METHOD FOR REMOVING SUPPORT STRUCTURE

Removal of the support structure from the workpiece is in an easily automated way. A method for removing support structure includes: suspending abrasive into a process liquid; cutting a support structure along a cutting surface from an additively manufactured workpiece having a support surface, the support surface including the support structure for fixing the workpiece to a build platform; installing the workpiece with the support structure remaining on the support surface in the process liquid with suspended abrasive; immersing a nozzle for ejecting a cavitation jet of the process liquid into the process liquid; and ejecting the cavitation jet onto the workpiece from the nozzle immersed in the process liquid such that an angle between an ejection axis of the cavitation jet ejected from the nozzle and the support surface is between 0 to 20 degrees to remove the remaining support structure adhered to the workpiece.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese Patent Application No. 2023-100630, filed on Jun. 20, 2023, the entire contents of which are hereby incorporated by reference.

BACKGROUND

1. Technical Field

The present invention relates to a method for removing a support structure.

2. Description of the Background

A support structure remains on a metal material produced by additive manufacturing. The support structure supports a workpiece to a build platform during additive manufacturing. The support structure is removed mainly by manual work or by cutting.

BRIEF SUMMARY

Removal of the support structure from the metallic material requires experienced skill. Quality stability and production automation are required in the removal process of the support structure.

An object of the present invention is to remove the support structure from the workpiece in an easily automated manner.

A first aspect of the present invention provides a method for removing support structure, including:suspending abrasive into a process liquid;cutting a support structure along a cutting surface from an additively manufactured workpiece having a support surface, the support surface including the support structure for fixing the workpiece to a build platform;installing the workpiece with the support structure remaining on the support surface in the process liquid with suspended abrasive;immersing a nozzle for ejecting a cavitation jet of the process liquid into the process liquid; andejecting the cavitation jet onto the workpiece from the nozzle immersed in the process liquid such that an angle between an ejection axis of the cavitation jet ejected from the nozzle and the support surface is between 0 to 20 degrees to remove the remaining support structure adhered to the workpiece.

The structure of the support structure is, for example, a block support, an adaptive cell support, a rod support, a line support, a tree support.

When additive manufactured, the workpiece is built from the build platform, supported by the support structure. The workpiece is separated from the build platform by cutting the support structure. The support surface is, for example, a portion of the workpiece surface that adheres to the support structure. A distal end of the support structure is attached to the support surface. The distal end of the support structure remains on the support surface. For example, the support structure remains slightly from the support surface of the workpiece. Here, a slight value is, for example, a height in the order of 0.3 to 1 mm (including both ends).

The angle between the nozzle and the support surface is from 0 degrees to 20 degrees, preferably from 10 degrees to 20 degrees.

The process liquid is, for example, water. The process liquid may include a rust inhibitor.

The abrasive is abrasive particles. The abrasive is, for example, ceramic. The abrasive is, for example, alumina, garnet, or zirconia.

Simultaneously with the removal of the support structure, the support surface is smoothed.

The present invention allows to remove the support structure from the workpiece in an easily automated manner.

DETAILED DESCRIPTION

As shown inFIG.1, in a method for removing a support structure for a workpiece according to the present embodiment, the workpiece3is additively manufactured first (step S1). Next, a support structure3bof the workpiece3is cut (step S2). Next, the workpiece3and a nozzle15are immersed in a process liquid1containing abrasives2(step S3). A cavitation processing is then performed (step S4).

In step S1, for example, the additive manufacturing is performed by 3D printing. The 3D printing is, for example, powder bed fusion (PBF). The additively manufactured workpiece3has a tensile residual stress. As shown inFIG.2, the additively manufactured workpiece3is supported on a build platform3cby a number of support structures3b.

In step S2, the support structure3bis cut at a cut surface9. This separates the workpiece3from the build platform3c. Preferably, the cut surface9is in the vicinity of the workpiece3. The workpiece3has a support surface3a. A distal end of the support structure3bis connected to the support surface3a. The support surface3amay be a curved surface.

As shown inFIG.3, a portion3b1of the support structure3badheres to the support surface3a. A length of the support structure3bvaries depending on the shape of the workpiece3and the posture of the workpiece3formed on the build platform at the time of manufacturing. The length3b2of the support structure3b1adhered to the workpiece3is, for example, 0.3 mm to 100 mm. Preferably, the length3b2of the support structure3b1is 0.3 mm to 20 mm, and more preferably 0.3 mm to 0.5 mm.

The support structure3bmay have a prismatic shape. The support structure3bmay be a block support, an adaptive cell support, a line support, or a tree support.

Next, a support structure removing apparatus10for the workpiece3will be described. As shown inFIG.4, the support structure removing apparatus10includes a processing tank11, a high-pressure process liquid source13, a nozzle15, a moving device16, a pressure gauge17, a stirring liquid source18, a stirring block19, and a stirring nozzle20.

The processing tank11opens upward. The processing tank11stores the process liquid1and the abrasive2. The high-pressure process liquid source13is, for example, a piston pump. The high-pressure process liquid source13pressurizes the process liquid1and supplies it to the nozzle15.

The moving device16is, for example, a robot such as a vertical articulated robot, a horizontal articulated robot, an orthogonal axis robot, or a parallel link robot. The moving device16may be a spindle head moving device of a column traverse type machining center.

The nozzle15, which is arranged in the moving device16, is moved by the moving device16. The nozzle15is immersed in the process liquid1stored in the processing tank11. The nozzle15ejects the process liquid1along an ejection axis15a. For example, the ejection axis15aextends in a direction between a horizontal direction and a vertically downward direction (vertically downward inFIG.4). Preferably, the nozzle15has a structure that generates a vortex between the process liquid1and a jet6to promote the generation of the cavity.

The pressure gauge17detects a discharge pressure from the high-pressure process liquid source13.

The stirring liquid source18is, for example, a centrifugal pump or a diaphragm pump. The stirring block19is disposed at the bottom of the processing tank11. The stirring block19is connected to the stirring liquid source18. The stirring block19includes the stirring nozzle20.

In step S3, the workpiece3is immersed in the process liquid1stored in the processing tank11. The support surface3ais installed toward the nozzle15(slightly inclined from vertical inFIG.4). The support surface3amay be arranged vertically, for example. The support surface3amay be inclined from vertical. An angle4between the ejection axis15aand the support surface3ais, for example, 0 to 90 degrees, preferably 0 to 20 degrees, and more preferably 10 to 20 degrees. The support surface3ais arranged obliquely or parallelly with respect to the ejection axis15a, thereby promoting the removal of the support structure3b1. Even if the support structure3b1is a strong support structure material such as a block support or an adaptive cell support, the support structure3b1can be effectively removed by setting the angle4to 0 to 20 degrees or 10 to 20 degrees.

In step S4, the stirring nozzle20ejects the process liquid1into the processing tank11to stir the abrasive2. The abrasive2floats the processing tank11to become a turbid liquid5. The workpiece3is in the turbid liquid5. The nozzle15is immersed in the process liquid1to eject the process liquid1. The jet6ejected from the nozzle15entrains the abrasive2and collides with the support surface3a. As indicated by arrow7, the jet6flows along the support surface3a. At this time, the abrasive2also flows in the direction of the arrow7. The support structural3b1is then removed. Further, the support surface3ais smoothed. As the abrasive2flows in the vicinity of the support structure3b1, the removal of the support structure3bis promoted.

Note that the jet6collides with the vicinity of the base of the support structure3b1(the boundary between the support structure3b1and the workpiece3) when the height3b2of the support structure3b1is high. At this time, the jet6with the abrasive2bends the support structure3b1from near the root. In addition, the jet6with abrasive2scrapes off the support structure3b1remaining on the support surface3a.

The jet6ejected from the nozzle15promotes the generation of the cavity. The cavity is a fine bubble that is generated and disappears in a short time due to a pressure difference in a fluid flow. The cavity is introduced around the support surface3aon the jet6. When the cavity disappears, the fluid flows locally rapidly and impinges on the surface of the support surface3ato be peening processed. When peening processing (hereinafter, cavitation peening) is performed by causing a cavitation jet to collide with the support surface3a, residual compressive stresses are applied to the surface of the support surface3a.

The support structure3b1remaining on the workpiece3is preferably removed. According to the present invention, the support structure3b1remaining on the workpiece3can be effectively removed.

In addition, there may be an incomplete melted region on the surface of the additively manufactured workpiece3. According to the present invention, the surface of the workpiece3can be ground to remove the incomplete melted regions remaining on the support surface3a.

According to the method for removing the support structure of the present embodiment, the support structure3b1can be effectively removed even when the workpiece3is in the form of a mesh. In addition, the support structure3b1disposed inside the workpiece3can be effectively removed.

The additive manufactured workpiece has a tensile compressive stress. It may be desirable to improve the fatigue strength of the additively manufactured workpiece. According to the present invention, as compressive residual stress is applied to the surface of the additively manufactured workpiece, fatigue strength is improved.

First Example

As shown inFIG.5, a workpiece103made of Ti-6Al-4V alloy was manufactured by additive manufacturing using a powder bed method. The workpiece103has a flat support surface103a. A support structure103b1is a block support. The support structure3bwas cut at 2 mm height from the support surface103a. The support structures103b1remaining on the workpiece103are uniformly disposed on one surface of the support surface103a. The ejection conditions are as follows.

Process liquid: Water

Amount of abrasive: 30% by weight based on the process liquid

Nozzle moving path: Path25(see an upper photo ofFIG.5) for scanning while folding back on a plurality of parallel lines having a spacing27

Number of passes: 7

The surface of the workpiece3before and after the liquid ejection was photographed by an optical microscope. The optical microscope utilized a Keyence VXH-6000. Further, the surface residual stress of the workpiece3before and after the liquid ejection was measured by an X-ray stress measurement method (cos a method). The X-ray stress measuring device utilized the Pulsetec Industrial Co. Ltd u-X360s portable X-ray residual stress measuring device. The residual stress was measured for a plurality of specific portions of the workpiece3.

Results

Photographs before and after the cavitation processing on the support surface103aof the workpiece3of the present example are shown inFIG.5. The upper photo inFIG.5is pre-processing. The lower photo inFIG.5is after processing. In the present example, the support structures103bremaining on the workpiece103were effectively removed. The surface residual stresses after the processing of this example were-205 MPa.

Second Example

As shown inFIG.6, a workpiece203made of a Ti-6Al-4V alloy was manufactured by additive manufacturing using a powder bed method. The workpiece203is a surgical implant. The workpiece203has a mesh structure. The workpiece203also has a support structure203b1therein. The support structure203b1is a rod support. The workpiece203is generally rounded. The height, width, and thickness of the support structures203b1vary from one support structure203b1to another. The dimensions of the support structure203b1remaining in the workpiece3are, for example, as follows.

Thickness (perpendicular to the page inFIG.6): 1 mm

The workpiece3was installed in the processing tank11so that the support structure203b1extends horizontally. The nozzle15was installed downward. That is, the support surface203ais substantially parallel to the ejection axis15a. The liquid ejection processing was performed on the workpiece203under the following ejection conditions.

Nozzle travel path: path29through the vicinity of the boundary between the support structure203b1and the workpiece203(upper photo inFIG.6)

Number of passes: 1

Other conditions are the same as in the first example.

Results

Photographs before and after the cavitation processing for the workpiece203according to the present example are shown inFIG.6. The upper photo inFIG.6is pre-processing. The lower photo inFIG.6is after processing. In this example, the support structures203b1remaining on the workpiece203were effectively removed. The support structures203b1fell into a large lump inside the tank. The surface residual stresses after the processing of the present example were −205 MPa.

Removal of the support structure is believed to proceed as follows. First, the support structure203b1is broken in the vicinity of the support surface203aand separated from the workpiece203by the kinetic energy of the abrasive and the process liquid. Next, the support structure203b1remaining on the support surface203ais removed by the flow of the abrasive, the dynamic pressure of the process liquid, and the impact force caused by the collapse of the cavity.

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