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Literature and most textbooks around the world describe Silver-Meal in such a way that periods with zero demand make Silver-Meal suggest a higher frequency of order replenishments than necessary and therefore higher total costs than necessary. Silver-Meal, still the best-known technique, is therefore inferior to other lesser-known techniques when the time interval in the calculations presently is days and not months. The purpose of this article is to show that another mathematical formulation of Silver-Meal avoids this trouble. We also point to characteristics such as Silver-Meal, Least Unit Cost, Part-Period Balancing, and lot-sizing techniques that are available in many textbooks for operations and supply chain management. We illustrate the techniques with different examples of periods without demand, declining demand, and varying demand. We point out possible problems with the different techniques. Literature mostly does not consider periods of zero demand, which was not so important before. Lot-sizing methods must cope with the important performance indicator “Days of inventory”. Numerous practical situations with zero demand periods exist where a lot of sizing techniques help for efficient operations. It is necessary knowledge and a tool for students (future users, performers, and managers). “Lägsta periodkostnad” is a restored and reformulated Silver-Meal, with Silver-Meal’s characteristics already presented in literature, except those difficulties with zero demand periods disappear.

Estimations of the amount of lithium-ion batteries reaching their end-of-life in 2025 and the amount being recycled indicates large deviations. To enable an efficient recycling process a well-defined and efficient supply chain network for the recovery of discarded lithium-ion batteries must be put in place. This includes analyzing the needs and restrictions of such a network. The aim of this paper is to provide decision support tools, to analyze input, and optimize a future supply chain for discarded lithium-ion batteries. A mixed integer programming model is developed and applied to the Swedish market. The findings show that several aspects will affect a reverse supply chain for discarded lithium-ion batteries, many of which are still uncertain and hard to predict.

In this paper, we investigate gift card's influence on retailers’ ordering decisions and analyse the benefits of issuing product-specific gift cards. We propose an optimal ordering model for retailers’ decision problems with gift cards being issued. We also solve the problem with the analytical forms of optimal order quantities and expected profits. By comparing the results with the classical newsvendor problem, we classify the benefits of issuing gift cards into three categories: (1) the demand stimulating; (2) the pre-payment, and (3) the non-redemption. We step further to explore a retailer's problem on how to determine the optimal discount for gift cards, which is characterized by a joint optimal policy on the ordering quantity and the discount. We derive the optimal condition on this joint policy. Numerical examples are conducted to illustrate the model results and analyse the influences of parameters. A sample average approximation method is also been introduced to solve the optimization model.

Cover-Time Planning, or Takt Planning, is presented. It is a system for calculating material requirements and start of purchases and production. Requested production rates of sales items, or alternative prefabricated modules in stock, are “broken down”, exploded, to create the need for components, for all underlying items (articles) in the Bill of Material. Inventory and already ordered replenishments are compared with the item’s desired production rate. How long already made actions are expected to cover the desired expected sales and production rates is compared with the item’s lead time; if a forward future shortage is likely the article is signalled for a refill. With examples is described how make-to-order production is done easily. The method is a type of reorder point system, but with time instead of quantity as decision variable. Unlike a traditional reorder point system increases and decreases of production can be planned. Future work load in various production sections can be estimated. It is described how an “Available-to-promise”-system should be designed and used. Cover-Time Planning (CTP) is a complete alternative to Materials Requirements Planning (MRP). CTP responds faster than MRP, since MRP for each structural level uses a batch size to “break down” and to magnify the need at the underlying level. In the end a large material acquisition needs to be ordered maybe just to build a single end item. CTP uses the end item requirement rates on all structural levels shifted with the lead times, when customer demand changes, the entire production chain react simultaneously.

Determining a rational planned lead time (PLT) is a critical and difficult problem in production planning, especially for a remanufacturing system. This paper considers an optimisation problem of t ...

A simple heuristic for vehicle routing - A variant of Clarke and Wright's saving method (International journal of Production Economics, 157 (2014), 74–79) contains a mistake that must be corrected. ...

Lessees may abuse equipment during the lease period since lacking of ownership, thereby increasing lessors’ repair cost and lessees’ downtime losses. This study integrates lessees’ effort to protect leased equipment during the lease period with lessors’ preventive maintenance (PM) into maintenance service strategies. It is proved in a non-cooperative game, neither party achieves the cooperative game’s ideal revenue, but improvement in the lessee’s effort level and lessor’s PM degree can increase the other party’s revenue. A cost-sharing contract model is designed to achieve the maximum revenue as in a cooperative game and ensure Pareto improvement of the leasing parties. In the contract, the lessor grants the lessee a rental discount, and the lessor’s PM cost and lessee’s effort cost are shared with cost-sharing coefficients. Conditions under which the ideal revenue and Pareto improvement can be achieved are discussed. Numerical examples are provided to illustrate the effects of contract parameters, unit penalty on the effort level, and revenue. Managerial insights are finally proposed for leasing parties. The results show: the effect of the effort level and PM degree on equipment failures is marginally diminishing; proposed cost-sharing contract model can achieve the ideal revenue and Pareto improvement; the rental discount has a greater impact on the lessee, while the cost-sharing coefficients have a greater impact on the lessor; and increasing the unit penalty decreases (increases) the lessor’s (lessee’s) revenue but maintains the effort level at constant.

We compare two different modes, i.e., dedicated mode and shared mode, used in packaging management in automotive parts logistics. In dedicated mode, every parts supplier uses his own packaging; while in shared mode, packages can be shared among the suppliers. For each mode, we calculate the total costs consisting of transportation cost and inventory holding cost, and prove that the total costs, the transportation cost and the inventory holding cost are all smaller under shared mode. We further illustrate the factors that influence the cost savings of shared mode, i.e., the total cost of dedicated mode minus that of shared mode. In particular, the cost savings are proved to be negatively related to the number of package categories, and are positively related to: (1) the demand gap of packages between areas, i.e., sum of the volume difference of every kind of packages that transported in and out of one area; (2) the failed ratio factor of the returned packages, i.e., the ratio of the packages that cannot be returned to the supplier because of broken, pilferage, misplace, etc.; and (3) the time savings of short distance transportation, i.e., the transportation time consumed between areas minus the transportation time within one area. Finally, numerical examples show that the cost savings can be considerable, and the number of package categories is the most important influence factor.

Efficient collection and distribution of items are important because fewer resources and less energy would be used and this would help the world to be more sustainable. Many goods are always in transit. Efficient collection from storage racks and depots, and efficient distribution to retailers and customers, etc., will decrease transport inventories. The paper presents a variant of the Clarke and Wright's saving method that is suitable for introducing the vehicle routing problem and the importance of efficient vehicle routing. The method uses only the first pair of calculated savings and uses these also when searching for complements or additions to an already decided route. The variant is simple, very fast and finds the best known solution to the Dantzig and Ramser (1959) –problem.

Policy-makers are developing regulation policies to drive down carbon emissions from industries. Independent remanufacturers (IRs), which remanufacture recycled products/components/parts, must manage and evaluate economic costs generated by the production under future carbon emission regulations. We present three optimisation models to determine the remanufacturing quantity that maximises the total profits under three common carbon emission regulation policies: (a) mandatory carbon emissions capacity, (b) carbon tax and (c) cap and trade. These models include sales revenue, remanufacturing cost, disposal cost, inventory holding cost, shortage cost and carbon emission cost. The max–min approach is used to solve the models, which assume limited information on demand distribution. We investigate how the three regulation policies affect remanufacturing decision-making for IRs and we also solve some numerical examples where we vary the magnitudes of incentives, penalties and stringency of constraints to provid...

This article provides a short historical overview from Harris and his Economic Order Quantity (EOQ) formula to the Economic Lot Scheduling Problem (ELSP). The aim is to describe the development of the ELSP field from the EOQ formula to the advanced methods of today in a manner that suits master and graduate students. The article shows the complexities, difficulties and possibilities of scheduling and producing several different items in a single production facility with constrained capacity. The items have different demand, cost, operation time and set-up time. Set-up time consumes capacity and makes the scheduling more complicated. Idle time makes the scheduling easier but is bad from a practical point of view since it creates unnecessary costs due to low utilisation of the facility. A heuristic solution method is used on a small numerical example to illustrate different solution approaches. The solution method creates a detailed schedule and estimates the correct set-up and inventory holding cost even if the facility works close to its capacity.

We explore the issue of supply chain coordination by considering trade credit and its risk. It shows that, in a retailer–manufacturer system, the manufacturer may deliver less than the retailer׳s order quantity when the payment is delayed, and the manufacturer׳s risk aversion makes this result hold in a wider range. These findings are different from the common sense believed in the retailer–manufacturer coordination literature, which suggests the manufacturer to entice the retailer to enlarge the lot size. The manufacturer׳s decision of decreasing the order quantity prevents the supply chain from operating in the optimal situation. In order to coordinate supply chain, we propose a modified quantity discount based on both order quantity and advance payment which means the manufacturer offers quantity discount if the retailer pays part of the payment in advance and enlarges her order quantity. The ranges of advance payment ratio and the quantity discount are derived. Numerical examples are used to demonstrate the conclusions.

Organisations focus on reducing costs in their supply chains to increase net income. In order to reduce costs a company needs to know how to measure Supply Chain Cost (SCC). This paper is concerned with SCC and how measurements of SCC are and can be used in industry. The paper describes a suggested model for measuring SCC. Representatives from 30 companies in 10 different business sectors are interviewed about how they measure costs in their supply chains compared against this model. The focus is also on identifying the difference between SCC based on estimated standard cost compared to actual cost. A case study describes and shows the difference between measuring SCC based on calculated standard cost and measuring it based on actual cost. Our studies show that general thorough cost and supply chain analyses in many companies can be improved and further developed.

Economic lot scheduling problem (ELSP) handles the problem of deciding what order quantities to use when different products/items are produced in the same capacity constrained production facility. It has previously been shown, and it is shown in this article, that it is possible to find a feasible solution fulfilling true feasibility conditions. However, if the utilisation of the production facility is high the production often has to start before the inventory reaches zero to avoid future shortages. Such ‘early starts’ creates an extra inventory holding cost that the traditional approximation for the inventory holding cost does not account for. This article presents an iterative solution procedure that computes the true inventory holding cost and minimises the total costs. Contrary to previous solution procedures, this procedure requires that the production is scheduled in detail. The heuristic solution procedure is illustrated by a numerical example, it is programmed in MATLAB and variants of the proble...

In this research we study the multi-product Economic Lot Scheduling Problem (ELSP) with manufacturing and remanufacturing opportunities. Manufacturing and remanufacturing operations are performed on the same production line. Both manufactured and remanufactured products have the same quality thus they fulfil the same demand stream. Tang and Teunter (2006) firstly studied this type of Economic Lot Scheduling Problem with Returns (ELSPR) and presented a complex algorithm for the optimal solution. More recently Teunter, Tang, and Kaparis (2009) proposed several heuristics to deal with the same problem using more computational efficient approaches. However, both studies have limited the attention to the common cycle policy with the assumption that a single (re)manufacturing lot is used for each item in each cycle. Relaxing the constraint of common cycle time and a single (re)manufacturing lot for each item in each cycle, we propose a simple, easy to implement algorithm, based on Segerstedt (1999), to solve the model using a basic period policy. Several numerical examples show the applicability of the algorithm and the cost savings. Funding Agencies|Italian Ministry of Research and Higher Education

This paper is a part and contribution to develop flexible and robust supply chain forecasting systems under changing market demands. It suggests new tools and models to evaluate forecasting error measurements. The paper especially studies slow moving or intermittent demand, when for items the forecasting time periods often have zero demand. For the difficult to forecast intermittent demand the Croston forecasting technique is mostly regarded as a better choice than single exponential smoothing. These two methods, Croston and single exponential smoothing, together with two modifications of the Croston method, are discussed and evaluated with real intermittent data. The apprehended performance of a forecasting technique is dependent of the chosen measurement of forecast errors. The main purpose is to examine and evaluate different forecasting error measurements. Traditional measurements of forecast errors are studied, mean absolute deviation ( MAD ), mean square error ( MSE ), etc. together with new suggested error and bias measurements: “periods in stock” ( PIS ) and “number of shortages” ( NOS ). PIS considers the time aspect of the forecast error, NOS considers the development of cumulated forecast error ( CFE ). A complementary measure for descriptive statistics of time series is also suggested, mean average change. The conclusion, through principal components analysis ( PCA ), is that a single measure of forecast errors does not present the total different dimensions of the errors; complementary error measures must be used.

We deal with a multi-echelon inventory system in which one warehouse supplies an item to multiple retailers. Customer demand arrives at each retailer at a constant rate. The retailers replenish their inventories from the warehouse that in turn orders from an outside supplier. It is assumed that shortages are not allowed and lead times are negligible. The goal is to determine replenishment policies that minimize the overall cost in the system. We develop a heuristic to compute efficient policies, which also can easily be used in a spreadsheet application. The main idea consists of finding a balance between the replenishment and the inventory holding costs at each installation. This new heuristic we compare with two other approaches proposed in the literature; the computational studies show that in most of the instances generated the new method provides lower costs.

This paper considers scheduling the production of several different items on a single machine with constrained capacity, commonly known as the economic lot scheduling problem (ELSP). Most traditional approaches for the ELSP consider the sum of the set-up cost and inventory holding cost and provide cyclic schedules that minimise this sum. In practice, there are not only costs for set-ups and inventory holding, but also costs for operating the production facility due to, for example, electricity, service, maintenance, tools, operators, etc, which depend on the number of hours the facility is operating per working day. In this paper, we modify the traditional cost function to include not only set-up and inventory holding cost but also a time variable cost for operating the production facility. The paper shows it is possible to adapt a previous heuristic procedure to this complemented cost. The model can help to determine cyclic schedules and the number of production hours per working day.

This article presents a simulation study over a small supply chain, where the amount of work-in-process (WIP) is restricted. The supply chain consists of five linked machines, or production facilities, with stochastic operation times. A number of test cases are made where the number of jobs in the machines and the buffer areas are restricted. The restrictions are designed both in the Kanban way, linked to every machine, and in the CONWIP way, connected only to the total production line. But no Kanban-cards and -cells are involved in our study, just restricted inventories between the machines. With the same amount of limited WIP, CONWIP-control compared to Kanban-control presents a higher throughput rate, less time between jobs out, but the jobs stay on average longer in the system. The stochastic operation times cause that the upstream machine sometimes consumes the jobs in a rate that the downstream machine does not catch up with, therefore all available storage room temporarily are not used. Kanban- and CONWIP-control presents the same amount of average outflow per time unit with the same variation in operation times and with the same amount of real average WIP. But Kanban-control causes a lower utilisation of present available storage room and storage equipment than CONWIP. The user of Kanban and CONWIP can only control maximum WIP and not average WIP; average WIP is a consequence of existing variations, so the difference is important. The coefficient of variation of the lead-times increases when WIP increases; this is very difficult to handle in practical applications. Restricted WIP that shortens the lead-time and decreases its variation is more important than if it is a “push” or “pull” system. Finally, it is argued that CONWIP-control is to prefer over Kanban-control in theory, but in practice there is a lack of CONWIP installation guidelines.

The paper considers the problem of choosing order quantities and a cyclic production pattern for several products that are produced in a common capacity constrained facility. The heuristic method from Segerstedt [Segerstedt, A. (1999). Lot sizes in a capacity constrained facility with available initial inventories. International Journal of Production Economics, 59, 469-475] is modified and improved. The method is compared with the heuristic technique according to Doll [Doll, C. L., & Whybark, D. C. (1973). An iterative procedure for the single-machine multi-product lot scheduling problem. Management Science, 20(1), 50-55; Goyal, S. K. (1975). Scheduling a single-machine multi-product system: A new approach. International Journal of Production Research, 13, 487-493]; the differences and similarities between the methods are illustrated in a common numerical example. It shows that feasible solutions can be found, both with our method and others; where the production can be scheduled during a time interval, the initial inventory level is the same as the final and the schedule can be repeated in a cyclic pattern without shortages. (This definition of feasibility differs from traditional.) However, it shows that the common approximation for the inventory holding costs (q"i2h"i(1-d"i/p"i)) does not fit. The real inventory holding cost becomes different compared to the approximated that is used in the calculations. The real inventory holding cost depends on the chosen scheduling, which makes it difficult to find an optimal solution. Different solutions and extensions are discussed.

In this paper, a heuristic method is presented which gives a novel approach to solve joint replenishment problems (JRP) with strict cycle policies. The heuristic solves the JRP in an iterative procedure and is based on a spreadsheet technique. The principle of the recursion procedure is to find a balance between the replenishment and inventory holding costs for the different items by adjusting the replenishment frequencies. The heuristic is also tested according to an extensive test template and shows pleasing results. It also performs well in comparison with many other heuristics. Validerad; 2007; 20061117 (ysko)

For a company's long-term profitability, the most important processes are the way it starts parts of the manufacturing process before the customer order arrives and the way it determines and promises delivery quantities and times for customer orders. In practical computer applications Material Requirement Planning (MRP) and/or Reorder point systems are the base techniques mostly used. This paper presents Cover-Time Planning (CTP), a variant of a reorder point system, which is developed with a forward-looking forecasted demand rate and the decision variable is ‘time’, instead of ‘quantity’ for an ordinary reorder-point system. MRP and CTP are introduced and compared through a numerical example. MRP and CTP must treat a practical ‘make-to-order’; therefore, this paper discusses available-to-promise, planning bills and other help systems for practical applications of Master Production Scheduling. The paper presents how and why, in practice, a Master Production Scheduling system with an available-to-promise f...

This paper considers the scheduling of several different items on a single machine, in literature known as the economic lot scheduling problem, ELSP. One of the characteristics of this problem is that the demand rate is deterministic and constant. However, in a practical situation demand usually varies. In this paper we examine if a deterministic model can be used if demand is stationary stochastic. A dynamic programming approach from Bomberger (Manage. Sci. 12(11) (1966) 778) and a heuristic method from Segerstedt (Int. J. Production Econom. 59(1–3) (1999) 469) are used to calculate lot sizes for four items. The production of these items is simulated with different variations in demand rates. Our conclusion is that a deterministic model of this kind can be used in a practical situation where the demand rate is stationary stochastic, but the models must be complemented by a decision rule; which item to produce and when to produce it. In our tests the heuristic method and the dynamic programming approach perform rather similarly with respect to costs and inventory levels, but the dynamic programming approach results in more backorders when there is small variation in demand rates. This study indicates that the model used for determination of lot sizes is of less importance than the decision rule used for identification of the item to produce and when to produce it.

An idea about how to tackle and solve the difficult problem of determining economic order quantities in capacity-constrained multilevel production is presented. The idea is based on frequencies during a variable time interval as variables instead of explicit order quantities. The presented heuristic model handles assumed constant demand for several items and calculates fixed-order quantities assumed to be possible to repeat in a cyclic pattern. In the model, every item is supposed to be manufactured at least once per year, or during another maximum period, to stop order quantities that are too large and therefore hinder inventories that are exceedingly large and/or obsolete. During a time interval, it was decided how many times each item should be produced. The paper starts with a common frequency for all items, i.e. the highest frequency possible for all items during this maximum time interval considering the capacity restrictions of the different machines. Thereafter, the frequency for items with high s...

This paper considers an inventory control system, primarily for a finished goods inventory. The purpose is to create a procedure that can handle both fast-moving items with regular demand and slow- ...

Polarica is a company in northern Europe buying, refining and selling wild berries and other specialty foods. During the last couple of years the volume of wild berries, mostly blueberries, has increased a lot. This expansion forces Polarica to consider investments in freezing‐in capacity and cold‐storage capacity. A simple heuristic model was constructed, from which it was concluded that additional volumes of frozen blueberries require more storage facilities and it was also recommended that the location should be based on load‐distance analysis. The way this problem is tackled and solved can be copied and hopefully it presents ideas for other similar studies.

To be a part of a supply chain network a company competing on the global market must mostly show short lead times and deliver at the right time. Is this really possible for a company placed in a rural or sparsely populated area? Pajala, a village and a municipality in the north of Sweden, has 7500 inhabitants in an area of 7900 km2 which means one inhabitant per km2. The number of inhabitants in the municipality of Pajala is decreasing. To stop this problem, Pajala needs more work opportunities and therefore they need more successful companies. Approximately 20 different conveyers/suppliers transport goods to and from companies in Pajala. But most of the conveyers/suppliers transport goods only once a week. Companies in Pajala, to be able to compete and be a part in a supply chain and a chain that competes with other supply chains, should have the opportunity to send and receive goods any day they want for shortening the delivery times to customers. One solution to this may be co-distribution. Co-distribution means that different conveyers/suppliers transport their goods in only one truck that goes for example in this case to and from Pajala. A preliminary study has been performed in Pajala to investigate if co-distribution has any benefits in rural areas. We find that the companies receive and distribute goods with a low frequency and that the trucks carrying loads to and from Pajala are often loaded less than 50%. This implies that to lower transportation costs and increase delivery services some sort of co-distribution is necessary to strengthen the capability of competing for the companies in Pajala. We have here studied specifically Pajala but we are convinced we would find almost the same result if we had studied other municipalities in rural areas of Sweden.

The paper presents the main routines of production and inventory control at ABB Motors, Vasteras and Volvo Wheel Loaders, Eskilstuna. The primary interest is to present how Material Requirements Planning (MRP) is used in these two companies. If the number of end items is large, the company assembles-to-order or makes-to-order then additions to pure MRP seem to be necessary. ABB Motors and Volvo Wheel Loader use: planning bills, a normal bill of materials with 'adding bills of materials', a master production schedule planning system with an available-to-promise function and a home-made 'system' for modules available-to-promise. One important measure for the both companies is the accumulative lead-time. An increase of the Master Production Schedule in a shorter time than the accumulative lead-time is avoided, because it will lead to suggestions of purchase in past time periods and therefore most probably to future material shortages.

This paper presents an heuristic method for deciding what items and what order sizes to produce in a capacity constrained facility. The available inventories on hand decide in what order the production should be performed for avoiding shortages. The recursion procedure finds the same solution to the Bomberger (Management Science 12 (11) (1996) 778–784) problem as Doll and Whybark (Management Science 20 (1) (1973) 50–55).

This paper emphasizes the importance to a manufacturing company of decreasing the product structures, both in width and depth, thereby shortening the throughput times, standardizing and reducing complexity, and identifying bottlenecks in order to increase efficiency and profitability. Having once been a production control and plant manager at Ericsson and Benzlers, the author has drawn upon his experience in researching this paper. Other influences include knowledge of well-known trends in production management, e.g. WorldClass Manufacturing, Lean Production, Time-Based Management, OPT, etc. The paper also stresses that it is difficult to present real new ideas concerning production management, but nevertheless discussions and publications of ideas and incentives to achieve an efficient production of products and services must continue.

This article describes the findings and results from an improvement project concerning a production line at an Ericsson plant in Sweden. The article is a type of a case study that describes activities and discussions in an improvement project. A value stream mapping showed that only a few percent of the throughput time was really adding value to the customer. In an improvement project the involvements of all employees are important. Interviewing and education of workers/operators lead to that they also contribute with suggestions to improve the production flow. Value stream mapping though often classified as a lean technique is a technique for improvements of most kind of productions, here it is applied to a situation that must be classified more agile than lean. A selection of generated, and rather general, solutions were implemented: reduced buffers; more of a ‘one-piece’ flow; a reduced waiting time by adding work tasks; a more levelled manufacturing and efficient flow was created by a recombination of processes and a reallocation of work tasks. Our article hopefully stimulates students and practitioners to find improvement activities in similar situations and projects. Validerad; 2013; 20130404 (ysko)

An accurate cost analysis is necessary to evaluate changes in a supply chain; this article shows how a rather simple framework can be used when evaluating changes in a supply chain. The framework is built on a Supply Chain Cost (SCC) model and customer service measurements, delivery precision and lead-time. Both suggested changes in a supply chain and already executed changes can be evaluated by the framework. Two different examples from the company Ericsson are presented to illustrate the framework, which is a 5 step analysis model. The existing, or pre-existing, supply chain is analysed, described and defined. The SCC and performance measures are mea-sured and/or estimated. Improvements are designed and defined. The same measures as before are measured again. The measures from before and after the change of the supply chain are evaluated to decide if the changes are improvements or not. Cutting costs in one area of the supply chain can be a mistake if not the total supply chain is considered and the total SCC. Considering both the SCC part and customer service measures present a wider understanding of the change. It is shown that SCC can be used as a tool to identify cost savings and evaluate if a change project will, or has, resulted in the cost savings the project aims for. Rough standard costs measures should be avoided instead actual costs should be used as much as possible. The used framework hopefully stimulate to similar analyses in other companies with other supply chains. Validerad;2013;20131015 (ysko);2017-05-10: Nedladdad 1 279 gånger t.o.m. september 2016. För nedladdningsstatisik efter september 2016, se ovan. (marisr)

This paper presents the main results from case studies in 10 Swedish manufacturing companies concerning their product costing. The main purpose of the study is to find out what models of product co ...

This paper presents a mathematical formulation of a capacity constrained multistage inventory and production control problem. It argues that most practical multistage inventory and production control problems can be summarised in the formulation. The model has a strong connection to the model of Billington, McClain and Thomas (1983) and is also inspired of a paper from Bard and Golany (1991). The revised Billington/McClain/Thomas model is formulated in a dynamic programming recursion. A numerical solution to a simple problem is presented. A scheduling problem concerning capacity constrained models are enlightened. Further, the paper points to differences and relationships between this capacity constrained model, MRP, Kanban and Cover-Time Planning.

This paper presents Cover-Time Planning, a method for calculation of material requirements. Cover-Time Planning resembles MRP but it lacks its automatic time-phasing ability. Basically Cover-Time Planning is a reorder point system based on demand rates and time instead of quantities.

This paper presents a model for inventory control where variation in lead times is allowed. No reorder point is computed. The mean value and the variance for the time between withdrawals, the order ...

This paper presents a new method to describe, analyse and estimate production system performances. Work-in-process (units), lead time (number of time units spent in the production system for each unit) and throughput (number of produced units per time unit) are basic performance measures, also used in this article. It is essential for industry to know about relations between system parameters and system performances in existing systems, and in not yet implemented system alternatives. Different performances are achieved by adjusting system parameters. Trade-offs between system parameters and its different performances are necessary to stay efficient and competitive in today's market. Queuing theory and simulation can help the decision makers to estimate system performances of existing and not yet implemented systems. When the complexity increases queuing theory becomes cumbersome, very difficult and eventually impossible to use. A single simulation presents limited information. Multiple simulations are necessary to ensure that the best alternative is chosen. A high number of simulations demand a lot of computer time and resources. Reduction of runs is desirable even with cheaper computer equipment. Currently, traditional two-dimensional charts are the only tools to present and analyse system performances. This article presents a new surrogate model for easier estimation and presentation of system performances, their internal relations, and relations to the system parameters. With the new surrogate model, system performances based on simulations are presented as positions in a three-dimensional environment. Parametric curves and surfaces of Bezier type are generated and adapted to these positions. System performances of other system alternatives can then be estimated without explicit simulation. The number of simulation calculations can thereby be moderated. The method is illustrated with a small production line system Validerad; 2010; 20100719 (andbra)

This paper presents Cover-Time Planning, a kind of a reorder “point” system which exploits the information available in the bill of material. Cover-Time Planning contrary to an ordinary reorder point system uses time as a decision variable instead of quantity. Cover-Time Planning has like Kanban a built in restriction of work-in-process. Not until previous production is consumed a new production is initiated.

Organisations focus on having an excellent supply chain to increase net income. But how to measure excellence in a supply chain? This paper is concerned with excellence within Supply Chain Management (SCM) and how this can be measured. The focus is on identifying and suggesting a model that can be used for measuring excellence in a supply chain. The result from a study of 30 companies with the aim to investigate how companies in 10 different sectors are working with supply chain excellence is an origin for the model. The paper suggests a coordinate and cooperate model, or index figure, that is based on a combination of the cost for the supply chain and performance towards the customer.

A critical issue for a company to gain a competitive position is to improve its supply chain performance. This study investigates with interviews how 30 Swedish companies in ten different sectors define an excellent supply chain and work with Supply Chain Management, performance measurements and Supply Chain Costs. It shows that the companies define excellence more by a performance focus than a cost focus. Delivery precision, inventory turnovers (days of inventory) and lead time are the most common performance measurements. The costs of the supply chain are measured in many different ways and with different accuracy.

Subsequent to the publication of Segerstedt (2004), in which the concepts of Segerstedt (1999) were developed to consider multi-level production, the author has been made aware of a paper (Goyal, 1975) that includes a clear and straightforward treatment of the ELSP problem, and contains a successful heuristic that finds the best known solution to the Bomberger (1966) problem. Readers interested in Segerstedt (2004) may find Goyal (1975) and also Goyal (1973 (a), 1973 (b), 1984) and Brander et al. (2004) interesting.