Solid Granule Medium Forming Research Articles

FE-DE coupling analysis of AZ31B sheet solid granule medium forming based on GTN model

In order to solve the problem of forming parts with complex shape and small local feature size, solid granules medium forming (SGMF) was adopted. A part of magnesium alloy AZ31B with double-cone shape was taken as an example to analyze the forming process. The parameters of Gurson–Tvergaard–Needleman (GTN) were identified by an inverse method, comparing the experimental results with the numerical results. Based on the GTN model, the coupled finite element and discrete element (FE-DE) method was applied to simulate the forming process of the double-cone part with SGMF technology, and the relevant forming experiments were carried out. The results show that the quality of the workpiece can be improved with different friction coefficient of different area of the part. The fracture behavior and final wall thickness distribution obtained by experiment consist with those by simulation. So, it demonstrates the applicability of the FE-DE method with GTN damage model in analyzing formability of magnesium alloy, and the FE-DE method could embody the medium discrete characteristics fully during SGMF technology.

The mechanical analysis of flexible die drawing for spherical parts based on weight function

With the development of sheet metal forming technology and the increase in the application of spherical shell parts, flexible male die drawing technology has become one of the research hotspots because of its merits on strong applicability and ability to significantly increase the forming limit of the sheet. As a new type of flexible male die drawing process, solid granule medium forming (SGMF) has been rapidly developed in recent years. During the granule medium drawing process, there is a significant reduction in the thickness of the sheet metal in the female die in addition to the flange deformation. Thus, the stress state and the required forming force during the sheet metal forming process are very different from those during the conventional drawing. Taking the deformation process of the spherical shell parts as research object, the stress state of the spherical shell and the pressure of the granule medium were studied between the single drawing deformation and the single bulging deformation. On this basis, the stress model, pressure model, and required forming force model of the spherical shell parts in the granule medium drawing process were established with the drawing weight and bulging weight. Theoretical analysis, experiments, and FEM-DEM numerical simulations were employed to study the deformation of the spherical shell parts. The results show that the mechanical model based on the weight function theory can accurately reflect the stress state of the spherical shell parts during SGMF and can fully reveal the sheet metal deformation mechanism during SGMF. In addition, the theoretical analysis model established in this paper provides necessary theoretical support for the selection of equipment for SGMF process in practical application.

FEM-DEM coupling analysis for solid granule medium forming new technology

Solid Granule Medium Forming (SGMF) is a new flexible die forming technology which uses solid granules as the soft die to form the sheet metal. The process numerical analysis of this technology involves the discrete element (granules) and the continuum solid element (sheet metal), as they belong to different solving system—the discrete element method (DEM) solving system and finite element method (FEM) solving system, now there is no effective simulation ways for this kind of problems. Based on this, this paper established a new FEM-DEM coupling method according to the force conservation principle. And the simulation platform based on this method is developed through Visual Basic, which can realize the interaction, inheritance and transmission of the calculating data between FEM and DEM, with it the problems of elastic-plastic mechanics in the contact between continuum and discontinuum are solved for the first time. Such as the influence laws of the shape and mechanical parameters of discrete object on the plastic deformation of the continuum could be obtained. The limitations and errors brought by using FEM alone to analyze the fission problems are also eliminated by this. Solid granule medium tube outer pressure compression forming is used as a carrier to build the FEM-DEM coupling model, with the simulation platform both the force transmission characteristics and the mesostructure variation rule of solid granule medium in the tube forming process were obtained, and the impacts of technical parameters on the plastic forming property of the tube were analyzed. The accuracy of FEM-DEM coupling method is proved by the forming tests. This article provides an efficient way to solve the coupling deformation problems between the continuum and discontinuum in the field of engineering and a good experience for the solution of complicated engineering problems which need to be worked out with the secondary development of software.

Study on the deformation theory of a parabolic part based on solid granules medium forming

Solid granules medium forming (SGMF), a new flexible die forming technology, uses solid granules instead of a rigid male or female die (or elastomer, liquid) for sheet metal drawing. The good fluidity and compressive capacity of a solid granules medium can improve the forming limit of complex shell parts. The sheet metal drawing process of SGMF is a compound process of drawing and bulging, which is very different from the conventional drawing process. A parabolic part is used as the research object for a study of the forming process. Two concepts, drawing weight and bulging weight, are originally proposed in the sheet metal drawing of SGMF (replacing the rigid male die), and the corresponding expressions are obtained. The computational formulas of geometrical conditions and strain in the sheet metal drawing of SGMF are established, and the radius of the strain dividing circle is obtained by calculation. The established theoretical model is applied to the research object, an aircraft part, to analyze the forming process. The results show that the proposed theory can be applied to analyze the strain in different deformation regions of SGMF. This original theory provides a new theoretical analysis for studying the sheet metal drawing of SGMF.

Frictional characteristics of granular system under high pressure

In order to reveal the force transmission features of the granules in the solid granule medium forming (SGMF) technology, the frictional characteristics of the non-metallic granule medium (NGM) under high pressure were investigated by tests and simulations. And the relevant changing curves of the internal friction coefficient of the granular system under different normal pressures were obtained by self-designed shear test. By the granule volume compression test, the accurate discrete element simulation parameters were obtained, based on this, the discrete element method (DEM) was adopted to reveal the evolution law of the NGM granules movement in the sample shear process from the microscopic view. Based on the DEM, the influence of granule diameter, surface friction coefficient, normal pressure and shear velocity on the internal friction coefficient of the granular system were studied. And the parameters were conducted to be dimensionless by introducing the inertia coefficient. Finally, the expression showing power-law relationship of inertia coefficient, surface friction coefficient and internal friction coefficient is obtained.

Numerical and Experimental Investigations on SGMF of GH3044 Superalloy Tube

According to the GH3044 nickel-based superalloy with high yield strength, a new approach for superalloy tube named Tube Solid Granules Medium Forming (SGMF) was present, and tube SGMF process principle and the mechanical model of solid granules were designed. The superalloy tube SGMF process was investigated numerically by using User subroutine of Abaqus software, the deforming simulations of two groups of tube products were performed separately, and the elongation rate and thickness distributions of the products were analyzed. An experimental system was designed and developed for tube SGMF, typical GH3044 superalloy tubes were deformed, good correlation was observed between the simulation results and experimental data.

Study on Lateral Pressure-Transfer Regularity of Tube SGMF under High Pressure

The mechanical model of Tube Solid Granules Medium Forming (SGMF) is simplified to three pressure-transfer models: uniform pressure model, unequal diameter model and tube SGMF model. Combining the conclusions of the SGMF investigation and the theories of powder mechanics, lateral pressure-transfer regularity of SGMF under high pressure has been investigated and the mathematical formulas of pressure distribution have been obtained. According to the theoretical analysis, the lateral pressure and the depth of solid granules can be expressed by a segmented function. An experimental set-up has been designed and manufactured to evaluate the theoretical results, good correlation has been observed between the theoretical results and the experimental data.

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 under 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.

Mechanical Analysis of Deep Drawing of Cylinder Based on Solid Granules Medium Forming Technology

Solid granule medium forming(SGMF) technology is applied to the deep drawing for cylinders of sheet metal,and the corresponding mechanical model under this condition is established.On the basis of the pressure-transfer attenuation model,the formula of desired unit punch pressure during the forming process has been obtained through mechanical analysis on the straight wall zone,which demonstrates that after the straight wall zone of the cylinder comes into being,the maximum unit punch pressure will linearly decrease gradually with the drawing coefficient increases;it also turns out that increment of friction coefficient between the sheet and the female die surface will result in a quite obvious tendency of increase in unit punch pressure;nevertheless,increment of that between the sheet and the solid granule medium will otherwise minish the unit punch pressure.Furthermore,with the increasing of the initial medium loading height,the unit punch pressure increases,which is resulted from the gradual attenuation of stress transfered by granule medium with the transferring distance grows.Additionally,magnesium alloy sheet as subject investigated,the deep drawing experiment and finite element simulation based on SGMF technology have been conducted,which has verified that the experimental and simulation results are in good agreement with the theoretical one.

Study on the Forming of Box-shaped Parts Based on Solid Granule Medium Forming

Solid granule medium forming(SGMF) is used for sheet metal deep drawing,where solid granule microsphere replaces the rigid punch or female die(or elastomer,liquid).Certain non-metallic granules(NMG) are selected as the research subjects.On the basis of the volume compression experiments and the ones of friction strength test,with both at a high stress level working on the solid particles medium,The finite element model of solid particles medium materials is constructed by the extended Drucker-Prager linear model in powder mechanics.The square box-shaped parts of non-axial symmetry is taken as an example,numerical analysis in respect of forming process of SGM is conducted;the flow characteristics of sheet and the wall thickness distribution law in the forming process are studied.Typical square box-shaped parts are successfully trial-produced.Loading curves,deformation characteristics in forming process and wall thickness distribution curves are proved in basic agreement with the result of finite element simulation.Studies show that the deformation characteristics and the force parameters,which is closed to the experiments can be generated from the numerical analysis on the SGM material model based on powder mechanic.At the same time,it can be the basis of the process plan which will in turn,play an important role in guiding the further application of the technique in sheet metal forming.

Research on Pressure-transfer Characteristics in the Solid Granule Medium Forming Based on the Discrete Element Method

Solid granules medium forming(SGMF) is an advanced forming technology used for deep drawing and bulging of sheet metals and pipes,where the rigid punch(or die) is replaced by solid granules medium,and it has unique advantages in precision forming of complicated parts,hard deformation materials forming,warm forming etc.To reveal the pressure-transfer characteristics of granules medium in SGMF,the stressed process of solid granule medium under uniaxial compression is numerically calculated in discrete/distinct element method(DEM),besides,the evolution law of micro structure of the solid granule medium in the compression process is analyzed in terms of force chains.To verify the discrete element method,a granules medium force-transfer performance test is designed,in which the stainless steel balls with diameter of 1mm are used as pressure-transfer medium,and the simulation result is in good agreement with the actually measured value.It is also found that the coordination number changes with the solid fraction in power function,so does the lateral pressure coefficient with the compressive stress,and the lateral pressure coefficient tends to be constant when the internal force chains structure keeps stable.In addition,the pressure decay law and limit pressure-transfer distance for solid granules medium are both deduced from mechanics of granular media,which has important significance for accurately controlling the pressure distribution and improving the formability of the workpieces.

Microscopic Study of Pressure-Transfer Characteristics in the Solid Granule Medium Forming

To reveal the pressure-transfer characteristics of the granular materials in the Solid Granule Medium Forming process, the stainless steel balls with diameter of 1 mm were selected as medium to conduct the axial compression experiment. The particle compression process was simulated by discrete element method, and then the variation law of the microstructure was analyzed from the perspective of force chain. The results showed that: In the gradual compression process of granule medium, its force chains distribution changes from the initial circular shape to the elliptical shape. As the stress increases, the force chains get denser and denser. In addition, the lateral pressure coefficient changes in power law with the compressive stress and it tends to be constant when the internal force chains structure gets stable.

New Process of Solid Granule Medium Forming

A new technology of solid granule medium forming(SGMF) is proposed to overcome the disadvantages of the traditional flexible die forming which has advanced the development of tube forming technology.The new technology not only can resolve the sealing problems in fluid medium forming and viscous medium forming, but also has advantages of nonuniform distribution of inter-pressure, easy control of workpiece forming, and improvement in material forming limit, thereby providing a new means for material preparation and manufacturing.In view of the pressure-transmitting characteristic of solid granule medium, the linear loading model and the cosinoidal loading model are presented.Plasticity theory is adopted to research the plastic deformation in free deformation area in the process of pipe forming under the action of nonuniform inter-pressure, and the theory of which is established.The formulas for calculating the stress, strain and wall thickness of the free forming area are derived and verified practically through experiments.

Solid Granules Medium Forming Technology and Its Numerical Simulation

Sheet metal flexible-die forming is the fastest growing one of the sheet forming technologies. For the traditional sheet flexible die forming technology has many defects, the sheet solid granules medium forming technology (SGMF) is brought forward as a new technology that overcomes the defects and derives their advantages of the existing flexible die forming technology. It is an advanced technology which uses solid granules medium instead of rigid punch (or elastomer, liquid) to form sheet. Its advantages are simple structure of the tool, good quality surface of the parts, the forming limit being improved effectively, saving die sets and equipments and so on. Deep typical curved parts are successfully developed by this technology. Solid granules medium is managed as the continuum medium, the finite element method simulation model has been established to simulate granules medium forming workpiece of which meridian plane is parabolic-shaped. In conclusion, the simulation results calculated using the continuum medium model are closed to experimental results.