| In order to solve the problem of magnesium alloy sheet forming with poor plastic deformability at room temperature,a layer of auxiliary sheet metal was added to the original AZ31 B magnesium alloy target sheet,and the friction heat generated between the tool and the auxiliary sheet metal was used as the auxiliary heat source to carry out the incremental forming experiment of double-layer sheet.It is found that the surface quality of the target plate is well improved while the formability of the target plate is improved.the main research contents and conclusions are as follows:According to the experimental study of incremental forming mechanism of single and double-layer sheet and the theoretical analysis of stress and strain of process parameters.The results show that through the grid strain on the sheet metal,it can be found that the metal in the sheet metal basically flows along the axial direction,and the target wall thickness of the double-layer incremental forming process with auxiliary sheet metal is higher than that of the single-layer sheet metal process.the change of wall thickness in the sheet metal deformation zone conforms to the cosine theorem.The friction and thermal incremental forming process of double-layer sheet metal is simulated and analyzed by using ABAQUS finite element software,and the variation rules of equivalent stress and strain and sheet metal thickness in the process of double-layer plate incremental forming are summarized,as well as the influence of process factors on the forming parts.In the forming process,the equivalent stress gradually increases with the decrease of the forming tool,and remains stable after reaching the ultimate strength of the material until the maximum Mises equivalent stress decreases after the end of tool withdrawal.The variation law of equivalent strain is consistent with that of sheet metal thickness.in the early and middle stages,the area of sheet metal sidewall reaches the maximum equivalent strain,and the thinning rate of wall thickness is the largest,which decreases to a certain extent and then tends to be stable.Through the influence of each single factor on the target forming parts,it is known that the smaller the layer feed is,the better the quality of the formed parts is;within the 1500r/min～2500r/min range,the plastic deformability of the forming parts increases with the increase of temperature;the influence of the tool diameter on the forming parts is very small,and the forming angle has a great influence on the forming parts,which is in line with the change trend of theoretical analysis.Through the straight groove experiment,the SUS304 stainless steel sheet was selected as the auxiliary plate to carry out four-factor and three-level orthogonal experiment to explore the influence of process parameters on the formed parts.According to the analysis of variance,the factors affecting the forming performance are in the following order: tool speed > layer feed > interaction between tool speed and layer feed > interaction between tool speed and feed speed.The factors that affect the surface quality are as follows: layer feed > tool speed > interaction between layer feed and tool speed > tool diameter > interaction between layer feed and tool diameter.The experimental data are analyzed by response surface method,and the regression model of maximum forming limit angle and minimum surface roughness,the optimal combination of process parameters and the prediction of response value are obtained.The result is: Tool speed 2266.73r/min,Tool diameter 8.72 mm,Layer feed rate 0.5mm,Feed speed 2997.12mm/min,Forming limit angle 69.1°,Surface roughness 0.662μm.In addition,the friction thermal incremental forming experiment was carried out by using the optimal combination of process parameters,and the target forming parts of single and double-layer plate processes were compared.it was found that the formability of AZ31 B magnesium alloy target plate could be improved by adding SUS304 stainless steel plate as auxiliary plate,and the surface roughness was greatly reduced by 62.8%.The surface morphology of double-layer plate process target forming parts was evenly distributed,and the surface quality was well improved. |
