Research On The Sidewall Upsetting Through Controllable Deformation Zone

One of the important methods to realize the lightweight structure is compact design of components and functional integration,resulting in increased parts complexity and new requirements imposed on forming processing.Under this background,sheet bulk metal forming(SBMF)was developed,which combines the advantages of sheet metal forming process and bulk metal forming process.The application of SBMF process is helpful to shorten the process chains,improve forming accuracy and save production costs,when manufacturing complex structural parts with non-uniform wall thickness or functional features.However,some challenges,such as buckling,unsatisfying filling and high forming load,occur during sidewall upsetting.Therefore,to overcome these difficulties,systematic investigations were carried out in this work as following:(1)A new method called as upsetting with controllable deformation zone(U-CDZ)was proposed,which is available to break through the limitation of slenderness ratio(the ratio of sidewall height to thickness).The buckling that usually appears in conventional upsetting method could be prevented.With the application of accessorial counter hydraulic cylinder,an experimental platform was built up to realize the relative movement among workpiece,punch,die and counter punch.Based on that,sidewall materials were pushed from holding cavity into forming cavity.The optimized tooling structure and counter force were beneficial to establish a stabilized deformation zone and thus to thicken the sidewall incrementally.Taking thin-walled shell parts with external gear as study object,the improvement of formfilling by U-CDZ method was verified for producing functional elements.(2)The upper bound model for sidewall upsetting with U-CDZ method was built to complete the quantitative analysis of forming load evolution.The mechanism of preventing steep increase of forming load in U-CDZ method was revealed.For simplified sidewall materials,based on the distribution of strain rate,the material gradually flows from the undeformed zone into the plastic deformation zone,and then transforms into the deformed zone.The stream function is used to characterize the material flowing,and the variation of forming load had direct relationship with the friction power,which is proportional to the change of side wall surface area.The forming load showed a stable trend with the establishment of stabilized deformation zone.(3)Based on the concept of U-CDZ method,the forming strategies for flange at arbitrary location is established.When the flange at the end of sidewall,using the U-CDZ method,adjusting the punch stroke can manufacture flange with arbitrary height.When the flange away from the ends,except buckling,dimple defect appeared.The counter punch is further optimized,adding a location cavity.Flange at arbitrary location could be manufactured without inside dimple flaws.And after forging streamline detection,the aforementioned strategies were available to form flanges at arbitrary location of the sidewall.(4)For the influences of the preforming on the sidewall upsetting,a process chain combing tailored blank and U-CDZ method was put forward.Taking sidewall-thickened cups as examples,the thinning at corner after stamping and its influence on the forging laps during the subsequent sidewall upsetting process were studied.A locally thickened tailored blank was designed,and coining process was adopted to realize local pile-up.Thus,a cup with sharp corner was prepared as billets for sidewall upsetting process,which is beneficial to avoid gaps between workpiece and tools.Based on that,forging laps were eliminated.Integral forming of complex structural parts with non-uniform wall thickness or local feature is realized under a high efficiency.