Feed Cutting Force Component in Up and Down Sawing of Pine Komponenta posmične sile rezanja pri istosmjernom i protusmjernom piljenju borovine

• The monitoring of cutting force components is one of the possibilities to control machining pro - cesses from the point of view of its stability, machine tool spindle or cutting tool loading. This paper presents and compares the results of experimental longitudinal sawing of pine wood with 4 saw discs with different teeth number (16 and 24) and rake angle (10° and 20°) during up (conventional) and down (climb) cutting with different revolu - tions (4000 min -1 , 5000 min -1 , 6000 min -1 ) and feed speed (15 m/min, 20 m/min, 25 m/min). The signal was obtained from Quart 3-components piezoelectric dynamometer.


INTRODUCTION 1. UVOD
Circular sawing is one of the most advanced technologies in woodworking industry.Saw discs (blades) are designed as universal rip saw blades for longitudinal or transversal cutting or trimming of all types of wood, soft or hard, dry or wet.Saw discs are used in single or multi-rip saw tools with single or double shaft or in splitting machines.Circular sawing has been in the focus of many researchers due to its widespread application.
Cutting forces are very important variables in machining performance; they affect surface roughness, tool life, energy consumption.
The process of material removing was studied from the beginning of machining; the studies are related to detachment of chips, shear angle, friction angle, grain orientation (Piispanen, 1948;Kivimaa, 1950;Fischer, 1979;Teng et al., 2014:).The research is also oriented on the influence of mechanical and physical properties or moisture content of the machined material on power consumption (Beer, 2002;Lučić et al., 2004;Dange et al., 2011;Nasir and Cool, 2018).Consumption of energy depends on the type of machined material.The medium density fibreboard was researched by Aquilera (2011), oak and Douglas fir by Goli and Porankiewicz (2014), beech and spruce were researched in the experiments of Aguilera and Martin (2001).The value of cutting moment or force components received from machining can be used for comparing different models of machining (Kivimaa, 1950;Orlowski et al., 2013;Orlowski et al., 2017;Hlaskova et al., 2019).The influence of technological factors on the main cutting force or its components or power parameters is analysed very often in the scientific papers (Ioras et al., 2002;Naylor et al., 2012;Palubicki, 2021).
For measuring cutting power, consumption energy or cutting forces were determined by different ex-perimental stands and methods.The pendulum dynamic tester was used (Dange et al., 2011) for studying energy consumption and cutting forces during orthogonal cutting with two blades, sharpened at 30° and 45°.Cutting velocity in the range between cca 2.3 m/s to 7.3 m/s was used.The experimental device with long arm (535 mm) rotated in vertical plane was used for monitoring and evaluation semi-orthogonal cutting and for designating multi-factors and dependency between tangential and normal force (Porankiewicz et al., 2011;Porankiewicz and Goli, 2014).On the other hand, measurement of cutting power and then calculation of the main cutting (tangential) force from electrical cutting power is used very often (Kopecky and Rousek, 2005).Another way how to reduce energy consumption is to reduce the friction between saw disc body and workpiece (Fekiač et al., 2022).

Material of workpieces 2.1. Materijal uzoraka
The workpieces of nominal dimensions of 170 mm × 100 mm and 23 mm thickness were prepared and before sawing all samples were air-conditioned to the moisture content of 14 %.The properties of Swiss stone pine are presented in Table 1.

Machine tool 2.2. Alatni stroj
The vertical CNC router Reichenbecher RANC 207 AMW (Figure 1) was used for experiments.Machine tool is defined as training centre and assigned for the machining of small and plane parts.All experiments were carried out in the laboratory of the University of Sopron, in Hungary.

Woodworking tools 2.3. Alati za obradu drva
The Polish company GASS Suwalki (at present ASPI sp.o.o./s.k.) prepared 4 saw discs (Figure 2) for the experiment; parameters are given in Table 2.The tips of teeth of all discs were from tungsten carbide.

Technological conditions 2.4. Tehnološki uvjeti
The experiment was designed as full factorial experiment based on a model of a classical experiment plan, with three independent factors.
The projection of saw disc up of workpiece: 10 mm.Dependent (measured) factors were: -feed force F f (as sum of force F c,f and F cN,f ) measured in Y axis of measure platform; -force F fN , perpendicular to feed force measured in X axis of experimental platform (Figure 3).

Experimental device 2.5. Mjerna oprema
Piezoelectric measuring system (Figure 5) made by Kistler (Kistler Instrumente AG, Switzerland) was used for measuring the cutting force components.The basic parts of the system were: 1. Quart 3-components dynamometer 9275B (parameters see Table 3).2. Multichannel Charge Amplifier 5070A.

REZULTATI I RASPRAVA
The components F f and F fN are the basis for determining the active force F a .Figure 5 illustrates the orientation of force components F f , F fN , and final (active) force F a based on the coordinate system of measure platform.This figure clearly shows that the feed force was positive for both types of cutting (down and up), but F fN was in harmony with the positive coordinate axis of the platform for down cutting, while this component was negative for up cutting.The data processing for every saw disc and technological parameters (i.e.type of sawing, revolutions, number of teeth, rake angle and feed speed) was the basis for evaluating feed force.The graphs (Figure 7) clearly show that feed force was smaller during down sawing for all revolutions, feed speeds and both rake angles.

Influence of sawing type 3.1. Utjecaj vrste piljenja
Influence of sawing type (valid for SD1, z=16, g=10°), Figure 7 A more detailed analysis of the values shows that the ratio between feed force during up sawing and feed force during down sawing oscillates within the range from 1.25 to 2.42 (Table 4 or Figure 7).Influence of sawing type (valid for SD4, z=24, g=10°), Figure 8 Analogous to saw disk SD1 that has 16 teeth and rake angle of 10°, the results of a similar analysis for saw disc SD4 with rake angle of 10° but 24 teeth are displayed in Table 5.In this case the ratio between feed force during up sawing and feed force during down sawing oscillates within the range from 1.30 to 1.83 (Table 5 or Figure 8).The maximal difference is 0.50 compared to 1.17 for SD1.It seems that increasing of teeth number from 16 to 24 made the process more even.The analysis of values displayed in Figure 9 and 10 shows partial results based on interactions of dependent variables: ratio between feed forces and different feed speeds during up and down sawing is: -for up sawing, revolutions 4000 min - For both cases (down and up sawing), the slope of a straight line is quite similar.
The ratio between feed speeds v f =20 m/min and v f =15 m/min is 1.33; ratio between v f =25 m/min and v f =20 m/min is 1.25; ratio between v f = 25 m/min and v f =15 m/min is 1.66.
As shown in Table 7 and 8, the rate of feed force is not the same as the rate of feed speed.The reason may lie in the fact that there are other force components, such as the depth of workpiece, etc.  Saw discs SD1 and SD2 have the same number of teeth but different rake angle.The graph in Figure 11 shows the values for up sawing and in Figure 12 for down sawing.
When comparing the results obtained during up and down sawing separately, there are small differences for various revolutions and feed speeds within limits from 1.36 N to 5.75 N (Figure 11) and from 0.24 N to N (Figure 12).The results show that the rake angle has some influence but, as there are many influencing factors such as wood structure, grains orientation, position of samples in tree trunk, it is very difficult to make explicit conclusions.

ZAKLJUČAK
The aim of this experiment was to confirm that feed force practically depends on feed speed proportionally, but the ratio of feed forces is not the same as the ratio of feed speeds.
The line slope depends on the type of sawing; it is higher for up (conventional) sawing than for down (climb) cutting.
The absolute value of feed force is higher for up sawing compared to down cutting.(On the other hand, the force perpendicular to feed force is higher for down cutting.) The results of this experiment did not confirm the hypothesis that higher rake angle generally leads to the decrease of the feed force.Acknowledgements -Zahvala A part of this article was created within the framework of Grand Project No. APVV-20-0403 "FMA analysis of potential signals suitable for adaptive control of nesting strategies for milling woodbased agglomerates" as a result of the author's research activity with the support of the agency APVV-SR.