It is known from experiments that the shape is substantially elliptical. As the wheel moves radially, the deformation also moves outward. Since the metal supporting portion at the outer end of the rotating wheel is gradually reduced, the rotating portion of the rotating portion of the deforming portion becomes larger. As the roller continues to move, the deformation zone develops to the edge and the shape of the final deformation zone becomes parabolic.
2 surface defects of the workpiece after spinning
3 analysis and preventive measures of surface defects
3. 1 local thinning and tangential cracking
The radial bending moment generated by the blank under the action of the rotating wheel and the spinning die causes the blank to undergo bending deformation.
In the A CDB area, the lower end of the blank is a spinning die. If the zone is considered separately, the spinning die can be regarded as a convex die when bending, so that the stress on the AB section is the maximum point B (tensile stress), and the minimum point A is (Compressive stress). In the ECDF zone, the upper end of the blank is a rotary wheel, and the same can be seen as a bending deformation of the punch. The stress E point on the EF cross section is the largest (pull stress) and the F point is the smallest (compressive stress). The above is only the analysis of a certain static moment, but in the actual spinning process, due to the radial movement of the spinning wheel, it is bound to produce a frictional force on the surface of the sheet, the magnitude of the force and the magnitude of the spinning force and the blank It is related to the coefficient of friction between the rotating wheels. The frictional force is bound to increase the tensile stress component in the deformation zone, thereby locally thinning the blank.
If the stress difference between point A and point B or point E and point F on the AB or EF section is large, the tangential fracture of the bottom of the billet and the rotating surface may be caused by the tensile stress during the spin forming process. Significant thinning of the thickness of the blank occurs before tangential cracking occurs.
In order to overcome the local thinning and tangential cracking, the stress difference between point A and point B or point E and point F should be as small as possible. To this end, a reasonable spinning scheme should be designed.
(1) The gap value between the rotary wheel and the spinning die should not be too small. If the gap value is too small, the excess material in the wall of the blank is discharged onto the flange. Although the tensile stress along the busbar is reduced, excess material is accumulated on the front side of the rotating wheel, which in turn causes the tensile stress along the busbar to increase sharply. crack.
(2) The radius of the front end of the spinning die should be greater than 3 to 5 times the thickness of the blank. The radius of the front end of the spinning die has a great influence on the bending deformation of the blank. In the extreme case, the fracture often occurs in the rounded portion.
(3) The radius of the rounded corner of the wheel should not be too small. Because its value is too small, it will cause cutting phenomenon, which will increase the wall thickness reduction rate of the workpiece and even cause cracking.
(4) The number of spinning channels should not be excessive.
(5) The feed ratio cannot be too large.
(6) The thickness of the blank should not be too large.
In addition, the quality of the blank also has a greater impact on the spinning results.
3. 2 wrinkles and radial cracking
The tangential direction in the deformation zone is mainly caused by the rotational pressure exerted by the rotary wheel to produce a bending distance in the tangential direction of the blank, so that the blank is tangentially bent. In addition, due to the diameter of the blank at the deformation zone of the billet, the diameter of the billet is reduced after forming, which in turn produces a tangential tensile stress. For this reason, the tangential stress of the deformation zone is shown by the synthesis of the two stresses.
Due to the compressive stress in the tangential direction of the billet, the billet may be unstable and wrinkled during the spinning process. When the initial wrinkles are rolled, the bending stress of the blank is generated in the wrinkle range. Constant tensile, compressive stress and alternating bending stress cause radial fracture.
In order to overcome the wrinkles and radial cracking, the tangential compressive stress of the blank should be reduced. To this end, the following aspects should be noted in the design of the spinning scheme.
(1) The gap value between the rotary wheel and the spinning die should not be too large. If the gap value is greater than the sine law, the wall thickness of the part is greater than the value determined by the sine law. The surrounding material needs to be replenished for replenishment, there is a spinning deformation, the periphery of the billet is unstable, the part is not pasted or pulled along the busbar. The stress increases, resulting in an increase in the limit spin angle.
(2) The number of spinning channels is too small. If the number of spinning passages is too small, the blank is broken by the combination of strong shearing and stretching at the initial stage of spinning, making the spinning process difficult to continue.
(3) The radius of the rounded corner of the wheel should not be too large. Because the value increases, the superimposed portion of the trajectory of the rotating wheel can be increased, so that the surface roughness of the spinning member is reduced and the spinning pressure is increased. At this time, the surface of the workpiece is unstable and wrinkled, and an angular phenomenon occurs.
(4) The feed ratio cannot be too small.
(5) Appropriately reduce the spinning ratio and reduce the blank diameter d 0 value.
(Finish)
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