Effect Of Pre-bulging On Deformation Process Of Single Point Incremental Forming Sheet

Incremental forming technology of sheet metal is a new flexible processing technology.The technology could form non-rotating body,asymmetric body and other complex sheet metal rapidly under the conditions of the non-mold or simply support mold.Although the technology development prospects are broad,three main problems exist in single point incremental forming(SPIF): Uneven thickness distribution,the existence of anomalous thinning area and the poor forming accuracy.In this paper,in order to solve the technical defects above,DC04 cold-rolled deep drawing steel plate was pre-bulged to a different height(15mm,25mm),and the different forming angle(55 °,65 °)cone will be finished by the Single Point Incremental Forming.The effect of pre-bulging on the forming deformation of Single Point Incremental Forming sheet metal was discussed.Based on the theory of metal plastic processing,the deformation state of bulging forming and SPIF are analyzed.Especially the stress and strain state of the first layer and the middle layer sheet,which provides a theoretical basis for the following process.The influence of parameters on the thickness,forming accuracy and forming limit in SPIF is summarized,the reason of the existence of abnormal thickness area is explained theoretically.The hybrid forming process(BF+SPIF)is provided basic on the SPIF.Two kinds of forming angles and two kinds of pre-bulging forming height were designed to forming the sheet into the same shape and size.Thickness distribution and Grain deformation are analyzed on the basis of the collect data.The FE model of the SPIF and BF+SPIF was established by Simufact12.0software.The Stress and Strain deformation rules during the forming progress and the Geometric accuracy were analyzed.The results show that: 1)In SPIF,the plastic deformation not only appears in the small local area under the tool,but also founded in some synergistic deformation area,and these areas’ deformation is related to the distance from the tool;The larger the forming angle,the larger thickness reduction and thickness distribution fluctuates.During the initial process of SPIF,the reducing influence of the flange area and the increasing work hardening as well as the different axial feed make the Abnormal Thinning area appear.During the following process,the combined effects of work hardening and springback makes the sheet wall thickness become steadily;2)It is effective to reduce the abnormal thinning area so that the sheet thickness distribution is improved by using the hybrid forming progress,and thegeometric accuracy is also optimized.The hybrid forming can also improve the grain distribution of the whole sheet and reduce the influence of the non-deformed metal on the deformation zone.The larger the forming angle is,the greater the tensile stress is,and the more uneven the strain distribution appears.Pre-bulging makes the strain distribution even more uniform.