In this type construction of the product is no simple. If in a flow shop there is a production belonging to the human ability and facility we meet the assembly lines. Assembly lines are commonly used to assemble consumer durable items such as cars, radios and domestic appliances interchangable parts are assembled together at a set of sequential work stations at each of which is performed a prespecified part of the total content. The assembly is usually moved mechanically, e.g. by belt, conveyor or indexing line. Provided that parts are available and that demand for the product is adequate,these traditional assembly lines can be highly efficient. The well defined sequence of operations minimized the need for control documentation. Manual handling is reduced. Work in progress is small and as each operator is responsible for only a limited amount of the work, training time can be reduced and semi-skilled labour used. However, assembly lines have several disadvantages. First the stringent requirements placed on component availability make assembly lines vulnerable to distruptions by internal, and external suppliers. The short cycle work with a low skill requirement can lead to poor job satisfaction, and there may be high labour turnover and absenteeism. Thirdly, many of the mass production industries have had quality problems. In an attempt to overcome these difficulties, several organisations have increased cycle times and moved to team working whatever aproaching is adopted, good balancing of individual or team work is essencial and helpful to all concerned and so current conditions have, if anything, increased the need for good assembly line design or re-design. Assembly lines can be grouped as one model lines, multi-model line and mixed model lines, that designed according to the number of products and, way of producing in assembly lines the works divided to the work stations, that, from one station to the other all the processes gets completed and the product obtained. Because of this assembly processes (work elements) must be well sequenced. This sequence belongs to the product and production technology. These factors and the precedence relationships are the datas of the assembly lines. Line balancing is an important production function because the efficiency of assembly lines is directly linked to the quality of the balance. It is a job requiring knowledge of the product, layout, processes, materials, tools, labor and rules for combining this information. In addition the engineer responsible must have an aptitude for fast accurate computing the balancing process and the subsequent evaluation of the assignment are often highly subjective and balances often have to be produced to some deadline. It is usual to begin with the production schedule, on table of standard performance times for operations, a list of all the operations in fairly broad outline and a desk calculator. Experience and logic are IXbrought to bear on this information and, after considerable expenditure of time and effort, a line balance can be produced. Each work station consists of worrk elements which have been previously derived from a breakdown of the assembly of a particular product. These work elements are usually defined in such a way that they are indivisible into smaller elements. Therefore no element of work will be split between operators because to do so would incur extra work in the form of handling time. The assembly line balancing problem is basically to pack these work elements into each work station, while obeying precedence constraints on the order in which the tasks can be accomplished, in such a way that the load on each operator is evenly balanced and there is as idle time as possible. The rudimentory knowledge necessary to balance a line consists of task times, precedence relationships, desired output rate or cycle time. Other than for very simple products the number of possible ways in which work elements can be assigned to work stations is immense. In practice, therefore, the manual balancing process is often based on an inspection of the precedence diagram. There are many line balancing techniques available including; enumerating all sequences, selecting a solution consistent with current company practice, deriving a solution by mathematical methods, deriving a solution by using heuristic rules, using rules which take account of the problem structure. All of these approaches have been investigated by different workers. Enumeration is impractical except for trivial problems. Jackson used enumeration but takes account of the problem structure to restrict the number of choices and so produce a practical method for deriving hand solutions to simple lines. Held used dynamic programming to obtain optimal solutions but this is competitionally expensive. Halgeson and Birnie and Kilbridge and Wester used heuristic methods as the basis of practical computer systems Arcus used heuristic methods in conjunction with random selection procedures to procedure a method which Wester showed to perform well in the comperative study of methods Salveson and Bowman improved a linear programming method for assembly lines but these methods got no chance to be used because of the long way of solving.In addition to the operation assignment algorithims, a realistic assembly line balancing program or solving method requires to take account of the practical restrictions to handle the data effectively and to procedure results in a form and with timeliness appropriate for the practical user. The timeliness constraint may often raise a requirement for on-line processing mixed models will raire a further requirement for mixed model balancing, i.e. assigning operations of several different models in a way which is consistent with skill and facility location. The assembly lines discussed so far have all been dedicated to the manufacture of a single product. However, in many cases one line is used to assemble more than one model of the same general product. The extreme example of this is in the automobile industry when one basic model can have thousands of combinations of customer variations, all of which have to be catered for using the same set of manufacturing facilities. Depending on the complexity of the product and the type of variations, companies using manual techniques approach mixed model line balancing in different ways. There are three major types; bolt it afterwards method for medium sized products, method for small batches, and set it up and start approaches again. Simulation is also a well known but a new using approach in assembly line balancing. In assembly line production simulation gained us new ways in investigating the balancing results. By the simulation method comparing the results of balancing studies get easier. Starting from this point in this study the target was determining the performance of a one model and mixed model assembly lines and comparing them by a simulation method, in a automotive industry firm. Today assembly line production and assembly line balancing is very important in order to product high amounts of products economically and quickly. For this reason, the aim of this study is to examine the problems of the assembly lines, to introduce basic concepts of assembly lines and balancing methods, to show the solution methods, to search about the importance of the assembly lines at production and to examine the new methods which are used at assembly lines balancing. XIAt the time to give a decision about establishing an assembly line, knowing the demand structure of product, determining the line design according to the place and searching the characteristics of product are the most important points. Today, many methods which published, are improved at the subject of assembly line balancing. These methods can be examined at the two main groups. The methods in which mathematical programming like linear programming are used, give absolute results. But it is very difficult to have a result by applying these methods to assembly lines which are complex and contain many operations. For that reason, today mathematical methods loose their importance -at using in the assembly line balancing. Instead of these methods intuition methods are prefered. Although they couldn't help to get the absolute solution, it is easy to reach a result and they can be adopted easily to the studies of computer aided assembly line balancing. Today, companies which produce similar products, begin to use assembly lines with complex models in order to minimize the costs assembly lines and to produce different products in the less amount of assembly lines. For that reason academic studies about these kinds of assembly line balancing increase. But there is an important problem in the assembly line balancing with single model or complex model. At these methods service times are accepted as constant, and all algorithm is based on this acceptance. At reality service times can be variable or the possibility of being constant is very little. In order to solve the problem or minimize the error ration, the standard times of operations on the line and performance of the workers have to be determined exactly. Human factor is an important problem at the assembly lines at which the operations are made by man power. The flexibility of human behaivours can't be determined exactly so it affects the studies of assembly line balancing. xix