Showing papers on "Job shop published in 1980"

Models for Understanding Flexible Manufacturing Systems

Abstract: The basic features of flexible manufacturing systems are reviewed and models for determining the production capacity of such systems are developed. These models show the desirability of a balanced work load, the benefit of diversity in job routing if there is adequate control of the release of jobs (a job shop can be better than a flow shop), and the superiority of common storage for the system over local storage at machines. The models are extended to allow for material handling delays between machines and for unreliable machines. It is also shown that production capacity models can be used to develop good approximations to the mean number of jobs in the system for given job arrival rates and machine utilizations.

Priority dispatching rules in job shops with assembly operations and random delays

Abstract: The article reports the results of an experimental investigation into priority dispatching rules for a job shop with assembly operations. A job is made up of several parts, where parts are individual entities requiring several operations in different machine centres. The study was directed towards rules which attempt to co-ordinate the completion time of parts required in the same job. This mainly involves rules that utilise job status information such as operation float, number of parts completed, and number of operations remaining on each part. Results indicate that job status information improves most of the measures of performance used.

Priority Update Intervals and Anomalies in Dynamic Ratio Type Job Shop Scheduling Rules

Abstract: Dynamic priority dispatching rules in job shops require the computation of all job priorities in a work center queue every time a machine in the work center becomes idle. This is extremely costly. Alternative priority update procedures are studied and comparative results in terms of performance measures and costs are reported. Ease of implementation of the various procedures in a real world job shop environment is discussed. A second problem related to an anomaly in ratio type dynamic priority rules is also studied; a simple modification to remove the anomaly is suggested and the performances of the "old" and "modified" procedures are compared.

Measuring flexibility of job-shop layouts

Abstract: It is generally agreed that flexibility in job-shop layouts is a desirable goal which must be planned for in a systematic fashion. Not generally available, however, are procedures by which alternate layout designs can be quantitatively evaluated with respect to the amount of flexibility a particular layout may possess. This paper is concerned with facilities design of job-shop layouts, and analysis of the ability of these layouts to respond to known and future product mixes. The ability of layouts to respond to known and future product mixes is defined as flexibility. Design of a facility is restricted to the spatial arrangement of machines, material-1product storage areas and entrances-exits. An approach is presented which uses annual material handlingtosts that vary from one design to another as a measure of a design's flexibility. The measure is tested on an actual shop and six alternative layouts. The example indicates not only that annual material handling costs can be used successfully as a relative...

Application of dynamic scheduling rules in maintenance planning and scheduling

Abstract: A maintenance planning and scheduling system often resembles that of a ‘job shop’ that is, the orders are one of a kind, and is characterized by having to schedule N orders through M or less tasks. The orders are of two types, e.g., (a) emergency—have to be done now, and (b ) non-emergency—can be delayed until later. In this type of ‘job shop’ the schedule becomes immediately out of date as soon as an emergency order is received. Consequently non-emergency orders are continually moved back in the schedule and forecasted completion dates are not met. Further if the orders entering the system exceed the normal available capacity, the backlog will continue to increase causing more disruption of schedules. The research, which is based on a large petrochemical plant, will deal with the above problems by (a) applying dynamic decision rules for day-to-day scheduling to ensure completion dates are met, (b) a method for controlling backlog, and (c) forecasting future load, and completion dates for orders. The resu...

Evaluation of Value Time Sequencing Rules in a Real World Job Shop

Abstract: This paper reports a case study carried out in an Engineering industry manufacturing nineteen types of products against orders. The objective of this research was to select the sequencing rule that will optimise the combined performance of work-in-process inventory in monetary terms and delivery performance. Past studies in this area show that rules based on either the value of the orders or the value-processing time of the orders have not been investigated. This study evaluates the performance of the two sequencing rules based on the value and processing time of the orders: (i) Lowest Value Time rule (LVT) (ii) Highest Value Time rule (HVT). Incidental to this study, a few other sequencing rules were evaluated. To carry out the investigations, a simulator using GPSS (General Purpose Simulation System) was developed.

Aspects of design for a spare parts provisioning system

Abstract: This thesis describes an investigation by the author into the spares operation of compare BroomWade Ltd. Whilst the complete system, including the warehousing and distribution functions, was investigated, the thesis concentrates on the provisioning aspect of the spares supply problem. Analysis of the historical data showed the presence of significant fluctuations in all the measures of system performance. Two Industrial Dynamics simulation models were developed to study this phenomena. The models showed that any fluctuation in end customer demand would be amplified as it passed through the distributor and warehouse stock control systems. The evidence from the historical data available supported this view of the system's operation. The models were utilised to determine which parts of the total system could be expected to exert a critical influence on its performance. The lead time parameters of the supply sector were found to be critical and further study showed that the manner in which the lead time changed with work in progress levels was also an important factor. The problem therefore resolved into the design of a spares manufacturing system. Which exhibited the appropriate dynamic performance characteristics. The gross level of entity presentation, inherent in the Industrial Dynamics methodology, was found to limit the value of these models in the development of detail design proposals. Accordingly, an interacting job shop simulation package was developed to allow detailed evaluation of organisational factors on the performance characteristics of a manufacturing system. The package was used to develop a design for a pilot spares production unit. The need for a manufacturing system to perform successfully under conditions of fluctuating demand is not limited to the spares field. Thus, although the spares exercise provides an example of the approach, the concepts and techniques developed can be considered to have broad application throughout batch manufacturing industry.