| In the stamping process,the die directly interacts with the material,causing the material to separate or deform under pressure.At the same time,the die is also subjected to the same reaction force,which makes the die bear harsh conditions such as high speed and heavy load under some working conditions.Therefore,it is of great significance to carry out die surface strengthening treatment,improve die service life and reduce stamping cost.The traditional die surface strengthening treatment technology can effectively improve the number of mold use,but most of the technology has such limitations as low efficiency and heavy pollution.Surface micro-texture has the effect of reducing friction and resisting wear.It has been widely used in tool friction reduction,cylinder liner piston ring friction reduction and other fields.The laser processing technology of micro-texture has the advantages of fast speed and no pollution,which is suitable for large-area rapid processing of die surface.By processing micro-textures in the grooves of the die surface array,it is expected to reduce the friction and wear of the die surface during the stamping process,improve the service life of the die,and improve the surface quality of the die and parts.Therefore,this study investigated the micro-texture processing technology of SKD11 die steel surface based on picosecond laser,clarified the corresponding relationship between laser process parameters and micro-texture characteristics.The effects of grooved micro-texture geometric parameters and distribution characteristics on the friction and wear properties of SKD11 die steel were studied by friction and wear tests,and the best micro-texture anti-friction micro-texture characteristics were determined.The friction and wear properties of microtextured die were studied by the combination of thermal-mechanical coupling finite element analysis and die stamping experiment.Firstly,the laser processing technology and material characteristics of micro-texture on the surface of die steel were studied.The ablation threshold of SKD11 die steel under different pulse numbers was obtained by numerical calculation.It was found that the ablation threshold decreases continuously when the number of pulses increases from 100 to 1000.The experimental study of hole processing and single groove processing was carried out,and the influence of different process parameters on the size and morphology of micro hole and single groove texture was obtained.The experimental study of linear array groove machining was carried out,and the corresponding relationship between laser processing parameters and grooved micro-texture characteristics was studied.Horizontal scanning,scanning spacing of 10μm,laser power of 30 W,processing times of 15 times,scanning speed of 200 mm/s,and repetition frequency of 100 kHz were selected as processing parameters.The content of different surface elements was analyzed.The change of element content on different surfaces was analyzed.It was found that the content of Fe and Cr elements on the textured surface decreased,the content of C element increased,and O element appeared at the same time.The content of O element on the surface of linear array groove texture was the highest.The hardness of the textured surface was tested.It was found that the hardness of the area near the groove texture was improved,and the hardness of the groove texture center was increased by 12.04%.Secondly,the friction and wear experiments of textured die steel surface under dry friction conditions were carried out.The effects of normal load and rotation speed on the friction and wear test results were studied.The normal load of 35 N and the rotation speed of 100 mm/s were selected as the working parameters.The effects of grooved micro-texture width,depth,area density and other geometric parameters on the friction and wear properties of die steel were studied.It was found that with the increase of width,the friction coefficient decreases and the wear volume increases.When the width was larger,the fatigue wear of the grooved microtexture edge increased and the surface quality decreased after wear.With the increased of depth,the friction coefficient and wear volume decreased,and the surface roughness decreased after wear.When the area density of the grooved micro-texture is 23.53%,the friction coefficient and wear volume were the smallest,and the surface roughness wear was the lowest,and the larger area density increased the wear amount.The effect of the angle between the grooved micro-texture and the motion direction on the friction and wear properties of the die steel was studied.It was found that the friction coefficient and wear volume of the groove texture surface with a 90 degree angle to the motion direction were the smallest,and the roughness Ra value of the surface after wear was reduced by 66.03%compared with the non-textured surface.Finally,the friction and wear properties of textured punching die and bending die were studied,and the anti-friction and anti-wear mechanism of die surface texture was revealed.The changes of stress field and temperature field in the stamping process of textured die were studied by thermal-mechanical coupling simulation analysis.It was found that the stress distribution of the textured die changed compared with the non-textured die.The stress at the edge of the punching die is reduced,but the maximum stress value of the whole die is increased.The area near the grooved micro-texture was prone to stress concentration.The maximum temperature of textured punching die and bending die decreased by 16.87%and 8.63%respectively.The grooved micro-texture increased the heat dissipation area of the die surface.The die stamping experiment was carried out.It was found that the wear volume of the textured area on the side of the punching die was 12.16%lower than that of the non-textured area,and the surface roughness was smaller after wear.There was groove filling in the textured area after wear.Comparing the wear morphology at the edge of the punching die after stamping,it was found that the ’edge collapse’ in the textured area was alleviated.Comparing the wear morphology of the top of the V-groove of the bending die after stamping,it was found that the typical furrow-like wear marks were found on the top edge of the V-groove in the non-textured area after stamping,but not in the textured area.The simulation and experimental results show that the grooved micro-texture processing on the side of the punching die and the top of the V groove of the bending die can enhance the anti-friction and anti-wear properties of both.In summary,the anti-friction and anti-wear mechanism of textured stamping die under dry friction conditions mainly includes storing abrasive debris to reduce three-body abrasive wear,reducing contact area,increasing hardness in laser processing area,changing stress distribution,and inhibiting friction temperature rise. |
PDF Full Text Request