Engineering Costs and Production Economics最新文献

In Poland, steel products have often been in shortage while the average level of their stocks at consumers stores was rising. The logistic system of steel products was controlled almost totally by the central economic management through “obligatory intermediation” in their distribution. That hidden form of rationing proved to be inefficient and failures of the distribution system were multiplied by faulty performance of the transport system. The whole process of orders location was becoming more and more complicated. Buyers of steel products were not satisfied by the operation of intermediating companies. Hence direct purchases from producers were always preferred rather than other forms of procurement. Together with the complex reform of the whole Polish economy also the logistic system of steel products has undergone essential changes. However, their results are not known yet.

This case study arose in a large plant manufacturing locks. The existing production control system involved partially a rudimentary MRP at the assembly level and a pull-system of an informal (r,Q) type for triggering component production. The expressed problem was: component shortages affecting assembly operations and load fluctuations as well as imbalances affecting component shops.

Coordination between assembly shop loading and component shops' loading was identified as crucial. The plant happened to have a considerable flexibility in production smoothing. A cyclic assembly planning system was considered, with minor variations from month to month. A policy for monthly joint planning of assembly and component shops' production was obtained. Consideration was given to presence of lead times for component production. For load balancing over time certain bin-packing heuristics were considered. For sequencing in assembly lines certain flow-shop heuristics were used. The component inventory control policy involved a restoration of month-end inventories towards steady state target values. The operational feasibility of the policy was verified on actual data.

The study includes approximate quantification of losses that would be caused in the original system due to component stockouts. Certain subproblems concerning component lotsizing under random tool failures were also settled adequately.

Granger causality tests are used to detect the relationships between investment and working capital credit, imports in convertible and non-convertible areas, and input and output inventory investments.

In this paper an inventory model with convex, non-decreasing costs, exogenous demand and spoilage is considered. The explicit forecast and decision horizons are obtained. The horizon problem is formulated as an optimal control problem. The essential ingredient in the proof is a version of the Pontryagin maximum principle.

An analysis of serial process configurations consisting of three processes and two machines shows interesting relations between the choice of batch mode (or batch structure), utilization of capacities and maximum throughput.

This paper considers trading processes in which, periodically, price and output decisions are made before the realization of a random demand. A major achievement is to extend the scope of outcomes for the lost sales trading processes by demonstrating that the class of PF₂ density functions preserves uniqueness and regularity of behavior without imposing any linearity requirements. A second achievement is to verify that the backlogging full payment process and the lost sales process share common qualitative features with the major difference arising in the properties of the system equilibria.

In recent years a small number of researchers have presented methods for the determination of the replenishment policy for a product whose demand is increasing linearly. Some of these methods have the same structure, and differ only by a single parameter in an equation. These will be compared on a range of problems, and an eclectic method suggested as a possible alternative.

The problem considered is a priori planning of spare parts inventory intended to keep operable a redundant system consisting of n identical and statistically independent elements. The system is subject to a certain mission proceeding in a number of successive time periods, called phases, during which environmental conditions and, thus, element reliabilities vary. Maintenance actions, intended to determine the system state and replace failed elements by new ones, may be performed only during overhauls between two successive phases. Spares inventories for replacement purposes are planned in advance for each overhaul assuming that spare parts remaining unused from previous overhauls can be used in succeeding ones. The mathematical model of the described system is developed in the paper and expressions for calculating relevant performances are derived. An optimization problem is stated in which the total purchase and holding costs are the criterion function and the stockout probabilities represent constraints.

This paper identifies and analyses the effect of two implicit assumptions made in the standard single-period deterministic inventory models, while valuing the level and carrying cost of average inventory. Relaxing these two assumptions we show the degree to which standard inventory models overestimate or underestimate, as the case may be, optimal inventory policies. A numerical example will be used throughout to highlight the results.