EFFICIENT PROCESSING OF POLYGONAL CROSS-SECTION TIMBER

Feedrate interpolation, which consists in generating the set points sent to the axis controllers from the initial path, constitutes a major line of the trajectory planning process. In multi-axis high-speed machining the feedrate is usually evaluated by a kinematic method as the maximum feedrate respecting the joint velocity, acceleration an jerk limits. However, this approach requires a difficult experimental tuning of the kinematic limits based on the observation of the axis behaviour that leads to a loss of productivity. The multiplication of the kinds of multi-axis machines in manufacturing leads to the need to take the dynamic behaviour into account, particularly for highly dynamic systems such as serial robots. A novel and efficient dynamic approach of the feedrate interpolation process is proposed in this paper. The system performance characteristics are checked through torque and torque rate limits at the actuator level. The integration of the dynamic model of the system enables to include different chosen effects such as inertia, centrifugal, Coriolis effects, gravity and friction forces. The dynamic model can be also easily adapted to different systems and processes such as serial manufacturing robots or multi-axis machining centers. Then, these new dynamic constraints lead to limit values based on the dynamic behaviour of the whole axis mechanical chain from the actuator to the end-effector and allow to be close from the system components technology. The efficiency of the proposed approach is demonstrated by several simulations on different systems and test paths and is compared to the usual kinematic method results.

This study investigates the reduction of defect waste in the metal forming process at PT XYZ, with a specific focus on the production of the reff D nose component. Recognizing the critical importance of quality in the aerospace industry, where even minimal defects can compromise safety and operational integrity, this research applies Lean Six Sigma methodology to address the observed defect rate, which averaged 4.6% over the period 2018–2023—significantly exceeding the company’s target of 1%. A comprehensive DMAIC (Define, Measure, Analyze, Improve, Control) framework was employed to systematically identify, quantify, and analyze the sources of defects. Data were collected from both primary sources, including direct observations and stakeholder interviews, and secondary sources such as production records and defect reports. Advanced tools such as SIPOC diagrams, Pareto analysis, Interpretive Structural Modeling (ISM), and the 5 Whys method for Root Cause Analysis (RCA) were utilized to determine the critical factors affecting process performance. The analysis revealed that issues related to raw material quality, suboptimal process parameter settings, machine conditions, operator competency, and production environment stability are the primary contributors to the elevated defect rates. Based on these findings, targeted improvement strategies were proposed to optimize process efficiency and enhance product quality.

High-speed milling (HSM) technology has been rapidly absorbed by the die and mould manufacturing industry and by the aeronautical sector. The new cutting tools can withstand much higher machining conditions than 10 years ago. Last-generation, high-speed machining centres are equipped with high-frequency spindles with hybrid ball bearings, leading to rotational speeds over 18 000 r/min. Multiaxis machining can be effectively carried out in five-axis machining centres of different architecture. These new and advanced machining processes are much more complex and provide the final component with a higher added value. However, the reliability of the whole process must be reconsidered, since collisions, tool breakage and dynamic problems can result in expensive machine repairs and some parts may be impossible to recover. In order both to minimize the above problems and increase machining performance, a new machining approach based on two ideas has been developed. First, virtual verification of the NC programs, avoiding collisions or tool – machine interferences that may arise during the machining of complex surfaces. Second, toolpath optimization in the machining of complex surfaces. For this purpose a utility to estimate the cutting forces before machining has been integrated in the computer-aided manufacturing (CAM) planning process stage. The estimation of cutting force uses a semi-empirical approach, in which the pair tool/material is characterized by six specific cutting force coefficients. The force model introduces the effect of part slope in calculations, just with tool geometry, cutting conditions, and material. The value of cutting force is used as an estimator for selecting the best cutting toolpaths for a complex surface. In this way a more accurate, better-finished surface is machined, and a reduced tool wear is withstood. The global CAM process is applied to three examples that are discussed. They are representative of a highly efficient high-speed process, without any risks of tool collisions, surface machined errors and low cutting forces.

This paper describes the design and operation of the multi-axis cartesian-based arm rehabilitation machine (MACARM), a new cable (wire) robot for upper limb rehabilitation. The prototype configuration is comprised of an array of 8 motors mounted at the corners of a cubic support frame that provides, via cables, 6 degree of freedom (DOF) control of a centrally located end-effector. A 6 DOF load cell mounted on the end-effector provides force measurement. Given its relatively simple architecture, the MACARM may provide an attractive alternative to serial robots for use in neurorehabilitation.

Bidirectional Texture Functions (BTFs) provide a realistic depiction of the appearance of many real-world materials as they contain the spatially varying light scattering behavior of the material surface. Since editing of existing BTF data is still in its early stages, materials have to be measured from real-world samples. In contrast to the related Spatially Varying BRDFs (SVBRDFs), the reflectance information encoded in a BTF also includes non-local scattering effects and therefore does not obey energy conservation or reciprocity. While this higher degree of freedom also contributes to an increased realism, it inadvertently calls for an extensive measurement of reflectance samples, as many regularization approaches from BRDF measurement do not apply. In this paper, we present an automated, parallelized, robust, fast and transportable setup for the acquisition of BTFs from flat samples as well as 3D objects using camera and light arrays: the DOME II. In contrast to previous camera array approaches, the present setup, which is comprised of high-quality industry grade components, overcomes several issues regarding stability, reliability and precision. It achieves a well balanced state-of-the-art acquisition performance in terms of speed and quality at reasonable costs.

A six degrees-of-freedom (DOF) parallel material testing machine (PMTM), which is based on Stewart Platform, is first proposed in this paper. Several essential issues including prototyping, compliant axis determination and controller design are investigated with specific methods or technologies. The compliant axis, along which the proposed machine has a better performance, is determined by the eigenscrew decomposition method. The proposed force controller incorporates the simplified inverse dynamic model output as a model-based portion of the controller and its validity is verified by means of simulations. Evaluation tests are performed to examine the practicability of the proposed controller and to determine the loading accuracy of the PMTM. Tensile tests and preliminary multiaxial loading tests are performed to verify the performance of the proposed PMTM. The experimental results illustrate that the proposed PMTM is capable of performing multiaxial loading tests of materials and thus a suitable candidate for multiaxial material testing machine.

Focusing on CNC process data, this paper provides an in-depth analysis, characterization and mining of macro machining processes by associating CAD and CAM models. The article introduces a Bayesian inference method to construct an association relationship between the manufacturing features of the query part and the macroscopic process of the manufactured part, which avoids the need for a direct similarity comparison between the geometry of the query part and the part to be manufactured. In addition, the study calculated the overall similarity between the query part and the CNC programming process data instances through the guidance of the process skeleton, thus realizing the precise evaluation from the CNC programming perspective. The algorithm for generating tool trajectories in multi-axis CNC programming is analyzed. By selecting representative surfaces and performing tool processing calculations, this study explores the process planning and tool parameter selection of usual parts of surfaces in multi-axis CNC programming machining. It optimizes the nonlinear error in tool trajectory processing by combining CAD/CAM technology. The results show that the optimized process proposed in this paper significantly improves the machining efficiency by 36.94%. In the cutting at tool corners, the maximum cutting force generated by the optimized machining process is only 190.3N, which is only 67.2% of the leading cutting force of the Cimatron process. In addition, when the engagement frequency is 780 Hz, the optimized process proposed in this paper has the smallest vibration amplitude, which is only 21.4% of the Cimatron strategy. Therefore, this study significantly improves the machining efficiency while ensuring the machining quality, which has important practical application value.

The computer aided design and manufacturing CAD/CAM integration systems were focused on product representation techniques or product modeling. In product design process trends are currently tend to use freeform surface that modeling by using (Non-Uniform Rational B-Spline Surface (NURBS), B-spline, Bezier) technique to suit aesthetic, functional and manufacturability requirements. Set of problem are faced difficulties in recognizing freeform feature such polishing process after the finishing machining process by multi-axis CNC machine, sheet metal forming, and freeform surface machining. In this research, a new developed methodology has been introduced for automatic recognition of the depression and protrusion features. The 3D CAD solid model is designed by freeform surfaces of non-uniform B-spline technique and then extracts their parameter by IGES standard format file. The developed methodology has four major steps: Subdivision of Non-uniform B-spline surface, surface analysis, primitives shape detection, and recognition of geometric features.

Inorganic non-metallic materials are widely used in many application areas such as precision optics, semiconductor technology, high-temperature technology or medical technology. This increasingly requires the application of precise multi-axis CNC machine technology and poses great challenges for the machining processes, especially with regard to the economic production of high-quality surfaces. In the field of optics technology, high surface qualities in the nanometer range are often required. The production machines designed for this purpose must therefore guarantee a high degree of accuracy and be constant with respect to their environmental factors. An influence on the quality of the machining results that should not be underestimated is the vibrations occurring on the machine, which are caused on the one hand by the operating vibrations generated by the running spindle, and on the other hand by resonance frequencies. A side effect of these vibrations can also be damage to the workpiece or the tool. In order to detect these influences, a modal analysis and a measurement of the operating vibration mode are carried out on an ultrasonic-assisted CNC grinding machine using a three-dimensional laser Doppler vibrometer system provided by Polytec GmbH. In addition, corresponding measurements are carried out by means of a one-dimensional laser Doppler vibrometer on a 5-axis CNC universal milling machine in order to establish comparability between an ultrasound-assisted and a conventional processing machine.

The demand for high-precision hard components and their molds/dies have increased in various industries such as in the optical, automotive, and communication industries, as well as in life and medical sciences. Some difficult-to-machine materials can be reliably machined using deterministic precision cutting processes. On the other hand, hard and brittle materials such as ceramics, carbides, hardened steel of molds, glassy materials, or semiconductor materials have to be machined using precision abrasive technologies with super abrasives of diamond or cBN. However, the machining of high-precision components and their molds/dies by abrasive processes, is much more difficult because of their complex and non-deterministic nature and textured surface. Furthermore, high-energy processes such as laser technology can assist abrasive technologies for ensuring higher precision and efficiency. In this sense, precision grinding and polishing process are primarily used to generate high-quality and functional components usually made of difficult-to-machine materials. The surface quality achievable by precision grinding and polishing processes becomes more important for reducing machining time and costs. This special issue features five research articles – five papers – related to the most recent advances in precision abrasive technology of difficult-to-machine materials. Their subjects cover various abrasive machining processes of grinding, polishing, abrasive flow machining, tooling technology, and laser technologies. We deeply appreciate the careful work of all authors and thank the reviewers for their incisive efforts. We also hope this special issue will trigger further research on abrasive technologies.

Micromilling mechanism studies are the fundamentals for high-quality micro components fabrications. Based on the finite element method (FEM), the simulation model for micromilling of the oxygen-free copper (OFC) was established in this paper. The influences of the key process parameters (feed engagement fz, axial depth of cut ap, radial depth of cut ae, and spindle speed n) on the milling forces were investigated. According to the simulation results, to achieve the minimum undeformed chip thickness, the critical feed engagement was identified to be 2.5 μm/z. when the axial depth of cut increased, the milling force was increasing linearly, but at the same time the milling force took an oscillator decreases due to the increasing of spindle speed. The overall trend of milling force under different radial depths of cut is upward. Therefore, the feed engagement should be greater than 2.5μm/z for micro milling of oxygen-free copper. Small radial depth of cut, small axial depth of cut, and appropriate spindle speed should be selected to obtain a high machining quality. Introduction As an excellent metal with extremely low oxygen content, high conductivity and high corrosion resistance, oxygen-free copper C10100 is widely used in the manufacturing of audio-visual equipment and communication components. With good ductility and no hydrogen embrittlement, it can also be processed into various precision micro parts. Compared with traditional cutting, high-speed micromilling is more suitable for machining micro-small parts. In order to obtain higher dimensional accuracy and better surface quality, it is necessary to study the milling parameters of OFC in the processing of precision parts. In the actual machining process, the changes of milling force caused by the changes of milling parameters can reflect the quality of the final machined parts more intuitively. Therefore, the adjustment of milling parameters can be guided by measuring the milling force in the milling process. In order to reveal the difference in mechanism between traditional cutting and micromilling, scholars have conducted a lot of studies. In the study of cutting poly-crystalling OFC with single crystalline diamond (SOD) micro-tools, X. Ding has proposed that the cutting strategy of reducing cross-feed can improve the cutting performance with using micro-tools. Constant cutting forces, burr size and an improved roughness of the machined surface have been obtained by employing this cutting strategy [1]. Niu has presented an innovative cutting force modeling concept by taking account of micro-cutting dynamics. Experimental cutting trial is conducted to validate the modeling approach and the cutting force model [2]. Qu has studied the impact of MQCL method on the machining results and mechanical properties of the component [3]. Yuan has proposed an innovative uncut chip thickness algorithm and developed the model for determining the instantaneous uncut chip thickness in micro end-milling processes [4]. D.DAS has studied the effect of stress parameters on ratcheting deformation stages of polycrystalline OFHC copper [5]. For the micromilling of pure copper, M. Rahman has studied the failure mechanism and factors which affect the micro end mill [6]. Liu has studied the relationship between size effect and burr in micromilling OFC and constructed a geometric model of exit burrs [7]. Liu has established SPH simulation model and carried out systematic research on formation mechanism of chip [8].For oxygen-free copper materials, Tian has established a constitutive model and carried out simulation analysis based on Abaqus [9]. Cheng has proposed 211

Linear and nonlinear spectroscopy techniques are widely used to study numerous important chemical and physical processes. However, the interpretation of these experimental spectra often becomes very complicated because a particular spectrum constitutes a mere footprint of a host of various, possibly intertwined, effects. In this spirit, calculations in the time-dependent picture provide a useful tool for decoding such spectra. Nevertheless, the ultimate challenge is to devise a theoretical framework that could yield sufficient efficiency as well as accuracy to describe the molecular system of interest in a satisfactory way. The strategy is relatively straightforward for low dimensional systems that are directly tractable, e.g., with exact quantum dynamics performed on an equidistant grid. Despite the formidable overall exponential scaling, these calculations can be significantly accelerated by using higher-order split-operator propagation schemes. In general however, one is forced to seek an affordable balance between physical accuracy on one hand and computational efficiency on the other by employing, for instance, some of the techniques from the broad family of semiclassical methods based on classical trajectories. To this end, the thawed Gaussian approximation (TGA) is combined with an on-the-fly ab initio scheme (OTF-AI). The resulting OTF-AI-TGA algorithm is efficient enough to treat all vibrational degrees of freedom (DOFs) on an equal footing even in case of larger molecules such as pentathiophene (105 DOFs). Moreover, in sharp contrast to popular approaches based on global harmonic approximation, OTF-AI-TGA reproduces almost perfectly the absorption and photoelectron spectra of ammonia, i.e., spectra with strong dependence on large amplitude motions. In addition to the mere reproduction of experimental spectra, a novel systematic approach is introduced to assess the importance and the dynamical couplings of individual vibrational DOFs. This is in turn used to gain a deeper insight into the associated physical and chemical processes by attributing specific spectral features to the underlying molecular motion. Specifically, in the case of oligothiophenes, this approach was used to assign the dynamical interplay between quinoid and aromatic characters of individual rings to particular spectral patterns and, furthermore, to explain the changes in the vibrational line shape with an increasing number of rings. Furthermore, in systems that are too large to be treated with accurate quantum methods, efficient methods such as OTF-AI-TGA are expected to be useful as a preliminary tool for identification of the subspace of the important DOFs. On this subspace, one can then unleash some of the less efficient yet better-suited methods. In summary, OTF-AI-TGA combined with this novel analysis approach is intended to provide the first crucial step in a hierarchical computational protocol for studying large molecules such as dyes.

The present dissertation describes the research work carried out towards: I. developing of analytical and numerical models for accurate and efficient analysis of laminates and sandwiches under different loading conditions (static analyses, impulsive loading and low velocity impacts); II. developing of techniques to improve structural performances of composites structures by tuning their energy absorption mechanism; A higher order theory (AD-ZZ) including zig-zag effects, transverse shear continuity, variable transverse displacement and layerwise representation is presented for analysis of laminates and sandwiches. This theory is cast in such a way that the unknowns in the model will involve only five variables like equivalent single layer models: the three displacement components and the two shear rotations of the normals on the reference surface. It is advantageous to formulate the theory in this way, as it provides the opportunity to refine its through-the-thickness representation by adding computational layers in the thickness direction without increasing the number of unknowns. After extensive evaluation of the accuracy obtained by the above mentioned theory for a variety of structures, the AD-ZZ model is enriched by adding a set of continuity functions in order to treat laminates and structures with in-plane discontinuities (e.g. bonded joints, two material wedge) under a unified approach without adding new unknowns. Speaking of techniques to improve structural performances, two approaches are presented: variable stiffness composites and stitching. The former tool works on the strain energy of the structure computing fibre distributions that minimize unwanted energy contributions and maximize the wanted ones. The latter prescribes the insertions of transverse reinforcements in sandwich structures. The homogenized mechanical properties of this structure, required by the AD-ZZ model to perform the analysis, are evaluated through virtual material tests using a 3D FE model. The results obtained applying these techniques demonstrate that both are effective in reducing transverse stresses at critical interfaces and, in certain cases, in improving bending stiffness. New C0 displacement-based and stress-based finite elements for analysis of laminated and sandwich plates based on the AD-ZZ model are developed. To achieve this goal, a new technique that converts derivatives of functional degrees of freedom contained in the AD-ZZ is presented. Both the elements satisfy all the requirements of computationally efficient finite element models for analysis of multilayered structures, namely 1) the number of degrees of freedom is independent from the number of layers; 2) no shear correction factors or penalty number are added in the formulation. Consistent shear fields are obtained for the present finite element formulations. Numerical results demonstrate that these new elements are robust, accurate and computationally efficient for analysis of multilayered structures. In order to study structures subjected to impact loading a new simulation procedure is developed. It is based on the AD-ZZ model and considers the crushing behaviour of soft-like media without performing each time a detailed 3D finite element analysis. Numerical results show that the response of composites undergoing low velocity impact is very accurately predicted with low computational effort. Overall, the present procedure holds great promise for analysis of laminated and sandwich structures undergoing low velocity impact

A four-node co-rotational quadrilateral shell element for smooth and non-smooth shell structures is presented. Each node of the element has three translational degrees of freedom and two or three vectorial rotational degrees of freedom. For the nodes of smooth shells or nodes away from the intersection of non-smooth shells, the two smallest components of the mid-surface normal vector are defined as the nodal rotational variables. For the nodes at intersections of non-smooth shells, two smallest components of one orientation vector, together with one smaller or the smallest component of another nodal orientation vector, are employed as rotational variables. In a nonlinear incremental solution procedure, the vectorial rotational variables are additive and the symmetric tangent stiffness matrices are obtained in both global and local coordinate systems, thus, one-dimensional linear storage scheme can be adopted, saving computer storage and computing time effectively. To alleviate membrane and shear locking phenomena, one-point quadrature is adopted in calculating the element tangent stiffness matrices and the internal force vector, and the physically stabilized method is employed to avoid the occurrence of spurious zero energy modes. The reliability and computational accuracy are verified through two smooth shell problems and two non-smooth shell problems undergoing large displacements and large rotations.

A novel family of controllable, dissipative structure-dependent integration methods is derived from an eigen-based theory, where the concept of the eigenmode can give a solid theoretical basis for the feasibility of this type of integration methods. In fact, the concepts of eigen-decomposition and modal superposition are involved in solving a multiple degree of freedom system. The total solution of a coupled equation of motion consists of each modal solution of the uncoupled equation of motion. Hence, an eigen-dependent integration method is proposed to solve each modal equation of motion and an approximate solution can be yielded via modal superposition with only the first few modes of interest for inertial problems. All the eigen-dependent integration methods combine to form a structure-dependent integration method. Some key assumptions and new techniques are combined to successfully develop this family of integration methods. In addition, this family of integration methods can be either explicitly or implicitly implemented. Except for stability property, both explicit and implicit implementations have almost the same numerical properties. An explicit implementation is more computationally efficient than for an implicit implementation since it can combine unconditional stability and explicit formulation simultaneously. As a result, an explicit implementation is preferred over an implicit implementation. This family of integration methods can have the same numerical properties as those of the WBZ-α method for linear elastic systems. Besides, its stability and accuracy performance for solving nonlinear systems is also almost the same as those of the WBZ-α method. It is evident from numerical experiments that an explicit implementation of this family of integration methods can save many computational efforts when compared to conventional implicit methods, such as the WBZ-α method.