Thickness Distribution And Control Method Of Incremental Sheet Forming

Incremental Sheet Forming(ISF)is a new flexible sheet metal forming process,which can form all kinds of complex parts without dedicate dies.Compared with traditional stamping process,this technology has many advantages,such as lower cost,shorter manufacturing time,lower forming load and so on.Besides,the formability of sheet increases in this process due to the local and incremental forming nature.So,this forming process can be a very good alternative to stamping for small-batched or customized products,which is especially true in the field of aerospace,biomedical and automotive development.However,the material deformation mode and boundary condition are all complex in ISF process,such as the local contact between the tool and sheet,the cyclic loading and unloading,other than traditional nonlinear problems in plastic mechanics.At present,no agreed conclusions achieve about the material deformation behavior.Besides,how to predict and control the thickness distribution of parts made by ISF is also a challenge.To predict and control the thickness distribution of parts made by ISF,deeper researches are made based on the mechanical analysis,finite element simulation and experiment.The main research contents and findings are briefly obtained as follows,which is funded by National Natural Science Foundation of China(N0.51675332).A quick geometrical model is proposed to predict the thickness distribution in ISF.The model can be used to predict the geometric profile of a part after each forming step and the moving trace of material point on the part surface,and then calculate the thickness distribution based on the volume invariant condition.Four case problems including a cone part,a parabolic cone part,a non-axisymmetric part and a hemisphere part are physically formed by using the AA5052 material to verify the proposed model.It is found that the proposed model can predict the part thickness with better accuracy than the Cosine law,especially in the case of multi-pass forming.Besides,the model can finish the calculation in dozens of minutes with higher calculation efficiency than the finite element simulation.The proposed model can also be used to predict the thickness of parts in both single-pass and multi-pass ISF.Besides,the rigid body motion is also considered in the proposed model so that the model can be used to check the feasibility of the pre-form shapes in multi-pass ISF.The finite element model is established for a deep drawing part made by ISF,and the deformation behavior is analyzed to explain the sever thinning of part combining with experiments.Then,the effects of the main process parameters and the tool path strategies on the part thickness are analyzed.It is found that the process parameters have little effect on the part thickness and can not be used to control the thickness distribution.Multi-pass strategy(the design of pre-form shape and the tool motion direction)can be used to control the thickness distribution.Especially,the change of tool motion direction can effect the thickness distribution greatly.For flanging parts made by ISF,a new flanging tool is proposed accompanying with the suitable tool path strategy.In order to obtain a better understanding of this new flanging approach,experiments have been conducted to observe the geometric accuracies,the thickness distributions and the forming forces of typical circle and square flange features formed by this new flanging tool.It is found that the new flanging tool accompanying with the tool path strategy is a very good forming method to improve the thickness distribution of flanging parts made by ISF.The mechanical analysis models and finite element models for parts under the new flanging tool and the conventional ball-nose tool are established.The stress and strain states are also analyzed to explain the different deformation modes under the two tools.Results indicate that the new flanging tool will generate stronger meridional bending other than stretching in conventional ISF in the area far from the pre-cut hole.The bending-dominated deformation mode and localized deformation nature under the new flanging tool enhances more uniform thickness distribution on the flanging part with better performance in resistance to fracture.