Research On Balancing Two-sided Assembly Line

The assembly lines have been a major production style and are applied in many fields, including car and electrical industries, etc. since Henry Ford built the first assembly line. With the development of device and technique, the style of assembly line appeared variable, from single-sided assembly line to two-sided assembly line, U-type assembly line and so on. Among them, the two-sided assembly line is used to assembly the large-size product, such as car, loader, etc.The two-sided assembly line have several advantages over traditional single-sided assembly line, including: (1) shorten the line length and reduce the throughout time; (2) enhance the usage rate of devices, tools, etc., lessen the investment cost; (3) reduce invalid work time and idle time, improve assembly workers'production rate and so on. Accompanied with the benefits, appeared several new constraints when balancing two-sided assembly line. The operational direction of task, the sequence-related finished time constraints, and so on, should be taken into account, besides the common constraints, such as precedence relation and cycle time constraints when balancing single-sided assembly line. Hence, the two-sided assembly line balancing problem becomes more complex and needs to develop new balancing technique.The article focuses on two-sided assembly line balancing problem (TALBP), make a full view of the problem, including formulate the mathematical model, bring forth the exact and heuristic methods, the real project application and so on. The main research conclusions are as follows:1,formulate the mathematical model of TALBPThe major difference between with single-sided and two-sided is parallel work. In the two-sided assembly line, workers can assembly parallel at both side stations. Hence, tasks assigned on both side stations can interfere with each other by precedence relation and produce sequence-related finish time constraint, etc. Such factors are not calculated in traditional single-sided assembly line balancing model.A new expression way has been introduced into formulating the mathematical model of TALBP. With a time variable( st i), which means the start time of task i at its allocated station, the tasks'operating sequence and the cycle time constraint can be determined definitely. It gives a solution to avoid calculating the complex sequence-related waiting time. With such solutions, the mathematical model is first built. The model not only gives the formal, concrete description firstly, but also makes the TALBP solved with mathematical method possible.2,bring forth exact algorithms to balance two-sided assembly line optimallyA task-oriented branch-and-bound method is brought forth to balancing the two-sided assembly line optimally. First, the task-oriented enumerated tree, which includes all feasible solutions, is built by designing proper structure for each node of the enumerated tree and makes special treatment with E type tasks. In order to reduce the enumeration effort, several reduction and dominant rules were studied and applied. With the experiment of the benchmark set, the task-oriented branch-and-bound algorithm show favorable performance, mostly problem can be solved optimally, among them, four cases are first solved optimally.A station-oriented branch-and-bound algorithm is also brought forth. Since the station arrangement between both sides interfere with each other, it is hard to enumerate all possible arrangements for single side station through precedence relation directly, such as applied in single-sided assembly line balancing. Hence, a time transfer function, which utilizes the precedence relation indirectly, was studied to construct the station solutions. And the station-oriented enumeration is realized with such method. The algorithm is also verified with the benchmark set, the result is favorable. Especially for those problems, whose optimal solutions do not open all the both side stations can be solved more quickly. Furthermore, two more problems are first solved optimally.3,bring forth a sequenced-based, combined coding genetic algorithm for large-size problemsA genetic algorithm, which calculated the special feature of two-sided assembly line balancing, was proposed. In this algorithm, a sequenced-based, combined coding scheme was adopted, which can solve the problem of solution space missed when adopted station-based coding scheme; the corresponding genetic operators were designed, which made the genetic algorithm only explored in the feasible space. With the experiment of up to 205 tasks'two-sided assembly line balancing problems, the results show that the genetic algorithm outperformed other heuristic methods.A practical ZL50F loader assembly line balancing problem was also solved by this genetic algorithm. If keeping the original cycle time (750s) constantly, a solution with one station less than original scheme can be found. If keeping the line length and number of stations constantly, a solution with minimal cycle time (660s) can be reached, the assembly line efficiency increased from original 79% to 91%.