Product Changeover Research Articles

Dosimetry studies to determine optimum processing parameters to minimize dose variations in non-uniform product

Industrial gamma irradiators are designed to optimize throughput and dose uniformity when large quantities of uniform product are processed. However, during normal irradiator operations some products will receive a wider range of doses as cycle times are adjusted to compensate for variations in product density, or to change to another product dose. The irradiation of small batches of products to widely differing doses may require flushing out the product with empty carriers or dummy product. The method used for product changeovers or for processing mixed densities will depend on the irradiator design and the acceptable dose range for the products. Dosimetry studies were performed at several irradiators to determine the dose variations for such operating conditions as partially loaded carriers, product changeovers and mixed product densities, to determine the optimum methods for minimizing dose variations.

Impact of flexible machines on automated manufacturing systems

Although the problem of scheduling dynamic job shops is well studied, setup and changeover times are often assumed to be negligibly small and therefore ignored. In cases where the product mix changes occur frequently, setup and changeover times are of critical importance. This paper applies some known results from the study of multi-class single-server queues with setup and changeover times to develop an approximation for evaluating the performance of job shops. It is found that the product mix, setup and changeover times, and scheduling rules affect the performance significantly, in particular at high levels of machine utilisation. This approach could be used to determine the required level of flexibility of machines and to choose an appropriate scheduling policy such that production rates remain within acceptable limits for foreseeable changes in the product mix.

Improvement curve analysis of changeovers in JIT environments

Abstract Improvement curves are extremely useful management tools for predicting and controlling labor time and cost. This paper reviews some progress curve models and uses the log-linear improvement model to analyze the impact of product set-ups or changeover on productivity.

Strategic Allocation of Inspection Effort In A Serial, Multi-Product Production System

Abstract For a multi-stage production system, optimal location of inspection activities is an important consideration in minimizing the inspection-related and salvage costs. Set-up and inventory carrying costs also become important factors when several products are produced on the same line due to the product changeovers involved. In this paper we discuss the effect of these additional costs (set-up and inventory carrying) on the inspection strategy, i.e., “all or none” versus partial inspection. We suggest a shortest path heuristic to determine the strategic location of inspection activities and the production lot sizes.

Production Planning of Style Goods with High Setup Costs and Forecast Revisions

In this paper we study a problem, common to a wide variety of manufacturing companies, of determining the production schedule of style goods, such as clothing and consumer durables, under capacity constraints. Demand for items is stochastic and occurs in the last season of the planning horizon. Demand estimates are revised in each period. We exploit the problem's two-level hierarchical structure, which is characterized by families and items. Production changeover costs from one family to another are high, compared to other costs. However, changeover costs between items in the same family are negligible. We first formulate this problem as a difficult-to-solve stochastic mixed integer programming problem. Then, exploiting the problem's hierarchical structure, we formulate a deterministic, mixed integer programming problem and solve it by means of an algorithm that provides an approximate solution. A lower bound is obtained by applying generalized linear programming to the approximate problem. We illustrate the procedure using the disguised data of a consumer electronics company. The computational results demonstrate the effectiveness of the proposed approach in a practical setting.

Short-term scheduling for multiproduct batch chemical plants

A computer program is described for the short-term scheduling of multiproduct batch chemical plants. Given available equipment, product delivery dates and equipment requirements for each product, batches are sequenced to meet the delivery dates while taking account of penalties associated with product changeovers and storage costs. Precedence constraints are considered for intermediate products, as are constraints on the availability of shared resources which limit the operations that can be carried out in parallel.

Micro routines for demonstrating G/T, JIT, KANBAN and MRP

Abstract Of the steps necessary for successful implementation of G/T, JIT and MRP, Classification and Coding of the parts should be first. In addition to reducing design and tooling proliferation, a G/T field in the item master record is of great assistance in the operation of an MRP, JIT or conventional production control systems. With the aid of a balanced runout model and graphics, the behavior of inventory in a mixed model, JIT production system can be portrayed. Production rates, initial inventory and changeover policies are varied and the inventory levels, fluctuations, and stockouts displayed. The computation of the number of KANBANs to be cycled in a JIT system is relatively simple but often customized. A computer routine for a manufacturing firm using JIT is explained. The logic of MRP can be demonstrated with a simple, interactive routine and some illustrative exercises in a scenario or ‘what if’ format. Integrating these concepts within a production environment is a challenge for manufacturing engineers and managers.

Welding cell gives flexibility and productivity

A UK manufacturer of tubular steel chairs is operating a robot welding cell that has increased its productivity by 30%. Also, product changeover times can be accomplished in two to three minutes.

A Review of Production Scheduling

Production scheduling can be defined as the allocation of available production resources over time to best satisfy some set of criteria. Typically, the scheduling problem involves a set of tasks to be performed, and the criteria may involve both tradeoffs between early and late completion of a task, and between holding inventory for the task and frequent production changeovers. The intent of this paper is to present a broad classification for various scheduling problems, to review important theoretical developments for these problem classes, and to contrast the currently available theory with the practice of production scheduling. This paper will highlight problem areas for which there is both a significant discrepancy between practice and theory, and for which the practice corresponds closely to the theory.

Minimum Change-Over Scheduling of Several Products on One Machine

Given a finite horizon delivery schedule for n products we wish to schedule production on a single machine to meet deliveries and minimize the number of change-overs of the machine from one product to another. A state space is defined and in it a network is constructed such that the shortest distance through the network corresponds to the minimum number of production change-overs. Certain properties of the optimal path are deduced from the dynamic programming formulation of the shortest route problem, and these properties are utilized in the construction of an algorithm that finds the optimal path. A numerical example illustrates the method.