Influence of the manner of excitation of a machining system on the stability of the process of periodic circular cutting of wood tissue

The article deals with dynamic analysis of the influence of the manner of excitation of a machining system on the stability of the process of periodic circular cutting of wood tissue at an invariable frequency of cutting, taking into account dynamic properties of the machining system. For stability analysis we used a dynamic model developed for this purpose (Bu?ar and Kopa? 1996). The manner of excitation of the machining system has been defined by the radial immersion of the tool and the workpiece, taking into consideration, in modelling the process of cutting, both internal and external modulation of the cutting or exciting force. The internal modulation is the result of the effect of the properties of the machined material which are given by specific cutting pressurek _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 result of the manner of excitation and dynamic properties of the machining system, are also the cause of self-excitation occurence. The results of analyses point to it that the manner of excitation of a machining system with known dynamic properties is of the essence for the stability of the process of periodic circular cutting of wood tissue.     

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.     

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.     

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.).     

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.     

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.     

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.).

     

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.     

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.     

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.     

拉削外回转表面时的切削层参数及切削力分析

以加工曲轴为例，依据拉削原理，通过加工过程中切削层参数的分析计算，指出：拉削外回转表面时的切削力可按照单位切削力计算原理来计算。     

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.     

Performance of laser-treated AISI-M2 cutting tools for peeling beech

For many wood machining processes, the interest of tool steels remains very important because of their good tool edge accuracy and easy grinding. The main problem is their low resistance to wearing and corrosion. In order to increase their performance, a laser melting and cladding applied on the tool edges is presented in this paper. Firstly, annealed AISI-M2 bar was melted, and M2 powder was cladded onto the AISI L2 substrate by a laser beam. The microstructure and microhardness of the M2 melted and M2 clad were characterised. Secondly, their wear resistance was tested for peeling beech wood. The experimental results show that metallurgical structure obtained by conventional heat treatment for the M2 was ferritic polycrystalline with coarse primary carbides, and the microstructure of the M2 melted and M2 clad, in which whole primary carbides were completely dissolved during laser melting and cladding, was observed to reveal fine iron dendritic structure. The M2 melted and M2 clad, which were almost the same in microhardness, had larger microhardness compared to the M2 conventional. The wear resistance and wear pattern of the M2 melted and M2 clad cutting tools in peeling beech were better than those of the M2 conventional cutting tool. Also the M2 melted and M2 clad cutting tools produced better surface quality of veneer and retained better cutting edges roughness compared to the M2 conventional.     

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.     

Mass transfer in cellular material at solid–liquid contacting interface

The effective mass transfer (water and solute) and volume shrinkage were measured during solid–liquid contacting process for red beet material tissue under a wide range of process parameters. The mass transfer process of each component in the solid–liquid system is affected not only by operating parameters, but also by the matrix properties of cellular material. The main driving force for the mass transfer phenomena of water out of red beet tissue and sucrose taken into red beet tissue from sucrose solution is attributed to the concentration gradient between external and internal red beet material, and the interaction among water, sucrose fluxes and tissue matrix. The coupled mass transfer fluxes across the interface in an isothermal solid–liquid system were analysed by means of a film model as a function of the concentration gradients, based on the generalized multicomponent mass transfer theories. The relation between individual flux and the independent driving force is nonlinear. The mass transfer model and parameters proposed in the present study is applicable to the unit operation such as osmotic treatment of cellular porous biomaterial.     

Konstruktionsmerkmale der Werkzeugeinspannung von Holzbearbeitungsmaschinen

This paper concerns the clamping of milling cutters for wood working machines. It stresses the importance of tool clamping on exactness of rotation for cutting edges. Effects of concentricity errors on tools and workpiece are explained. Tool clamping may influence the total stiffness at the spindle nose. Potential concentricity erros due to deviations in tool shape and spacers and to angularity errors in shaft nuts are pointed out. Measurements of centering clamping systems gave slight reclamping errors and high radial stiffness.     

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.     

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.     

Mechanical properties of green asparagus

The mechanical properties of three sections (upper, middle and lower) of the spears of green asparagus (Asparagus officinalis) were investigated as affected by storage and cooking. A range of methods based on cutting, compression and puncture was employed to measure mechanical properties of spear sections. A transverse puncture test was the most suitable for measuring mechanical properties of fresh and cooked spear sections, and it was observed that strength increased along the spear from the upper to the lower section of fresh asparagus. Postharvest storage resulted in strengthening, mainly located in the last portion of the stem. A softening phenomenon was detected in every section as a consequence of cooking. The results of a tensile test on two different tissue types separated from the middle and lower portions of the stem showed that the external tissues were stronger and stiffer than the internal tissues, and both increased in strength and stiffness after 3 days of storage. However, the effect of cooking was different: while the external tissues decreased in stiffness and strength, as expected, a significant increase was observed for the internal tissues of the stem. © 2002 Society of Chemical Industry