| Mold is known as the mother of industry and an important basic industry.Die surface performance is the key factor to determine die performance and forming part quality.It is found that the optimum friction distribution exists on the surface of the die,which optimizes the forming performance of the workpiece optimal.For this reason,the composite texture with concave shape reducing friction and convex shape increasing friction were used to actively regulate the friction characteristics of mold/workpiece interface and avoid the parts forming defects.However,there was no systematic method system for optimal design and manufacturing of die surface texture,and there was no study on the influence of texture on the microscopic mechanism of sheet metal plastic forming.Therefore,this paper aims to explore the influence of composite texture on the material flow of the workpiece in the plastic forming of the cylindrical mold.The main contents of this paper were as follows.Firstly,physical and mechanical analysis was carried out on the plastic forming process,and stress and strain analysis was carried out on each area of typical cylindrical drawing parts to find out the area where the workpiece is prone to failure;Through the analysis of the friction characteristics of each region of the cylindrical parts,the key friction sensitive areas of the die surface were found out,and the friction characteristics of the die surface were optimized by using the surface texture,so as to reduce the forming defects such as cracking and wrinkling.Secondly,Dynaform was used to simulate the drawing process of cylindrical parts.The simulation results showed that the friction coefficient of the die surface has a great influence on the quality of the formed part.The risk of wrinkling and cracking can be reduced by increasing the friction coefficient of punch or decreasing the friction coefficient of die.Moreover,the strain in the bottom region of the cylindrical part obtained by the optimized drawing was more uniform,and there was a larger annular safety region in the forming limit diagram.The spherical crown convex texture and micro-concave texture were selected,and their shape characteristics were assigned to the surface of the mold.The forming process of the composite texture die was simulated.The results indicated that the maximum thinning rate of the composite texture drawing cylindrical parts decreases by about 4.5%,the maximum thickening rate also decreases,and the strain distribution is more uniform.It is also found that 20% texture density can minimize the maximum thinning rate of the rounded corner area at the bottom of the cylinder,while the convex texture type has little influence on the thickness.Thirdly,the forming mechanism of texture morphology was analyzed,and it was found that the formation of convex morphology was mainly due to the convection of Marangoni,while the concave morphology was the result of the gasification caused by the irradiation of materials.The single factor rotation method was used to analyze the influence law of laser power and pulse width on texture morphology size,and it was found that the type,diameter,height of convex point were closely related to laser power and pulse width,while the depth and diameter of concave morphology were mainly determined by laser pulse width,and had little relationship with power.Finally,according to the results of the process test,the composite texture with concave shape reducing friction and convex shape increasing friction were set up in the sensitive area of the surface friction of the mold,and the comparison test between the texture and non-texture mold deep drawing cylindrical parts was carried out.It was found that compared with the non-textured mold,the thickness of the formed part drawn by the composite texture mold decreases by 4% and 2.2% in the flange area and the flange fillet area,and increases by about 4.5% and 2.5% in the cylinder bottom fillet area and the straight wall area,which was consistent with the simulation results.The radial strain variation in each region of the cylinder was also similar to the thickness variation.It was also found that the surface of the material in contact with the concave texture is smoother and the internal grain size is larger,which indicates the resistance to deformation is weaker and the force is prone to flow.However,there were embossing pits on the surface of the material in contact with the convex morphology,and the internal grain size is relatively fine,which indicates that the plastic deformation resistance is large and the force flow is difficult.This also proved that the concave morphology can reduce friction and promote the material flow,while the convex morphology can increase friction and hinder the material flow. |
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