Abstract
In the classical approach, cutting forces and cutting power in sawing processes of orthotropic materials such as wood are generally calculated on the basis of the specific cutting resistance kc (cutting force per unit area of cut). For every type of sawing kinematics (frame saws, band saws and circular sawing machines) different empirical values of specific cutting resistance kc have to be applied. It should be emphasised that sources in the scientific literature and handbooks do not provide any information about wood provenance, nor about cutting conditions in which cutting resistance had been determined. In analyses of sawing processes in which the offcut is formed by shear, Atkins’s ideas that all cutting forms a branch of elastoplastic fracture mechanics can be applied. Thanks to this modern approach it was possible to reveal, using experimental results data of fracture toughness and shear yield stresses of Polish pine (Pinus sylvestris), the significant effect of the raw material provenance (source of wood) on cutting power. In the common model for circular sawing machine kinematics, which is similar to metal milling, the sum of all uncut chip thicknesses of the all the teeth simultaneously engaged represented the mean uncut chip thickness. In this work predictions of the newly-developed model for the circular sawing machine are presented. In the model, beside uncut chip thicknesses changes, appropriate changes in shear yield stress and toughness with tooth/grain orientation have been taken into account. The conducted analyses have demonstrated that values of RMS of cutting power obtained with the new developed model are slightly larger than experimental values. On the other hand computed values of cutting power with the use of the mean uncut chip thicknesses in the model are a bit lower from the empirical one.
Highlights
Theoretical and experimental determination of values of forces acting in the cutting process belongs to the fundamental and simultaneously the most explored field of mechanics of the machining process
In wood cutting processes it could be emphasised the use of some elements of fracture mechanics: in the calculation models of cutting forces developed by Laternser et al (2003), analyses made by Merhar and Bučar (2012), theoretical and experimental studies of sawing of pine wood on sash gang saws by Orlowski and Palubicki (2009), in theoretical and empirical studies of circular sawing by Hellström et al (2013) and Kopecký et al (2014), in experimental studies on formation of wood surfaces and chips by Marchal et al (2009)
It should be emphasized that values of shear yield stresses and fracture toughness were obtained empirically in the cutting tests in the industrial conditions according to the methodology presented in the paper by Orlowski et al (2015)
Summary
Theoretical and experimental determination of values of forces acting in the cutting process belongs to the fundamental and simultaneously the most explored field of mechanics of the machining process. The radial axis is normal to the growth rings, while the tangential axis is perpendicular to the grain but tangent to the growth rings (Kretschmann et al 2010, Laternser et al 2003, Porankiewicz and Goli 2014). These specific features might be taken into account in analyses of energetic effects thanks to building surface energy for separation (i.e. material’s fracture toughness) into the models for forecasting of energetic effects (cutting force or cutting power). In wood cutting processes it could be emphasised the use of some elements of fracture mechanics: in the calculation models of cutting forces developed by Laternser et al (2003), analyses made by Merhar and Bučar (2012), theoretical and experimental studies of sawing of pine wood on sash gang saws by Orlowski and Palubicki (2009), in theoretical and empirical studies of circular sawing by Hellström et al (2013) and Kopecký et al (2014), in experimental studies on formation of wood surfaces and chips by Marchal et al (2009)
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