Study On Prediction For Die Wear During Cold Forming Of AHSS Sheets

The high intensity level of AHSS can lead to higher contact stress and temperature during cold forming,thus resulting in serious surface damage of sheet metal and die wear,which is also a technical challenge to the application of AHSS.In order to study friction wear on the interface between the die and blank during cold sheet forming of AHSS,this paper carried out the research on friction coefficient on the radius of die,surface damage of sheet metal,and the prediction for die wear during cold forming of AHSS sheets,analyzed the influence of material factors and process factors on surface damage to sheet metal,and established prediction method for die wear.(1)Study on sliding friction coefficient based on bending test.Put forward a new method for calculating friction coefficient on the die radius with consideration of bending force and anti-bending force,on base of which,studied the material factors and process factors‘ influence on sliding friction coefficient on die radius.The investigation shows that: the bending friction coefficient is obviously higher than the plate drawing friction coefficient;strength of material can influence bending friction coefficient,the higher the material strength is,and the lower the friction coefficient is.Process parameters can affect the friction coefficient,too.With the decrease of die corner radius,the increase of BHF and the decrease of stamping speed,the friction coefficient will increase;lubrication can reduce the friction coefficient.(2)Experimental study on surface damage to AHSS sheet.Studied the material factors and process factors‘ influence on surface damage to AHSS sheet based on physical simulation experiment,and studied the influence of the processing parameters on the maximum value of the temperature field based on finite simulation,gave a further interpretation of surface damage.The investigation shows that: strength of material can influence the surface damage;under the same consideration,the higher the strength is,the higher the contact pressure is,and the more serious the surface damage is.Process parameters can affect the surface damage,too.With the decrease of die corner radius,the increase of BHF and the increase of stamping speed,the surface damage will be more serious;lubrication can reduce the damage to sheet surface.(3)Prediction for die wear based on friction energyObtained the association between process parameters and friction energy by means of numerical simulation,and established the connection between the friction energy and die‘s repair limitation through experiment.In addition,this paper also studied process factors‘ influence on the distribution of friction energy on die radius.The investigation shows that: at the beginning of the die‘s corner,the friction energy is the biggest,and then decreases along the corner,while at about 40° on the radius,friction energy increases to a peak value,then reduces to zero.Process parameters can affect friction energy,with the decrease of relative corner radius,the increase of stamping speed and the strength of material,the friction energy will increase;while BHF has a very tiny influence on the friction energy.