A Study on Super Speed Forming of Metal Sheet by Laser Shock Waves

Metal sheet plastic deformation or forming is gener at ed through a mechanical pressure or a thermal variation. These pressure variatio ns or thermal variations can be created by a variety of means such as press form ing, hydroforming, imploding detonation and so on. According to the magnitude of the strain rates all these forming methods can be divided into quasi-static fo rming and dynamical forming. Up to now there are no reports of forming methods w ith the strain rates above 10 5sec -1, even though the exploding forming. In this article, we work on a dynamic super-speed forming method driven by lase r shock waves and advanced a novel concept of laser shock forming. The initial o bservation of the laser shock forming is done through a bugle testing with speci mens of SUS430 sheet metal, using a neodymium-glass laser of pulse energy 10J～ 3 0J and duration of 20 ns (FWHM). The investigation revealed that the plastic de formation during the laser shock forming is characterized as ultrahigh strain ra te up to 10 7sec -1. We indicate that plastic deformation increases nonlin early when the energy density of the laser varies. By investigating the hardness and residual stress of the surfaces, we conclude that laser shock forming is a combination technique of laser shock strengthening and metal forming for introdu cing a strain harden and a compressive residual stress on the surface of the wor k-piece, and the treated surface by laser shock forming has good properties in fatigue and corrosion resistance. This technique can achieve forming wit h or without mould.

Numerical simulation of temperature field in plasma-arc flexible forming of laminated-composite metal sheets

Flexible forming of laminated-composite metal sheets (LCMS) using plasma arc is a latest technique, which produces LCMS components by thermal stress without mould and external force. Considering that the controllable temperature field is the key during the forming process, a three-layer FEM model, based on the characteristics along LCMS thickness direction, was developed to study the variation rules of temperature field, which was verified robustness by experimental validation. Besides, the influences of process parameters such as plasma arc power, scanning speed and plasma arc diameter on LCMS temperature field were performed. The comparisons of LCMS with single layer metal sheet (SLMS) show the temperature difference of LCMS along thickness direction is smaller than that of SLMS, but the heat-affected zone of LCMS along X axis is wider than that of SLMS under the same process parameters.

NUMERICAL MODELLING OF GOLD-ROLLBONDING OF CLAD METAL SHEETS

An analytical model based on the rigid-plastic finite-element formulation for slightly compressible materials is newly proposed to examine the bonding behavior at the roll gap during clad metal sheets rolling. The interfacial elements inserted between the two metals, which are characteristic of the shear-susceptible deformation with the help of the shear factor in the expression of effective strain rate,are used to model the relative slidding at the interface. It is found that the proposed method is applicable to the simulation of clad metal sheets rolling.

Flexible-die forming process with solid granule medium on sheet metal

Certain non-metallic granules （NMG） were selected as the research object. It was proposed to conduct the volume compression experiments as well as those on the NMG physical properties at high stress levels. Then, not only the volume compression ratio curve but also the extended Drucker-Prager linear model were obtained. In addition, through the friction strength tests, parameters of the Mohr-Coulomb model were gained, which proved in basic agreement with those of the extended Drucker-Prager linear model. Additionally, curves of the friction coefficients between the NMG and the sheet metal trader different pressures were also obtained. Based on the material performance experiments, numerical analysis in respect of flexible-die forming process with solid granule medium （SGM） was conducted. The die and device for experiments of solid granule medium forming （SGMF） on sheet metal were designed and manufactured. Typical parabolic parts were successfully trial-produced. The tests and simulation results show that the sheet formability is significantly improved for the extraordinary friction performance during interaction between the SGM and the sheet metal surface. The process control and die structure are simple, and the shaped work-pieces enjoy many advantages, such as satisfactory surface quality and favorable die fitability, which offers a brand-new method and means for processing and preparation of sheet metals.

Sheet Metal Forming Simulation and Its Application in Stamping Process of Automobile Panels

The paper starts with a brief overview to the necessity of sheet metal forming simulation and the complexity of automobile panel forming, then leads to finite element analysis (FEA) which is a powerful simulation tool for analyzing complex three-dimensional sheet metal forming problems. The theory and features of the dynamic explicit finite element methods are introduced and the available various commercial finite element method codes used for sheet metal forming simulation in the world are discussed,and the civil and international status quo of automobile panel simulation as well. The front door outer panel of one certain new automobile is regarded as one example that the dynamic explicit FEM code Dynaform is used for the simulation of the front door outer panel forming process. Process defects such as ruptures are predicted. The improving methods can be given according to the simulation results. Foreground of sheet metal forming simulation is outlined.

Establishment of size-dependant constitutive model of micro-sheet metal materials

The inherent mechanism of size effect in micro-sheet material behavior of plastic forming was explained by the surface layer model and theory of metal crystal plasticity. A size-dependant constitutive model based on the surface layer model was established by introducing the scale parameters and modifying the classical Hall-Petch equation. The influence of the geometric dimensions and the grain size on the flow behavior of the material was discussed using the new material constitutive model. The results show that, the flow stress decreases while the sheet metal thickness decreases when the grain size keeps constant, and the micro-sheet metal with a larger grain size is more easily to be influenced by the size effects. The material constitutive model established is validated by the stress-strain curve of the micro-sheet metal with different thicknesses derived from the tensile experiments. The rationality of the material model is verified by the fact that the calculation results are consistent with the experimental results.

Prediction of Failure Modes during Deep Drawing of Metal Sheets with Nickel Coating

To optimize the process parameters, it is necessary to exactly predict failure modes during deep drawing of coated metal sheets, where two main failure forms are fracture and wrinkling. In this paper, finite element simulations based on continuous damage mechanics were used to study the failure behavior during a cylindrical deep drawing of metal sheets with nickel coating. It is shown that taking the effect of blank holder force into account, these two failure modes can be predicted. The simulation results are well consistent with that obtained from experiments.

Improved knowledge-based neural network(KBNN)model for predicting spring-back angles in metal sheet bending

We develop an efficiently improved knowledge-based neural network(KBNN)associated with optimization algorithms and finite element analysis(FEA)to accurately predict spring-back angles in metal sheet bending.The well-known V and U prevalent processes of bending are considered.The KBNN predictive results are based on the empirical model and artificial neural network(ANN)modeling.The empirical model is constructed from the FEA results using response surface method,while the multilayer perceptron is employed to create the ANN.The trained KBNN can accurately model the relation-ship between the spring-back angles and process parameters.The obtained results are validated against other existing methods showing a high accuracy.

GENERAL COMPUTER MODEL FOR SHEET METAL DEEP-DRAWING PROCESS

A new comprehensive computer model was developed for sheet metal deep-drawing process, based on the theory of plastic anisotropy and under consideration of the effects of bending, blank-holding force, strain-hardening, the variation of thickness and tooling geometry. The model could be used to simulate the deforming stages of deep-drawing process and get the continuous distributions of stress and strain from the radial drawing region of material over a die and the stretch-forming region of material over a punch. It is concluded that the total strain theory can be used as a substitute for the incremental strain theory to analyse the force and deformation in sheet metal deep-drawing process. In addition, the effect of bending was also obtained.

New Methods Testing of Adhesion of the Coating to Sheet Metal by Bending

The article is deals for new experimental equipment for effective test adhesion for selected coating STEEL, applied cold on the coated metal sheet with Al (aluminum). Explanation to the word STEEL: STEEL coating has significant anti- corrosive properties and he is resistant for main oxidizing agents such as acids, alkalis, salt vapors etc. Resists tem- peratures to 600?C and create an elastic film that is resistant to abrasion, as soon as it was to complete po-lymerization. It is very simple to applied to metallic and nonmetallic surfaces. Dries quickly and is dry to the touch after 90 to 120 seconds. STEEL is the best possible solution anywhere, if needs arises powerful local protection against atmospheric and corrosive agents or to elevated temperatures. STEEL is also useful as a method for protect of welds on stainless steels instead of traditional staining procedures. Broad application is in automotive industry to modify the surfaces of block vehicle, car-body repairs, welds needing protection, in heating industry for example boilers, in air condition with heat exchanger and in shipping industry. [1-3].In experiments with a new test equipment is showed that for bending radius of interval from range R11 to R35 there is a change deposited coating STEEL from original coating Al and this coating was part of test metal sheet of thickness 1.5 mm. In the next stage of solution was developed technological process, which allowed increase of adhesion coating STEEL for bending up to or maximum 180? (shape U). Result of new technology is documented in article. Experiments was implementing with cooperation of the Masaryk University in Brno.

A LOOP DRAWBEAD RESTRAINING FORCE MODEL IN SHEET METAL DEEP DRAWING PROCESS

In sheet metal forming, drawbeads are often used to control uneven material flow which may cause defects such as wrinkles, fracture, surface distortion and springback. Appropriate setting and adjusting the drawbead force is one of the most important pa- rameters in sheet metal forming process control. This paper derives the model of loop drawbead restraining force (DBRF) using plastic forming theory, and gives the min imum blankholding force. Experiments are carried out to verify the proposed DBRF model. The good agreement between the calculated values and experiments data justi- fies the proposed loop drawbead restraining force model.

Multi-Point Forming Technology for Sheet Metal

Multi-point forming (MPF) is an advanced manufacturing technology for three-dimensional sheet metal parts. In this paper, the MPF integrated system is described that can form a variety of part shapes without the need for solid dies, and given only geometry and material information about the desired part. The central component of this system is a pair of matrices of punches, and the desired discrete die surface is constructed by changing the positions of punches though the CAD and control system. The basic MPF process is introduced and the typical application examples show the applicability of the MPF technology. Wrinkle and dimple are the major forming defects in MPF process, numerical simulation is a feasible way to predict forming defects in MPF. In conventional stamping, the mode to form sheet metal with blankholder is an effective way to suppress wrinkling; the same is true in MPF. A MPF press with flexible blankholder was developed, and the forming results indicated the forming stability of this technique. Based on the flexibility of MPF, varying deformation path MPF and sectional MPF were explored that cannot be realized in conventional stamping. By controlling each punch in real-time, a sheet part can be manufactured along a specific forming path. When the path of deformation in MPF is designed properly, forming defects will be avoided completely and lager deformation is achieved. A work piece can be formed section by section though the sectional MPF, and this technique makes it possible to manufacture large size parts in a small MPF press. Some critical experiments were performed that confirmed the validity of two special MPF techniques.

SIX SIGMA OPTIMIZATION IN SHEET METAL FORMING BASED ON DUAL RESPONSE SURFACE MODEL

Iterations in optimization and numerical simulation for the sheet metal forming process may lead to extensive computation. In addition, uncertainties in materials or processing parameters may have great influence on the design quality. A six sigma optimization method is proposed, by combining the dual response surface method （DRSM） and six sigma philosophy, to save computation cost and improve reliability and robustness of parts. Using this method, statistical technology, including the design of experiment and analysis of variance, approximate model and six sigma philosophy are integrated together to achieve improved quality. Two sheet metal forming processes are provided as examples to illustrate the proposed method.

FAST ACCURATE PREDICTION OF BLANK SHAPE IN SHEET METAL FORMING

By using the Finite Element Inverse Approach based on the Hill quadratic anisotrop-ically yield criterion and the quadrilateral element, a fast analyzing software-FASTAMP for the sheet metal forming is developed. The blank shapes of three typical stampings are simulated and compared with numerical results given by the AUTOFORM software and experimental results, respectively. The comparison shows that the FASTAMP can predict blank shape and strain distribution of the stamping more precisely and quickly than those given by the traditional methods and the AUTOFORM.

Uniaxial tensile behavior of porous metal fiber sintered sheet

A novel porous metal fiber sintered sheet （PMFSS） with a three-dimensional reticulated structure was fabricated by multi-tooth cutting and high-temperature solid-phase sintering process with copper fibers. A uniaxial tensile test was conducted to investigate the effect of fiber length and natural aging factor on the tensile properties of the PMFSS. Results indicated that, under given stress, the increase of fiber length helped reinforce the tensile strength. The elongation of the PMFSS with medium length fiber of 15 mm exhibited the optimal performance, reaching about 13.5%. After natural aging treatment for a month, the tensile strength of PMFSS significantly decreased, but the change of elongation was negligible except for the one with the shortest fiber length of 5 mm, whose elongation was effectively improved. The morphological fracture features of PMFSSs were also characterized.

Sheet Metal Forming Optimization by Using Surrogate Modeling Techniques

Surrogate assisted optimization has been widely applied in sheet metal forming design due to its efficiency. Therefore, to improve the efficiency of design and reduce the product development cycle, it is important for scholars and engineers to have some insight into the performance of each surrogate assisted optimization method and make them more flexible practically. For this purpose, the state-of-the-art surrogate assisted optimizations are investigated. Furthermore, in view of the bottleneck and development of the surrogate assisted optimization and sheet metal forming design, some important issues on the surrogate assisted optimization in support of the sheet metal forming design are analyzed and discussed, involving the description of the sheet metal forming design, off-line and online sampling strategies, space mapping algorithm, high dimensional problems, robust design, some challenges and potential feasible methods. Generally, this paper provides insightful observations into the performance and potential development of these methods in sheet metal forming design.

Frictional characteristics of sheet metals with superimposed ultrasonic vibrations

The forming performance of sheet metals in the deep-drawing process with ultrasonic vibrations can be improved by the surface effect between the sheet metal and the die.A sheet metal friction test with ultrasonic vibrations is performed to explore the cause of the surface effect.The frictional characteristics are investigated,and the corresponding friction expressions are established based on the contact mechanics and the elastic–plastic contact model for rough surfaces.Friction is caused by the elastic–plastic deformation of contacting asperities under normal loads.The actual contacting region between two surfaces increases with normal loads,whereas the normal distance decreases.The normal distance between the contacting surfaces is changed,asperities generate a tangential deformation with ultrasonic vibrations,and the friction coefficient is eventually altered.Ultrasonic vibrations are applied on a 40Cr steel punch at the frequency of 20 kHz and the amplitude of 4.2μm.In the friction tests,the punch is perpendicular to the surface of the magnesium alloy AZ31B sheet metals and is sliding with a relative velocity of 1 mm/s.The test results show that the friction coefficient is decreased by approximately 40%and the theoretical values are in accordance with the test values;Ultrasonic vibrations can clearly reduce wear and improve the surface quality of parts.

Process of back pressure deep drawing with solid granule medium on sheet metal

The experimental die apparatus of the solid granules medium forming on sheet metal was designed and manufactured.Typical parts,such as conical,parabolic,cylindrical and square-box-shaped components,were successfully trial-produced as well.According to the analysis of the changing trends of the cross-section shape and the wall thickness during the process,it can be found that the shape of the free deformation zone of the sheet metal,which is the most critical thinning area,can be described as an approximately spherical cap.According to this forming feature,back pressure deep drawing technology with solid granules medium on sheet metal was proposed to restrain drastic thinning at the bottom of the part through the joint friction effect of solid granules medium,the back pressure tringle and the sheet metal.Therefore,the deep drawing limit of the sheet metal is significantly improved.In order to fabricate thin-walled rotary parts with great drawing ratio and complex cross-sections,a finite element model based on the material property test of the solid granules medium was established to optimize the scheme of the back pressure deep drawing.The effects on the forming performance of sheet metal from back pressure load and the approach of blank holding control were analyzed through this model.

DETERMINATION OF BLANK HOLDER FORCE IN SHEET METAL DEEP DRAWING PROCESS

Blank holder force (BHF) is an important measure to control the sheet metal forming. BHF is identified quickly using artificial neural network (ANN) on the basis of its analytical description. And critical rupture and wrinkle BHF curves are given. A close-loop control system is established to finish the forming process.

Simulation and Experiment on Workability for Cold Pressure Forming of Sheet Metal Part with Step Cross-section

In modem manufacturing, a new type of sheet metal part with step cross-section in both inner hole and outer edge is proposed. The traditional stamping separating processes can only produce sheet metal part with vertical cross-section. According to the latest developing theory and potential of cold pressure forming： combination of pressure and cold forging, a new flow control forming of sheet metal（FCF） is excogitated based on blanking process of general stamping and combined with cold forging processes such as extrusion and coining, etc, which is aiming at the above-mentioned new type of sheet metal part. With utilization of this new process, the new type of sheet metal parts can be manufactured. In order to shorten the testing period, the numerical simulation was carried out by using DEFORM-3D software, and both deformation and mechanics rules were analyzed. Based on the simulation, both punching part and blanked parts of this new type were successfully developed. Then a new conception of optimal distance between the step walls of inner hole and outside edge was proposed and the design principle for its numerical value was inferred. Furthermore, a mold set for combination of stamping ＆ cold forging was designed and manufactured, by which the technologic experiments were taken for validation with Aluminum plate of thickness 2.35 mm for power battery cover board, which verified the principle of the distance between the step walls. The research of cold pressure forming of thin sheet metal with step cross-section is significant, not only to the development of modem mechanical manufacture, but also to metal plastic forming science.