Study On GH4169 High Strength Precision Bolt Forming Process

GH4169 alloy was used as the material of high-strength bolts,and the bolt rod forming,bolt head forming and thread rolling processes were studied.A complete set of GH4169 high-strength bolt forming process is summarized to achieve the purpose of improving bolt performance,improving production efficiency and reducing production cost.The specific research contents are as follows:(1)Research on the cold extrusion forming process of the bolt rod.The design and optimization of the cold extrusion die was carried out.After more than 100 repeated experiments,the mold remained intact,which proved the rationality and excellence of the die structure.And using Forge software for simulation,the reasonable process parameters were obtained: friction factor 0.05,pressing speed 3.6mm/s.Moreover,based on the surface treatment scheme of austenitic stainless steel,a surface treatment scheme specially applied to the cold extrusion deformation of GH4169 alloy is proposed.It has been found through experiments that the friction between the blank and the mold is effectively reduced,and the quality of the cold extrusion is improved.At the same time,it solves the problem that the "bang,bang..." loud noise often occurs during the cold extrusion process.(2)The mechanical and tissue properties of the bolt rod after cold extrusion were tested.Through the mechanical property test,the tensile strength of the bolt rod is up to1917 MPa,which is 116% higher than the 883 MPa before cold extrusion.The hardness is up to HV496,which is 92% higher than the HV258 before cold extrusion.However,the hardness of the bolt head that is not involved in the main deformation is not obviously rising,which creates favorable conditions for the formation of the bolt head.Moreover,through the observation of the structure,it was found that the axial structure grains were elongated to form a fibrous structure;the radial structure became more dense and uniform,confirming the superiority of the bolt rod cold extrusion forming process.(3)Research on hot heading process of the bolt head.A three-dimensional finite element model of head hot forming was established by using Forge software.The influence of the shape and size of the billet and the heating scheme on the head forming was analyzed.A reasonable process plan is obtained: conical billet,local heating 950?.Combined with the actual production of the factory,the reliability of the simulation was verified.(4)Research on cold heading process of the bolt head.A set of cold forming die was designed.In the cold forming experiment,Lower core was broken and the bolt head was “snapped” in the upper core cavity.The reason was analyzed and the improvement scheme was proposed: the lower core's material is selected as CT80,and the lower core and the lower core shell are subjected to interference fit,and the interference is 0.06 mm.In addition,the upper core cavity is provided with a 1°draft slope.(5)The thread rolling process was studied.Using the characteristics of electric induction heating "skin effect",the surface layer of the high-strength bolt rod is heated rapidly,which reduces the deformation resistance of the surface layer of the metal,and ensures that the strength of the core is not affected.