Study On Incremental Forming Method Of Magnesium Alloy Sheet With Warm Liquid Medium Assisted Support

As the lightest metal structural material,it is feasible to apply magnesium alloy in engineering across the world now.With excellent performance,it can meet the requirements of thin-walled and lightweight of various products.Thus,it achieved a broad application in aerospace,transportation,electronic communication and other fields.Nevertheless,there are also some bottleneck problems restricting the application and promotion of magnesium alloy materials,which are caused by its poor plasticity and forming properties at room temperature According to some researches,it can be seen that the plasticity of magnesium alloy is improved and the deformation resistance is decreased when the forming temperature is increased Therefore,in the field of metal plastic processing,more and more attention has been paid to the development of warm forming technology of magnesium alloy sheet.Metal sheet thermal progressive forming technology refers to a kind of warm and flexible forming technology,which adopts the idea of layered manufacturing while heating the sheet metal.In this way,the parts can be processed in order,so as to achieve final integral forming.It’s no denying that this technology is quite suitable for the research and development of magnesium alloy products and customized small batch production.Aiming to realize the extensive application of magnesium alloy thermal progressive forming technology in industry,this thesis conducted systematic researches on the quality of magnesium alloy thermal progressive forming,offering theoretical basis and technical supports for its optimization of process parametersThis paper put forward a method of warm liquid medium supporting incremental forming of magnesium alloy.Applying plastic bending theory and finite element analysis method,it method,it studied the affects of liquid support on the various aspects in the process of progressive forming of magnesium alloy,including stress,strain and forming force.Meanwhile,the stress-strain changes of different joints in sheet metal forming area was studied as well at the moment of contact between tool head and workpiece.Based on the above,two important laws were summarized,which included the distribution law of stress-strain in forming process and the influence law of process parameters on stress-strain.Thus,the change rules of thermal progressive forming force with time and contact point were obtained eventuallyThe influence of liquid or no liquid support on the wall thickness of magnesium alloy was compared and its causes were also analyzed.The relationships between the thickness of the part wall in the forming area and various aspects were studied,such as the diameter of the tool head,the forming angle and the spacing between layers.The influence of liquid support,forming temperature,forming angle,layer spacing,diameter of tool head,feeding direction of tool head on forming limit of hot progressive forming sheet metal are analyzed.In this way,a significant reference for the practical application of thermal progressive forming can be offeredThe thesis carried out study on the mechanism of residual wave crest and surface scale,as well as an analysis on the effect of scale on surface roughness.Then,it established mathematical relationship between the length scale on the workpiece surface and the feed speed,as well as the rotation speed of the tool.At the same time,the effect of the period length of scale on the surface roughness of the workpiece was also revealed.According to the theoretical analysis and experimental results,the optimizing combination of of feed speed,rotational speed and tool material was proved to be able to control the surface quality of thermal progressive forming effectivelyIn this thesis,the following related aspects were analyzed and studied,including the influence of the parameters of magnesium alloy sheet hot progressive forming process on the forming accuracy,the influence of residual stress and process parameter changes on the forming accuracy,and the affects of the size of liquid medium support force on the forming accuracy were obtained through analysis.In addition,it studied the thermal incremental forming microstructure evolution law,under the condition of different heat preservation time through the analysis of the microstructure of the sheet metal forming,revealing the sheet neutrosphere migration,as well as the offset and grain size on the influence law of forming a springback amount.It’s a good guide for control of springback parts value.This thesis studied the influence of the factors such as liquid support,bottom side length,forming temperature,layer spacing,forming Angle and initial thickness of sheet metal on the bulging of the forming parts,analyzed the cause of the bulging in different areas of the forming parts,established the analysis expression of the bulging height,and offered an analysis method for effectively restraining the bulging defects.