Model and analysis of integrated production–inventory system: The case of steel production

The study originated from an industrial case study in the field of steel production, but it presents a larger interest, as many other manufacturing fields have similar concerns (e.g. foundries, food, textile and paper industries). A significant phase of steel manufacturing is the product cooling (likewise, drying in paper and textile production, or maturing in food production). This phase may be completed in different ways, but (1) it must be carried out in the finished product warehouse and (2) it must meet both production optimisation and customer needs. The latter requirement acquires a strategic relevance in JIT environments. The present study proposes a mathematical model to find the optimal production schedule of steel billets, based on the relevant parameters of the productive system (set-up and processing times, demand profile). In the industrial case examined, the negative impact of holding costs on cash flows is also linked to the space required by the cooling process, which depends on the production schedule adopted. In other words, the finished product storage can be considered a part of the manufacturing cycle and impacts on it. In the case of steel plants operating in JIT environments, the warehouse must be promptly emptied and carefully managed to exploit the available space. Thus, the effect of inventory costs is examined in a production–inventory system with finite capacity, where products are made to order and share the same manufacturing facility. The study is completed by an experimental analysis to investigate the effect of variations in the relevant parameters of the problem.     

ADVANCES IN LOGISTICS AND THE GROWTH OF INTRA‐FIRM TRADE: THE CASE OF CANADIAN AFFILIATES OF U.S. MULTINATIONALS, 1984–1995*

Intra‐firm trade in intermediates between U.S. multinational parents (MNCs) and their Canadian manufacturing affiliates increased dramatically in the 1984–1995 period (i.e., it roughly doubled). Tariff and transport cost declines were far too small to explain this phenomenon. But we show that the advent of improved logistics management practices, including the ‘just‐in‐time’ (JIT) production system, can explain much of the growth of intra‐firm trade. JIT lowers the inventory carrying cost component of intra‐firm trade, and, by 1984, this was more important than tariff and transport costs in many industries. We combine regression analysis with numerous case studies to draw our conclusions.     

Environmentally responsible inventory models: Non-classical models for a non-classical era

Mathematical models of inventory typically include the three inventory associated costs of surplus, shortage and ordering. These classic inventory models are then analysed so as to choose inventory parameters that usually minimise the total cost of operating the inventory system being investigated.Unfortunately, classic inventory models do not provide a meaningful basis for analysing many real and increasingly important practical inventory problems and situations. It is therefore not surprising that over recent years, several authors have discussed these issues in broad terms and suggested that a new paradigm needs to be developed.This paper develops some specific aspects of this discussion. In particular, the paper identifies a range of inventory problems that are not covered appropriately by traditional inventory analysis. One of these is to design responsible inventory systems, i.e. systems that reflect the needs of the environment. The paper then examines the importance of inventory planning to the environment in greater detail. For example, packaging is important, not only because of its costs and the protection that it provides to the inventory items, but also because of its eventual effects on the environment in terms of the use of resources and potential landfill. For similar reasons, waste, which can result from poor inventory management, is highly important. The location of stores is important because location affects transport costs. Thus the influence of the secondary aspects of most inventory models; packaging, waste and location are important but, even more important are the inter-relations with the total system. In particular, the location of the manufacturing plants and the effect that inventory planning has on the logistics chain, potentially have considerable environmental implications. Inventory is part of a wider system.However, until the cost charged for an activity reflects the true environmental cost of that activity, it is likely that decisions will be made on the basis of erroneous data. In that situation, we are faced with either determining the environmental cost of specific actions or to use environmental costs that are somewhat contrived; in which case it may be more sensible to use very different performance measures and models. The paper discusses these ideas and ways in which inventory policies may reassure us with our environmental concerns.     

Economic lot-sizing and dynamic quantity competition

We study a problem of dynamic quantity competition in continuous time with two competing retailers facing different replenishment cost structures. Retailer 1 faces fixed ordering costs and variable procurement costs and all inventory kept in stock is subject to holding costs. Retailer 2 only faces variable procurement costs. Both retailers are allowed to change their sales quantities dynamically over time. Following the structure of the economic order quantity (EOQ) model, retailer 1 places replenishment orders in batches and retailer 2 follows a just-in-time (JIT) policy. The objective of both retailers is to maximize their individual average profit anticipating the competitor's replenishment and output decisions. The problem is solved by a two-stage hierarchical optimization approach using backwards induction. The second-stage model is a differential game in output quantities between the two retailers for a given cycle length. At the first stage, the replenishment policy is determined. We prove the existence of a unique optimal solution and derive an open-loop Nash equilibrium. We show that both retailers follow contrary output strategies over the order cycle. The EOQ retailer, driven by inventory holding costs, decreases his market share whereas the output of the JIT retailer increases. Moreover, depending on the cost structure, the EOQ retailer might partially be a monopolist. At the first stage, the EOQ retailer determines the cycle length, anticipating the optimal output trajectories at the second stage.     

The relationship between UK manufacturers’ inventory levels and supply,internal and market factors

A major survey of UK manufacturing plants was carried out to explore the relationships between certain factors and inventory levels. These factors include procurement lead time, customer delivery lead time, manufacturing lead time and levels of predictability of raw materials availability and customer demand levels. The sample for the study comprises UK manufacturing plants in different industrial sectors including engineering, process, electronics, household products and food sectors. The results of a correlation analysis show that supply chain management issues such as the procurement lead time and the frequency of raw materials delivery are significantly linked with the inventory level of manufacturing plants. Also, manufacturing lead times were found to be associated with inventory levels but there was no significant relationship between customer delivery lead times and inventory levels.     

Integrated product specifications and productivity decision making in unreliable manufacturing systems

This paper considers joint production control and product specifications decision making in a failure prone manufacturing system. This is with the knowledge that tight process specifications, while leading to a product of more reliable quality and higher market value, are at the same time associated with higher levels of non-conforming parts, a higher rate of parts rejection and thus a lowering of overall plant productivity. The decision making is further complicated by the lack of reliability of the production process, which imposes that an adequate, also to be designed, level of inventory of finished parts be maintained. The overall optimal decision policy is defined here as one that maximizes the long term average per unit time profit of a combined measure of quality and quantity dependent sales revenue, minus inventory and backlog costs, in the presence of random plant failures and random repair durations. Policy optimization is achieved via a revisited model of the Bielecki–Kumar theory for Markovian machines and a simulation and experimental design based methodology for the more general cases.     

Non-cooperative strategies for production and shipment lot sizing in one vendor-multi-buyer system

The supply chain structure examined in this paper consists of a single vendor (or manufacturer) with multiple heterogeneous buyers (or retailers). A continuous deterministic model is presented. To satisfy buyers demands, the vendor will deliver the product in JIT shipments to each buyer. The production rate is constant and sufficient to meet the buyers’ demands. The product is shipped in discrete batches from the vendor's stock to buyers’ stocks and all shipments are realized instantaneously. Special production-replenishment policies of the vendor and the buyers are analyzed. That is, the production batch is transferred to each buyer in several sub-batches in each production distribution cycle (PDC).This paper offers game model without prices, where agents minimize individual costs. It is a non-cooperative (1+N)-person game model with agents (a single vendor and N-buyers) choosing numbers and sizes of transferred batches. The model describes inventory patterns and cost structure of PDC. It is proved that there exist Nash equilibria in several types of sub-games of the considered game.     

Manufacturing Plants' Use of Temporary Workers: An Analysis Using Census Microdata

Using plant‐level data from the plant capacity utilization survey, we explore how manufacturing plants' use of temporary workers is associated with the nature of their output fluctuations and other plant characteristics. We find that plants tend to use temporary workers when their output is expected to fall; this may indicate that firms use temporary workers to reduce costs associated with dismissing permanent employees. In addition, we find that plants whose future output levels are subject to greater uncertainty tend to use more temporary workers. We also examine the effects of wage and benefit levels for permanent workers, unionization rates, turnover rates, seasonal factors, and plant size and age on the use of temporary workers; based on our results, we discuss various views of why firms use temporary workers.     

Reengineering the production planning process in the food industry

This paper addresses managerial process reengineering and in particular the reengineering of the production planning process. The reengineered process highlights planning options to avoid the process imbalance and loss of production potential that can follow innovation in a facility that is fully committed to JIT production.The study was motivated by production problems following product innovation within the food industry but the reengineering conclusions and procedures are applicable to all similarly structured industries. An example based on data from a snack food manufacturing company illustrates the reengineered procedure for a plant that is typical of the food processing industry.     

Optimal production–inventory strategies for a HMMS-type reverse logistics system

The aim of the paper is to find optimal inventory policies in a reverse logistics system with special structure. It is assumed that demand is a known continuous function in a given planning horizon and return rate of used items is a given function. There is a constant delay between the using and return process. We investigate two stores. The demand is satisfied from the first store, where the manufactured and remanufactured items are stored. The returned products are collected in the second store and then remanufactured or disposed. The costs of this system consist of the quadratic holding costs for these two stores and the quadratic manufacturing, remanufacturing and disposal costs.The model is represented as an optimal control problem with two state variables (inventory status in the first and second store) and with three control variables (rate of manufacturing, remanufacturing and disposal). The objective is to minimize the sum of the quadratic deviation from described inventory levels in stores and from described manufacturing, remanufacturing and disposal rates. In this form, the model can be considered as a generalization of the well-known Holt et al. (Planning Production, Inventories, and Work Forces, Prentice-Hall, Englewood Cliffs, NJ, 1960) model with two warehouses. After solving the problem, we give some numerical examples to represent the optimal path in dependence of the demand rates.     

Optimal policies in hybrid manufacturing/remanufacturing systems with product substitution

In hybrid control systems for simultaneous remanufacturing of used products and manufacturing of new ones, the two operations are not directly interconnected if remanufactured items are downgraded and have to be sold in markets different from those for new products. Sometimes a connection between these markets is given by a downward substitution property which allows the producer to offer a new item instead of a remanufactured one in case of a shortage of a remanufactured product. Thus, shortage costs can be avoided, but a loss in profit due to sale of a high-graded product at the price of a low-graded one has to be accepted. For a single-period problem with stochastic returns of used products and stochastic demands of serviceable ones, it is shown how the manufacturing and remanufacturing decisions have been coordinated in order to maximize the total expected profit. It turns out that under strictly proportional costs and revenues a medium-simple ‘order-up-to policy’ with two parameters and two parameter functions is optimal. However, optimal policies in situations where manufacturing leadtimes exceed leadtimes for remanufacturing turn out to be different from those in the opposite leadtime case. The research presented combines methods for policy analysis in stochastic manufacturing/remanufacturing problems and in stochastic inventory control problems with substitutable products.     

Efficient location of industrial activity cells in a global supply chain

Inefficient locations for production, distribution and reverse logistics plants will result in excess costs no matter how well material requirements planning (MRP), inventory control, distribution and information sharing decisions are optimized. In this paper we study ways in which aspect of activity cell location decisions can be analyzed within an extended MRP model. This model has previously been extended by including distribution and reverse logistics components in a compact form, presented in Grubbström et al. (2007). Our aim is to demonstrate the basic differences between an approach to location problems with MRP “under the same roof” as the global supply chain, in which transportation time delays and direct transportation costs have substantial influence. We discuss possibilities of how to present location aspects in the supply chain model obtained from combining input–output analysis and Laplace transforms in four sub-systems, namely manufacturing, distribution, consumption and reverse logistics, and show how the transportation costs and lead time influenced by the location of all these activities affect the resulting net present value (NPV). Our aim is to build a model supporting decisions concerning the structure of a supply chain as an alternative to a mixed integer programming formulation. The model developed is based on the use of continuous functions describing spatial distributions of cost and customer demand. Continuous functions are embedded in the MRP extension previously introduced in Grubbström et al. (2007).Location decisions influence (i) production costs, because timing influences the cost of activities involved in creating a product, cf. (Grubbström and Bogataj, submitted for publication), and (ii) logistics costs, which refer to the procurement and physical transmission of materials through the supply chain. In this current paper we wish to combine both of these aspects into a comprehensive model, where we show the interaction between the “space of flows” and the “space of places” as Giovanni Arrighi distinguishes one from the other in his book The Long Twentieth Century.     

Cost Accounting and Performance Measurement in a Just-in-Time Production Environment

There are normative statements in the literature, backed up by case observations and anecdotal evidence, which indicate that manufacturing companies operating just-in-time (JIT) production management systems should also change their cost accounting systems and place greater reliance on non-financial performance indicators. This study provides empirical evidence suggesting that JIT manufacturing companies which have made some degree of modification to their costing system demonstrate higher performance than JIT companies which have not made changes. The results also suggest that greater use of non-financial performance indicators is associated with higher performance irrespective of the production management system adopted.     

Architectures,methods and tools for enterprise engineering

In today's highly competitive global economy, the demand for high-quality products manufactured at low costs with shorter cycle times has forced a number of manufacturing industries to consider various new product design, manufacturing, and management strategies. Recently, due to the rapid advances in Information Technology (IT), new paradigms have successively emerged such as CIM, JIT, lean manufacturing, concurrent engineering, business process engineering and more enterprise engineering (EE). Enterprise modeling is currently in use either as a technique to represent and understand the structure and behavior of the enterprise, or as a technique to analyze business processes, and in many cases as support technique for business process reengineering. However, architectures and methods for EE have also to cover the integration of quality, information system, cost, human and organizational aspects and have to support the EE process from goal and requirements definition up to implementation and operation (Vernadat, 1999. Proceedings of CARS&FOF 99 Conference, Aquas de Lindoia, Brazil).This paper provides an overview of architectures, methods and tools for EE. It then points out substantial results achieved so far as well as presents a methodology and a related tool in more detail, which supports all phases and aspects of EE.     

The possibility of price umbrellas in Canadian manufacturing industries

The paper looks for evidence of ‘price umbrelias’ within Canadian manufacturing industries. Price umbrellas occur when relatively low-cost firms, trading-off market share against profit margins, set a price high enough to allow relatively high-cost firms to remain in business (the latter have an ‘umbrella’ held over them). The disaggregated data appear to show (1) that there are significant differences in average costs between the plants within an industry, (2) that the marginal costs of the low-cost plants are non-increasing with output. Together, these findings imply that output could be transferred from high- to low-cost plants with a reduction in total-industry costs, consistent with the existence of price umbrellas. The numbers are quite large.     

Taylorism, new technology and just-in-time systems in Japanese manufacturing

This article attempts to examine what is believed to be a significant overall Taylorist influence in Japanese manufacturing as well as a specific manifestation of this phenomenon, namely the unique flow requirements of the generic Toyota system (JIT). The use of unbufferred flow, it is argued, is feasible only with consistent quality, thus making non-discretionary Taylorist job design a necessary condition.     

Ground beef recalls and subsequent food safety performance

The U.S. Food Safety Inspection Service recalled more than 370 million pounds of meat and poultry products and oversaw 680 Class 1 recalls over 1998–2014. The cost to firms was about $109 million in lost market value (Pozo and Schroeder, 2016). Thomsen and McKenzie (2001) argue that firms internalize the costs of recalls, and Marino (1997) asserts that high food safety costs lead to food safety investment, but no research has examined the impact of recalls on plant food safety performance. Using performance on tests for Salmonella conducted by the Food Safety Inspection Service as a measure of food safety, this article examines the performance on Salmonella tests of ground beef plants with Class 1 recalls. The results show that plants have high Salmonella levels before and during the year of the recall and have much lower levels afterward. The paper also shows that ground beef plants with recalls are less likely to meet the FSIS standard for Salmonella and that the likelihood of failing to meet the standard increases as the standard becomes more stringent.     

Impact of contracts in high yielding varieties seed production on profits and yield: The case of Nepal

Nepal’s population continues to grow, but the agricultural sector’s performance remains almost stagnant. This has led to a decline in the per capita availability of food. Increasing agricultural productivity is the key to agricultural growth, and one strategy for increasing agricultural productivity is to use improved seeds. This study investigates the impact of contract farming (CF) in high yielding varieties (HYV) of paddy seed production on costs, yield, and profits of smallholder farms in Nepal. Using farm-level data and a non-parametric propensity score matching estimator, the study finds a significant positive impact of contract HYV seed farming on revenues, profits, and yield, and a significant negative impact on total costs of production. Additionally, very small farms (⩽0.43 ha) with CF in HYV paddy seeds tend to gain the most when it comes to yield per hectare. Our estimates reveal that the average smallholder household in Nepal engaged in CF with input conditions receives higher profits. However, farmers engaged in CF with output conditions tend to have higher yields but smaller profits. Finally, farmers engaged in CF in HYV paddy seeds with both input and output conditions have the highest yield gains and significantly higher profits.     

Profitability, Ownership Structure and Technical Efficiency of Enterprises in the People's Republic of China: A Case of Manufacturing Industries in Shanghai

This paper studies the relationship between accounting profits and technical efficiency of manufacturing enterprises in Shanghai during the period 1989–1992 and examines which factors affect the profitability of manufacturing enterprises. We first estimate the average technical efficiency of four major manufacturing industries in Shanghai. Then, we test for the presence of ownership effects of technical efficiency on profits of those enterprises in these four industries.     

Integrated multi-period cell formation and subcontracting production planning in dynamic cellular manufacturing systems

In this paper, an integrated mathematical model of the multi-period cell formation and production planning in a dynamic cellular manufacturing system (DCMS) is proposed with the aim of minimizing machine, inter/intra-cell movement, reconfiguration, partial subcontracting, and inventory carrying costs. This paper puts emphasis on the effect of the trade-off between production and outsourcing costs on the re-configuration of the cells in cellular manufacturing systems (CMSs) under a dynamic environment, in which the product mix is different from a period to another resulting in the operational dynamism in the cells. The proposed model is verified by a number of numerical examples and related sensitivity analysis.