Optimization Of The Stamping-forging Hybrid Forming Process And Die Structure For Countersunk Hole

In this paper,aiming at 90° countersunk hole and stepped countersunk hole as the research object,basing on the stamping-forging hybrid forming,three kinds of stamping-forging hybrid forming methods for 90° countersunk hole and stepped countersunk hole were worked out respectively.The process-load curve,effective stress and strain distribution and material flow of each forming method were analyzed and compared by the finite element simulation software DEFORM.The forming mechanism and the optimal forming process of 90° countersunk hole and stepped countersunk hole were obtained.The optimal forming process for the 90° countersunk hole is to punch the pre-hole first and then to extrude the 90° countersunk head.The optimal forming process of the stepped countersunk hole is to punch the pre-hole first,then press the step,and punch hole finally.Done stamping-forging experiment of countersunk hole according to the optimal forming process obtained by simulation,and analyzed the metal streamline.The results show optimal process could get uniform size and uniform deformation countersunk holes.Based on the optimal forming process of countersunk hole,the progressive die forming process of the 90° countersunk holes and the stepped countersunk holes in chain part was worked out.Problems such as breaking,gnawing,serious wear and poor accuracy of parts often occurred in actual production.Combining with the production practice and the finite element analysis,it’s found that the material flow along the length direction would lead to the elongation of the working part,which made a lateral force on the punching and shaving punches of the front and back.The influence of blankholder force,friction coefficient and diameter of punch hole on the elongation of working parts was analyzed.The isolation method and the grooming method were proposed.The isolation method is to reduce the initial length of the workpiece and add big blocks before and after the forging countersunk hole process;the grooming method is to punch a connecting belt between the two workpiece end to end before forging the countersunk hole to absorb the elongation deformation.In actual production,the main failure modes of the punch includes fracture and wear.The length of punch working section was obtained by theoretical calculation,that is 15.6 mm ≤ L ≤ 49.8 mm.The reason for the punch fracture is stress concentration according according to the effective stress distribution of punch in misalignment punching,and the hardness,metallographic and surface roughness of punch.The hardness of part was measured,it’s found that the parts are hardened around the countersunk holes,resulting in small punch wear.The influence of punch hardness,friction coefficient,blank holder force,clearance between punch and die on the wear depth was analyzed.Eight punch edge shapes,such as the flat edge,the corner edge,and the the different punch length were designed.The blanking force and the effective stress of the punch are analyzed.The results show that the optimal punch is a round angle edge structure.According to the optimal process and die structure production practice was carried out,and the qualified workpiece was obtained,and the life of the punch has been greatly improved from less than 20000 to more than 50000.