Slow-moving Parts Research Articles

A reliable and ensemble forecasting model for slow-moving and repairable spare parts: Data mining approach

Reliable prediction of spare parts is one of the most prevailing challenges for the manufacturing industry and equipment owners, which acts as a double-edged sword. If the objective function focuses on the lack of spare parts, it will cause capital sleep, and otherwise, it would make spare parts shortage. Therefore, the accuracy and reliability of this prediction have always been consequential. Howbeit, the non-uniformity of the spare parts in the real world is remarkable. Some of these parts have intermittent uses (fast-moving type), and some have less and irregular consumption (slow-moving type). Due to this uneven structure of slow-moving spare parts, the application of classical methods has low reliability and performance in forecasting. Therefore, this study concentrated on predicting slow-moving spare parts by developing a reliable and ensemble data mining approach with considering the managerial characteristics (e.g., repair ability and the irregularity of maintenance such as MTBF and MTTR…) along with their history of consumption (the amount of each order and the time interval between two charges). In the proposed approach, the amount of spare parts and the time of the following order is predicted based on an ensemble data mining model from the prediction of future consumption and the probability of scraping in the repair process. This simultaneous attention to data types (consumption and repairs) for slow-moving parts improves data adequacy. Whereas the focus of the literature has been more on improving the data mining models’ performance than on improving data adequacy; by emphasizing both issues at the same time, we can get more reliable results in predicting parts requests with more fluctuations in consumption. A clustering management model for classifying spare parts has been presented during the data preparation process to implement this model. And 51,335 slow-moving spare parts of a Steel Company have been organized and predicted. The results of this study reveal that the application of the proposed approach and ensemble model significantly increases the reliability of spare parts inventory (accuracy by up to 80% and newly defined reliability (RI) by up to 10%).

Taming the Long Tail of Inventory: Gambler's Fallacy in Intermittent Demand Management

Items with intermittent or demand often tie up valuable warehouse space and capital investment of manufacturers and retailers. Traditional inventory solutions were not designed for items with these demand characteristics. In the case of long tail products, the paucity of demand data poses additional challenges for model estimation and performance evaluation. Furthermore, while most inventory policies in the OR literature were conceived to maximize long run average cost per time period or expected total cost over a finite horizon, in reality, practitioners are more concerned with KPIs such as inventory turnover ratio or gross margin return on investment, metrics that often normalize the profit or cost performance with the number of sales generated in a finite horizon. The nature of intermittent demand product further accentuates the impact of these effects on the performance of inventory policies under these KPIs. We analyze the average cost per unit of goods sold for inventory policies over a finite horizon with intermittent demand product. Our analysis is motivated by the recent surprising observation that the gambler's fallacy phenomenon holds actually in a random sequence of independent events, due to the finite horizon effect. We use this to analyze the performance of stationary policies in finite horizon, and provide justification for the use of replenishment-delay policies for very slow-moving parts, even if the demand distribution is stationary and independent across time. This is surprising as the constant base stock policy is known to be optimal for items with these demand characteristics in the classical settings. More generally, we propose a class of stationary staggered base stock policy to minimize the average inventory cost per unit of goods sold for slow-moving items over a finite horizon. We call this the HBR (histogram-based robust) policy, obtained using a distributionally robust inventory control model with the Wasserstein uncertainty set on the nominal interarrival-demand distribution. Interestingly, to deal with the finite horizon effect, we need to bias the true interarrival and demand distribution to account for the gambler's fallacy phenomenon. We implement our policy and other benchmark methods on real data and find that our robust policy can reduce inventory cost compared to the benchmarks in all scenarios with varying cost parameters.

Numerical research on intense pulsed ion beam ablation plasma expansion into ambient gases

The mechanisms are different for intense pulsed ion beam ablation plasma expanding into ambient gas of different pressure or into vacuum. The former is complicated by the interaction between plasma and the ambient gas. The 2D gas dynamical model has been built to describe the process, and the plasma expansion into ambient gas of pressures from 10-6 atmosphere to 1 atmosphere have been calculated. The results show that the phenomena of plasma expanding into ambient gases vary as the pressure changes. It can expand into vacuum freely, but into atmosphere its movement is confined. And the ejection into ambient gas of one thousandth atmosphere or so is special, the ‘snowplow’ phenomenon is observed and the plume plasma splits into fast- and slow-moving parts.

Ice-Shelf Topography and Structure Determined Using Satellite-Radar Altimetry and Landsat Imagery

The glaciological structure and dynamics of West and Shackleton Ice Shelves, East Antarctica, are qualitatively determined using a combination of satellite remote-sensing techniques. Sketch maps traced from unenhanced imagery show the ice edge, grounding lines, flow lines, and rifts. Surface-elevation profiles and contour maps from radar altimetry provide free-board elevations of the floating ice and show flow-line undulations and rumples characteristic of grounded ice. West and Shackleton Ice Shelves consist of a combination of fast-moving ice tongues from outlet glaciers and slow-moving parts constrained by islands, ice rises, and ice rumples.

Ice-Shelf Topography and Structure Determined Using Satellite-Radar Altimetry and Landsat Imagery

The glaciological structure and dynamics of West and Shackleton Ice Shelves, East Antarctica, are qualitatively determined using a combination of satellite remote-sensing techniques. Sketch maps traced from unenhanced imagery show the ice edge, grounding lines, flow lines, and rifts. Surface-elevation profiles and contour maps from radar altimetry provide free-board elevations of the floating ice and show flow-line undulations and rumples characteristic of grounded ice. West and Shackleton Ice Shelves consist of a combination of fast-moving ice tongues from outlet glaciers and slow-moving parts constrained by islands, ice rises, and ice rumples.

Inventory Management of Slow-Moving Parts

We present in this paper a simple, fast, and accurate method for determining optimal stock levels for slow-moving parts which we worked out in March 1955. Independently of our work, Whitin and Youngs studied the same problem and published their results in a recent paper. “A Method for Calculating Optimal Inventory Levels and Delivery Time” in the Naval Research Logistics Quarterly, September 1955. While both studies are basically the same, our solution seems to be the more practical. Essential differences are the use of a second criterion (not so complete as the “costs,” but more easily accepted by managers)—the customer's satisfaction, and the graphical presentation, which allows the immediate determination of the optimal level. For practical reasons we assumed that the distribution of demand is Poisson, conceptually the distribution may be arbitrary. The method is restricted to slow-moving, non-seasonal parts with fairly long replenishment periods.