Ergonomik etmenler dikkate alınarak montaj hatlarında dengeleme yapılması ve bir fabrika uygulaması
Assembly line balancing problem by considering the ergonomic factors and a factory application
Yazar: KERİMAN GİZEM GÖRGÜLÜ
Danışman: DOÇ. DR. MURAT BASKAK
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Endüstri Mühendisliği Ana Bilim Dalı / Endüstri Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2019
Konu: Endüstri ve Endüstri Mühendisliği = Industrial and Industrial Engineering

Özet:
Yaşadığımız yüzyılda çoğalan nüfusa paralel olarak tüketim mallarına olan talep hızla artmaktadır. Bu nedenle arzın karşılanabilmesi için kitle üretimine yönelmek kaçınılmazdır. Kitle üretimi ise ancak iş gücünün etkin şekilde dağıtılması ile olanaklıdır. Bunun sonucu olarak montaj hatları kavramı ortaya çıkmıştır.
Montaj hatları bir ürünü oluşturmak üzere o ürünün parçalarının, bir akış hattı boyunca insan ve/veya makina yardımı ile birleştirilmesi sonucu oluşturulan üretim sistemleri olarak tanımlanabilir. Montaj hatlarının kurulması ve bakımları, işletmeye ciddîbir mâliyet yaratmaktadır. Bu nedenle montaj hatlarının dengelenmesi yâni bir başka ifâde ile hattaki boş zamanın enküçüklenmesi ile montaj hatları etkin bir şekilde çalışabilmektedir. Dolayısıyla montaj hatlarındaki en önemli unsur montaj hatlarının dengelenmesi işleminin yapılmasıdır.
Montaj hattı dengeleme problemi, literatürde birçok araştırmacı tarafından irdelenmiştir. Bununla birlikte yapılan çalışmaların pek azında insan etmeni dikkate alınmıştır. İnsan etmeninin ilk sırasında ise ergonomik kısıtlar gelmektedir. Ergonomik kısıtlar, işlerin insan fizyolojisinin uygunluğuna göre iş istasyonlarına atanmasını sağlamaktadır. Dolayısıyla yapılan çalışmaların birçoğunda sözkonusu ergonomik kısıtlar gözardı edildiği için, elde edilen sonuçlar gerçek durumu yansıtmamaktadır.
Yapılan bu tez çalışmasında ergonomik etmenler dikkate alınarak bir montaj hattının dengelenmesi irdelenmiş ve gerçek veriler kullanılarak bir fabrika uygulaması yapılmıştır. Bu amaçla öncelikli olarak üretim ve montaj hattı dengeleme ilkeleri incelenmiştir.
Çalışmanın sonraki aşamasında, montaj hatlarının dengelenmesine yönelik kavramlar ayrıntılı olarak irdelenmiştir. Montaj hatlarının dengeleme yöntemlerinin sınıflandırılması yapılmış ve literatürde yer alan sayısal örnekler uygulamalı olarak gösterilmiştir.
Çalışmanın üçüncü kısmında ise, ergonomik etmenler altında montaj hattı dengeleme ile ilgili literatür araştırmaları yapılmıştır. Bu amaçla literatürde bulunan ergonomik risk düzeyi yöntemleri incelenmiştir. Ayrıca gözleme dayalı sayısal örneklere yönelik uygulamalar da verilmiştir.
Yapılan çalışmanın son aşamasında, halihazırda üretim yapılan ArçelikÇayırova Çamaşır Makinası işletmesindeki gövde grubu montaj hattında sayısal uygulama yapılmıştır. Bu amaçla GAMS programı ve CPLEX çözücüsü kullanılarak sözkonusu hattın ergonomik koşulları dikkate alınarak hat dengelemesi yapılmıştır. Elde edilen sonuçlar, ergonomik koşullar dikkate alınmadan yapılan montaj hattı dengeleme sonuçları ile karşılaştırılmıştır.

Abstract:
In parallel with the increase in population in the present century, demand on consumer goods is also rapidly increasing. It is therefore inevitable to turn towards mass production in order to meet this demand. Mass production is possible only by distributing the workforce in an effective way by using the concept of assembly lines.
An assembly line can be defined as a production system established to assemble the parts of a product with the help of manpower and/or machines through a flow line in order to create the product. On the other hand, construction and maintenance of these assembly lines result in high costs for factory. 
For this reason, the assembly lines can be effectively operated by solving the assembly lines balancing problems, i.e. minimizing the idle time. Otherwise, a non balanced line cause a loss of production and also cost will increase rapidly. Therefore, primary problem for the management of assembly lines is balancing of the assembly line
The assembly lines balancing problem is deeply studied by many researchers in the literature. Studies are focused on minimizing the number of stations and/or decreasing the cycle time. However, human factor was not taken into consideration during these studies except for a few ones. For this reason, the results obtained do not reflect the truth as these ergonomic factors are usually neglected in most of the studies.
The first aspect of the human factor is ergonomic factors. Ergonomic factors enable the distribution of tasks to the working stations in accordance with the human physiology. Repetition of the similar jobs by the same workes along the assembly line increases the pressure on the employee and also the probability of the defective manufacturing. 
In addition, working on assembly line that is not balanced in terms of ergonomic factors increase the occupational diseases. Therefore, ergonomic constraints should be taken into consideration during the assembly line balancing problem. Thus, assembly line balancing including the ergonomic constraint is not only increases the efficiency of worker on assembly line but also makes cost saving. 
In this study, balancing of an assembly line was investigated. During the study ergonomic constraints are taken into consideration. In addition, a factory application was realized using real-time data to obtain the assembly line balancing problem including ergonomic constraints for the real life application in order to analyse the problem more realistic.
Definition of the production and assembly lines principles were given in the first part of the study. In this regard, production can be defined as a set of activities that enable the creation of products and/or services to meet the requirements of society. Production systems can be generally divided into two main groups, conventional and modern. Fitting together the component parts of the product by considering the priority order is called the assembly. Production lines in which assembly processes are conducted, defined as assembly line. 
Productions in automotive, electronics etc. industries are commonly based on assembly lines. For instance, some components of the washing machine manufacturing are thermostat, pump, shock absorbers, main cable groups, motor, capacitor etc. The assembly lines for the production of the washing machine are the lines in which all these main and internal parts assembled on a line (assembly line) to produce the final product.
In the next phase, concepts on assembly line balancing were studied in detail. In this regard, the main issue affecting the cost saving is finalizing the product in assembly line within the minimum time. Therefore, primary problem in assembly line management is to perform assembly line balancing. This can be achieved by grouping of tasks of consecutive workstations.
Constraints such as time, position, priority of process, can be assigned for the assembly line balancing problem. These constraints are effective especially in objective function for assembly line balancing problems. Therefore, it is necessary to assign tasks to the workstation optimally by considering the certain constrains in assembly line balancing problem.
Categorization of assembly lines balancing problem methods was also performed and numerical examples from the literature were investigated in second phase of this study. In this regard, an integer programming algorithm and ranked positional weight technique for assembly line balancing problem is examined. 
In the third phase, literature research related to the assembly line balancing problems considering the ergonomic factors was conducted. Accordingly, methods of ergonomic risk levels in the literature were studied. In this regard, Occupational Repetitive Actions Index (OCRA), Rapid Upper Limb Assessment (RULA), Rapid Entire Body Assessment (REBA) etc. are the main methods based on simple observation while The Visual Decision Platform (VDP), 3D Match, TRAC, Ergo-Man, Sammie Cad, 3DSSPP, Jack Model, Human Builder Model etc. are the improved observation methods.
In addition, some numerical studies were provided based on observation in third part of this thesis. In these numerical studies, Rapid Upper Limb Assessment (RULA) method and Rapid Entire Body Assessment (REBA) method are taken into consideration and ergonomic scores based on these simple observations are obtained by using the formula defined in this study.
In the final phase of this study, a numerical application was conducted in the Arçelik Washing Machine factory. This factory is located in Çayırova, Kocaeli, Turkey and the production already continues. Therefore, real time inputs such as workstations (totally 51 workstations), processing time and also Rapid Entire Body Assessment (REBA) scores are used for the assembly line problem. Thus, obtained results from assembly line balancing problem reflects the real life application not only more precisely but also more realistic.
First of all, precedence diagram is achieved and thereafter precedence matrix is generated. Secondly, assembly line balancing problem is implemented into the software in order to obtain the results with/without the ergonomic factors.
Assembly line balancing problem including the ergonomic constraints was investigated by using the General Algebraic Modeling System (GAMS) program and the IBM ILOG CPLEX Optimization Studio solver. During the analyses 0-1 integer programming model is used.
Solution of the assembly line balancing problem without ergonomic factors shows that totally 18 workstations is required. The maximum workstation time is obtained as 15.3 second. The maximum REBA score is calculated as 20. On the other hand, assembly line balancing problem is solved also by considering the ergonomic constraints. The total workstation and workstation time is obtained as 18 and 15.3 respectively. The maximum REBA score is calculated as 13 since the ergonomic constraints are taken into consideration during solution.
Performance criteria based on time, REBA score and total are also investigated during the analyses. Moreover, sensitivity analyses are also performed. Results were compared with the results of the assembly line balancing without considering the ergonomic constraints.
According to the obtained results, totally 51 tasks are assigned to the 18 workstations. Time performance of the assembly line is achieved as 9.38%. REBA performance of the assembly line is calculated as 45.73% for the problem not considered the ergonomic constraints and 26.92% for the problem based on ergonomic constraints. The total performance criteria is obtained as 27.55% and 18.15%, respectively for the problem not considered the ergonomic constraints and the problem based on ergonomic constraints. The results show the increasing in performance criteria.
The following studies may expand the research by implementing the other methods such as RULA or OCRA instead of REBA score for the ergonomic constraints. In addition, the effect of increasing the tasks in assembly line balancing problem can be investigated. Moreover, parallel lines can be taken into consideration during analyses. Assembly line balancing problem can be investigated not only for the minimizing the number of workstation but also minimizing the cycle time and also increasing the line efficiency in future studies.