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The work described in this paper concerns a novel method for directly forming curved profiles/sections from billets in one extrusion operation using two opposing punches. Its mechanics are based on internal differential material flow, and it has been given the acronym, differential velocity sideways extrusion (DVSE). A tool set enabling sideways extrusion to be performed using opposing punches moving with different velocities was used for a series of experiments in which punch velocity ratio and extrusion ratio were process parameters. Plasticine was used as a model work-piece material and a series of compression tests were undertaken, to determine its constitutive properties and gain an estimate of work-piece die friction for use in process simulation. Curvature of extrudate can be controlled and varied using a difference between the velocities of the two punches, defined by velocity ratio. Greater curvature is achieved with lower velocity ratio. Curvature is also dependent on extrusion ratio, an increase in which increases curvature, although curvature is less sensitive to it than to velocity ratio. The extent of work-piece flow velocity gradient across the die exit orifice, which causes curvature, has been identified. Severe plastic deformation of the extrudate occurs in a way similar to channel angular extrusion (CAE), thus a greatly promoted effective strain level is achieved, though it is not always uniform across a section. The inner bending region of an extrudate experiences maximum localised effective strain, which decreases with decrease in curvature. To the authors' knowledge this is the first publication in which extrudate curvature is deliberately induced using opposing punches with differential velocities. Although only fixed velocity ratio values have been used in the work described in this paper the ability to change during operation exists and the process has the potential for the production of a profile with different curvature along its length. [ABSTRACT FROM AUTHOR]

Microstructure features directly reflect mechanical responses during material deformation and can influence the surface integrity of machined components, which is of great interest to both academic communities and industries. This paper summarizes the state of the art in modeling approaches for the effect of the microstructures and its evolution during metal-cutting processes. The aim of this paper is to analyze the advantages and drawbacks of current methods to improve modeling work and direct future orientations. First, dominant numerical modeling approaches for metal-cutting processes are reviewed. The finite element method (FEM) and mesh-free methods widely applied in professional research are discussed. Following this, approaches to modeling the effect of microstructures and their evolution are reviewed for two major categories—homogeneous field distribution and heterogeneous characteristics. Both the advantages and disadvantages of these two categories are analyzed and discussed in detail. Experimental techniques based on advanced characterization approaches to the validation of pertinent models are also discussed. Finally, a brief summary is presented and an outlook for future work is delineated. [Display omitted] • Numerical modeling approaches with the consideration of microstructure features towards metal cutting are reviewed. • Modeling through treating microstructures as homogeneous characteristics and pertinent validation techniques are reviewed. • Modeling of heterogeneous microstructure evolution in metal-cutting and pertinent characterization techniques are reviewed. • Future orientations of modeling the effect of the microstructure and its evolution in metal-cutting are recommended. [ABSTRACT FROM AUTHOR]

Singularities in five-axis machining are a series of deadly positions, which may cause unstable axis movements and deteriorate the performance of machine tools. This paper presents an optimization strategy to locally deform the tool path so that singularities of five-axis machine tools can be avoided. To achieve this purpose, a new concept of “forbidden circle”, which is the projection of the three dimensional “singular cone” associated with tool orientations in a two dimensional space named P-plane, is established for the first time to transform the complicated three dimensional problem into a two dimensional problem. Based on this idea, the projected points in P-plane are interpolated as B-spline first, and then, the B-spline control points are locally optimized by taking the “forbidden circle” as the geometrical constraint to keep the B-spline from crossing it. Especially, in the optimization procedure, the constraints are linearized with the changes of B-spline control points to change the whole optimization problem as a typical positive definite quadratic programming problem, which can achieve one and only global optimal solution. By doing so, singularity is avoided, and at the same time, the machining errors caused by tool path deformation can be minimized. Simulation and experimental results verify the effectiveness of the singularity avoidance method. [ABSTRACT FROM AUTHOR]

Tool tip frequency response function (FRF) is essential for chatter stability diagram in machining. But new modal tests are required for different tool-holder-spindle assemblies. To avoid these tests, receptance coupling substructure analysis (RCSA) method has been developed. Previous research proved that the full receptance matrix, which contains rotational and moment contributes, influences the RCSA accuracy. By improving the accuracy and efficiency in acquiring the full receptance matrix, this paper presents a new RCSA methodology to predict the tool tip dynamics when a new tool is selected. To identify the contact dynamics between the tool and tool holder, one required receptance matrix is experimentally measured with a reference tool attached on the machine. Comparing to the classical RCSA technique, an enhanced approach is proposed to better estimate the receptance matrix. Only one impact positon is required in the experiment. The enhanced approach introduces two compensation strategies to process the measuring data from impact test. Each compensation strategy can be chosen to improve the estimation accuracy. The measured receptances, together with the finite element models of the reference tool and the new tool, are used to predict the unknown tool tip FRF. Both numerical simulation and practical experiment are conducted to validate the proposed methodology. The results show that the proposed method is preferred when multiple modes should be considered. [ABSTRACT FROM AUTHOR]

This paper proposes a streamlined method to model, analyze and assess the overall performance of small mobile machines that can move along large parts to perform the required machining operations, conventionally called portable machines. The method is based on virtualization techniques and combines a process-force mechanistic model and a reduced machine stiffness model synthesized from virtual and experimental reduced models of subsystems. The model is used to assess and improve the performance of portable machines by examining the time-domain response of the tool center point in representative operations, rather than limiting the study to the frequency domain. A practical application to a particular portable machine is presented and used to conduct the presentation of the work. With the results of the analysis, the accuracy of the use of the portable machines is studied. The procedure also proves to be a useful tool to optimize the machine design to fit particular applications. The method has been experimentally evaluated in a conventional three axis milling machine to ensure the accuracy of the simulations. [ABSTRACT FROM AUTHOR]

This paper proposes an efficient actual inverse kinematics method to compensate the geometric errors of five-axis machine tools. The analytical expressions of corrected numerical control (NC) code are derived according to the invertibility, associative law of multiplication, and block calculation of homogenous transformation matrix (HTM). No additional analysis and models are needed for the compensated expressions, appropriate conversion with the geometric error model based on HTM is sufficient. It is simple, convenient and universal for geometric error compensation. The corrected NC code can be obtained through algebraic operation, without time-consuming iteration, differential, or pseudo-inverse algorithm. Then compensation accuracy and efficiency of the method are simulated. And the results indicate higher efficiency compared to existing method. At last, the method is verified by cutting experiment on a five-axis machine tool. Both simulation and experiment results can validate the feasibility of the method. The proposed method significantly improves the computation efficiency and is considered more suitable for real-time compensation. [ABSTRACT FROM AUTHOR]

Five-axis position independent geometric errors (PIGEs), which are caused by imperfect assembly of machine tools, need to be identified and compensated in order to improve the accuracy of machined parts. In traditional PIGEs identification model based on differential motion matrices (DMM), PIGEs elements are defined in the local frames attached to the previous axis, which is inconvenient to do redundance analysis. In order to fully but un-redundantly identify five-axis PIGEs, this paper proposes a new PIGEs identification model based on DMM in the global coordinate frame. The transfer matrix which realizes the transformation of PIGEs between global and local definitions is derived at first. Then the Jacobian function of the tool center motion errors related to PIGEs defined in the global frame is calculated and adopted for PIGEs identification with the least-square algorithm. For the proposed PIGEs identification model in the global frame, the minimum set of PIGEs can be easily found to make sure full but un-redundant identification, by properly setting up the machine tool coordinate frame using the method of ISO 230-1:2012. The proposed new Jacobian function and PIGEs identification model in the global frame are verified through simulation and experiments with ball-bar tests. [ABSTRACT FROM AUTHOR]

Backlash is one of the most commonly encountered nonlinear phenomena in feed drives, which degrades the contouring accuracy of machine tools. The full-closed loop could suppress the adverse effects of backlash significantly. However, a transient backlash error (TBE) remains. Unfortunately, the mechanism of the TBE is completely different from that of the conventional backlash error. The purpose of this paper is to reveal the mechanism of the TBE. First, for the demonstration of the TBE, a general model is derived from an industrial feed drive with the closed loop control. Subsequently, the model is simplified further. Based on the simplified model, the mechanism is described and clarified in detail, and furthermore, the analytical formulations of TBEs are derived for the cases of straight line and circle, respectively. Finally, several simulations and experiments are given to validate the proposed models and formulations. [ABSTRACT FROM AUTHOR]

Laser shock punching is a recently developed technique, which is very efficient for punching microholes in thin metal sheets. However, processing large areas with laser shock punching is difficult because the processing area is limited by the size of the laser spot. Moreover, as the duration of the laser-induced shock pressure is considerably less than that of the explosive used, the thickness of the punchable metal sheet is in the order of a few tenths of the punch diameter. In this paper, we report an efficient approach that enables micropunching over a large area of a metal sheet in a single step. This micropunching method uses an underwater shock wave generated by the explosion of a plastic explosive charge. This approach is successfully used to punch circular holes over a large area of a 0.1-mm thick A1100 sheet, forming multiple holes with a diameter of 300 μm each. The pressure profiles of the underwater shock waves measured using piezo film gauges are used to analyze the micropunching process using ANSYS Autodyn software. The punching process is numerically simulated, and it is observed that the simulation and experimental results are in good agreement. The proposed approach can be applied to high-strength materials and thick sheets that are difficult to process using laser-induced shock waves. • Micropunching method using explosives for punching a wide range of metal sheets. • The new method can be applied to high-strength materials and thick sheets. • The punching area can be increased by changing the shape of the explosive. • The shock pressure and duration can be used to control punching conditions. • The shape of the hole edge depends on the shock pressure. [ABSTRACT FROM AUTHOR]