David P. Christy

The information center concept: a normative model and a study of six installations

The principal current concern of corporate information centers is the support and management of end-user computing. This paper presents a normative model of an information center in terms of the end-user computing environment, discusses the results of extensive field interviews with information center managers, staff, and end-users, and draws conclusions and generalizations that are relevant for both future research and information center management.

Manufacturing systems with forbidden early shipment: Implications for setting manufacturing lead times

SUMMARY The authors compare two well-known methods for setting manufacturing lead times (flow allowances) in a general job shop when early shipment of completed jobs is forbidden. One of the methods for setting a jobs allowance is to make it proportional to the total processing time for the job. This method, referred to as TWK., is compared to a second method PPW. With the PPW method, a jobs allowance is obtained by adding to the total job-processing time an allowance for waiting that is proportional to the number of operations that the job requires. The two allowance methods are compared using a computer simulation of an 8-machine job shop. The model is unique in that jobs are not permitted to leave the shop early. This feature of forbidding early shipment (FES) complicates the comparison between allowance methods because it draws the issue of finished-order inventory management into the analysis. Results of computer simulations over a wide range of average due-date difficulty suggest that TWK is the d...

Incorporating maintenance activities into production planning; integration at the master schedule versus material requirements level

SUMMARY This study evaluates the impact of incorporating alternative scheduled maintenance policies or predicted emergency maintenance activities into the MRP system. The results indicate that it is critical to evaluate the failure and utilization characteristics of each machine individually so an appropriate maintenance policy can be established. Otherwise, a firm may implement scheduled maintenance when the costs of the policy actually outweigh the benefits gained by reducing emergency maintenance. Additional results suggest that by incorporating emergency maintenance into the MRP system as a dependent demand item, firms may be able to plan and allocate their resources more efficiently.

Manufacturing systems with forbidden early shipment: implications for choice of scheduling rules

SUMMARY Recent progress in manufacturing systems research has identified the feature of forbidding early shipment (FES) of orders as a prevalent characteristic of real systems. This report examines the implications of this feature on the choice of scheduling rules within a job shop. Simulation results of a simplified job shop reconfirm the superiority of the modified due date approach when the criterion is mean job tardiness. However, when the criterion is system inventory, the slack time per remaining operation ratio approach performs slightly better than modified due date. The shortest operation processing time yields very poor results in job shops that include the FES assumption.

An investigation of the effect of machine flexibility and number of part families on system performance

SUMMARY Flexibility of manufacturing systems and the diversity of parts that may be produced by these systems is of great importance to managers. The effects of both product diversity and the ability of machines to perform a variety of operations, defined here as flexibility, are investigated. As product diversity increases, the deterioration of system performance is measured. A unique approach is adopted. In order to eliminate the interaction between the factors in this study, optimally designed systems are compared. The methodology adopted is a combination of computer simulation, response surface methodology and the Hooke-Jeeves procedure. We conclude that more flexibility is not necessarily better than less flexibility, and that as product diversity increases, for a given system there is a level of flexibility that will optimize system performance and minimize the rate of its deterioration.

Determination of optimal production rates on a single facility with dependent mold lifespan

Abstract In this paper, we consider a situation where several dedicated items are produced on a single facility and production rates can be controlled within maximum and minimum limits. Thus, this problem is a modification of the economic lot scheduling problem (ELSP). We also take into account two different manufacturing costs that are functions of the production rate: (1) operating cost of the facility, and (2) mold cost. Operating cost is modeled as a linearly increasing function of the ratio between demand rate and production rate. Mold cost is modeled as an exponentially decreasing function. A mathematical model is developed and a heuristic iterative solution procedure is suggested. The objective of this problem is to minimize annual production-related cost in a model whose decision variables are common production cycle time and production rate for each product.

Structure and function of information centers: case studies of six organizations

Abstract The information center ( ic ) is a concept advocated by many information systems professionals for effectively supporting end-user computing. Detailed interviews with the managers of six ics and with users of ic services indicate that the structure and organizational location of the ic may effect its staffing, service mix, and vision of the future.

Evaluating the design of flexible manufacturing systems

Evaluating the design of flexible manufacturing systems is complex. Developing a measure of performance useful for evaluating alternate designs continues to be interesting. Here, total productivity of the system is proposed as an appropriate measure. Specification of parameters based upon strategic considerations for this measure are discussed. Finally, the usefulness of the measure is demonstrated through an example.

A simulation study for dynamic scheduling in a hybrid assembly/job shop considering the JIT context

This paper is a report of a simulation study that investigates a dynamic approach to scheduling jobs in a hybrid assembly/job shop, with special application to welding shop operations. Both JIT arrival and JIT delivery are considered. Various dispatching rules with different utilization are tested for the following performance measures; mean flow time, percentage of tardy jobs, mean tardiness, sum of mean tardiness and mean earliness. The results indicate that the SPT rule is the best for the mean flow time. The MSLACK rule, that we suggest in this paper, is the best for mean tardiness, the sum of mean tardiness and mean earliness. However, it is not clear which rule is the best for the percentage of tardy jobs. We also investigate the effect of changing the release time on the performance measure.