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.     

Cutting energy and surface roughness in medium density fiberboard rip sawing

Medium density fiberboard (MDF) is a?wood based panel which main feature is the distribution of wood fibers, uniform and dense in the full panel thickness, allowing for very precise machining on the edges and in the faces of the board. However, and due to its manufacturing process, a?density profile is produced with external layers being heavier than the core of the panel. These differences generate a?variable surface quality across the panel when machined. The tool characteristics and the cutting process kinematics also determine the resulting surface roughness of the processed material. With regard to the cutting energy, there are important variations when machining conditions are modified, or when some tool characteristics are changed. The aim of this paper is to determine the cutting energy required to rip sawing MDF and to study its relationship with the resulting surface roughness across the panel profile when the density of the material changes. The findings lead to the conclusion that there is a?close relationship between cutting energy and surface roughness, being particularly sensitive to changes in specific gravity within the profile of the panel, and in particular to changes in cutting condition expressed as mean chip thickness.     

Influence of mechanical properties and mineral salts in wood species on tool wear of high-speed steels and stellite-tipped tools – Consideration of tool wear of the newly developed tip-inserted band saw

This paper is the third in a series of work done on a novel technique for bandsawing, which uses a tip-inserted saw, and is gaining increasing popularity in Japan. It builds up on previous reports on the novel technique for bandsawing, which considered cutting tool hardness, tool wear, accuracy of kerf width, washboarding, and surface profiles of the workpiece. In this paper, ash content analysis and three-point static bending tests were conducted to clarify the influence of mineral salts and mechanical properties of wood samples of Elais guineensis (Oil palm), Strombosia glaucescens (Afina), and Cryptomeria japonica (Sugi) on cutting tool wear. The cutting tools were made from Stellite and High Speed Steels (HSS) of designations SUS420J2 and TiN coated SKH 51 according to the Japan Industrial Standards (JIS). Among the tested wood samples, the highest cutting tool edge recession when machining with SUS420J2 and TiN coated SKH 51 tools were recorded in Oil palm in spite of Afina possessing the highest mechanical strength properties. On the contrary, Stellite in spite of possessing the smallest hardness (HV580) among all the tested cutting tools recorded the lowest cutting tool edge recession when machining wood samples of Oil palm. However, Stellite recorded the highest edge recession when machining Afina, a high density species. Ash content analysis and a scanning electron micrograph of wood samples of the tested wood species show the presence of high proportions of mineral salts in the transverse, radial and tangential sections of Oil palm. This could perhaps account for the high cutting tool edge recessions recorded in wood samples of the Oil palm. The studies have demonstrated that silica accumulation species could have significant effect on tool wear of high speed steels.     

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.).     

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.     

On-line control of feed-speed in circular sawing

An adaptive control optimization system was developed to produce a desired surface finish roughness by automatic control of the work-piece feed-rate in circular sawing. The system developed in this study consists of the interconnection of an adaptive controller with a numerically controlled circular saw. The AE signals and cutting forces were measured to monitor the machining process continuously in this system. The signals were provided to the adaptive controller to evaluate the surface finish roughness and adjust the workpiece feed-rate automatically in the machining process. Sensing of AE signals and of cutting forces was compared to determine which technique is more convenient. Experiments were carried out with a carbide-tipped circular saw. Cross cutting was done with counter-cutting during the experiments. The cutting parameters controlled were workpiece feed-rates and cutting speeds. Japanese beech (Fagus crenata Blume) and Yezo spruce (Picea jezoensis Carr.) were used as the workpiece. Experimental results indicated that adaptive control optimization took place in the system developed for circular sawing. The desired surface finish roughness was produced by automatic control of the workpiece feed-rate using the sensing technique of AE signals as well as that of cutting force. However, the system using AE signals is more convenient than taht using cutting force.     

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.

     

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.).

     

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.     

A new methodology for wood cutting optimization in the secondary manufacturing processes

The determination of cutting conditions may help to control design and manufacturing processes. The machining database is important in wood machining. It is specific for each tool-machine. For each kind of wood piece, particular machining conditions are needed to reach a properly surface roughness and a safe work. The Couple Tool Material (COM) method is applied as a new methodology in wood working, centered in secondary wood processing industry, defining the working field of cutting tools taking in mind cutting parameters and limiting the number of experiments. Working perspectives are wide with the appearance of new cutting materials and high speed cutting processes, thus to create better working conditions in wood cutting will be easier with COM data utilization.

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Neue Verfahren zur Schnittoptimierung bei Holzverarbeitungs-prozessen

Zusammenfassung Die Bestimmung von Schnittbedingungen kann helfen Design und Verarbeitungsprozesse zu kontrollieren. Die maschinelle Datenbank in der Holzwirtschaft ist von großer Wichtigkeit und spezifisch für jede Werkzeugmaschine. So werden auch für jede Art von Holzstück besondere Maschinenbedingungen benötigt, um eine saubere Oberflächenrauhigkeit und eine sichere Arbeit zu erzielen. Die Couple-Tool-Material-Methode (COM) wird (wie ein) als ein neues Verfahren in der Holzwirtschaft angewandt, zentral in der sekundären Holzverarbeitungs-Industrie, indem das Arbeitsfeld der Schnittwerkzeuge definiert wird und man die Schnittparameter sowie das Limitieren der Zahl der Experimente beachtet. Ein breites Spektrum von Arbeitsperspektiven eröffnet sich mit dem Aufkommen neuer Schnittmaterialien und Hochgeschwindigkeits-schnittprozessen. Durch die Verwendung von COM-Daten wird es einfacher den Bedürfnissen für bessere Arbeitsbedingungen beim Holzschneiden gerecht zu werden.

     

Untersuchungen zum Kegelstirnplanfräsen und Stirnplanfräsen am Institut für Werkzeugmaschinen der Universität Stuttgart

Slab milling with a conical shaped milling tool and slab milling with a face milling tool are wood machining techniques which meet the current requirements of wood machining and processing (e.g. changing batch sizes, flexible machines and equipment). That is why the Institute for Machine Tools at University of Stuttgart has already conducted comprehensive basic research in this field (Heisel 1997). Research on slab milling with a face milling tool was especially promoted as an alternative to slab milling with a peripheral milling tool (also known as planing) due to its low noise emission and low energy consumption. Amongst others, slab milling with a face milling tool as pre-milling procedure when calibrating wood-based panel products was examined under technical and economic aspects. The results showed higher service life and continuously better surfaces when choosing the right geometry of the cutting tools as compared to conventional slab milling with a peripheral milling tool. Notwithstanding the high costs, diamond cutting edges are more cost-effective than carbide insert tips due to their longer service life (Heisel 2004).     

Up-milling and down-milling wood with different grain orientations – theoretical background and general appearance of the chips

Peripheral milling 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 anisotropic materials leads to different cutting geometries when up-milling or down-milling and when changing the depth of cut. This results in a relative orientation of the grain depending on the process adopted. In this paper the geometrical interactions between tool and wood grain have been analysed theoretically and supported by experimental evidence. To achieve this result, Douglas fir has been processed with different depths of cut and grain orientations, the resulting chips have been collected and analysed. The experiments show how a shift of the cutting phenomenon and the chip type can be observed to support the theoretical background.     

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.     

欧式木窗用异形框架集成材切削加工节能经济性分析

欧式木窗用异形框架集成材由实木板材通过异形胶拼而成,它不仅具有许多实体木材所没有的优点,而且可节约木材、降低切削加工能耗、减少切削刀具损耗.本文以窗用异形框架集成材为例,通过对指接板材进行异形拼接,制成欧式木窗用异形框架集成材,并且分析了其在切削加工中节约木材、降低切削功耗、提高刀具寿命等方面的经济性优势.     

A review of wood cutting tool wear literature

The current state of knowledge about wood cutting tool wear is assessed by reviewing the published work in this area. Research concerned with tool wear which deals primarily with the tool material, with the work material and with tool-work interactions is considered.     

Minimizing dust emission during routing operation of rubberwood

The study evaluated airborne dust emission (0.1–10 µm) during the routing operation of Rubberwood (Hevea brasiliensis) in the furniture industry in South East Asia. It was found that the average chip thickness of 0.1 mm and wood moisture content of 12–14% minimized dust emission, while the cutting tool rake angle had little influence on dust emission. The study shows that adverse economic implications due to health hazards posed by airborne dust emissions during wood machining can be reduced by manipulating the average chip thickness and work-piece moisture content.     

Apparatus for viscoelastic thermal compression of wood

Viscoelastic Thermal Compression (VTC) of wood is a treatment which greatly improves material properties by means of densification with mechanical compression perpendicular to the grain. VTC is similar to other wood densification processes, but is designed for thin lamina and employs dynamic temperature and steam pressure conditions. A?device was constructed that is capable of producing VTC wood. Details of the construction and operation of the VTC device are presented. The device consists of a pressurized chamber with variable volume. Wood density may be modified from the initial density of the virgin wood up to approximately 1400?kg/m³. Control of steam pressure and temperature insures that the wood cell walls are not fractured during the process. The device is designed for batch operation and may be adapted to a conventional laboratory hot-press. An example operating schedule is described, but other procedures are possible within the design parameters of the device.     

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.     

Minimizing dust emission during routing operation of rubberwood

The study evaluated airborne dust emission (0.1–10 μm) during the routing operation of Rubberwood (Hevea brasiliensis) in the furniture industry in South East Asia. It was found that the average chip thickness of 0.1 mm and wood moisture content of 12–14% minimized dust emission, while the cutting tool rake angle had little influence on dust emission. The study shows that adverse economic implications due to health hazards posed by airborne dust emissions during wood machining can be reduced by manipulating the average chip thickness and work-piece moisture content.     

用单位矢量法求刀具角度

用数学分析方法精确求解木材切削刀具的角度。在求解过程中,用单位矢量来代表刀刃线和刀面的外法线方向,简化了推导过程和计算公式。同时区分了刀刃在坐标平面上的投影角和刀面相对坐标平面的倾斜角,并用实例计算说明这两种角度有时差值较大。因此,精确计算刀具角度对提高木制品的加工精度,提高刀具的强度、寿命及锋利性是有意义的。