| Blank sheet forming is a common sheet forming process,which is widely used in the manufacturing industry.With the development of the times,the forming demand of 3D surface parts in the manufacturing fields such as transportation,construction and Aeronautics & spacecraft is increasing rapidly.When the traditional edge pressing forming process in forming a large 3 D curvature,The cost of mould manufacturing is high and the period is long,and often forming defects such as wrinkling and cracking,which seriously restricts the industrial production;we need a new forming process can occur,inhibit the forming defects to improve forming quality,improve production efficiency and reduce the cost of production.Therefore,it is of great significance to study the new and effective flexible forming process.Flexible blank holder stamping is a new flexible forming technology.Its basic principle is to use flexible blank holder instead of traditional rigid blank holder,and use traditional integral mold or multi-point digital mold to finish stamping of curved workpiece.The flexible edge stamping process has the characteristics of high flexibility,large forming size and good forming quality.In this paper,we use the finite element software Abaqus to establish the finite element model of flexible blank holder forming of spherical parts,and flexible side of the half pipe forming process was studied.The prediction of sheet wrinkling defect condition,influence of process parameters on the forming results carried out,and the relevant experiments,to provide theoretical guidance for the flexible press forming.The main contents and conclusions of this paper are as follows:1.The principle and characteristics of flexible edge forming.The forming principle of common sheet flexible forming technology and the present research status at home and abroad are analyzed.A flexible edge stamping forming with multi point digital die and discrete edge forming is proposed.The forming process of flexible edge forming is studied.The finite element equations and related problems of thenumerical simulation of the plastic forming of thin plates are described.The finite element model of flexible edge forming is established.Numerical simulation and flexible edge forming experiments for spherical parts under the same conditions.The results show that the experimental results are in good agreement with the simulation results.The correctness of the finite element model of flexible edge forming is verified.2.Research on flexible blank forming of spherical parts.The finite element theory and dynamic explicit finite element method for the numerical simulation of thin sheet flexible blank forming process are studied.The finite element model of flexible edge stamping forming is established and the selection of key parameters in the process of finite element modeling is introduced,such as unit type,contact model,friction condition,loading condition,etc.Numerical simulation and forming experiment of free edge and flexible edge forming of spherical parts.It is proved that the flexible blank forming can effectively control the flow of sheet material than without edge forming.Wrinkle defects in forming process is controlled.3.Study on the effect of edge block in flexible edge forming process.The thickness distribution of the two cases is compared with the flexible blank holder and the non-use of the flexible blank holder.To discuss on the influence of flexible edge on forming.The experimental results show that the forming of wrinkles can be effectively suppressed by a flexible edge pressing device,which is consistent with the results of numerical simulation.Numerical simulation analysis of flexible blank forming for spherical parts.Compared with pressing strip and not using pressing strip under two kinds of situations of stress and thickness distribution.To discuss the effect of pressure on the forming results of the strake.The simulation results show that the use of pressing strip can effectively inhibit the forming of wrinkles.The establishment of a finite element model for flexible edge forming by using the general numerical simulation software Abaqus.The distribution of stress,strain and thickness in two cases of flexible edge forming and flexible edge forming.To discuss the influence of flexible edge forming and flexible edge forming on the forming results.The simulation results show that flexible edge forming is more effective than flexible edge forming to suppress forming wrinkles.4.Influence of edge size on forming in flexible blank forming process.The numerical simulation analysis of the effect of the blank holder on the forming results of the 24 mm series and 50 mm series is carried out.To compare stress of forming parts,strain of forming parts and the thickness of forming parts.The simulation results show that the wrinkling defects can be effectively suppressed by using 24 x 10 mm and 50 x 10mm blank holder blocks,and the stress concentration is avoided.And it can make the strain distribution more uniform in the effective forming region,decrease the thinning rateof maximum thickness and make the thickness distribution more uniform in the effective forming region.Through the analysis,it is found that the forming effect of 24 x 10 mm is better.The experimental results show that the effect of forming defects is best when using24 x 10 mm edge block.The results are in agreement with the results of numerical simulation.5.Flexible blank holder forming numerical simulation of pressure strip.The effect of pressure on the forming results of layers of strake is simulated and analyzed,three cases compared with one layer and two layer and three laminated strip under the stress,strain and thickness distribution analysis,forming inhibition of wrinkling ability,discuss pressing strip layers on the forming results influence.The simulation results show that using the three best results when forming laminated strips;influence of pressure on the forming results of material edge is analyzed numerically.The comparison of two kinds of material combinations of stress,strain and thickness distribution,analysis of the situation of controlling forming defects,discuss the influence on the forming results of pressing strip material.The simulation results show that the material of 65 Mn spring steel,forming the best effect;on pressure effect on the forming results of layered strake is simulated and analyzed,the pressing strip thickness unchanged,respectively,on one layer,two layer and three laminated strips under three kinds of situations of stress,strain and thickness distribution analysis,forming the defect of wrinkling,discussed the impact of pressure on the forming results of layered strips.The simulation results show that the use of 3 1mm thick layer of pressing strip forming,can be indicators of forming good.The experimental results show that the use of 3 1mm thick layer pressing strip forming the best effect,consistent with the results of numerical simulation;analyze on the influence on pressing strip width on the forming results of numerical simulation,compares a variety of combinations of stress,strain and thickness distribution,analyze the situation of controlling wrinkling,discuss the influence the width of the pressing strip forming.The simulation results show that under the same conditions,forming a wide use of pressing strip of high quality can be obtained.6.Numerical simulation of the influence of other technological parameters on the forming results of flexible edge forming.Carry out the simulated analysis of the influence of friction coefficient and forming result,compare of μ=0.05,μ=0.10,μ=0.20,μ=0.30 and μ=0.40 under the stress,strain and thickness distribution,analyze the forming quality of the forming,discuss the influence of friction coefficient on the forming results.The simulation results show that high quality forming parts can be obtained when the friction coefficient is μ=0.05.Effect on the sheet material on the forming results were studied by numericalsimulation.Analyze the comparison made of 304 stainless steel,1010 steel and 2024-O three under the condition of stress,strain and thickness distribution,forming defects occur,discusses the influence on the results of the forming of sheet material.The simulation results show that when the 304 stainless steel and 1010 steel are used,high quality parts can be obtained.When 2024-O is used,the breakage defects of the forming parts need to be adjusted,and the model parameters need to be adjusted.Carry out the simulated analysis of the effect of blank holder force on the forming results,compare blank-holding force into 3 cases of 2MPa,5MPa and 10 MPa under the stress,strain and thickness distribution.Analyze the forming inhibition of forming defects.Discusses the influence of BHF on the forming results.The simulation results show that when the blank holder force is 5MPa,the wrinkling defect can be effectively suppressed,and the high quality forming parts with uniform distribution of stress,strain and thickness in the effective forming area and small maximum thinning ratio can be obtained.7.Numerical simulation of flexible edge forming of half pipe.The establishment of a finite element model for flexible edge forming of half pipe by a general numerical simulation software Abaqus.The thickness and stress distribution of the forming parts in the half tube blank holder forming and the flexible blank holder forming respectively.The results show that for half tube forming,the effect of flexible edge forming is better than that of holistic blank forming.The thickness and stress distribution of the forming parts and the effect of restraining the wrinkling are studied when the inner side pressure is 5MPa and 7.5MPa,respectively.Discussion on the effect of inner side pressure on forming.The results show that the increase of inner side pressure helps to restrain the flow of sheet material and inhibit the wrinkling of the inner plate.The thickness and distribution of the forming parts are compared when the gap between the upper and lower dies is 0.05 mm and 0.5mm.Research on the influence of the upper and lower die gaps on the forming results.The results show that the wrinkling of the forming parts can be suppressed by reducing the gap between the upper and lower dies,reducing the range of stress distribution,and make the thickness of the plate more evenly distributed.The related conditions of the forming parts are analyzed when the radius of the lower die is3 mm and 6mm.Analyze the influence of the falling angle of the lower die on the forming.The results show that the maximum stress value,the minimum stress value and the stress distribution range decrease with the decrease of the lower die chamfering angle.Because the flow of sheet material is restrained by the smaller down die chamfering angle,the maximum thickness of the sheet and the thinning rate of the maximum thickness are increased.The effect of sheet cutting angle on forming is discussed.The results show that the sheet flow is more uniform in the forming process after the sheet cutting angle.Maximum stress,strain and thickness of forming parts,the distribution of stress,strain and thickness is reduced.In these two situations,displacement loading and force loading,the friction coefficient were μ=0.08 and μ=0.15,and in these two situations,use 08 Al and 304 stainless steel sheet material,the stress,strain and thickness distribution of forming,and analyzes the forming parts forming defects,discuss the influence method of loading,friction coefficient and sheet material on the forming results.The simulation results show that has no effect on the forming results using displacement loading and force loading;To use the coefficient of friction of μ=0.08 forming,the stress and the thickness distribution of uniform forming,maximum thickness reduction ratio is smaller;on the use of 08 Al and304 stainless steel sheet material forming,can obtain better forming quality flexible tube,half edge forming has the versatility and effectiveness of certain. |
PDF Full Text Request