Kazimierz A. Orlowski

Application of fracture mechanics for energetic effects predictions while wood sawing

In the classical approach, energetic effects (cutting forces and cutting power) of wood sawing process are generally calculated on the basis of the specific cutting resistance, which is in the case of wood cutting the function of more or less important factors. On the other hand, cutting forces (or power—more interesting from energetic point of view) could be considered from a point of view of modern fracture mechanics. Cutting forces may be employed to determine not only toughness but also shear yield strength, which are then applied in the models. Furthermore, forecasting of the shear plane angle for the cutting models, which include fracture toughness in addition to plasticity and friction, broadens possibilities of energetic effects modelling of the sawing process even for small values of the uncut chip. Mentioned models are useful for estimation of energetic effects of sawing of every kinematics. However, for band saws and circular sawing machines, the chip acceleration power variation as a function of mass flow and tool velocity ought to be included in analysis of sawing at larger cutting speeds.

Recent progress in research on the cutting processes of wood. A review COST Action E35 2004–2008: Wood machining – micromechanics and fracture

Abstract Recent progress in research on the cutting processes of wood is presented, particularly in regard to new methods of accomplishing an increase in volume recovery by sawmills. The suitability of modern fracture mechanics was demonstrated for the estimation of the cutting power for saws in which kerfs are different from saws used in cutting tests, and whereby the data of sawn material – such as the specific work of surface formation (toughness) and the shear yield stress – were determined. Cutting tests were carried out on the modern frame sawing machine (sash gang saw) for narrow-kerf sawing with the hybrid dynamically balanced driving system and elliptical teeth trajectory movement.

The critical rotational speed of circular saw: simple measurement method and its practical implementations

Operation safety during sawing operations as well as dimensional accuracy and surface roughness depend on circular saw dynamic features among other factors such as circular saw blade accuracy and static/dynamic properties of the machine tool. Manufacturers of saw blades have an obligation to mark tools with a value stating the maximum allowed rotational speed for each saw. However, in some cases the value indicated on the saw corresponds to the critical rotational speed or is dangerously close to this critical value. Saw operation at the critical rotational speed is inadvisable and may result in serious injury or depreciation of product quality. This report outlines a simple methodology for evaluation of circular saw critical rotational speed. The assessment was conducted with a camera vision technique on the basis of an impulse test. Results are compared with theoretically calculated critical rotational speeds and the marks on saw blades.

Study washboarding phenomenon in frame sawing machines

The paper concerns washboarding phenomenon where for every kind of sawing a very regular pattern is characterised by a sinusoidal – like variation in board thickness. That pattern is an effect of the saw blade lateral vibrations. It is palpable that these vibrations are detrimental to the cutting process, and lead to poor surface quality and dimensional accuracy, and raw material waste.For band saws in the contemporary literature models explaining a washboarding phenomenon are supported on self-excited (self-induced) vibration theories. However, these explanations cannot be simply broadened into the washboarding phenomenon in frame sawing machines. In this work based on theoretical and experimental investigation the washboard pattern formation is clarified by the authors with the use of a theoretical model, in which the rugged surface is an effect of vibrations generated by lateral cyclic loading and lagged wave formation. The authors hope that their obtained results contribute significantly to further understanding of this important but complicated phenomenon. ZusammenfassungDas vorliegende Manuskript beschäftigt sich mit dem Waschbrettschnitt, der beim Sägen entsteht und durch eine sinusartige Veränderung der Brettdicke gekennzeichnet ist. Die Ursache dafür sind seitliche Schwingungen des Sägeblattes. Es ist offensichtlich, dass diese Schwingungen dem Einschnittergebnis abträglich sind und zu schlechter Oberflächenqualität, Masshaltigkeit und Materialausnutzung führen.In der jüngeren Literatur veröffentlichte Erklärungsmodelle für den Waschbrettschnitt bei Bandsägen, gehen von der Theorie sich selbst anregender Schwingungen aus. Diese Modellansätze können jedoch nicht ohne Weiteres auf Gattersägen übertragen werden. In der vorliegenden Arbeit wird das Entstehen eines Waschbrettschnittes auf der Grundlage theoretischer und experimenteller Untersuchungen mittels eines Modellansatzes erklärt, der unterstellt, dass die raue Oberfläche durch Schwingungen des Sägeblattes infolge einer seitlich-gerichteten, periodischen Beanspruchung und einer verzögerten Wellenbewegung entsteht. Die Autoren hoffen, dass die Ergebnisse dieser Untersuchung massgebend dazu beitragen, dieses wichtige, aber schwierige Phänomen besser zu verstehen.

The Effect of Circular Saw Blade Clamping Diameter on its Resonant Frequencies

In this paper results of comparison of characteristic resonant frequencies of circular saw blades as a function of the saw clamping diameter from the impact test are presented. Obtained results revealed that proportionally with the increase of the saw clamping diameter also the dynamical stiffness of the saw blade increased. As a consequence of that the resonant frequencies of the saw blade move to higher values. Moreover, with the increase of the saw blade clamping diameter for higher frequencies of forcing vibrations of the saw blade the amplitude of vibration are expected to be decreased.

THE EFFECT OF ALTERNATIVE CUTTER PATHS ON FLATNESS DEVIATIONS IN THE FACE MILLING OF ALUMINUM PLATE PARTS

In this paper the relationships between the alternative machining paths and flatness deviations of the aluminum plate part, were presented. The flatness tolerance of the main surface of the plate part has crucial meaning due to the assembly requirement of piezoelectric elements on the radiator. The aluminum bodies under investigation are the base part of the radiators with crimped feathers for the train industry. The surface of the aluminum plate part was milled using three different milling strategies: along of longer or shorter side of workpiece and at an angle of 45°. The aluminum bodies were machined on milling centre ecoMILL 70 DMG MORI. The flatness deviation measurements were carried out on the Coordinated Measuring Machine Altera 7.5.5 Nikon Metrology NV. These measurements were made during the manufacturing process of the radiator, namely after machining, however, before the process crimping of feathers. The results that were obtained enables the validation of assumed milling path strategies in connection of the subsequent machining and assembly processes.

A newly-developed model for predicting cutting power during wood sawing with circular saw blades

In the classical approach, cutting forces and cutting power in sawing processes of orthotropic materials such as wood are generally calculated on the basis of the specific cutting resistance kc (cutting force per unit area of cut). For every type of sawing kinematics (frame saws, band saws and circular sawing machines) different empirical values of specific cutting resistance kc have to be applied. It should be emphasised that sources in the scientific literature and handbooks do not provide any information about wood provenance, nor about cutting conditions in which cutting resistance had been determined. In analyses of sawing processes in which the offcut is formed by shear, Atkins’s ideas that all cutting forms a branch of elastoplastic fracture mechanics can be applied. Thanks to this modern approach it was possible to reveal, using experimental results data of fracture toughness and shear yield stresses of Polish pine (Pinus sylvestris), the significant effect of the raw material provenance (source of wood) on cutting power. In the common model for circular sawing machine kinematics, which is similar to metal milling, the sum of all uncut chip thicknesses of the all the teeth simultaneously engaged represented the mean uncut chip thickness. In this work predictions of the newly-developed model for the circular sawing machine are presented. In the model, beside uncut chip thicknesses changes, appropriate changes in shear yield stress and toughness with tooth/grain orientation have been taken into account. The conducted analyses have demonstrated that values of RMS of cutting power obtained with the new developed model are slightly larger than experimental values. On the other hand computed values of cutting power with the use of the mean uncut chip thicknesses in the model are a bit lower from the empirical one.

Development of the in-field sensor for estimation of fracture toughness and shear strength by measuring cutting forces

Knowledge on the fracture properties of materials is essential to assure structural integrity and proper design of mechanical connections in timber constructions. Measurement of this property is, however, a very challenging task. The linear fracture mechanics is usually used for its assessment assisted with experimental data acquired by means of various techniques, usually of destructive nature. The cutting force is an energetic effect of splitting material, and might be therefore considered from a point of view of modern fracture mechanics. The original methodology of simultaneous determination of the fracture toughness and of the shear yield strength on the basis of cutting forces was adopted here for timber characterisation. The set of experimental data was generated in a simple cutting test by using slightly modified off the shelf instrumentation. The resulting data are the slope and intercept of linear regression function of cutting forces versus chip thickness estimated for five European wood species. Both parameters are usable for computation of fracture toughness and shear yield strength in the shear plane, separately for two anatomical directions of wood. The simplicity and reliability of this method provides a wide range of practical applications, including structural health assessment of the timber structures.

The diagnostic ambiguity of the impact test in empirical research of circular saw blades for wood

Zachowanie piły podczas pracy – zarówno w trakcie przecinania, jak i na biegu luzem – zależy w dużym stopniu od konstrukcji piły i częstotliwości własnych narzędzi, które można określać doświadczalnie za pomocą testu harmonicznego bądź impulsowego. Wyniki badań wykazały, że ten ostatni nie gwarantuje prawidłowego przypisania częstotliwości charakterystycznych widma do odpowiadających im rzeczywistych postaci drgań wynikającym z testu harmonicznego. SŁOWA KLUCZOWE: piła tarczowa, test impulsowy, test harmoniczny, krytyczna prędkość obrotowa

Analyses of the effect of the design features of the spindle of the sliding table saw upon its critical rotational speeds

Producenci pilarek formatowych do drewna dązą do zwiekszania dokladności przecinania. Mozna to osiągnąc np. przez poprawe zachowania sie wrzeciona, gdyz od niego w duzej mierze zalezą efekty przecinania. Przedstawiono metodyke wyznaczania predkości krytycznych wrzeciona pilarki formatowej w funkcji cech konstrukcyjnych wrzeciona i jego napedu.