Study On Workpiece Features And Control Methods Of Single Point Incremental Forming

Single point incremental forming is a new type of die-free flexible sheet forming technology with local dynamic loading and gradually accumulation inhomogeneous deformation.The sheet material is formed layer by layer according to the presupposed forming trajectory through specific forming tools without special moulds,and finally the required part shape is obtained.Compared with the traditional sheet metal stamping process,it has the advantages of fast,flexible,green and low cost.The forming process is especially suitable for forming the sheet parts of customization and small batch.Although the single point incremental forming technique has many significant advantages,it difficult to precisely control the characteristics of the forming parts because the sheet metal deformation in the forming process is complex,and the number of forming parameters is large,which seriously restricts the development and industrial application of single point incremental forming technology.Therefore,based on the analysis of the friction condition in the contact area between sheet and tool head,the method of theoretical analysis,finite element numerical simulation and experimental research is used to systematically study on the workpiece features such as forming precision and surface quality in single point incremental forming process.This research has important theoretical significance and application value.The mechanical model of single point incremental forming process with variable friction condition is established.The analytical relations between the friction coefficient,the forming force and the forming parameters are obtained.The friction coefficients of different forming parameters are obtained by substituting the experimental forming force into the analytic formula.The direct relation between forming parameters and friction coefficient is established by response surface method,and the effect of forming parameters on friction coefficient is analyzed.According to the characteristics of the finite element modeling in single point incremental forming and the solution method of the friction coefficient,the finite element simulation model of forming process considering friction condition is established.The theoretical calculation method and the finite element model are verified by comparison between simulation and experimental results.Based on the sheet state obtained by the dynamic explicit algorithm as the initial state of unload process,the method of simulating the forming part unload process springback is present by using the calculation method of static implicit algorithm.The distribution of residual stress in formed parts is studied by simulation results,and the influence of forming parameters on the residual stress and springback of forming parts is analyzed.Besides,the relationship between residual stress and springback is established.The microstructure and surface roughness of the formed parts in different areas are obtained by experiments,and the relationship between residual stress and microstructure is analyzed.Multi-objective parameter optimization is carried out with geometric precision and surface roughness,and the optimum forming parameter combination is obtained,which provides a reference for controlling the workpiece features by selecting forming parameters.The normal vector of STL triangular path combined with the residual height forming adaptive layering method of single point incremental forming path is presented,which is suitable for semispherical tool and rectangle tool.A mixed feed path of the pressure point dispersion is generated by avoiding the plastic deformation zone of the pressure point in order to solve the problem which is local indentation and global torsion of formed parts caused by concentrated pressure points and unidirectional forming track in forming process.The G code generation module for different NC systems is designed,and a single point incremental forming path generation software is developed using C++ as the programming language on Qt Creator platform.The G code that can be used in different numerical control systems is obtained.Finite element simulation and experiment research are carried out with different types of forming paths,and the influence of forming paths on the workpiece features of forming parts is studied.The results provide an important basis for the effective control workpiece features by optimizing the forming trajectory.The feasibility of the method and the practicability of the system are verified by confirmatory experiment.The single point increment compound forming method of flexible support with static pressure is presented,and the static pressure flexible support device is developed.The mechanical model of the flexible single point incremental forming process with static pressure is established,and the theoretical formulas of triaxial stress and softening coeff-icient of stress state in contact area are obtained by theoretical analysis.Based on that,the influence of static pressure on forming process is analyzed.Besides,the finite element model of static pressure flexible supporting single point incremental forming process is established.Meanwhile,the effects of static pressure on forming force,equivalent plastic strain,residual stress and springback are studied,and the influence laws of static pressure on the workpiece features of forming parts are obtained.The results of simulation and experiment show that applying appropriate static pressure can effectively improve the precision of the parts and reduce the global deformation of the forming parts,which provides a new method for improving the workpiece features of forming parts.