The hottest mold surface is shot peened and streng

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Mold surface shot peening strengthening (Part 2)

shot peening machines used for shot peening include pneumatic shot peening machines and centrifugal shot peening machines

pneumatic peening machine is supplied with compressed air by air compressor. When the compressed air passes through the spray gun, it causes negative pressure to suck the projectile into the nozzle and eject it at high speed, forming a projectile flow to the surface of parts. There is also a mechanism to make the parts move in the shot peening machine, which can ensure the uniformity of shot peening and a certain coverage

another key factor to ensure the quality of shot peening is to select the appropriate shot according to the material and size characteristics of the part. The bullets often used are round bullets with diameters ranging from 0.05mm to 1.5mm. The diameter of the projectile is determined by the size of the groove, groove and fillet of the part. It is necessary to ensure that the diameter of the projectile is smaller than the size of the groove, groove and fillet that need to be strengthened

the commonly used shot blasting media (shot) are:

a, cast iron shot: cast iron shot is hard and brittle, easy to break, and has been rarely used at present. b. Steel shot: at present, the most used steel shot is made of spring steel (diameter 0.6mm ~ 1.2mm). The hardness HRC of steel shot is generally 45 ~ 50, and the service life of steel shot is about 20 times higher than that of cast iron shot. c. Glass pellet: developed in the 1970s, the hardness of glass pellet is HRC 48, and its fracture toughness is high. It is mainly used in the aviation industry

(2) selection of main process parameters of shot peening strengthening

shot peening strengthening can significantly improve the residual compressive stress on the surface, thus improving the fatigue life of parts. However, reasonable selection of shot peening parameters should be made, which should not only consider that the residual compressive stress reaches a certain value, but also prevent excessive shot peening, so as to avoid surface defects and reduce the strengthening effect

practice shows that the residual compressive stress increases gradually with the increase of shot peening time; With the increase of the rotating speed of steel shot, the residual compressive stress also increases gradually; The diameter of the shot is large, and the efficiency of shot peening is high, but the surface smoothness of the workpiece is reduced

application and effect of shot peening strengthening of die

(1) shot peening strengthening of CrWMn steel wire cutting die

after EDM cutting, the mold is not shot peened. 4. The experimental equipment controlled by microcomputer is equipped with measurement and control software before leaving the factory for grinding and tempering. When it is directly assembled and used, it is often prone to edge collapse, fracture and fragmentation. Even if these phenomena do not appear, the service life is not high. The reason is that the tensile stress produced by heat treatment and wire cutting are superimposed, which is easy to reach the strength limit of the material and produce cracks. Tempering, grinding, shot peening and tempering can effectively remove the white hard layer and improve the hardness and stress distribution of the cutting layer. The white hard layer can also be removed by grinding, but the stress distribution in the stress zone cannot be improved. Therefore, the crack and edge collapse of the die cannot be fundamentally solved. Applying shot peening and aging treatment at 120 ~ 160 ℃ for 6 ~ 10h to the white hard layer of wire cutting die can double the service life of the die

the grinding life of CrWMn steel wire cutting die of a factory is 10700 times when it is directly used; 11180 times after tempering at 160 ℃ for 2h; 4860 times after grinding and removing the white hard layer; 7450 times when the white hard layer is removed by grinding and tempered at 160 ℃ for 2h; 28743 times after removing the white hard layer by grinding; Shot peening and tempering treatment at 160 ℃ for 2h are 220000 times

(3) shot peening to improve the performance of Cr12 Steel wire cutting blanking die

cr12 steel washing machine motor stator and rotor blanking dies, when directly used after quenching, tempering and wire cutting, often break and fail. The average service life is only more than 30000 times in order to save trouble. After adding a shot peening strengthening process after EDM, the performance of the variable quality layer of the wire cutting blanking die can be improved, and the service life can be increased to 100000 strokes

to sum up, shot peening strengthening technology is a mold surface strengthening technology with simple use, low cost and wide application range. The strengthening effect is particularly significant and immediate, and greatly prolongs the service life of the mold bearing alternating load, which is unmatched by other strengthening methods of b-constant

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