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Processes of classification
The classification of items is very important to manufacturing logistics of industrial enterprises. It supports the stock management and helps to realize potentials. Additionally, a classification of items can assist determining the material planning strategy of the different items ([1] Bruckner and von Wrede, 1998). There are many different possibilities to classify items, which can be applied depending on the objective. Main techniques include the ABC analysis (ranking the items according to the annual turnover) and the XYZ analysis (analysis of the usage regularity) as well as further alternatives, which can be found in ([1] Bruckner and von Wrede, 1998; [10] Wiendahl and Nyhuis, 2002). The characteristic which is used to classify the items with the ABC analysis is the periodic turnover. It is determined as the product of: the cost of a unit and its consumption rate within a certain period. If characterizing the items by classes A, B and C the ideal Pareto principle can be found with comparably few, however valuable A-items and numerous but inexpensive C-items ([5] Jung, 2006).
The XYZ analysis distinguishes between items according to their fluctuations in consumption. Classes become summarized as follows ([2] Errasti et al. , 2010; [9] Wassermann, 2001):
- X: some extent constant consumption, fluctuations are rather rate.
- Y: stronger fluctuations in consumption, usually for trend-moderate or seasonal reasons.
- Z: completely irregular consumption.
For the XYZ analysis the feature characteristic of statistic measurement is the coefficient of variation ([4] Hoppe, 2005; [8] Schönsleben, 2007), which is the ratio of the standard deviation of item consumption over a certain period and the average consumption. Due to it is broad application spectrum the ABC analysis is regularly applied as the primary analysis and supported by the XYZ analysis ([4] Hoppe, 2005; [8] Schönsleben, 2007; [6] Reese and Geisel, 1997; [7] Reiner and Trcka, 2004). Hence the classification matrix (AX, BX, CX, AY, BY, CY, AZ, BZ, CZ) evolves.
One of the advantages of these analyses is the integration of items with similar characteristics to process them with the same material planning parameters. Since the demand of an item over the past cycles is crucial for its classification it is important to perform the item classification with consistently defined standards in periodic...