Study On Residual Strain In Metal By Tiaht Grid Method

Die casting moulds will have fatigue caused by various reasons during use.Residual stress is the most fundamental cause of material fatigue.But stress is inevitable when the material is in use.Therefore,in order to alleviate the fatigue phenomenon during use,we proposed a hammering method to modify the stress distribution inside the material.To investigate the influence of the hammering method on the plastic zone inside the material,we use the abutting grid method to perform large-scale quantitative calculation and analysis on the strain of the plastic zone of the material.In this paper,the internal strain phenomenon of the plastic zone of the material is studied by tight grid method,and an industrial robot is used to plan the path and put it into practice.The tight grid method is an improved method based on the tight-hammering method.We use the accuracy of the micrometre to draw grid lines with a pitch of 0.2 mm,which is placed on the tighted surfaces.Then,we tightened the specimen with a U-shaped frame and a compression beam,performing single-hammer test and static-load pressure test at the seams.The equipment for a single hammer test is an original self-made device that allows a certain weight of weight to fall freely along a track perpendicular to the horizontal plane for a certain distance,and finally reaches the end of the punch that contacts the sample against the seam.The free fall hammer height of the experimental is designed to be 50 mm to 150 mm;the static pressure load is designed to be 1 kN-5 kN;the spherical punch of the cemented carbide punch is designed to be 5 mm,10 mm and 15 mm;the sample has DT 4E special grade electromagnetic pure iron,4Cr5MoSiV1(H13 according to ASTM standard)hot work die steel.The tighted surfaces were observed by VHX-500 Keyence digital microscope,and the strain value at each point was calculated.Finally,the dynamic strain gauge was used to measure the strain at the seam and the strain at the solid at different distances.The experimental results show that:1)There is compressive strain in the depth direction of the hammer point.The maximum compressive strain is at the center point,reaching a maximum of-0.0902.There is tensile strain in the tangential direction.The maximum tensile strain is 0.8 mm from the center point,and reaching a maximum of 0.257.2)There is an obvious strong strain zone in the radial tensile strain.The boundary between the strong strain zone and the weak strain zone can be found more accurately by mathematically finding the tangent point of the curve and the slope.The strong strain zone is one-third of the entire plastic zone.The pressure in the depth direction also has a strong strain zone,but it is not as obvious as the above.Similarly,by mathematically finding the tangent point of the curve and the slope,the boundary between the strong strain zone and the weak strain zone can be found more accurately;the strong strain zone accounts for about 1/2 of the entire plastic zone.