Material Requirements Planning System Research Articles

MRP contributes to a company's profitability

Material requirements planning (MRP) systems have become the most effective and widely used inventory control systems across the world. Many operation managers have found the vast knowledge that MRP systems provide is absolutely necessary to effectively and competitively succeed in the current global economy. Although MRP systems have been in existence for almost 25 years, they have had their share of problems and are both challenged and enhanced by new supply chain management techniques and enterprise resource planning (ERP) systems. As the world wide web evolves into a global market of information, the information provided by MRP systems, in particular ERP systems, will be necessary in order for businesses to compete in the global marketplace.

The impact of using multiple freeze fences on costs in MRP systems

There are two approaches to managing freeze fences when planning master production schedule (MPS) in material requirements planning (MRP) systems--namely, single freeze fence and multiple freeze fences. The approach of using a single freeze fence gives no schedule change flexibility within the freeze fence, while the multiple freeze fences approach allows a schedule change within a semi-frozen interval. The concept of multiple freeze fences was introduced by Yeung et al. (1999). However, little research has been done to evaluate the performance of multiple freeze fences. This research is the first study in examining the cost impact of using multiple freeze fences in multi-product, multi-level MRP systems. The influences of environmental factors and cost factors on the total system cost when using multiple freeze fences and a single freeze fence are evaluated. The results of this research show that multiple freeze fences outperform single freeze fence in almost all environments when total inventory holding cost is of major concern. In terms of total shortage cost, multiple freeze fences also perform better in a high commonality product structure. This research also found that, in many environments, the total system costs can be lowered by using multiple freeze fences to shorten the frozen interval, which contradicts previous findings that it is more economical to have a frozen interval to cover the cumulative lead time. The result provides an insight into situations in which manufacturers should consider using multiple freeze fences to improve their flexibility in this dynamic, highly demanding and competitive marketplace.

Development of Load Balancing Systems in a Parallel MRP System

The application of parallel computing system to MRP (Material Requirements Planning) is essential to achieve a real-time demand forecasting for a whole Supply Chain which consists of Multiple enterprises near future. The MRP using loosely connected multi-computer system is examined here. New methods of synchronization, load balancing and data access are required to keep high parallel efficiency increasing PE’s(Processing Elements). In this paper load balancing and data access methods are proposed. The prototype system can keep 96% parallel efficiency for the MRP with 120, 000 items on the 6 PE’s structure and can be robust against unbalanced load. The processing speed increases in liner fashion.

Evaluating dampening effects of alternative lot-sizing rules to reduce MRP system nervousness

System nervousness in material requirements planning (MRP) has received considerable attention. Although there are different perceptions of system nervousness, it is generally considered as the negative effects of open orders rescheduling. Several methods are suggested to cope with system nervousness. The use of lotsizing rules to cope with MRP system nervousness is investigated here in this paper. Extra inventories need to be carried with most lot-sizing rules, which can be used to accommodate schedule changes. Thus, the nervousness-dampening mechanism is a built-in feature of these lot-sizing rules. The aim of this paper is to focus on the investigation of the effectiveness of using lot-sizing rules to dampen system nervousness in MRP systems by a simulation study. A factorial design was used to examine the dampening effect of various lot-sizing rules considered here. We find that the part-period balancing rule and least total cost rule turn out to be two effective lot-sizing rules to reduce system nervousness.

Operations Management: A Tool to Increase Profitability

Operations management enables the efficient utilization of the production systems in a business. This paper will address several key elements in the business competency of operations management. Specifically, this discussion will review the components of a material requirement planning system and a "just-in-time" system for inventory control and time management to enable the dentist to monitor a portion of the practice's overhead costs.

MRP system performance under lumpy demand environments

Material requirements planning (MRP) systems are deemed to deal with master schedules with lumpy demand patterns better than any other production scheduling system. Past studies have advocated important advantages of using MRP systems. The objective of this paper is to look into the impact of patterns of demand lumpiness on the performance of MRP systems by a simulation study. Results show that there is an important threshold point in terms of degree of lumpiness at which MRP system performance starts to deteriorate in the operating conditions considered. If master production schedules (MPS) can be controlled by manufacturers, MRP users should exercise caution to introduce demand lumpiness in MPS to improve system performance. If not, MRP users should then examine the given lumpiness and choose an appropriate lot-sizing rule that has been shown to take advantage of the effect of demand lumpiness.

An MRP system for surgical linen management at a large hospital.

Materials Requirements Planning (MRP) has been used extensively in manufacturing and other industries to improve on-time delivery and to reduce costs. In this paper, we illustrate how an MRP-type system was developed to monitor surgical linen at a large teaching hospital. We also describe a bar-code scanning 'tag and recapture' study to estimate total inventory. The hospital implemented several changes based upon our recommendations that resulted in time savings and a smoother flow of materials throughout the surgical linen supply chain.

Changing class behaviors at run-time in MRP systems

This paper presents an architecture that can be used to develop and maintain class behaviors in object-oriented material requirements planning (MRP) systems at run-time. The architecture provides this capability through a user-interface, and does not require knowledge of any programming language. The architecture is based on the concept of software reuse, it utilizes a library of fine-grained pre-compiled objects to develop and maintain class behaviors. The architecture is a dynamic-object application builder implemented on top of an object-oriented run-time environment.

Building an active material requirements planning system

A material requirements planning (MRP) system is usually implemented with several constraints, such as replenishment of inventories on a period-by-period bases, which obstruct its dynamic performance. This research proposes an active, bucketless, and real-time MRP system. The active MRP system utilizes hybrid architecture that includes an object-oriented database, fuzzy logic controllers, and neural networks. The object-oriented database, which maintains static data relationships, provides superior capabilities in reusability, complex structure operations, and potential integration. The complementary combination of fuzzy logic controllers and neural networks provides a model-free, human-like decision system. Adding triggers and assertions forms an active MRP model.

A finite capacity material requirements planning system

In a discrete parts manufacturing environment, material requirement planning (MRP) is carried out without considering the manufacturing resource capacity. As a result, during implementation, adjustments in planned orders may become necessary. This paper presents a finite capacity material requirements planning algorithm (FCMRP) to obtain capacity-based production plans. These plans need no costly adjustments to satisfy the capacity constraints. Performance of the FCMRP system, when studied through a set of test examples, has been found to be superior to the existing MRP system.

Further developments on safety stocks in an MRP system applying Laplace transforms and input–output analysis

In a sequence of previous papers, the Laplace transform and Input–Output Analysis have been applied to formulate a theoretical basis for material requirements planning (MRP) under different levels of generalisation. Searching for the optimal safety stock is one of the extensions of this theory. This paper investigates the safety stock properties in the case that the time interval of demand is Gamma-distributed. The Generalised Leontief inverse plays an effective role in describing the multi-level production–inventory system when the subordinate products are produced according to a lot-for-lot (L4L) policy.

A net present value approach to safety stocks in a multi-level MRP system

The Laplace transform and input–output Analysis have been used for formulating a basic theory for material requirements planning (MRP) in a sequence of recent papers. The transform has been used for describing time developments and lags of the relevant production, demand and inventory variables in a compact way including effects of order flows and lead times. Secondly, the transform has functioned as a generating function, and thirdly, the transform has been applied for assessing cash flows adopting the net present value (NPV) principle (or the annuity stream which is a variation of NPV). Input-output Analysis, in particular, the input matrix, has been applied for describing multi-level product structures. This has made the analysis compact and distinct. In the current paper the analysis of determining optimal safety stock levels in MRP systems is extended from a single-level model recently investigated to a multi-level system assuming production to take place according to a lot-for-lot (L4L) policy when applying the NPV as the objective criterion and disregarding the opportunities for joint set-ups. Relaxing the L4L assumption is also discussed.

Reliability analysis of aeroplane brakes

The reliability of wear/failure data of brake assemblies of a commercial aeroplane (Boeing 737) is analysed using the Weibull model. This model can be effectively integrated into an aviation maintenance facility computerized material requirement planning system to forecast the number of brake assemblies needed for a given planning horizon. Copyright © 1999 John Wiley & Sons, Ltd.

Evaluating the effectiveness of using lot-sizing rules to cope with MRP system nervousness

Different lot-sizing algorithms lead to various lot sizes of planned orders in the materials requirements planning (MRP) schedule. With the 'built-in' protective stock of a majority of lot-sizing rules, small deviations in production schedules can be resolved by the extra inventories carried without modifying the due dates of open orders on the shop floor. Therefore, system nervousness in MRP systems can be reduced. The objective of this paper is to examine the effectiveness of using lotsizing rules to cope with MRP system nervousness under such operating environments as lead time uncertainty and demand variation by a simulation study. The results indicate that the conventional wisdom of using lot-for-lot at the end item level to reduce system nervousness works only in certain operating environments. It is found that such lot-sizing rules as part-period balancing and Silver-Meal algorithms perform well, in terms of total cost, and dampen system nervousness in most of the operating environments studied

A net present value approach to safety stocks in planned production

In a number of recent papers, the Laplace transform together with input-output analysis has been applied for the sake of formulating a basic theoretical description of material requirements planning (MRP). The transform approach has had a threefold use; on the one hand, it has been useful for describing time developments of the relevant production, demand and inventory properties in a compact way including effects of order flows and lead times. Second, the transform also captures stochastic properties by functioning as a generating function, and, third, the transform is easily applied for assessing the resulting cash flows when adopting the net present value (NPV) principle (or the annuity stream principle which is a variation of NPV). Input-output analysis, in particular the input matrix, is applied for describing multi-level product structures, which has made the analysis concise and distinct. In this paper we extend the analysis of determining optimal safety stock levels for a sequence of planned production decisions (a one-level MRP system) by applying the annuity stream as a criterion to a simple model instead of the average cost approach previously used.

Correlating MRP system nervousness with forecast errors

The purpose of this paper is to examine the impact of forecasting errors on the scheduling instability in a material requirements planning (MRP) operating environment. A sophisticated forecasting method is supposed to provide an accurate forecasting result, which, in turn, should create stable down-stream operating conditions. Through a simulation experiment, we find that forecasting errors may not cause a higher degree of scheduling instability given the forecast errors considered in this study. The scheduling instability, or MRP system nervousness, can be mitigated by using an appropriate lot-sizing rule. Thus, it is important for schedulers to understand this correlation between forecast errors and scheduling stability. After schedulers take reasonable efforts to find a good forecasting method, they don't need to be overly concerned with the associated forecast errors. The selection of an appropriate lot-sizing rule is capable of coping with forecast errors.

A study on MRP practices in Egyptian manufacturing companies

States that a review of the literature on materials requirements planning (MRP) implementation in less developed countries in general, and in Egypt in particular, revealed that no systematic study has attempted to investigate how manufacturing companies have been implementing MRP systems. Thus attempts to investigate the state of the art of MRP implementation in Egypt. States the major mail survey findings of the 93 responses received, of which 52 were MRP companies which operated in quite different business environments within the Egyptian industrial sector. The findings of the current study may permit MRP managers and users to obtain a better understanding of MRP promoters, suggest some ideas for further research and acquaint the reader elsewhere in the world how manufacturing companies in less developed countries such as Egypt are implementing new production management systems like MRP systems. The findings of the study suggest that MRP implementation in Egypt is relatively similar to implementation in manufacturing companies in the newly industrialised countries in the west.

Capacity-constrained reorder intervals for materials requirements planning systems

This paper develops a model for the reorder interval problem for general production systems with constant demand, multiple capacity constraints, commonality, non-instantaneous production, and non-nested reorder intervals. We present this model in the context of a materials requirements planning (MRP) system. Four simple greedy heuristics are presented to find solutions to the model. A six-factor experiment with 192 test problems is used to evaluate the heuristics. The factors in the experiment included the procedures, number of items, capacity tightness, degree of commonality, setup cost to carrying cost ratio, and setup time to run time ratio. For smaller problems the heuristics are compared with optimal solutions found with an exact branch-and-bound algorithm. For larger problems, the heuristics are compared with a lower bound. The results of the experiment show that the heuristics provide excellent solutions across all experimental factors. Computing times for the proposed heuristics appear to be practical even for realistic MRP environments with many thousands of items.

Buffering from material recovery uncertainty in a recoverable manufacturing environment

Remanufacturing is becoming an increasingly important alternative to firms as they develop environmentally sound strategies aimed at minimizing waste and resources. Remanufacturing helps minimize costs through such methods as extending product life cycles via refurbishments and technical upgrades which require only a fraction of the resources and energy associated with a new product. The remanufacturing environment is characterized by a far greater degree of uncertainty than new manufacturing, due to such factors as material recovery uncertainty and probabilistic routings. In this study the use of safety stocks, with a material requirement planning system, to deal with the high inherent uncertainty in the system is examined. It is shown that some safety stocks must be kept in the system but have limited applicability. Additional safety stocks do not provide the manager in this environment with any added benefit beyond that obtained by keeping a minimum recommended level. The results obtained are somewhat counter-intuitive, since adding additional levels of safety stock does not add additional coverage when lead times are greater than one planning period. This lead time effect is explained fully and recommendations as to safety stock level to invest in are made.

A reliability study of Fokker F-27 airplane brakes

The wear/failure data of brake assemblies of a commercial type airplane (Fokker F-27) is statistically analyzed, and interpreted in a reliability framework. A three parameter Weibull model is used for reliability characterization of the brake assemblies. A spreadsheet format of analysis is proposed to analyze the data. This reliability model can be effectively integrated into an aviation facility computerized material requirement planning system to forecast the number of brake assemblies needed for a given planning horizon.