Linking performance drivers in production planning and inventory control to process choice

This study investigates how process choice relates to production planning and inventory control decisions. We empirically examine the validity of deductively derived patterns about these types of decisions. More importantly, we look for normative insights by exploring how production planning and inventory control decisions affect operations performance. Our findings show that production line and continuous flow plants use more of a level production strategy, and carry less raw material and work-in-process inventory. The performance drivers for these plants, through which the operations function excels, are effective utilization of equipment, reduced finished goods inventory, and reduced setup down time. To gain forward demand visibility and batching economies, job and batch shops rely much more on backlogs in their planning process. These plants use more of a production chase strategy and position inventory lower in the bills of materials. Four performance drivers for top-performing job and batch shops are to find ways that better anticipate customers' orders, have a more responsive chase strategy, carry less raw material or purchased inventory, and shorten production planning horizon, partly through less reliance on backlogs. It is intriguing that top-performing plants not only do the expected things, given their choice of process, but also excel in selected dimensions—some of which fit the profile normally associated with a different process choice. To monitor and continuously improve operations, evaluation ‘scorecards’ should pay particular attention to performance drivers, which change depending on the plant's process choice.     

Maintenance management: Keeping up with production's changing trends and technologies

Current trends in manufacturing have led to reduced levels of work-in-process inventory and increased levels of automation and machine complexity. These changes have two important implications for maintenance management. First, machine breakdowns not only cause a loss of output from the down machine, but also result in lost production on downstream machines. This occurs because of the elimination of buffer stock between workstations. Second, the gap between the technological expertise of the operators and the technological sophistication of their machines has widened. This gap decreases the ability of operators to make adjustments and minor repairs to their own machines.These two factors cause an increase in maintenance costs associated with machine downtime and maintenance labor. Historically, the proportion of preventive and corrective maintenance has attempted to balance these costs. As buffer stock is reduced and more machines are coupled, the costs of downtime will increase, increasing the need for preventive maintenance and decreasing its cost compared to the cost of lost production.Increases in the use of computer-based planning systems have resulted in the development of computerized preventive maintenance systems that have proven to be successful in planning for maintenance labor and materials. Integrating planning methods with corrective maintenance tasks will help reduce breakdowns, make more efficient use of maintenance craft labor, and provide information for inventory control of maintenance, repair, and operating (MRO) materials.This article examines methods of reducing machine downtime costs, maintenance labor costs, and MRO inventory costs in today's changing production environment. Techniques for reducing these costs are explored in the areas of maintenance planning, maintenance methods improvement, and MRO inventory control.     

The effects of workforce strategies on manufacturing operations

This paper tests the effects of three workforce strategies on a multistage, multiproduct manufacturing system under various operating conditions. These three strategies are those that are predominant in today's world economics. One type is a chase strategy, often used by firms that employ low skilled workers and faced with seasonal product demands, where workforce levels fluctuate according to increases and decreases in production requirements. A level-flexible strategy, commonly called the Toyota system, keeps the aggregate workforce at a constant size but by having flexibly trained workers it can allow transfers of workers between various departments and processes as production requirements dictate. The third major type is a level-inflexible strategy, such as that used on mass-assembly lines employed by American automobile manufacturers. Under this strategy, the number of workers remains constant in each department as well as at the aggregate level regardless of short term changes in the production requirements. The manufacturing system is envisioned as a sequential planning process with interrelated decisions made at the levels of aggregate planning, master production scheduling, and departmental planning. This process is modeled as a zero-one mixed integer program. The operating conditions under which the strategies are tested are the variability of demand, the level of service, and the degree of inventory investment. The strategies are statistically tested as to their effects on five criteria: average weekly workforce size, average quarterly inventory investment, average weekly overtime, total setups and the average weekly ratio of departmental load to capacity.Using four different products and an experimental manufacturing environment described within the paper, we tested for any statistical differences between the three strategies. We found that none of the strategies had significantly different workforce sizes. Also, the chase strategy had the smallest average quarterly inventory investment. This implies that the “Japanese” level-inflexible strategy does not have the smallest workforce or lowest inventory as claimed by some.We also tested the effects of the operating conditions on the workforce strategies. The level-flexible strategy was most insulated from the seasonality, inventory restrictions, and service level. Thus again the claims made for the level-inflexible strategy about being insulated from its environment were not substantiated. It was found that the seasonality of demand had the greatest impact on the three workforce strategies. Also, the level of service greatly affected the utilization of labor resources.The major overall conclusion is that the level-flexible strategy which is associated with some Japanese manufacturing firms does not achieve the claims that some of its adherents have made for it. It does not have the smallest workforce or the lowest inventory nor is it best insulated from its environment. Furthermore, the seasonality of demand and the level of service do effect this strategy.     

生产管理中计划调度的组织架构优化设计

针对企业生产管理中存在的计划调度组织层级较低且职能分散的情况,提出精简组织架构、简化业务流程、提升生产管理效率的组织架构优化方案,以期实现企业的劳动生产率、生产产值、产品销售额、企业利润率、存货周转率、资金周转率等企业运营关键业务指标的大幅提升,极大增强企业竞争力。     

供应链环境下的可维修备件共享库存和集中维修模式

对于资产密集的流程式生产企业而言,设备库存管理和设备维修管理是企业管理的重要工作。传统上企业分散管理和维修的方式通常会导致高库存成本和低服务率的同时存在。本文研究同一区域同类企业同类备件的库存共享和集中维修模式,针对不同企业和同一集团下的不同工厂提出了相适应的共享库存管理模式。     

Managing returnable transport items in a vendor managed inventory system

This paper addresses a closed-loop inventory routing problem with demand uncertainty, which manages the delivery operations to customers and pick-up operations of empty returnable transport items (RTIs) from customers. The problem involves decisions regarding forward and backward vehicle routes, the delivery and collection quantities, the amount of production in terms of the number of filled RTIs, and the number of RTIs produced/ bought by the vendor during the defined planning horizon. The problem considers the holding costs, fixed cost of operating vehicles, fuel consumption cost, producing/buying costs, cleaning costs of RTIs, and loading and unloading costs. We formulate the problem as a mixed integer linear programming model and propose a Relax and Fix based solution approach to solve large instances. We conduct extensive analyses on a case study derived from a fruit and vegetable distribution network and several hypothetical instances. Our analyses investigate the effects of several problem parameter changes (i.e., average collection rate, customer service level, cost of buying crate and handling cost) on the total logistics cost. Additional numerical analyses are performed to demonstrate the usage of the model for evaluating the cost of being more green and environmental-friendly. Moreover, experiments on relatively large-scaled problems allow us to demonstrate the potential benefits of the proposed heuristic     

A lot sizing and sequencing algorithm for dynamic demands upon a single facility

A heuristic algorithm is developed and applied to determine lot sizes and production sequence on a single facility. The various product demands are treated as deterministic and time varying (dynamic) over a finite planning horizon, such as that generated from a material requirements planning (MRP) system.In contrast to other approaches available, the algorithm considers the sequencing decision in each period by realistically assuming inventory holding cost occurrence in the period of production, and in addition, it is capable of considering set-up times where such set-up times consume available productive capacity. The ability to handle numerous products, and the capability of being able to specify maintenance time and holidays is an integral aspect of the algorithm.The results of an application of the algorithm in a medium size bearing company have shown very significant reduction in the controllable inventory holding cost while eliminating late deliveries. In an effort to cope with potential realistic schedule alterations, different solutions were developed for managerial evaluation providing greater flexibility but at a higher cost.     

Break through to 98 percent inventory record integrity in just 120 days.

Companies have tried to live without inventory integrity, but high performance and high profitability depend on high levels of inventory integrity. Good decisions require good facts, and inventory is often the most important fact upon which business decisions are based. This article explains how to attain an inventory integrity level of between 95 and 98 percent or even higher in 120 days or less and how to keep it there.     

A reformulation of the aggregate planning problem

This article proposes a reformulation of the aggregate planning problem which more closely agrees with situations frequently encountered in practice. The proposed reformulation assumes that a firm's production planners want to determine the expected service and inventory levels for a given production profile in the face of uncertain seasonal demand. By using several different production profiles that are each consistent with the firm's staffing, subcontracting, and overtime policies, it is possible to pick the profile that best meets the firm's preferences for service level and inventory turns. Actually, the trade-offs between inventory and service levels are examined so that an informed choice can be made by all of those concerned.One of the advantages of the proposed model is that communications can be established among production, marketing, and finance managers who often have conflicting goals. Also, levels for inventory turns, service, and production can be set that are consistent with each other. Furthermore, several alternative production profiles can be examined in a relatively short time through the use of the simulation model proposed.An application of the model to the Wagner Spray Tech Company, a producer of painting equipment, is presented. In this particular case, where forecasting errors are quite high, some of the potential uses of the model are presented. Also, reasons are given why this particular reformulation of the aggregate planning problem was found to be useful.     

Sales and marketing's partnership role in class A MRP II (material requirements planning)

As the material and requirements planning (MRP) II process has evolved, many companies have discovered that the process is greatly enhanced when the entire business participates. The sales and operations planning process is the forum for the businesswide decisions concerning sales, production, and inventory. Sales and marketing must be integral parts of these decision-making activities.     

Joint decision of procurement lot-size,supplier selection,and carrier selection

The joint decision making of procurement lot-size, supplier selection, and carrier selection has potential to reduce buyer's purchasing expenditures. Furthermore, the total logistics cost can also come down through economies of scale in the purchasing and transportation costs, and reduction in supply chain disruptions such as rejections and late deliveries. We study a procurement setting in which a buyer needs to purchase a single product from a set of suppliers over finite discrete time periods to satisfy service level requirements. The suppliers offer all-unit quantity discounts, and transportation cost depends on carrier capacity as well as geographical location of suppliers. This paper proposes an integer linear programming model to simultaneously determine the timings of procurement, lot-sizes, suppliers and carriers to be chosen so as to incur the least total cost over the planning horizon. A numerical example is included to demonstrate the effectiveness of the proposed model in establishing tradeoffs among purchasing cost, transaction cost, and inventory holding cost. Sensitivity analysis has been carried out to understand the effects of the model parameters on the purchasing decisions and total cost. Managerial insights of this study serve as a reference for decision makers to develop effective procurement strategies.     

Production and supply management strategies in Nordic paper mills

The traditional production management strategy in paper manufacturing is based on a volume-intensive approach. This involves the measurement of overall performance or productivity, while aiming at a high level of capacity utilisation and minimum waste levels. This approach has proved successful in mills producing high volumes with a limited and standardised product range. The situation changes radically when paper and board products are being tailored to customer-specified dimensions and quantities. The volume-based approach is no longer appropriate, and production has to be controlled by an approach that considers inventory performance along the full length of the supply chains. This paper presents five empirical examples to illustrate the use of the two strategies. The detailed analyses of production cycles, the logistical solutions applied and the inventory levels at various stages of the supply chain, show that the Nordic paper industry is slow, with average lead times of 79 days to market. When production cycles are reduced and logistical alternatives are fully exploited, it can be seen that 30% of the inventories can be regarded as slack. The summary of the cases shows that speedier operations easily generate direct cost savings amounting to 2–5% of annual turnover. All these results can be achieved without additional investment; all that is required is a change in production planning principles and logistical control procedures. The paper concludes with a challenge to the Nordic paper industry to be the first in its field to achieve the higher level of productivity that faster operations can generate.     

The cost of inflated planned lead times in MRP systems

Much of the current literature in the field of production and inventory control systems stresses the need to revise traditional forms of thinking regarding production processes, the role of inventories for work in process, and the need for reduced lead times or flow times. Group technology, manufacturing cells, and other means of incorporating repetitive manufacturing techniques into traditional job-shop settings constitute the leading edge in system development.Still, there is resistance to these dramatic changes, and traditional “business as usual” methods still predominate. This study attempts to illustrate graphically the cost justification associated with reduction in lead times which generally results from these new concepts. In most job shops today, lead times are much longer than they need to be due to inflation of lead time estimates. Actual lead times for the manufacture of fabricated and assembled products have been shown to be a direct consequence of the planning lead times used in the MRP planning process—a form of self-fulfilling prophesy.The research employs a simulation model of a factory using MRP as a planning tool in a multiproduct, multilevel production environment. Manufacturing costs constitute the dependent variable in the experiments, defined as the sum of material costs (including expedite premiums), direct labor costs (including overtime premiums), inventory carrying costs, and overhead costs. The independent variable being manipulated is the planned lead time offset used in the MRP planning process. Twenty values of planned lead time are evaluated ranging from a value that includes no slack time at all (pure assembly line) up to a value that allows 95% slack (queue) time which, unfortunately, is not uncommon in many job shops today. Stochastic variables in the model include customer demand and actual processing times—the sum of set-up and run times.The result of the study is a cost curve formed over the range of independent lead time variables that is constructed using nonlinear regression techniques. The conclusions from the resultant graph clearly indicate the cost consequences of long lead times, with exponential cost increases beyond the 80–90% queue time level. Total costs are 41% higher at the maximum lead time allowance compared to the minimum. Clearly, this study demonstrates the need for lead time reduction, either through downward adjustment of MRP planned lead times or by introducing new manufacturing concepts.     

企业内部二级库存系统中库存策略比较研究

针对随机需求下企业内部由中心仓库和下设的地区仓库组成的二级库存系统,运用推动式库存模型通过对相同服务水平下有中心仓库和无中心仓库两种情况的成本进行比较分析,来确定在企业内部二级库存系统中是否也设立中心仓库,以供决策者对库存策略进行合理规划。     

On the interpretation of cointegration in the linear–quadratic inventory model

The traditional formulation of the linear–quadratic inventory model with unit roots predicts cointegration between inventories and sales. That formulation implies that marginal production costs and the marginal benefits of inventories are both tending to ∞, and the cointegrating coefficient reflects the optimal trade-off between these competing factors. This paper suggests a reformulation of the problem in which marginal production costs and marginal inventory benefits are both stationary and in which the cointegrating coefficient is the same as the value that characterizes the target inventory level in the cost function.     

动态持有成本下的库存成本模型研究

对制造业企业来说,更大的生产能力就有机会带来更多的销量,所以在库存模型中需求率是与库存量正相关的变量,而并非在整个在库时间内都保持为常量。论文提出了一种库存成本与需求率分别和库存时间与库存量相关的模型,并针对两种成本结构各设计了一种优化算法以确定最优订购量和最优库存时间。     

公司库存优化方法浅析

库存是企业生产管理的重点内容之一,库存管理所要解决的核心问题是如何保证在不断提升客户服务满意度的前提下将库存成本控制在最低的范围之内。每个企业应当根据自身的现实条件和市场环境来确定最适合本企业的库存管理方案。N公司想要保持一个较低的库存水平,首先需要对库存材料进行分类．得出真正需要重点关注的物料清单,运用合适的采购订货策略．力求达到在按时满足客户需求的前提下使库存成本最低．．     

ABC理论在ERP系统的应用研究

ERP(企业资源计划)是支持供应链系统运作的一个综合计算机系统。基于活动的作业成本计算理论(ABC-Ac鄄tivity-BasedCosting)与供应链管理有极其相似性的原理-面向过程的绩效管理与优化。ABC理论用于ERP系统包括标准成本计算、财务管理、库存管理、生产计划与控制等;把ABC理论用于ERP系统,能使ERP系统各子系统紧密地联系在一起,形成面向过程的生产组织管理方式,有利于分析企业价值链变化情况,有利于业务流程的改造与优化。     

浅论我国零售业仓储存货成本控制

随着社会主义市场经济不断发展,零售业在社会经济发展中的作用越来越突出,同时,零售业间的竞争也越来越激烈。而仓储存货成本在零售业成本中占有重要比例。目前,各类仓储存货成本高成为制约我国零售业发展的一个关键因素。本文分析了我国零售业仓储存货成本控制存在的主要问题,并提出加强零售业仓储存货成本控制的对策,以提高零售业的利润率。     

零库存实施条件方法研究

在一定的服务水平下降低企业的库存成本,一直是企业物流管理的一个重要目标。零库存是库存状态为零的理想阶段。本文分析了零库存实施条件的,提出了企业实施零库存的几种方法,并就零库存实施的收益与风险进行了分析。