KR19990086137A - Apparatus and method for ultra high pressure water jet peening. - Google Patents

Abstract

The present invention relates to an apparatus and method for peening a material by means of an ultrafast waterjet. The apparatus includes means for generating and maintaining three-dimensional relative motion of the workpiece and the jet. The control unit can form complex shapes pinned to a uniform depth or pinned to different depths and can automatically change relative speeds, separation distances, angles and pressures. The method according to the invention comprises the use of missing particles suspended in a water jet to facilitate pinning.

Description

Apparatus and method for ultra high pressure water jet peening.

The present invention relates to material processing. In particular, the present invention relates to the pinning of the surface of a material to change its properties by local compression to a crystal structure. The method includes apparatus for using missing particles carried in a jet and for carrying out the method described above.

The material has been pinned by various methods according to the prior art. Pinning can be defined as the process of changing the material surface by impact. Initially, the pinning process was developed after the blacksmith discovered that if the metal is cold when hammered, the metal is hardened by repeated hammering. Desired properties can often be lost if the metal is heated or beaten while heated. For this reason, the above-mentioned process is called "cold processing." This effect is similar to a phenomenon known as "work hardening." The pinning process makes the material more resistant to corrosion and weakening.

The pinning process is generally accomplished by the use of an air propelled shot or centrifugal propelled shot that impacts the surface of the material to be pinned. The shot is a metal shot or a ceramic ball. The impact of the shot squeezes the surface of the part beyond the flexural strength that allows the hard dip material to retain the surface material upon compression. It is the surface residual compressive stress that prevents corrosion and weakening of the metal. Today pinning is widely used in a variety of metals such as iron alloys, titanium, vortex skins and ISO grid panels as well as conventional materials. Shot peening is used to work harden and shape the surface of the material. Pinning has been widely used in the nucleic acid and aircraft industries.

The conventional short peening method suffers from various problems. Difficulties include waste disposal, process control and contamination of the used short. Many materials will be contaminated by shots, especially in the case of metals. Small shots may block the passage if used in areas such as aircraft engines. Short contamination can change the properties of the workpiece, including unwanted alloying and corrosion nucleation. Process control becomes difficult when dealing with ball propulsion shorts. In addition, if the radius is short, large shots cannot pass through and fillets cannot be properly processed. Small shots are always satisfactory in order to solve the above-mentioned drawbacks, since sufficient energy cannot be supplied to adequately cold work the material and a desired compression depth exceeding the flexural strength of the material to be pinned cannot be achieved. It's not a trivial solution. Finally, it is difficult to recover the shots used if ceramics are used to eliminate the possibility of magnetic separation. This problem is particularly noticeable when processing required position pinning of reactor components. Waste shorts can block important cooling and control passages here. Damage to the clad metal can also damage the fuel rods. Air may be contaminated by floating metal particles in the air.

As an alternative to the above-mentioned problems with shot peening, the use of liquid jets for peening has been proposed. An example can be found in Enomoto US Pat. No. 5,305,361. Enomoto describes the process of peening reactor components using a vibrating nozzle water jet. According to the invention of Enomoto it is considered necessary to vibrate the nozzle to form a cavity in the jet stream. Breakage of the formed cavity increases the force transmitted to the material to be pinned. Enomoto states that the use of non-vibrating jets is impractical due to the ultrahigh pressure required to modify the material surface. Enomoto's invention is of limited use in the special case of peening the inner surface of a reactor. According to Enomoto's invention, because of the low pressure and high flow rate, the fuel rod has to be removed before the pinning process, so the size of the device must be large enough to withstand the reaction force and therefore high cost.

The present invention provides an apparatus and method for peening a material using an ultra high pressure water jet. The invention detailed herein is applicable to a variety of materials from titanium to aluminum vortex steel. The present invention provides a method of controlling the pinning force to a higher degree compared to the prior art. The device according to the invention imparts a pinning of a type which cannot be pinned by conventional short peening methods. The method according to the invention prevents contamination of the pinned surface. Since no shot is used, there is no need to handle the shot. The method according to the invention is feasible with a compact device which is relatively economical. No shot gets stuck in a small cavity.

The method according to the invention uses a single ultra high pressure waterjet nozzle. The ultrahigh pressure fluid exits the nozzle and taps on the metal surface slightly apart. The ultrahigh pressure should speed up the jet enough to burst the cavitation bubbles, accelerate the particles in the fluid or bend the metal surface directly. The jet moves with respect to the workpiece. This movement is achieved by moving the workpiece in two or three dimensions relative to the jet, or by moving only the jet itself. One or two of the three directions can be rotated by the present method. The method according to the invention changes not only the angle and the force but also the relative speed of movement. The control of each of the factors described above should be maintained to compensate for variations in all other factors.

The device according to the invention comprises an ultra high pressure water jet. This jet supplies fluid and particles properly. The jet is attached to a manipulator that allows the jet to move in three dimensions. This 3D can be applied to general Cartesian coordinates. According to another application, the jet can move along an entire plane but has unlimited rotational freedom. Finally, the jet can move along the line compartment and have two degrees of freedom of rotation. In the three classes of devices described above, the movement of the workpiece can be replaced by the movement of the jet. In addition, during the pinning operation, the device changes the pinning force of the jet. In addition to changes in the intensity and position of the jet, the relative speed of movement can be changed continuously. The apparatus according to the invention controls all of these functions simultaneously for accurate cold processing of the material.

In summary, the apparatus and method according to the present invention enable the pinning of various materials in a form that cannot easily be made by conventional pinning techniques. The apparatus and method according to the invention can be used in a variety of places where conventional short peening is not possible.

1 is a front view showing a method of the present invention.

2 is a precise perspective view of the apparatus according to the second embodiment of the present invention.

3 is a precise perspective view of the apparatus according to the third embodiment of the present invention.

4 is a perspective view of the embodiment shown in FIG.

5 is a front view according to a fourth embodiment of the present invention in a nuclear reactor.

* Sign Description

1 ... workpiece 2 ... nozzle assembly

3 ... jet 5 ... pinning face

In all embodiments according to the present invention, it has been found that there are various factors required for a process not previously known. The first factor is the presence of an incubation period. Cavitation studies revealed the presence of incubation periods. Incubation period means a period in which a material causes cavitation bubble rupture but no material loss. Ultra high pressure water jet peening is done during the incubation period to cold work the workpiece without causing material loss.

The second factor is about the effect and determination of the standoff in the peening process. The separation distance corresponds to the distance from the nozzle to the workpiece. The separation distance determines the mechanism and strength of the pinning process. It is desirable to place the nozzle as close to the workpiece as possible when cutting the water jet. The distance between the nozzle and the workpiece must be sufficient to allow cavitation bubbles to form and rupture in the ultra high pressure waterjet peening process. If the peening is only effected by impact pressure, the separation distance should be short. Therefore, the optimum separation distance must be adapted to the operating conditions.

Finally, the third factor is the temperature effect. If the fluid temperature approaches boiling point, it tends to increase to cavitation. All embodiments of the present invention heat the fluid to enhance the cavitation and pinning effects.

1 is a front view of the method according to the invention. A basic form of carrying out the method according to the invention is shown.

The surface of the unpinned workpiece 1 is disposed adjacent to the ultrahigh pressure nozzle assembly 2. Ultra high pressure flow can move through the nozzle assembly (2). According to the invention ultrahigh pressure is defined as a pressure exceeding 20,000 p.s.i., preferably a pressure exceeding 50,000 p.s.i. Suitable nozzle assemblies are shown in US Pat. No. 5,320,289. The ultra high pressure water jet 3 flows out of the nozzle 2 when the ultra high pressure fluid is applied to the nozzle 2. The nozzle 2 moves across the surface of the workpiece 1. When the jet 3 contacts the workpiece, the impact pressure of the jet 3 is applied to the surface 5 of the workpiece. The thrust load acting on the nozzle 2 is proportional to the product of the square root of the flow rate and the pressure. For example, with a flow rate of 2.5 gallons per minute, 60,000 pressures produce 1 relative drust. The energy available for plastic deformation of the surface 1 is about the cube of pressure. This means that four times the pressure increases the pinning strength by 64 times. It takes 88 horsepower to generate this pressure, and the flow of large pumps increases efficiency.

In contrast, the relative thrust of a vibrating pressure jet with a pressure of 15,000 p.s.i produces a relative thrust of 4 at a flow of 20 gallons per minute. This nozzle requires a 176 horsepower pump to generate 1/64 of pinning power. To produce a pinning strength comparable to ultra high pressure nozzles, high pressure vibrating nozzles require expensive support structures and large pumps to absorb reaction forces.

2 is a precise perspective view of a device according to a second embodiment of the present invention. The embodiment shown in FIG. 2 can be used for peening the interior of the cylindrical workpiece 10. The waterjet nozzle 11 is disposed in the workpiece 10. Workpiece 10 is adapted for rotation 13 relative to nozzle 11. Rotation 13 may be effected by rotating workpiece 10 or rotating nozzle 11. The water jet 12 extends from the nozzle 1 and is closest to the work 10. The nozzle 14 is adapted to move in the longitudinal direction 14 parallel to the length of the workpiece 10. In operation such that the helical path is followed by a jet 12 along the inner surface of the workpiece 10, the workpiece 10 rotates along 13 and the nozzle moves longitudinally along 14. The pinning operation is performed in the same manner as described above with reference to FIG.

3 is a precision of the apparatus according to the third embodiment of the present invention. In the third embodiment the work piece 22 is attached to the rotatable platter 20 which moves the work piece 22 and the platter 20 in the direction of the arrow 23. The waterjet nozzle 21 lies above and adjacent to the workpiece 22. The water jet 25 extends from the nozzle 21 and impacts the workpiece 22. The nozzle 21 can move in the radial direction 24. In operation, the workpiece 22 rotates along 23 and the nozzle moves in the radial direction 24 so that the helical path is followed by the jet 25 along the upper surface of the workpiece 22. The pinning process is performed in the same manner as described above with reference to FIG. 1.

4 is a perspective view of an apparatus according to a third embodiment of the present invention. The device is suitable for pinning surfaces of materials with a single axis of symmetry that can be rotated. For example, there are discs, cylinders, cones and spherical parts. The device listed is the prototype of the pinning center. The parts and parameters used are similar to conventional systems, and the device includes a plurality of pinning control devices not shown in FIGS. 1-3.

Workpiece 31 is attached to platter 32. Workpiece 21 is discoid in the figure. The platter 32 is suitable for rotation by the motor 33. The water jet 36 rests on the workpiece 31. The waterjet 36 can be moved in the x or horizontal direction by the traversing system 37. The waterjet 36 may also be moved in the y or vertical direction by the traversing system 37. The waterjet 36 can also be moved in the z direction by the traversing system 37. The transversal system 37, called the x-y-z manipulator, is a generally available system that allows movement in Cartesian three coordinates. Therefore, in this device, the waterjet can move in all directions along the Cartesian coordinates. The workpiece 31 can move along the axis of rotation of the platter 32. The apparatus shown in the figures is very similar to a milling machine capable of cold working irregular surfaces in three dimensions. The water jet 36 receives the high pressure liquid from the ultra high pressure pump 30 through the supply line 26. Particles such as ice or dry ice are supplied from the hopper 31 through the shutoff valve 32 and the supply line 33. The parts 31, 33, 34, 36 are optimally arranged in a water storage tank 34 having the function of retaining liquid in order to prevent contamination of the work area. The operation of all parts is controlled by the computer 41 which is in contact with the system controller 42.

Workpiece 31 is attached to platter 32 to operate the device of FIG. 4. In this embodiment the disc is pinned. The motor 33 is operated so that the platter 32 and the work piece 31 rotate. The high pressure fluid is then supplied to the water jet 36 via the feed line 39 with particles in the hopper 31. The traversing system 37 moves the waterjet 36 across the top surface of the workpiece 31. In operation, the waterjet 36 pins the workpiece 31. The process continues until the workpiece 31 is pinned to the desired depth over the entire surface. When the desired degree of pinning is performed, the pressure applied to the water jet 36 decreases.

Control of the sweep ratio provides a second method to change the pinning process of the finished product. In this way the center plane or other part of the pocket can be pinned deeper than the edges. Alternatively, the separation distance of the abrasive jets 36 may be changed by the manipulator 38 to control the pinning ratio. The above-described method can be used to compensate for the change in the tangential velocity due to the shape of the workpiece 1 or to perform uniform pinning. The angle of the workpiece 36 relative to the workpiece 31 can control the pinning speed. After the pinning process is complete, the valve 32 must be shut off and the work piece 31 removed. The device shown in Fig. 4 is suitable for pinning cylindrical, conical or other irregularly shaped objects by program inputting the shape of the workpiece into the computer.

5 is a front view of a nuclear reactor according to a fourth embodiment of the present invention. As mentioned above, the reactor is a particularly difficult part for peening. This is because in addition to cracks created by corrosion and abrasion, cracks may be formed due to corrosion. This requires the required position pinning processing of the reactor components. Under these conditions, loss and processing of shots is a particularly difficult problem. This problem prevents the required position pinning operation to date. The process described herein is applicable to boiling water reactors, pressurized water reactors and other paint reduction reactors. An embodiment of the present invention is shown as a boiling water reactor with two identical crawlers 52 and 55.

The reactor 50 is a typical boiling water reactor with a protective side plate 51. The protective side plate 51 is made of stainless steel susceptible to intergranular stress corrosion cracking at the weld surface. The cracking of the protective side plate 51 is clearly undesirable. Pinning has been considered a satisfactory method for preventing cracking in other applications. Unfortunately, shot peening is unsatisfactory due to waste disposal problems and short radius fillets. The crawler 52 is suitable for peening. The crawler 52 has an ultra high pressure water jet as shown in FIG. As shown in FIG. 5, the ultra high pressure is applied to the crawler 52 from the ultra high pressure pump 54 through the supply line 56. The supply line 56 is pulled from the support rails 57 to allow longitudinal movement. The support rails 57 are supported in the support rail carriage 58 which can move along the circumference of the protective side plate 52. Drive sprockets 59, 60 move carriage 58 around protective side plate 51. The controller 61 transmits information to the control sprockets 59 and 60 and the rails 57 through the wire 62. An automatic alignment vertical laser 63 mounted on the RPV is attached to the controller 61 and via the wire 64 the data collection unit 66 provides information about the position of the crawler 52 and feeds the crawler 52. Allow back control. The crawler 52 measures the degree of pinning processing and feeds back data to the unit 66. This information is used to control the pinning process.

In operation, the crawler 52 is lowered by the rails 57 along a vertical line, at which time an ultra high pressure water jet is activated to create a vertical pinning line. The carriage 58 then proceeds along the width of the pinning line and repeats this operation. The pinning process is performed in the same manner until the entire inner surface of the protective side plate 51 is machined. The operation ends while the protective side plate is filled with water.

It has been found that water jets operate more effectively in water so that the nozzles operate deeper, to a depth of about 45 feet. This is because the effect of bubble burst is increased. This effect decreases with increasing depth in order to suppress the formation of cavitation bubbles and to equalize in air at about 90 feet depth.

The foregoing embodiments are merely illustrative of the invention as defined in the appended claims.

Claims (20)

Generating an ultrahigh pressure flow rate; Transferring the ultrahigh pressure fluid to the ultra high pressure water jet cutting nozzle; Ultra high pressure water is discharged to form an ultra high pressure water jet, and ultra high pressure water across the metal side to be pinned so that the ultra high pressure water jet contacts and compresses the metal side until all the surfaces to be pinned are contacted and compressed by the jet. And a step of moving the jet and stopping the operation of the jet. The method of claim 1, wherein the pressure of the fluid exceeds 20,000 p.s.i. The method of claim 1, wherein the pressure of the fluid is greater than 50,000 p.s.i. 2. The method of claim 1, wherein the movement of the water jet is helical. The method of claim 1, wherein the nozzle and the workpiece are submerged in water to increase cavitation to enhance the peening process. The method of claim 1, wherein the distance between the nozzle and the work piece is selected to be sufficient to cold work the work without the need to remove material from the work piece. The metal peening processing method according to claim 1, comprising a step of adding solid particles to the water jet in order to increase the pinning efficiency. The metal peening processing method according to claim 7, wherein the solid particles are lost after the peening processing is completed. 10. The method of claim 8, wherein the solid particles are ice. The method of claim 1, wherein the waterjet is moved along an adjacent line until the entire surface of the metal to be pinned is subjected to straightening after the waterjet is linearly moved along one line. A pump for producing ultrahigh pressure fluid; A conduit connected to the pump for delivering ultra high pressure fluid; A nozzle connected to the conduit device to form an ultra high pressure water jet; A pinning machine consisting of a converter for moving the ultrahigh pressure waterjet across the metal face to be pinned such that the ultrahigh pressure water jet contacts and compresses the metal face until all the faces to be pinned are contacted and compressed by the jet . 12. The pinning machine of claim 11, wherein the flow rate is greater than 20,000 p.s.i. 13. The pinning machine of claim 12, wherein the flow rate is greater than 50,000 p.s.i. 12. The peening machine according to claim 11, wherein the conversion device moves the water jet helically. 12. The peening processing machine according to claim 11, comprising an immersion apparatus for immersing the nozzle and the metal in the liquid to increase the cavity to enhance the pinning. 12. The peening machine according to claim 11, comprising a separation distance control device for adjusting the distance between the nozzle and the workpiece to be sufficient for cold working the workpiece without removing material from the workpiece. 12. The peening machine according to claim 11, comprising a particle injection device for adding solid particles to the water jet to increase the peening efficiency. 18. The pinning machine of claim 17, wherein the solid particles are lost after the pinning operation is terminated. 19. The peening machine according to claim 18, wherein the solid particles are ice. 12. The peening process according to claim 11, wherein the conversion device moves the water jet along an adjacent line after moving the water jet along a line until the entire surface of the metal to be pinned is pinned. machine.