Jan Riezebos

Review of inventory systems with deterioration since 2001

This paper presents an up-to-date review of the advances made in the field of inventory control of perishable items (deteriorating inventory). The last extensive review on this topic dates back to 2001 (Goyal S.K. and Giri B.C., Recent trends in modeling of deteriorating inventory, European Journal of Operational Research, 134, 1–16). Since then, over two hundred articles on this subject have been published in the major journals on inventory control, indicating the need for a new review. We use the classification of Goyal and Giri based on shelf life characteristics and demand characteristics. Contributions are highlighted by discussing main system characteristics, including price discounts, backordering or lost sales, single or multiple items, one or two warehouses, single or multi-echelon, average cost or discounted cash flow, and payment delay.

Lean Production and information technology: Connection or contradiction?

The principles of Lean Production have enabled organisations in the manufacturing and service sectors to significantly improve their competitiveness. The application of Lean principles, derived from the Toyota Production System has enabled many organisations to simultaneously improve productivity, quality and customer service. Similar benefits have been achieved through the application of information technology (IT). The application of IT and Lean principles are claimed to be interdependent and complimentary by some; whilst others have seen as the approaches as being mutually exclusive. This article presents reviews the role of IT in achieving the principles of Lean Production. Three important topics are reviewed: the use of IT in production logistics; computer-aided production management systems; and advanced plant maintenance. It is shown that the roots of different ways of working were similar, but that subsequent developments followed in opposite directions. Later, when the acceptance of Lean Production became more pervasive, the practices typically converged into hybrid production systems, applying elements of several systems in a way that is consistent with the principles with Lean Production.

Lean production and ERP systems in small- and medium-sized enterprises: ERP support for pull production

It is generally accepted that lean production improves manufacturing processes through the systematic application of lean practices, and equally assumed that present day IT systems, particularly ERP systems, are essential for companies seeking efficiency through organisational integration. Though lean production and ERP co-exist in many companies today, there is an ongoing argument in the scientific literature as to whether or not ERP systems can be used to support lean production principles, particularly pull production. By applying a multiple-case-study approach, we assess the functionality offered by ERP systems to support pull production. We develop and apply a capability maturity model that can be used to assess the extent to which the usage of a companys current ERP system supports pull production practices and to suggest modifications to the ERP system in order to better serve the companys pull system. We focus on the application of lean production and ERP within small- and medium-sized enterprises, as in these companies decisions on lean and ERP are generally made by the same decision maker, which improves construct validity.

Workload balancing capability of pull systems in MTO production

Pull systems focusing on throughput time control and applicable in situations with high variety and customisation are scarce. This paper compares three unit-based pull systems that can cope with such situations: POLCA, CONWIP and m-CONWIP. These systems control the shop floor throughput time of orders by limiting the number of orders on the shop floor. However, their effectiveness in terms of reducing total throughput time is questioned. Theory states that an improvement in the average total throughput time will be due to the workload balancing capability of a pull system, but that many pull systems lack this capability. This paper shows that this workload balancing capability exists for POLCA and m-CONWIP, but not for CONWIP. The magnitude of the effect differs strongly, depending on the configuration of the system, the order arrival pattern and the variability of the processing time of the orders.

Design of POLCA material control systems

POLCA is a material control system designed for make-to-order or engineer-to-order companies. These firms have to cope with a high variety of customised products, and strong pressure to provide short throughput times. POLCA constrains the amount of work in progress on the shop floor in order to achieve a short average shop floor throughput time. Earlier work has shown that the POLCA system has the capability to reduce both the average shop floor throughput time and the average total throughput time, but it is only effective if the POLCA system has been appropriately designed. The design of the POLCA system is therefore being investigated and discussed in this paper. We give an extensive literature review and give attention to the authorisation mechanisms of POLCA, the design of control loops, the route-specific capacity signals (POLCA cards), and specific facilities needed to use the POLCA system in practice. Finally, we report on the design of a POLCA system in practice, the first complete implementation of POLCA in The Netherlands, and present the quick scan that was used in the design of the POLCA system for this SME.

Improving a practical DBR buffering approach using Workload Control

This paper deals with improving the lead-time performance of a small packaging manufacturer in the Netherlands that had already implemented several facets of Theory of Constraints (TOC) in 1997. Since then, delivery reliability and profits have increased and lead-times reduced substantially. In an attempt to achieve further lead-time improvements in 2001, the firm recently encountered some limitations of its partial TOC implementation. In this paper we focus on the modifications of its order acceptance and buffer management system that were necessary in order to obtain the desired lead-time reduction. We describe how Workload Control principles were introduced to improve the buffering approach and planning procedures the firm had been using since 1997. It shows that Workload Control provides effective tools that can be used in combination with the Drum-Buffer-Rope mechanism in order to balance the flow of work to the production floor.

Editorial: Advancing lean manufacturing, the role of IT

This introduction to the special issue discusses the changing role of information technology (IT) in advancing lean production. Lean principles and techniques have been applied in a wide variety of organisations, from make-to-stock to engineer-to-order industries, and even in typical service sectors, such as healthcare. In order to apply lean principles in various areas, variants were developed of well-known techniques, such as Kanban, Kaizen, SMED, and 5S. IT is used to develop such variants. Over the years, the role and use of IT in the application of the lean principles has changed. In this introduction, we discuss the main findings of the papers that were selected for publication in this special issue.

Period batch control : classic, not outdated

Period Batch Control was developed and first applied during the Second World War. The historic roots are discussed and the principles of this classic production planning approach explained, PBC compared to other production control concepts, and it is demonstrated that it may still be fruitfully applied, especially in combination with cellular manufacturing. It is therefore considered as a classic, but not outdated production planning concept.

Placement of Effective Work-In-Progress Limits in Route-Specific Unit-Based Pull Systems.

Unit-based pull systems control the throughput time of orders in a production system by limiting the number of orders on the shop floor. In production systems where orders can follow different routings on the shop floor, route-specific pull systems that control the progress of orders on the shop floor by placing limits on the number of orders in (parts of) a routing, have shown to be effective in controlling throughput times. This is because route-specific pull systems are able to create a balanced distribution of the amount of work on the shop floor, which leads to shorter and more reliable throughput times. The placement of limits on work-in-progress in a route-specific pull system determines to a large extent the workload balancing capability of such a system. This paper shows how the placement of work-in-progress limits affects the workload balancing capability and thereby the throughput time performance of a route-specific unit-based pull system, namely POLCA.

Flow shop scheduling with multiple operations and time lags

A scheduling system is proposed and developed for a special type of flow shop. In this flow shop there is one machine at each stage. A job may require multiple operations at each stage. The first operation of a job on stage j cannot start until the last operation of the job on stage j - 1 has finished. Pre-emption of the operations of a job is not allowed. The flow shop that the authors consider has another feature, namely time lags between the multiple operations of a job. To move from one operation of a job to another requires a finite amount of time. This time lag is independent of the sequence and need not be the same for all operations or jobs. During a time lag of a job, operations of other jobs may be processed. This problem originates from a flexible manufacturing system scheduling problem where, between operations of a job on the same workstation, refixturing of the parts has to take place in a load/unload station, accompanied by (manual) transportation activities. In this paper a scheduling system is proposed in which the inherent structure of this flow shop is used in the formulation of lowerbounds on the makespan. A number of lowerbounds are developed and discussed. The use of these bounds makes it possible to generate a schedule that minimizes makespan or to construct approximate solutions. Finally, some heuristic procedures for this type of flow shop are proposed and compared with some well-known heuristic scheduling rules for job shop/flow shop scheduling.