Dynamic model for the determination of instability of periodic circular cutting of wood tissue

Shown is a dynamic model of periodic circular cutting of oriented wood tissue in which both the properties of the material and the dynamic properties of the machining system have been considered. The cutting or exciting force is the result of internal and external modulation. The internal modulation is the result of the effect of the properties of the machined material which are given by specific cutting pressure k _s, while the external modulation is the consequence of the varying material flux which is affected by relative displacements between the workpiece and the tool. Relative displacements, which are the consequence of the manner of excitation and dynamic properties of the machining system, are also the cause of self-excitation occurrence. As in the process of cutting, the cutting or self-exciting force depends on relative displacements between the tool and the workpiece, the dynamic model developed is non-linear. By simulation of a dynamic model it is possible to analyse the process of cutting wood tissue in its entirety, and it can thus be employed to optimize the selection of tools and the processing parameters of machining.     

Lateral cutting force during machining of wood due to momentary disturbances in the wood structure and degree of wear of the cutting tool

The paper presents a study of the effect of momentary disturbances due to variations in wood structure on the lateral cutting force. Density, shape and fibre-direction of the disturbances, and the degree of wear of the cutting tool are taken into consideration. The paper shows that high density gradients result in high lateral forces. The highest momentary lateral force noted has a value of approximately 40 N. The geometrical shape of the cutting tool in terms of degree of wear has a big impact on the lateral force. The work indicates a potential to increase the cutting performance by a more accurate supervision of the condition of the cutting tools.     

Modelling the collapse of wood cells during the cutting process

Sharpness affects the performance of a wood cutting tool, particularly the surface finish and cutting forces on the wood. Because the mechanisms involved with cutting wood are not well understood, the amount of cutter sharpness required to produce a high quality cutting edge is not defined. An optimum economic sharpness for a cutter is when any increase in benefit from making the cutter sharper is less than the increase in cost of sharpening.This paper details a hybrid cellular/macroscopic finite element analysis of wood during the cutting process. Different radii were applied to the cutting edge to simulate different sharpnesses. It was found that the interaction between cutter and wood changed as the cutter was sharpened. A changeover point between two cutting mechanisms occurred when the radius of the cutting edge was less than the radius of curvature of the wood fibres in bending. Below this radius, the cutter acted a point load, above this radius, the cutter distributed its force around the radius.The cutting forces for Pinus radiata in the LR direction were experimentally measured. The empirical results confirmed the validity of the model.

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Modellbildung über den Zellkollaps während des Schneidevorgangs

Zusammenfassung Die Schärfe des Schneidwerkzeugs beeinflusst dessen Leistung, besonders im Bezug auf die Qualität der Oberfläche und den Auswirkungen der Schneidkräfte auf das Holz. Da die Mechanismen, die beim Schnitt des Holzes wirken, nicht sonderlich gut erforscht sind, ist der Schärfegrat, der benötigt wird, um ein Messer hoher Qualität herzustellen, nicht definiert.Das ökonomische Schärfemaximum ist erreicht, wenn der zusätzliche Nutzen einer weiteren Schärfung geringer ist als die daraus entstehenden Kosten.Dieser Artikel beschreibt eine FE-Analyse aufgrund zellulärer und makroskopischer Eigenschaften des Holzes während des Schneidprozesses. Verschiedene Radien wurden für das Schneide verwendet, um unterschiedliche Schärfegrade zu simulieren. Es wurde herausgefunden, dass sich der Effekt des Schneidwerkzeuges auf das Holz mit zunehmender Schärfe änderte. Ein Wendepunkt zwischen zwei Schneidemechanismen trat auf, wenn der Radius der Schneide kleiner war als der Krümmungsradius der gebogenen Holzfasern war. Unterhalb dieses Radius übte die schneide punktuellen Druck aus, darüber verteilte sich die Kraft über den gesamten Radius.Die Schneidkräfte bei Pinus radiata in LR Richtung wurden experimentell gemessen. Die empirischen Resultate bestätigten die Richtigkeit des Modells.

     

The influence of the specific cutting force and cross-sectional geometry of a chip on the cutting force in the process of circular rip-sawing

f_s in the process of circular rip-sawing of wood tissue. The specific cutting force represents a complex interaction between the geometry of the blade, the physical and mechanical properties of the tissue and the direction of cutting, i.e. the rotating angle of the tool. The analyses carried out confirm the appropriateness of the definition of the specific cutting force as the parameter independent of the cross-sectional geometry of the chip, i.e. independent of the technological parameters. The results of the analysis of the relation between the tangential component of the cutting force and the feed velocity, which at invariable values of the entrance and exit rotating angle of the tool directly determines the mean thickness of the chip, confirm the hypothesis on an exponential relation between the said variables. In the case of invariable geometric parameters of the tool, the specific cutting force is constant, while the relation between the cutting force and the technological parameters is merely a consequence of the influence of the parameter of cross-sectional area of the chip f _hm . For this research wood of two tree species was used, namely celtis wood (Celtis zenkeri Engel.) and manilkara wood (Manilkara fouilloyana Aubrev et Pellegr.).

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f_s im Verfahren des L?ngss?gens von Holz. Die spezifische Schnittkraft stellt eine komplexe Interaktion zwischen der Geometrie der Schneide, den physikalischen und mechanischen Eigenschaften des Holzes und der Richtung des Schneidens, bzw. des Drehwinkels des Werkzeugs dar. Die durchgeführten Analysen best?tigen die Zweckm?ssigkeit der Definition der spezifischen Schnittkraft als den Parameter, der von der Querschnittsgeometrie des Spanes, bzw. den technologischen Parametern unabh?ngig ist. Die Resultate der Analyse des Zusammenhangs zwischen der tangentialen Komponente der Schnittkraft und der Vorschubgeschwindigkeit, der bei konstanten Werten des Eintritts- und Austrittsdrehwinkels des Werkzeugs unmittelbar die mittlere Spandicke bestimmt, best?tigen die Hypothese über die exponentielle Abh?ngigkeit der genannten Variablen. Im Falle der unver?nderlichen geometrischen Parameter des Werkzeugs ist die spezifische Schnittkraft konstant, die Abh?ngigkeit zwischen der Schnittkraft und den technologischen Parametern ist aber nur die Folge der Einflusses des Parameters der Querschnittsgeometrie des Spanes f _{h m} . In der Untersuchung wurde das Holz von zwei Baumsorten angewandt und zwar Celtis (Celtis zenkeri Engel) und Manilkara (Manilkara fouilloyana Aubrev et Pellegr.).

     

The influence of the specific cutting force and cross-sectional geometry of a chip on the cutting force in the process of circular rip-sawing

in the process of circular rip-sawing of wood tissue. The specific cutting force represents a complex interaction between the geometry of the blade, the physical and mechanical properties of the tissue and the direction of cutting, i.e. the rotating angle of the tool. The analyses carried out confirm the appropriateness of the definition of the specific cutting force as the parameter independent of the cross-sectional geometry of the chip, i.e. independent of the technological parameters. The results of the analysis of the relation between the tangential component of the cutting force and the feed velocity, which at invariable values of the entrance and exit rotating angle of the tool directly determines the mean thickness of the chip, confirm the hypothesis on an exponential relation between the said variables. In the case of invariable geometric parameters of the tool, the specific cutting force is constant, while the relation between the cutting force and the technological parameters is merely a consequence of the influence of the parameter of cross-sectional area of the chip f _hm . For this research wood of two tree species was used, namely celtis wood (Celtis zenkeri Engel.) and manilkara wood (Manilkara fouilloyana Aubrev et Pellegr.).     

加工工艺对机械零件表面完整性的影响

研究了多步制孔快进给、多步制孔慢进给和一步复合制孔3种加工工艺对高强度材料7075铝合金板材紧固孔表面完整性的影响。结果表明：1）多步制孔快进给和慢进给工艺的表面粗糙度相近，而多步制孔慢进给和一步复合制孔工艺的表面微观形貌、表层硬化程度、残余应力分布状况等质量评价指标均优于多步制孔快进给工艺；2）一步复合制孔工艺加工表面粗糙最小，加工硬化程度最小，应力分布稳定，几乎没有变质层，是一种高效、快捷、零件加工表面完整性好的加工工艺。鉴于此，评价零件表面加工质量，仅以表面粗糙度为指标是不全面的，就根据表面完整性的全部技术指标来综合评价。     

基于UMAC高速木材复合加工中心控制系统的研究

随着科技的进步,高新技术在木工机械行业的应用也越来越广泛。尤其是数控技术和高速切削（HSC）技术的使用,为高效利用木材资源。加强环境保护发挥了重要作用。高速木材复合加工中心是木工机械行业的关键装备。文中阐述了当代木材加工行业的发展现状,分析了高速木材复合加工中心控制系统的原理。并且以UMAC为核心器件,在配合其硬件和软件的基础上开发了一种用于高速木材复合加工中心控制系统。该控制系统具有性能稳定、高速高效、结构简单、配置灵活等优点。     

木材加工剩余板皮高效利用分析与展望

阐述了木材加工剩余板皮的利用及研究现状,介绍了以木材加工剩余板皮进行高效制备木丝单元的方法及木丝集成人造板的成型工艺,提出了以木丝为原料进行木丝集成材料的研制与开发是高效利用木材加工剩余板皮料的有效途径。     

Ultrasonic cutting of foods: Effects of excitation magnitude and cutting velocity on the reduction of cutting work

The effects of vertical cutting velocity and the magnitude of ultrasonic excitation on the reduction of the work necessary to separate various food materials were investigated. Generally, cutting work increased with increasing cutting velocity but, at each particular cutting velocity, decreased with increasing magnitude of the ultrasonic excitation of the cutting tool. Interactions between cutting velocity and the maximum vibration speed at the cutting edge, which is determined by both excitation amplitude and excitation frequency, are significant. Depending on the food under action, the relative amount of cutting work reduction is either affected by the maximum vibration speed or, additionally, by vertical cutting velocity. No distinct effects of the excitation frequency (20 or 40 kHz) were observed.

Industrial relevance

Ultrasonic cutting is used in the food industry, especially for the separation of products consisting of layers with different rheological properties to achieve minimally damaged cut surfaces. The results of the study may be useful for selecting operational variables (cutting velocity, excitation amplitude) during cutting to achieve a controlled reduction of the cutting work.     

Influence of pressing parameters on dimensional stability and density of compressed beech wood

European beech (Fagus sylvatica) wood specimens were subjected to thermo-mechanical densification, and the influence of pressing parameters on dimensional stability, mean density and density profiles was evaluated. The specimens with two initial moisture contents, 18% and the fibre saturation point, were compressed by 20 and 40% at temperatures of 160, 180, 200, and 220 °C for several times, specified in the Methods, ranging from 6 to 12 min. Dimensional changes were observed immediately after the removal from the hot press and subsequent conditioning (20 °C, 65% relative humidity). The properties of the compressed beech wood were influenced by all the pressing parameters. This influence, however, varied based on the factor and property. The analysis showed as most appropriate: an initial moisture content ranging from 17 to 20%, a pressing temperature?≥?180 °C and pressing time?≥?10 min for the given thickness. As for the compression degree, it is necessary to consider the purpose of compression and the wood properties required.     

带锯条和圆锯片的切削刃磨损

在每种木材加工操作中木工刀具的磨损是一个连续的问题,虽然其实际机理尚未完全清楚。这种情况,部分是由于切削刃在高速运行时很难监测刀刃的磨耗过程。木材化学成份和木材宏观、微观结构组成的复杂性和多样性,使了解磨损机理很困难。     

The influence of spruce wood heat treatment on its thermal stability and burning process

This paper deals with the assessment of the influence of heat treatment of Norway spruce wood (Picea abies L.) on its thermal stability and burning process. Three types of samples were used for the research. The first group was comprised of untreated samples. The second group was comprised of samples heat treated according to the ThermoWood—Thermo-S thermal programme (maximum temperature during heat treatment is 190 °C), and the third group was modified according to the ThermoWood—Thermo-D thermal programme (maximum temperature during heat treatment is 212 °C). The influence of heat treatment on the burning process was assessed based on the heat release rate, effective heat of combustion and the yield of carbon monoxide. The influence of heat treatment on the thermal stability was assessed based on the resistant residue weight. Heat release rate, effective heat of combustion, yield of carbon monoxide and resistant residue weight were determined with a cone calorimeter for different heat flux densities. The results obtained prove that the spruce wood heat treatment has an important influence on the decrease of the maximum heat release rate and the increase of resistant residue weight. The results obtained further prove that the heat treatment has only a modest influence on the increase of the carbon monoxide yield, and its influence on the effective heat of combustion significantly depends on the heat flux density.     

热处理对实木地板尺寸稳定性影响的研究

探讨热处理对两种实木地板坯料尺寸稳定性的影响,结果表明,真空热处理的板材抗膨胀率明显高于常压热处理板材的抗膨胀率。     

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.     

Minor cutting edge angles of sawing teeth: effect on cutting forces in wood

European Journal of Wood and Wood Products - Optimising the cutting tool geometries can reduce waste while increasing timber yield. The industry is moving towards thin-kerf bandsawing of timber,...