Study on the normal component force in oblique cutting of wood

Based on a series of experiments, the relationships between normal component forces and oblique angles of cutting edge, and normal rake angles in oblique cutting of wood were studied. The experiments consist both of the 90°-0° and the 0°–90° oblique cutting situation. Each type of experiment includes two wood species and two kinds of thickness. Through the experiments, the rules of the effect of oblique angles of cutting edge and normal rake angles on normal component force were found out. The calculation methods of normal component force were studied by mathematical analysis.     

Cutting forces in bandsaw processing of oak and beech wood as affected by wood moisture content and cutting directions

Cutting forces in bandsaw processing of oak and beech wood were measured at two levels of wood moisture content (about 12 % and FSP) for four cutting directions (90°–90°, 90°–0°, 0°–90° and 90°–45°). A constant cutting speed of 40 m/s and a feed rate of 20 m/min were applied. A piezoelectric dynamometer (KISTLER type 9257A) mounted on the carriage of the vertical bandsaw machine (ESTERER model EB 1400) was used to measure the parallel, normal and lateral cutting forces. Results revealed that all cutting forces depend on the wood moisture content and cutting direction. The greatest parallel force was observed for oak wood at 12 % MC for 90°–90° cutting direction (44 N/mm) whereas the lowest one was for beech wood at 30 % MC for 0°–90° cutting direction (20 N/mm). In contrast to the little change of lateral force at various cutting directions, the change in parallel force was significant.     

Microbevel for cemented tungsten carbide wood cutting tools

The microbevel method for increasing the rake angle of carbide tools was investigated. Relationship between the microbevel width, angle and the fracture of the cutting edge was established for cutting dry western hemlock knots. Also wear rate of microbevelled tool was investigated. Relatively small microbevel widths at a 30° bevel angle completely prevented edge and corner breakage of carbide tools with rake angles up to 50. Unbevelled carbide tools failed at rake angles larger than 30°. Tool life was not affected by the microbevel.     

切削参数对人造板切削力影响的研究

通过对中密度纤维板和刨花板的闭式切削实验,研究了不同锯齿前角、切削厚度、切削速度等参数对切削力的影响规律。结果表明:主切削力和法向力皆随前角的增大而呈减小趋势;通常情况下,相同锯齿前角切削时,刨花板的主切削力和法向力皆比中纤板大。切削厚度对切削力的影响显著,主切削力和法向力均随切削厚度增加而增加。切削速度对切削力的影响相对较小,随着切削速度的增加,主切削力和法向力均略有减小。     

Parallel and normal cutting forces in peripheral milling of wood

In this paper, the parallel and normal cutting forces on the tip of the tool are examined when altering a number of parameters in peripheral milling. The parameters studied are rake angle, chip thickness and upward/downward milling. The evaluation of the forces has been performed during cutting of the chip and the variation in the forces has been recorded. In this way, important information can be obtained in order to arrive at cutting data and tool geometries that will reduce surface defects such as torn and raised grain. In the past, very few investigations have been carried out on peripheral milling, probably because of the difficulties of measurement. Nowadays, however, new measuring techniques and equipment make it possible to measure cutting forces even in standard milling machines. In this work, a sensor was placed under the workpiece to measure the forces in three directions at frequencies up to 7000 Hz. To obtain detailed data, a plastic material was used so that the cutting (revolution) speed could be kept at a minimum, thereby maximizing the number of readouts per incision. The results show how the normal force (the force component perpendicular to the workpiece) varies during the cut and how it is dependent on the examined parameters. This force changes from negative to positive during the cut. When altering the machining parameters, the normal force changes in both direction and magnitude. The other force component, the parallel force, also shows a dependence on the parameters. The objective of this research is to find parameters that minimize the normal forces in order to avoid damage to the wood.     

切削参数对竹材切削力影响的研究

研究了竹材切削不同刀具前角、切削量与切削速度对切削力的影响.刀具前角对主切削力的影响较为显著,随刀具前角的增大,所需主切削力明显减小.主切削力与切削量成正相关关系.切削速度对切削力的影响不大.     

Peripheral milling properties of compressed wood manufactured from planted China-fir

Softwood exhibits different physical and mechanical properties in early wood and late wood, which often becomes the cause of some cutting defects during processing. These problems, however, can be partially solved by conversion into compressed wood. It can be expected that density and strength of the compressed wood increase with the increase in compression, thus affecting cutting resistance. The study on the machinability of compressed wood in order to justify its application is needed. In the test, green China-fir wood (Cunninghamia lanceolata) grown in plantations was compressed in radial direction using various compression sets, followed by peripheral milling parallel to the grain. The results showed that the horizontal cutting force increased with an increase in compression and depth of cut, but decreased with rake angle increase. The vertical cutting forces increased with an increase in cutting depth. No apparent relationship between vertical cutting force and compression was found. No significant difference existed in horizontal cutting forces beween up cutting and down cutting.     

Assessment of surface properties and solvent-borne coating performance of red oak wood produced by peripheral planing

Coating performance on wood could be affected for different aspects including the manner in which the surface is prepared. Peripheral planing is one of the most used machining processes in woodworking. Improving this process would allow to enhance coating performance. As a result, the effects of wavelength and rake angle on surface properties and coating performance were evaluated in an attempt to improve peripheral planing of red oak wood. Surface quality was assessed through roughness, scanning electron micrographs, and wettability analyses. The performance of a solvent-borne coating was measured by adhesion strength before and after accelerated aging. Surface roughness and energy components increased as rake angle increased. As wavelength increased, cell damage and surface roughness increased. Surfaces prepared with a rake angle of 25° had more cell-wall fibrillation, which was assumed to be responsible for increased surface energy and improved coating adhesion after weathering. Samples machined with this rake angle combined with a short wavelength resulted in the lowest loss of adhesion after aging and presented an acceptable level of surface roughness.     

Visual and visuo-tactile preferences of Malagasy consumers for machined wood surfaces for furniture: acceptability thresholds for surface parameters

In wood machining operations, target surfaces are chosen to achieve technical functions (gluing, finishing), or aesthetic functions (raw wood, varnishing) in order to produce a surface which consumers will appreciate. Although the literature often refers to the optimization of cutting conditions to improve the surface quality, there is currently no specific criterion to define what good surface quality is. The purpose of this study was to investigate quantitative criteria related to consumer preferences and to find an acceptability threshold for each criterion in order to determine the best cutting conditions. To this end, 32 surfaces from Chrysophilum boivinianum (Sapotaceae) were machined in various cutting conditions which yielded surfaces ranging from very rough to smooth. The primary surface profile, roughness and waviness parameters, and machining defects (raised grain, torn grain, chip marks, cutting traces) were measured on each surface. Visual and visuo-tactile tests were then carried out with a panel of 174 consumers. The results show that touch allowed better appreciation of surface defects than a simple visual observation. Consumers like smooth surfaces without visible defects and less visible peaks of waviness. The acceptability thresholds of surface parameters correlated with consumer preferences were determined. The rotational speed and the feed speed affect the most the surface quality. To obtain good surface quality for consumers, the rotation speed should be greater than 5000 rpm, with a maximum feed rate per tooth of 0.5 mm, and a maximum average chip thickness of 0.18 mm. This knowledge will help industries to better optimize the cutting of wood.     

Up-milling and down-milling wood with different grain orientations – the cutting forces behaviour

Peripheral milling of wood with up milling and down milling techniques is very well known from a geometrical point of view. However, in processing anisotropic materials such as wood, these geometrical aspects imply relevant differences when machining. In fact, milling of anisotropic material leads to different cutting geometries when up- or down-milling and when increasing or decreasing the depth of cut resulting in different grain orientations depending on the adopted process. In this paper, tests performed when processing Douglas Fir with different depths of cut and grain orientations are described. The cutting forces were measured, and the dependence of the cutting forces with respect on the cutting geometry are analysed and discussed.     

Effect of surface modification and knife penetration angle on the Quasi-Static Knife Penetration Resistance of para-aramid fabrics

The focus of this paper is to describe the effect of change in surface friction of single layer para-aramid (Twaron^®) square woven fabric and change in knife penetration angle on its Quasi-Static Knife Penetration Resistance (QSKPR). The surface friction of fabric was changed by depositing SiO₂ on its surface by using water glass as a precursor. Six different knife penetration angles (0°, 22.5°, 45°, 67.5°, 90° and 135°) were selected. Untreated and treated fabric samples were compared for change in QSKPR. It was observed that the deposition of SiO₂ on the surface of Twaron^® fabric increased the surface friction which resulted in the increase in QSKPR. The response of fabric against QSKPR changed from partial yarn cutting to individual yarn cutting in fewer steps and load was distributed to a larger area due to decrease in yarn slippage. The change in penetration angle changed the distance, knife cutting edge travelled to cut each next yarn(s) and when this distance increased, the QSKPR was reduced. The post-penetration image analysis of damaged fibres showed that the load distribution among warp and weft yarns was complementary and change in penetration angles changed the distribution of stabbing load among the warp and weft yarns. When yarns with higher tensile strength and less slippage were loaded, the fabric showed highest resistance to penetration. A QSKPR prediction model was also proposed at the end.     

Machining qualification of solid wood of Fagus silvatica L. and Piceaexcelsa L.: cutting forces, power requirements and surface roughness

Fagus silvatica) and spruce (Picea excelsa). The machining process was carried out on a shaper with specific devices. The concerned variables were: cutting depth, feed rate and cutting speed. The mean chip thickness and cutting width were constant. The machining process was done in two different ways: conventional and climb cutting; thus it was possible to compare both working directions with the same machining parameters and watch their influence on the cutting forces, the power consumption and the surface roughness. The most important variables on the cutting forces are depth of cut, wood density and feed direction. With regard to power consumption, it was detected that the most important variables were cutting speed, feed direction, depth of cut and wood density. It was further demonstrated that the measured and calculated power have a very good correlation, and that the cutting forces can be determined by the calculated power. Thus, if cutting power is measured for a specific condition of wood and machine, the cutting forces can be estimated. The surface roughness was very homogeneous in all the tests. The better machining process was obtained when applying conventional cutting. Then the cutting forces, the power requirements and the roughness standard deviation reach smaller values.

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Fagus silvatica ) und Fichtenholz (Picea excelsa). Der Bearbeitungsprozess erfolgte auf einer speziellen Holzhobelmaschine. Die relevanten Variabeln waren: die Schnitttiefe, der Vorschub und die Schnittgeschwindigkeit. Die mittlere Spanst?rke und die Schnittbreite waren konstant. Die Bearbeitung wurde auf zwei verschiedene Arten durchgeführt: im Gleichlauf und im Gegenlauf, somit war es m?glich, beide Bearbeitungsrichtungen unter Beibehaltung der Parameter zu vergleichen und ihren Einfluss auf die Schnittkr?fte, den Leistungsbedarf und die Oberfl?chenrauhigkeit zu prüfen. Die wichtigsten Einflu?variabeln bezüglich der Schnittkr?fte waren die Schnitttiefe, die Materialdichte und die Vorschubrichtung. Den Leistungsbedarf betreffend kamen wir zu dem Ergebnis, da? sowohl die Vorschubrichtung, die Materialdichte als auch die Schnittkr?fte, -geschwindigkeit und -tiefe die Haupteinflu?faktoren waren. Es konnte gezeigt werden, da? die gemessene und berechnete Leistung gut korreliert sind, und da? die Schnittkr?fte mittels der berechneten Leistung bestimmbar sind. Es ist daher m?glich, durch Messen des Leistungsbedarfs einer Bearbeitung einer bestimmten Holzart auf einer definierten Maschine die Schnittkr?fte abzusch?tzen. Die Oberfl?chengüte war gleichbleibend in allen durchgeführten Versuchen. Die besten Versuchsergebnisse wurden in Gegenlaufbearbeitung erzielt. Die Schnittkr?fte, der Leistungsbedarf und die Standardabweichung der Oberfl?chenrauhigkeit erreichen hier jeweils ihre Minimalwerte.

     

Effects of cutting parameters on surface quality of paper birch wood machined across the grain with two planing techniques

Helical planing and face milling were applied across the grain to surface paper birch wood prior to coating application. Three feed speeds and three cutting depths were evaluated for face milling while three cutting depths were studied for helical planing. The roughness and wetting properties of wood as well as pull-off strength of a solvent-borne coating after aging were evaluated. For helical planing, no significant effects of the cutting depth on roughness and wetting properties were found. For face milling, the cutting depth had no significant effect on the surface roughness while it had a significant impact on the wetting properties. The feed speed affected significantly both parameters. Furthermore, none of these parameters had a significant effect on the pull-off strength. However, helical planing produced smoother surfaces with equivalent wetting properties and higher pull-off strength than face milling. Scanning electron microscopy showed more exposed cell lumina and sound cells for helical planed surfaces, which enhanced their wetting and adhesion properties.     

Influence of grinding direction and wheel translation on microsharpness of cemented tungsten-carbide tips

The attempt has been made to determine the grinding direction and the wheel translation which produce the best microsharpness for carbide-tipped tools, such as carbide-tipped saws. Other grinding variables considered were rake angle, grinding depths and diamond-grit size. The results suggest that the grinding direction should be adjusted to an angle of 45° or larger to the cutting edge and that the grinding wheel may be fed parallel to the plane of grinding, but should always be retracted perpendicular to it. Grinding direction in grinding the first face was found not to influence the microsharpness of the cutting edge.     

Effect of thermal rectification on machinability of Eucalyptus grandis and Pinus caribaea var. hondurensis woods

Thermally rectified wood acquires colors similar to those observed in tropical woods, improved resistance to fungi and weathering, higher dimensional stability and lower hygroscopicity. Little information is available on the effect of heat treatments on the machining properties of wood. In this work, relatively low-valued woods (Eucalyptus grandis and Pinus caribaea var. hondurensis) underwent a variety of thermal rectification treatments (from 140°C to 200°C), performed in presence or scarcity of oxygen. Heat-treated wood underwent peripheral knife-planing (15°, 20°, and 25° rake angles) and sanding tests (60?C80, 80?C100, and 100?C120 grit). Surface quality was evaluated as a function of the incidence of machining defects and uniformity of texture (planed surfaces), and roughness and wettability (sanded surfaces). Thermally rectified samples provided better surface quality after planing, and increased surface roughness after sanding, compared to control samples. The increment of treatment temperature caused an increase in wetting time, which indicates reduced hygroscopicity.     

Effect of tooth front bevel angle on cutting accuracy and chip formation for cicular rip saws

When using sawdust in the pulp making process the wood fibres should be as long as possible. Circular saws with alternatively front or top beveled teeth produce saw dust with such characteristics. In this study the effect of bevel angle on cutting accuracy, surface finish, and saw dust quality was studied. A bevel angle of 15° maintained good cutting accuracy, produced good surface finish, and produced fibre quality superior to that obtained from saws with no bevel.     

Characterizing surface defects in machine-planing of rubberwood (Hevea brasiliensis)

Despite its extensive application in the furniture manufacturing industry throughout the South East Asian region, the machine-planing characteristics of rubberwood (Hevea brasiliensis) are not completely understood. In an effort to optimize the process, a series of experiments were undertaken using a Weinig 22A Unimat moulder (cutter-head rpm of 6000, cutter ? 120 mm) to produce machined rubberwood surfaces with differing pitch lengths ranging from 0.8 mm to 1.5 mm, by altering the feed speed. The results showed that surfaces with a pitch length of cutter marks of 1.2 mm or more and a high knife rake angle were more prone to manifest machining defects, such as torn grain. This study shows that for machine planing of rubberwood the recommended cutter marks pitch length of 1.2 mm, achieved with a knife rake angle of 20°, will ensure the highest resultant surface quality and processing yield.     

Synthesis and hydrophobic evaluation of the electro-spun nano-TiO2/PET fibrous bats after treatment with an alkaline solution and fluorocarbon material

Superhydrophobicity of a substrate is the result of a low surface energy and proper surface roughness. In the present research, the potential roughening effect of using nano-TiO₂ (NT) in a PET electro-spinning solution followed by an alkaline modification of the synthesized bats was investigated to create appropriate surface roughness while a low surface energy was achieved in owing to a layer of fluorocarbon coating. The results were evaluated via employing FTIR, SEM, digital microscopy, 3 M water repellency, water contact angle, and sliding angle. The best result of hydrophobicity was achieved by the alkaline modified-fluorocarbon coated NT (5.5%)/PET fibrous bat with the 3 M water repellency of 10, contact angle of more than 150° (155.9 ± 0.1°), and sliding angle of less than 10° (6.1 ± 1.9°) due to a multiscale surface roughness obtained by the fibrous bat structure itself, and roughening effect of the NT as well as alkaline solution surface etching.     

Non-conventional fermentation at laboratory scale of cocoa beans: Using probiotic microorganisms and substitution of mucilage by fruit pulps

In a non-conventional lab-scale fermentation of cocoa beans using probiotic microorganisms and substituting the cocoa pulp for fruit pulp, physicochemical, microbiological and quality parameters were investigated. Two hundred grams of beans were fermented in a controlled environmental chamber (temperature ramp rate of 25°C for 48 h; 35°C for 48 h and 45°C for 48 h; and 65% HR). pH, titratable acid, citric, lactic and acetic acids, as well as sugars and ethanol were measured. A cut test was also performed on the cocoa beans fermented 5 and 6 days. As the fermentation time progressed, citric acid concentration decreased until 0.53 g kg⁻¹, whereas both lactic and acetic acids increased until 0.44 and 16.58 g kg⁻¹, respectively. Sucrose content decreased from 12.26 g kg⁻¹ (in fresh) to 6.54 g kg⁻¹ on the 6th day. Fructose and glucose contents increased in the cotyledons from day five, reaching a maximum concentration of 1.14 and 1.01 g kg⁻¹, respectively, on day six. Yeasts were the main microorganisms during the first 24–48 h (8.4 log CFU g⁻¹), while bacterial counts reached its highest number (7.8 log CFU g⁻¹) on day four. Beans fermented 5 and 6 days resulted in more fermented beans (>81%) and less violet ones (<18.4%) than the control.     

Response surface methodology modeling of protein concentration,coagulum cut size,and set temperature on curd moisture loss kinetics during curd stirring

The effects of the independent variables protein concentration (4–6%), coagulum cut size (6–18 mm³), and coagulation temperature (28–36°C) on curd moisture loss during in-vat stirring were investigated using response surface methodology. Milk (14 kg) in a cheese vat was rennet coagulated, cut, and stirred as per semihard cheesemaking conditions. During stirring, the moisture content of curd samples was determined every 10 min between 5 and 115 min after cutting. The moisture loss kinetics of curds cut to 6 mm³ followed a logarithmic trend, but the moisture loss of curds from larger cut sizes, 12 or 18 mm³, showed a linear trend. Response surface modeling showed that curd moisture level was positively correlated with cut size and negatively correlated with milk protein level. However, coagulation temperature had a significant negative effect on curd moisture up to 45 min of stirring but not after 55 min (i.e., after cooking). It was shown that curds set at the lower temperature had a slower syneresis rate during the initial stirring compared with curds set at a higher temperature, which could be accelerated by reducing the cut size. This study shows that keeping a fixed cut size at increasing protein concentration decreased the level of curd moisture at a given time during stirring. Therefore, to obtain a uniform curd moisture content at a given stirring time at increasing protein levels, an increased coagulum cut size is required. It was also clear that breakage of the larger curd particles during initial stirring can also significantly influence the curd moisture loss kinetics. Both transmission and scanning electron micrographs of cooked curds (i.e., after 45 min of stirring) showed that the casein micelles were fused at a higher degree in curds coagulated at 36°C compared with 28°C, which confirmed that coagulation temperature causes a marked change in curd microstructure during the earlier stages of stirring. The present study showed the dynamics of curd moisture content during stirring when using protein-concentrated milk at various set temperatures and cut sizes. This provides the basis for achieving a desired curd moisture loss during cheese manufacture using protein-concentrated milk as a means of reducing the effect of seasonal variation in milk for cheesemaking.