Microstructure and texture of commercially pure titanium in cold deep drawing

The development of microstructure and texture during cold deep drawing of commercially pure titanium（CP-Ti） was investigated.Three parts,stretching region,drawing region and flange region,were sequentially formed in the deep drawing process of the hemispheric surface part,with reference to deformation modes and strain regimes.Results show that the plastic strain is accommodated by dislocation slip and deformation twinning in the whole deep drawing process.The texture of the CP-Ti sheet and its drawn part consists of rolling texture component and recrystallization texture component.The intensity and type of the initial texture varied during the drawing process are related to the production of deformation twinning and dislocation slip.Twinning weakens the initial texture by randomizing the orientations of crystals,especially for the recrystallization texture.The recrystallization texture in the drawing region disappears due to the significant forming of twinning.Furthermore,over drawing would result in the predominance of dislocation slip and the texture is strengthened.

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.

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.

EFFECTS OF SPECIFIED BLANK SIZE ON BODY WRINKLING DURING HYDRODYNAMIC DEEP DRAWING OF TAPERED RECTANGULAR BOX

In this paper, the forming features of tapered rectangular box during hydrodynamic deep drawing are studied by means of FEM.The effect rules of square blank corner corner amount on body wrinkling are recognized and corresponding methods are discussed. At last, the results of FEM are verified by experi- ment.

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.

RESEARCH ON THE EVALUATION METHOD OF FRICTION AND LUBRICATION IN DEEP DRAWING

The deformation characteristic of bland in deep drawing is discussed. It is pointed out that the friction and lubrication conditions in for drawing are different from that in mechanical motion or machine work or other plastic process. The common test methods in laboratories are analyzed. It shows that though all those test methods can test the friction coefficient, the probe test method is most suitable for the research of friction and lubrication and the process in deep drawing, for this method is identical with the actual work condition either from the test principle or deformation status of the blank. Last the successful application in the deep drawing simulator newly developed the the probe method are intro- duced in detail.

Subsurface macro-inclusions and solidified hook character in aluminum-killed deep-drawing steel slabs

Subsurface macro-inclusions and hooks are detrimental to the surface quality of deep-drawing steel sheets. However, little is known about the relationship between macro-inclusions and hooks. Thus, in this work, two ultralow carbon （ULC） steel slabs and two low carbon （LC） aluminum-killed steel slabs were sampled to study the relationship between hooks and subsurface macro-inclusions, which were detected on the cross-sections of steel samples with an area of 56058 mm2 using an automated scanning electron microscopy/energy-disper-sive X-ray spectroscopy system. Results show that subsurface inclusions larger than 200 μm were almost entrapped by hook structures, whereas the location of other inclusions smaller than 200μm had no obvious dependence on the location of solidified hooks. Furthermore, the number density （ND） of subsurface inclusions larger than 200μm decreased from 0.02 to 0 cm-2 in ULC steel as the mean hook depth decreased from 1.57 to 1.01 mm. Similar trends were also observed in LC steel. In addition, the detected inclusions larger than 200μm were concentrated in the region near the slab center （3/8 width-5/8 width）, where hook depths were also larger than those at any other locations. Therefore, minimizing the hook depth is an effective way to reduce inclusion-induced sliver defects in deep-drawing steels.

Effects of Loading Paths on Hydrodynamic Deep Drawing with Independent Radial Hydraulic Pressure of Aluminum Alloy Based on Numerical Simulation

In order to meet the forming demands for low plasticity materials and large height-diameter ratio parts, a new process of hydrodynamic deep drawing （HDD） with independent radial hydraulic pressure is proposed. To investigate the effects of loading paths on the HDD with independent radial hydraulic pressure, the forming process of 5A06 aluminum alloy cylindrical cup with a hemispherical bottom was studied by numerical simulation. By employing the dynamic explicit analytical software ETA/Dynaform based on LS-DYNA3D, the effects of loading paths on the sheet-thickness distribution and surface quality were analyzed. The corresponding relations of the radial hydraulic pressure loading paths and the part＇s strain status on the forming limit diagram （FLD） were also discussed. The results indicated that a sound match between liquid chamber pressure and independent radial hydraulic pressure could restrain the serious thinning at the hemisphere bottom and that through adjusting radial hydraulic pressure could reduce the radial tensile strain and change the strain paths. Therefore, the drawing limit of the aluminum cylindrical cup with a hemispherical bottom could be increased significantly.

Investigation of SUS304 Stainless Steel with Warm Hydro-mechanical Deep Drawing

Basing on warm mechanical property of SUS304 stainless steel and hydro-mechanical deep drawing process, warm hydro-mechanical deep drawing process is proposed and discussed with experiments in this paper. The experiments are performed at four different temperatures. The results show that the formability of stainless steel is improved under the condition of warm temperature. Warm hydro-mechanical deep drawing raises limiting drawing ratio of SUS304 effectively, and limiting drawing ratio 3.3 is obtained, which is beyond 2.0 with conventional deep drawing. The temperature of 90℃ is beneficial to the forming of SUS304 stainless steel, the strain-induced martensite is controlled effectively, and the thickness distribution is more uniform.

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.

Effect of Friction Coefficient on Deep Drawing of 6A16 Aluminum Alloy for Automobile Body

Based on the ABAQUS/Explicit finite element method,the forming force changing trend of deep drawing test for 6A16 aluminum alloy plate after pre-aging and storage at room temperature for one month was simulated under friction coefficient ranging from 0 to 0.22.The lubricants selected for the tests were mechanical oil,butter and dry film lubricant,and the friction coefficient of these lubricants were 0.05,0.10 and 0.15,respectively.Microstructural evolution of 6 A16 aluminum alloy plate during drawing forming was investigated by OM,SEM and EBSD.The results showed that,with the increase of friction coefficient,the stress,strain and deformation degree in deformation zone increased,while the grain size in deformation zone decreased.Thus,the hardness of the cup-typed component increased with the increase of friction coefficient.Butter-lubricated cups had the highest tensile strength and yield strength after paint-bake cycle.The combination of simulation results and microstructure analysis of 6A16 aluminum alloy plate after drawing forming indicates that the appropriate lubricant is butter.

Influence of variables in deep drawing of AA 6061 sheet

Deep drawing is one of the most important processes for forming sheet metal parts.It is widely used for mass production of cup shapes in automobile,aerospace and packaging industries.Cup drawing,besides its importance as forming process,also serves as a basic test for the sheet metal formability.The effect of equipment and tooling parameters results in complex deformation mechanism.Existence of thickness variation in the formed part may cause stress concentration and may lead to acceleration of damage.Using TAGUCHI's signal-to-noise ratio,it is determined that the die shoulder radius has major influence followed by blank holder force and punch nose radius on the thickness distribution of the deep drawn cup of AA 6061 sheet.The optimum levels of the above three factors,for the most even wall thickness distribution,are found to be punch nose radius of 3 mm,die shoulder radius of 8 mm and blank holder force of 4 kN.

Experimental Investigation on Micro Deep Drawing of Stainless Steel Foils with Different Microstructural Characteristics

In the present work,austenitic stainless steel(ASS)304 foils with a thickness of 50μm were first annealed at temperatures ranging from 700 to 1100℃for 1 h to obtain different microstructural characteristics.Then the effects of microstructural characteristics on the formability of ASS 304 foils and the quality of drawn cups using micro deep drawing(MDD)were studied,and the mechanism involved was discussed.The results show that the as-received ASS 304 foil has a poor formability and cannot be used to form a cup using MDD.Serious wrinkling problem occurs on the drawn cup,and the height profile distribution on the mouth and the symmetry of the drawn cup is quite non-uniform when the annealing temperature is 700℃.At annealing temperatures of 900 and 950℃,the drawn cups are both characterized with very few wrinkles,and the distribution of height profile,symmetry and mouth thickness are uniform on the mouths of the drawn cups.The wrinkling becomes increasingly significant with a further increase of annealing temperature from 950 to 1100℃.The optimal annealing temperatures obtained in this study are 900 and 950℃for reducing the generation of wrinkling,and therefore improving the quality of drawn cups.With non-optimized microstructure,the distribution of the compressive stress in the circumferential direction of the drawn foils becomes inhomogeneous,which is thought to be the cause of the occurrence of localized deformation till wrinkling during MDD.

Formation of Aluminum-magnesium Alloy Cup by Hydrodynamic Deep Drawing with Twin-loading Paths

In order to overcome the limitation of hydro-rim deep drawing, a new process of hydrodynamic deep drawing （HDD） with independent radial hydraulic pressure was proposed. By employing the dynamic explicit analytical software ETA/DynaformS.5 which is based on LS-DYNA3D, the effects of independent radia! hydraulic pressure on the stress, strain and the sheet-thickness of aluminum-magnesium cylindrical cup with a hemispherical bottom were analyzed by numerical simulation. The feature of stress distribution is that there exists a stress-dividing circle in the flange, and the radius of dividing circle was determined by theoretical analysis and stimulation. The experimental results indicate that the reasonable match of independent radial hydraulic pressure and liquid chamber pressure can effectively reduce the thinning at the bottom of hemisphere, decrease the radial stress-strain, and improve the drawing limit of aiuminum-magnesium alloy cylindrical cup.

Finite element simulation on the deep drawing of titanium thin-walled surface part

The deep drawing of titanium thin-walled surface part was simulated based on a self-developed three-dimensional finite element model. After an investigation on forming rules, a virtual orthogonal experimental design was adopted to determine the significance of processing parameters, such as die radius, blank holder force, and friction coefficient, on the forming process. The distributions of thickness and equivalent plastic strain of the drawn part were evaluated. The results show that die radius has a relative major influence on the deep drawing process, followed by friction coefficient and blank holder force.

Process window diagram of conical cups in hydrodynamic deep drawing assisted by radial pressure

Major defects in forming of conical cups are wrinkles and rupture.Hydrodynamic deep drawing assisted by radial pressure（HDDRP） is a sheet hydroforming process for production of shell cups in one step.In this work,process window diagrams（PWDs） for Al1050-O,pure copper and DIN 1623 St14 steel are obtained for HDDRP process.The PWD is determined to provide a quick assessment of part producibility for sheet hydroforming process.Finite element method is used for this purpose considering the process parameters including pressure path,and the blank material and its thickness.Numerical results are validated by experiments.It is shown that the sheets with less initial thickness and higher strength show better formability and uniformity of thickness distribution on final product.The results demonstrate that the obtained PWD can predict appropriate forming area and probability of rupture or wrinkling occurrence under different pressure loading paths.

Research on Thermal Deep-drawing Technology of Magnesium Alloy (AZ31B) Sheets

Forming technology of Mg alloy (AZ31B) sheets can be investigated by thermal deep drawing experiments. In the experiments, the blank holder and die contacting with the blank were heated to the same temperature as the blank by using the heating facility. The circular blank heated in an oven is formed at a temperature range of 100~400 ℃ to obtain the optimum forming temperature range and the effects of major technical parameters on the workpiece quality. It is found that the blank is brittle at temperatures lower than 200℃. Temperatures higher than 400℃ are not suitable for forming of the sheets because of severe oxidation and wrinkling. AZ31B shows an excellent formability at temperatures from 300 to 350℃ and can be formed into a workpiece with good quality. When the blank holder force is 9 kN, extruded sheets with a thickness of 1 mm can be formed into cups without wrinkling. Workpieces show strong anisotropic deformation behavior on the flanges.

Hydrodynamic deep drawing of double layered conical cups

Hydrodynamic deep drawing assisted by radial pressure is an advanced sheet forming technology with great advantages such as higher drawing ratio, good surface quality and higher dimensional accuracy. In this process, both the bottom surface and the peripheral edge of sheets are under hydrodynamic pressure, so that the forming procedure is more uniform with low failure probability. Multi-layered sheets with complex geometries could be formed more easily with this technique compared with other traditional methods. Rupture is the main irrecoverable failure form in sheet forming processes. Prediction of rupture occurrence is of great importance for determining and optimizing the proper process parameters. In this research, a theoretical model was proposed to calculate the critical rupture pressure in production of double layered conical parts with hydrodynamic deep drawing process assisted by radial pressure. The effects of other process parameters on critical rupture pressure, such as punch tip radius, drawing ratio, coefficient of friction, sheet thickness and material properties were also discussed. The proposed model was compared with finite element simulation and validated by experiments on Al1050/St13 double layered sheets, where a good agreement was found with analytical results.

Prediction of Eight Earings in Deep Drawing of 5754O Aluminum Alloy Sheet

Earings appear easily during deep drawing of cylindrical parts owing to the anisotropic properties of materials.However,current methods cannot fully utilize the mechanical properties of material,and the number of earings obtained differ with the simulation methods.In order to predict the eight-earing problem in the cylindrical deep drawing of 5754O aluminum alloy sheet,a new method of combining the yield stress and anisotropy index(r-value)to solve the parameters of the Hil 148 yield function is proposed.The general formula for the yield stress and r-value in any direction is presented.Taking a 5754O aluminum alloy sheet as an example in this study,the deformation area in deep drawing is divided into several equal sectorial regions based on the anisotropy.The parameters of the Hill48 yield function are solved based on the yield stress and r-value simultaneously for the corresponding deformation area.Finite element simulations of deep drawing based on new and existing methods are carried out for comparison with experimental results.This study provides a convenient and reliable way to predict the formation of eight earings in the deep drawing process,which is expected to be useful in industrial applications.The results of this study lay the foundation for the optimization of the cylindrical deep drawing process,including the optimization of the blank shape to eliminate earing defects on the final product,which is of great importance in the actual production process.

Numerical Study on Welding Line Behavior of Deep Drawing TWB Process

The FEM technology is used to analyze the welding line movement behavior of deep drawing TWB sheet with different thickness. It is found that high stress fields are concentrated around the welding line and large residual stresses are left. The effect of the welding line movement is like a rigid string and the selected nodes of the thin part near the welding line show the related larger strain.