The crankshaft, whether it is an automobile engine crankshaft, a marine engine crankshaft, or an industrial pump crankshaft, is subjected to a combination of alternating bending and alternating torsional loads during rotation, and the dangerous sections of the crankshaft, especially the journal and the crank The crankshaft is often broken due to the high concentration of stress. Therefore, the service conditions require the crankshaft to have enough strength to ensure that the crankshaft does not break during operation. At present, the change of anti-fatigue performance of crankshaft by shot peening has been widely used in a wide range of applications, and the effect is quite satisfactory.
Compared with the defects of the traditional rolling technology, that is, due to the limitation of the machining technology of the crankshaft, the roundness of each journal is difficult to match with the roller, which often results in the round-cut phenomenon, and the crankshaft after the rolling is greatly deformed. ,not effectively. The mechanism of shot peening is the use of pellets with strictly controlled diameter and certain strength. Under the action of high-speed air flow, the pellet flow is formed and continuously jetted onto the metal surface of the crankshaft, just as it is hammered with countless hammers to make the surface of the crankshaft. Extremely strong plastic deformation occurs, resulting in a cold hardened layer. In simple terms, because the crankshaft is subjected to various mechanical cutting forces during machining, the stress distribution on the surface, particularly at the transition fillet where the crankshaft section is changed, is extremely uneven, and the work is subjected to alternating stress, so it is easy. Stress corrosion occurs and the fatigue life of the crankshaft is reduced. The shot peening process is to offset the tensile stress that the part will receive in the subsequent working cycle by introducing a pre-stress stress, thereby improving the fatigue resistance and the safe service life of the workpiece.
In addition, the crankshaft forging blanks are made by directly ingot-opening or hot-rolled steel forging. If the forging and rolling processes are not controlled properly, there will be component segregation in the embryo, coarse grains in the original structure, and unreasonable internal distribution. The metallurgical and structural defects make it possible to reduce the fatigue life of the crankshaft. The strengthening process can refine the microstructure and significantly improve its fatigue performance.
There are two most critical parameters for the shot peening process. One is the stress intensity, which is usually measured using the "Almen test piece". A plurality of test strips are fixed on different surfaces of the crankshaft, in particular the transition fillets of the crankshaft sections with the most concentrated stress, and the shot peening is performed together. The compressive stress generated on the test strips causes the test piece to bow. The change in curvature is proportional to the impact energy of the pellets. Another major parameter that determines the quality of shot peening is coverage. The so-called coverage rate refers to the ratio of the area occupied by the reinforced surface craters to the total reinforced surface. This parameter is defined by the design engineer of the crankshaft, usually 100% - 200%. Some crankshaft applications may require a coverage rate higher than 200%. .
Depending on the hardness of the crankshaft and the ideal induced compressive stress strength, the pellets used for crankshaft shot peening generally have a hardness of 50 - 55 HRC and a size of S 280 - S 330 (0.7 mm - 0.84 mm). This results in an intensity range of approximately 0.008 - 0.010 C (0.025 on the A scale) in the "Almen test piece".
Compared with shot blasting, the monitoring of process parameters for shot peening is more stringent. For crankshaft hardening applications, the parameters to be monitored include:
Shot peening speed
Shot peening intensity
Pellet diameter
Shot peening distance
Enhanced time
Coverage Changes in any one of these parameters will affect the effect of crankshaft surface hardening to varying degrees.
Compared with the defects of the traditional rolling technology, that is, due to the limitation of the machining technology of the crankshaft, the roundness of each journal is difficult to match with the roller, which often results in the round-cut phenomenon, and the crankshaft after the rolling is greatly deformed. ,not effectively. The mechanism of shot peening is the use of pellets with strictly controlled diameter and certain strength. Under the action of high-speed air flow, the pellet flow is formed and continuously jetted onto the metal surface of the crankshaft, just as it is hammered with countless hammers to make the surface of the crankshaft. Extremely strong plastic deformation occurs, resulting in a cold hardened layer. In simple terms, because the crankshaft is subjected to various mechanical cutting forces during machining, the stress distribution on the surface, particularly at the transition fillet where the crankshaft section is changed, is extremely uneven, and the work is subjected to alternating stress, so it is easy. Stress corrosion occurs and the fatigue life of the crankshaft is reduced. The shot peening process is to offset the tensile stress that the part will receive in the subsequent working cycle by introducing a pre-stress stress, thereby improving the fatigue resistance and the safe service life of the workpiece.
In addition, the crankshaft forging blanks are made by directly ingot-opening or hot-rolled steel forging. If the forging and rolling processes are not controlled properly, there will be component segregation in the embryo, coarse grains in the original structure, and unreasonable internal distribution. The metallurgical and structural defects make it possible to reduce the fatigue life of the crankshaft. The strengthening process can refine the microstructure and significantly improve its fatigue performance.
There are two most critical parameters for the shot peening process. One is the stress intensity, which is usually measured using the "Almen test piece". A plurality of test strips are fixed on different surfaces of the crankshaft, in particular the transition fillets of the crankshaft sections with the most concentrated stress, and the shot peening is performed together. The compressive stress generated on the test strips causes the test piece to bow. The change in curvature is proportional to the impact energy of the pellets. Another major parameter that determines the quality of shot peening is coverage. The so-called coverage rate refers to the ratio of the area occupied by the reinforced surface craters to the total reinforced surface. This parameter is defined by the design engineer of the crankshaft, usually 100% - 200%. Some crankshaft applications may require a coverage rate higher than 200%. .
Depending on the hardness of the crankshaft and the ideal induced compressive stress strength, the pellets used for crankshaft shot peening generally have a hardness of 50 - 55 HRC and a size of S 280 - S 330 (0.7 mm - 0.84 mm). This results in an intensity range of approximately 0.008 - 0.010 C (0.025 on the A scale) in the "Almen test piece".
Compared with shot blasting, the monitoring of process parameters for shot peening is more stringent. For crankshaft hardening applications, the parameters to be monitored include:
Shot peening speed
Shot peening intensity
Pellet diameter
Shot peening distance
Enhanced time
Coverage Changes in any one of these parameters will affect the effect of crankshaft surface hardening to varying degrees.
Tube Laser Cutting Machine,Sheet Metal Laser Cutting Machinery,Laser Cut Tube Equipment,Pipe Laser Cutting Machines
Herolaser , https://www.hclaserwelding.com