Modelling of part shape and deformation evolution in the conventional forming of large sheet-metal components

This paper deals with algorithms implemented in production software used for the modelling of conventional three-piece die sheet-forming processes. The topics considered are the CAD interface, the initial evaluation of forming severity based on an “ideal deformation” algorithm, the development of addendum surfaces, the application of finite-element algorithms for the calculation of the binder wrap surface and the blank shape, the interactive control of material flow during die design, and die try-out simulation.     

Thermoelectric properties of ScCoSb, ScNi0.86Sb and MgNiSb compounds

Blends of 90 wt.% Ti and 10 wt.% W powders were consolidated by powder metallurgy, using an initial W powder size that was very fine (0.7 and 2 μm) or very coarse (<250 μm). Dissolution of W powders in the Ti matrix during consolidation was almost complete for the former blends (thus forming Ti–10W “alloys”) but very limited for the latter blend (thus forming a Ti–10W “composite”). The Ti–10W alloys exhibit much higher yield and tensile strengths than the Ti–10W composite, indicating that tungsten strengthens titanium more efficiently as a solute atom (solid-solution strengthening) than as a second phase (composite strengthening by load transfer). The Ti–10W alloys also exhibit much higher ductility than the Ti–10W composite, whose brittle W particles exhibit fracture or pull-out from the matrix.     

Development of optimum process design system by numerical simulation

Now, the development of optimum forming process design system based on computer simulation to reduce the time consumption is strongly required in the industries. In this study, the optimum process design system is newly developed in conjunction with the nonlinear FEA code and the nonlinear optimization code. In the latter code, “Sweeping Simplex Method” is newly proposed, which can find the global minimum. The accuracy and quickness of this method to find the global minimum of objective function, which have several local minimum points, is confirmed by comparison with the grid method.

This numerical system is applied to the process design of complicate shaped cup deep drawing. In order to form the sheet metal with uniform thickness, “Deviation of thickness from uniform average thickness” is employed as the objective function, and the global minimum point in the design variable space is searched by “Sweeping Simplex Method”. For the design variables, the heights of two punches in first stage forming are employed. The optimum process condition was determined by using this numerical code and also the validity of this code was confirmed by the comparison with the experimental observation results.     

Two novel rolling processes of porous metal preforms prepared by spray deposition technique using conventional rolling mill

For the spray deposited preforms with the porosity up to 10–15%, densification processing is necessary to produce fully dense products. In this paper, two novel processes named as “Frame-Confined Rolling” and “Ceramic Rolling” are presented. The experimental results show that these two methods can improve the workability of the porous preforms without forming cracks on surface and edge during rolling.     

On the influence of fibre texture on the compression creep behaviour of a short fibre reinforced aluminium alloy

The creep behaviour of Al–Zn/8 vol.% “Saffil” metal matrix composites (MMCs) with a random planar fibre texture (“fibre plane”) was found to depend on the orientation of the fibre plane with respect to the loading axis and on the sign of the applied load. The results are discussed and compared to findings for MMCs with higher volume fractions.     

Pressured-assisted injection forging of thick-walled tubes

Numerous engineering components may be created in a hollow form without detracting from their performance requirements; the difficulty, however, is in the conversion of tubular materials into such components. Hollow components may be formed from tubular materials if these can be prevented from collapsing during the forming cycle. Further, die-filling during injection forging, is especially difficult at the terminal stages of the process; the use of a pressurising medium within the material could effect die-filling more effectively.The scope for the forming of thick-walled tubes into hollow components was investigated using different pressurising media to support the material during the forming cycle. A tubular hexagonal form was the basis for the evaluation of the forming requirements of the process. Several pressurising-media were tested experimentally to determine suitability and the process was stimulated using FE techniques to establish the “optimal” processing sequence.The pressurising-medium influences the forming sequence for the production of a component of acceptable quality. The forming sequence has three distinct stages. Injection forging of the tube has to be proceeded by an initial internal pressurisation while subsequent injection has to be matched by increases in pressurisation; the final stage is characterised by a rapid increase in pressurisation to complete the filling of the die. Failure to establish the correct sequence will result in different forms of failures; the correct sequence will enable the production of a component of “uniform” wall-thickness.     

Hole flanging with cold extrusion on sheet metals by FE simulation

Flange height and lip thickness are generally restricted by the formability of sheet metals in the conventional hole flanging operation. In the current work, cold extrusion was applied and a special forming die set was designed with a stripper subjected to counter-pressure with an aim to obtain a more substantial flange. FEM software DEFORM was utilized to simulate this flange extrusion process with two forming conditions: forming with a fixed die cavity and forming with the stripper subjected to counter-pressure. The results showed the cup preform tended to buckle on its bottom with insufficient counter-pressure. The cup preform would start extruding a flange when critical counter-pressure was reached. The magnitude of the critical counter-pressure increased in flange extrusion of smaller inner diameters. The corresponding overall forming load was greatly reduced as compared to flange extrusion with a fixed die cavity.     

Tool wear monitoring and breakage detection based on “intelligent filtering”

Several physical quantities can be used for indirect tool wear monitoring and breakage detection. Cutting forces are appropriate, since they determine the suitability of a tool for cutting. However, disturbances make the accurate and fast tool condition monitoring based upon force analysis difficult. To eliminate disturbances averaging or filtering within a predetermined bandwidth has often been applied. A new method of decomposing the force signal into components having close relationships with physical phenomena taking place during cutting is presented. The term “intelligent filtering” denotes decomposition based on on-line identification of model(s) of the cutting process. Application of “intelligent filtering” for the milling process with two cutting insert tools is discussed.     

H型钢质量缺陷成因分析及控制策略

采用异形坯轧制的H型钢表面存在腹板裂纹、腹板凹坑、翼缘烂钢和R角裂纹等缺陷,通过金相显微镜组织观察、SEM观察及能谱测定、异形坯开坯后温度场ANSYS数值模拟等手段对裂纹形成机制分析。认为H型钢腹板裂纹形成主要与异形坯R角附近纵裂有关,腹板麻面形成主要与皮下气泡和加热炉加热制度有关,翼缘烂钢主要与保护渣卷渣有关,R角裂纹主要与BD-Ur-E-Uf轧制过程温度场梯度大导致应力差异性大有关。针对成因提出了改进措施。     

Prediction of surface roughness profiles for milled surfaces using an artificial neural network and fractal geometry approach

Artificial neural networks (ANNs) models were developed for the analysis and prediction of the relationship between the cutting conditions and the corresponding fractal parameters of machined surfaces in face milling operation. These models can help manufacturers to determine the appropriate cutting conditions, in order to achieve specific surface roughness profile geometry, and hence achieve the desired tribological performance (e.g. friction and wear) between the contacting surfaces. The input parameters of the “ANNs” models are the cutting parameters: rotational speed, feed, depth of cut, pre-tool flank wear and vibration level. The output parameters of the model are the corresponding calculated fractal parameters: fractal dimension “D” and vertical scaling parameter “G”. The model consists of three-layered feed-forward back-propagation neural network. ANNs models were utilized successfully for modeling and predicting the fractal parameters “D” and “G” in face milling operations. Moreover, W–M fractal function was integrated with the developed ANNs models in order to generate an artificially fractal predicted profiles at different cutting conditions. The predicted profiles were found statistically similar to the actual measured profiles of test specimens.     

H型钢立辊轴心可变式万能轧制法的实验研究

将万能轧机的立辊轴心向出口侧移动的轧制法，翼缘宽展量增加约６．４％，平辊轧制力减少１２％，且板形得到改善     

Compatibility stresses in fatigued bicrystals: Dependence on misorientation and small plastic deformations

Compatibility stresses are calculated for twist boundaries about [1¯49] and a “random” high angle boundary between a [1¯49] grain and a [100] grain, assuming piecewise homogeneous elastic fields and copper as model material. The “in-plane” compatibility stresses produced by uniaxial tension perpendicular to the boundary are a strong function of the crystallography of the grains and their misorientation. The effects of small plastic strains via crystallographic slip are also studied for three particular misorientations ([1¯49] 90° and 180° twist boundaries and the “random” misorientation) and the type and amount of slip close to the boundary predicted by minimizing the elastic energy and using experimental measurements of the axial component of the plastic strain. The predictions agree quite well with experimental observations of slip traces close to the boundaries of copper bicrystals with those misorientations tested under high cycle fatigue conditions.     

基于分流法的大模数半轴伞轮冷精锻工艺研究

针对半轴圆锥直齿轮冷锻载荷大、模具寿命低、齿腔难充填等技术难题,采用分流法的封闭式锻造工艺冷锻半轴圆锥齿轮。研究了型腔充填规律、载荷曲线特点等,并分析了模具运行方式、冲孔连皮位置、坯料尺寸对成形结果的影响。结果表明：分流法能大幅度地降低成形载荷;闭塞式锻造工艺对成形结果没有改善;冲孔连皮的位置及坯料直径对成形结果影响较大。     

Development of an applied roll forming pass design expert system based on the shape element idea

A new design idea, based on the “shape element”, is introduced to develop a roll forming pass design expert system. Shape elements recognizing knowledge base, bend angle distribution knowledge base, rolls arranging knowledge base and related reasoning engines are constructed in the system by using object-oriented method. Pass flower and rolls design can be automatically done. Some examples show that this expert system is practical and effective.     

Micro-machinability of monocrystal silicon by direct etching using excimer laser

The high flexibility of laser direct writing and its potential capability of fabricating micro-mechanical structure are discussed. Aiming at providing knowledge for micro-engineering application, experiments on direct etching of monocrystal silicon with focusing KrF excimer laser beam (λ = 248 nm) were carried out. The validity of non-thermal excimer laser material processing was examined by SEM observation on the “heat-affected zone (HAZ)”. An empirical formula establishing the relationship of etching depth versus laser energy per pulse and the number of laser pulses has been derived from the experiments. Impact damage at the underside of silicon wafer has been observed. Its relevant causes are analyzed.     

H型钢轧制翼缘不同压下量的应力应变分析

应用ＭＡＲＣ软件并对其进行二次开发, 建立了Ｈ 型钢轧制模型, 在腹板相对压下量不变条件下研究了翼缘不同的压下量对轧制过程中应力应变的影响。增大翼缘压下量可改善腹板的力学性能, 同时使翼缘的力学性能下降。     

Cutting performance of thick web drills with curved primary cutting edges

In order to improve the cutting performance of drills, a thick web drill with curved primary cutting edges was devised. The curved primary cutting edge was mathematically determined by changing the distribution of the tool orthogonal rake angle along the primary cutting edge. A three-dimensional finite element analysis based on the torsional rigidity of the drill was applied to obtain the “secondary” flute shape of the drill with curved primary cutting edges and to specify the web thickness. Experiments were conducted to evaluate the drill's cutting performance. Compared with conventional twist drills of different web thicknesses, the thick web drill with curved primary cutting edges shows greater effectiveness in reducing the thrust force, the torque, and the tool wear, thus providing a better cutting ability and a longer tool life.     

Ring rolling process simulation by the three dimensional finite element method

The finite element code “RING” was developed for the analysis of ring rolling. A special feature of the program is the updating procedure in three-dimensional deformation. A spatially fixed mesh system including deforming region of the workpiece is constructed based on the shape changes of the ring at each time step. Several simulations are performed with the program “RING”, and the results are compared with experimental data found in the literature. Good agreement between the simulation results and experiments was obtained in terms of geometrical changes of rings in plain ring rolling and T-shaped profiled ring rolling.     

Servo design of a vertical axis drive using dual linear motors for high speed electric discharge machining

This paper proposes a synchronous control scheme for a linear servo system applied to the vertical axis drive of a die-sinking electric discharge machine (EDM) tool. The investigated vertical axis drive is constructed with dual parallel linear motors, which are arranged to jointly drive the feed axis for improvement of the overall thrust and structural stiffness. A pneumatic cylinder is employed to compensate the gravitational effect of the feed axis with its electrode and holder. A mechanical coupling is designed to firmly bridge the two linear motors and carry the feed axis. Therefore, synchronous control for the motors is critical for not only position accuracy, but also machine safety. Moreover, by controlling the thrust outputs and positions of the motors to be as equal as possible, the potential “pull and drag” effect between the motors can be reduced and loads can also be equally shared. The proposed “position/thrust hybrid synchronous control” scheme is applied to the EDM to achieve high-speed, accurate machining, and the experimental results show that the synchronization error between the two parallel motors and the positioning accuracy are both satisfactory when operated under high-speed conditions.     

On the extrusion of silver-sheathed superconducting billets fabricated by explosive compaction of YBa2Cu3O7 powder

Explosive compaction of YBa₂Cu₃O₇ superconducting powder and forward extrusion of the produced “green” billet were employed to fabricate high critical temperature, T_c, superconducting composite rods consisting of a superconducting YBa₂Cu₃O₇ core and a silver metallic sheath. Experimental observations regarding the “soundness” of the fabricated component with respect to the compacting and processing conditions used as well as to the properties of the superconducting powder are reported. Microstructural and stochiometric changes and defects occuring in the “green” compacted billet and the extruded rod are indicated and discussed.