Developing maintenance craft labor efficiency through an integrated planning and control system: A prescriptive model

The area of maintenace management has been placed under increasing pressure because of changes in the manufacturing production planning and control systems. In the last few years plant management has been asked to respond to productivity and quality challenges unmatched in business history. The maintenance department plays an important, indeed vital, role in the attainment of improved levels of productivity and quality.This article examines the relationship between production and maintenance management systems. A conceptual model is developed that integrates the preventive and corrective aspects of maintenance planning with the priority and capacity activities of the production planning system. The model assists management in scheduling maintenance craft labor for additional efficiency and effectiveness.     

Optimal maintenance center inventories for fault-tolerant repairable systems

In many military and commercial contexts, complex equipment which is expected to perform very reliably is often designed to be fault-tolerant, that is, able to function although some of the parts have failed. A popular fault-tolerant design is the m-out-of-n system, where there are n identical parts, at least m of which must be functional for machine operation. Complex equipment of this type often undergoes scheduled maintenance overhauls at regular intervals during which all failed components are replaced. Failure to have replacements on hand for failed parts requires emergency measures at premium cost. When repairable parts are highly reliable and expensive, both holding and shortage costs are high. A reasonable objective is to choose initial spares inventory to minimize the sum of holding costs and expected shortage costs.We first develop a model to determine the optimal repairable parts inventory for a maintenance center servicing machines containing a single m-out-of-n system. The model is then extended to handle a related problem, finding optimal maintenance center inventories for machines containing several m-out-of-n systems of different parts, minimizing total expected costs subject to a constraint on total inventory investment.We assume that there is a fleet of machines, which experience identical workloads. There is a cycle time of T days between overhauls for an individual machine. A machine arrives at the maintenance center for overhaul each day. At the overhaul, all failed parts are removed and sent to a repair shop, from which they eventually return to the maintenance center to be used again as spares. The total number of spares undergoing repair and on hand is a constant. There are no backorders; if the number on-hand spares is insufficient to meet demand at an overhaul, a shortage penalty is assessed which depends on the number and type of spares required.While computing holding costs is straightforward, computing expected shortage costs is more complex. Expected shortage costs are dependent upon several factors, including component failure rates, the values of m and n, part repair rates, and the initial number of spares on hand. We assume that the system of interest is well specified, so that the parameters of the model are known except for the number of initial spares of each type, which are the decision variables. We model the on-hand inventory of each type of part as a Markov chain with the number of spares on hand at the end of each day as the states, under the assumptions that failure rates are constant and repair times follow independent exponential distributions. We then calculate the steady-state probabilities of stockout of various numbers of spares, as a function of the initial spares inventory. The expected shortage costs for a given type of spare may then be calculated by finding the product of the penalty cost for lacking p spares and the probability of lacking p spares and summing over all possible p values.Solutions to the problem of finding optimal initial inventory level for a machine containing a single m-out-of-n system may be found easily by enumeration. Solutions to the constrained problem where the machine contains several independent m-out-of-n systems, may be found by dynamic programming. Sensitivity analysis of costs to changes in the inventory investment constraint is clear, and computational effort is reasonable. A simple example is included to illustrate the solution method for both problems.     

Resolving uncertainty in manufacturing systems

This paper examines the effectiveness of three commonly practiced methods used to resolve uncertainty in multi-stage manufacturing systems: safety stock under regenerative material requirements planning (MRP) updates, safety capacity under regenerative MRP updates, and net change MRP updates, i.e., continuous rather than regenerative (periodic) updates. The use of safety stock reflects a decision to permanently store materials and labor capacity in the form of inventory. When unexpected shortages arise between regenerative MRP updates, safety stock may be depleted but it will be replenished in subsequent periods. The second method, safety capacity, overstates the MRP capacity requirements at the individual work centers by a prescribed amount of direct labor. Safety capacity either will be allocated to unanticipated requirements which arise between MRP regenerations or will be spent as idle time. The third method, net change, offers a means of dealing with uncertainty by rescheduling instead of buffering, provided there is sufficient lead time to execute the changes in the material and capacity plans.Much of the inventory management research has addressed the use of safety stock as a buffer against uncertainty for a single product and manufacturing stage. However, there has been no work which evaluates the performance of safety stock relative to other resolution methods such as safety capacity or more frequent planning revisions. In this paper, a simulation model of a multi-stage (fabrication and assembly) process is used to characterize the behavior of the three resolution methods when errors are present in the demand and time standard estimates. Four end products are completed at an assembly center and altogether, the end products require the fabrication of twelve component parts in a job shop which contains eight work centers. In addition to the examination of the three methods under different sources and levels of uncertainty, different levels of bill of material commonality, MRP planned lead times, MRP lot sizes, equipment set-up times and priority dispatching rules are considered in the experimental design.The simulation results indicate that the choice among methods depends upon the source of uncertainty, and costs related to regular time employment, employment changes, equipment set ups and materials investment. For example, the choice between safety stock and safety capacity represents a compromise between materials investment and regular time employment costs. The net change method is not designed to deal effectively with time standard errors, although its use may be preferred over the two buffering alternatives when errors are present in the demand forecasts and when the costs of employment changes and equipment set ups are low. The simulation results also indicate that regardless of the method used, efforts to improve forecasts of demands or processing times may be justified by corresponding improvements in manufacturing performance.     

A cost evaluation method for dynamic line balancing

A procedure is presented for calculating stochastic costs, which include operator (labor) and inventory costs, associated with dynamic line balancing. Dynamic line balancing, unlike the traditional methods of assembly and production line balancing, assigns operators to one or more operations, where each operation has a predetermined processing time and is defined as a group of identical parallel stations. Operator costs and inventory costs are stochastic because they are functions of the assignment process employed in balancing the line, which may vary throughout the balancing period, and the required flow rate. Earlier studies focused on the calculation of the required number of stations and demonstrated why the initial and final inventories at the different operations are balanced.The cost minimization method developed in the article can be used to evaluate and compare the assignment of operators to stations for various assignment heuristics. Operator costs and inventory costs are the components of the cost function. The operator costs are based on the operations to which operators are assigned and are calculated for the entire work week regardless of whether an operator is given only a partial assignment which results in idle time. It is assumed that there is no variation in station speeds, no learning curve effect for operators' performance times, and no limit on the number of operators available for assignment. The costs associated with work-in-process inventories are computed on a “value added” basis. There is no charge for finished goods inventory after the last operation or raw material before the first operation.The conditions which must be examined before using the cost evaluation method are yield, input requirements, operator requirements, scheduling requirements and output requirements. Yield reflects the output of good units at any operation. The input requirement accounts for units discarded or in need of reworking. The operator requirements define the calculation of operator-hours per hour, set the minimum number of operators at an operation, and require that the work is completed. The scheduling requirements ensure that operators are either working or idle at all times, and that no operator is assigned to more than one operation at any time. The calculation of the output reflects the yield, station speed, and work assignments at the last operation on the line.An application of the cost evaluation method is discussed in the final section of the article. Using a simple heuristic to assign operators, the conditions for yield, inputs, operators, scheduling, and output are satisfied. The costs are then calculated for operators and inventories.In conclusion, the cost evaluation method for dynamic balancing enables a manager to compare the costs of assigning operators to work stations. Using this method to calculate the operator and inventory costs, a number of different heuristics for assigning operators in dynamic balancing can be evaluated and compared for various configurations of the production line. The least cost solution procedure then can be applied to a real manufacturing situation with similar characteristics.     

考虑役龄阈值的最佳缓冲区库存维修策略研究

预防性维护PM对于生产系统有重要的作用。由于设备维护时会造成生产停滞,影响企业的经济效益,所以在生产线上下游设备之间建立库存缓冲区,保证生产的持续进行。考虑引入设备役龄阈值,构建费用模型和维护策略模型。以设备役龄阈值和缓冲区库存量为自变量,以最小化周期内总费用为目标,获得最佳的设备役龄阈值和缓冲区库存量。最后运用Matlab仿真软件进行了算例分析,验证了模型的有效性。     

综述：供应链库存成本研究的现状及其发展趋势

从生产／库存系统、库存／配送系统、生产－库存－配送系统、库存分配（Ａｌｌｏｃａｔｉｏｎ）等四个方面综述了供应链库存成本研究的现状,指出了当前研究的特点,存在的不足及其发展趋势。     

库存管理与国家石油储备

本文试用库存管理、"牛鞭子效应"、安全库存和库存成本等库存管理的基本理论,结合我国石油开采量与消费现状分析建设国家石油储备的重要性、迫切性和石油储备的相关成本。     

Optimal inventories for repairable redundant systems with aging components

Complex systems that are required to perform very reliably are often designed to be “fault-tolerant,” so that they can function even though some component parts have failed. Often fault-tolerance is achieved through redundancy, involving the use of extra components. One prevalent redundant component configuration is the m-out-of-n system, where at least m of n identical and independent components must function for the system to function adequately.Often machines containing m-out-of-n systems are scheduled for periodic overhauls, during which all failed components are replaced, in order to renew the machine's reliability. Periodic overhauls are appropriate when repair of component failures as they occur is impossible or very costly. This will often be the case for machines which are sent on “missions” during which they are unavailable for repair. Examples of such machines include computerized control systems on space vehicles, military and commercial aircraft, and submarines.An interesting inventory problem arises when periodic overhauls are scheduled. How many spare parts should be stocked at the maintenance center in order to meet demands? Complex electronic equipment is rarely scrapped when it fails. Instead, it is sent to a repair shop, from which it eventually returns to the maintenance center to be used as a spare. A Markov model of spares availability at such a maintenance center is developed in this article. Steady-state probabilities are used to determine the initial spares inventory that minimizes total shortage cost and inventory holding cost. The optimal initial spares inventory will depend upon many factors, including the values of m and n, component failure rate, repair rate, time between overhauls, and the shortage and holding costs.In a recent paper, Lawrence and Schaefer [4] determined the optimal maintenance center inventories for fault-tolerant repairable systems. They found optimal maintenance center inventories for machines containing several sets of redundant systems under a budget constraint on total inventory investment. This article extends that work in several important ways. First, we relax the assumption that the parts have constant failure rates. In this model, component failure rates increase as the parts age. Second, we determine the optimal preventive maintenance policy, calculating the optimal age at which a part should be replaced even if it has not failed because the probability of subsequent failure has become unacceptably high. Third, we relax the earlier assumption that component repair times are independent, identically distributed random variables. In this article we allow congestion to develop at the repair shop, making repair times longer when there are many items requiring repair. Fourth, we introduce a more efficient solution method, marginal analysis, as an alternative to dynamic programming, which was used in the earlier paper. Fifth, we modify the model in order to deal with an alternative objective of maximizing the job-completion rate.In this article, the notation and assumptions of the earlier model are reviewed. The requisite changes in the model development and solution in order to extend the model are described. Several illustrative examples are included.     

Enhancing capacity planning through forecasting: An integrated tool for maintenance of complex product systems

Despite the extensive amount of data generated and stored during the maintenance capacity planning process, Maintenance, Repair, and Overhaul (MRO) organizations have yet to explore their full potential in forecasting the required capacity to face future and unprecedented maintenance interventions. This paper explores the integration of time series forecasting capabilities in a tool for maintenance capacity planning of complex product systems (CoPS), intended to value data that is routinely generated and stored, but often disregarded by MROs. State space formulations with multiplicative errors for the simple exponential smoothing (SES), Holt’s linear method (HLM), additive Holt-Winters (AHW), and multiplicative Holt-Winters (MHW) are assessed using real data, comprised of 171 maintenance projects collected from a major Portuguese aircraft MRO. A state space formulation of the MHW, selected using the bias-corrected Akaike information criterion (AICc), is integrated in a Decision Support System (DSS) for capacity planning with probabilistic inference capabilities and used to forecast the workload probability distribution of a future and unprecedent maintenance intervention. The developed tool is validated by comparing forecasted values with workloads of a particular maintenance intervention and with a model simulating current forecasting practices employed by MROs.     

预防性养护新措施在南百高速公路的应用

文章介绍了预防性养护与矫正性养护的特点,分析了南百高速公路病害现状,重点介绍了高速公路沥青路面微表处、雾封层、超薄罩面、裂缝处治等预防性养护技术措施和养护机械化及养护时机的选择,为应用和推行高速公路沥青路面预防性养护技术提供参考。     

基于数据包络分析的汽车行业库存绩效评价研究--以某汽车公司为例

文中利用DEA模型方法,结合某汽车公司汽车零部件库存数据对企业的库存控制绩效进行评价研究。研究证明,某汽车公司库存管理中高投入低产出现象较明显,库存控制效率水平较低。企业应该减少安全库存持有量,降低仓储成本,提高库存资金周转率。对于汽车行业这种大型生产企业来,应该创立新的库存管理方式---虚拟联合库存管理,提高企业库存控制效率。     

发出存货计价方法浅析

选择不同的存货计价方法将会导致不同的成本水平、报告利润和存货估价,并对企业的税收负担,现金流量产生较大影响。文章在分析影响发出存货计价方法选择因素的基础上,提出基于税务筹划的发出存货计价方法。     

聚集效应对安全库存的影响研究

安全库存是一种额外持有的库存，也是一种缓冲器，它对库存成本有很大影响。本文从分析供应链是怎样运用库存聚集着手，研究在不降低产品供给情况下，聚集效应是怎样影响安全库存量。     

Monetary transmission right from the start: On the information content of the Eurosystem's main refinancing operations

The Eurosystem's main refinancing operations (MROs) are key for the interbank money market and the monetary transmission process in the euro area. This paper investigates how money market rates respond to the information revealed by various aspects of an MRO auction outcome. Our results confirm that the level of MRO rates governed short-term money market rates before the financial crisis. Since the start of the financial crisis, however, the information content of MRO rates has changed. While the levels of MRO rates have lost much of their pre-crisis significance, the spread between the weighted average and the marginal MRO rate has become an important barometer for the actual situation in the money market during the crisis.     

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.     

基于3PL_Hub的电信运营商库存管理技术研究

随着电信运营商之间的竞争逐渐加剧,为取得竞争优势,电信运营商也已开始与供应商、物流企业合作,采用3PL_Hub模式进行库存管理,降低供应链成本。但因行业不同,电信运营商基于3PL_Hub的库存管理运作模式与技术都与传统制造业有所不同。为此作者研究了电信运营商基于3PL_HUB的协同物流组织与运作模式构建、基于3PL_HUB协同运作下补货决策技术及3PL_Hub协同下IT支撑系统构建等用以支承电信运营商基于3PL_Hub库存管理的关键技术,并在中国电信部分省公司的协同物流建设应用。     

基于AHP与灰色关联分析法的航空发动机维修供应商评价与选择研究

航空公司通常将飞机发动机维修业务外包给专业维修供应商。合理的评价和选择维修供应商可以控制维修质量,提高飞机的安全性与可靠性。建立一套航空发动机维修供应商评价指标体系,利用(AHP)层次分析法确定指标权重,并建立了基于层次分析法和灰色关联分析法的维修供应商选择评价模型。     

冷冻机及操作

随着社会的发展、生产的扩大,为了实现更好地生产,化工操作工要熟练操作设备,并且做好设备的维护,减少生产损失,这样就可以减少检修带来的人力物力及停滞生产所带来的利润损失。在化工生产中主要有换热器、压缩机、冷冻机及泵,在此主要以冷冻机为例,介绍冷冻机的原理、组成、开车准备、操作、遇到积液的判断与处理,不断提高操作人员对冷冻机的操作,保护好设备并减少对设备的损伤。     

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。     

供应链库存成本降低措施研究

从牛鞭效应、最优批量等几个方面分析了影响供应链库存成本的因素，然后综合这些影响因素，提出了供应链库存成本降低措施，即选择合适的供应商、推行JTT采购方式等，以提高供应链效率。