Abstract
In the classical approach, energetic effects (cutting forces and cutting power) of wood sawing process are generally calculated on the basis of the specific cutting resistance, which is in the case of wood cutting the function of more or less important factors. On the other hand, the cutting forces (power) problem may be tackled with an innovative, up-to-date fundamental analysis of the mechanics of sawing based on modern fracture mechanics. This line of attack is an improvement on traditional approaches for cutting forces and power, many of which are empirical and based upon limited information. Such formulae do not permit generalisation to new conditions of operation of sawmills, such as the use of narrow-kerf blades e.g.. The presented algebraic model, for cutting power determination while sawing, in addition to timber ‘strength’ and friction between tool and workpiece takes into account the property called ‘fracture toughness’ (resistance to cracking), which is a vital ingredient. Furthermore, forecasting of the shear plane angle with this model is achievable even for small values of uncut chips. Moreover, the mentioned model is a universal one, and useful for determination of energetic effects of sawing of every kinematics such as: frame sawing machines, bandsawing machines and circular sawing machines.
Highlights
In the classical approach, energetic effects of wood sawing process are generally calculated on the basis of the specific cutting resistance, which is in the case of wood cutting the function of more or less important factors
The cutting forces problem may be tackled with an innovative, up-to-date fundamental analysis of the mechanics of sawing based on modern fracture mechanics
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 Uncut chip thickness / debljina strugotine, mm Results of predictions of cutting powers obtained with the use of cutting models that include work of separation in addition to plasticity and friction, and chip acceleration power variation in the case of sawing of pine coming from different Polish regions with one saw blade are shown: in Fig. 8 for the frame sawing machine DTRB 63, in Fig. 9 when using the bandsawing machine ST100R, and in Fig. 10a and Fig. 10b for cutting on the rip saw PWR422
Summary
The mechanics of cutting wood has traditionally been interpreted in terms of the Ernst-Merchant model for cutting ductile metals in which, for given blade geometry and uncut chip thickness, the important parameters are mainly the strength of the material and friction between blade and workpiece (Manžos, 1974; Orlicz, 1988; Orlowski, 2007; Scholz et al, 2009; Naylor et al 2011). In case of cutting with circular saw blades, uncut chip thickness h (an average value e.g.) instead of feed per tooth fz should be taken into account, the cutting power may be expressed as:. That in these analyses, it was assumed that the power Pac is not a function of the number of working teeth In case of both the circular sawing machine and the bandsawing machine, the chip acceleration power Pac is several hundred times larger in comparison with the sash gang saw (Orlowski et al, 2013), for the latter machine tool, the last term of Eq(1) can be omitted. G-vc is and the cutting speed direction (Fig. 1b)
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