LOCATION OF QUALITY INSPECTION STATIONS: AN EXPERIMENTAL ASSESSMENT OF FIVE NORMATIVE HEURISTICS

A number of heuristic decision rules have been proposed to aid in the location of quality inspection stations within a production line. Although these rules apparently enjoy an intuitive appeal, as yet no empirical investigation of their individual efficacies has been undertaken. This research identifies the relations between various cost and/or process characteristics and a designated “operative condition” that motivates the apparent rationale of five of these rules-of-thumb. Experimental results suggest that for several of the heuristics the operative condition was not associated with the performance of the rule. In addition, constraints in the processing environment were found to influence the effectiveness of the heuristics.     

Economic Models for Single Sample Acceptance Sampling Plans,No Inspection,and 100 Percent Inspection

Once a process is stabilized using control charts, it is necessary to determine whether this process is capable of producing die desired quality, as determined by the specifications, without the use of some additional inspection procedure such as 100 percent inspection or acceptance sampling. One common method of making this determination is the use of process capability ratios. However, this approach may lead to erroneous decisions due to the omission of economic information. This paper attempts to remedy this situation by developing economic models to examine the profitability of different inspection policies. These models employ the quadratic loss function to represent the economic cost of quality from external failures, which is commonly omitted or overlooked. Moreover, assuming a normal distribution for the quality characteristic allows the use of simplified formulas that are provided. Thus the calculations can be made using standard normal tables and a calculator. Additionally, these economic models may be used to determine if additional inspection procedures should be reinstated if the quality of the process was to decline, to make capital budgeting decisions involving new equipment that produces parts of a higher quality, and to determine the preferred 100 percent inspection plan or acceptance sampling plan.     

The Impact of Alternative Vendor/ Buyer Communication Structures on the Quality of Purchased Materials

This paper examines the critical interface between manufacturing, purchasing, and quality assurance by exploring the impact of two alternative structures of buyer and vendor communication on attempts to improve the quality of purchased items. Those two structures of communication are the parallel structure and the serial structure. The research analyzes and compares the advantages and disadvantages of these two specific communication structures; the results have implications for both researchers and managers. The analysis of data suggests that the parallel structure is associated with significantly higher levels of quality than the serial structure. From a managerial perspective, the results of the research suggest that manufacturers must consider the parallel communication structure as a viable alternative for improving the quality of purchased components. While this study has helped frame some key managerial issues, the need and opportunity for further research in related areas is delineated.     

A COMPARISON OF INVESTMENT ALLOCATION STRATEGIES FOR DISTRIBUTION INVENTORIES

Management goals in distribution inventories are often expressed in terms of the maximum percentage of aggregate sales that should be back ordered. This paper compares several strategies for allocating total inventory investment to each item stocked in order to meet such goals. Computational results are given from a wholesale distribution inventory. The results show that multi-item strategies (which consider the interactions between items) require substantially less investment to meet management goals than strategies that treat each line item independently. All models in this research are approximations based on the assumptions commonly used in practice.     

REQUIREMENTS PLANNING FOR CONTROL OF INFORMATION RESOURCES

Producing reports assembled from files, records, and raw data is a major function of the computer in modern organizations. Transaction processing, records management, file organization, and data-base management are aspects of the information production function that have received a good deal of attention. But planning, scheduling, and controlling the production of information products have been neglected. For complex applications involving assembly of reports from multilevel information sources, the requirements planning model is suggested as an effective alternative to present methods. Thus, our suggestion is that the computer be used to plan, schedule, and control computer production of information products. Presently available material requirements planning software may be employed with minor modifications that depend on the given information system characteristics. In this paper an example of requirements planning as applied to production of information in a satellite control system is presented.     

PROCEDURES FOR DETERMINING RELATIVE FREQUENCIES OF PRODUCTION/ORDER IN MULTISTAGE ASSEMBLY SYSTEMS*

We show that the problems of determination lot sizes in a multistage assembly system for the case of instantaneous production and constant demand for the end item can be reduced to the problems of determining relative frequenceis of production/order for items at each production stage. We further show that such frequencies are independent of the demand levels. Optimal and near-optimal solution procedures for this reduced problem are provided. The near-optimal procedure successively treats each stage of production as a final production stage while simulatenously incorporating decisions made at lower stages into decisions made at higher stages. Experimental results show that the near-optimal procedure results in optimal solutions 75 percent of the time and performs considerably better than representative heuristics available in the literature. Further, its performance is relatively less susceptible to product/structural characteristics of the system.     

Graphical Presentations of Data Envelopment Analyses: Management Implications from Parallel Axes Representations*

The conversion of multivariate data analysis into information that managers can readily use in their decision making has always been a challenging task. In this paper we provide a parallel axis representation of multivariate data and demonstrate how this representation may be used as a tool for implementing the results of data envelopment analysis. We use an analysis of the efficiency of electricity generating plants to illustrate the technique.     

Producer's and Consumer's Risk When Proportion Defective Is a Random Variable

In acceptance sampling, producer's and consumer's risk are traditionally based on assumed fixed values of p, the proportion of the lot which is defective. A more useful definition of producer's risk would be the probability of rejecting a lot in which the proportion defective falls within some range of acceptable values. Similarly, a more useful definition of consumer's risk would be the probability of accepting a lot in which the proportion defective falls within some range of unacceptable values. In this paper, we construct measures of these more useful definitions of risk by assuming that p follows either a uniform or triangular probability distribution. The proposed measure yields consumer's risk values, β', which are smaller than the traditionally computed values by a factor of up to twenty times. The proposed measure of producer's risk, α', gives values smaller than traditional values by a factor of two to four times. Decision makers who adopt the proposed measures may be able to reduce sample sizes substantially while maintaining given risk levels.     

Vendor Performance and Alternative Manufacturing Environments*

Today, many American firms are demanding a high level of performance from their major suppliers while at the same time reducing the number of them. Vendor performance is an important aspect of maintaining low production costs and high product quality. In this study, we examine the effects of poor vendor quality and vendor lead time uncertainty in a variety of manufacturing environments using a comprehensive simulation model. The results indicate that the effect of poor vendor performance on various manufacturing firms depends on the number of stocking points and the degree of component commonality. Moreover, disruption of the manufacturing system caused by poor vendor performance can be manifested in higher levels of inventory and order backlogs. We introduce the concept of supplyside uncertainty, as it relates to component-part commonality, to demonstrate that in certain environments commonality reduces order backlogs but increases total inventories and creates an environment that is very sensitive to vendor quality problems. Finally, several conjectures are posited for future research.     

Notes and Communications REPLANNING FREQUENCIES FOR MASTER PRODUCTION SCHEDULES

Updating production plans typically is achieved by rolling the planning horizon forward one period at a time, each time including the latest information in order to determine the best course of action to pursue in the present period. Theoretical planning-horizon studies have identified the conditions by which the production decisions in the current and some specified number of future periods remain optimal given some set of future demands. Motivated by these findings, this study addresses the replanning frequency in a hierarchical production planning problem where no planning-horizon theorems are available. In this problem the aggregate production plan and the master production schedule are linked by a rolling-horizon practice. Empirical experimentation indicates that under certain cost and demand conditions the master production schedule need not be updated every period. If a schedule does not need to be updated for several periods, the schedule for these periods can be frozen to provide stability for planning components at lower levels in the bill of material of the products. The results of this study thus provide some reference for the determination of the frozen portion of the master production schedule.     

“A JOINT ECONOMIC-LOT-SIZE MODEL FOR PURCHASER AND VENDOR”: A COMMENT*

Banerjee [1] developed a joint economic-lot-size model for the case where a vendor produces to order for a purchaser on a lot-for-lot basis under deterministic conditions. The assumption of lot-for-lot bases is restrictive in nature. In this note, a more general joint economic-lot-size model is suggested and it is shown to provide a lower or equal joint total relevant cost as compared to the model of Banerjee.     

DESIGNING HIGH-CONTACT SERVICE SYSTEMS: APPLICATION TO BRANCHES OF A SAVINGS AND LOAN*

The customer-contact model represents one of the few conceptually based approaches for designing service systems. This paper develops that concept further for high-contact systems, relative to efficiency and effectiveness notions. Four design features (contact technologies, contact training, data bases, and contact roles) are developed and a simple design methodology (built around the four design features) is presented. A demonstration of the design methodology is provided through its applications to branches of a savings and loan. Areas for additional theoretical and practical refinement of the model and the desirability of multidisciplinary research are discussed.     

A Simple Heuristic for Lot Sizing with Setup Times

This paper presents an easily understood and computationally efficient heuristic algorithm for the capacitated lot sizing problem (CLSP), the single machine lot-sizing problem, with nonstationary costs, demands, and setup times. The algorithm solves problems with setup time or setup cost. A variation of the algorithm can solve problems when limited amounts of costly overtime are allowed. Results of experimentation indicate that the most significant effects on solution quality are due to the level of setup costs relative to holding costs and the size of the problems as determined by the number of items. Also affecting solution quality are tightness of the capacity constraint and variability of demand in a problem. When the capacity constraint is extremely tightly binding, it sometimes has difficulty finding solutions that do not require overtime.     

THE HARMS SHOE COMPANY: DEVELOPMENT OF A COMPUTER MODEL FOR THE CLASSROOM

This paper describes a case that examines five key topics in production and operations management [1]—forecasting, inventory control, transportation planning, aggregate planning, and the disaggregation of the aggregate plan—in an integrated, realistic manner for upper-level undergraduate business majors [3]. The case structure stresses the linkage of these interrelated subjects and supplements the regular classroom presentations dealing with them. The case relies on computer calculations at each stage to provide the information input for calculations at the next stage. It is a static model with a twelve-month planning horizon. Students complete several exercises and assume several roles as the case unfolds. They act on their own in filling some roles and as members of teams in performing others. They do not compete with each other, as the purpose of the case is to help them develop an appreciation of the factors that persons performing the role must consider.     

NEW TECHNOLOGY INVESTMENTS IN MULTISTAGE PRODUCTION SYSTEMS

The introduction of new technologies in production and manufacturing (such as robotics, flexible manufacturing systems (FMS), and computer-aided design and manufacturing (CAD/CAM)) frequently motivates capital investment decisions. Traditionally, the need for additional capacity has motivated the evaluation of investment decisions which were undertaken based on financial factors such as the net present value (NPV), internal rate of return, taxation, and depreciation. This research integrates investment decisions with operational decisions for the case of multistage production assembly systems. We show that for such systems investment decisions affect not only the financial structure but also production scheduling and material flow in the system.     

A DISCRETE PRODUCTION SWITCHING RULE FOR AGGREGATE PLANNING

Aggregate planning (AP) is a necessary activity for manufacturing and services alike. A shift toward high-volume batch and continuous flow processes within American manufacturing has given rise to increasing numbers of crew-loaded facilities. A majority of AP approaches incorporate continuous decision variables and require frequent adjustments to both production and work-force settings. Despite the availability and diversity of these approaches, few significant applications have been reported. This paper presents the detailed development of a discrete AP switching rule that can be applied to a variety of cost environments. Inventory costs are estimated using an interval approach rather than traditional point estimates. The model allows incorporation of overtime options and is interactive in nature. Decision variables from the model can be disaggregated and linked directly to lower-level planning activities. Actual results of model implementation are reported. An overview of the model's incorporation into the larger context of hierarchical production planning is found in [21].     

Cautions on the Use of the SERVQUAL Measure to Assess the Quality of Information Systems Services

The SERVQUAL questionnaire (Parasuraman, Zeithaml, & Berry, 1988) is one of the preeminent instruments for measuring the quality of services as perceived by the customer. In a recent Decision Sciences article, Kettinger and Lee (1995) suggested the use of a modified SERVQUAL instrument to assess the quality of the services supplied by an information services provider. However, a number of problems with the SERVQUAL instrument are discussed in the literature. This article provides an illustrative example utilizing data collected from 138 executive and information systems professional customers of a multibillion dollar information services provider in order to examine the validity and reliability of Kettinger and Lee's (1995) modified SERVQUAL instrument. Results of analyses do not confirm the findings of Kettinger and Lee. Moreover, it appears that the use of difference scores in calculating SERVQUAL contributes to problems with the reliability, discriminant validity, convergent validity, and predictive validity of the measure. These findings suggest that caution should be exercised in the use of SERVQUAL scores and that further work is needed in the development of measures for assessing the quality of information services.     

PRODUCTION/OPERATIONS MANAGEMENT: PURE PREDICTIONS FOR THE '80s1

The future of production/operations management is examined. Following a lead-in designed to grab your attention and to demonstrate the relation between production/operations management and health care, 14 specific and irrefutable pure predictions are presented. Briefly, they are 1,2, and 3, followed by 4 through 12, and closing with 14 and 15.     

A DISCRETE DYNAMIC OPTIMIZATION MODEL FOR MADE-TO-ORDER COST ANALYSIS

A model is presented that yields optimal production rates for a firm producing a contracted order. The model is unique in that it considers the influence of production rate and learning on total program cost. An application to the specific characteristics of two military production programs is presented. As demonstrated by the application, models of this type may be used as decision-making tools when negotiating the cost impact of contract modifications.