Forming Process And Numerical Simulation Research On Multi-point Forming With Flexible Blank-holder For Sheet Metal

Sheet metal forming is an important part of modern industrial production.It has the advantages of high dimensional accuracy,short production time,high processing efficiency,easy to realize mechanization and automation.For parts with complex shapes or large deformations,due to the different flow of each part of the plate,defects such as wrinkles and cracks are easily generated.Usually,the blank-holder device is used to restrict the flow of the plate to suppress these.The traditional method of pressing does not meet the stress requirements of the sheet itself,and the metal flow is often limited,which tends to cause metal accumulation or reduction,and defects such as wrinkles or cracks..The multi-point forming with flexible blank-holder technology is method combining multi-point forming and flexible blank-holder.Multi-point mold can quickly form three-dimensional complex parts and the mold production cost is reduced and the same time,and can rapidly realize flexible forming of the sheet.The flexible blank-holder device consists of blank-holder strip(or ring)and discrete blank-holder block(or hydraulic cylinder).In the forming process of the pressing,the position of the blank-holder blocks can be reasonably arranged according to the shape of the forming part,and the magnitude of the blank-holder force can be appropriately changed,so that the stress,strain and thickness distribution of the formed part are more uniform.The main contents and conclusions of this paper are as follows:(1)The analysis of flexible blank-holder forming principle and deep drawingTaking the box-shaped part as the research object,the technical characteristics and design idea of multi-point forming of flexible blank-holder are discussed and analysis the concept and theoretical of deep drawing.According to the forming characteristics of the box-shape and the uneven force characteristics during the stamping forming process,thegeometrical shape is divided and the stress and strain state in the forming process of each area is analyzed.(2)The experiment of multi-point forming with flexible blank-holderThe multi-point forming design idea and principle of flexible blank-holder are discussed.The process is experimentally studied to confirm the feasibility and forming advantages.During the experiment,flexible blank-holder device and multi-point die were used to shape parts.The results show that when forming the same depth box-shaped,the optimal forming part can be obtained under the combination of proper blank-holder force,thicker edge strip and more layering of the strip.(3)Multi-point forming with flexible blank-holder finite element model is establishedBased on the plastic forming theory,the yield criterion and plastic flow criterion of sheet deformation are discussed.According to the large deflection plastic deformation of thin sheet,the basic equations and virtual principle of dynamic finite element analysis are studied.Based on the finite element theory,the finite element model of flexible blank-holder is established.The process of establishing the finite element model is introduced,including defining the contact conditions,friction type,load size and boundary constraints in the geometric model,and meshing of each component.(4)Effect of blank-holder strip parameters on flexible blank-holder formingThe finite element model of different parameters of strip was established.The different layering methods,thickness and material of the blank-holder strips on the forming result were systematically studied.The results show that the quality of the formed parts obtained by using the strip is better than that of the without;the more the thickness of the blank-holder strip of the same thickness,the more uniform the stress strain and thickness distribution,the more reasonable the sheet;When forming with different material strips,the65 Mn spring steel with larger modulus of elasticity has a uniform stress-strain distribution than the 2024-O,and the control wrinkles are obvious,and the forming depth is also larger.(5)Effect of blank-holder force parameters on flexible blank-holder formingThe effects of different blank-holder force and friction coefficients on multi-point forming of flexible blank-holder were studied by numerical simulation.The results show that the blank-holder force within the range of 0.1~3MPa,with the increase of the force,the stress and strain of the formed part and the thickness distribution of the sheet tend to be uniform,and the quality of the formed part becomes better.The friction coefficient is in the range of 0.05~0.5,with the increase of friction coefficient,the stress distribution interval ofthe formed part decreases,the thickness distribution is more uniform,and when the friction coefficient is 0.5,the cracking phenomenon occurs.Therefore,by selecting a reasonable blank-holder force and friction coefficient,the part with uniform stress and strain distribution and a small reduction ratio can be obtained.