Search

The two-roller straightening process has an irreplaceable position in the finishing process of metal bars. In this paper, the deformation of bar is macroscopically recognized by analyzing the deformation path in the roller gap. Graphic method and mathematical induction are adopted to analyze the deformation process of the section of bar. The equation of residual curvature and the unified equation of residual curvature are established. It is proved that although the initial curvature of each section of bar is different, the difference of initial curvature is eliminated by the reciprocating bending, and the process mechanism of the two-roller straightening is revealed. The speed of curvature unification is determined mainly by the ratio of plastic modulus to elastic modulus. The greater the ratio of plastic modulus to elastic modulus is, the slower the speed of curvature uniformity is, and the more the bending time required. Then, the quantitative analysis model and finite element model of the two-roller straightening process are established by taking the threesection constant curvature roller gap model as an example. The stress, strain, and straightness are discussed, and the variation of the elastic area ratio, the residual curvature, and the residual deflection with the bending time is quantitatively analyzed. The results verify the process mechanism of the tworoller straightening, and the design principle of roller shape is given. [ABSTRACT FROM AUTHOR]

The numerical simulation of contact problems is nowadays a standard procedure in many engineering applications. The contact constraints are usually formulated using either the Lagrange multiplier, the penalty approach or variants of both methodologies. The aim of this paper is to introduce a new scheme that is based on a space filling mesh in which the contacting bodies can move and interact. To be able to account for the contact constraints, the property of the medium, that imbeds the bodies coming into contact, has to change with respect to the movements of the bodies. Within this approach the medium will be formulated as an isotropic/anisotropic material with changing characteristics and directions. In this paper we will derive a new finite element formulation that is based on the above mentioned ideas. The formulation is presented for large deformation analysis and frictionless contact. [ABSTRACT FROM AUTHOR]

In the thread and spline synchronous rolling (TSSR) process, the thread rolling deformation couples with the spline rolling deformation. The deformation behavior in the synchronous rolling process is very complex due to multi-die constraint, multi-axes motion, and multi-parameter association. Exploring the deformation characteristics in the TSSR process is important for parameter optimization and process control of the TSSR process. In this paper, the finite element method (FEM) was adopted to investigate the deformation in the TSSR process. The data were extracted from FE code DEFORM and were processed in code MATLAB. The deformation characteristics in the TSSR process were studied by mean of analyzing displacement, strain, and invariants of deviatoric stress tensor. The results in the present study indicated that: direction of rotation of workpiece has an influence on the direction of axial displacement in cores of threaded section and splined section; the influence of tooth profiles (such as threaded profile, splined profile) on the TSSR process only presents in the superficial zone; the deformation-affected region along radial direction in the threaded section is larger than that in the splined section; the deformation in the threaded section and splined section has little influence on axial regions. [ABSTRACT FROM AUTHOR]

Ti-6Al-4V alloy is known as a typical difficult-to-machine hard material due to its inherent properties such as low thermal conductivity, low elastic modulus, and high reactivity with cutting tool materials. This paper proposes a two-dimensional coupled thermo-mechanical model of plane strain orthogonal cutting for Ti-6Al-4V alloy deformation near the exit edge. Johnson-Cook material constitutive model and Cockroft-Latham damage criterion are utilized in the model for better understanding the plastic behavior and chips formation during the cutting process. The machining parameters such as cutting speed, tool edge radius, rake angle, and cutting depth are taken into account in the simulation. The results show that an edge defect generates at the exit edge after machining. The edge defect consists of two fracture surfaces, namely, the first fracture surface of opening-mode crack and the second fracture surface of sliding-mode crack. Besides, the edge defect sizes are greatly sensitive to machining parameters. This study provides a better understanding of burr/breakout formation mechanism near the exit surface and optimization of machining parameters in cutting Ti-6Al-4V alloy. [ABSTRACT FROM AUTHOR]

Incremental sheet forming (ISF) is a highly versatile and flexible process for producing low batches of sheet metal parts. Although finite element (FE) method is a key approach in the study of material deformation in metal forming processes, the application of FE in ISF process is still limited. This is due to the enormous simulation time required for ISF processes. Focusing on this problem, this paper presents a new selective element fission (SEF) approach for simulation of ISF process based on LS-DYNA. In the approach, the computational efficiency is improved by reducing the unnecessary calculations of elements outside the localized deformation zone in the ISF process. The introduction of a background mesh for simulation data storage and a separate simulation mesh with varied mesh density for simulation ensures both the efficiency of computation and accuracy of results. To verify the proposed SEF method, two ISF case problems including a hyperbolic cone part and a pyramid part are studied by comparing to the conventional FE approach and the H-adaptive approach in terms of the CPU time, the forming load, the final part profile, and thickness distribution. The influence of two key factors: element size ratio and toolpath segment length is also studied. The results suggested that the developed SEF approach can save the CPU time by up to 74 % with satisfactory accuracy as compared to conventional FE method, which demonstrates both the effectiveness and robustness of the developed SEF approach. [ABSTRACT FROM AUTHOR]

The development of precision machine tools requires an accurate understanding of the thermal behaviour of the tools. Therefore, by developing highly accurate machine tool thermal behaviour simulations, it can accurately forecast the functional performance of a machine tool at the prototype design stage and provide guidance on its design and performance optimization. To improve the accuracy of the thermal simulation of machine tools, it proposed whole-machine temperature field and thermal deformation modeling and a simulation method for vertical machining centers. Based on the studies of thermal-structure coupling finite-element data flow and its critical conditions, it also proposed design and computational methods for obtaining the heat-source power, when various rotational speeds, the forced convection heat transfer coefficient between a rotating surface and the air, the combined heat transfer coefficient between a stationary surface and the air/environment, and key contact surface thermal resistances were considered. Furthermore, this paper performed finite-element simulation analysis based on the constructed whole-machine thermal model, and the temperature characteristics and heat deformation mechanism/state were obtained. After comparing the simulation and experimental results, it verified the effectiveness of the finite-element simulation model and the relevant methods and confirmed that the simulation accuracy for both the temperature characteristics and the thermal deformation had been improved significantly, with a simulation error less than 10 %. [ABSTRACT FROM AUTHOR]

As a widely used engineering material, optical glass is very difficult to process because of its high hardness and brittleness. The material removal mechanism still needs further investigation. In this paper, a mesh-free simulation method—smooth particle hydrodynamics (SPH)—is introduced and an ultra-precision cutting model for K9 glass is provided. Compared with conventional finite element method, the SPH method can effectively avoid mesh distortion when dealing with large deformation problems such as cutting. Several numerical simulations were carried out to further investigate the critical value of transition. Simulation results indicate that when cutting depth is small enough, the K9 glass can be machined in ductile mode and a relatively smooth machined surface without crack can be obtained. The chip is always in irregular and discontinuous way no matter what the cutting mode is. Three cutting tools with different rake angle were used in simulation and the effect of rake angle is analyzed. [ABSTRACT FROM AUTHOR]

In the current metal-forming industries, productivity, product quality, and production cost are three overriding issues. Product quality, however, is the most critical issue and the designed forming process must be able to produce the quality parts with desirable geometries and without defects. In micro- and meso-forming processes, the formation mechanism of flow-induced defects has not yet been fully investigated. In this paper, the flow-induced defects in meso-forming of a designed part are investigated and the defect formation mechanisms are explored and revealed via the finite element simulation of the entire process. To develop a defect-free forming process, a feature-based method for defect-free process design is proposed to identify the best forming sequence/process for defect-free deformation. By employing the proposed method, two meso-forming processes, viz., four steps extrusion and backward extrusion, are proposed to fabricate the designed part without folding defects. The applicability of the meso-forming processes for defect avoidance is verified by numerical simulation and physical experiment. The experiments also corroborate the findings of finite element simulations. On the other hand, the proposed feature-based method is further verified by the effectiveness of the generated two meso-forming processes for their efficiency in forming of the meso-scaled part without the flow-induced defects. [ABSTRACT FROM AUTHOR]

Welding deformations play an important role in sealing capabilities and service life of welded pipe-flange joints. A numerical procedure for modeling of tack welds in girth butt-welding of such joints is of vital importance for the prediction of transverse shrinkage and flange face deformation, which is directly related to the joint sealing capability. This paper presents a 3-D finite element simulation of a pipe-flange joint to describe the numerical procedure for modeling of tack welds in circumferential joints. Sequentially coupled nonlinear transient thermo-mechanical analysis is performed to simulate Metal Inert Gas (MIG) welding. Single pass butt weld geometry with single “V” for 100 mm nominal diameter pipe with same sized weld neck type ANSI flange of class no. 300 is used. Temperature dependent material properties are used and deposition of filler metal is obtained by element birth and death feature. The peak temperature of the tack during the butt-welding of the tacked model is concluded a key parameter for numerical prediction of deformations, whereas tack temperature has negligible effect on the residual stresses. [ABSTRACT FROM AUTHOR]