ELBOW FORMED BY CUTTING AND METHOD FOR MANUFACTURING SAME

Abstract

A hole is formed in an elbow through the steps of: forming a starting hole in a material, the starting hole having an undercut remaining on a hole surface; finishing an inner diameter of the starting hole (11.sub.-3) on one end side by revolving a side cutter (II) including an arc-shaped cutting edge and having an outer diameter smaller than a finishing hole diameter while rotating the side cutter (II) in such a posture that the side cutter (II) is inclined in a predetermined direction relative to the material (12), the revolving being carried out so that the side cutter moves along a hole surface to be finished; and finishing the inner diameter of the starting hole (11.sub.-3) on another end side by revolving the side cutter (II) while rotating the side cutter (II).

Claims

1. A method of manufacturing an elbow having a center axis that is bent smoothly at a predetermined curvature, the method comprising: preparing a metal material having a through hole; and finishing an inner surface of the through hole using a cutter, having cutting edges around an axis of the cutter and having an outer diameter smaller than a diameter of the through hole, by rotating the cutter to form the inner surface while the cutter is inclined at a constant angle with respect to the metal material and revolving along a helical trajectory, such that any cross-section of the through hole that is parallel to an end surface of the cutter and perpendicular to the center axis of the elbow is cut into a circle, whereas any cross-section of the through hole that is parallel to the end surface of the cutter and not perpendicular to the center axis of the elbow is cut into an oval.

2. The method of claim 1, further comprising machining the metal material such that a tube wall thickness on an outer side of a bend in the elbow is larger than a tube wall thickness on an inner side of the bend in the elbow, wherein the through hole is formed such that a center axis of the through hole is eccentrically located with respect to a center axis of an outer surface of the elbow.

3. The method of claim 2, wherein the through hole is formed and finished such that the outer side of the bend is located at a position separated by 180 from a position of the inner side of the bend.

4. The method of claim 2, wherein the through hole is formed and finished such that a wall thickness of the elbow gradually increases from the inner side of the bend to the outer side of the bend.

5. The method of claim 2, wherein the through hole is formed and finished such that the tube wall thickness on the outer side of the bend is larger than the tube wall thickness on the inner side of the bend.

6. The method of claim 1, wherein the through hole is formed and finished such that the through hole has a center axis that is bent smoothly at a predetermined curvature, without any machining remainder part inside and having a cross section, orthogonal to the center axis, that is a true circle, and wherein the method further comprises machining the metal material to comprise a straight part on at least one end side of the elbow.

7. The method of claim 1, further comprising machining the metal material to comprise integral flanges at both end portions of the elbow.

8. A method of manufacturing an elbow having a center axis that is bent smoothly at a predetermined curvature, the method comprising: preparing a metal material having a through hole; and finishing an inner surface of the through hole using a cutter, having cutting edges around an axis of the cutter and having an outer diameter smaller than a diameter of the through hole, by rotating the cutter to form the inner surface while the cutter is inclined at a constant angle with respect to the metal material and revolving along a helical trajectory, such that each cross-section of the through hole that is parallel to an end surface of the cutter and not perpendicular to the center axis of the elbow is cut into an oval, and such oval cross sections include a first oval cross-section and a second oval cross-section, and the first oval cross-section of the through hole is different in size and shape from the second oval cross-sections of the through hole.

9. A method of manufacture comprising: preparing a metal material having a through hole; and finishing an inner surface of the through hole using a cutter, having cutting edges around an axis of the cutter and having an outer diameter smaller than a diameter of the through hole, by rotating the cutter to form the inner surface while the cutter is inclined at a constant angle with respect to the metal material and revolving along a helical trajectory, such that any cross-section of the through hole that is parallel to an end surface of the cutter and perpendicular to a center axis of the through hole is cut into a circle, whereas any cross-section of the through hole that is parallel to the end surface of the cutter and not perpendicular to the center axis of the through hole is cut into an oval.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0043] [FIG. 1A] A perspective view illustrating an example of a machined elbow manufactured by a method according to the present invention.

[0044] [FIG. 1B] A view of the elbow of FIG. 1A in a cross-section perpendicular to its axis.

[0045] [FIG. 2A] Aperspective view illustrating a half of an elbow machining region of a material.

[0046] [FIG. 2B] A plan view of the half machining region of FIG. 2A.

[0047] [FIG. 3A] A view illustrating a step of a former stage of starting hole processing.

[0048] [FIG. 3B] A view illustrating a step of the former stage of starting hole processing.

[0049] [FIG. 3C] A view illustrating a step of the former stage of starting hole processing.

[0050] [FIG. 3D] A view illustrating a step of the former stage of starting hole processing.

[0051] [FIG. 4A] A view illustrating a step of a latter stage of starting hole processing.

[0052] [FIG. 4B] A view illustrating a step of the latter stage of starting hole processing.

[0053] [FIG. 4C] A view illustrating a step of the latter stage of starting hole processing.

[0054] [FIG. 4D] A view illustrating a step of the latter stage of starting hole processing.

[0055] [FIG. 4E] A view illustrating a step of the latter stage of starting hole processing.

[0056] [FIG. 5A] A view illustrating postures of the material and a side cutter when one end side of the starting hole is finished.

[0057] [FIG. 5B] A perspective view illustrating a half of the starting hole whose one end side is finished.

[0058] [FIG. 6A] A view illustrating revolution movement of the side cutter in the finishing of the one end side of the starting hole.

[0059] [FIG. 6B] A view illustrating the revolution movement of the side cutter in the finishing of the one end side of the starting hole.

[0060] [FIG. 6C] A view illustrating the revolution movement of the side cutter in the finishing of the one end side of the starting hole.

[0061] [FIG. 6D] A view of the revolution movement of the side cutter when viewed from above correspondingly to FIGS. 6A to 6C.

[0062] [FIG. 6E] Aview of the revolution movement of the side cutter when viewed from above correspondingly to FIGS. 6A to 6C.

[0063] [FIG. 6F] A view of the revolution movement of the side cutter when viewed from above correspondingly to FIGS. 6A to 6C.

[0064] [FIG. 7A] A perspective view illustrating an unfinished state of the other end side of the starting hole.

[0065] [FIG. 7B] A perspective view illustrating a finished state of the other end side of the starting hole.

[0066] [FIG. 8A] A perspective view illustrating another example of the machined elbow manufactured by the method according to the invention.

[0067] [FIG. 8B] A view of the elbow of FIG. 8A in a cross-section perpendicular to its axis.

[0068] [FIG. 8C] A view of the elbow of FIG. 8A in a cross-section horizontal to its axis.

[0069] [FIG. 9] Aperspective view illustrating still another example of the machined elbow manufactured by the method according to the present invention.

[0070] [FIG. 10] A perspective view illustrating further another example of the machined elbow manufactured by the method according to the present invention.

[0071] [FIG. 11A] A perspective view illustrating an example of a rotary cutting tool for use in roughing of a hole and an outer diameter in the method according to the present invention, under a state in which the rotary cutting tool is mounted on an arbor.

[0072] [FIG. 11B] A side view of the cutting tool of FIG. 11A.

[0073] [FIG. 12A] A perspective view illustrating an example of a side cutter for use in finishing of the hole in the method according to the present invention.

[0074] [FIG. 12B] A side view of the above-mentioned cutter under a state in which the cutter is mounted on an arbor.

[0075] [FIG. 13] Aside view illustrating an example of a ball end mill for use in finishing of the outer diameter in the method according to the present invention.

DESCRIPTION OF EMBODIMENTS

[0076] Now with reference to the attached drawings, description is made of a method of manufacturing an elbow by cutting, embodying the present invention, and an elbow manufactured by this method.

[0077] First, examples of rotary cutting tools used in the method according the present invention are illustrated in FIGS. 11A to 13. The cutting tool illustrated in FIGS. 11A and 11B is a commercially-available indexable milling cutter (face milling cutter) I including a plurality of arc-shaped cutting edges 2 circumferentially arranged at intervals around the leading end of the cutter body 1. The milling cutter I is used to form a starting hole in a material to be formed into the elbow and to roughly cut the radially outer surface of elbow. To perform such rough cutting with high efficiency, the milling cutter I shown, in which the cutting edges 2 are formed by removable round inserts, are preferably mounted on an arbor 3. But a milling cutter other than the face milling cutter shown, such as a radius end mill or a ball end mill, may be used instead.

[0078] FIGS. 12A and 12B illustrate a side cutter II including a plurality of arc-shaped cutting edges 5 circumferentially arranged at intervals around the cutter body 4. The side cutter II is used to finish the starting hole formed in the material for the elbow. The illustrated side cutter II is a cutter obtained by modifying a commercially available cutter of which the cutting edges 5 are formed by removable round inserts so that the cutter can be firmly fixed to a specially ordered arbor 6. Specifically, the side cutter II is mounted on the leading end of the arbor 6. The side cutter II has an outer diameter smaller than the diameter of the starting hole. The outer diameter of the arbor 6 is further smaller than the outer diameter of the side cutter II.

[0079] FIG. 13 illustrates a commercially available indexable ball end mill III. In the method embodying the invention, this indexable ball end mill III or alternatively, a solid ball end mill is used to finish the radially outer surface of the elbow.

[0080] An example of the machined elbow manufactured by the method according to this invention is illustrated in FIGS. 1A and 1B. The elbow 10 shown is a 90 elbow without a flange, and includes a hole 11 having a center axis bent smoothly at apredetermined curvature.

[0081] Description is now given how the 90 elbow 10 of FIGS. 1A and 1B is manufactured using the above-mentioned cutting tools as an example. Reference numeral 12 of FIGS. 2A and 2B is an elbow material in the shape of a square block shape. For easy understanding of the processing situation, section views are illustrated in a manner that the material 12 is cut into half, and the cutter is illustrated in a simplified manner.

[0082] The material 12 is placed on a rotary table (not shown) of a processing machine such that the center axis O of the hole of the elbow 10 formed is on a plane parallel to the surface of the rotary table (the table surface is perpendicular to the rotation axis of the table). The cutter and the material 12 are inclined relative to each other as described later by rotating the rotary table.

[0083] The milling cutter I is set on the main shaft (not shown) of the processing machine, and as illustrated in FIG. 3A, the milling cutter I is fed in the axial direction so as to cut into an A surface of the material 12 while changing the cutting position and the cutting depth. In this manner, a blind hole 11.sub.-1 is formed as illustrated in FIG. 3B, which has a small undercut on the hole surface on the outer side of the bend.

[0084] Next, as illustrated in FIGS. 3C and 3D, the material 12 is positioned such that its B surface which is orthogonal to the A surface faces the milling cutter I. In this state, in the same manner as the hole is formed in the A surface with the milling cutter I, the milling cutter I is fed in the axial direction so as to cut into the B surface while changing the cutting position and the cutting depth until the hole thus formed communicates with the blind hole 11.sub.-1, thus forming a through hole 11.sub.-2 formed with an undercut 13 swelled in the hole diameter direction on the inner side of the bend.

[0085] Thus, in this state, the undercut 13 still remains in a large amount. That is, the side cutter II of FIGS. 12A and 12B cannot completely remove the undercut by finish cutting. To reduce the undercut, with the material 12 inclined at with respect to the milling cutter I such that the leading end of the cutter I is located nearer to the inner side of the bend of the elbow as illustrated in FIG. 4A, the milling cutter I is fed in the axial direction while changing the cutting position, to partially remove the undercut 13.

[0086] This operation is repeated several times while gradually increasing the relative inclination angle between the milling cutter I and the material 12, to thereby sufficiently reduce the remaining amount of the undercut 13. The relative inclination angle between the material 12 and the milling cutter I in this processing is set in accordance with the type of the material so that an excess cutting load is not imparted to the cutter. In an evaluation test, of FIG. 4A is set to 15, 1 of FIG. 4B is set to 25, 2 of FIG. 4C is set to 35, and 3 of FIG. 4D is set to 45, but the angles are not limited thereto.

[0087] The undercut 13 may be removed by feeding the cutter from both ends of the through hole 11.sub.-2. But in many cases, the undercut 13 can be removed sufficiently by feeding the cutter from one end only of the through hole 11.sub.-2. This reduces the number of times the cutter is fed into the hole.

[0088] At the end of these steps, a starting hole 11.sub.-3 as illustrated in FIG. 4E is formed in the material 12. Then, the tool mounted on the main shaft of the processing machine is replaced with the side cutter II of FIGS. 12A and 12B, and the side cutter II is used to finish the starting the starting hole 11.sub.-3.

[0089] The finishing is performed as follows. With the side cutter II inclined at an angle of 4 relative to the material 12 such that the end surface of the side cutter II is more remote from the opening of the starting hole 11.sub.-3 on the inner side of the bend of the elbow 10 to be cut, as illustrated in FIG. 5A, the side cutter II is revolved while being rotated about its axis so that the side cutter II cuts into the hole surface of the starting hole 11.sub.-3. At this time, the side cutter II is revolved so that the cutter moves on a helical trajectory along a hole surface to be finished. In this case, it is conceived that the relative inclination angle 4 between the side cutter II and the material is always constant. But this is not an essential requirement.

[0090] FIGS. 6A to 6F are views illustrating a state in which the side cutter II is revolved in the counterclockwise direction while being rotated about its axis and fed in the axial direction. Since the side cutter II is fed in the axial direction while being revolved, side cutter II moves on a helical trajectory.

[0091] The hole 11 of the elbow 10 has such a shape that it has a completely circular cross-section when taken along a line perpendicular to the center axis of the hole 11 of the elbow 10 before being finished and parallel to the end surface of the side cutter, which is perpendicular to the center axis of the side cutter II and inclined at an angle of 4 relative to the material 12 (i.e. when taken along the line Y-Y of FIG. 5A), while all the other cross-sections parallel to the end surface of the side cutter, including the cross-sections taken along lines X-X and Z-Z of FIG. 5A are oval. Any of such oval cross-sections is different in size and shape from all the other such oval cross-sections. The side cutter II is moved while being revolved along the hole surface to be finished, which has the above-mentioned cross-sectional shapes.

[0092] In this case, the finishing at the position exceeding the line Z-Z (the other end side of the hole) is performed so that the cutter is moved along the hole cross-section only on the outer side of the bend of the hole, to thereby prevent the arbor 6 from interfering with the material. In the finishing of the starting hole from the one end, only a half of the hole is required to be processed. Therefore, the cutter does not need to be forcedly moved along the hole cross-section on the inner side of the bend.

[0093] If a large amount of material has to be removed during finish cutting, the finish cutting may be performed several times to reduce the cutting load per one time. Through adoption of a method in which the machining remainder part is gradually cut off in several times to finish the product to have a target inner diameter in the final processing, excess cutting load is not imparted, and processing stability and processing accuracy are improved.

[0094] With the processing using the side cutter subjected to movement control, the undercut remaining in the starting hole 11.sub.-3 is largely removed, and thus the inner diameter of the starting hole on the one end side is finished.

[0095] In the processing of the starting hole from the one end, there is a processing restriction due to the hole shape, and hence it is impossible to finish the entire region of the starting hole as in FIG. 5B. Therefore, subsequently, the starting hole 11.sub.-3 is processed also from the other end to finish the hole. The side cutter II is arranged on the other end of the starting hole 11.sub.-3 as illustrated in FIG. 7A, and an operation similar to that described above is performed (the movement control in the same conditions as above is not necessary), and thus the remaining part of the undercut 13 is cut off.

[0096] In this manner, the hole 11 of the elbow has such a shape that its cross-sections taken along any plane perpendicular to the axis of the hole 11 is a true circle, with the hole surface moderately bent in parallel to its center axis.

[0097] After finishing the hole 11 in this manner, the radially outer surface of the elbow is subjected to rough cutting using the milling cutter I of FIGS. 11A and 11B, and then finished using the ball end mill III of FIG. 13. The desired elbow is thus completed.

[0098] The radially outer surface of the elbow is preferably finished after forming the hole because with this arrangement, the material can be held in position more stably while forming the hole and because there is no possibility of damaging the finished radially outer surface when forming the hole. But the radially outer surface may be finished before forming the hole.

[0099] The milling cutter I or the side cutter II may be inclined relative to the material 12 by inclining the main shaft of the processing machine on which the cutter is mounted.

[0100] Although the control of the processing machine becomes a little complicated, the object of the invention can be also achieved by performing the finishing step of the radially inner surface of the starting hole 11.sub.-3 on the one end as follows. The side cutter II is revolved while being rotated about its axis to cut into the starting hole 11.sub.-3, and while inclining the side cutter II and the material 12 relative to each other in accordance with the hole bent state at a position at which the hole 11 of the elbow is bent so that the movement of the side cutter II is performed in a plane substantially perpendicular to the center axis of the hole to be provided in the elbow as a finished product, the inner diameter of the starting hole 11.sub.-3 on the one end side is processed halfway from the one end toward the other end of the hole. Then, from the position at which the relative inclination angle between the side cutter II and the material 12 reaches an allowance upper limit, the relative inclination angle is fixed.

[0101] Since the method according to the present invention employs machining, it is possible to manufacture an elbow 10 as illustrated in FIGS. 8A to 8C, in which the center O.sub.1 of the hole 11 of the elbow is eccentrically located with respect to the center O.sub.2 of the radially outer surface of the elbow to increase the wall thickness and strength of the elbow on the outer side of the bend.

[0102] FIG. 8A is a perspective view of this elbow 10, FIG. 8E is a sectional view of the elbow 10 when viewed from the direction indicated by the arrow B-B in FIG. 8A, and FIG. 8C is a sectional view of a part indicated by the arrow C-C of FIG. 8A.

[0103] In such an elbow 10, as illustrated in FIG. 8B, by adjusting the eccentricity amount between the center O.sub.1 of the hole 11 of the elbow and the outer diameter center O.sub.2 of the elbow, the wall thickness of the elbow on the outer side can be set to a dimension corresponding to the strength to be required.

[0104] Cracks may develop in the flank of the elbow due to vibration load. Cracks tend to develop in an area indicated by the dashed-dotted line in FIG. 8A. The elbow of this embodiment can have a desired wall thickness at its flank, and hence exerts a significant effect even against vibration cracks as described above.

[0105] In FIG. 8B, the center O.sub.1 of the hole 11 of the elbow is eccentrically located on the diameter of the elbow 10, but the present invention is not limited thereto, and the center O.sub.1 may be eccentrically located at any point other than on the diameter of the elbow 10.

[0106] According to this embodiment, it is possible to manufacture an elbow as illustrated in FIG. 9, which includes a straight part 14 on at least one end portion, or an elbow as illustrated in FIG. 10, in which flanges 15 for connection are integrally formed at both ends.

[0107] In this case, it is preferred that the outer side of the bend be located at a position separated by 180 from the position of the inner side of the bend, and the wall thickness be gradually increased from the inner side toward the outer side of the bend. On the other hand, it is possible to increase or decrease the wall thickness of a desired part as necessary to any desired thickness.

[0108] In the aviation industry and the like, development of an ultra-thin elbow called a duct has been long awaited. Conventionally, a product has been formed by bending and welding an iron plate or the like. However, the thickness is as ultra-thin as 1.0 mm or less, and hence a uniform product cannot be formed due to the unevenness of the thickness during pressing. Further, the product is made of an extremely low machinability material such as titanium and Inconel, and hence studies have not been carried out.

[0109] In contrast, according to the invention, even with such materials, it is possible to process a thin elbow having an inner diameter of 2 inches to 5 inches and a wall thickness of 0.8 mm to 1.5 mm.

[0110] Also in this case, the wall thickness can be setarbitrarily as described above on the outer side and on the inner side.

EXAMPLES

[0111] A 90 elbow having an inner diameter of 190 mm, a center bend radius of 200 mm, and a wall thickness of 10 mm was experimentally produced by the method according to the present invention. As the material for the elbow, wood was used because this was a test for verifying the processing method.

[0112] The following rotary cutting tools were used. As the milling cutter I of FIGS. 11A and 11B, there was used a round-insert mounting indexable face milling cutter having an outer diameter of 50 mm, a radius of curvature of the arc-shaped cutting edges of 8 mm, and the number of the cutting edges of 4. As the side cutter II of FIGS. 12A and 12B, there was used a round-insert mounting indexable side milling cutter having an outer diameter of 127 mm, a radius of curvature of the arc-shaped cutting edges of 6 mm, and the number of the cutting edges of 5. As the ball end mill III of FIG. 13, there was used a ball end mill having an outer diameter of 30 mm.

[0113] As the processing machine, there was used a CNC horizontal boring machine owned by the applicant. This CNC horizontal boring machine includes a world's most advanced rotary table having a divided indexing accuracy of 1/10000 degrees. The material was set to this rotary table, and the material and the cutter were inclined relative to each other by a method of controlling the rotary table.

[0114] The processing was performed along the procedures described with reference to FIGS. 3A to 7B. The finishing of the starting hole by the side cutter was performed by adopting a method in which the cutting region remaining uncut was processed on a 2 mm basis to finally finish with no machining remainder. As a result, it was possible to obtain a machined elbow in which no machining remainder part was present inside the hole, the hole was a true circle and the hole surface was parallel to the center axis of the elbow, and further, the wall thickness around the tube (a wall thickness t of each part of the circumferential cross-section illustrated in FIG. 1B) was uniform.

[0115] With use of a processing machine including a rotary table having a highly-accurate indexing accuracy as described above, the high-accuracy processing can also be performed without a problem by such a method that, while inclining the side cutter and the material relative to each other in accordance with the hole bent state of the elbow so that the side cutter is halfway revolved in a plane substantially perpendicular to the center axis of the hole to be provided in the elbow as a finished product, the inner diameter of the starting hole is subjected to finishing, and then, from a position at which the relative inclination angle between the side cutter and the material reaches an allowance upper limit, the side cutter is revolved on the elliptical trajectory under a state in which the relative inclination angle is fixed.

INDUSTRIAL APPLICABILITY

[0116] According to one or more embodiments of the present invention, it is possible to manufacture, by machining, an elbow which has no unnecessary thickness inside, has a circular shape in a cross-section perpendicular to its axis in each axial part, and further, has a hole including a hole surface gently bent along an center axis. Thus, the method according to one or more embodiments of the present invention can be advantageously used as a method of manufacturing an elbow.

REFERENCE SIGNS LIST

[0117] I milling cutter, II side cutter, III ball end mill, 1, 4 cutter body, 2, 5 cutting edge, 3, 6 arbor, 10 elbow, 11 hole, 11.sub.-1 blind hole, 11.sub.-2 through hole, 11.sub.-3 starting hole, 12 material, 13 undercut, 14 straight part, 15 flange, A, B surface orthogonal to surface of material, t tube thickness.