Research On The Friction Mechanism And Influence Of Single Point Incremental Forming Of Sheet Metal

Single Point Incremental Forming(SPIF)is a new technology for rapid prototyping of sheet metal with local dynamic loading and layer by layer uneven deformation.It has the advantages of flexible,rapid,green,low cost and so on.It can realize thin-walled parts forming with complex geometric shape.The friction state between forming tool and sheet metal during the forming process has great influence on the surface quality of the parts and the formability of the sheet metal.In this thesis,the friction mechanism between the forming tool and the sheet metal in the process of single point incremental forming and the effect of friction on the forming of the parts are studied by means of theoretical analysis,numerical simulation and experimental research.It is of great significance to improve the quality of the forming parts and the formability of the sheet.Based on the basic friction theory in plastic forming,the friction characteristics and friction models of the single point incremental forming process are analyzed.The contact area between the forming tool and the metal sheet is taken as the analysis object,and the stress condition under the friction force is analyzed and expressed,and the relationship between the forming force and the friction coefficient is established.In view of the characteristics of single point incremental forming,the finite element model of the simulation of forming process is established,and the relationship between the forming force and the coefficient of friction is analyzed,and the influence of the friction coefficient on the equivalent stress,the equivalent plastic strain,the torsion of the sheet and the thinning of the sheet thickness during the forming process is analyzed.Using the Box-Behnken experimental design(BBD)in the response surface method(RSM),a single point incremental forming experiment system is established.Through the forming force test,the friction coefficient of different process parameters is calculated and the influence of the forming parameters on the friction coefficient distribution is analyzed.Based on this,the RSM prediction model of the friction coefficient is established.Through the surface roughness of parts measurement,the surface morphology of parts observation and the surface hardness of parts test,the influence of the lubrication methods on the surface quality and surface hardness of the forming parts is analyzed.Through the test of the damaged depth of the variable angle cone,the formability is evaluated by the maximum forming angle,and the influence of the lubrication methods on the forming limit,the damage morphology and the microstructure is analyzed,and the influence mechanism of the friction on the forming process and the result is further revealed from the micro level.The experimental results confirm the correctness and effectiveness of the theoretical analysis and numerical simulation results.This thesis provides a theoretical basis and technical guidance for improving the surface quality of the forming parts and improving the formability of the sheet by improving the friction state of the forming tool and the sheet in the process of single point incremental forming.