Timothy D. Fry

Capacity-based order review/release strategies to improve manufacturing performance

Given the increased emphasis by manufacturing organizations to reduce work-in-progress inventories thereby shortening their manufacturing lead times, more attention is being given to the control of the materials released to the shop floor. The control of input into the shop is one of the activities associated with order review/release (ORR). A common assumption of the published literature on ORR is that all orders received by the shop will be accepted, regardless of shop conditions. In this paper, this assumption is relaxed such that in times of high shop congestion, it may be better to reject an order to allow the customer to seek another supplier than to accept the order and deliver it to the customer late. When the shop is highly congested, accepting all orders will jeopardize the ability of the shop to meet customer due dates. In an industry that demands fast and reliable turnaround of customer orders, not meeting due dates may result in customers placing their orders with other more reliable supplier...

Minimizing Weighted Absolute Deviation in Single Machine Scheduling

Abstract This paper presents a procedure to minimize the total penalty when jobs are scheduled on a single machine subject to earliness and tardiness penalties. This performance criterion has been shown to be non-regular thus, requiring a search among schedules with inserted machine idle time to find a solution. A procedure to optimally insert idle time is also presented.

The effects of product structure and sequencing rule on assembly shop performance

SUMMARY Single-stage job-shop scheduling has received a great deal of attention in the published literature. Significantly less research has been done in the area of assembly job shops. With the onslaught of MRP implementations designed to plan and control assembly job shops, practitioners have been confronted head-on with the need to improve dispatching procedures. This paper examines the effect of three different product structures on the performance of selected priority dispatching rules in a six-machine assembly job shop. Results indicate that significant relationships exist between the structure of the product bill of materials and the priority dispatching rule, and that specific rules are indeed better suited to certain product structures.

Modeling simultaneous worker learning and forgetting in dual resource constrained systems

Abstract This paper addresses issues related to modeling worker learning and forgetting effects in Dual Resource Constrained (DRC) systems. The learn-forget-learn (LFL) model of Carlson and Rowe (Carlson, J.C., Rowe, A.J., 1976. Industrial Engineering 8, 40–47) is used to critically evaluate several worker training related issues that are associated with the learning and forgetting phenomenon. A numerical analysis is performed on the LFL model within a DRC system to gain insights into the nature of relationships between the extent of worker flexibility, forgetting rates, attrition rates, and flexibility acquisition policies. Results suggest that in the presence of higher attrition and forgetting rates, a worker may not be able to achieve full efficiency in as little as two different departments. Thus acquiring even incremental worker flexibility under such conditions may be infeasible. We also show that managers can use different flexibility acquisition policies designed in this study to reduce relearning losses and consequently improve the system performance.

Multi-level heterogeneous worker flexibility in a Dual Resource Constrained (DRC) job-shop

The majority of research on labour flexibility in a DRC job-shop has focused on the situation where all workers are equally trained. In practice, it is likely that workers would not be trained equally and would possess different skills. In this paper, the situation where workers receive different levels of training across the various departments as well as possessing different levels of proficiency at each task is studied. Research results suggest that, even at the same level of shop flexibility, the mixture of cross training can have a significant impact on shop performance. Indeed, results suggest that it is better to have a mix of workers with no flexibility and some workers with very high flexibility rather than all workers with equal flexibility.

A preliminary investigation of multi-attribute based sequencing rules for assembly shops

This paper updates the current literature on assembly shop scheduling to include multi-attribute based sequencing rules that have recently been introduced and measures of shop performance that more accurately reflect managements view toward tardiness and inventory. In addition, a new set of sequencing rules, called importance ratio (IR), is proposed. The operation of a hypothetical assembly shop is simulated to test the performance of eight sequencing rules on three distinct sets of product structures. Four measures of system inventory and four measures of job tardiness are used to evaluate sequencing rule performance. The study shows that sequencing rules which incorporate attributes of both job shop and assembly shop scheduling do not necessarily produce the best performance. Moreover, multiple measures of inventory and tardiness performance do provide important insight into the operation and particular benefits of different sequencing rules. Finally, the importance ratio rules introduced are viable ca...

The role of management accounting in the development of a manufacturing strategy

A well developed manufacturing strategy is becoming increasingly important to many manufacturing organizations. A major feature of such a strategy is the definition of a manufacturing infrastructure that is consistent with how products and services compete in the selected market. The managerial accounting system is a key component of this infrastructure. Reports the results of a survey of 85 manufacturing companies. Finds that many companies use an accounting system that appears to be inappropriate. The systems are often ill suited to their marketplace and inconsistent with an appropriate manufacturing strategy. Discusses recommendations for change for companies currently developing a manufacturing strategy.

Due Date Assignment in a Multistage Job Shop

Abstract In a Materials Requirements Planning (MRP) system, component lead times are generally assumed to be known and constant. Since a requirement of a MRP system is that components finish on time, slack is often built into component lead times to insure that actual job flowtimes equal planned job lead times. In this study, job characteristics and shop characteristics are investigated to determine which has a greater impact on predicting job flowtimes. This is accomplished by determining which characteristic most greatly influences the deviation of planned job lead times from actual job flowtimes. After identifying those factors which have the greatest influence on the jobs flowtime, due date assignment rules are developed. A simulation study is then made to determine. which of the due date assignment rules perform best for varying product structures, as defined by various Bills of Materials (BOMs), and various shop conditions. Simulation test results are presented and discussed.

Managing worker flexibility and attrition in dual resource constrained job shops

Worker flexibility is an attractive option for enhancing manufacturing performance, since it provides several strategic advantages, and also allows the firm to buffer against uncertainty. In this paper, we investigate issues related to acquiring a flexible work-force in those dual resource constrained (DRC) job-shops that have high learning costs and the presence of worker attrition. Our results show that significant improvement in traditional shop related measures can be attained at even very high attrition rates by incrementally training each worker in one additional department. However, this improvement comes at the expense of productivity losses which shop managers may not be willing to accept. The nature of the tradeoffs that exist in acquiring this incremental worker flexibility are addressed. Two strategies for improving shop performance, based on incrementally training workers or reducing attrition rates, are also recommended for the DRC shop modelled in our study. Conditions under which either of...

A Service‐oriented Manufacturing Strategy

Introduces the concept of a manufacturing strategy based on a service orientation. Traditional manufacturing strategies have often been driven by cost minimization decisions and have encouraged the over‐reliance by managers on inventories to satisfy demand. In today′s business environment, a reliance on inventory is often not feasible. Suggests a reliance on capacity available to meet demand, as used by the service industry. Such a strategy is in direct conflict with most cost‐accounting systems because of the absorption of overhead costs based on direct labour. Proposes two alternatives for changing the accounting system, to enhance the move towards the service‐based strategy. Lastly, presents a case study of a US plant to illustrate the results that a company adopting this approach should expect.