Ongoing Production Process Research Articles

Economic design of a complete inspection plan with interactive quality improvement

Consider the monitoring of an ongoing production process subject to complete inspection. Inferior quality products are either reworked or scrapped to assure good outgoing quality. Whenever the quality characteristic of a product exceeds a predetermined action limit, remedial action is taken to restore the process to an in-control state. In addition, the decision maker has a learning opportunity to improve the process by investing in resources to identify and eliminate the causes of deviation from the target quality. Taking a learning action would improve the mean value of the quality characteristic of items produced in an out-of-control state. This paper proposes a cost model to determine the optimal number of learning actions to be taken and the optimal action limit. The model considers the trade-off between quality cost and process improvement cost.

Interactive quality improvement of a process subject to complete inspection

An ongoing production process produces products with quality characteristics following a known probability distribution. Two process states, in-control and out-of-control, are assumed. The process is subject to complete inspection. Whenever the quality characteristic of a product produced exceeds a predetermined action limit, remedial action is taken to restore the process to the in-control state. In addition, the decision maker has a learning opportunity to improve the process by investing resources to identify and eliminate the causes of non-conformance to the target characteristic value. A learning action taken would reduce the probability of shifting from the in-control state to the out-of-control state. A cost model is developed in this paper to determine the optimal number of learning actions to be taken and the optimal action limit. The model gives insight into the tradeoff of cost of quality and cost of prevention.

ESTIMATING ACCEPTANCE-SAMPLING PLANS FOR DEPENDENT PRODUCTION PROCESSES

Abstract When acceptance sampling is used to judge the quality of an ongoing production process, the quality of successive items may exhibit statistical dependence that is not accounted for in standard acceptance-sampling plans. Computing the probabilities required to design sampling plans for general dependent processes is often complex, and sometimes intractable. This paper presents an efficient method for estimating single-sampling attribute plans for any production process model that can be simulated. Numerical illustrations are given.

THE EFFECTS OF LABOUR STRIKE ACTION ON A LARGE SCALE DAIRY ENTERPRISE

Abstract Industrial labour practices in southern Africa are new to all those involved with agriculture. The impact of a strike on an on-going biological production process has far more serious long term implications than does a similar stoppage in a factory production line producing with inert (non-living) materials. On a large irrigated scheme in the Eastern Cape, which includes a pasture based dairy enterprise, a number of work stoppages have taken place over the past 18 months. The paper quantifies the immediate and longer term financial impacts of work stoppages. The immediate consequences of the stoppages are loss of milk sales and market share, and the longer term consequences include the cost of premature drying off, lost production due to lower lactation over the recovery period as well as the cost of missed heats and inseminations on extended inter-calving periods. The various work stoppages were undermining the scheme which led to the resultant involvement of a recognised trade union in the area...

Interactive Process Quality Improvement

An ongoing production process produces defective parts at random intervals. Each defective part provides a learning opportunity which the decision maker may use to improve the process by investing resources to identify and remove the causes of the defective. For various cost criteria, it is optimal to invest in learning until the probability of producing a defective becomes sufficiently small. This policy has economic interpretations in terms of marginal benefits. In addition, the optimal policy for expected discounted present cost has an interpretation in terms of tradeoffs between “cost of failure” and “cost of prevention”. The shape of the tradeoff curve gives insight into the controversy between the traditional and zero defects views towards cost of quality.

A Bayesian Approach to Controlling Percent Defective A Model and Application

Abstract The purpose of this paper is to develop a general model for controlling the percent defective of an ongoing production process. The model is developed in a Bayesian decision theory framework so that, using dynamic programming, optimal (least cost) control decisions can be found. An application of the model to a real world production process is described in detail. The problems of estimating the model parameters are discussed along with some approaches to overcoming the estimation problems. Finally, the optimal control policies for the real world process are presented and are shown to be straightforward and easily implemented.