ULTRASOUND ENHANCING METHOD FOR PROLONGING FATIGUE LIFE OF METAL WORKPIECE AND USE THEREOF

Abstract

An ultrasonic strengthening method for improving the fatigue life of a metal work-piece and its application, by clamping the metal work-piece on the ultrasonic machining lathe, ultrasonic machining of the surface of the metal work-piece with ultrasonic machining tool. The present invention focuses on presetting the compressive stress on the surface of the metal work-piece by adjusting the pressure of the ultrasonic machining tool on the surface of the metal work-piece, to eliminate the residual stress and to improve the fatigue life of the work-piece eventually. Meanwhile, the present ultrasonic strengthening method can refine the surface grain of the metal work-piece, improve the surface microhardness, wear resistance, and corrosion resistance of the surface of the metal work-piece, eventually to improve the fatigue life of the metal work-piece.

Claims

1. An ultrasonic strengthening method for improving the fatigue life of a metal work-piece, characterized in that, comprising the following steps: clamping the metal work-piece on the ultrasonic machining lathe, ultrasonic machining of the surface of the metal work-piece with ultrasonic machining tool, the parameters of ultrasonic machining are: linear velocity is 2-120 m/min, feed rate is 0.08-0.8 mm/r, the pressure imposed on the surface of the treated work-piece by ultrasonic machining tool is 1000-2400N; the times of ultrasonic machining is 1-3.

2. The ultrasonic strengthening method for improving the fatigue life of a metal work-piece as claimed in claim 1, characterized in that, the parameters of ultrasonic machining are: linear velocity is 3.08 m/min, feed rate is 0.08 mm/r, the pressure imposed on the surface of the treated work-piece is 1500N, the times of ultrasonic machining is 3.

3. The ultrasonic strengthening method for improving the fatigue life of a metal work-piece as claimed in claim 1, characterized in that, the amplitude of ultrasonic machining is 5-25 m.

4. The ultrasonic strengthening method for improving the fatigue life of a metal work-piece as claimed in claim 1, characterized in that, clamping the aero-engine blade on the ultrasonic machining lathe, ultrasonic machining of the surface of aero-engine blade which is rotating around the main spindle with ultrasonic machining tool, the parameters of ultrasonic machining are: linear velocity is 2-10 m/min, feed rate of ultrasonic tool is 0.08-0.8 mm/r, the pressure imposed on the surface of the treated work-piece by ultrasonic machining tool is 1000-2500N, the times of ultrasonic machining is 1-3.

5. The ultrasonic strengthening method for improving the fatigue life of a metal work-piece as claimed in claim 4, characterized in that, linear velocity is 2 m/min, feed rate of ultrasonic tool is 0.08 mm/r, the pressure imposed on the surface of the treated work-piece by ultrasonic machining tool is 1000-2500N, the times of ultrasonic machining is 3.

6. The ultrasonic strengthening method for improving the fatigue life of a metal work-piece as claimed in claim 4, characterized in that, the amplitude of ultrasonic machining is 5-25 m.

7. The ultrasonic strengthening method for improving the fatigue life of a metal work-piece as claimed in claim 5, characterized in that, comprising the following steps: clamping the locomotive wheel on the ultrasonic machining lathe, ultrasonic machining of the surface of aero-engine blade which is rotating around the main spindle with ultrasonic machining tool, the parameters of ultrasonic machining are: linear velocity is 15-120 m/min, feed rate of ultrasonic tool is 0.08-0.2 mm/r, the pressure imposed on the surface of the treated work-piece by ultrasonic machining tool is 1250-3000N; the times of ultrasonic machining is 1-3.

8. The ultrasonic strengthening method for improving the fatigue life of a metal work-piece as claimed in claim 7, characterized in that, the said linear velocity of locomotive wheel is 15 m/min, the said feed rate is 0.08 mm/r, the said pressure imposed on the surface of the treated work-piece by ultrasonic machining tool is 1250-3000N.

9. The ultrasonic strengthening method for improving the fatigue life of a metal work-piece as claimed in claim 7, characterized in that, the amplitude of ultrasonic machining is 5-25 m.

10. An ultrasonic strengthening method for improving the fatigue life of a metal work-piece, characterized in that, comprising the following steps: clamping the axle on the ultrasonic machining lathe, ultrasonic machining of the surface of the axle which is rotating around the main spindle with ultrasonic machining tool, the parameters of ultrasonic machining are: linear velocity of the sucker rod is 10-120 m/min, feed rate is 0.6-0.6 mm/r, the pressure imposed on the surface of the treated work-piece by ultrasonic machining tool is 1750-3000N; the times of ultrasonic machining is 1-.

11. The ultrasonic strengthening method for improving the fatigue life of a metal work-piece as claimed in claim 10, characterized in that, the parameters of ultrasonic machining are: linear velocity of the axle is 120 m/min, feed rate is 0.6 mm/r, the pressure imposed on the surface of the treated work-piece by ultrasonic machining tool is 1750-3000N, the times of ultrasonic machining is 3.

12. The ultrasonic strengthening method for improving the fatigue life of a metal work-piece as claimed in claim 10, characterized in that, the amplitude of ultrasonic machining is 5-25 m.

13. The ultrasonic strengthening method for improving the fatigue life of a metal work-piece, characterized in that, comprising the following steps: clamping the sucker rod on the ultrasonic machining lathe, ultrasonic machining of the surface of the rod or/and screw thread of the sucker rod which is rotating around the main spindle with ultrasonic machining tool, the parameters of ultrasonic machining are: linear velocity of the sucker rod is 2-120 m/min, feed rate is 0.08-0.8 mm/r, the pressure imposed on the surface of the treated work-piece by ultrasonic machining tool is 1500-3000N, the times of ultrasonic machining is 1-3.

14. The ultrasonic strengthening method for improving the fatigue life of a metal work-piece as claimed in claim 13, characterized in that, linear velocity of the sucker rod is 2 m/min, feed rate is 0.08 mm/r, the pressure imposed on the surface of the treated work-piece by ultrasonic machining tool is 1500-3000N.

15. An ultrasonic strengthening method for improving the fatigue life of a metal work-piece as claimed in claim 13, characterized in that, the amplitude of ultrasonic machining is 5-25 m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 is the curve graph of pressuresurface compressive stress in embodiment 1;

[0031] FIG. 2 is the curve graph of pressuresurface compressive stress in embodiment 3;

[0032] FIG. 3 is the curve graph of cycle timesfatigue limit before and after the ultrasonic strengthening of metal work-piece in embodiment 3;

[0033] FIG. 4 is the curve graph of pressuresurface compressive stress of locomotive wheel in embodiment 5;

[0034] FIG. 5 is the curve graph of pressuresurface compressive stress of axle in embodiment 7;

[0035] FIG. 6 is the curve graph of pressuresurface compressive stress of sucker rod in embodiment 9;

[0036] FIG. 7 is the metallographic graph of the surface of sucker rod after the ultrasonic strengthening treatment in embodiment 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] This invention will be further illustrated by the following embodiments and the accompanying drawings, but not limited thereto.

Embodiment 1

[0038] This embodiment provides an ultrasonic strengthening method for improving the fatigue life of a metal work-piece, ultrasonic machining of a bearing with ultrasonic machining tool, that is, ultrasonic machining of outer ring raceway, inner ring raceway and rolling element of the bearing with ultrasonic machining tool, the parameters of ultrasonic machining of outer ring raceway, inner ring raceway and rolling element of the bearing are the same: linear velocity is 2 m/min, feed rate is 0.08 mm/r, the pressure imposed on the surface of the treated work-piece by ultrasonic machining tool is 300-2400N. The said pressure imposed on the surface of the work-piece by ultrasonic machining tool is normal force, with ultrasonic machining 3 times.

[0039] The curve graph of compressive stress on the surface of bearing after ultrasonic strengthening is obtained as shown in FIG. 1 with changing the pressure of the ultrasonic machining tool to the surface of the treated work-piece while other parameters remain the same. Referring to FIG. 1, when the pressure of the ultrasonic machining tool imposed on the surface to be machined is around 1000N, the preset compressive stress on the surface of the work-piece reaches a maximum of 900 MPa, as the pressure increases, the preset compressive stress on the surface of the work-piece does not change much hereafter.

[0040] After ultrasonic strengthening of the outer ring raceway, the inner ring raceway and the rolling element with the ultrasonic strengthening method of the present embodiment, the fatigue life of the bearing can be increased by more than 5 times compared with the conventionally processed bearing.

[0041] The curve graph of compressive stress on the bearing surface after ultrasonic strengthening is still the same curve graph as shown in FIG. 1 with changing the pressure of the ultrasonic machining tool to the surface of the treated work-piece while other parameters remain the same, the said other parameters are: linear velocity is 100 m/min, feed rate is 0.8 mm/r, the pressure imposed on the surface of the treated work-piece by ultrasonic machining tool is 300-2400N. The said pressure imposed on the surface of the work-piece by ultrasonic machining tool is normal force, with ultrasonic machining 3 times. The fatigue life of the bearing can be increased by more than 5 times compared with the conventionally processed bearing. Thus, the preset compressive stress on the surface of the metal is generally only related to the pressure imposed on the surface of the treated work-piece by ultrasonic machining tool.

Embodiment 2

[0042] This embodiment provides an ultrasonic strengthening method for improving the fatigue life of a metal work-piece, specifically ultrasonic machining of a bearing with ultrasonic machining tool, that is, ultrasonic machining of outer ring raceway, inner ring raceway and rolling element of the bearing with ultrasonic machining tool, the parameters of ultrasonic machining of outer ring raceway, inner ring raceway and rolling element of the bearing are the same: linear velocity is 3.08 m/min, feed rate is 0.08 mm/r, the pressure imposed on the surface of the treated work-piece by ultrasonic machining tool is 1500N. The said pressure imposed on the surface of the work-piece by ultrasonic machining tool is normal force, with ultrasonic machining 3 times.

Embodiment 3

[0043] This embodiment provides an ultrasonic strengthening method for improving the fatigue life of a metal work-piece, ultrasonic machining of a aero-engine blade with ultrasonic machining tool, the parameters of ultrasonic machining are: linear velocity of ultrasonic tool is 2 m/min, feed rate is 0.08 mm/r, the pressure imposed on the surface of the treated work-piece by ultrasonic machining tool is 300-2500N. The times of ultrasonic machining is 3.

[0044] The curve graph of compressive stress on the surface of aero-engine blade after ultrasonic strengthening is obtained as shown in FIG. 2 with changing the pressure of the ultrasonic machining tool to the surface of the treated work-piece while other parameters remain the same. Referring to FIG. 2, when the pressure of the ultrasonic machining tool imposed on the surface to be machined is around 1000N, the preset compressive stress on the surface of the work-piece reaches a maximum of 720 MPa, as the pressure increases, the preset compressive stress on the surface of the work-piece does not change much hereafter.

[0045] The curve graph of cycle times and fatigue limit after the ultrasonic strengthening of aero-engine blade in this embodiment is FIG. 3, the fatigue life of the blade can be increased by more than 6 times.

Embodiment 4

[0046] An ultrasonic strengthening method for improving the fatigue life of a metal work-piece, ultrasonic machining of a aero-engine blade with ultrasonic machining tool, the parameters of ultrasonic machining are: linear velocity of ultrasonic tool is 10 m/min, feed rate of ultrasonic tool is 0.8 mm/r, the pressure imposed on the surface of the treated work-piece by ultrasonic machining tool is 800-1000N. The times of ultrasonic machining is 3.

Embodiment 5

[0047] An ultrasonic strengthening method of metal work-piece, ultrasonic machining of a locomotive wheel with ultrasonic machining tool, that is, ultrasonic machining of the surface of locomotive wheel which is rotating around the main spindle with ultrasonic machining tool, the parameters of ultrasonic machining are: linear velocity of locomotive wheel is 15 m/min, feed rate is 0.08 mm/r, the pressure imposed on the surface of the treated work-piece by ultrasonic machining tool is 300-3000N.

[0048] The curve graph of compressive stress on the surface of locomotive wheel after ultrasonic strengthening is obtained as shown in FIG. 4 with changing the pressure of the ultrasonic machining tool to the surface of the treated work-piece while other parameters remain the same. Referring to FIG. 4, when the pressure of the ultrasonic machining tool imposed on the surface to be machined is around 1250N, the preset compressive stress on the surface of the work-piece reaches a maximum of 850MPa, as the pressure increases, the preset compressive stress on the surface of the work-piece does not change much hereafter.

[0049] The locomotive wheel is machined with the ultrasonic strengthening method in this embodiment, fatigue life before and after the ultrasonic strengthening of the locomotive wheel is shown in Table 1.

TABLE-US-00001 TABLE 1 Fatigue Life of Locomotive Wheels Before and After Ultrasonic Strengthening Fatigue life Fatigue life before after Stress ultrasonic ultrasonic range/ strengthening/ strengthening/ No. MPa (10.sup.6) (10.sup.6) 1 225 15.2 33.1 2 247 6.3 14.2 3 264 3.25 6.81 4 282 1.6 3.52 5 3.4 0.68 1.45 6 322 0.335 0.84 7 345 0.14 0.30

[0050] It reads from Table 1, when different pressures are given to the same 7 locomotive wheels, the fatigue life of each locomotive wheel can be increased by 2 times compared with the locomotive wheels without ultrasonic strengthening.

Embodiment 6

[0051] An ultrasonic strengthening method of metal work-piece, ultrasonic machining of a locomotive wheel with ultrasonic machining tool, that is, ultrasonic machining of the surface of locomotive wheel which is rotating around the main spindle with ultrasonic machining tool, the parameters of ultrasonic machining are: linear velocity of locomotive wheel is 57 m/min, feed rate is 0.1 mm/r, the pressure imposed on the surface of the treated work-piece by ultrasonic machining tool is 1200N.

Embodiment 7

[0052] An ultrasonic strengthening method of metal work-piece, ultrasonic machining of an axle with ultrasonic machining tool, that is, ultrasonic machining of the surface of the axle which is rotating around the main spindle with ultrasonic machining tool, the parameters of ultrasonic machining are: linear velocity of the axle is 120 m/min, feed rate is 0.6 mm/r, the pressure imposed on the surface of the treated work-piece by ultrasonic machining tool is 300-3000N. The times of ultrasonic machining is 3.

[0053] The curve graph of surface compressive stress of axle after ultrasonic strengthening is obtained as shown in FIG. 5 with changing the pressure of the ultrasonic machining tool to the surface of the treated work-piece while other parameters remain the same. Referring to FIG.5, when the pressure of the ultrasonic machining tool imposed on the surface to be machined is around 1750N, the preset compressive stress on the surface of the work-piece reaches a maximum surface of the work-piece does not change much hereafter.

[0054] Traditional turning+grinding machining and ultrasonic strengthening separately employed for the axle samples of the same material, the results are as follows:

TABLE-US-00002 TABLE 2 Traditional Turning + Grinding Machining of the Axle Samples Weight Total Weight Total Load No. (N) (N) (MPa) Cycles 1 335 433 310.6 156, 4800 2 325 423 303.4 429, 1300 3 315 413 296.2 376, 7900 4 305 403 289.1 1070, 9000 5 315 413 296.2 1148, 0600 6 325 423 303.4 147, 8600 7 315 413 296.2 1021, 6600 8 325 423 303.4 52, 4500 9 315 413 296.2 244, 6300 10 305 403 289.1 1113, 7900 11 315 413 296.2 410, 3900 12 305 403 289.1 1005, 1300

TABLE-US-00003 TABLE 3 Ultrasonic Strengthening of the Axle Samples Weight Total Weight Load No. (N) (N) (MPa) Cycles 1 475 573 411.0 X 2 465 563 403.9 X 3 455 553 396.7 4 465 563 403.9 5 475 573 411.0 X 6 465 563 403.9 7 475 573 411.0 X 8 465 563 403.9 X 9 455 553 396.7 X 10 445 543 389.5 11 455 553 396.7 12 465 563 403.9 X 13 455 553 396.7 Note: X means more than 10.sup.7 times, means less than 10.sup.7 times.

[0055] Fatigue limit is:

.sub.1= 1/10[(403.9+396.7)+(403.9+411)+(403.9+411)+(396.7+389.5)+(396.7+403.9)]=401.72MPa

[0056] Standard deviation is:

[00001]$\begin{array}{c}{S}_{{}_1}=\sqrt{\frac{\underset{i}{\overset{k}{.Math.}}.Math.{\left({}_i\right)}^2-\frac{1}{k}.Math.{\left(\underset{i}{\overset{k}{.Math.}}.Math.{}_{-1}\right)}^2}{k-1}}\\ =\sqrt{\frac{2{\left(400.3\right)}^2+2{\left(407.45\right)}^2+{\left(393.15\right)}^2-5{\left(401.72\right)}^2}{5-1}}\\ =12\end{array}$

[0057] Comparing Table 2 to Table 3, it is seen that the fatigue strength of the axle increases from about 300 MPa to about 401 MPa with ultrasonic strengthening process, the fatigue life of axle is greatly improved after ultrasonic strengthening comparing to the results of the traditional turning+grinding machining.

Embodiment 8

[0058] An ultrasonic strengthening method of metal work-piece, ultrasonic machining of an axle with ultrasonic machining tool, that is, ultrasonic machining of the surface of the axle which is rotating around the main spindle with ultrasonic machining tool, the parameters of ultrasonic machining are: linear velocity of the axle is 10 m/min, feed rate is 0.1 mm/r, the pressure imposed on the surface of the treated work-piece by ultrasonic machining tool is 300-3000N. The times of ultrasonic machining is 3.

Embodiment 9

[0059] An ultrasonic strengthening method of metal work-piece, ultrasonic machining of the surface of the rod or/and screw thread of the sucker rod which is rotating around the main spindle with ultrasonic machining tool, the said sucker rod is a semi-finished sucker rod, and the said surface roughness of the said semi-finished sucker rod is 3.2 m. The parameters of ultrasonic machining are: linear velocity of the sucker rod is 2 m/min, feed rate is 0.08 mm/r, the pressure imposed on the surface of the treated work-piece by ultrasonic machining tool is 300-3000N.

[0060] The curve graph of compressive stress on the surface of sucker rod after ultrasonic strengthening is obtained as shown in FIG. 6 with changing the pressure of the ultrasonic machining tool to the surface of the treated work-piece while other parameters remain the same. Referring to FIG. 6, when the pressure of the ultrasonic machining tool imposed on the surface to be machined is around 1500N, the preset compressive stress on the surface of the work-piece reaches a maximum of 830 MPa, as the pressure increases, the preset compressive stress on the surface of the work-piece does not change much hereafter.

[0061] The metallographic graph of the surface of sucker rod after the ultrasonic strengthening treatment is shown in FIG. 7.

[0062] The results of comparative test for the fatigue life of the sucker rod before and after the ultrasonic strengthening are shown in Table 4.

TABLE-US-00004 TABLE 4 Report of the Comparative Test for the Fatigue Life Samples Without Samples With Ultrasonic Ultrasonic Strengthening Strengthening Diameter Diameter No. (mm) Cycles No. (mm) Cycles 1 7.02 1.193 10.sup.6 9 7.01 >1.0 10.sup.7 (Passed) 2 7.02 5.82 10.sup.5 10 7.02 >1.0 10.sup.7 (Passed) 3 7.01 6.51 10.sup.5 11 6.99 >1.0 10.sup.7 (Passed) 4 7.00 1.594 10.sup.6 12 7.02 >1.0 10.sup.7 (Passed) 5 7.02 1.339 10.sup.6 13 7.01 >1.0 10.sup.7 (Passed) 6 6.98 4.56 10.sup.5 14 7.01 >1.0 10.sup.7 (Passed) 7 6.98 3.28 10.sup.5 15 7.02 >1.0 10.sup.7 (Passed)

[0063] It can be seen from Table 4 that the times of cycle use of sucker rod after ultrasonic strengthening is significantly more than that of the sucker rod without ultrasonic strengthening. Sucker rod with ultrasonic strengthening has obvious advantages.

Embodiment 10

[0064] An ultrasonic strengthening method of metal work-piece, ultrasonic machining of the surface of the rod or/and screw thread of the sucker rod which is rotating around the main spindle with ultrasonic machining tool. The parameters of ultrasonic machining are: linear velocity of the sucker rod is 120 m/min, feed rate is 0.8 mm/r, the pressure imposed on the surface of the treated work-piece by ultrasonic machining tool is 300-3000N. The said sucker rod is a semi-finished sucker rod. The surface roughness of the said semi-finished sucker rod is 10 m.