Stations In Assembly Line Research Articles

Developing a metaheuristic model for the general assembly line balancing optimization based on a new workforce performance index: a case study in the garment industry

In garment industries, it is very important to assign fairly workers and tasks to the stations of an assembly line while the precedence relations and resource constraints are satisfied. Many objectives were treated to optimize the working group selection, but consider objectively the workers skills to judge the balancing effectiveness are still non-existent. This paper proposes a new approach for solving the Assembly Line Balancing Problem with workers’ competence hierarchical assignment using the ant colony optimization. According to this approach, the workforce’s performance index is appreciated with a global Competence Index ‘CIg ’ developed on the basis of measurable criteria to rank hierarchically the workers. The global Competence Index ‘CIg ’ is designed integrating 3 objective criteria: global Quality index ‘QIg’, global Activity degree ‘Ag’ and global Attendance Rate ‘ARg’, which are related to 3 parameters expressing, respectively, the work quality degree, the labour efficiency level and the assiduity for a working group. The global Competence Index is considered as a new ‘objective function’ for the ant colony optimization algorithm called ‘ACO−CIg ’. The aim is to find the best solution assigning workers and tasks to an assembly line stations so that the global competence index is maximized. The results showed that the algorithm implementation was useful in real manufacturing process dealing with hierarchical workforce assignments in a reasonable time and allowing to select the best balancing solution, hence, to predict and control the production line’s performance.

A bi‐objective ergonomic assembly line balancing model with conic scalarization method

AbstractThe most important factor affecting efficiency and ergonomic risk levels in an assembly line design is the problem of assigning certain tasks to certain stations, namely the assembly line balancing problem. In the literature, assembly line balancing problem has often been studied, but studies that consider ergonomic risks are deficient. Recently, it has been one of the issues that have started to attract great attention with the realization of health problems caused by assembly lines. To this end, in this study, a bi‐objective mathematical model is developed that considers balancing assembly line station time and ergonomic risk levels, simultaneously. It is aimed to minimize both station time and the total deviations of ergonomic risk scores for the stations. Weighted sum and conic scalarization methods are applied to solve the bi‐objective model. To analyze the outcomes of the developed model, an application is proposed and tested on a real industrial case, at a home appliance assembly line. The deployment of the OMAX method is a contribution to the literature since it shows an analysis tool which evaluates the results of assembly line balancing. This method evaluates the performance of the stations based on different criteria such as station time and ergonomic risk. The number of high‐risk stations is obtained as 13 in the single‐objective model aiming to minimize the station time, while it is found to be nine in the bi‐objective model solved with CSM, without an increase in the total number of stations.

Heterogeneous-vehicle distribution logistics planning for assembly line station materials with multiple time windows and multiple visits

Aiming at distribution logistics planning in green manufacturing, heterogeneous-vehicle vehicle routing problems are identified for the first time with multiple time windows that meet load constraints, arrival time window constraints, material demand, etc. This problem is expressed by a mathematical model with the characteristics of the vehicle routing problem with split deliveries by order. A hybrid ant colony optimization algorithm based on tabu search is designed to solve the problem. The search time is reduced by a peripheral search strategy and an improved probability transfer rule. Parameter adaptive design is used to avoid premature convergence, and the local search is enhanced through a variety of neighborhood structures. Based on the problem that the time window cannot be violated, the time relaxation rule is designed to update the minimum wait time. The algorithm has the best performance that meets the constraints by comparing with other methods.

Assembly line balancing for personalized production

Assembly line balancing problems aim to an efficient and effective assignment of all the required tasks to workstations in a flow oriented production system. Nowadays, assembly lines have to face the manufacturing of extremely personalized products (e.g. cars) as requested by an increasingly higher portion of the market demand. Several literature contributions focus on different balancing problems affected by the wide variety of the final product, e.g. mixed and multi model assembly lines. However, no contribution seems to tackle the personalized production of goods. Such products require to assemble a certain number of tasks whatever the final product personalization is, and a variable number of optional of different type determined by the specifications of every single costumer. This paper faces the generalized assembly of personalized goods proposing an innovative two step methodology to optimize the workload balancing between the assembly line stations, considering traditional tasks and the optional required by the product personalization, which could occur with different frequencies and pairings. The first phase of the developed methodology executes a clustering of product options required by the costumers based on a similarity index. This phase leads to the definition of several sets of optional typically requested together by the customer and with similar mounting time. The methodology second phase leverages the defined clusters of optional. Indeed, optional of the same cluster shouldn’t be assigned to the same workstation to reduce the overload or underload of the assembly operators. An integer programming model is proposed to assign both traditional tasks and optional to stations, to maximize the assembly line balancing considering the order frequency and assembly time of the clusterized optional. An industrial case study is adopted to test and validate the proposed two steps methodology. The obtained results highlight a consistent time balancing between assembly line workstations and a significant limitation of the operator overloads.

A Problem Specific Heuristic for Smoothing the Workload in Simple Assembly Lines

Workload smoothing techniques have been used to establish a balance among stations in assembly lines by assigning the tasks evenly to stations. Smoothing facilitates planning the workforce and optimizing the resource allocation problems. Considering these advantages, we address smoothing simple assembly line in this research and develop a problem specific heuristic algorithm to solve the large instances effectively. We test the effectiveness of the algorithm with experimental study.

Human factors’ complexity measurement of human‐based station of assembly line

AbstractCognitive heterogeneity causes operation time variability and high human error rates at human‐based stations of assembly lines. It will affect the performance of the production activities, the design process of which depends on reliable estimate of operation time. To quantify operator cognition, we measured the human factors’ complexity of human‐based stations using an information entropy approach in aspect of operation time. Initially, the influence of the operators’ cognition on the operation time is analyzed. Based on the analysis, the operation time model that considers cognition is presented. Then, the operation time model is modified by applying a correction method using the behavior correction factor, and, finally, the human factors’ complexity measurement model is built. A case study is used to illustrate the application of the proposed method in order to measure the influence of human cognition on the performance of the human‐based station.

Scheduling of Multiple Autonomous Guided Vehicles for an Assembly Line Using Minimum Cost Network Flow

This paper proposed a parallel automated assembly line system to produce multiple products having multiple autonomous guided vehicles (AGVs). Several assembly lines are configured to produce multiple products in which the technologies of machines are shared among the assembly lines when required. The transportation between the stations in an assembly line (intra assembly line) and among stations in different assembly lines (inter assembly line) are performed using AGVs. Scheduling of AGVs to service the assembly lines and the corresponding stations are purposed. In the proposed problem the assignment of multiple AGVs to different assembly lines and the stations are performed using minimum-cost network flow (MCF). It optimizes weighted completion time of tasks for each short-term window by formulating the task and resource assignment problem as MCF problem during each short-term scheduling window.

Design and Optimization of Core Assembly Line for Turbo Charger

This study investigates ‘Manufacturing design for productivity’ surveying a case study of an existing assembly line for Turbo charger Core. The main aim is to investigate the possibilities of operational improvement by reducing number of stations in assembly line in a cost-effective manner by reducing the number of grippers used in complete assembly layout. An assembly line is selected for the case study. An existing assembly is redesigned by using the concepts of methods engineering. Then both cases are analyzed and discussed in terms of their output ability and manufacturing time. After the analysis of redesigned assembly layout it is observed that we can reduce average Operation time by 15 % at the end of this study. At the end of this project, we increased the production quantity from 824 to 955 products. Because efficiency of station work has increased with the redesigned assembly line with aid of dual arm robot. The new assembly line reduces the station idle time and increases its efficiency in operation. The existing assembly line was covering 8 m2 it got reduced to 4 m2 approximately in optimized layout. It is observed 15.89% productivity increased for the same period of time. By the standardization and the elimination of the station operations, and reducing the labor cost the company could increase its competitive strength through the optimized layout design.

Parallel autonomous guided vehicle assembly line for a semi-continuous manufacturing system

Purpose This paper aims to propose a parallel automated assembly line system to produce multiple products in a semi-continuous system. Design/methodology/approach The control system developed in this research consists of a manufacturing system for two-level hierarchical dynamic decisions of autonomous/automated/automatic-guided vehicles (AGVs) dispatching/next station selection and machining schedules and a station control scheme for operational control of machines and components. In this proposed problem, the assignment of multiple AGVs to different assembly lines and the semi-continuous stations is a critical objective. AGVs and station scheduling decisions are made at the assembly line level. On the other hand, component and machining resource scheduling are made at the station level. Findings The proposed scheduler first decomposes the dynamic scheduling problems into a static AGV and machine assignment during each short-term rolling window. It optimizes weighted completion time of tasks for each short-term window by formulating the task and resource assignment problem as a minimum cost flow problem during each short-term scheduling window. A comprehensive decision making process and heuristics are developed for efficient implementation. A simulation study is worked out for validation. Originality/value Several assembly lines are configured to produce multiple products in which the technologies of machines are shared among the assembly lines when required. The sequence of stations is pre-specified in each assembly line and the components of a product are kept in machine magazine. The transportation between the stations in an assembly line (intra assembly line) and among stations in different assembly lines (inter assembly line) are performed using AGVs.

Detection of Nut Welding Using Poka-Yoke Roller Coaster Jig

This paper describes the proposal of Poka Yoke Roller Coaster (PKYC) jig as a device to detect nut weld missing of door patch base line model (BLM) at assembly line station. The PKYC was proposed in order to detect nut weld missing problem and to reduce cycle time and manpower that lead to higher cost by applying quality management concept as a problem-solving tool. This special purpose tool was capable to meet specific job based on industrial need by providing repeatability, interchangeability and accuracy in the manufacturing of products. A Quality Control (QC) approachcalled the Zero Quality Control (ZQC) was used to achieve zero defects at production line. In order to reach zero defects, poka yoke method was applied in this research. Outcomes indicate that PKYC can be utilised as a custom-tailored jig for detecting nut weld missing as well as fulfilling other objectives.

Dynamic material flow control in mixed model assembly lines

This study investigates the control of material flow in mixed model assembly lines. It focuses on the use of tugger trains to feed stations in assembly lines by materials and parts from a warehouse or a supermarket. The movement of tugger trains is based on the principle of in-plant milk run. The study considers a strategy to deal with disturbances such as machine breakdown, line stoppage, defective parts, and resequencing of product models. These disturbances lead to unexpected fluctuations in stations demand for parts. The strategy is applied using a mix between the demand-oriented and e-kanban systems to facilitate the planning of three problems, namely, train routing, scheduling, and loading. The information obtained using e-kanban is combined with the information about the expected stations demand based on previously known sequence of product models and the materials needed for each model. Routing was investigated analytically while scheduling and loading problems were investigated using integer programming. Results showed that the method proposed outperforms the traditional methods of material flow planning.

P-1470 - Organizational stresses of women manufacturing workers

In the light of global industrialization, much attention has been focused on occupational factors and their influence on the health and welfare of workers. This was a cross sectional study using stratified sampling technique based on industry sizes. The study sampled 24 industries, 6 were small scale industries and 9 each for medium and large scale industries. Among the 500 respondents, majority were female (88.8%), single (69.6%) and worked in the production or assembly-line station (87.4%). For females, the most prevalent hazards were exertion involving back (76.2%), excessive work (69.3%), heat (66.9%), poor ventilation (56.6%), and chemical exposure (52.4%). Sickness absenteeism was relative high among the workers in this study accounting for almost 54% among females and 48% among males. Many of the workers also reported of poor performance at work, boredom, tardiness and absenteeism. From the data generated, important issues that must be dealt with in work organizations include the quality of work life, and health and safety issues. Based on these findings, we can conclude that there are still issues on occupational health and safety (OHS) in the target site of export processing zones in the Philippines. There must be an active campaign for OHS in industries that are produce for the global market such as the target industries in this study.

Bi-directional work sharing in assembly lines with strict and flexible assembly sequences

Work sharing between stations in assembly lines can reduce cycle time and improve throughput rate. This research addresses assembly lines in which tasks may be shared with their immediate upstream or downstream stations only. This study consists of three stages. In the first stage, we assume that all work content in the line can be shared. Then, the balanceability of the line, which is defined as its ability to achieve a perfect balance (identical workload in all workstations) via work sharing, is examined. An algorithm and a linear programming formulation is proposed to provide the sharing proportion, namely, the percentage of the cycles each station performs the shared task. In the second stage, a line with partial sharing is investigated; conditions for balanceability are provided as well as a solution approach for obtaining the sharing proportions of the shared tasks. The last stage considers the most practical model in which sharing costs are involved, and the identity of the shared tasks is to be determined. Mixed-integer linear-programming models and a custom-made search algorithm are developed to minimise the cycle time given a limited sharing budget, for strict and flexible assembly sequences. Experimentation to evaluate the performance of the formulations and the effect of the problem parameters on the run time is conducted.

The use of dynamic work sharing production methods to reduce the impact of labour turnover in serial assembly lines

Labour turnover is one of the major complications that industry faces on a daily basis. Turnover is particularly harmful to serial assembly lines. The learning process that a new operator must undergo when first introduced to an assembly line station generates blockage and starvation in the previous and successive stations, causing a reduction in the line’s throughput. In this paper, we analyse different work allocation strategies for serial assembly line designs in order to determine which designs perform best under the presence of labour turnover and a task-learning process. In particular, we compare the traditional balanced line with two other assembly line designs, a variant of the bucket brigades (BB) and a hybrid method – the modified work sharing (MWS) method. By making a judicious use of control buffers, the MWS method seeks to combine the positive characteristics of both the BB and traditional balanced lines to naturally adapt to different levels of labour turnover. The results presented in this paper show that the MWS outperforms the BB and the balanced designs.

Product quality and plant build complexity

This paper assesses the hypothesis that plant build complexity impacts quality, suggests mechanisms to explain how complexity impacts quality, and offers countermeasures to mitigate this impact. We analyse automotive assembly data that supports the proposition that plant build complexity negatively impacts quality. In addition, this paper provides actual automotive assembly line work instructions and shows how they can be represented by the Gilbreths’ fundamental work elements and plant build complexity impacts these work elements. To highlight complexity's adverse impact on quality, we compare the actual work instructions at two automotive assembly line stations–one with very little complexity and one with extreme complexity. We list common automotive assembly quality lapses and describe how they can be caused or exacerbated by complexity. Finally the paper presents practical countermeasures to mitigate complexity's impact on quality. While based on the automotive industry, the lessons apply to all complex assembly lines.

Manufacturing Work and Organizational Stresses in Export Processing Zones

In the light of global industrialization, much attention has been focused on occupational factors and their influence on the health and welfare of workers. This was a cross sectional study using stratified sampling technique based on industry sizes. The study sampled 24 industries, 6 were small scale industries and 9 each for medium and large scale industries. From the 24 industries, a total of 500 respondents for the questionnaire was taken. For occupational health and safety standards that industries have to comply with, there was low compliance among small-scale industries relative to the medium and large scale industries. Only one industry had an air cleaning device for cleaning contaminated air prior to emission into the external community. Among the 500 respondents, majority were female (88.8%), single (69.6%) and worked in the production or assembly-line station (87.4%). Sickness absenteeism was relative high among the workers in this study accounting for almost 54% among females and 48% among males. Many of the workers also reported of poor performance at work, boredom, tardiness and absenteeism. For association between work factors and personal factors, the following were found to be statistically significant at p=0.05. Boredom was associated with lack of skills training, lack of promotion, disincentives for sick leaves, poor relationship with boss and poor relationships with employers. On the other hand, poor performance was also associated with lack of skills training, lack of promotions, job insecurity, and poor relationship with employers. From the data generated, important issues that must be dealt with in work organizations include the quality of work life, and health and safety issues. Based on these findings, we can conclude that there are still issues on occupational health and safety (OHS) in the target site of export processing zones in the Philippines. There must be an active campaign for OHS in industries that are produce for the global market such as the target industries in this study.

An Evolutionary Algorithm for Sequencing Production on a Paced Assembly Line

A new sequencing method for mixed‐model assembly lines is developed and tested. This method, called the Evolutionary Production Sequencer (EPS) is designed to maximize production on an assembly line. The performance of EPS is evaluated using three measures: minimum cycle time necessary to achieve 100% completion without rework, percent of items completed without rework for a given cycle time, and sequence “smoothness.” The first two of these measures are based on a simulated production system. Characteristics of the system, such as assembly line station length, assembly time and cycle time, are varied to better gauge the performance of EPS. More fundamental variation is studied by modeling two production systems. In one set of tests, the system consists of an assembly line in isolation (i.e., a single‐level system). In another set of tests, the production system consists of the assembly line and the fabrication system supplying components to the line (i.e., a two‐level system). Sequence smoothness is measured by the mean absolute deviation (MAD) between actual component usage and the ideal usage at each point in the production sequence.The performance of EPS is compared to those of well‐known assembly line sequencing techniques developed by Miltenburg (1989), Okamura and Yamashina (1979), and Yano and Rachamadugu (1991). EPS performed very well under all test conditions when the criterion of success was either minimum cycle time necessary to achieve 100% production without rework or percent of items completed without rework for a given cycle time. When MAD was the criterion of success, EPS was found inferior to the Miltenburg heuristic but better than the other two production‐oriented techniques.

Optimizing the number of stations in assembly lines under learning for limited production

This paper considers finding the optimal number of stations for an assembly line producing a limited quantity of a new product under learning conditions. This type of production characterizes heavy products (such as airplanes and communication systems) and science-based industries (e.g. laser cutting devices and special equipment for hospitals). These products are manufactured in assembly line fashion in small batches of a few hundred. Since the products are assumed to be totally new to the workers, the learning phenomenon is significant (i.e. task times decrease from cycle to cycle as experience is gained). Therefore, standard balancing methods are no longer applicable. Determining the number of stations has a large effect on the production rate while the actual assignment of tasks to stations helps to fine tune the cycle time. Thus, the number of stations can be regarded as a strategic decision variable . This paper discusses two ways for determining the optimal number of stations, namely as a cost minimization problem and as a profit maximization problem.

A comparative analysis of sequencing procedures for mixed-model assembly lines in a just-in-time production system

In this paper several procedures for sequencing products on a mixed-model assembly line in a just-in-time production system are statistically compared using simulation analysis. The procedures include two 'goal chasing' heuristics developed at Toyota that focus on constant component usage, an algorithm developed by Miltenberg designed to achieve uniform production rates for each model, a time spread method developed by the authors that smooths the work load at each assembly line station, and the familiar batch sequencing procedure frequently used in practice. These five sequencing procedures are evaluated according to four measures of assembly line inefficiency, work not completed, worker idleness, worker station time and a measure of variability in uniform component usage. The results provide assembly line managers with guidelines for selecting the most effective sequencing procedure for achieving their operational objectives.

Optimal distribution of technological operations on an assembly line

A mathematical formulation is proposed for optimal assignment of technological operations to assembly line stations. The properties of feasible and optimal solutions are investigated. Algorithms for the solution of the relevant problems are given.