多工位冲孔冲形落料级进模

本文运用超料厚小孔模具的工作原理加工照相机夹板,把单一的冲孔发展到多工位的级进模上,通过对模具特点的系统分析,着重阐述了模具的结构,级进模中的定距块的改进,双侧刃定距和临时导正销的作用,以及侧刃粗定位和导正销定位相结合的定距方法,圆形凸模和非圆形凸模的固定方法,模具限位钉的安装,模具的润滑,浮动弹性顶料装置的改进等特点。

Forming defects in aluminum alloy hot stamping of side-door impact beam

The forming defects, including thinning, rupture, wrinkling and springback, usually arising in producing a side-door impact beam, were investigated by trial and numerical simulation. A temperature-related constitutive model specific to the temperature range from 350 °C to 500 °C was established and used for the numerical simulation. The trial and numerical simulation were conducted to clarify the quantitative characteristics of forming defects and to analyze the effects of process parameters on the forming defects. Results show that the rupture situation is ameliorated and the springback is eliminated in the aluminum alloy hot stamping. The wrinkling severity decreases with increasing blank holder force (BHF), but the BHF greater than 15 kN causes the rupture at the deepest drawing position of workpiece. The forming defects are avoided with lubricant in the feasible ranges of process parameters: the BHF of 3 to 5 kN and the stamping speed of 50 to 200 mm/s.

Formability of aluminum-silicon coated boron steel in hot stamping process

Flow behavior of the Al-Si coated boron steel was investigated with Gleeble-3500,in comparison with the uncoated one.Effect of deformation conditions on the coating integrity was characterized by optical microscopy.Facture surfaces of the coated steels were inspected under SEM.Experimental results indicate that the ultimate tensile strength and ductility of the Al-Si coated boron steel are lower than those of the uncoated steel under test conditions.Extensive cracks occur in the coating after tensile tests;the width and density of cracks are sensitive to the deformation temperatures and strain rates.The bare substrate exposed between the separate coating segments is oxidized.Appearance of the oxide degrades the Al-Si coating adhesion.Remarkable difference between formability of the coating layer and the substrate is confirmed.The formability of the Al-Si coating could be optimized by controlling the phase transformation of the ductile Fe-rich intermetallic compounds within it during the austenization.

Numerical simulation and optimization of process parameters in fineblanking process

Fineblanking process is a typical large localized plastic deformation process. Based on its forming characteristics, a numerical model is established and an elasto-plastic simulation is performed using the finite element method （FEM）. The re-meshing method is used when the severe element distortion occurs to facilitate further computation and avoid divergence. The McClintock fracture criterion is adopted to predict and determine the time and site of crack initiation and propagation. Based on this numerical model, the distribution and developing trend of the stress and strain in the shearing zone are predicted. Furthermore, the influence of several process parameters, such as punch-die clearance, edge radius of punch and die, V-ring force, counter force, etc., on the blanked quality is analyzed. The discipline is in accordance with the actual manufacture situation, which can be a guidance to optimization of process parameters.

链环钩加工新工艺

应用连杆机构一次可以将链环钩冲成形 ,克服杆件在弯曲中的反弹 ,设计简单的胎膜具 ,合理安排下料 ,冲形、整形 ,车削过扣工序 。

Effect of microstructure on impact toughness of magnesium alloys

Microstructures of as-cast and extruded ZK60-xRE （RE=Dy, Ho and Gd, x=0-5, mass fraction） alloys were investigated. Meanwhile, the impact toughness was tested and then the relationship was discussed. The results show that as-cast microstructure is refined gradually with increasing the RE content. Mg-Zn-RE new phase increases gradually, while MgZn2 phase decreases gradually to disappear. Second phase tends to distribute along grain boundary in continuous network. Extruded microstructure is refined obviously to reach the micron level. Broken second phase tends to distribute along the extrusion direction in zonal shape. Impact toughness value -nK increases from 9-17 J/cm2 for as-cast state to 26-54 J/cm2 for extruded state. With increasing the value of -nK, fracture macro-morphology changes from a rough plane via multi-plane with step to V-type plane; and from single radiation zone to two zones of fiber and shear lip, respectively. Fracture micro-morphology changes from the brittle fracture to the ductile fracture. Fine grain and few fine dispersed second phase can enhance the impact toughness of magnesium alloys effectively.

Dynamic Response of Stepped Beams Under Impulsive Loading

Aim To analyze dynamic failure of aerospace strutures subjected lateral impulsive loading. Methods Structures were modeled as rigid-perfectly plastic free-free stepped beams. Basic equations of motion un set up for analysis. Results Final pat deformation and rigid motion solutions were determined for a uniform impulsive loading. The critical rupture conditions for a space shuttle and a missile were obtained. Conclusion Failure is possible for aerospace structures under a uniform impulsive loading, but it is mere difficult in space.

Seismic facies response of tectonics and direction of block movement in the northeastern South China Sea

The close relationship between the structure,evolution,and resources environment of the South China Sea is a current research focus and also a focal point of our study.In this paper,we use regional seismic sections to analyze the relationship between seismic facies and the structure and tectonic evolution of the northeastern South China Sea and propose new points about the structure and the direction of block（land mass） motion.First,the tectonic features are clear and can be divided into five different structural units which are both linked and independent of each other.Second,it doesn＇t matter if the South China Sea basin pattern is extensional,weakly compressive,or strongly compressive,the regional tectonic stress field is unified.For the first time we find that two shallow subduction zones are recognized in the seismic profiles.All the tectonic blocks have accordion-fold-style structures,converging in the east,and the South China Sea exhibits different stages of basin development：growth, maturity,end,and termination.The block subduction and regional block dip directions are all aligned with the regional stress field.

Effect of friction coefficient in deep drawing of AA6111 sheet at elevated temperatures

The effect of friction coefficient on the deep drawing of aluminum alloy AA6111 at elevated temperatures was analyzed based on the three conditions using the finite element analysis and the experimental approach.Results indicate that the friction coefficient and lubrication position significantly influence the minimum thickness,the thickness deviation and the failure mode of the formed parts.During the hot forming process,the failure modes are draw mode,stretch mode and equi-biaxial stretch mode induced by different lubrication conditions.In terms of formability,the optimal value of friction coefficient determined in this work is 0.15.At the same time,the good agreement is performed between the experimental and simulated results.Fracture often occurs at the center of cup bottom or near the cup corner in a ductile mode or ductile-brittle mixed mode,respectively.

Broadband Vibrational Cooling of Cold Cesium Molecules： Theory and Experiments

The use of a broadband, frequency shaped femtosecond laser on translationally cold cesium molecules has recently demonstrated to be a very efficient method of cooling also the vibrational degree of freedom. A sample of cold molecules, initially distributed over several vibrational levels, has thus been transfered into a single selected vibrational level of the singlet X^1∑g ground electronic state. Our method is based on repeated optical pumping by laser light with a spectrum broad enough to excite all populated vibrational levels but limited in its frequency bandwidth with a spatial light modulator. In such a way we are able to eliminate transitions from the selected level, in which molecules accumulate. In this paper we briefly report the main experimental results and then address, in a detailed way by computer simulations, the perspectives for a ＂complete＂ cooling of the molecules, including also the rotational degree of freedom. Since the pumping process strongly depends on the relative shape of the ground and excited potential curves, ro-vibrational cooling through different excited states is theoretically compared.

Local Scour and the Laws of Scour Pit's Shape Downstream of Debris Flow Sabo Dam

The erosion shape and the law of development of debris flow sabo dam downstream is a weak part in the study on debris flow erosion. The shape and development of scour pit have an important effect on the stability and safety of debris flow sabo dam, which determines the foundational depth of the dam and the design of protective measures downstream. Study on the scouring law of sabo dam downstream can evaluate the erosion range and reasonably arrange auxiliary protective engineering. Therefore, a series of flume experiments are carried out including different debris flow characteristics （density is varying from 1.5 t/m3 to 2.1 t/m~） and different gully longitudinal slopes. The result shows that the scour pit appears as an oval shape in a plane and deep in the middle while superficial at the ends in the longitudinal section, the position of the maximum depth point moves towards downstream with an increase of flume slope angle. The maximum depth of scour pit is mainly affected by the longitudinal slope of gully, density of debris flow, and the characteristics of gully composition （particle size and the viscosity of soil）. The result also indicates that the viscosity of soil will weaken the erosion extent. The interior slopes of scour pit are different between the upstream and the downstream, and the downstream slope is smaller than the upper one. For the viscous and non-viscous sands with the same distribution of gradation, the interior slope of non- viscous sand is smaller than the viscous sand.According to tbe regression analysis on the experimental data, the quantitative relationship between the interior slope of scour pit, slope of repose under water and the longitudinal slope of gully is established and it can be used to calculate the interior slope of scour pit. The results can provide the basis for the parameter design of the debris flow control engineering foundation.

Calculating changes in fractal dimension of surface cracks to quantify how the dynamic loading rate affects rock failure in deep mining

The split-Hopkinson pressure bar(SHPB)and digital image correlation(DIC)techniques are combined to analyze the dynamic compressive failure process of coal samples,and the box fractal dimension is used to quantitatively analyze the dynamic changes in the coal sample cracks under impact load conditions with different loading rates.The experimental results show that the fractal dimension can quantitatively describe the evolution process of coal fractures under dynamic load.During the dynamic compression process,the evolution of the coal sample cracks presents distinct stages.In the crack propagation stage,the fractal dimension increases rapidly with the progress of loading,and in the crack widening stage,the fractal dimension increases slowly with the progress of loading.The initiation of the crack propagation phase of the coal samples gradually occurs more quickly with increasing loading rate;the initial cracks appear earlier.At the same loading time point,when the loading rate is greater,the fractal dimension of the cracks observed in the coal sample is greater.

Hot shear deformation constitutive analysis of fine-grained ZK60 Mg alloy sheet fabricated via dual equal channel lateral extrusion and sheet extrusion

Dual equal channel lateral extrusion(DECLE)process with various passes followed by sheet extrusion process was performed to produce fine-grained ZK60 alloy sheets.The coarse grain structure of the annealed sample after applying sheet extrusion(size:68μm)changed to fine grains of 6.0 and 5.2μm after 3 and 5 passes of DECLE and following extrusion.The hot shear deformation behavior of samples was studied by developing constitutive equations based on shear punch test(SPT)results.SPT was carried out in the temperature range of 200−300℃ and strain rate range of 0.003−0.33 s^(–1).The activation energy of 125−139 kJ/mol and the stress exponent of 3.5−4.2 were calculated for all conditions,which indicated that dislocation creep,controlled by dislocation climb and solute drag mechanism,acted as the main hot deformation mechanism.It was concluded that material constants of n and Q are dependent on the microstructural factors such as grain size and second phase particle fraction,and the relationship of which was anticipated using a 3D surface curve.Moreover,the similar strong basal texture of extruded sheets gave rise to the same deformation mechanisms during SPT and similar n and Q values for ZK60 alloy.

A Review on Fiber Lasers

After a half century of development, fiber laser has evolved from a concept to a great family penetrating into various fields of applications. This paper reviews the history and current development of fiber lasers, with topics covering both continuous wave and short pulse fiber lasers. Important issues such as the major rare earth dopants, fiber laser brightness, polarization effects, clad pumping technology, beam combination, mode locking and pulse shaping are discussed in this paper.

Efficient energy absorption of functionally-graded metallic foam-filled tubes under impact loading

The deformation behavior and crashworthiness of functionally-graded foam-filled tubes(FGFTs)under drop-weight impact loading were investigated.Closed cell aluminum,A356 alloy and zinc foams fabricated by the liquid state processing were used as axial grading fillers for the manufacture of single-layer and multilayer structures with different configurations.The results indicate that the deformation of multilayer foam filled tubes initiates from the low-strength components,and then propagates in the high-strength components through the gradual increment of stress.The use of more A356 alloy and aluminum foam layers provides greater specific energy absorption(SEA)for the graded structures,whereas the high-strength zinc foam has no positive effect on the crash performance.The progressive collapse of graded structures consisting of the aluminum and A356 alloy foams occurs in a symmetric mode under quasi-static and drop-weight impact conditions.However,the zinc foam causes a combination of symmetric and extension modes as well as greater localized deformation under dynamic loading and greater local rupture in quasi-static loading condition.The Al−A356 foam-filled tubes with a combination of the highest SEA(10 J/g)and the lowest initial peak stress(σmax of 10.2 MPa)are considered as the best lightweight crashworthy structures.

Influence of process parameters and defect analysis in hot deep drawing process of aluminum alloy AA6082

In this study, a novel punch toolset was developed to investigate the hot stamping of AA6082-T4 sheet. The effect of the process parameters, including forming temperature, punching velocity, friction coefficient, and blank holder force(BHF) on formability was quantified using Taguchi design, analysis of variance(ANOVA) and mathematical statistics. The finite element(FE) model has been established in software Pamstamp for simulation and analysis of their effects on the minimum thickness and thickness variation of the hot-stamped component. The major factors influencing the minimum thickness of the hot-stamped part has been found to be BHF and friction coefficient with influence significance of 35.3% and 34.88%, respectively. Additionally, punch velocity and BHF affect the thickness deviation significantly with influence significance of 40.43% and 35.42%, respectively. Furthermore, a serious thinning occurs on the punch corner region of the hot-stamped cup when the BHF is larger than 2.4 kN. The thickness deviation of the hotformed cup has been found to be firstly decreased and then increased with the increase of punch velocity. Low friction coefficient between punch and blank led to crack at bottom centre of the cup. Moreover, different type, phenomenon and mechanism of defects occurring during hot stamping process, such as crack and wrinkling, were discussed. The crack mode was dimple-dominated ductile fracture, which was induced by micro-void nucleation, growth and coalescence.

Multi-objective optimization of stamping forming process of head using Pareto-based genetic algorithm

To obtain the optimal process parameters of stamping forming, finite element analysis and optimization technique were integrated via transforming multi-objective issue into a single-objective issue. A Pareto-based genetic algorithm was applied to optimizing the head stamping forming process. In the proposed optimal model, fracture, wrinkle and thickness varying are a function of several factors, such as fillet radius, draw-bead position, blank size and blank-holding force. Hence, it is necessary to investigate the relationship between the objective functions and the variables in order to make objective functions varying minimized simultaneously. Firstly, the central composite experimental(CCD) with four factors and five levels was applied, and the experimental data based on the central composite experimental were acquired. Then, the response surface model(RSM) was set up and the results of the analysis of variance(ANOVA) show that it is reliable to predict the fracture, wrinkle and thickness varying functions by the response surface model. Finally, a Pareto-based genetic algorithm was used to find out a set of Pareto front, which makes fracture, wrinkle and thickness varying minimized integrally. A head stamping case indicates that the present method has higher precision and practicability compared with the "trial and error" procedure.

Characteristic test of analog integrated circuit frequency

This paper presents an analog circuit built-in-test （BIT） structure based on boundary scan and realizes the BI＇I. It predigests the test process and improves the test precision by taking the rectangular pulse as stimulator and analog switch as auxiliary bridge. The experiment of uA741 shows that the design is feasible. Compared with the traditional test method, it is better regarding reliability and measurability of the analog circuit system.

Congenital left ventricular aneurysms and diverticula： an entity in search of an identity

Congenital left ventricular aneurysm or diverticulum are rare cardiac malformations described in 809 cases since the first description in 1816, being associated with other cardiac, vascular or thoraco-abdominal abnormalities in about 70%. It appears to be a developmental anomaly, starting in the 4th embryonic week. In an experimental study, targeted knockdown of cardiac troponin T in the chick was performed at day 3, after the heart tube has formed. Morpholino treatment of gene TNNT2 at this stage led to the development of left ventricular diver- ticula （LVD） in the primitive left ventricular wall. Diagnosis of left ventricular aneurysms （LVA）/LVD can be made after exclusion of coro- nary artery disease, local or systemic inflammation or traumatic causes as well as cardiomyopathies. Clinically, most of LVA and LVD are asymptomatic or may cause systemic embolization, congestive heart failure, valvular regurgitation, ventricular wall rupture, ventricular tachycardia or sudden cardiac death. Diagnosis is established by imaging studies （echocardiography, magnetic resonance imaging or left ventricular angiography） visualizing the structural changes and accompanying abnormalities. Mode of treatment has to be individually tai- lored and depends on clinical presentation, accompanying abnormalities and possible complications, options include surgical resection （espe- cially in symptomatic patients）, anticoagulation after systemic embolization, radiofrequency ablation or implantation of an implantable car- dioverter defibrillator （ICD） in case of symptomatic ventricular tachycardias, and occasionally combined with class I- or III-antiarrhythmic drugs. Cardiac death occurs usually in childhood, is significantly more frequent in LVA patients and caused by congestive heart failure in most of the cases, whereas patients diagnosed with LVD died more frequently from rupture of the LVD.