What is a heuristic name and explain several that can be used in assembly line balancing

An assembly line is generally used for mass production and has been a matter of concern of researchers for a long time. A straight line balancing may be defined as processes of assigning tasks to the workstations in such a manner that all workstations have approximately the equal amount of work assigned to them. During assignment of the tasks to the workstations precedence relations among these tasks should not be violated. Many heuristics have been reported for the assembly line balancing (ALB) (Chiang & Urban, 2006).

In recent years, many manufactures have adopted Just-in-Time (JIT) approach for manufacturing, as it is capable to improve productivity, profits and product quality. JIT is beneficial for companies that are engaged in job shop, repetitive types of jobs and process manufacturing. An important change resulting from JIT implementations is the replacement of the traditional straight lines with U-shaped production lines (Aase, Olson, & Schniederjans, 2004).

The U-shaped assembly line has become an amicable alternative for assembly production system since operator may perform more than one task located to different places of assembly line. Moreover, the U-type line disposition allows for more possibilities on how to assign the tasks to the workstations therefore the number of workstations needed for a U-shaped line layout is never more than the number of workstations needed for the traditional straight assembly line. In the traditional ALB, for a given cycle time (the time interval between two successive outputs), the set of possible assignable tasks is confirmed by those tasks whose predecessors have already been assigned to workstations, whereas in the U-type line balancing problems, the sets of assignable tasks is determined by all those tasks whose predecessors and successors have already been assigned (Liu, Ong, & Huang, 2003).

One of the important characteristics that make U-shaped assembly lines different from straight assembly lines is that the entrance and the exit of these lines are at the same position (Monden, 1993). Products enter the U-shaped assembly line at the front-side and exit from the back-side of the line. The lengths of front-side and back-side of the U-shaped assembly line are equal and operators work inside of the U-shaped assembly line. Studies on U-shaped assembly lines provide evidence for their potential to improve visibility and communication skills between operators, reduce operator requirements, increase quality, reduce work-in-process inventory, and facilitate problem-solving and efforts to adjust to changes in the external environment of the firm (Aase et al., 2004, Kara et al., 2011, Miltenburg, 1998, Miltenburg, 2001). Cheng, Miltenburg, and Motwani (2000) have listed the following factors that enhanced the wider acceptance of U-shaped lines:

Volume flexibility: The production rate of a line in a JIT environment changes frequently. In such an environment, a U-shaped is preferred to a straight line because of its volume flexibility. By increasing or decreasing the number of operators on the line, a company can adjust the production rate as required. This level of volume flexibility is harder to obtain with a straight line.

Operator flexibility: Since walking distance is shorter in a U-shaped than on a straight line, it is easier for an operator to oversee on several work station.

Number of workstations: The number of workstations required for a U-shaped is never more than, that required on a straight line. There are more possibilities for grouping tasks into workstations on a U-line.

Material handling: A U-line eliminates the need for special material-handling equipment such as conveyors and other special material-handling operators those are necessary in straight line. Instead, production operators move products from machine to machine.

Visibility and teamwork: In a straight line layout operators are spread out along a long line and may be separated by walls of inventory. The compact size of a U-line improves visibility and communication. This enhances teamwork, gives a sense of belonging, and increases responsibility and ownership compared to a straight line.

Rework: In a U-line, the distance to return the defective product is short. It is easier to correct a quality problem quickly by returning a defective product to the station where product was produced. This is in contrast to the traditional policy of sending the defective product to a separate rework area.

In this paper an analysis of labor productivity for U-shaped line and traditional straight has been carried out using bi-directional assignments and with a CPM based approach. In Section 2, the relevant literature has reviewed, while Section 3 depicts precise description of the U-shaped and traditional straight-line layout. In Section 4, the applied approach has been described and in Section 5 a practical example and computational results have been shown with the conclusion in Section 6.

Literature review

Assembly line balancing problem has become a matter of concern for academicians and researchers for a long time. Many heuristics, exact algorithms and optimization techniques have been deployed for the assignment of the tasks to workstations. However, majority of the past studies has been focused on the traditional straight assembly line layouts.

Baybars (1986) has developed a single pass heuristic for single-model deterministic line balancing, for different priority rules. Gokcen, Agpak,

U-shaped and traditional straight-line layout

Manufacturing of a product needs the completion of a set of tasks. Each task has a processing time and a distance that is the amount of space the task occupies on the line. The order in which tasks may be completed is constrained by a set of precedence relations that reflect technological requirements for production of a product. The work content in a station is the total time an operator requires travelling to the locations of the tasks and processing them. The maximum work content of a

Proposed heuristic

The proposed heuristic is a modification of the heuristic that was proposed by Yeh and Kao (2009). In case of heuristic proposed by Yeh and Kao (2009), the tasks can be assigned to different workstation from both ends of the assembly line on different workstations and these tasks cannot be assigned to same workstation from both ends of the line and precedence graph. In case of proposed U-shaped assembly line the tasks can be assigned to same workstation from both ends of the line and precedence

Example and computational results

In this section the procedure of the proposed heuristic has been illustrated by an example and the productivity has been calculated for both U-shaped line and straight line. Fig. 3 shows the precedence diagram of the selected problem having 7 tasks. The nodes represent the task and the arrow represents the direction of process. The number within the nodes represents tasks number or name and the arrow connecting the nodes specifies the precedence relations. The number over the nodes represents

Conclusion

Now a day, U-shaped layouts have been utilized in many assembly lines in place of the traditional straight line. This is just because of the use of just-in time principles in production industries. The U-shaped lines improve visibility and allow the worker to perform tasks on both sides of the line. As compared to straight assembly line, this unique feature of U-shaped line, combined with cross-trained workers and provide much more flexibility in designing of workstation.

The heuristic based on

Cited by (48)

• Econometric modeling of productivity and technical efficiency in the Chilean manufacturing industry

  2020, Computers and Industrial Engineering

  Therefore, the objective of this study is to propose and derive, within the context of “Industry 4.0”, an econometric model for the Chilean manufacturing sector and, simultaneously, to suggest an alternative method for selecting variables when there is a large set of theoretically appropriate variables for measuring a particular factor. To that end, it is first proposed to determine the variables that best represent the labor and capital factors, which are often considered as important in the manufacturing industry (Avikal, Jain, Mishra, & Yadav, 2013; Zheng et al., 2018). Subsequently, our implementation is based on the results obtained from the proposed model.

• Mathematical model and grey wolf optimization for low-carbon and low-noise U-shaped robotic assembly line balancing problem

  2019, Journal of Cleaner Production

  For mathematical programming approaches, Gökçen et al. (2005) proposed shortest route method; Ogan and Azizoglu (2015) developed branch-and-bound method. For heuristic algorithms, Avikal et al. (2013) designed critical path method; Li et al. (2017) proposed a rules-based heuristic approach. For meta-heuristic algorithms, Özcan et al. (2011), Rabbani et al. (2012) and Rabbani et al. (2016a) developed genetic algorithms; Manavizadeh et al. (2013), Jayaswal and Agarwal (2014) and Roshani and Giglio (2015) proposed simulated annealing algorithms; Zha and Yu (2014) developed ant colony algorithm; Nourmohammadi et al. (2013) designed imperialist competitive algorithm; Nilakantan et al. (2015) proposed particle swarm optimization to balance the U-shaped assembly lines.

• Optimization of workcell layout for hybrid medical device fabrication

  2019, Journal of Manufacturing Systems

  In order to further prove the effectiveness of the proposed MOCO model, these Optimized Layouts, namely L3, will be compared with the more commonly used layouts in the manufacturing world (i.e. the straight line layout and the U-shaped layout). Previous works had proven that U-shaped layouts outperformed the traditional straight line layouts in terms of flexibility, time saving, material handling, operator productivity as well as communication [38–40]. As such, we identify the U-shaped layout as the Semi-Optimized Layout (L2) and traditional straight line layout as the Not Optimized Layout (L1), as part of our evaluation process.

Recommended articles (6)