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Mechanika procesu řezání pilovým kotoučem
Hlásková, Luďka
The main aim of the dissertation thesis is to develop an alternative methodology for the calculation of the cutting resistance, which is based on the fracture properties of the wood, with the incorporating of the Ernst-Merchant theory into the conditions of the circular saw blade. Cutting resistance is an important property of machined material that affects the amount of energy consumption during machining. The energy effects can be calculated theoretically using conventional methods based on the specific cutting resistance, which is a function of many factors. These coefficients are derived from experiments conducted in the 1950s and are therefore currently inaccurate. In contrast to traditional computing methods, the new model uses only two main parameters: fracture toughness and shear yield stress. Based on the Ernst-Merchant diagram, the magnitudes of the forces affecting the workpiece and tool are calculated. Further, this model is depend on the determination of the internal work for bending and subsequent separating of the chip, on the energy needed to overcome the friction between the workpiece and the blade of the tool and last but not least, on the specific work for forming the new surface of the workpiece. Experiments were carried out on the laboratory equipment designed for the saw blade research, and one partial experiment was executed in cooperation with Gdańsk University of Technology using a frame saw. Samples of spruce wood (Picea Abies) and beech wood (Fagus Sylvatica) were used. The results calculated by the new method were compared with the experimentally measured data and the results calculated by the conventional methods. The main parameters of the proposed method are founded on the made measurements, so the newly designed calculation model shows the best match with the experimental data. From the conventional methods, only the Technology-Statistical Method had a better match with the experiment. Further experiments were used to determine the cutting parameters for modified beech wood samples (Bendywood, DMDHEU and Lignamon). For all the measurements made, the basic relations for the calculation of the fracture characteristics of the material (fracture toughness and shear strength, without complicated fracture tests) were derived for the axial-perpendicular saw blade cutting model. The data obtained could be applied to calculate the energy effects of other types of wood machining.
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