Cavitation Surface Processing Method

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.

The present invention relates to a cavitation surface processing method.

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).

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:

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

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.

As shown in, a cavitation processing apparatusaccording to the present embodiment includes a processing tank, a nozzle, a pump, and a moving device. The processing tankhas an opening at the upper side. The processing tankstores processing liquidand abrasives. The abrasivesare suspended in the processing liquid.

The nozzleis disposed on the moving device. The moving devicefreely moves the nozzlein the left-right direction (X direction), the front-rear direction (Y direction), and the vertical direction (Z direction). The nozzleis connected to a pump. The nozzleis a flat spray nozzle.

is a cross-sectional view of the nozzlein a YZ plane passing through an ejection axis. As shown in, the nozzleincludes a nozzle headand a nozzle tip. The nozzle headhas a round pipe shape.

The nozzle headincludes a flow channel, a nozzle chamber, and a jet passage portin this order from the basal end (upper side in). The flow channelis a cylindrical hole. The nozzle chamberhas a right cylindrical shape. The nozzle chamberis connected to the flow channel. For example, the nozzle chamberhas a smaller diameter than the flow channel. The jet passage port, which is located at a distal end of the nozzle head, is connected to the nozzle chamber. The jet passage portis a cylindrical hole. The jet passage porthas a smaller diameter than the nozzle chamber

The nozzle tip, which has a cylindrical shape, is disposed in the nozzle chamber. Preferably, the nozzle tipabuts the nozzle chamber. The nozzle tipis formed of, for example, a jewel, an artificial jewel, or a sintered body of an artificial jewel. The nozzle tipincludes, in order from the basal end, an inlet, a choke, and a discharge channel. The inletand the chokeare arranged around the ejection axis. The inlet, which is a right cone, has a smaller diameter toward the distal end. The chokehas a right elliptic cylindrical shape. As shown in, the chokehas a major axis extending in the X-direction. The chokeis directly connected to the inlet. The chokeopens into the discharge channel. As shown in, the discharge channel, which is located on the distal end surface of the nozzle tip, extends in the X-direction. As shown in, the discharge channelhas a semicircular cross section in YZ plane.

As shown in, a collision areabetween a cavitation jetand a workpiecehas, for example, an elongated elliptical shape. A spray angleof the cavitation jetis 5 to 10 degrees. Here, the spray angleis an opening angle of the cavitation jetin the vicinity of an ejection port in XZ plane.

The workpiecehas a target surface. The target surfaceis a plane. The workpieceis, for example, laminated and shaped by a powder bed method. A tensile residual stress is applied to the target surface. The target surfacecomprises unmelted powder (a-case). The target surfaceis a surface of the workpiece. The target surfaceis 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. First, the workpieceis disposed at the bottom of the processing tank. The workpieceis immersed in the processing liquid. The target surfaceextends in XY plane. The nozzleis positioned by the moving deviceat a position which is apart from the target surfaceby an offset distance (a stand-off distance). The nozzleis immersed in the processing liquid. The ejection axisextends in the Z direction. The moving devicerotates the nozzleat a rotational speed. Preferably, the rotational speedis from 100 RPM to 200 RPM.

Then, the pumppressurizes the processing liquidand supplies it to the nozzle. The pressure (ejection pressure) of the processing liquidis preferably 50 MPa to 200 MPa. The processing liquidpasses through the flow channel, the inlet, and an opening of the choke, and is ejected as the cavitation jet. At this time, the cavitation jetspreads in a plate shape when it is accelerated by the inletand discharged from the choke. Then, a vortex is generated by a velocity difference near the interface between the processing liquidstored in the processing tankand the cavitation jet, and a pressure difference is generated to promote the generation of the cavity. The cavitation jetincludes a large number of cavities. The cavitation jetpasses through the jet passage portto collide with the workpiece. The moving devicemay move the nozzlealong a predetermined movement pathat a constant speed while maintaining the offset distance.

shows continuous photographs of the cavitation jettaken 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 photographsto. The cavities contained in the cavitation jetappear as white clouds.

As shown in, the cavitation jetis directed toward the workpiecesuch that a thin ribbon is helically twisted. Then, the cavities are collapsed in the vicinity of the workpiece. The abrasivesare entrained in the cavitation jet. The abrasivesflow along the cavitation jetunder the fluid drag of the cavitation jet. The abrasivescollide with the workpieceand flow radially around the ejection axisalong the workpiece.

According to the cavitation processing of the present embodiment, as the abrasivesare entrained in the cavitation jet, the amount of collision of the abrasiveswith the workpieceincreases. In addition, the amount of the abrasivesflowing on the surface of the workpieceincreases. This increases the amount of grinding of the workpiece.

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 jetspreads was the X direction, and the movement pathwas the Y direction.

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.

As shown in, in the present embodiment, the cavitation processing is performed on a workpiece. The workpiecehas a hollow (target hole). The hollowhas an axial lineand a wall surface (target surface). Preferably, the axial lineextends in the Z-direction. The hollowis, for example, a through-hole. The axial lineis aligned with the ejection axis. The moving devicerotates the nozzleat 100 to 200 RPM. The moving devicemay move the nozzlein the axial direction.

The cavitation jetbecomes a thin helical ribbon shape that entrains the abrasivesinto the hollow. The cavitation jet, together with the abrasives, collides with the wall surface. Then, the abrasivesand the cavity cloud flow along the wall surface. When the cavity collapses in the vicinity of the wall surface, compressive residual stress is applied to the surface of the wall surface

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.