Subhash C. Sarin

A survey of the assembly line balancing procedures

The assembly line balancing problem consists of assigning tasks to an ordered sequence of stations such that the precedence relations among the tasks are satisfied and some performance measure is optimized. Due to the complexity of the problem, heuristic procedures appear to be more promising than the optimum-seeking algorithms. For the single-model, deterministic version, there are numerous exact and heuristic algorithms developed, while for the other more complex but more realistic versions, the research published consists mainly of heuristic procedures. In this paper, the heuristic procedures are critically examined and summarized in sufficient detail to provide a state-of-the-art survey. An evaluation of the procedures and some further research topics have also been presented.

The machine loading and tool allocation problem in a flexible manufacturing system

Abstract In this paper the machine loading and tool allocation problem of an FMS is discussed, A mathematical model is developed to determine the routings of parts through the machines and to allocate appropriate cutting tools to each machine to achieve minimum overall machining cost. Computational experience with this model is presented under various system and operation parameter values. Computational refinements based on lagrangean relaxation are also discussed.

A methodology for solving single-model, stochastic assembly line balancing problem

In this paper, a methodology is developed to solve the single-model, stochastic assembly line balancing problem for the objective of minimizing the total labor cost and the expected incompletion cost arising from tasks not completed within the prescribed cycle time. The methodology is based on determining an initial DP based solution and its improvement using a branch-and-bound procedure which uses an approximate solution instead of a lower bound for fathoming nodes. Detailed experimentation shows the superiority of this method over the most promising one from the literature.

A near-optimal heuristic for the sequencing problem in multiple-batch flow-shops with small equal sublots

In this paper, we consider the lot-streaming problem of sequencing a set of batches, to be processed in equal sublots, in a flow-shop, so as to minimize makespan. A new heuristic procedure, called the bottleneck minimal idleness heuristic, is developed. Results of an experimental study are presented. It is shown that the proposed procedure generates solutions that are very close to the optimal solutions, and that the solutions generated are better than those obtained by using the fast insertion heuristic, considered to be a good heuristic for solving the flow-shop scheduling problem, when applied to the problem on hand.

A survey of dispatching rules for operational control in wafer fabrication

Production scheduling in semiconductor wafer fabs is a non-trivial task owing to the complexity of wafer fabrication. Dispatching rules are the most commonly used tools for shop floor control in this industry. Over the years, advanced dispatching rules, capable of impacting multiple performance measures and utilising both upstream and downstream information in assigning lot priorities, have been introduced. This article aims to provide an overview of these rules and explores the effectiveness of their performance as they pertain to different areas in a wafer fab. Based on this overview, several future directions on developing new dispatching rules are also proposed.

New tighter polynomial length formulations for the asymmetric traveling salesman problem with and without precedence constraints

We propose a new formulation for the asymmetric traveling salesman problem, with and without precedence relationships, which employs a polynomial number of subtour elimination constraints that imply an exponential subset of certain relaxed Dantzig-Fulkerson-Johnson subtour constraints. Promising computational results are presented, particularly in the presence of precedence constraints.

Design, modeling, and analysis of a feedstock logistics system.

Given the location of a bio-energy plant for the conversion of biomass to bio-energy, a feedstock logistics system that relies on the use of satellite storage locations (SSLs) for temporary storage and loading of round bales is proposed. Three equipment systems are considered for handling biomass at the SSLs, and they are either placed permanently or are mobile and thereby travel from one SSL to another. A mathematical programming-based approach is utilized to determine SSLs and equipment routes in order to minimize the total cost. The use of a Side-loading Rack System results in average savings of 21.3% over a Densification System while a Rear-loading Rack System is more expensive to operate than either of the other equipment systems. The utilization of mobile equipment results in average savings of 14.8% over the equipment placed permanently. Furthermore, the Densification System is not justifiable for transportation distances less than 81 km.

An improved branching scheme for the branch and bound procedure of scheduling n jobs on m parallel machines to minimize total weighted flowtime

Abstract A branch and bound procedure to solve the n job, m parallel machine problem for the weighted flowtime criterion has been developed by Elmaghraby and Park (1974) and further modified by Barnes and Brennan (1977). This paper proposes a branching scheme different from theirs and shows its superiority. Also, some new and simple results are presented which are easy to implement to obtain an efficient branch-and-bound algorithm. In addition, a new and improved lower bound is developed which is easy to compute.

Sequencing jobs on a single machine with a common due date and stochastic processing times

Abstract This paper presents a procedure for sequencing jobs on a single machine with jobs having a common due date and stochastic processing times. The performance measure to be optimized is the expected incompletion cost. Job processing times are normally distributed random variables, and the variances of the processing times are proportional to their means. The optimal sequences are shown to have a W- or V-shape. Based on this property computationally attractive solution methods are presented.

Evaluation of the potential benefits of lot streaming in flow-shop systems

Abstract Lot streaming is the process of splitting a production lot into sublots, and then scheduling the sublots in overlapping fashion on the machines, in order to improve the overall performance of the production system. Simulation-based and industry-based reports have confirmed that substantial benefits are possible via lot streaming. In this paper, we present, for the first time, analytical results pertaining to the potential benefits of lot streaming in flow-shop systems. The results are developed using three common performance measures. These measures are (a) lakespan (i.e., the total completion time of all the lots), (b) mean flow time, and (c) average WIP level. For each, an expression of the ratio of the measure under lot streaming to the measure without lot streaming is developed. These expressions can be used to evaluate the benefits of lot streaming under certain operating conditions. It is further shown that, in special extreme cases, these expressions purely depend upon the problem parameters (i.e., the number of machines, the number of lots, the lot-sizes, etc.)