Simulation analysis of cellular manufacturing systems with external routing flexibility

Dışsal rota esnekliğine sahip hücresel üretim sistemlerinin benzetim analizi

Abstract

Group technology is a manufacturing philosophy which attempts to identify and economically exploit the underlying sameness of parts and manufacturing processes. Cellular manufacturing applies group technology principles to the design and management of a manufacturing system. In other words, the main idea of cellular manufacturing concept is the formation and operation of manufacturing cells dedicated to the processing of a set of part families. A manufacturing cell can be defined as a group of functionally dissimilar machines located in close proximity to one another to produce a part family. A part family is a collection of parts which are similar in terms of shape design, or manufacturing features. Cellular manufacturing systems are proposed as an alternative to the job shop systems in batch manufacturing environment. The application of cellular manufacturing concept results in the mass production effect to the multi-product, small-lot-sized batch manufacturing. Cellular layout is the opposite of shop layout where sets of functionally similar machines placed together and dedicated to producing dissimilar parts. It should be noted that the cellular manufacturing layout involves the physical arrangement of the production facilities. Cellular manufacturing is a well-established approach which has been proven to offer many advantages when implemented correctly. The benefits of cellular manufacturing and group technology have been well documented in published case studies, surveys, and articles by the industrial exponents of the technique and the academicians. There are numerous advantages attributed to cellular manufacturing and the main advantages are the following:• reduced set-up time,• reduced throughput times which give fasterresponse and more reliable delivery, • reduced work in progress and finished inventory level, • improved quality, • reduced material handling effort, • a smaller variety of tools, jigs and fixtures, • reduced product design variety, • better production planning and control, • better space utilization,• improved operator expertise, • improved human relations, job satisfaction, morale and communication.There exist also some disadvantages associated with cellular manufacturing which are as follows:• increased capital investment, • lower machine utilization,• reduced manufacturing flexibility.In order to obtain a competitive advantage many firms engaged in batch production recently consider the improved manufacturing flexibility as a vitally important manufacturing objective. Cellular manufacturing, however, is aimed at stable situations in which manufacturing flexibility is reduced to some extent since the machines are dedicated to the production of part families in order to gain the improved performance of mass production. Manufacturing flexibility can be designed into cellular manufacturing systems and there are numerous types of manufacturing cells ranging from pure group technology cells to flexible cells.The performance of cellular manufacturing systems may diminish when they operate under the unexpected workload imbalance between the cells caused specially by the changes in part mix and demand distributions. This work investigates the level of performance improvment that can be obtained by applying a decision rule developed in the work and that exploits the external routing flexibility of a cellular system experiencing workload imbalances between the cells caused by the changes in part mix and demand distributions. Because of the complexity of the matter, the size of the problem and the dynamic nature of the manufacturing environment, the manufacturing simulation approach has been chosen as the research vehicle to investigate the problem considered. The statistical and graphical analysis of the results of simulation experiments have showed that the average throughput time performance measure of a cellular system can be improved to an important degree when the proposed decision rule exploiting the external routing flexibility of the system is implemented. However, the improvement seem to be related to the level of load imbalance, the level of percentage increase in operation time and the level of percentage increase in set up time.

Özet

Hücresel üretim, parti üretimi alanında, atölye tipi üretim karşısında bir seçenek sunmaktadır ve hücresel yerleşim düzeni atölye tipi yerleşimden farklıdır. Her bir üretim hücresi kendine ait parça ailesinin üretim amacı ile fonksiyonel bakımdan farklı makinaların birbirine yakın bir şekilde yerleştirilmesi ile oluşturulur. Düşük üretim içi stoklar ile üretim yapılması ve gruplanan makina kapasitelerinin ürün grupları arasında paylaşılması sonucu makina arızaları, işgücü performansındaki dalgalanmalar, aşırı yüklenme ve özellikle ürün karışımı veya ürünlerin talebindeki değişimlerin neden olduğu yük dengesizliği gibi, beklenmedik içsel ya da dışsal etkiler karşısında hücresel üretim sistemleri hassas ve zayıf konuma düşmektedir. Özellikle ürün karışımı veya ürünlerin talebindeki değişimlerin neden olduğu hücreler arası yük dengesizliği koşulunda faaliyette bulunan hücresel üretim sistemlerinin performansı oldukça kötüleşebilir. Bu çalışmada, geliştirilen bir dışsal rota esnekliğini kullanma kuralının değişen ürün karışımı şartlarında faaliyet gösteren hücresel üretim sistemlerinde uygulanması sureti ile sistem performansının iyileştirilme olanağı incelenmektedir. Konunun karmaşıklığı, problemin boyutu ve üretimin gerçekleştirildiği çevrenin dinamik doğası nedeni ile bu çalışmanın konusu olan problemin incelenmesi için üretim benzetimi yöntemi kullanılmıştır. Benzetim sonuçlarının istatistik ve grafik analizi neticesinde çalışmada geliştirilen rota esnekliğini kullanma kuralının iş akış süresi performans ölçütünde iyileşme sağlayabildiği ve sistem performansındaki bu iyileşmenin çalışmada dikkate alınan yük dengesizliği düzeyi, işlem süresi artış yüzdesi ve hazırlık süresi artış yüzdesi faktörlerinin seviyelerine bağlı olduğu belirlenmiştir.