Anders Segerstedt

Supply chains in the construction industry

Purpose - The purpose of this paper is to introduce a special issue about the construction industry and the management of its supply chains. It aims to discuss and point to some differences and pos ...

Inventory control with a modified Croston procedure and Erlang distribution

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- ...

Inventory control with variation in lead times, especially when demand is intermittent

Abstract 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 size and the lead time are measured by exponential smoothing. These variables are assumed to be Gamma distributed. Together with the constants: the inventory on hand plus on-order, passed time since the last withdrawal and time to the next inspection; the probability for a shortage is calculated. If the probability is greater than the service level requires then a replenishment order must be placed.

Effects of carbon emission regulations on remanufacturing decisions with limited information of demand distribution

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 provide implications to policy-makers. The results indicate that remanufacturers should aim to improve yield rate to maximise the profit irrespective of the implemented carbon emissions policy. Policy-makers should prefer the carbon tax policy, if any of the other two policies must be performed, a remanufacturing discount such as a higher carbon emission cap or lower penalty should be implemented to better promote the development of remanufacturers.

Multi-product economic lot scheduling problem with manufacturing and remanufacturing using a basic period policy

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.

Performance measurements in supply chains within Swedish industry

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.

A new heuristic to solve the one-warehouse N-retailer problem

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.

A scheduling policy for adjusting economic lot quantities to a feasible solution

A heuristic scheduling policy is introduced for a multi-item, single-machine production facility. The scheduling policy uses the presumed optimal order quantities derived from solving an Economic Lot Size Problem and checks that the quantities obtain a feasible production schedule according to current inventory levels and expected demand rates. If not, the scheduling policy modifies the order quantities to achieve a possible solution without shortages. The scheduling policy is inspired by modification of the similar heuristic Dynamic Cycle Lengths Policy by Leachman and Gascon from 1988, 1991. The main characteristics of this scheduling policy are successive batches of the same item are treated explicitly, due to that it is quite possible that one item be manufactured several times before one other item is manufactured once more; the batches are ordered in increasing run-out time; if the existing situation creates stock-outs with ordinary order quantities, then the order quantities are decreased with a common scaling factor to try to prevent inventory shortages; in case the decrease of the order quantities changes expected run-out times, the batches are reordered after new run-out times; no filling up to an explicit inventory level is done, the filling up is done by the desirable order quantity; to prevent possible excess inventory the policy suggests time periods where no production should be performed. The scheduling policy contains no economical evaluation; this is supposed to be done when the order quantities are calculated, the policy prevents shortages and excess inventory. A numerical example illustrates the suggested scheduling policy. Finally, it is discussed as to how the policy can also take into account stochastic behaviour of the demand rates and compensate the schedule by applying appropriate safety times.

Measurements of excellence in a supply chain

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.

Economic lot scheduling problems incorporating a cost of using the production facility

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.