Knowledge that Transforms

This is a study of a single‐machine scheduling problem with the objective of minimizing the sum of a function of earliness and tardiness called the earliness and tardiness (ET) problem. I will show that if priority weights of jobs are proportional to their processing times, and if earliness and tardiness cost functions are linear, the problem will be equivalent to the total weighted tardiness problem. This proves that the et problem is np‐hard. In addition, I present a heuristic algorithm with worst case bound for the et problem based on the equivalence relation between the two. When earliness and tardiness cost functions are quadratic, I consider the problem for a common due date for all jobs and for different job due dates. In general, the et problem with quadratic earliness and tardiness cost functions and all job weights equal to one is np‐hard. I show that in many cases, when weights of jobs are proportional to their processing times, the problem can be solved efficiently. In the published results on the et problem with quadratic earliness and tardiness cost functions other researchers have assumed a zero starting time for the schedule. I discuss the advantages of a nonzero starting time for the schedule.

Work flows in a job shop are influenced by the load per release and time interval between release factors. We focus on the latter factor, job release times. Building on Elvers' work, this study evaluates the impact of different job release time distributions on shop performance. Using a computer simulation of a random job shop and a full factorial experimental design, we demonstrate that the type of distribution does affect performance–a finding consistent with results from job shops characterized by good shop floor control practices. These findings are explained by examining the shape and variance traits of the underlying job release time distributions.

Over the past few years we have witnessed a sharp decline in the domestic and international market share of U.S. manufacturing organizations. The decline in U.S. manufacturing has provided an avalanche of criticism and attention in the literature and popular press. Recently, however, several organizations have implemented new work‐force management policies to reverse the decline. We describe the case of Rohm and Haas Kentucky, Incorporated, a plant that has implemented work teams. The outcomes of these innovations include a decline in worker grievances and turnover, an improvement in the safety record of the plant, as well as an increase in productivity.

We consider an environment where a production facility modeled as a single machine needs to assign delivery dates to several orders and find a feasible sequence. Tardy jobs are not allowed. The delivery dates are to be at prespecified fixed intervals. The objective is to minimize the due date penalty and the cost of earliness. We provide a dynamic programming‐based solution procedure that runs in polynomial time. We develop several dominance results that reduced the computational requirement by an order of magnitude in our computational study.

Market globalization, higher requirements for improved quality, and tough, faster‐pace, price‐sensitive competition have led to two parallel and visible quality thrust: the Baldrige Award in the U.S. and, internationally, the ISO 9000 standards. The relationship between the Baldrige Award and ISO 9000 registration is widely confused. Two common misper‐ceptions stand out: (1) that they both cover the same requirements and (2) that they both address improvement, relying on high quality results, and thus, are both forms of recognition. Many have concluded that the Baldrige Award and ISO 9000 are equivalent and that companies should choose one or the other. These conclusions are incorrect. The Baldrige Award and ISO 9000 registration differ fundamentally in focus, purpose, and content. The focus of the Baldrige Award is on enhanced competitiveness. The Award Criteria reflect two key competitiveness thrusts: (1) delivery of ever‐improving value to customers and (2) improvement of overall operational performance. The Award's central purpose is educational‐to encourage sharing knowledge and experience of competitiveness and to drive this learning, creating an evolving fund of knowledge. By contrast, the focus of ISO 9000 registration is on conformity to practices specified in the registrant's own quality systems. Its central purpose is to enhance and facilitate trade. The Baldrige Award addresses competitiveness factors either not addressed in ISO 9000 registration or addressed differently. These factors include a customer and market focus, results orientation, continuous improvement, competitive comparisons, a tie to business strategy, cycle time and responsiveness, integration via analysis, public responsibility, human resource development, and information sharing. Overall, ISO 9000 registration covers less than 10% of the scope of the Baldrige Award Criteria and does not fully address any of the 28 Criteria items. As a result, the national drive to improve competitiveness could be diminished. Companies required to or electing to seek ISO 9000 registration are encouraged to integrate their conformity efforts with the Baldrige Award competitiveness improvement framework.

As manufacturing firms push to achieve shorter lead times and higher levels of customer service, the basic capability of underlying manufacturing processes must be reexamined. The capacity and operational variability of a process dictate a certain set of realistic performance goals. In this paper, we examine this fundamental relationship from an economic perspective using two levels of analysis. At the aggregate level, we model the manufacturing process as a single server queue and compare the traditional roles of marketing and manufacturing in setting performance and process design parameters. Insights gained at this level are incorporated into the analysis of a realistic multiserver, multistation manufacturing line. We develop an interaction decision tool to guide the selection of process and performance parameters in this more complex environment.

We have developed an improved implementation of the Wagner‐Whitin algorithm for economic lot‐sizing problems based on the planning‐horizon theorem and the Economic‐Part‐Period concept. For many rigorous test conditions, this algorithm is about twice as fast and requires only half the array storage capacity of the previously fastest algorithm. Its execution time is approximately linear in the number of periods in the planning‐horizon.

Originally conceived by Frank and Lillian Gilbreth, the “tabletop improvement experiments” have been used in Japan since 1925 to teach important principles of continuous improvement. The experiments, designed for classroom use, communicate their lessons in a striking and memorable way. The work‐related experiments categorize the sources of resistance to change and show how to neutralize them. The process‐related experiments sharpen understanding of where the biggest opportunities for process improvement usually lie. Surprisingly, the experiments are hardly known in the West. We describe all of them and document their history for the first time.

Recent theoretical work suggests that quality‐improvement activities can yield significant indirect effects through process improvements and reduced factory congestion and confusion, benefits that are overlooked or hidden in most management accounting or cost of quality systems. Using time series data from two consumer durables manufacturing plants, I estimate the indirect productivity gains from quality improvement. The evidence from the plants indicates that the indirect effects from improved quality are at least two to three times the direct benefits attributable to lower scrap, rework, and inventory holding costs. An important implication of these findings is that companies that justify investments and measure performance based only on the direct costs of poor quality will motivate managers to make suboptimal decisions regarding quality‐improvement activities.

This is a case study of workforce scheduling in the U.S. postal system. We use it to analyze the benefits of scheduling flexibility at postal distribution systems, which can come from several sources. We focus on the additional flexibility deriving from increasing the proportion of part‐time employees, as well as from increasing the cross‐training of part‐time employees. These two dimensions of scheduling flexibility are decision points of particular interest to the postal management. We used a large‐scale simulation model of the dynamic functioning of the postal distribution system in conjunction with a staff‐scheduling model to obtain insights into policy issues of interest. Our results show that the operating environment at a distribution station affects cost and customer service performance, and that gains from greater scheduling flexibility are situationally dependent. The benefit of cross‐training part‐time workers is modest over the range of levels considered realistic for distribution stations. Our overall recommendation is for postal managers to increase the proportion of part‐time employees, allowing more efficient matching of resources with the varying demands for mail delivery on different routes. For the range of conditions we modeled, cost reductions from more part‐time workers average over six percent when capacity utilization is low. Customer service improvements are even larger, and range between 20 and 43% when capacity utilization is high. Improvements at the upper end of the range are achieved when demand variability is also at its highest.