Flexible-die Forming Research Articles

Quality Research of Metal Parts Produced by Cold Sheet Forming

Sheet metal forming is one of the most popular technologies for obtaining finished products in automotive industries. The main techniques of sheet metal forming: sheet microforming, warm/hot forming, incremental sheet forming, flexible-die forming, Electromagnetic sheet forming, Electrohydraulic forming, Spinning and Shear Spinning, Shear Spinning and Flow Forming and cold sheet forming. One most popular cold stamping process. In the production line of Ravne VPS400 1992, we take twenty details for looking quality review, looking for surface damage reasons - a little changing tonnage and speed. The biggest deformation, when velocity is the slowest the tonnage don’t have an impact on this radius deformation.
 Firstly, we measured the surface for all twenty details with Contourograph CV-2100 M4. In one measurement point we have ten points which is the biggest or slowest tolerance, these results can be the reason why the detail is damage. These details make one tact process. We can say the recommendation – if the detail will be making for one more tact process, detail not be damage, but this extra process is a very grown the price.
 Second, we see metal steel chemistry alloy elements, and we can be looking which elements have some reason mechanical properties of steels.
 Our samples have not enough elasticity, and in steel structure we can recommend taking more carbon C, Silicon Si and Vanadium V. Silicon Si, is important for a machinability and tensile properties as well and this element is essential in steel structure.
 Thirsty, we used the 3D coordinate measuring machine Mitutoyo SurfaceMeasure 606T, looking for tolerances differences.
 And we see in detail which places will have a damage, we have the results lowest from the layout, we see the blue color. If we made detail not one tact process, but more tact’s making detail the thickness would be evenly gradually. The crystalline structure of the metal broke due to excessive thinning.

Investigation on the stress-strain rate curve of MR fluids in a combined mode and its application in sheet flexible-die forming

During the sheet flexible-die forming process using a magnetorheological (MR) fluid, the MR fluid is always subjected to a three-dimensional stress state, working in a combination of squeezing mode and valve mode. However, there is a lack of deep understanding of the stress-strain rate curve for MR fluids in the combined mode. In this paper, through extrusion test and finite element simulation, the mechanical properties of an MR fluid with a magnetic particle content of 43% and three kinds of viscous mediums used in viscous pressure forming (VPF) were compared and analyzed for the first time. It shows that the adjustment range of the MR fluid’s mechanical properties under different magnetic fields is much larger than that of a viscous medium with a molecular weight of 700 kg/mol. Besides, by changing the magnetic field, the mechanical property of an MR fluid can cover the mechanical properties of viscous mediums with different molecular weights. It is proved that the stress-strain rate curve of the MR fluid changes from a linear relationship to a power exponent one with the increase of magnetic flux density. Meanwhile, the strength coefficient increases, while the strain rate sensitivity index decreases. The obtained curves were applied to the numerical simulation of sheet flexible-die forming, which can well explain the experimental phenomena through the analysis of velocity, pressure, stress, and strain distribution. The results can provide theoretical guidance in the optimization of processing parameters in sheet flexible-die forming using an MR fluid.

Recent Developments and Trends in Sheet Metal Forming

Sheet metal forming (SMF) is one of the most popular technologies for obtaining finished products in almost every sector of industrial production, especially in the aircraft, automotive, food and home appliance industries. Parallel to the development of new forming techniques, numerical and empirical approaches are being developed to improve existing and develop new methods of sheet metal forming. Many innovative numerical algorithms, experimental methods and theoretical contributions have recently been proposed for SMF by researchers and business research centers. These methods are mainly focused on the improvement of the formability of materials, production of complex-shaped parts with good surface quality, speeding up of the production cycle, reduction in the number of operations and the environmental performance of manufacturing. This study is intended to summarize recent development trends in both the numerical and experimental fields of conventional deep-drawing, spinning, flexible-die forming, electromagnetic forming and computer-controlled forming methods like incremental sheet forming. The review is limited to the considerable changes that have occurred in the SMF sector in the last decade, with special attention given to the 2015–2020 period. The progress observed in the last decade in the area of SMF mainly concerns the development nonconventional methods of forming difficult-to-form lightweight materials for automotive and aircraft applications. In evaluating the ecological convenience of SMF processes, the tribological aspects have also become the subject of great attention.

Feasibility study of cam-shaped tube production using elastomeric tool versus fluid forming method

Nowadays, the flexible-die forming (FDF) technology is widely used for manufacturing the complex tubular components in industries. In this present study, the forming feasibility of a cam-shaped 304 stainless steel tube by using an elastomeric tool has been investigated, and the results have been compared with hydroforming method as well. In bulging by using a polyurethane rod, the tube was placed into the desired location of the die cavity and formed by the pressure exerted inside the tube through the flexible interface. The 3D finite element simulation of the bulging process was carried out based on arbitrary Lagrangian-Eulerian (ALE) adaptive meshing for the rubber tool and forming limit diagram damage criteria assigned to the seam-welded tube. The experimental apparatuses have been prepared for both processes. Furthermore, the tube was meshed by circular grids, and strain distribution was measured after forming. Experimental and numerical implementation showed that unlike using the elastomeric tool, in the hydro-bulging process of the cam-shaped tube, the mandatory axial feeding of the tube is necessary to fabricate a defect-free part. The results showed that in terms of tube deformability, the rubber pad forming can compete with fluid forming if the process variables are set properly. Of course, by using fluid bulging medium versus solid elastomeric rod, it is far easier to fill the small radius of the die.

Rheological experimental properties and numerical modeling of a pressure-transmitting silicone rubber used in sheet metal flexible-die forming

In this paper, the rheological behaviors of a silicone rubber used in sheet metal flexible-die forming were analyzed experimentally and numerically. Firstly, six silicone rubber samples with different molecular weights were subjected to three tests: oscillation, creep recovery, and shear viscosity test by using dynamic shear rheometer (DSR). Then, the responses of the silicone rubber to the load were categorized into three groups as elasticity, viscoelasticity, and viscoplasticity depending on whether they were time dependent and recoverable during the unloading period. By applying Perzyna’s theory, a visco-elasto-plastic model was proposed to simulate the rheological behaviors of the silicone rubber numerically. Finally, a finite element-element-free Galerkin (FE-EFG) code was implemented on the basis of this numerical model. Employing the program into polymer extrusion and sheet metal flexible-die forming process, on the substation of parameters obtained from experiments, good matches were found between numerical results and experimental ones.

A multi-deformable bodies solution method coupling finite element with meshless method in sheet metal flexible-die forming

Abstract In this paper, a multi-deformable bodies solution method which includes both sheet metal elastoplastic deformation and bulk deformation of pressure-transmitting medium (PTM) in sheet metal flexible-die forming was proposed. The elastoplastic deformation of sheet metal was analyzed with finite element method (FEM), and the bulk deformation of PTM was analyzed with a meshless method, called element-free Galerkin method (EFGM). Aiming at the coupled deformation characteristics and strong nonlinear features between sheet metal/FEM and PTM/EFGM, a node-to-point contact method based on slave-master concept was employed to treat the frictional contact between these two deformable bodies. A numerical example of sheet metal flexible-die forming was presented to demonstrate the effectiveness of the proposed method.

Effects of viscosity on viscous pressure bulging (VPB) of Al1060 sheet

The properties of pressure-transmitting medium have a great effect on the formability of sheet metal in sheet flexible-die forming, such as rubber-pad forming and viscous pressure forming (VPF). In this study, viscous pressure bulging (VPB) experiments were used to investigate the effects of viscosity on Al1060 sheet. At the same dome height, the configurations of bulging specimen varied with three different viscosity viscous mediums (1#, 550,000 g/mol; 2#, 700,000 g/mol; and 3#, 900,000 g/mol). The thickness strain distributions of specimen formed by a higher viscosity medium had a relatively uniform distribution. In order to further study the effects of viscosity on VPB, a CDSB-FEM-EFGM program was used to analyze viscous pressure bulging process. The configuration, stress, strain, and wall thickness distributions of bulging specimen were obtained. The numerical analysis results had a good agreement with the experimental ones, which also showed that properties of the viscous medium had a great effect on the formed specimen. The formability of sheet metal can be further improved through increasing the viscosity of viscous medium.

Numerical analysis of coupled finite element with element-free Galerkin in sheet flexible-die forming

A numerical method for coupled deformation between sheet metal and flexible-die was proposed. Based on the updated Lagrangian (UL) formulation, the elastoplastic deformation of sheet metal was analyzed with finite element method (FEM) and the bulk deformation of flexible-die was analyzed with element-free Galerkin method (EFGM). The frictional contact between sheet metal and flexible-die was treated by the penalty function method. The sheet elastic flexible-die bulging process was analyzed with the FEM–EFGM program for coupled deformation between sheet metal and bulk flexible-die, called CDSB–FEM–EFGM for short. Compared with finite element code DEFORM-2D and experiment results, the CDSB–FEM–EFGM program is feasible. This method provides a suitable numerical method to analyze sheet flexible-die forming.

Sectional finite element analysis of coupled deformation between elastoplastic sheet metal and visco-elastoplastic body

The present paper is devoted to developing a new numerical simulation method for the analysis of viscous pressure forming (VPF), which is a sheet flexible-die forming (FDF) process. The pressure-carrying medium used in VPF is one kind of semisolid, flowable and viscous material and its deformation behavior can be described by the visco-elastoplastic constitutive model. A sectional finite element model for the coupled deformation analysis between the viscoelastoplastic pressure-carrying medium and the elastoplastic sheet metal is proposed. The resolution of the Updated Lagrangian (UL) formulation is based on a static explicit approach. The frictional contact between sheet metal and visco-elastoplastic pressure-carrying medium is treated by the penalty function method. Coupled deformation between sheet metal and visco-elastoplastic pressure-carrying medium with large slip is analyzed to validate the developed algorithm. Finally, the viscous pressure bulging (VPB) process of DC06 sheet metal is simulated. Good agreement between numerical simulation results and experimental measurements shows the validity of the developed algorithm.

Numerical Analysis of Coupled Finite Element with Meshfree in Bulging Process of Sheet Elastic Flexible-Die Forming

Sheet flexible-die forming processes have been playing a good application on sheet metal forming in the industry field. Because of the coupled deformation between sheet metal and flexible-die, it is necessary to utilize numerical simulation technology to analyze it. In this paper, a numerical analysis method for coupling the deformation of sheet metal and flexible-die is developed. The deformation of sheet metal is analyzed with finite element method (FEM) and the bulk deformation of flexible-die is analyzed with the Element free Galerkin method (EFGM). The sheet flexible-die bulging process is analyzed with the developed FEM-EFGM method. This paper proposes a suitable numerical method to analyze sheet flexible-die forming.

Prediction of wrinkling and fracturing in viscous pressure forming (VPF) by using the coupled deformation sectional finite element method

Viscous pressure forming (VPF), which uses a kind of semisolid, flowable and viscous material as pressure-carrying medium (PCM), is a new flexible-die forming (FDF) process of sheet metals. In VPF, wrinkling and fracturing are two major failure modes. It is more difficult to predict the occurrence of wrinkling and fracturing in VPF than the conventional sheet metal forming processes due to the coupled deformation of sheet metal and viscous medium. In this paper, a sectional finite element method (SFEM) for analysis of the coupled deformation of sheet metal and viscous medium is developed. The C-B wrinkling criterion based on the energy method and a ductile fracture criterion on the basis of Lemaitre damage theory are proposed to analyze the VPF process of aluminum ladder part via combining with SFEM. The wrinkling and fracturing defects occurred in VPF are thus predicted. The effects of blank holder pressure and the interface condition between sheet metal and viscous medium on the wrinkling and fracturing formation in VPF are investigated. Based on the simulation results of SFEM, the comparison with the experimental data is conducted and the efficiency of the developed approach is thus validated.

Numerical study on the deformation behaviors of the flexible die forming by using viscoplastic pressure-carrying medium

The flexible die forming (FDF) of sheet metal with the aid of viscoplastic pressure-carrying medium (VPCM) is one of the advanced forming technologies for forming complex sheet metal components with large plastic deformation. The technology has been used in industries by employing different VPCMs, the epistemological understanding of the deformation and process behaviors of this process, however, has not yet been fully addressed. In this paper, numerical study is conducted to look into the deformation behaviors of this process by explicit 3D-FE simulation under the ABAQUS platform, in which the counter pressure variations of VPCM is applied via user subroutine VDLOAD and the ductile fracture criterion is implemented by using VUMAT. Three case study parts, viz., barrel, conic and parabolic parts with large Limit Drawing Ratio (LDR) are studied. The comparison between the conventional deep drawing (CDD) and VPCM-based FDF is conducted in terms of wall-thickness reduction, hydrostatic pressure, principal stress distribution and damage factor. The uniqueness and the deformation behaviors of the VPCM-based FDF are then highlighted. The simulation results show that the higher VPCM pressure could result in the higher hydrostatic pressure throughout the process and further resist wall thinning and prevent fracture of the sheet metal. The formability is thus increased significantly.

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.

Formability of 6k21-T4 car panel sheet for viscoelastic–plastic flexible-die forming

The service performance of a car body is obviously improved by using aluminum alloy panels. Because of the lower hardness and elastic modulus of aluminum alloy sheets, the car panels are easily scraped to reduce the surface quality, and the dimensional accuracy of sheet parts is affected due to higher spring-back after forming. In order to overcome forming problems of aluminum alloy panels, the viscoelastic–plastic flexible-die forming method is proposed to form the aluminium alloy panels in this paper. The scrape defect and the spring-back are improved by making use of the characteristics of the viscoelastic–plastic flexible-die. The forming limit curve of 6k21-T4 sheet is obtained through viscoelastic–plastic flexible-die bugling experiments. The car outer door with scale-down simulating dimensions is chosen as experimental parts for panels, and the viscoelastic–plastic flexible-die forming experiments are carried out to analyze the effect of the relationship between viscoelastic–plastic flexible-die pressure and BHF on the formability of aluminum panels. Experimental results indicate that the viscoelastic–plastic flexible-die forming can meet the formability of the aluminium alloy panels by using the proper BHF.

Process parameters and products quality analysis of flexible-die deep-drawing using a viscoplastic pressure-carrying medium

An attempt is made in an exploratory way to discover a new deep-drawing technology of sheet-metal forming by way of flexible-die forming (FDF) using a viscoplastic pressure-carrying medium (VPCM). The new sheet-metal forming technology has been used in manufacturing practical components due to the advantages it has when compared with the conventional FDF. In this paper, the technology is used to produce three cup-type workpieces with different bottom shapes, and issues including forming process parameters and product quality are addressed. The experimental results indicated that the pressure of the VPCM in the medium container is significant in a successful deep-drawing. In order to investigate the VPCM pressure variation during the deep-drawing process, a pressure-measuring device was designed to measure the VPCM pressure in the forming process. Furthermore, the deep-drawing force required and its variation during the forming process were identified. Qualitative and quantitative analyses of product quality are also presented. The results show that the product quality, formability and feasibility of the technology are satisfactory for the practical use of this technology to manufacture complicated sheet-metal parts. The results presented in this paper can thus be used as a basis to provide solutions for practical usage.

High-precision sheet-metal workpieces manufactured by flexible-die forming using a visco-plastic pressure-carrying medium

The new technology of sheet-metal flexible-die forming (FDF) using a special visco-plastic pressure-carrying medium (VPCM) has a lot of advantages compared with conventional FDF which uses pressure-carrying media such as liquid, gas, or a rubber or polyurethane pad. The advantages can be illustrated in the manufacturing of three high-precision hemispherical workpieces, these hemispherical workpieces being assembled together and used in a special machine. Because conventional sheet-metal forming technology and conventional FDF technology do not meet the requirements, an exploratory attempt is made to manufacture these hemispherical workpieces by the new FDF using the VPCM. The experimental results show that the workpieces can be manufactured successfully by the new FDF technology, the quality of the products meeting their technological requirements. In this paper, the forming process has been specified and the die structure designed in compliance with the features of the workpieces and the new FDF technology. The experimental results indicate that it is important to control the process parameters. Further, the variation of the drawing force, blank-holding force and VPCM pressure in the medium container with the stroke are given. On the basis of the experimental results, empirical equations for the VPCM pressure in the container are given. Both qualitative and quantitative analysis has been undertaken in respect of the quality of the product.

A note on mathematical models of cup drawing by the guerin and marform processes

Both the Guerin and Marform processes are flexible-die forming operations that use rubber-pad pressure, the essential difference between the two being that the latter uses a blank-holder. Flexible-die forming has many advantages over rigid-die forming and these two processes find many applications such as in the forming of flanges, beads and ridges (Guerin), and flanged cups, spherical domes, and square and rectangular shells (Marform). In this paper, investigations into cup drawing by the two processes are reported. Using factorial experimental design, mathematical models for cup drawing by the two processes have been obtained. In both cases blank thickness is found to be major factor governing the limiting drawing ratio.