The Influence of the Coating on the Saw Blade on the Energy Intensity of Cross-Cutting of Wood

Abstract

Cutting wood in the transverse direction is the most widespread in the logging process, and it is used in felling trees, shortening the length of trunks, and assortment production. In practice, it is particularly important that the entire wood processing process starts with the least energy-intensive process (i.e., the energy demand of the entire process). The aim of the study is to determine the effect of coatings on the energy demand of saw blades. The conditions of the experiment were taken from previous experiments. In the experiment, two types of saw blades of the same type, EN 41 9418 or 75 Cr1 (DIN 1.2003), were selected. Two types of saw blades (SB with SC (cemented carbide) slices and PK without SC (cemented carbide) slices) and two types of wood (beech and spruce) were used in the experiments. The saw blades were coated with three types of PVD coatings (physical method of layer deposition). The results show that the least energy-demanding saw blade is HSS_M (tool steel saw blade without SK blades with Maximizer coating) at a feed speed of 12 m·min⁻¹ and a cutting speed of 60 ms⁻¹, with a power of 1310.63 W. When sawing spruce wood, it was proven that the most energy-demanding saw blade is HSS_K_I at a feed rate of 12 m·min−1 and a cutting speed of 60 ms⁻¹, with a power of 2113.56 W. The least energy-consuming saw blade is HSS_M at a feed rate of 12 m·min⁻¹ and a cutting speed of 60 m·s⁻¹, with a power of 1251.54 W. The results provide a comparison of the measured values of the performances of the cross-cutting wood process using a statistical program.

1. Introduction

Cutting wood by circular saw blades is a complex process [1]. For obtaining ideal operating conditions, it is important to know the mutual interactions between the tool and the product, and the influence of technical and technological factors affecting the cutting power and final quality of the product [2]. It is possible to obtain the required quality by setting these factors and parameters. Cutting quality is affected by tool wear [3]. It is very important to understand the phenomena of the mutual interaction between the tool and the workpiece in terms of optimizing and intensifying the machining process. It is necessary to know the impact of the technical and technological factors on the cutting potential and workpiece quality. The correct selection of the mentioned factors leads to quality assurance of the product, which plays an important role in the market. The wear of the cutting wedges also impacts the cutting quality. The cutting wedges (teeth) of the saw blades are produced from different materials, such as tool steel EN 41 9418 (75Cr1) [2], sintered carbide plates or stellite [4]. During the wood cutting, the saw blade teeth overheat, which is caused by several factors. These are the technological parameters of sawing, saw blade construction, cut type, wood homogeneity, wood defects and others [5]. Published studies state, according to experiments, that at a distance of 0.5 mm from the main cutting edge, the temperature reaches up to the 500 °C and at the distance of the teeth heel, the temperature is around 800 to 1110 °C. In the zone of the surface micro-layers of the teeth, the temperature reaches 800 to 1100 °C [2,6,7,8]. The lifetime of the tool depends on the manufacturability and exchangeability [9]. To improve the properties of saw blades when sawing wood, a coating is used. A highly effective way of improving the properties of cutting materials is the creation of a thin isotropic coating on the functional surfaces of the cutting edge, i.e., j. coating. The different conditions of the machining processes give rise to the need for a wide range of cutting materials with different chemical-physical, mechanical, and technological properties. The mentioned method of increasing the working properties of tools represents a significant contribution to the efficiency of sawing processes [10,11]. Coating is the process of covering or applying a thin layer of material (coat) on the surface of an object (substrate), which improves its characteristics [12]. The objective of the coat is functional, decorative, or both. Coats are applied by plasma techniques in vacuum, which assures high process cleanness without the presence of any impurities that could deteriorate the coat quality (www.staton.sk, accessed on 17 October 2018). Each coat is characterized by a large set of basic characteristics and parameters that can control chemical and phase composition, microstructure, thickness, and the presence of impurities in the interphases. Coatings utilized for cutting tools can fulfill other important characteristics, such as resistance against wear and the influence of the coating on the tool lifetime and surface roughness of the machined area. According to several studies [13,14], the hardness of the material and the friction between the blade and workpiece are the most important parameters with respect to the particular saw blade tooth geometry. The wood cutting parameters (energy consumption), the emerging product parameters (dimensional accuracy and created surface quality), and the produced chip parameters (dimensions and particle size composition) depend on the teeth shape, teeth dimensions and number, cutting tool geometry, sharpness, and technological conditions of the process, such as feed speed, feed force, and cutting speed [15,16,17,18,19]. Several researchers have been involved in determining the factors that affect the cross-cutting process, but the question of how coatings affect the energy consumption of saw blades has not yet been answered, since research is mainly concerned with the effect of coatings on wear and tool life.

2. Materials and Methods

The aim of the experiment was to determine the effect of the saw blade coating on the energy consumption and parameters of the cross-cutting of wood. In practice, this involves finding out the values of the torque on the crankshaft of the experimental device with respect to the course of the frequency of revolutions under certain conditions, and finally evaluating the results. The chemical composition of the coatings used in the PVD coating (physical vapor deposition) process is AlTiN, AlTiCrN and AlTiCrSiN. These coatings were selected based on manufacturers’ recommendations and have been used in practice for a very long time. Likewise, the cutting parameters (cutting speed, feed speed, type of saw blades, wood) were chosen based on previous experiments, measurements, and calculations [2,20]. Two types of saw blades were used for the experiment, which were also used in previous experiments, namely:

• made of tool steel without SK blades with a diameter of ø 600 × 3.5 × 30 with 56 evenly spaced teeth and a cutting-edge angle of 20° (referred to as HSS);
• with SK blades with a diameter of ø 600 × 3.5 × 30 with 54 evenly spaced teeth and a cutting-edge angle of 20° (marked as SK).

2.1. Coating Maximizer AlTiN

The samples were coated by the PVD coating Maximizer AlTiN. The coating is designed to resist high fatigue and shearing stresses. It is adapted to resist cutting temperatures up to 850 °C. The coating temperature ranges from 450 °C to 550 °C. The coating color is blue–black. Further technical parameters of the selected coating are stated in

Table 1. Technical parameters of Maximizer AlTiN coating (www.ionbond.com, accessed on 10 October 2018).

Coating Composition	Al Ti N
Operational temperature	850 °C
Coating temperature	450–550 °C
Hardness HV 0.05	3500
Color	blue/black

. The first sample was coated by the coating Maximizer AlTiN (Figure 1). The coated sample No. 3 with the sintered carbide plate was marked as sample C2.

2.2. Coating CRONAL I

The PVD coating CRONAL I. (C_I), based on aluminum—titanium—chromium—silicon—nitrogen (Al-TiCrSiN), was coated on the second pair of saw blades in Figure 2 and is highly temperature-resistant to wear (

Table 2. Technical parameters of CRONAL I coating, AlTiCrSiN.

Coating Composition	Al Ti Cr Si N
Operational temperature	1000 °C
Coating temperature	500 °C
Hardness HV 0.05	1200
Color	blue/black

). CRONAL I PVD coating contains a high amount of chromium (Cr). It is specially designed for extreme cutting conditions when machining hard materials and hardened steels up to 1200 HV and hardened steels up to 55 HRC. On the other hand, CRONAL I surface layers are not suitable for machining cast iron. The coating is suitable for machining at high cutting speeds and high operating temperatures. Typical for this coating is the coating of monolithic carbide cutters, drills and cutting tools for computer numerical control (CNC) machining centers. It is very suitable in applications where high corrosion resistance is required.

2.3. Coating KTRN I

PVD coating KTRN I (K_I), based on aluminum—titanium—chromium—nitrogen (AlTiCrN), was coated on the third pair of saw blades (Figure 3) and is highly temperature resistant to wear. PVD coating KTRN is suitable for applications where high chemical and thermal resistance is required (

Table 3. Technical parameters of KTRN I coating, AlTiCrN (www.ionbond.com, accessed on 10 October 2018).

Coating Composition	Al Ti Cr N
Operational temperature	1000 °C
Coating temperature	500 °C
Hardness HV 0.05	1200
Colour	blue/black

), e.g., computer numerical control (CNC) machines with the possibility of machining without cooling. KTRN I is a universal coating that is suitable for machining easy and difficult to machine steels, stainless steels, nonferrous metals, and cast iron, and is used for extremely difficult cutting conditions with a continuous or intermittent cut (milling and turning). It is used for solid carbide cutters, drills and cutting discs, and is also suitable for high-speed steel tools, e.g., cutters, drills, saw blades, where its high heat resistance of up to 900 °C prevents the cutting edge from overheating.

2.4. Analysis of the Coated Samples

In the Institute of Materials and Machine Mechanics of SAS (Slovak Academy of Science), detached branch (INOVAL, Žiar nad Hronom, Slovakia) the samples were cut by water jet WEDM and prepared for microscopic analysis. The coated samples were cut so that a piece of SK plate and a piece of the basic material could be analyzed. In the initial analysis, we found that the basic material of both saw blades was identical (material 19 418 [21]); therefore, no specific analysis was performed on the sample from the saw blade without the SK plate. Sample analysis was performed using the optical microscope KEYENCE VHX 2000 (KVANT s.r.o., Bratislava, Slovakia). The first examined sample was C2.

Electron microscopy was performed with a Maximizer AlTiN coating at a magnification of ×25 and a voltage of 20.0 kV. Next, details of the coated SC plate were obtained and the thickness of the coating was measured. The value of the measured thickness is D1 = 4.52 µm. Furthermore, we focused on verifying the chemical composition of the coating, whether it corresponds to the parameters stated by the manufacturer. The chemical composition of the coating is Al 33.78%, Ti 37.55% N 28.66%.

The TiAlN coating was measured in the same way as the first one, i.e., at a voltage of 20.0 kV and a 25-fold magnification. In this case, the thickness of the coating was evaluated on the SC plate. Its thickness was D1 = 2.84 µm. After measuring the thickness, a chemical analysis of the coating was performed. The chemical composition was W 39.7%, Ti 37.55%, N 28.66% and Cr 33.78%. Tungsten was also present in the composition, the reason being that during the application process, tungsten can diffuse from the SC board into the coating. The results show that all saw blades were coated according to the thicknesses specified by the manufacturers.

2.5. Experimental Transverse Cutting

Measurements of the values of transverse wood cutting were performed on the testing equipment (see Figure 4). All measurements of cutting conditions during wood cutting were carried out on the Stend. The Stend was designed, manufactured, and further modernized in the Department of the Environmental and Forestry machinery in the workplace of the Technical University in Zvolen. The equipment is composed of two primary parts: the feeding part and the cutting part. The transmission of torque to the saw blade is ensured by a belt transmission from the electric motor (cutting mechanism). The feeding part serves to fix and pass the machined material into the cut Stend—the measuring equipment (Figure 4) is composed of a three-phase asynchronous electric motor with capacity of 7.5 kW. Torque is transmitted by means of a belt, safety coupling GIFLEX GFLL 28 (HBM s.r.o. Brno, Czech Republic), input coupling of the torque sensor, torque sensor (HBM T20WN HBM s.r.o. Brno, Czech Republic), output coupling of the torque sensor and headstock for the circular saw blade.

2.6. Test Samples

The measurements were performed on samples of spruce wood (Picea abies) (Technical University in Zvolen, Forestry Industry, Zvolen, Slovakia) and beech wood (Fagus sylvatica) (Technical University in Zvolen, Forestry Industry, Zvolen, Slovakia) with dimensions of 200 mm × 200 mm × 1000 mm. The dimensions were selected based on the technical parameters of the testing machine. Moisture readings were obtained via gravimetric analysis by ISO 12570 [22]. Humidity results of the wood species are beech 61.22% and spruce 46.91%. The experiment was performed by comparing two saw blades at different feeding speeds (vf = 6 m∙min⁻¹ and 12 m∙min⁻¹), rotational speeds (n = 1900 min⁻¹, 2230 min⁻¹, and 2550 min⁻¹), and cutting speeds (vc = 60 m∙s⁻¹, 70 m∙s⁻¹, and 80 m∙s⁻¹). The samples of beech wood and spruce wood were used. The samples were placed 50 mm below the axis of the spindle.

3. Results and Discussion

The aim of the measurement was to find out to what extent the coating of the saw blade affects the related factors (performance) in the process of transverse cutting of wood. During the implementation of the experimental measurements, the main task was to monitor and record the torque with respect to the size of the spindle revolutions of the measuring stand depending on the changing parameters characterizing the process of transverse wood sawing (feed speed, cutting speed, wood species, and type of saw blade). From the obtained results of the magnitudes of the torque Mk for individual saw blades and types of wood, we subtracted the max. values of Mk. From the course of the torque curve Mk when cutting with a saw blade, one can see a large increase in the value during the initial penetration of the tool (saw blade) into the cut, followed by a certain decrease in the value, which may be due to the inertia of the saw blade and the gradual stabilization of the cutting process. Subsequently, the cutting process takes place at a certain constant value (the amount of torque changes minimally), until after the end of the cutting process, where it reaches the value at which the saw blade spins at idle without the load of the cutting process (Figure 5). All interactions between individual parameters were repeated six times in order to achieve the best possible statistical significance and eliminate measurement errors [23]. In total, we performed 1152 experimental measurements using eight types of saw blades.

Cutting performance (P) was calculated from the relation to the torque calculation using the spindle revolutions,

P_C = (M_K·n)/9550

(1)

where Pc is power (kW), Mk is torque (N·m), and n is speed (rpm).

Table 4. Average performance values of saw blades (beech wood).

Saw Blades	Feed Speed [m·min−1]	Cutting Speed [m·s−1]	Power [W] (Average)
HSS	12	60	1820.61
HSS_M	12	60	1310.63
HSS_K_I	6	60	1826.08
HSS_C_I	10	60	1969.01
SK	12	60	1529.77
SK_M	12	60	1628.19
SK_K_I	12	60	1866.39
SK_C_I	6	60	2079.32

and

Table 5. Average performance values of saw blades (spruce wood).

Saw Blades	Feed Speed [m·min−1]	Cutting Speed [m·s−1]	Power [W] (Average)
HSS	8	60	1621.13
HSS_M	12	60	1251.54
HSS_K_I	12	60	2113.56
HSS_C_I	10	60	2098.21
SK	6	60	1797.48
SK_M	12	60	1509.93
SK_K_I	12	60	2013.19
SK_C_I	10	60	1913.99

show the average calculated power values for individual measurements of saw blades. The measured values were evaluated in the program STATISTICS 12 (DataFriends, s.r.o., vesions 12, Plzeň, Czech Republic) using a multifactor performance analysis depending on the coating, cutting speed, feed speed and wood. When examining the individual properties of the selected files, it is also important to compare these files with each other in the statistical evaluation. Comparing such sets allows us to analyze their structure, in other words, their variances. Analyzing them gives us answers to the question of the structure of the basic files in relation to the examined sample files, and it provides us with information about the reasons for finding measured data and no other data. The primary goal of the analysis of variance is to break down the observed variability into individual components that can be assigned to individual causes of variability.

From the analysis of the basic statistical characteristics of average values and variances, we can judge, with the help of variance, the nature of not only the changing factors but also the basic sets of measured values that were selected. Our criterion for statistical significance is the significance level (p) of the F-test, which represents the probability that a factor has or does not have a statistically significant effect on the measured values of experimental measurements. Using multivariate analysis of variance (ANOVA), we investigated the statistical interdependence between the dependent variable (torque converted using revolutions to power) and the independent variable (saw blades, wood, feed and cutting speed). Due to the assumption that the individual quantities interact, we performed the Duncan Test to generalize the test of statistical significance. For each combination of 4 factors (2 woody plants, 8 discs, 3 cutting speeds and 4 sliding velocities = 192 combinations), representative intervals of values of the physical quantities examined (Mk, n, P) were filtered. The results of each physical quantity were evaluated by multifactor variance analysis.

The multi-factor variance analysis model can be mathematically written using the equation:

$$y_{ijklP}=\overline{y}+a_i+b_j+c_k+d_l+a{b}_{ij}+a{c}_{ik}+a{d}_{il}+b{c}_{jk}+\dots +ab\dots \dots +abc{d}_{ijkl}+e_{ijklP}$$

(2)

where: $y_{ijklP}$—P-th (n-th, M_k-th) value at i-th first, j-th second, k-th the third, l-th fourth factor,

$\overline{y}$—the total average level of the physical quantity evaluated (P, M_k, n),

$a_i$—the effect of the i-tej level of the first factor,

$b_j$—the effect of the j-tej level of the first factor,

$c_k$—the effect of the k-tej level of the first factor,

$d_l$—the effect of the l-tej level of the first factor,

$a{b}_{ij}$, $a{c}_{ik}$, $a{d}_{il}$, $b{c}_{jk}$, $b{d}_{jl}$, $c{d}_{kl}$,—two-factor interactions,

$ab{c}_{ijk}$, $ab{d}_{ijl}$, $bc{d}_{jkl}$, $ac{d}_{ikl}$,—three-factor interactions,

$abc{d}_{ijkl}$—four-factor interaction,

$e_{ijklP}$—random deviation at the P-th (M_k-th, n-th) value of the i-th first, j-th second, k-th third, l-th fourth factor,

i—wood (BEECH and SPRUCE),

j—saw blade (without SK slices, with SK slices, with coating, without coating),

k—cutting speed (60, 70, 80 m·s⁻¹),

l—feed speed (6, 8, 10, 12 m·min⁻¹).

Multifactorial variance analysis evaluates the significance, i.e., the non-zeroness and statistical significance of the individual variable components in Equation (2). Specifically, we test the null hypotheses H0 versus the alternative hypothesis H1 among all interactions.

• H₀:    $\overline{y}$ = 0     versus     H₁:  $\overline{y}$ ≠ 0
• H₀:    $a_i$ = 0    versus    H₁:  $a_i$ ≠ 0
• H₀:    $b_j$ = 0    versus    H₁:  $b_j$ ≠ 0
• H₀:    $c_k$ = 0    versus    H₁:  $c_k$ ≠ 0
• H₀:    $d_l$ = 0    versus    H₁:  $d_l$ ≠ 0
• ...

Table 6. Basic table of multifactor analysis of power variance depending on coating, cutting and feed speed and wood species.

Source of Variability	Sum of Squares	Degrees of Freedom	Variance	F-Test	p-Level of Significance
Abs. member	6.164104 × 10−9	1	6.164104 × 10−9	2,559,047	0.000000
St	8.304495 × 10−7	7	1.186356 × 10−7	4925	0.000000
WS	1.617926 × 10−4	1	1.617926 × 10−4	7	0.009696
vf	1.573577 × 10−6	3	5.245258 × 10−5	218	0.000000
vc	1.262143 × 10−8	2	6.310716 × 10−7	26,199	0.000000
St·WS	2.437381 × 10−6	7	3.481973 × 10−5	145	0.000000
St·vf	7.711793 × 10−6	21	3.672282 × 10−5	152	0.000000
WS·vf	2.829735 × 10−5	3	9.432451 × 10−4	39	0.000000
St·vc	9.134908 × 10−5	14	6.524935 × 10−4	27	0.000000
WS·vc	1.975272 × 10−4	2	9.876362 × 10−3	4	0.016860
vf·vc	7.944500 × 10−4	6	1.324083 × 10−4	5	0.000013
St·WS·vf	2.741593 × 10−6	21	1.305520 × 10−5	54	0.000000
St·WS·vc	3.697694 × 10−5	14	2.641210 × 10−4	11	0.000000
St·vf·vc	1.012590 × 10−6	42	2.410928 × 10−4	10	0.000000
WS·vf·vc	1.490149 × 10−5	6	2.483582 × 10−4	10	0.000000
St·WS·vf·vc	8.469191 × 10−5	42	2.016474 × 10−4	8	0.000000
Error	2.312400 × 10−6	960	2.408750 × 10−3

Surface treatment—St, Wood Species—WS, Feed Speed—vf, Cutting speed—vc.

describes the degree of importance of factors such as coating, cutting speed, feed speed, and wood, and their interaction. With 100% reliability, we can say that the size of the resulting performance affects the coating used, cutting speed, feed, and wood, and their interaction. Table 6 shows that the cutting speed has the greatest statistical significance and, therefore, the greatest impact on the energy demand of the cross-cutting process. Next come the saw blade and feed rate. Wood has the least statistical significance and, therefore, has the least impact on energy demand.

In the experimental process of cross-cutting wood, when there is a critical decrease in the revolutions of the saw blade, as a rule, we always started measurements from the point of view of kinematics with the worst possible conditions, i.e., high feed and low revolutions. In the case of inhomogeneity of the material when the saw blade hit a bump, the cutting process stopped (in rare cases). We always ended the experimental measurement with the best possible conditions in terms of kinematics, the lowest displacement and the highest speed. The process with the given parameters went smoothly. When observing the wood cutting processes for individual wood species, we came to the conclusion that sawing spruce wood is less demanding than cutting beech wood and the sawing process was not so problematic. However, this does not apply if the spruce wood was lumpy and, thus, caused greater problems during the sawing process than the beech wood, in which lumps occurred only rarely. From the point of view of electricity consumption, however, this is not the case, and the less energy-demanding wood for cutting is beech wood, which is also confirmed by the 95% confidence interval for the average power values of the wood.

Figure 6 shows 95% confidence intervals for mean power values depending on the coating used. It is clear from the graph that the MAXIMIZER coating influences the resulting performance, which is lower with this coating than without. The most pronounced effect of the MAXIMIZER coating is visible on the HSS disc. The other two coatings CRONAL I and KTRN I had the opposite effect, and the resulting performance was significantly higher than with uncoated discs.

Figure 7 shows 95% confidence intervals for performance as a function of the coating used and sliding speed. In the group of saw blades without SK blades, the saw blade with MAXIMIZER (AlTiN) coating has the significantly lowest energy consumption. In the group of saw blades with SK blades, performance overlaps at a feed speed of 6 m·min⁻¹ for blades without coating and with MAXIMIZER (AlTiN) coating, and at other feed speeds, saw blades with SK blades and MAXIMIZER (AlTiN) coating have the lowest statistical significance. In the case of saw blades with KTRN I (AlTiCrN) and CRONAL I (AlTiCrSiN) coatings, we can say that wood is not a homogeneous material and caused such large differences between individual saw blades. The MAXIMIZER coating reduced the resulting cutting performance, and the lowest performance value was precisely this coating applied to the HSS disc and feed speed vf = 12 m·min⁻¹.

Figure 8 clarifies the interactions between the saw blades of the two groups and the cutting speeds. In the group of saw blades without SK blades, the saw blade with MAXIMIZER (AlTiN) coating has the significantly lowest energy consumption at every cutting speed. Although the saw blade with SK blades without coating differs very little, the saw blade with SK blades with MAXIMIZER (AlTiN) coating has the lowest statistical significance in the group of saw blades with SK blades.

Statistical evaluation showed that the most energy-intensive saw blade for sawing beech is SK_C_I at a sliding speed of 6 m·min⁻¹ and a cutting speed of 60 m·s⁻¹, with an output of 2079.32 W (Figure 8). The least energy-intensive saw blade is HSS_M at with a feed speed of 12 m·min⁻¹ and a cutting speed of 60 m·s⁻¹, with an output of 1310.63 W. During the sawing of spruce wood, it was proved that the most energy-intensive saw blade is HSS_K_I at a feed speed of 12 m·min⁻¹ and a cutting speed 60 m·s⁻¹, with an output of 2113.56 W. The least energy-intensive saw blade is HSS_M at a feed rate of 12 m·min⁻¹ and a cutting speed of 60 m·s⁻¹, with an output of 1251.54 W. Figure 9 shows that the performance difference between the two types of wood is minimal. It is statistically significant in interactions with the coating. Therefore, we can say that the type of wood has an effect on the performance of the transverse sawing process. The difference in performance was also caused by random factors (inhomogeneous properties of wood). The objective of the experiment was to evaluate the associated factors during the process of transverse wood cutting. In the past, authors [2,4,24] have dealt with the issue of transverse cutting, and so we could compare the results. Kováč et al. concluded that when cutting with the saw blade made of HSS steel, the course of torque Mk is characterized by a surge to maximal value and consequently a slight fall and finally a sharp fall, which is caused by wood cutting. Our values of Mk torque confirm and coincide with the results of Kováč, J. and Mikleš, M. 2015. These claims can be supported by the knowledge that wood is not a homogeneous material, and has caused such great differences between individual saw blades. In the process of sawing beech wood, the greatest decrease in average speed values is observed compared to spruce wood. This phenomenon is caused by the composition and mechanical properties of individual woods. Beech wood has a higher tensile strength than spruce wood. For beech wood with a density of 720 kg·m⁻³, the saw blade must overcome a shear stress of 12.3 MPa, and for spruce wood with a density of 440 kg·m⁻³, it is only 5.3 MPa. The critical decrease in performance in some cases, in which it should be higher, is caused by random influences, such as the natural frequency of the saw blade, inhomogeneous material, changes in wood moisture.

At a low frequency of rotation of the saw blade, caused by the performance characteristic of the electric motor, the speed of the chip removed during the sawing process is also reduced. At the moment when the cutting off the chip occurs, the potential energy changes into the energy of elastic deformation, and then changes into the kinetic energy of the movement of the chip.

We compared our values with the values of Siklienka, M. et al. 2013 [25], and even in our experiment, the saw blades with a head angle of 20° are the most suitable for the process of transverse wood cutting. Further on, the use of coats appropriate for saw blade coatings improves their efficiency, prolongs the durability, and so decreases the wear, which should increase the cutting quality and decrease their energy intensity. Based on the change of the input factors that interacted in the cutting process (feed speed (vf), minimum overhang, and type of circular saw blade), feed rate (vf) appeared to be the most important determinant of energy performance in the cutting process and, thus, cutting input power. Here, we show that plating circular saw blades with certain metals can help to reduce the electrical charging of wood dust during cutting, which has significant implications for occupational safety, healthcare, and the lifetime of filter systems [26]. From the measured values, we can note that the PVD coating MAXIMIZER (AlTiN) has a positive effect on the energy intensity of the wood cutting process and reduces the size of the cutting power when sawing beech and spruce trees. Reducing and optimizing wood processing parameters was also dealt with by Kubovský et al. [27]. PVD coatings KTRN I (AlTiCrN) and CRONAL I (AlTiCrSiN) do not show a positive effect on the cross-cutting process of wood and increase the energy intensity of the process. We believe that this is due to the surface treatment process, which was different from the MAXIMIZER surface treatment, and its treatment could improve the resulting performance values.

4. Conclusions

We carried out experimental measurements of the process of cross-cutting of wood using coated and uncoated saw blades in order to determine the energy demand for each type of saw blade at different parameters of the cutting process. The experiments were carried out with two species of trees, which have the largest presence in Slovakia. Performance parameters were determined depending on the type of wood, type of saw blade, and determined cutting and feed speed. When changing the cutting speed, the power changes linearly and, at the same time, has the greatest impact on the amount of electricity consumption, while the power varies from 1251.54 W to 2113.56 W. These are calculated maximum values from the measurement record. The statistical evaluation showed that the most energy-demanding saw blade when cutting beech wood is SK_C_I at a feed speed of 6 m·min⁻¹ and a cutting speed of 60 m·s⁻¹, with a power of 2079.32 W. The least energy-demanding saw blade is HSS_M at a feed speed 12 m·min⁻¹ and a cutting speed of 60 m·s⁻¹, with a power of 1310.63 W. When sawing spruce wood, it was proven that the most energy-demanding saw blade is HSS_K_I at a feed speed of 12 m·min⁻¹ and a cutting speed of 60 m s⁻¹, with a power of 2113.56 W. The least energy-demanding saw blade is HSS_M at a feed speed of 12 m·min⁻¹ and a cutting speed of 60 m·s⁻¹, with a power of 1251.54 W. The obtained results did not exhaust the topic of the work, as the work represents a partial result of the investigation of the given issue. Therefore, due to the scope and difficulty of the issue, we will conduct further experiments.