High speed power chucks are important function units in high speed turning.The gripping force loss is the primary factor limiting the rotational speed of high-speed power chucks.This paper proposes a piecewise model c...High speed power chucks are important function units in high speed turning.The gripping force loss is the primary factor limiting the rotational speed of high-speed power chucks.This paper proposes a piecewise model considering the difference of wedge transmission's radial deformation between low-speed stage and medium-to-high-speed stage,the friction forces of chuck transmission,and the compressibility of hydraulic oil in rotary hydraulic cylinders.A corrected model of gripping force loss is also established for power chucks with asymmetric stiffness.The model is verified by experiment results.It is helpful to use the piecewise model to explain the experimental phenomenon that the overall loss coefficient of gripping force increases with the rotational speed increasing at medium and high speed stages.Besides,the loss coefficients of gripping force at each stage during speeding up and the critical rotational speed between two adjacent stages are discussed.For wedge power chucks with small wedge angel(α<20°) and ordinary lubrication(μ0>0.06),the local loss coefficient of gripping force at the low speed stage is about 70% of that at the medium to high speed stage.For wedge power chucks with larger wedge angel(α>20°) or low friction coefficient(μ0<0.06),the wedge transmissions cannot self-lock at high speed stage,and the gripping force loss at the high speed stage is related to the hydraulic lock and hydraulic oil in the rotary hydraulic cylinder;the local loss coefficients of gripping force at the third stage is about 1.75 to 2.13 times that at the second stage.This work is helpful to understand the mechanism of the gripping force loss thoroughly and to optimize power chucks.展开更多
The Large-size Conical Cylinders with Inner Transverse High Ribs(LCCWITHR) can reduce the weight of the parts while maintaining high rigidity and strength. Radially Loading Rotary Extrusion(RLRE) forming technology ca...The Large-size Conical Cylinders with Inner Transverse High Ribs(LCCWITHR) can reduce the weight of the parts while maintaining high rigidity and strength. Radially Loading Rotary Extrusion(RLRE) forming technology can achieve integral forming of LCCWITHR through the synergy of radial and rotary movements of dies. The flow law of the material during the forming process is the key to forming large-size inner ribs. At present, there is no unified understanding of the metal flow law of RLRE forming technology. An analytical expression was derived to predict the Radial Direction(RD) deformation loads. The FE simulation and process experiment were carried out to investigate the effects of the inclination angle, thickness factor and transition arc radius of the split top dies on the spacing of the metal diversion plane, the metal flow velocity of the rib area and the final radius of the inner rib. The influence of the split top dies loading distance and the bottom die rotation angle of each pass on the inner radius of the inner rib was verified. And the optimal combination of dies shape parameters and loading paths which can make the metal flow orderly was obtained: the inclination angle is 140°, the thickness factor is 3.64, the transition arc radius is 16 mm;the top dies loading distance is 15 mm, the bottom die rotation angle is 45°.The FE simulation results have been found to be in close agreement with physics experiment.The research results reveal the metal flow law of rib growth in the RLRE of LCCWITHR, which lays a theoretical foundation for subsequent thorough research and process optimization.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 50875234)the National Science and Technology Support Program of China (Grant No. 2006BAF01B09-7)
文摘High speed power chucks are important function units in high speed turning.The gripping force loss is the primary factor limiting the rotational speed of high-speed power chucks.This paper proposes a piecewise model considering the difference of wedge transmission's radial deformation between low-speed stage and medium-to-high-speed stage,the friction forces of chuck transmission,and the compressibility of hydraulic oil in rotary hydraulic cylinders.A corrected model of gripping force loss is also established for power chucks with asymmetric stiffness.The model is verified by experiment results.It is helpful to use the piecewise model to explain the experimental phenomenon that the overall loss coefficient of gripping force increases with the rotational speed increasing at medium and high speed stages.Besides,the loss coefficients of gripping force at each stage during speeding up and the critical rotational speed between two adjacent stages are discussed.For wedge power chucks with small wedge angel(α<20°) and ordinary lubrication(μ0>0.06),the local loss coefficient of gripping force at the low speed stage is about 70% of that at the medium to high speed stage.For wedge power chucks with larger wedge angel(α>20°) or low friction coefficient(μ0<0.06),the wedge transmissions cannot self-lock at high speed stage,and the gripping force loss at the high speed stage is related to the hydraulic lock and hydraulic oil in the rotary hydraulic cylinder;the local loss coefficients of gripping force at the third stage is about 1.75 to 2.13 times that at the second stage.This work is helpful to understand the mechanism of the gripping force loss thoroughly and to optimize power chucks.
基金co-supported by the National Natural Science Foundation of China(No.52075501)the Fundamental Research Program of Shanxi Province,China(No.20210302124206).
文摘The Large-size Conical Cylinders with Inner Transverse High Ribs(LCCWITHR) can reduce the weight of the parts while maintaining high rigidity and strength. Radially Loading Rotary Extrusion(RLRE) forming technology can achieve integral forming of LCCWITHR through the synergy of radial and rotary movements of dies. The flow law of the material during the forming process is the key to forming large-size inner ribs. At present, there is no unified understanding of the metal flow law of RLRE forming technology. An analytical expression was derived to predict the Radial Direction(RD) deformation loads. The FE simulation and process experiment were carried out to investigate the effects of the inclination angle, thickness factor and transition arc radius of the split top dies on the spacing of the metal diversion plane, the metal flow velocity of the rib area and the final radius of the inner rib. The influence of the split top dies loading distance and the bottom die rotation angle of each pass on the inner radius of the inner rib was verified. And the optimal combination of dies shape parameters and loading paths which can make the metal flow orderly was obtained: the inclination angle is 140°, the thickness factor is 3.64, the transition arc radius is 16 mm;the top dies loading distance is 15 mm, the bottom die rotation angle is 45°.The FE simulation results have been found to be in close agreement with physics experiment.The research results reveal the metal flow law of rib growth in the RLRE of LCCWITHR, which lays a theoretical foundation for subsequent thorough research and process optimization.
