Sequence Of Workstations Research Articles

General multi-state rework network and reliability algorithm

A rework network is a common manufacturing system, in which flows (products) are processed in a sequence of workstations (nodes), which often results in defective products. To improve the productivity and utility of the system, the rework network allows some of the defective products to go back to the “as normal” condition after the rework process. Since 2017 [1, 2], the traditional study proposed an algorithm to correct more than 21 archive publications regarding the rework network reliability problem, which is an important real-life problem. In addition to traditional research, we provide an accurate general model based on the novel state distribution with a smaller number of limitations. Furthermore, we propose an algorithm to calculate the reliability of the multi-state rework networks using the proposed novel state distributions.

Optimisation of line configuration and balancing for reconfigurable transfer lines considering demand uncertainty

Reconfigurable transfer lines (RTLs), which are highly responsive to demand fluctuations, have gained increasing attention. This research deals with the line configuration design and balancing problem of RTLs under uncertain demand where line configuration can be changed to satisfy a given demand with minimum cost. It is assumed that the demand of a single product is in interval form. Such RTL is composed of a sequence of workstations and each workstation consists of several identical CNC machining centres. The RTL production capability could be adjusted by adding/removing machines or overtime work. The line configuration and balancing decision is to determine the number of workstations, specify the set-up and the number of machines in each workstation, then assign operations to workstations with various constrains satisfied. Interval optimisation theory is introduced to cope with demand uncertainty. A two-stage optimisation model is developed to handle the primary RTL design and the necessary system reconfiguration. A heuristic algorithm based on greedy randomised adaptive search procedure combined with variable neighbourhood search is given for operation assignment. An industrial case study is carried out and multiple near-optimal solutions are obtained. The feasibility and effectiveness of the proposed method is verified by the comparison of computational experiments.

Implementation of an Overall Design of a Flexible Manufacturing System

Abstract In this study, an implementation of the design of an FMS is performed to calculate necessary number, utilization and sequence of workstations and plant layout for given production quantities of different parts, processing sequence and times. Analytical bottleneck model and rank order clustering techniques are used in the calculation and analysis of the system. Manufacturing cells are constituted for similar parts to simplify the analysis of the system and to efficient use of workstations. Results are compared with the conventional manufacturing conditions to determine the effectiveness of the implementation.

Balancing reconfigurable machining lines via a set partitioning model

We consider the problem of constructing an optimal machining line as a sequence of workstations performing specific sets of operations. The line is required to satisfy the given precedence order on operations, inclusion, exclusion and accessibility constraints. The cycle times of workstations are computed taking into account the processing and sequence dependent set-up times of operations and must not exceed the given bound. For solving the problem, we propose a reduction of this machining line design problem to a set partitioning type problem. This approach implies generating all possible workstations and, for each workstation, solving a scheduling problem in order to find the sequence of operations which minimises the total set-up time. To do this, a dynamic programming algorithm is developed. Several preprocessing procedures are suggested to reduce the number of workstations. A set of exact algorithms are proposed to solve the obtained set partitioning type problem: a constraint generation, a branch and cut, and a parallel branch and cut algorithms. Our experimental investigation demonstrated that the proposed method achieves a significant improvement in CPU times over those required by a previous study that is based on a different model formulation, and also, that the proposed method is able to solve large-sized problem instances.

Assembly Line Balancing in Manufacturing Processes: Using Simulation Model

Assembly line design is an important part of the production system in manufacturing processes. An assembly line, which consists of a sequence of workstations, is an efficient method of manufacturing high-volume products such as automobile parts and microcomputers. In designing an assembly line, it is common practice to "balance" the line so that a more uniform flow is maintained. The Assembly Line Balancing (ALB) scheduler evaluates the effect of the different online sequence of parts on production cycle, balances workload and utilization ratio, minimizes span of the assembly line. The simulation model approach in this study to obtain the scenarios which are reducing the unbalancing time. The simulator presented herein, named Assembly Line Simulator (ALS), can be used as supporting tool in finding solutions of the assembly line balancing problem. Throughout the scenarios of the optimum method will be chosen which scenario is represented minimum idle time it will be the optimum balance of the assembly line.

Integrated Decision Making in Flow Line Balancing

A flow line consists of a sequence of workstations through which one or more products move one way in order to be processed. Designing such a line represents a long-term decision problem involving different crucial decision stages, often solved iteratively because of their complexity. Line balancing problem is one of them; it mostly deals with assigning the set of indivisible units of work (named tasks or operations) to a sequence of lineally ordered workstations. In this paper, we present a brief overview of flow lines balancing problems recently appeared in the literature, which try to expand the core optimization problem dealing with assigning tasks by solving it jointly with other decision problems, such as process planning, configuration design or detailed line scheduling. In spite of the fact that, previously, the most attention was paid for the balancing problems concerning the assembly systems, the approaches and formulations of flow line balancing in machining environment are analyzed as well.

A reactive GRASP and Path Relinking for balancing reconfigurable transfer lines

A line balancing problem for reconfigurable transfer lines with sequence-dependent setup times and parallel machines was studied. These lines are paced and serial, i.e. a part to be machined passes through a sequence of stations. Stations are composed of CNC (Computer Numerical Control) machines. At least one CNC machine is installed at each station. These CNC machines are mono-spindle head machines, hence setup times between operations have to be taken into account. The origins of setup times are various, for example, the necessity to rotate the part, change and displace the tool, etc. Because of setup times, the station workload depends on the sequence in which the operations are assigned to the station. In addition, accessibility constraints have to be considered. The objective consists of assigning a given set of operations as well as machines to a sequence of workstations in order to minimise the total cost of the line. Keeping in mind the industrial importance of this problem and the lack of available methods in the literature tackling it efficiently, we propose a new heuristic based on GRASP combined with Path Relinking. A MIP approach is used to select the sequences of operations on workstations. Numerical experiments are presented and show that the proposed heuristic can provide good solutions even for large-sized instances while requiring a computational time that is fully compatible with a practical application. An industrial case study is also described.

Designing of an Assembly Line based on Reliability Approach

The problem of Assembly Line Balancing is to assign a set of tasks to an ordered sequence of workstations without violating the precedence constraints. The efficiency of the line will increase when tasks are more evenly distributed. In general, the efficiency measure(s) should be optimized subject to cycle time restriction and precedence constraints. Under the deterministic setup, efficiency of the system can be measured in various ways. Research works, reported so far, mainly deal with balancing loss as an inverse measure of efficiency. As a result, in earlier works balancing loss has been minimized subject to precedence constraints. In case the work elements are best described in terms of stochastic time, the entire problem has to be addressed with a different measure of efficiency. Expected variance of the idle times of workstations can be viewed as an inverse measure of stability of the system. A more appropriate and direct measure could be the reliability of the system such that each workstation adheres to assigned cycle time with high chance. The present work defines the reliability of the assembly line in terms of cycle time and distribution of the tasks times and offers an optimization formulation for the problem under precedence constraints. For demonstration purpose, one well known example in the literature has been addressed under stochastic setup.

Optimum assembly line balancing: A stochastic programming approach

Article history: Received 1 June 2010 Received in revised form 9 July 2010 Accepted 9 July 2010 Available online 10 July 2010 Assembly line balancing problem is an approach of assigning a set of tasks to an ordered sequence of workstations. This assignment needs to be made in such a way that the underlying precedence constraints are not violated and efficiency measures are optimized subject to the restriction of the cycle time constraint. Research works, reported so far, mainly deal with the minimization of balancing loss, subject to precedence constraints. Lack of uniqueness in those optimum solutions and pressing demand to include system loss in the objective function have led to the present work of minimization of both balancing and system loss. As there is no standard measure for system loss, the current work proposes a measure for system loss and offers solution to this bi-objective problem. © 2011 Growing Science Ltd. All rights reserved.

Optimum assembly line balancing by minimizing balancing loss and a range based measure for system loss

Article history: Received 30 June 2010 Received in revised form 28 October 2010 Accepted 29 October 2010 Available online 29 October 2010 An assembly line is a sequence of workstations, connected together by a material handling system, which is used to assemble components into a final product. The economic importance of assembly as a manufacturing process has led to extensive efforts for designing an assembly line to ensure efficiency and cost effectiveness of assembly operations. These efficiency and effectiveness can be maximized by minimizing balancing loss and system loss. The current work offers a range based measure for System loss and describes a technique for jointly minimizing balancing loss and system loss. To arrive at the optimum solution of the joint minimization problem, the same has been reduced to sequential marginal minimization problems and simulation technique has been installed for obtaining the optimal solution. For demonstration purpose, one example has been worked out to indicate the strength of the suggested method. © 2010 Growing Science Ltd. All rights reserved.

Effective Cycle Time: A Real World Balancing Index for Paced Assembly Lines

Assembly Line Balancing (ALB) aims at optimally assigning the work elements required to assemble a product to an ordered sequence of workstations, while satisfying precedence constraints. Notwithstanding the advances and developments in ALB over the years, recent and thorough surveys on this field reveal that only a small percentage of companies employ ALB procedures to configure their assembly lines. This paradox may be attributed, to some extent, to the fact that ALB is addressed mostly under ideal conditions. Despite the time variability inherent in manufacturing tasks, there is a strong research trend towards designing and implementing algorithms that consider ALB on a deterministic basis and focus on the optimality of the proposed task assignments according to existing ALB performance measures. In this paper, the need to assess the performance of the proposed solutions of various algorithms in the literature is corroborated through simulation experiments on a benchmark ALB problem under more realistic conditions. A novel ALB index, namely the Effective Cycle Time, ECT, is proposed to assess the quality of alternative assembly line configurations in paced assembly lines operating under task times variations.

Enhancing the Largest Set Rule for Assembly Line Balancing Through the Concept of Bi-Directional Work Relatedness

The process of optimally assigning the timed tasks required to assemble a product to an ordered sequence of workstations is known as the Assembly Line Balancing (ALB) problem. Typical approaches to ALB assume a strict mathematical posture and mostly treat it as a combinatorial optimization problem with the objective of minimizing the idle time across the workstations, while satisfying precedence constraints. The actual nature of the tasks assigned is seldom taken into consideration. While this approach may yield satisfactory cycle time results on paper, it often leads to inconvenient task assignments in an actual work environment. It has been postulated in the literature that assigning groups of related tasks to the same workstation may lead to assembly lines that exhibit increased robustness in real-world situations at the expense of a slightly increased cycle time. The prototypical example of such an approach, Agrawal’s Largest Set Rule (LSR), utilizes backward work relatedness to assign a set of cohesive tasks to the proper workstation. In this paper, we enhance the performance of the original LSR algorithm through the concept of bi-directional work relatedness, where backward and forward relationships are taken into consideration for task assignments. The proposed concept leads to comparable cycle time and improved work relatedness. Applying this novel concept to a benchmark ALB problem demonstrates the feasibility and applicability of the proposed approach.

A systematic approach to design and operation of disassembly lines

This paper presents a systematic approach to the disassembly line (DL) design in meeting the requirement of variant orders for multiple used parts with different due dates. An extended disassembly Petri net model is proposed for the hierarchical modeling in order to derive the disassembly path with the maximal benefit in the presence of some defective components. An algorithm for balancing DLs to maximize the productivity of a disassembly system is presented. The results of simulation runs of the proposed methodology and algorithms applied to a simplified personal computer disassembly are provided. This work lays a foundation for designing efficient industrial automatic and semiautomatic disassembly systems. Note to Practitioners-Disassembly is rapidly growing in importance as manufacturers face increasing pressure to deal with obsolete products in an environmentally responsible and economically sound manner. This process can be performed at a single workstation or on a disassembly line (DL) that is organized as a sequence of workstations, each with one or more machines/operators to handle a certain type of disassembly task. Compared to a single workstation, DL provides higher productivity and greater potential for disassembly automation. However, it still faces serious scheduling and inventory problems because of a high degree of uncertainty in discarded products and disparity between demands for certain parts and their yield from disassembly. To address this challenge, this paper proposes a two-level systematic approach, aiming to maximize system throughput and system revenue by dynamically configuring the disassembly system into many DLs, while considering line balance, different process flows, and meeting different order due dates. The research results can help engineers build better disassembly systems.

A graph theoretic approach for stamping operations sequencing

This paper presents initial work to develop a novel, mathematical technique that is capable of generating a stamping sequence automatically in the design of progressive stamping dies. A graph is used to represent a stamping part and define the relationships between its stamping features. These stamping features are then clustered into workstation sets using a graph colouring algorithm. Next, the sets are ordered in order to determine an optimal sequence of workstations. The objective function for optimization is ‘minimization of the torque difference between two sides of the progressive die’.

Engineering a circuit board assembly line for a desired capacity and flowtime

Abstract This paper describes a study done to engineer a circuit board assembly line for a desired capacity and flowtime. The type of line studied is often referred to as a flexible flow line and is organized as a sequence of workstations, each with one or more identical machines. Many different types of boards are to be produced. Engineering requires determining the number of different types of machines needed, sizing the buffers, and determining the input lot sizes and loading sequence. All this is done based on the forecast of a typical product mix, estimated processing times, and estimated machine downtimes. To achieve the desired flowtime, the in-process inventory must be tightly controlled with the adverse consequence of a loss in capacity. Three alternatives are explored for this purpose. The capacity is susceptible to long machine breakdowns as well as an unbalanced product mix. This study shows that proper lot sizing and sequencing can increase the capacity of the line by more than 10%.