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.     

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.     

Surface roughness in sapwood and heartwood of Blackwood (Acacia melanoxylon R. Br.) machined in 90-0 direction

The resulting surface roughness is studied for Blackwood (Acacia melanoxylon) during peripheral milling of sapwood and heartwood samples. It is known that the surface roughness is sensitive to a change in cutting conditions, tool wear, cutting geometry and direction change, but also when some material parameters vary like the species, moisture content and wood density. The bite or better the mean chip thickness is strongly related to the resulting surface quality as well as to the needed cutting forces, whereas other studies have shown these relationships with regard to changing cutting conditions. The aim of this paper is to evaluate and quantify the resulting surface roughness for Acacia melanoxylon considering a change in the mean chip thickness for both types of wood: sapwood and heartwood, and to evaluate the results considering changes in the rotational speed and the feed speed.     

Performance of helical edge milling cutters in planing wood

A new design of a milling cutter with solid helical edge has been developed for improving the performance of cutting wood. Development of the new helical edge milling cutter with its geometries for planing wood has been followed by some research progresses. In this work, a conventional edge milling cutter and helical edge milling cutters were tested in planing spruce wood (Picea abies). The purpose of the research work was to investigate chip flow, power consumption, noise emissions, edge wear, and surface roughness characteristics of the helical edge milling cutters in planing spruce wood. Experimental results showed that the helical edges compared to the conventional edge milling cutter provide better chip flows with nearly axial direction and low flight velocity. Though the extreme helical edges up to 75° inclination angle generate comparable or slightly larger cutting power than the conventional edge, they considerably generate lower sound pressure level of up to 5 dB(A). The helical edge milling cutters are better in wear resistance, suffer less edge fractures, and produce better surface quality of planed wood than the conventional edge milling cutter.     

Application of a novel technique for band sawing using a tip-inserted saw regarding surface profiles

One way of achieving a successful forest management leading to biodiversity conservation is to ensure that wood is processed in an efficient manner. The authors succeeded in developing a new technology for bandsawing using a tip-inserted saw. The material used for the tipped edge was High Speed Steel (HSS) of designation SHK 51 according to the Japan Industrial Standard (JIS). The efficiency of the tip-inserted saw was investigated considering its effectiveness in controlling tooth marks and washboarding patterns that sometimes occur during bandsawing. The surface profile of the workpiece generated after sawing with 700 mm and 1100 mm diameter bandmills of the laboratory and industrial type respectively were determined using a CCD laser displacement sensor of scanning length 250 mm and scanning speed of 3 mm/sec at a sampling rate of 50 Hz. Under a setup wheel rotation speed of 200 rpm and feed speed of 1 m/min, washboardings were induced during sawing with the tip-inserted saw of uniform pitch. Thereafter, a tip-inserted saw of random pitch was constructed without removing the saw from the pulley and cutting tests were performed under the same cutting conditions when washboardings were induced during sawing with the uniform pitch tipped-inserted saw. It was observed that the washboarding pattern disappeared completely. Thus the tip-inserted saw of random pitch was very effective in controlling the washboarding pattern. Comparisons of the surface profiles of the workpiece generated by sawing with uniform pitch tip-inserted and stellite-tipped saws under both laboratory and industrial conditions indicate that regardless of the type of bandmill used, the surface profile measured with the laser displacement sensor was smoother for tip-inserted saws than stellite-tipped saws.     

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.     

Effect of species and grinding disc distance on the surface roughness parameters of medium density fiberboard

Surface quality of medium density fiberboard (MDF), as a very important criterion for further finishing and utilization, was evaluated using a wide range of measuring parameters (instruments, filters, filtering cut-off length, measuring length, measuring resolution, roughness parameters). However, these various approaches make any data comparison rather difficult. Furthermore, filtering the measured data with a simple Gaussian filter has proved unreliable for wood surfaces. A new, more robust approach by using a Robust Gaussian Regression filter together with a previously tested set of measuring and evaluating parameters was used in this paper in order to quantify the surface roughness of MDF manufactured from different species (beech, poplar, birch, Scots pine, mixture 50 % Scots pine and 50 % beech) and using three different grinding disc distances (0.06, 0.15 and 0.6 mm). If manufacturing parameters are kept constant, the processing roughness of MDF is similar, but variable species anatomy and fuzziness effects will give differentiation in total roughness. The results indicated that fibers made of a mixture of wood chips from Scots pine and beech led to the smoothest MDF surface, followed closely by poplar, birch, and Scots pine. The roughest surface was measured for the panels made of beech fibers. Investigating the influence of the grinding disc distance, the roughest MDF surface was obtained when a grinding gap of 0.6 mm was used. However, surface roughness was found to be quite similar applying a grinding disc distance of 0.06 mm slightly lower for 0.15 mm. This finding indicates that a too fine grinding gap does not improve the MDF surface roughness.     

Investigation of the wetting characteristics of medium density fibreboards (MDF) by means of contact angle measurements

The influence of some parameters (wood species, binder content, water repellent finish, wood humidity and roughness) on the wetting of MDF was investigated by means of contact angle measurements with selected test liquids (water, glycerol, ethylene glycol and diiodmethane) using the sessile drop method. The investigations show that contact angle measurements are mainly disturbed by the penetration of the liquids into the MDF and by the high roughness of the surface. Therefore, the results have principally qualitative character. They represent the following tendency for the five parameters: the use of water repellent finish, increased wood humidity and increased roughness made wetting less effective with water repellent finish showing by far the biggest effect. MDF made of beech showed predominantly better wetting behaviour than that made of spruce. The influence of the binder content could not be unambiguously ascertained.     

Investigation of the interrelations between defibration conditions,fiber size and medium-density fiberboard (MDF) properties

Defibration conditions and raw material properties affect wood fiber characteristics, and thereby the properties of fiber-based panels such as high-density fiberboard (HDF), medium-density fiberboard (MDF) and wood fiber insulation board. This study investigates the influence of steaming conditions (time and temperature), grinding disc distance, wood species (pine, beech, birch and poplar), method of refiner discharging (radial and tangential stock outlet) and wood chip size on fiber length and fiber length distribution, and further the influence of fiber size on MDF properties. Fiber lengths were determined applying the recently developed image analysis-based fiber size measuring system FibreCube. This system enables an automated and nearly complete mechanical separation of woolly-felted fiber samples prior to image acquisition, software-supported post-separation of overlapped-lying fibers at the beginning of image analysis, and flow line tracing-based length measurement. It was found that grinding disc distance and wood species are the most influential parameters on fiber length characteristics. Especially the content of undefibrated fiber bundles (shives) was found to strongly correlate with the grinding disc distance. Wood anatomical differences between hardwood and softwood were reflected clearly by the fiber length characteristics. Fiber size was found to be one of the parameters influencing panel properties. However, other fiber characteristics—in particular the chemical nature of the fiber, which is responsible for its wettability with water (thickness swelling) and glue (mechanical properties)—have to be considered as important influencing parameters on panel properties.     

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.

     

Gas pressure measurements during continuous hot pressing of particleboard

Knowledge about the development of the internal gas pressure during hot pressing of wood-based composites is important for the optimization of panel properties and production speed. The gas pressure heavily affects the thermodynamic conditions inside the wood furnish mat, and a too high maximum value at press opening might cause an impairment of the panel properties. In this paper, gas pressure and temperature measurements inside a particle mat while passing through a continuous hot press are presented for the first time. The measurements were performed with a transportable system, consisting of a steel tube attached to a miniature pressure transducer and a data logger. The particleboards had a target thickness of mainly 16 mm, but also of 28 mm and 38 mm, respectively. The measurements show a distinct horizontal gas pressure distribution in both directions, in production direction and across the mat’s width. In contrast, cross-sectional gas pressure gradients were only visible inside the panels after leaving the press. By comparing the gas pressure curves measured for particleboard with those for medium density fiberboard (MDF), characteristic differences became evident. Overall, the gas pressure is higher in MDF compared to particleboard. Finally, a comparison between the gas pressure levels measured for three different panel thicknesses showed a clear relation between panel thickness and gas pressure, with a decreasing panel thickness resulting in an increase in gas pressure. The results of this paper will contribute to our understanding about the events inside wood furnish mats during continuous hot pressing.     

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.).     

Einfluß der Lagerung von Industrierestholz der Klefer und Fichte auf seine Eignung für die Herstellung von Spanplatten und mitteldichten Faserplatten (MDF)

Particle- and medium density fibreboards (MDF) were prepared from chips of spruce and pine, a byproduct of sawing wood in a saw mill with a profiling unti. The wood residues were stored in piles of 40 m³ volume for different time periods. The physical-technological properties of the particle- and fibrebroads prepared therefrom were evalutated and the formaldehyde release of the boards was assessed. The results reveal: In general, there is a positive influence of storage on the thickness swelling and internal bond strength of UF-bonded particleboards; the bending strength of UF-bonded particleboards showed no pronounced response to storage. The prositive influence of storage onthe thickness swelling and internal bond strength was much higher in case of boards made from pine chips than in case of spruce boards. On using PMDI as a binder for particleboards no significant influence of storage on the thickness swelling, internal bond strength and bending strength was detected. The influence of storage on the thickness swelling of UF-bonded MDF from pine fibres was much less pregnant than on that of UF-bonded particleboards. On UF-bonded MDF from spruce the influence of storage, if any, was negligible. On using PMDI as a binder for MDF there was no detectable change in the thickness swelling due to storage. The internal bond strength of UF-bonded MDF experiences only subtle positive change due to storage of pine wood chips. However, no notable change was detected in case of MDF from spruce. Storage has almost no influence on the chemical properties of boards.     

Influence of climatic conditions and surface roughness on the wettability of medium density fiberboards (MDF)

Wettability of wood surface is measured by the contact angle between the liquid and the surface of the wood. In this study, the wettability of MDF surfaces was measured using different mixtures of distilled water and isopropanol. The results reveal that TF-bonded MDF made from fresh and recycled fibers showed better wettability than the corresponding MUF-bonded MDF. Moreover, the entire results indicate that roughness is one of the most important influencing factors on the wettability of MDF surfaces.     

Influence of climatic conditions and surface roughness on the wettability of medium density fiberboards (MDF)

Wettability of wood surface is measured by the contact angle between the liquid and the surface of the wood. In this study, the wettability of MDF surfaces was measured using different mixtures of distilled water and isopropanol. The results reveal that TF-bonded MDF made from fresh and recycled fibers showed better wettability than the corresponding MUF-bonded MDF. Moreover, the entire results indicate that roughness is one of the most important influencing factors on the wettability of MDF surfaces.     

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.     

Planing of Norway spruce with very varied ring width

A way of defining a “machining ability” is proposed. Cutting forces: The samples from the slow grown spruce give well known results. In this case the cutting forces are linked with specific gravity by a linear relation. For the samples coming from the fast grown spruces (A), there is no significant relationship between the cutting forces and the specific gravity. These different behaviours are illustrated by the aspect of the chips produced by both batches of spruce. Dimensions scattering. Analysis shows clearly that distributions of dimension quality are similar for spruces A and B. That means there is no compression in the thickness of the samples (z axis). Surface, roughness: More than one roughness criterion is needed to describe surface quality. The 8 criteria used in this work describe the vertical distribution of the roughness measurements. For all the samples, best results are measured on A sample.     

Studies of the main cutting force at and near a cutting edge

The present work is a study of how various parameters affect the cutting forces at, and near a cutting edge when cutting wood at full speed and with all cutting edges of the tool. Statistical methods from experimental results are used to develop a model.     

Yield improvement in Rubberwood sawmilling through the saw, dry and rip (SDR) technique

The volume recovery, product quality and process economics of Rubberwood sawmilling using the conventional live sawing process and the saw dry and rip (SDR) process is described. The results showed that the SDR process, together with high temperature drying resulted in higher volume recovery and product quality compared to the conventional live sawing process.     

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.