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The influence of prestress on shot peening forming

Abstract: the experimental research on prestressed shot peening forming is carried out, and it is pointed out that prestress can change the size relationship between its corresponding pre deformation and prestressed shot peening deformation. In the shot peening forming with the main purpose of improving the longitudinal straightness of the shot peening surface, considering the low motion frequency of this part, the pre strain value of 0.5/1000 ~ 1/1000 is more appropriate

key words: prestress; Shot peening forming

I. preface

prestressed shot peening forming refers to a forming method of shot peening forming on the surface of metal components that form a pre tensile stress layer with the help of external forces. Usually, this method is used to increase the shot peening bending deformation in the direction of tensile stress on the surface of metal components (hereinafter referred to as transverse), reduce the bending deformation in the direction perpendicular to the tensile stress (hereinafter referred to as longitudinal), or control the deformation trend of metal components during shot peening. However, people still have one-sided understanding of prestressed shot peening and blindness in its application. Therefore, this paper makes an experimental study on the law of prestressed shot peening, and gives a conclusion with practical guiding significance

II. Test process

test equipment: SPW-1 numerical control shot blasting testing machine; Pellet specification: S460; Projectile flow: 34kg/min; Test piece feeding speed: 2m/min; Material of test piece: LY12CZ flat plate with thickness of 5mm; Prestrain: see Table 1. Because the shot peening process requires that the prestrain must be within the elastic range, and Hooke's law is followed between the elastic prestress and the strain, and the strain value is easy to measure and calculate, therefore, the rational prestress to avoid oil pollution on the mechanism mentioned in the following part of this paper generally refers to prestrain; The pre camber height value in Table 1 refers to the transverse camber height value of the surface of each prestressed specimen measured respectively under the corresponding pre strain conditions before shot peening (the measurement span of the corresponding curvature meter is 160mm). Table 1

specimen serial number pre strain 1/10000.491.101.652.242.783.153.574.16 pre arc height mm0.6231.4152.1132.8723.5784.0534.6045.372

III. test results and analysis

the arc height on the shot peening surface directly reflects the shot peening deformation degree of the specimen. After the shot peening forming test, the horizontal and longitudinal arc height data on the surface of the prestressed shot peening specimen are shown in Table 2. Table 2

specimen s/N prestrain

1/10000.491.101.652.242.783.153.574.16 transverse arc height mm1.4951.5321.8212.0502.4302.6963.1163.397 longitudinal arc height mm0.2630.1730.2050.1630.2000.1550.1360.092

the relationship between transverse arc height, longitudinal arc height and pre arc height of prestressed shot blasting specimen and prestrain is shown in Figure 1

Figure 1 Effect of prestrain on arc height

from curve 1, it can be seen that the import increased by 61.3% year-on-year Of course, it can be seen that with the increase of pre strain value, the transverse arc height increases slowly at first, and then rapidly, and the whole curve shows a monotonic increasing trend; Different from the above characteristics, the longitudinal arc height gradually decreases with the increase of prestrain, and the whole curve shows a monotonic decreasing trend; The pre arc height increases linearly. The above situation shows that the transverse and longitudinal deformation on the prestressed shot peened specimen increases and decreases with the increase of prestrain

The pre strain of4/1000 is very close to the elastic limit of the test piece material LY12CZ. Therefore, the corresponding pre arc height value is also close to the corresponding elastic arc height limit when the displacement measuring instrument is adjusted to the zero point. The corresponding transverse and longitudinal arc height values of the surface of the prestressed shot peened specimen are basically the corresponding transverse maximum and longitudinal minimum arc height values under the shot peening conditions. Therefore, it can be considered that although the prestressed shot peening method can increase the transverse shot peening deformation and reduce the longitudinal shot peening deformation, this increase or decrease is not infinite, that is, the increase is limited rather than infinite, and the decrease is also limited rather than reduced to zero. Therefore, it is unrealistic to hope that the shot peening deformation in a certain direction will be infinitely increased or infinitely reduced to zero through prestressed shot peening. Therefore, it is not difficult to see that in order to improve the longitudinal straightness of the shot peening surface, the reasonable and economic pre strain value should not be too large, and the pre strain value of 0.5/1000 ~ 1/1000 is more appropriate

the pre arc height curve intersects with the transverse arc height curve on the surface of the prestressed shot peening specimen, which reflects that there is always such a pre strain value when the prestressed shot peening is formed under certain shot peening conditions, which makes the transverse arc height on the shot peening surface equal to the pre arc height value. Before, after and after the intersection of the two curves, the pre arc height curve shows the numerical relationship that the pre arc height value is less than, equal to and gradually greater than the horizontal arc height value under, above and above the horizontal arc height value curve respectively. It shows that there is not always a simple relationship between the pre arc height and the corresponding horizontal arc height, but a different size relationship and change trend due to different shot peening conditions and prestress value range. Therefore, the phenomenon of "springback" during pre-stressed shot peening (i.e. the horizontal arc height is less than the corresponding pre arc height) also occurs, which does not exist in free stress (i.e. zero prestress) shot peening

the variation law between the pre arc height and the corresponding transverse arc height is of great significance to comprehensively understand and correctly apply the prestressed shot peening technology

in addition, the phenomenon that the pre arc height is equal to the corresponding horizontal arc height will have increasingly important practical application value

the processing results of the test data show that there is an exponential relationship between the transverse arc height and the corresponding pre strain and pre arc height

IV. conclusion

(1) prestress can increase the transverse deformation of prestressed shot peening surface within a certain range. At the same time, it can also change the size relationship between pre deformation corresponding to prestress and pre peening deformation, and there is an exponential relationship between pre peening deformation, pre strain and pre deformation

(2) prestress can reduce the longitudinal deformation of prestressed shot peening surface, but it cannot eliminate the shot peening deformation in this direction. It is suggested that in the application of prestressed shot peening with the main purpose of improving the longitudinal straightness of the shot peening surface, a smaller pre strain value should be selected, and the value range of 0.5/1000 ~ 1/1000 is more suitable

(3) prestress can make the corresponding pre deformation equal to the transverse deformation of the prestressed shot peening surface, so that the fixture can accurately control the prestressed shot peening surface. (end)

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