Research And Quality Control On Warm-cold Composite Precision Forging Process Of Hollow Thin-walled Parts

In precision forging technology,warm-cold composite forming process has the advantages of warm and cold forging,and obvious forming superiority,which is widely used in machinery manufacturing industry.Hollow thin-walled parts are widely various,thin-walled,and complex,besides the demand of their dimensional accuracy and mechanical properties is very high.They are in great demand in the automotive transmission system,chassis system and engine system.At present this kind of parts are usually produced with warm-cold composite precision forging process,but there are still many problems in the rationality of process design,the control of manufacture accuracy and forming quality.So the study of process characteristics of hollow thin-walled parts and eliminating the typical forming defects by process improvement have important guiding significance to production quality improvement of the parts.In this paper,according to the shape of parts,hollow thin-walled structure parts are divided into cup type,cup-rod type,flanged and toothed type.Also the structure of various parts and the main forming process are analyzed and proposed respectively.Quality problems of hollow thin-walled parts arising easily in practical production are summed up,besides a study on insufficient filling,low dimensional accuracy,microstructural nonuniformity and crack problems in the forming of parts is carried out and the process solution is put forward.Filling problems of the toothed and the cup parts are researched and analyzed,and using flanged outer gear ring part and thin-walled steel tube part as examples.The optimization schemes of the process are proposed to improve the deformation quality.For forming problems of the flanged outer gear ring in production such as insufficient filling and large forming force,hole divided flow improvement process and warm extrusion tooth process are put forward to improve tooth filling ability and reduce the deformation force.Also the best tooth cold finishing value is received.And simulation results show that tooth profile filling is full and forming force is low after the forming of two warm extrusion tooth schemes,which not only shortens the production time but also improve the forming quality.In order to solve the problem of the cylinder bottom clearance in the existing cold finishing process for thin-walled steel tube parts,an increase of the cutting angle of the shoulder before the cold forging can significantly reduce the clearance value.In this paper,an example of a steel cylinder is used to analyze the flow process of the metal in the cold finishing process,and the change rule of the cylinder bottom clearance value is obtained,then the reasonable range of shoulder angle is put forward.Through setting several simulation schemes the influence law of the shoulder angle and concave die semiangle on the cylinder bottom clearance and the cylinder bottom thickness is got,and the optimal angle of the shoulder and concave die semiangle are obtained.Then after improving the structure of reverse extruding concave mold,the shoulder angle is obtained directly,and simulation results show that this scheme can not only eliminate the machining process,but also the final shape and size precision of the forging meet the production requirements.The crack problems arising in the forming are researched.Using an accumulator shell part as an example,to eliminate the crack problem in cold forming the pre-forming design and heat treatment improvement schemes are put forward.Two kinds of preform shapes are simulated and analyzed,and the best preform structure is confirmed.In addition,the stress relief annealing process in the original forming scheme is changed into isothermal annealing process,which greatly improves the forging structure of cold forming and eliminates the bottom crack.What's more,the scheme has been put into practical prduction.