CAVITATION SURFACE PROCESSING METHOD

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese Patent Application No. 2024-097382, filed on Jun. 17, 2024, the entire contents of which are hereby incorporated by reference.

BACKGROUND

1. Technical Field

The present invention relates to a cavitation surface processing method.

2. Description of the Background

A cavitation surface processing method called cavitation abrasive surface finishing (CASF) is known in which a surface roughness of a workpiece is smoothed and peened using a cavitation jet (US 2024/0001509 A1).

BRIEF SUMMARY

According to the conventional cavitation processing method, a grinding speed of the surface may be slow. An object of the present invention is to increase the grinding speed of a surface by a cavitation processing method.

A first aspect of the present invention provides a cavitation surface processing method, including:

• • suspending abrasives into processing liquid;
  • immersing a workpiece and a flat spray nozzle into the processing liquid;
  • ejecting a cavitation jet spreading in a plane on a surface of the workpiece while the flat spray nozzle is rotating about an ejection axis; and
  • smoothing the surface of the workpiece to apply a compressive residual stress on the surface of the workpiece.

A second aspect of the present invention provides a cavitation surface processing method, including:

• • ejecting a cavitation jet containing cavities spreading in a helical ribbon shape from a flat spray nozzle rotating about an ejection axis at 100 to 200 RPM, the flat spray nozzle having a spray angle of 5 to 10 degrees about the ejection axis;
  • entraining abrasives by the cavitation jet to collide with a target surface which is a surface of a workpiece; and
  • applying a compressive residual stress on the target surface by the cavities being collapsed near the target surface and cavity cloud flowing along the target surface to grind the target surface.

The processing liquid is, for example, water. The processing liquid may include a rust inhibitor. The rust inhibitor is, for example, an organic amine. The abrasives are abrasive particles. The abrasives are, for example, ceramic or metal. The abrasives are, for example, alumina, garnet, zirconia, or stainless steel. The abrasives have, for example, an irregular shape, a spherical shape (bead), or a needle shape. The ejection pressure is 50 MPa to 200 MPa. The ejection flow rate is 2 L/min to 20 L/min. The workpiece is, for example, metal or fiber-reinforced plastic. The metal is, for example, light metal, steel, corrosion-resistant steel, or heat-resistant steel. The workpiece is mainly aluminum, an aluminum alloy, titanium, a titanium alloy, a copper alloy, a nickel alloy, molybdenum steel, and chromium molybdenum steel. A typical workpiece is an additive manufactured workpiece.

According to the cavitation processing method of the present invention, the grinding speed of the surface is increased.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a cavitation processing apparatus according to a first embodiment.

FIG. 2 is a longitudinal sectional view of a nozzle according to the first embodiment.

FIG. 3 shows a view seen from arrow III arrow in FIG. 2.

FIG. 4 shows continuous photographs of a cavitation jet according to the first embodiment.

FIG. 5 is a schematic diagram of a cavitation processing apparatus according to a second embodiment.

DETAILED DESCRIPTION

First Embodiment

As shown in FIG. 1, a cavitation processing apparatus 10 according to the present embodiment includes a processing tank 11, a nozzle 12, a pump 23, and a moving device 21. The processing tank 11 has an opening at the upper side. The processing tank 11 stores processing liquid 5 and abrasives 7. The abrasives 7 are suspended in the processing liquid 5.

The nozzle 12 is disposed on the moving device 21. The moving device 21 freely moves the nozzle 12 in the left-right direction (X direction), the front-rear direction (Y direction), and the vertical direction (Z direction). The nozzle 12 is connected to a pump 23. The nozzle 12 is a flat spray nozzle.

FIG. 2 is a cross-sectional view of the nozzle 12 in a YZ plane passing through an ejection axis 1. As shown in FIGS. 2 and 3, the nozzle 12 includes a nozzle head 13 and a nozzle tip 17. The nozzle head 13 has a round pipe shape.

The nozzle head 13 includes a flow channel 13a, a nozzle chamber 13b, and a jet passage port 13c in this order from the basal end (upper side in FIG. 2). The flow channel 13a is a cylindrical hole. The nozzle chamber 13b has a right cylindrical shape. The nozzle chamber 13b is connected to the flow channel 13a. For example, the nozzle chamber 13b has a smaller diameter than the flow channel 13a. The jet passage port 13c, which is located at a distal end of the nozzle head 13, is connected to the nozzle chamber 13b. The jet passage port 13c is a cylindrical hole. The jet passage port 13c has a smaller diameter than the nozzle chamber 13b.

The nozzle tip 17, which has a cylindrical shape, is disposed in the nozzle chamber 13b. Preferably, the nozzle tip 17 abuts the nozzle chamber 13b. The nozzle tip 17 is formed of, for example, a jewel, an artificial jewel, or a sintered body of an artificial jewel. The nozzle tip 17 includes, in order from the basal end, an inlet 17a, a choke 17b, and a discharge channel 17c. The inlet 17a and the choke 17b are arranged around the ejection axis 1. The inlet 17a, which is a right cone, has a smaller diameter toward the distal end. The choke 17b has a right elliptic cylindrical shape. As shown in FIG. 3, the choke 17b has a major axis extending in the X-direction. The choke 17b is directly connected to the inlet 17a. The choke 17b opens into the discharge channel 17c. As shown in FIG. 3, the discharge channel 17c, which is located on the distal end surface of the nozzle tip 17, extends in the X-direction. As shown in FIG. 2, the discharge channel 17c has a semicircular cross section in YZ plane.

As shown in FIG. 1, a collision area 34 between a cavitation jet 32 and a workpiece 3 has, for example, an elongated elliptical shape. A spray angle 37 of the cavitation jet 32 is 5 to 10 degrees. Here, the spray angle 37 is an opening angle of the cavitation jet 32 in the vicinity of an ejection port in XZ plane.

The workpiece 3 has a target surface 3a. The target surface 3a is a plane. The workpiece 3 is, for example, laminated and shaped by a powder bed method. A tensile residual stress is applied to the target surface 3a. The target surface 3a comprises unmelted powder (a-case). The target surface 3a is a surface of the workpiece 3. The target surface 3a is a target part in which unmelted powder is removed and a compressive residual stress is applied.

A cavitation processing method according to the present embodiment will be described with reference to FIG. 1. First, the workpiece 3 is disposed at the bottom of the processing tank 11. The workpiece 3 is immersed in the processing liquid 5. The target surface 3a extends in XY plane. The nozzle 12 is positioned by the moving device 21 at a position which is apart from the target surface 3a by an offset distance (a stand-off distance) 35. The nozzle 12 is immersed in the processing liquid 5. The ejection axis 1 extends in the Z direction. The moving device 21 rotates the nozzle 12 at a rotational speed 31. Preferably, the rotational speed 31 is from 100 RPM to 200 RPM.

Then, the pump 23 pressurizes the processing liquid 5 and supplies it to the nozzle 12. The pressure (ejection pressure) of the processing liquid 5 is preferably 50 MPa to 200 MPa. The processing liquid 5 passes through the flow channel 13a, the inlet 17a, and an opening of the choke 17b, and is ejected as the cavitation jet 32. At this time, the cavitation jet 32 spreads in a plate shape when it is accelerated by the inlet 17a and discharged from the choke 17b. Then, a vortex is generated by a velocity difference near the interface between the processing liquid 5 stored in the processing tank 11 and the cavitation jet 32, and a pressure difference is generated to promote the generation of the cavity. The cavitation jet 32 includes a large number of cavities. The cavitation jet 32 passes through the jet passage port 13c to collide with the workpiece 3. The moving device 21 may move the nozzle 12 along a predetermined movement path 33 at a constant speed while maintaining the offset distance 35.

FIG. 4 shows continuous photographs of the cavitation jet 32 taken with a high-speed camera. Photographs were taken continuously for each 0.024 s without any abrasives in the tank. The results are shown in the order of photographs 411 to 415. The cavities contained in the cavitation jet 32 appear as white clouds.

As shown in FIG. 4, the cavitation jet 32 is directed toward the workpiece 3 such that a thin ribbon is helically twisted. Then, the cavities are collapsed in the vicinity of the workpiece 3. The abrasives 7 are entrained in the cavitation jet 32. The abrasives 7 flow along the cavitation jet 32 under the fluid drag of the cavitation jet 32. The abrasives 7 collide with the workpiece 3 and flow radially around the ejection axis 1 along the workpiece 3.

According to the cavitation processing of the present embodiment, as the abrasives 7 are entrained in the cavitation jet 32, the amount of collision of the abrasives 7 with the workpiece 3 increases. In addition, the amount of the abrasives 7 flowing on the surface of the workpiece 3 increases. This increases the amount of grinding of the workpiece 3.

WORKING EXAMPLES

The cavitation processing was performed under the following conditions. The grinding amount is a depth from a surface of a raw workpiece to a surface after processing. A surface roughness was measured with a stylus type surface roughness measuring instrument. A surface residual stress of the workpiece was measured by X-ray stress measurement method (cos a method). The Pulsetec Industry Co., Ltd. μ-X360 s portable X-ray residual stress measurement device is used as the X-ray stress measurement device. When the rotation speed was zero, the direction in which the cavitation jet 32 spreads was the X direction, and the movement path 33 was the Y direction.

• • Workpiece: Laminated molded article of Ti alloy by powder bed method
  • Processing liquid: Water
  • Abrasives: Alumina powder (particle size: 60 μm to 70 μm)
  • Flow rate of cavitation jet 32: 6.5 L/min
  • Spray angle 37: 10 degrees
  • Offset distance 35: 150 mm
  • Moving speed: 50 mm/s
  • Rotational speed: 0 to 300 (1/min)

As a result, the obtained grinding amount is shown in Table 1. The rotational speeds of 100 to 200 RPM significantly increased the grinding amount. The surface residual stress after processing was-609 MPa.

Second Embodiment

As shown in FIG. 5, in the present embodiment, the cavitation processing is performed on a workpiece 103. The workpiece 103 has a hollow (target hole) 103b. The hollow 103b has an axial line 103c and a wall surface (target surface) 103a. Preferably, the axial line 103c extends in the Z-direction. The hollow 103b is, for example, a through-hole. The axial line 103c is aligned with the ejection axis 1. The moving device 21 rotates the nozzle 12 at 100 to 200 RPM. The moving device 21 may move the nozzle 12 in the axial direction.

The cavitation jet 32 becomes a thin helical ribbon shape that entrains the abrasives 7 into the hollow 103b. The cavitation jet 32, together with the abrasives 7, collides with the wall surface 103a. Then, the abrasives 7 and the cavity cloud flow along the wall surface 103a. When the cavity collapses in the vicinity of the wall surface 103a, compressive residual stress is applied to the surface of the wall surface 103a.

The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention, and all technical matters included in the technical idea described in the claims are the subject of the present invention. While the above embodiments have been shown by way of example, those skilled in the art will recognize that various alternatives, modifications, variations, and improvements can be made from the disclosure herein, which fall within the scope of the appended claims.

REFERENCE SIGNS LIST

• • 1 Ejection axis
  • 3 Workpiece
  • 3a Target surface
  • 5 Processing liquid
  • 7 Abrasives
  • 10 Cavitation processing apparatus
  • 12 Flat spray nozzle
  • 32 Cavitation jet