Study On Forming Technology Of Progressive Turning Holes Of Curved Profiles Without Dies

The traditional hole-turning process is difficult to meet the needs of fast and efficient turning of thin-walled parts because of the need for special tooling.In addition,in actual engineering applications,many curved reaming parts with complex shapes are often encountered,which is difficult to process using traditional reaming methods.The flexible forming process using progressive turning not only saves the cost of the mold,but also can complete the turning of the curved surface with special shapes.At present,there are some practical applications,but the existing progressive forming still has a single part shape,low processing accuracy and complicated process And other issues,there is also a lack of in-depth understanding of the complex turning of curved surfaces.To this end,this paper has carried out research on the application of the progressive forming process in the forming of curved holes,in order to grasp the relevant laws of deformation.Among them,the method for calculating the geometric dimensions of prefabricated holes for surface turning is studied;the deformation and its influencing factors of oblong and rectangular progressive turning holes are analyzed with curved surfaces such as round tubes,square tubes and spherical surfaces;the progressive turning of curved surfaces is studied The change of the tool head load during the hole process analyzes the main factors that affect the forming accuracy of the surface turning hole;discusses the generation and control of common defects.The main conclusions are as:(1)The calculation of the size of the prefabricated hole should take into account the deformation of the progressive turning hole.In order to obtain the correct size of complex shaped hole-turning parts,it can be combined with the geometric expansion method formula or graphical method,and then corrected by numerical simulation.(2)Theoretical analysis of the force in the pre-turning process of curved surface reaming shows that unlike the flat reaming,the forming force of the pre-turning process of the curved strip is larger than that of the shaping stage;compare the curved strip and the flat strip It is found that the required forming force of each part of the curved strip hole is relatively close;due to the geometry of the curved strip hole and the difference in material flow,the thinning rate at different positions is different,and: arc end>transition end> straight Wall end.(3)In the process of forming a curved strip with progressive turning,the position of the in feed point,the starting machining position of the adjacent cycle,the pre-turning amount and the forming amount have an influence on the final forming quality of the part.Feeding from the straight section of the hole,increasing the amount of pre-turning and adopting a progressive method combining clockwise and counterclockwise can improve the final forming quality and help avoid the common defects of progressive turning.(4)A single factor and response surface analysis of the spring back during the pre-turning of the special-shaped turning hole of the curved surface,considering the influence of the surface thickness t,curvature,and pre-turning angle ? on the maximum spring-back angle ?a of the pre-turning,found the degree of influence on the spring back The order of magnitude is: pre-turning angle ?> surface thickness t>curvature.(5)Due to the non-axial symmetry of the progressive turning of the curved surface,the load and spring back trend required for forming at different positions are different,and the forming force,spring back trend and dimensional deviation all increase with the curvature of the blank.