A blasting-like lubricating process(combination of shot blasting and lubricating processes)is proposed.In this process,the specimens to be treated,alloy shots,and solid lubricating powder are rotated together in a rol...A blasting-like lubricating process(combination of shot blasting and lubricating processes)is proposed.In this process,the specimens to be treated,alloy shots,and solid lubricating powder are rotated together in a roller.The surface pockets formed due to the impact by the shots can store lubricants,and the lubricant can also adhere to the specimen surface by hitting.The effects of process parameters,including rolling time,rotational speed,mass of alloy shots,and the diameter of shots,on the surface topography of the steel specimen are investigated using 13 experimental schemes.The distribution ratio and average depth of surface pockets on the defined areas of the specimen are quantitatively analyzed.Four selected schemes with the MoS_(2) solid lubricating powder are further carried out to lubricate the cylindrical billets,and the lubricating effect is evaluated using the steady combined forward and backward extrusion test.The indicated friction factor of the novel blasting-like process is smaller than that of the conventional phosphate-soap coating process.展开更多
Stress analysis and optimization of combined die structure with two stress rings were performed.Using thermoelastic deformation,the contact pressure at the interfaces between layers was calculated.Then,theoretical exp...Stress analysis and optimization of combined die structure with two stress rings were performed.Using thermoelastic deformation,the contact pressure at the interfaces between layers was calculated.Then,theoretical expressions of stress distribution for the combined die were derived.The thermal-mechanical effect under working conditions was considered.To verify the theoretical expressions,simulation work was performed.Optimization of die design was carried out by defining radius ratio and shrink fit coefficient as optimization variables.The objective was to minimize the effective circumferential stress at the inner surface of the die insert,under the constraint that the maximum equivalent stress values of die insert and stress rings did not exceed their respective yield stresses.The Kriging model was used to describe the influence of shrink fit and die dimensions on the objective function and the maximum equivalent stress.Using a genetic algorithm,optimum parameters were found with a minimum circumferential stress of 442.9 MPa under a working stress of 1800 MPa.Further analysis of five selected optimal results was carried out,and the specific design parameters of these combined dies are different under the same level of circumferential stress,and the combined die is overdesigned if the thermal effect is ignored.展开更多
In hot deformation, the flow stress curves of steels always present as two typical types: at relatively high temperature and low strain rate, the flow stress may first increase and then attain a steady value without r...In hot deformation, the flow stress curves of steels always present as two typical types: at relatively high temperature and low strain rate, the flow stress may first increase and then attain a steady value without reaching an obvious peak stress; in other situations, the flow stress decreases after reaching peak stress and then attains a steady value. A new phenomenological model,described by a sine-function equation, is proposed to define the relationship between flow stress and deformation parameters. A series of isothermal compressions for a carbon steel were carried out, as a case study, to obtain basic experimental data.Parameters of the new model were sequentially determined. The predicted results of the proposed model were compared with actual measured data. Good accuracy was found in the standard statistical parameters of correlation coefficient, root mean square error, and average absolute relative error with the values of 0.935, 7.137 MPa and 4.352%, respectively. Discussion of applications of different models in finite-element simulation demonstrated the benefit of the new model. When comparing the simulation results of three different deformation patterns with large strain, the new model showed 10%–20% lower predicted forming load than the original Arrhenius equation, and better applicability and reliability than modified Arrhenius equations.展开更多
On the multi-layer forging die used in daily life,stressed ring can strength the die structure within elastic deformation and the die material can be self-strengthened through uniform plastic deformation by autofretta...On the multi-layer forging die used in daily life,stressed ring can strength the die structure within elastic deformation and the die material can be self-strengthened through uniform plastic deformation by autofrettage effect,whereas the thermal effect generated during forging process can directly influence the stress state and dimension of the forging die in service.In this study,an analytical solution of the thermo-elastic-plastic deformation in the forging die is derived.The relationships between the radial and circumferential stresses and the temperature distribution,which are directly related to geometric parameters,material properties and working pressure,are determined.This helps to better understand the thermo-elastic-plastic deformation behavior of the die and design the combined forging die to achieve long service life and high accuracy product.展开更多
基金the National Natural Science Foundation of China(No.51475294)。
文摘A blasting-like lubricating process(combination of shot blasting and lubricating processes)is proposed.In this process,the specimens to be treated,alloy shots,and solid lubricating powder are rotated together in a roller.The surface pockets formed due to the impact by the shots can store lubricants,and the lubricant can also adhere to the specimen surface by hitting.The effects of process parameters,including rolling time,rotational speed,mass of alloy shots,and the diameter of shots,on the surface topography of the steel specimen are investigated using 13 experimental schemes.The distribution ratio and average depth of surface pockets on the defined areas of the specimen are quantitatively analyzed.Four selected schemes with the MoS_(2) solid lubricating powder are further carried out to lubricate the cylindrical billets,and the lubricating effect is evaluated using the steady combined forward and backward extrusion test.The indicated friction factor of the novel blasting-like process is smaller than that of the conventional phosphate-soap coating process.
基金the National Natural Science Foundation of China(No.51475294)。
文摘Stress analysis and optimization of combined die structure with two stress rings were performed.Using thermoelastic deformation,the contact pressure at the interfaces between layers was calculated.Then,theoretical expressions of stress distribution for the combined die were derived.The thermal-mechanical effect under working conditions was considered.To verify the theoretical expressions,simulation work was performed.Optimization of die design was carried out by defining radius ratio and shrink fit coefficient as optimization variables.The objective was to minimize the effective circumferential stress at the inner surface of the die insert,under the constraint that the maximum equivalent stress values of die insert and stress rings did not exceed their respective yield stresses.The Kriging model was used to describe the influence of shrink fit and die dimensions on the objective function and the maximum equivalent stress.Using a genetic algorithm,optimum parameters were found with a minimum circumferential stress of 442.9 MPa under a working stress of 1800 MPa.Further analysis of five selected optimal results was carried out,and the specific design parameters of these combined dies are different under the same level of circumferential stress,and the combined die is overdesigned if the thermal effect is ignored.
基金supported by the National Natural Science Foundation of China(Grant No.51475294)
文摘In hot deformation, the flow stress curves of steels always present as two typical types: at relatively high temperature and low strain rate, the flow stress may first increase and then attain a steady value without reaching an obvious peak stress; in other situations, the flow stress decreases after reaching peak stress and then attains a steady value. A new phenomenological model,described by a sine-function equation, is proposed to define the relationship between flow stress and deformation parameters. A series of isothermal compressions for a carbon steel were carried out, as a case study, to obtain basic experimental data.Parameters of the new model were sequentially determined. The predicted results of the proposed model were compared with actual measured data. Good accuracy was found in the standard statistical parameters of correlation coefficient, root mean square error, and average absolute relative error with the values of 0.935, 7.137 MPa and 4.352%, respectively. Discussion of applications of different models in finite-element simulation demonstrated the benefit of the new model. When comparing the simulation results of three different deformation patterns with large strain, the new model showed 10%–20% lower predicted forming load than the original Arrhenius equation, and better applicability and reliability than modified Arrhenius equations.
基金National Natural Science Foundation of China(No.51875348)。
文摘On the multi-layer forging die used in daily life,stressed ring can strength the die structure within elastic deformation and the die material can be self-strengthened through uniform plastic deformation by autofrettage effect,whereas the thermal effect generated during forging process can directly influence the stress state and dimension of the forging die in service.In this study,an analytical solution of the thermo-elastic-plastic deformation in the forging die is derived.The relationships between the radial and circumferential stresses and the temperature distribution,which are directly related to geometric parameters,material properties and working pressure,are determined.This helps to better understand the thermo-elastic-plastic deformation behavior of the die and design the combined forging die to achieve long service life and high accuracy product.
