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In spite of considerable advances toward the understanding of the mechanics of micro-cutting operations their dynamics and stability that are dominated by the influence of nonlinear effects imposed by the minimum chip thickness and grain size effects and the dominance of ploughing over shearing still remain largely uncharted. Hence, the objective of this paper is to explore the fundamental mechanisms that lead to instabilities in micro-cutting. For dynamic stability analysis, linear stability theory was adopted to model regenerative chatter. The rationale for using linear stability theory is to perform a rigorous parametric study of the major factors that influence stability in light of the nonlinear phenomena that dominate micro-cutting processes. A linearized micro-cutting dynamic force model and a linear structural dynamics model are presented to formulate stability criteria for the different characteristic operating regimes encountered in micro-cutting. It has been shown that the three physical operating regimes, pure ploughing, simultaneous ploughing and shearing and the shearing dominant, govern the micro-cutting process. They are primarily a function of the relationship between the undeformed chip thickness and cutting edge radius and exert different influences on process stability. Based on the linearized cutting dynamics models characterizing these regimes, a generalized approach to dealing with nonlinear force effects was proposed for process stability analysis. The method is applicable for cutting process nonlinearities at all scales if they are present. [ABSTRACT FROM AUTHOR]

Micro-end-milling is capable of machining complex structures in a wider variety of materials at the micro- and meso-scales as compared to other micro machining processes. However, the exact prediction of cutting forces in micro-end-milling is still not fully developed. In order to predict the general three-dimensional cutting force components, the related cutting edge radius size-effect, tool run-out, tool deflection and the exact trochoidal trajectory of tool flute are considered and presented in the proposed analytical prediction model. The proposed cutting force model also includes an algorithm for the calculation of the variable entry and exit angles caused by tool run-out and tool deflection. In the cutting force prediction model, the actual instantaneous uncut chip thickness is evaluated by considering the theoretical instantaneous uncut chip thickness, the minimum uncut chip thickness and a certain critical chip thickness value governed by three types of material removal mechanisms, in the elastic and the elastic–plastic deformation region and the complete chip formation region, respectively. To verify the model, the parameters of tool run-out and tool deflection were obtained from experimental measurements. The proposed cutting force model is validated through micro slot end milling tests with a two-flute carbide micro-end-mill on Al6061 workpieces. The experimental results agree with simulation results very well. The proposed theoretical model offers a basis for real-time machining process monitoring as well as cutting parameters optimization. [ABSTRACT FROM AUTHOR]

This paper presents a 3-DOF (degree of freedom) translational parallel manipulator named the Tri-pyramid Robot. Compared to the developed 3-DOF translational parallel manipulators, the Tri-pyramid Robot is designed based on conical displacement subset to exhibit better kinematic characteristic. The inverse position solution is obtained through closed-loop constraint analysis and used to formulate the overall Jacobian matrix of constraints and actuations based on the theory of reciprocal screws. Furthermore, by considering the stiffness of all links, joints, actuators, fixed, and moving platforms, the output stiffness matrix of the Tri-pyramid Robot is derived by the transformations of loads and deformations in the closed-loop form. The relations between the virtual input-output displacements are analyzed by the overall Jacobian matrix and used to build the manipulator's stiffness model. Stiffness performance is evaluated by the extreme eigenvalues of the output stiffness matrix in the reachable workspace. By considering the variations of the structural parameters and the distribution of the output stiffness, the maximal stiffness workspace is obtained through numerical optimization, providing, thereby, basic constraints for the parametric design of the Tri-pyramid Robot. [ABSTRACT FROM AUTHOR]

Abstract: General applications of spatial overconstrained linkages are limited by their special output motions without pure rotations or translations. To promote more widespread industrial applications and to develop the potential capabilities of such linkages, this paper presents novel parallel hybrid-loop manipulators and a novel design method based on the constrained motion properties of related spatial overconstrained linkages and general parallel mechanisms. The conventional topological connecting relationships between subchains and platforms are categorized into ten basic forms, among which a novel parallel hybrid-loop form of topological arrangement is presented for the design of parallel hybrid-loop manipulators. In the presented examples of structural design, the Bennett linkage, the threefold-symmetric Bricard linkage and two linkages that will be derived, i.e., the twofold-symmetric 8-bar and the threefold-symmetric 12-bar spatial single-loop linkages are adopted as the basis for the synthesis of the structures of parallel hybrid-loop manipulators with kinematotropic property and deployability based on variable constraint analysis and the structural properties of these linkages. Other similar parallel hybrid-loop manipulators can also be developed based on the presented design method. Possible applications of parallel hybrid-loop manipulators are also highlighted. [Copyright &y& Elsevier]

Using the multi-stand chatter models derived in Part 1, a stability analysis, based on the integral criterion of stability for delay differential equations, will be carried out for the regenerative mechanism to better understand the effects of rolling parameters on regenerative instability. It will be shown that the interactions between consecutive stands through the time delay effect of the strip thickness variations consistently boost the tendency of each stand to chatter and, therefore, reduce the stability of the rolling process. Simulations will demonstrate stable and unstable behaviors of multi-stand rolling mills and aid in verifying stability charts created through stability analysis based on analytical models. They will be instrumental in identifying the critical vibration propagation paths of the regenerative mechanism in multi-stand mills through strip thickness and instant inter-stand tension variations. The critical vibration propagation paths of the regenerative mechanism will explain the modulation frequency observed in tandem mills that, as it will be shown, is inversely proportional to the shortest time delay during strip transport from the upstream stands to the downstream stands. [ABSTRACT FROM AUTHOR]

Many different modes of chatter in rolling and their possible causes have been identified after years of research, yet no clear and definite theory of their mechanics has been fully established and accepted. In this two-part paper, stability of tandem mills is investigated. In Part 1, state-space models of single- and multi-stand chatter are formulated in a rigorous and comprehensive mathematical form. Then, the stability of the rolling system is investigated in the sense of the single- and multi-stand negative damping effects. First, a single-stand chatter model in state-space representation is proposed by coupling a dynamic rolling process model with a structural model for the mill stand. Subsequently, a multi-stand chatter model is developed by incorporating the inter-stand tension variations and the time delay effect of the strip transportation based on the single-stand chatter model. Stability criteria are proposed and stability analyses are performed to create corresponding stability charts in terms of the single- and multi-stand negative damping mechanism through numerical simulations. Particularly, the effect of friction conditions on chatter is examined and an explanation is given for the existence of an optimum friction condition. In Part 2, the regenerative effect and resulting instabilities are examined. Suitable stability criteria for each mechanism are established and stability charts are demonstrated in terms of relevant rolling process parameters. [ABSTRACT FROM AUTHOR]

Abstract: The elliptical vibration texturing process is an innovative machining method for the fast generation of textured surfaces. It adds a tertiary motion component to the tool tip, which introduces deliberate elliptical vibrations between the cutting tool and the workpiece. The elliptical locus lies in the plane that is defined by the cutting direction and the radial direction in the turning operation. This paper proposes a new design for a resonant mode 2D tertiary motion generator (TMG) that can deliver the required elliptical trajectory at an ultrasonic frequency. The device works in the resonant mode, with tangential and normal vibrations at a nearly identical resonant frequency. Simulation and experiments were carried out to perform a modal analysis of the system. Different design parameters were adjusted to achieve large vibration amplitudes in both tangential and normal directions. The elliptical vibration texturing process was implemented by integrating the newly developed TMG into a turning operation. Preliminary test results of dimple array patterns are presented that validate the performance and principle of the proposed design. [Copyright &y& Elsevier]

Abstract: The elliptical vibration texturing process is a vibration assisted machining method for the fast generation of micro structured surfaces. It adds a higher order motion component to the cutting tool that leads to periodic changes in the cutting depth during the machining process. This results in the creation of micro-dimples on the machined surface, whose shape is a function of the tool geometry and trajectory. This paper studies the surface generation mechanics of the elliptical vibration texturing process through experimentation and modeling. A surface generation algorithm is presented for this newly developed process. The model fully describes the motion and the 3D geometry of the cutting tool including its rake face, flank face, and the cutting edge, since all these tool features influence the topography of the generated surface. Since the process takes place in the micro/meso-scale cutting regime, the model includes the minimum chip thickness and elastic recovery effects. The experimental results are shown to validate the simulation model. The simulation model is used to characterize the influences of the process parameters on the texture patterns. The effects of the tool geometry on the process, including the cutting edge radius, are also analyzed. [Copyright &y& Elsevier]

The parallel wedge precision positioning stage (PW-PPS) presents a novel configuration of a parallel mechanism for precision positioning applications. Based on its specific parallel configuration, the corresponding inverse andj-Orward kinematic models were developed and used to formulate the volumetric error model of the mechanism. The error model that considers the influence of manufacturing errors is built in two steps. In the first, the structural parameter-induced errors associated with the PW-PPS's structural parameters and input variables were considered, while in the second, the joint clearanceinduced errors produced by joint clearances were taken into account. The structural parameter-induced errors were modeled based on complete differential-coefficient theory, while the joint clearance-induced errors due to joint clearances were modeled based on the virtual work and deterministic method. In the latter case, the kinetostatic model and joint error contact modes were analyzed to build a joint clearance-induced error model. The relationship between the different error sources and the output pose error of the mechanism's moving platform was obtained. Finally, considering practical values for the mechanism's parameters and errors, the error distribution in the PWPPS's workspace was evaluated to determine the distributive rules of the various error components. [ABSTRACT FROM AUTHOR]

Electrically-assisted double-sided incremental forming (EA-DSIF) is a flexible forming method suitable for processing hard-to-form materials and complex-shaped parts. A challenge in EA-DSIF experiments is temperature measurement. Since the localized forming zone is blocked by the tools, it is not possible to measure the actual forming temperature distribution in the forming zone. To address this issue, we propose an artificial neural network (ANN) framework for predicting the forming temperature using measurements of the surrounding temperature and toolpath features. The ANN model was trained using the temperature outputs of finite element models. A simplified EA-DSIF simulation model was developed for computational efficiency needed for synthetic data generation. Model simplifications were justified in multiple cases and validated with experimental data by comparing the temperatures from positions that is visible to an infrared camera. The feasibility of applying the developed ANN model to untrained geometries and in practical applications was demonstrated. The findings generated from this study are crucial for selecting optimum process parameters, estimating the forming force, and predicting microstructure evolution during EA-DSIF. [ABSTRACT FROM AUTHOR]

A preface for the June 2008 issue of the "Journal of Manufacturing Science and Engineering," is presented.

Based on the spade drill point's mathematical models established in Part 1 of this paper, a detailed methodology for the analysis of the cutting edges and angle distributions along these edges is given. The analysis addresses the most important geometric elements of the bit including the tip, major cutting edge, and the chisel edge profiles, as well as the rake and clearance angle distribution along these cutting edges. In unison, the geometric model of the spade bit and the analysis procedure described in this part of the paper have laid the foundation for a methodology and a software package for a detailed geometric analysis of all relevant cutting mechanics related geometric entities of the drill. This, in turn, constitutes the first prerequisite for assessing the cutting performance of these tools. [ABSTRACT FROM AUTHOR]

Spade bits, widely and routinely used in the construction industry, have not received any attention in the technical literature, yet there is a pressing need to improve the performance of these bits whose basic design has not changed for decades. To facilitate such improvements, a thorough understanding of the geometric, manufacturing, and cutting mechanics aspects of these tools is necessary. In this two-part paper, the point geometry and manufacturing issues will be discussed. To fundamentally understand the spade drill bit's behavior, a complete mathematical model of its principal topological elements will be established. In conjunction with this model, the corresponding analytical formulations of the geometry and kinematics of the appropriate manufacturing procedures will also be formulated. In unison, these models will lay the foundation for a methodology and a software package for a detailed geometric analysis of all relevant cutting angle distributions and edge profiles of the spade bit. This will facilitate, at a later point, new point developments rooted in rigorous analytical models. [ABSTRACT FROM AUTHOR]

Micro-drills were modeled as long twisted beams. Models for the critical speeds and the critical buckling loads were developed based on the finite element method of analysis. The effects of transverse shear, rotary inertia and gyroscopic moments were included in this analysis. The models have the capability of analyzing a wide variety of geometrical cross-sections. A computer program was developed for the calculation of the variations of the critical speeds and of the buckling loads. The effects of drill geometry, boundary condition, rotational speed, and cross-sectional area on the buckling loads and the critical speeds were analyzed. [Copyright &y& Elsevier]

In this part of the paper the analytical models for the prediction of the force system, established in Part 1, in conjunction with a complete geometric model of the spade bit, will be used in a systematic simulation analysis of the spade drill's performance. The aim of this analysis is to identify the most desirable geometric characteristics of the different topological features of the spade bit that would result in desirable performance measures expressed in terms of reduced torque and thrust force. The obtained results are intended to guide the development of more efficient tools of this type. [ABSTRACT FROM AUTHOR]

The purpose of this work is to present an investigation of the force system generated during spade drill-bit drilling processes that is a prerequisite for the design of spadedrills with improved performance. The technical literature offers no references to this type of bit and process; hence an approach based on the well-established mechanistic force prediction methods will be used. The force and torque prediction models are based on a complete analytical model of a generalized spade bit that takes into account the cutting action of all the characteristic cutting edges of the spade bit, namely of its chisel edge, tip and major cutting edges. In conjunction with the model an efficient model calibration method is also introduced and experimentally verified. [ABSTRACT FROM AUTHOR]

The purpose of this work is to present the development and experimental performance assessment of a new generation of spade drill bits. Rigorous point geometry and drilling force models that describe the topology of the drill and its cutting behaviour have guided the development of these new drills with unique topological features. It is shown, both analytically through simulations and through a systematic experimental study, that the performance of the newly developed topologies exceeds that of the commercially available designs. The new spade bits yield lower thrust and torque over the whole range of pragmatic operating conditions. [Copyright &y& Elsevier]

The article offers brief profiles of Darek Ceglarek, Brian K. Paul, and Mary Lynn Realff, who contributes to the writing of the journal.

3D elliptical vibration-assisted cutting (EVC) is a method for rapidly creating ultra-precision free-form surfaces with features at the micro-scale, which have a wide array of industrial applications. Displacement coupling and low stiffness limit the applications of current 3D EVC mechanisms in machining difficult to cut materials and precise micro-features. To overcome these limitations and improve overall performance, an innovative 3D EVC mechanism with a parallel layout with flexure hinges will be presented. The mechanism was specifically designed to be capable of generating decoupled output displacements in three directions and assuring high stiffness. An analytical model of the mechanism's kinematics will be formulated to facilitate the prediction of the loci of the tooltip and design and realization of the prototype device. The vibration characteristics of the mechanism were verified through both finite element analysis and experimental modal analysis using swept sine testing. To validate the machining performance of the mechanism, two groups of micro-texturing turning and simulation experiments were performed. The performance tests and comparison results between the generated and simulated micro-textures indicate that the proposed 3D EVC mechanism is capable of generating different micro-feature shapes. [ABSTRACT FROM AUTHOR]

Micro end-milling is widely used in many industries to produce micro products with complex 3D shapes. The accurate modeling and prediction of surface roughness are important for evaluating the productivity of the machine tools and the surface quality of the machined parts. This paper presents an accurate surface roughness model based on the kinematics of cutting process and tool geometry by considering the effects of tool run-out and minimum chip thickness. The proposed surface roughness model is validated by micro endmilling experiments with the miniaturized machine tool. The results show that the proposed surface roughness model can accurately predict both the trends and magnitude of the surface roughness in micro end-milling. [ABSTRACT FROM AUTHOR]

Various micro-texturing methods have been used to control surface topography. However, most of the available methods are inherently difficult to adopt for the efficient generation of intricate micro-textures on cylindrical surfaces. In this paper, a novel ultrasonic elliptical vibration-assisted cutting technique based on a micro-texturing model is proposed to fabricate hybrid micro-textures with different geometric characteristics. In the proposed elliptical vibration-assisted hybrid micro-texturing method an intricately shaped primary micro-texture is generated by elliptical vibration-assisted cutting, while the desired secondary textures are simultaneously constructed through a controlled intersection with neighboring elliptical vibration-assisted cutting loci. The cutting loci for the fabrication of the hybrid micro-textures is mathematically calculated according to a geometric model of hybrid micro-texturing. The topography of the hybrid dimples is analyzed to verify the correctness of the cutting locus generation method. Locus compensation methods, considering the elliptical vibration locus and the tool nose radius are proposed to reduce fabrication errors during the hybrid dimple generation process. Micro-scale hybrid dimples, which are in close compliance with the results of the mathematical calculations, were successfully fabricated on machined cylindrical surfaces. The comparison of the results shows that the proposed method is satisfactory and can be used to predict and generate hybrid micro-textures on cylindrical surfaces. [ABSTRACT FROM AUTHOR]

The article discusses various topics within the issue including an obituary for professor emeritus Nathan Henry Cook and biography of associate editors S. Jack Hu and Thomas Kurfess.

Editorial. Discusses the author's plans for improving the periodical 'Journal of Manufacturing Science and Engineering,' following his appointment as editor in 2003. Increased page allocation; Paper submission and review process; Preparations for the implementation of an entirely electronic or paperless submission and review process. [ABSTRACT FROM AUTHOR]

Alumina (Al2O2) is an extremely hard and brittle ceramic that is usually used as an abrasive or a cutting tool insert in manufacturing. However, its growing applications in industrial products make it necessary to conduct a study of the machinability of alumina themselves with a cost-effective and flexible method, rather than conventional diamond grinding or laser-assisted processing methods. In this paper, polycrystalline diamond tools are used to investigate the machining of nonporous pure alumina by applying an inclined ultrasonic elliptical vibration cutting (IUEVC) method. First, a theoretical analysis is presented to study the effects of the machining parameters on cutting peiformances during raster cutting procedures from the prospective of the material removal rate (MRR), tool-chip contact area, cutting edge angle, etc. Then, experiments are carried out to investigate the cutting forces and the areal surface roughness (Sa) in connection with the theoretically established relationships. The results show that the cutting forces are remarkably reduced, by up to more than 90%, and that the machined surface finish is also improved compared with conventional methods. [ABSTRACT FROM AUTHOR]

The understanding of rock removal mechanisms, as one of the essential elements for advancing the cutting performance of polycrystalline diamond compact (PDC) cutters, is still incomplete. This paper is seeking to formulate a cutting theory to analytically explain how rock interacts with PDC cutters in a simple cutting configuration – linear cutting. In the proposed approach, a rock crushing zone is introduced at the rock-cutter interface beneath the cutter's rake face, namely the Tip Crushing Zone (TCZ), which, as a destruction kernel, is responsible for both the crushing and chipping phenomena occurring in the cutting process. The physical aspects of these two disparate chip formation mechanisms are discussed. Moreover, closed form expressions for the cutting and thrust forces are derived based on the equilibrium of moments and on the minimum chipping energy principle. To evaluate the force model, comprehensive linear rock cutting tests were conducted on a newly developed rock cutting facility. Both the chip formation phenomena and force responses are in good agreement with the newly proposed theory. [ABSTRACT FROM AUTHOR]

Ultrasonic vibration cutting is an efficient cutting process for mechanical micro-machining. This process can generate intricate surface textures with different geometric characteristics. Micro-grooves/micro-channels are among the most frequently encountered micro-structures and, as such, are the focus of this paper. The effectiveness of both the linear and ultrasonic elliptical vibration-assisted machining technique in micro-groove turning is analyzed and discussed in the paper. The paper first investigates the mechanisms of micro-groove generation induced by the linear and elliptical vibration modes. A simplified cutting force analysis method is given to compare the effectiveness of the two modes in micro-groove turning. The surface roughness of the generated micro-grooves is analyzed next and theoretical expressions are given for the two cases. Finally, micro-groove turning experiments are conducted to compare the influences of the two vibration modes on the cutting forces and the surface roughness. The experimental results show that linear vibration-assisted micro-groove turning leads to better surface roughness as compared to the elliptical vibration-assisted case, while elliptical vibration-assisted micro-groove turning shows advantages in terms of decreasing the cutting forces. [ABSTRACT FROM AUTHOR]

The increasing demand for customized products and rapid prototyping triggers the development of dieless forming process where the need of part-specific dies is eliminated compared to conventional forming processes. This paper presents a heat-assisted three-roll incremental rolling system capable of producing rods and tubes of various diameters without the need for die/tool replacement. The system incorporates two possible heating mechanisms, namely, an induction heater and a high-current power supply for electrically assisted forming. Due to its high flexibility and hot forming ability, this rolling system is ideal for low volume production or scientific research. The newly fabricated rolling machine was initially evaluated using low carbon steel rods. The experiments have shown that the machine can produce metallic rods down to 6 mm in diameter without apparent spiral marks on the outer surface of the rolled product using multiple passes. The finite element method (FEM) was used to analyze the reaction moment, depth of the spiral marks, and the effect of axial feeding speed on the spiral marks. The simulation model predicted the results of the experiments with less than a 10% error. The work established a flexible rolling platform for possible future research, which can include the study of interface behavior in the thermo-mechanical rolling processes, and the study of material behavior in this multi-axial multi-physics environment. [ABSTRACT FROM AUTHOR]

The increasing demand for customized products and rapid prototyping triggers the development of dieless forming process where the need of part-specific dies is eliminated compared to conventional forming processes. This paper presents a heat-assisted three-roll incremental rolling system capable of producing rods and tubes of various diameters without the need for die/tool replacement. The system incorporates two possible heating mechanisms, namely, an induction heater and a high-current power supply for electrically assisted forming. Due to its high flexibility and hot forming ability, this rolling system is ideal for low volume production or scientific research. The newly fabricated rolling machine was initially evaluated using low carbon steel rods. The experiments have shown that the machine can produce metallic rods down to 6 mm in diameter without apparent spiral marks on the outer surface of the rolled product using multiple passes. The finite element method (FEM) was used to analyze the reaction moment, depth of the spiral marks, and the effect of axial feeding speed on the spiral marks. The simulation model predicted the results of the experiments with less than a 10% error. The work established a flexible rolling platform for possible future research, which can include the study of interface behavior in the thermo-mechanical rolling processes, and the study of material behavior in this multi-axial multi-physics environment. [ABSTRACT FROM AUTHOR]

The increasing demand for customized products and rapid prototyping triggers the development of dieless forming process where the need of part-specific dies is eliminated compared to conventional forming processes. This paper presents a heat-assisted three-roll incremental rolling system capable of producing rods and tubes of various diameters without the need for die/tool replacement. The system incorporates two possible heating mechanisms, namely, an induction heater and a high-current power supply for electrically assisted forming. Due to its high flexibility and hot forming ability, this rolling system is ideal for low volume production or scientific research. The newly fabricated rolling machine was initially evaluated using low carbon steel rods. The experiments have shown that the machine can produce metallic rods down to 6 mm in diameter without apparent spiral marks on the outer surface of the rolled product using multiple passes. The finite element method (FEM) was used to analyze the reaction moment, depth of the spiral marks, and the effect of axial feeding speed on the spiral marks. The simulation model predicted the results of the experiments with less than a 10% error. The work established a flexible rolling platform for possible future research, which can include the study of interface behavior in the thermo-mechanical rolling processes, and the study of material behavior in this multi-axial multi-physics environment. [ABSTRACT FROM AUTHOR]

Abstract: Cutting temperature and its distribution in the cutting zone are a critical factor that significantly affects tool life and degrades part accuracy during metal removal operations. However, issues surrounding their modeling and experimental validation in the immediate cutting zone still remain an unresolved issue. A major impediment is the unavailability of adequate temperature measurement methods with sufficient temporal and spatial resolution to measure actual temperatures and validate predictive models. In this paper, a model for the dry orthogonal cutting process with thermo-mechanical coupling effects, i.e., interactions between the stress state, strain rates and the temperature softening of material in the plastic deformation zone, is proposed to predict cutting temperature distribution in the cutting zone. The feasibility and prediction accuracy of the model is verified by experimental measurements through Thin Film Thermocouple (TFTC) arrays embedded at the immediate vicinity of the cutting zone into Polycrystalline Cubic Boron Nitride (PCBN) tooling. The experimental verification is performed under hard turning conditions. It has been shown that the predictions of the proposed model are in very close agreement with the experimentally measured results including the cutting forces, chip thickness and cutting temperature distributions on the rake and flank faces in the cutting zone. Furthermore, the modeling results have also provided an essential understanding on the stress distributions at the tool/chip and work/tool interfaces as well as of the nature of the chip flow velocity along the rake face of the cutting tool. [Copyright &y& Elsevier]

Complex .three-dimensional miniature components are needed in a wide range of industrial applications from aerospace to biomedicine. Such products can be effectively produced by micro-end-milling processes that are capable of accurately producing high aspect ratio features and parts. This paper presents a mechanistic cutting force model for the precise prediction of the cutting forces in micro-end-milling under various cutting conditions. In order to account for the actual physical phenomena at the edge of the tool, the components of the cutting force vector are determined based on the newly introduced concept of the partial effective rake angle. The proposed model also uses instantaneous cutting force coefficients that are independent of the end-milling cutting conditions. These cutting force coefficients, determined from measured cutting forces, reflect the influence of the majority of cutting mechanisms involved in micro-end-milling including the minimum chip-thickness effect. The comparison of the predicted and measured cutting forces has shown that the proposed method provides very accurate results. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this paper is to further extend the theoretical understanding of the dynamic end milling process and to derive a computational model to predict the milling force components. A comparative assessment of different cutting force models is performed to demonstrate that the instantaneous shear plane based formulation is physically sound and offers the best agreement with experimental results. The procedure for the calculation of the model parameters used in the cutting force model, based on experimental data, has been presented. The influences of the helix angle on the shear stress, friction angle, and shear angle have also been investigated. The helix angle effect on the cutting force model was experimentally determined and it was shown that the cutting force model is applicable for a wide range of cutter helix angles. The validity of the proposed computational model, based on a discrete representation of the end milling process, has been experimentally verified through a series of cutting tests. The resultant cutting forces were computed as the sum of elemental cutting forces composed of a chip shearing and of a tool–workpiece contact force component. [Copyright &y& Elsevier]

This two-part paper is aimed at developing a theoretical and numerical simulation basis for initial penetration phenomena that profoundly influence hole tolerances and shape. In Part 1, dynamic force models are developed followed by models of the drill's dynamic behavior in Part 2. Next, these models are combined and used to predict initial penetration behavior and hole shape. A comparison of simulated and experimental results concludes Part 2. In this part, by considering the effects of drill grinding errors and drill deflections, dynamic cutting chip thickness models are developed which, in combination with workpiece surface inclination effects, allow the formulation of expressions for the dynamic chip thickness and cutting chip cross-sectional area. By using these quantities to replace their static counterparts, static drilling force models are extended to facilitate the prediction of dynamic cutting forces. Separate thrust, torque, and radial force models for the major cutting edges, secondary cutting edge, and for the indentation zone are formulated. The effects of drill installation errors on the radial cutting forces acting on the chisel edge and the major cutting edges are also included. [ABSTRACT FROM AUTHOR]

This part of the paper is aimed at the development of models for the drill tip's transverse and angular motions, the definition of models for establishing the drilled hole's profile and, by combining these results with the dynamic force models of Part 1, the formulation of the complete model for drill skidding and wandering. An experimental verification of the models concludes the paper. For the development of the drill motion models the drill is simplified as a pretwisted beam subjected to a compressive axial load and radial forces acting on its tip. The governing equations are developed using Hamilton's principle. Subsequently, the weak form of the governing equation is formulated to facilitate their solution by the finite element method. The corresponding boundary conditions for the motion model are also defined for three drilling phase, i.e., drill skidding, drill wandering and stabilized drilling. Based on the drill tip's wandering locus and drill rotation, a mathematical model for describing the drilled hole's profile is developed. [ABSTRACT FROM AUTHOR]

The eigenstructure assignment algorithm is proposed for controlling machining chatter by changing the response of the machine tool structure to dynamic cutting forces through the change of its modal properties so that the interaction between the tool and workpiece can be altered. The determination of the desired modal shapes is derived from a concept similar to gain scheduling in adaptive control system theory. By using computer simulations, the desired eigenstructure of the machine tool structure for different cutting conditions is determined and used to form the scheduling table. The gain matrix is adjusted according to the scheduling table and cutting conditions. It was found from experimental results that by changing the principal direction of the machine tool structure, the machining system could be stabilized and that the use of the proper eigenstructure to suppress machine tool chatter could significantly increase the material removal rate. Simulations have shown that the responses of the controlled machining system have been altered from unstable to stable, proving the feasibility of the proposed chatter control concept. [Copyright &y& Elsevier]

This paper presents the modification of wettability by nanosecond laser surface textured followed by silanization to fabricate the superhydrophobic zirconia surface. Surface modification by varying the pitch between channels leads to micro‐channel and micro‐grid pattern with different surface roughness. The generated morphological and metallurgical modifications of the surface are measured by scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS). Numerous micro‐pits and cracks in the laser‐treated areas can be observed from SEM, which indicates crack propagation dominating the process of laser ablation of zirconia. The surface is superhydrophilic with laser‐texturing instantly, whose wettability is modified over time. By analyzing the XPS, carbon content, especially C‐C (H) groups, is important for the time‐dependent wettability. The hydrophobicity of all laser‐textured surfaces is improved after silanization. Laser texturing with smaller pitch (50 μm and 70 μm) leads to superhydrophobic surfaces after silanization, which may be due to the modification of physicochemical properties of substrate by very rapid local heating and cooling on the thick surface layer. Overall, the investigations indicate that wettability modifications can be attributed to the surface's microstructure, which depend on laser processing parameters, and chemical composition, especially in terms of −CF3, −CF2, and C‐C (H). [ABSTRACT FROM AUTHOR]

Abstract Water Jet Incremental Micro-Forming (WJIMF) is a novel alternative to Single-Point Incremental Micro-Forming (SPIMF). Instead of using a rigid tool to form the sheet metal, a high-speed and high-pressure water jet is employed to induce plastic deformation. Dieless WJIMF has the capability to form a variety of shapes, but the total depth of the formed shape, which is affected by several process parameters, cannot be well controlled. To alleviate this problem, supporting dies can be used. This paper systematically studies the WJIMF process with several types of micro-machined supporting dies to produce micro-scale shell parts with designed geometries. It has been shown that the design of the toolpath has a profound impact on the final geometry of the part even with the same supporting die. The experimental results suggest that supporting dies with different geometries require unique toolpath strategies to achieve high geometric accuracy. Furthermore, it has been determined that water jet pressure plays an important role in the plastic deformation of the metal foil and that inappropriate combinations of toolpath and water jet pressure lead to buckling which is not found in macro-scale Water Jet Incremental Forming (WJIF). A numerical model in ABAQUS was developed to simulate the process and predict part geometry. [ABSTRACT FROM AUTHOR]

Conventional single-point incremental forming (SPIF) is already in use for small batch prototyping and fabrication of customized parts from thin sheet metal blanks by inducing plastic deformation with a rigid round-tip tool. The major advantages of the SPIF process are its high flexibility and die-free nature. In lieu of employing a rigid tool to incrementally form the sheet metal, a high-speed water jet as an alternative was proposed as the forming tool. Since there is no tool-workpiece contact in this process, unlike in the traditional SPIF process, no lubricant and rotational motion of the tool are required to reduce friction. However, the geometry of the part formed by water jet incremental microforming (WJIMF) will no longer be controlled by the motion of the rigid tool. On the contrary, process parameters such as water jet pressure, stage motion speed, water jet diameter, blank thickness, and tool path design will determine the final shape of the workpiece. This paper experimentally studies the influence of the above-mentioned key process parameters on the geometry of a truncated cone shape and on the corresponding surface quality. A numerical model is proposed to predict the shape of the truncated cone part after WJIMF with given input process parameters. The results prove that the formed part's geometric properties predicted by the numerical model are in excellent agreement with the actually measured ones. Arrays of miniature dots, channels, two-level truncated cones, and letters were also successfully fabricated on stainless-steel foils to demonstrate WJIMF capabilities. [ABSTRACT FROM AUTHOR]

Highlights • A two degrees-of-freedom vibration-assisted machining method is proposed to enable the efficient generation of freeform surfaces with hierarchical micro/nano-structures. • The basic tool trajectory is theoretically determined, and the surface generation algorithm is presented by taking into account the high frequency vibration of the tool. • The hierarchical sinusoidal surface and discontinuous cubic surface array were fabricated, showing a good consistency with simulation results. • Wettability tests were carried out, and the results indicate a clear increase in wetting angle for hierarchical freeform surfaces compared to their smooth counterparts. Abstract In this paper, instead of the commonly used fast tool servo method, a two degrees-of-freedom (2D) vibration-assisted machining method is proposed to enable the efficient generation of freeform surfaces with hierarchical micro/nano-structures. With this method, the freeform component of the surface is realized by 1D vibrations in the depth-of-cut direction, whereas the hierarchical micro/nano-structures are generated by elliptical vibrations at high frequency and small vibration amplitudes. The determination of the tool vibration path, considering tool geometry and the interference between the tool's flank surface and the machined surface, is presented and used as the basis to propose a surface generation algorithm for topography prediction. Using a developed 2D vibration compliant cutting system, experiments were conducted to machine hierarchical sinusoidal and discontinuous cubic surface arrays for demonstration. The results show a high consistency between the simulated and generated topographies demonstrating the effectiveness of the proposed method for the efficient machining of hierarchical freeform surfaces. In addition, wettability tests were undertaken to demonstrate that larger wetting angles can be obtained on hierarchical freeform surfaces as compared to their smooth counterparts. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Abstract In this study, we investigated the use of an electrically-assisted (EA) forming process to reduce the forming force of ODS ferritic steels. The effects of a continuous electric current on 14YWT, which is a kind of ODS material, during plastic deformation were evaluated. First, EA uniaxial tension tests show that the electric current is able to reduce the flow stress of 14YWT. 14YWT exhibits a ductility minimum at a current density of 34.5 A/mm2 which is consistent with fractography results. Hardness measurements and TEM results indicate that oxide particles are stable during the EA process. Second, microstructure analysis was performed on the sample in its as-received state and after current treatment. The microstructures are stable when subjected to high current density. Third, a thermal model was developed to predict the Joule heating temperatures. The temperatures were compared with the experimental results. Finally, a temperature-dependent hardening model was used to explore the mechanisms acting during EA deformation. Since the model can accurately predict the yield strength of 14YWT under EA conditions without the incorporation of non-thermal effects, it can be concluded that the reduction in yield strength is due to the Joule heating generated under continuous current loading conditions. An oven-heated pure thermal tension test was conducted to confirm this conclusion. The findings generated from this study will result in the development of innovative manufacturing processes such as the electrically-assisted tube forming processes. [ABSTRACT FROM AUTHOR]

Highlights • A dynamic model of ball screw drives is proposed by considering torque transmission. • A new method is proposed to identify the friction in key components simultaneously. • The simulation accuracy reaches 93% to 98% during the uniform velocity stages. • The mechanical tracking errors are reduced by up to 86% through compensation. Abstract Dynamic mechanical tracking errors occur in ball screw drives typically due to inertial, frictional and external forces. This results in axial elongation and compression of key components of the drive that deteriorate the dynamic tracking accuracy. In order to improve tracking accuracy, this paper presents a feedforward compensation method of dynamic mechanical tracking errors. A dynamic model is proposed to offset the position commands that are fed to the servo controller. The accuracy of the model can be improved by considering the torque transmission between the nut and the ball screw, which is not considered in existing models. To obtain the stiffness and friction parameters in the model, a new method of parameter identification is proposed. The method can simultaneously identify friction in key components leading to greatly improved efficiency and accuracy. The dynamic model and parameter identification method are validated by comparing simulation and experimental results for trapezoidal and sinusoidal trajectories. To validate the simulation results, the sinusoidal trajectories are used to compensate the tracking errors of the ball screw. The results confirm that most of the dynamic mechanical tracking errors are eliminated after compensation. Therefore, the compensation method based on the proposed dynamic model and parameter identification method is effective in improving the tracking accuracy of ball screw drives. [ABSTRACT FROM AUTHOR]

Abstract Shearing is the most widely exploited method to fracture and remove rock formations in many man-made rock-opening activities. During shearing, rock breaks into chips due to the periodic nucleation, propagation, and coalescence of numerous micro-cracks. The crack interactions along with the rock's complex physical properties lead to extreme challenges in reaching a consensus on the rock's failure behavior in shearing. In this paper, force-drop events, as a quantitative measure of the global rock breakage occurrence, were recorded and analyzed. A power-law distribution with a tunable cut-off between the frequency of the force-drop events and their magnitudes is shown. The obtained results, for the first time, reveal the rock's tuned critical behavior in shearing which is intrinsically similar to its failure behavior widely observed in earthquakes. [ABSTRACT FROM AUTHOR]

• An improved model capable of analyzing the effects of ambient gas on laser polishing is proposed. • Mass transfer, solutocapillary force, and chemical reaction are added to the model. • Convection is the main mass transfer mechanism in the molten pool, not diffusion. • The solutocapillary force always acts in the opposite direction to the melt flows. • The dissolved oxygen enhances the thermocapillary force driving the melt to flow inward. Laser polishing, as an effective surface finishing process, is significantly affected by ambient gas. Previous studies on the contribution of ambient gas to laser polishing mostly focused on experiments, but rarely on numerical simulations. Given this, this paper proposes an improved model capable of analyzing the effects of ambient gas on the laser-polished surface's morphology evolution mechanisms, by expanding an existing laser polishing model with the influences of mass transfer, solutocapillary forces, and chemical reactions. Argon and air were used as ambient gasses for comparison. Through this model, the surface morphology evolution of laser polishing in air was compared with that in argon in terms of the velocity field, temperature field, concentration field, melt surface velocity, molten pool surface profile, and surface forces. The respective contributions of chemical reaction heat, oxygen mass flux, mass transfer, and surface forces were also presented. Furthermore, the numerical model was verified on 304 stainless steel from the perspectives of polished surface roughness, molten pool depth, and oxygen element distribution. [Display omitted] [ABSTRACT FROM AUTHOR]

This article presents a novel two-degrees-of-freedom (2-DoF) piezo-actuated parallel-kinematic micro/nano-positioning stage with multi-level amplification. The mirror symmetric stage consists of four leverage mechanisms, two Scott-Russell mechanisms, and a Z-shaped flexure hinge (ZFH) mechanism. Taking advantage of the ZFH mechanism, 2-DoF motions with final-level flexural amplification and decoupled motion guidance are achieved. Analytical models of the stage are developed and validated through finite element analysis to characterize its working performance. Practical testing of a prototype stage is conducted to demonstrate the design process and to quantify its response characteristics. Due to the utilized multi-level amplification, a practical amplification ratio of 13.0 is realized by the prototype. The decoupled output motion guidance feature of the stage makes it amenable for implementation in raster scanning type of measurements. [ABSTRACT FROM AUTHOR]

Double-sided incremental forming (DSIF) is a subcategory of general incremental sheet forming (ISF), and uses tools above and below a sheet of metal to squeeze and bend the material into freeform geometries. Due to the relatively slow nature of the DSIF process and the necessity to capture through-thickness mechanics, typical finite element simulations require weeks or even months to finish. In this study, an explicit finite element simulation framework was developed in LS-DYNA using fully integrated shell elements in an effort to lower the typical simulation time while still capturing the mechanics of DSIF. The tool speed, mesh size, element type, and amount of mass scaling were each varied in order to achieve a fast simulation with minimal sacrifice regarding accuracy. Using 8 CPUs, the finalized DSIF model simulated a funnel toolpath in just one day. Experimental strains, forces, and overall geometry were used to verify the simulation. While the simulation forces tended to be high, the trends were still well captured by the simulation model. The thickness and in-plane strains were found to be in good agreement with the experiments. [ABSTRACT FROM AUTHOR]

High-speed machining of thin-walled workpiece is widely used in aerospace industry. To optimize the machining parameters in milling operations, the related process stability is required to be predicted. Compared to the existing two-dimensional (2D)milling stability model, a more completed three-dimensional (3D) regenerative process stability prediction model of thin-walled workpiece is presented based on the newly developed dynamic model. The efficiency and accuracy of the regenerative milling stability can be improved in the presented 3D model. The analysis procedure of the stability of flexible dynamic milling is developed in details. The 3D stability lobes are calculated according to the full discretization method and direct integration scheme. To verify the accuracy of presented 3D stability model, the thin-walled workpiece milling sound pressure signal and surface quality are determined in experiments. [ABSTRACT FROM AUTHOR]

In the present study, a novel process, namely rotary spatial vibration (RSV) assisted diamond cutting, is introduced to overcome cutting velocity induced cutting parameter inconsistencies as well as the cutting direction induced insufficient utilization of vibration assistance in vibration-assisted turning and milling of brittle materials. In RSV-assisted diamond cutting, a rotary motion component, generated by the rotation of the machine's spindle, is superimposed onto the three-degrees-of-freedom translational vibrations of the diamond tool. The resulting complex motions of the diamond tool assure the possibility of consistent cutting performance that is always guaranteed even when processing arbitrarily large areas. In practice, the feasibility and superiority of this technique for processing brittle materials is well demonstrated by fabricating a set of circular micro-grooves on monocrystalline silicon wafers with gradually varying depth-of-cut. [ABSTRACT FROM AUTHOR]

In accumulated double-sided incremental forming (ADSIF), two hemispherical tools impart the local deformation to the sheet via their programed in-plane spiral motion and the depth of the part is achieved via rigid body motion of the already formed part. Unlike single point incremental forming (SPIF) and double-sided incremental forming (DSIF), ADSIF does not impose forces on the already-formed part and, therefore, has the potential of achieving higher geometric accuracy. A systematic method is proposed in this work to study the influences of the relative tool positions on the local formed shape and the final geometry, which is essentially the accumulation of all previously formed local deformations. Meanwhile, the concepts of the stable angle and the peak angle are introduced to better describe the cross-sectional geometry of a formed part with a constant wall angle at that particular cross section. It is recommended that, while multiple combinations of the relative positions of two forming tools may achieve the same stable angle that the positioning parameters should be chosen such that the resultant forming force or the wall angle variation between the stable and peak angles is minimized. [ABSTRACT FROM AUTHOR]

Double-sided incremental forming (DSIF) is a relatively new dieless forming process which uses two hemispherical ended tools, one on each side of the sheet, moving along a predefined trajectory to locally deform a peripherally clamped sheet of metal. DSIF provides greater process flexibility, higher formability, and eliminates the tooling cost when compared to conventional sheet forming processes. While DSIF provides much improved geometric accuracy compared to other incremental forming processes, current toolpath planning strategies suffer from long forming times. A novel mixed double-sided incremental forming (MDSIF) toolpath strategy is proposed in the present study. It simultaneously reduces the total forming time by half while preserving the best currently achievable geometric accuracy. The effect of the forming parameters, i.e., of the incremental depth and of tool positioning on the geometric accuracy of the parts formed with MDSIF was investigated and compared to those formed by traditional DSIF strategies. [ABSTRACT FROM AUTHOR]

Micro-structured surfaces are assuming an ever-increasing role since they define the ultimate performance of many industrial components and products. Micro-channels, in particular, have many potential applications in micro-fluidic devices, micro heat exchangers, and friction control. This paper proposes an innovative vibration-assisted machining method to generate micro-channels on the external surface of a cylinder. This method, referred to as elliptical vibration texturing, was originally developed by the authors to generate dimple patterns. It uses the modulation of the depth-of-cut by tool vibrations to create surface textures. The most promising features of the proposed method are its high efficiency, low cost, and scalability for mass production. It is shown that with proper combinations of the process parameters the created dimples start to overlap and form channels. An analytical model is established to predict channel formation with respect to the overlapping ratios of the dimples. Channel formation criteria and expressions for channel geometries are given along with a channel generation map that relates channel geometry to the process parameters. Experimental results are given to verify the model. A further example of micro-pattern generation is also given to showcase the flexibility of the process. [ABSTRACT FROM AUTHOR]