Research On The Service Life And Mechanism Of Extrusion Die Based On Laser Shock Peening

In this paper, the research object was H13 hot-work die steel and H13 extrusion dies. According to the mechanism caused by laser shock peening and the spread of shock waves in material and the interaction effect between shock wave and material, the paper studied the mechanism of prolonging service life of extrusion die though numerical analysis and experiment. The main research conclusions of this paper were as follows:Under the same condition, by changing the parameters, such as shock number and laser power density, the paper analyzed the laser shock loading process and the static rebound process after laser shock peening, the paper also explored the effects of changing parameters on the properties H13 hot-work die steel. The results showed that with the increasement in shock number, the maximum residual compressive stress of the surface and residual stress layer depth were both increasing, but the amplitude of the maximum residual compressive stress and residual stress layer depth was reducing. When the shock number was three, the maximum residual compressive stress and residual stress layer depth nearly reached limit. In the simulation the maximum residual compressive was 765 MPa and the residual stress layer depth was 0.8mm. The optimal range of laser power density was from 23GW/cm2 to 36GW/cm2, in this range the maximum residual compressive stress and residual stress layer depth increased with the increasement of laser power density. When laser power density was under 23GW/cm2, the effect of laser shock peening was not obvious. When laser power density exceeded 36GW/cm2, the maximum pressure of the laser-induced shock wave was greater than 2.5HEL, this would lead to the decreasement in the surface residual compressive stress.The paper studied the effects of laser shock number on the surface morphology and roughness of H13 material. The results showed that when the shock number was one, the roughness value was 0.14μm, shock number was in the range of 2 to 4, their corresponding value were 0.23μm, 0.16μm, 0.35μm respectively. Three corresponded to the highest flatness of the surface. By studying the micro-structure of H13 material, the paper found that with the increasement in shock number, the grain refining was increasing and dislocation density was becoming greater. But when the number was four, there came a new kind of inclusion, which reduced the shocking effect. By measuring the residual stress distributed on the H13 surface and along the depth direction, the paper found that the maximum residual stress nearly reached limit when the number was three. The maximum residual stress was about 750 MPa and residual stress layer depth was about 0.87 mm. This was in good agreement with the simulation, which proved that the simulation results were dependable. By measuring the microhardness along the depth direction, the results indicated that with the shock number increasing, the microhardness of the surface was also increasing, but the amplitude was decreasing, in the end microhardness value became steady. The experimental result showed that laser shock can indeed affect the surface hardness of H13, the maximum affected depth of material was about 0.9mm.The research results about prolong the service life of extrusion die indicated that die without processed by laser shock needed some repair before the work times reached 4000. But if the die was processed it did not need repair until the work times reached 6175. After processed by laser shock, the service life of die was increased by 54.4%, this proved that laser shock can significantly improve, the service life of die.