Description:
FIELD OF THE INVENTION :

[001] This invention is related to the development of a method for manufacturing a smaller diameter three-dimensional (3D) impeller of a centrifugal compressor by a Robotic TIG welding work cell for conducting external welding.

BACKGROUND OF INVENTION/PRIOR ART :

[002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[003] The impeller is a very vital component of the centrifugal compressor, which is attached to the rotating shaft, gives kinetic energy to the fluid passing through it. However, the impeller provided in a centrifugal compressor has a complicated shape in which the flow path (Fig 1b) is curved in each of an axial direction (rotational axis direction) and a radial direction. The impellers are manufactured by different methods, such as integral process shaping, molding by casting, welding joining, joining by brazing, and additive manufacturing. Some centrifugal compressors are custom designed and manufactured as per the requirement. They are generally designed in a number of stages with a dedicated impeller in each stage. These kinds of impellers need to be machined on a CNC machine and joined using the welding process only as other methods are not economical. It mainly includes two parts i.e., Hub (Fig 1) and shroud (Fig 2).

[004] The hub part comprises of twisted vanes (Fig 1a) machined on it. The shroud part is welded to the hub part by an internal welding process to make it a closed impeller (Fig 3). In this internal welding process, there should be sufficient access needed for the welder to insert the welding electrode between the bottom surface of the shroud and the vanes on the hub. Due to this, the welding of complete vane length is not possible, so the welding is carried out till access is available. This manufacturing restriction causes size constraints for the 3D impeller, which restricts to manufacture of bigger diameter (above 450 mm) size only.

PRIOR ART OF THE INVENTION:

[005] Reference may be made to the following patents:

[006] JP4428044B2 discloses an impeller 1 is equipped with a core panel 3, whose external shape is a head-cut circular cone; side plate 5, located in a place apart from the external circumference face of the core panel 3 and encircling the external surface of the core panel as it is formed so as to correspond to the outer surface of the core panel 3; and a plurality of vanes 7 with three-dimensional shapes, formed between the side plate 5 and the core panel 3. Faces of more than two impeller parts 1a, 1b, and 1 c, which are split by faces that pass through the side plate 5 and the core panel 3 and cross the rotational axis, these faces are on the sides meeting the rotational axis of the impeller formed at least on the side plate 5 and the core panel 3, are called contact faces 13 and 15. It is arranged that the impeller parts 1a, 1b, and 1c contact one another on these contact faces 13 and 15. Based on this constitution, there arise no running channels where welding or cutting tools are difficult to be inserted into any of the impeller parts 1a, 1b, or 1c, so that manufacturing by means of automatic welding machines or automatic lathes will be possible. Thus, manufacturing of three-dimensional impellers fitted with side plates can be automatized.

[007] US10865647B2 discloses a method of manufacturing a turbo-machine impeller, which includes a hub and a plurality of blades, using powder material in an additive-manufacturing process. The method includes: applying energy to the powder material by way of a high energy source, and solidifying the powder material. At least one bulky portion of the hub is irradiated such that the powder material solidifies in a lattice structure surrounded by an outer solid skin structure enclosing the lattice structure.

[008] JP4523032B2 discloses a compressor impeller and a method of manufacturing the compressor impeller. The magnesium alloy compressor impeller as a die-cast part comprises a hub shaft part, a hub disk part having a hub surface extending from the hub shaft part in the radial direction, and a plurality of vane parts disposed on the hub surface. The impeller can be manufactured by a die-cast method in which a magnesium alloy heated to a liquidus temperature or higher is supplied into molds with cavities corresponding to the shape of the impeller for a filling time of 1 sec. or shorter, a pressure of 20 MPa or higher is applied to the magnesium alloy in the cavities, and the pressurized state is maintained for a time of 1 sec. or longer.

[009] CN106238705B discloses a manufacturing method for a large thin-walled impeller. An upper mold body of a mold is internally provided with annular grooves and exhaust plugs so that exhausting can be improved, a cooling cone is arranged on the upper mold body and cooling rings are arranged on the upper surface of the upper mold body so that the cooling speed of castings can be increased, and meanwhile a sand mold is used at the bottom of a gypsum core so that heat preservation of molten aluminum at the bottom and feeding of the castings can be facilitated. The program allowing integral casting of the thin-walled and large-size impeller to be achieved by improving exhausting and cooling is adopted for the mold, the forming quality is good, and precision is high; a first concave part is arranged to position the first circular face of the end portion of the impeller, the impeller is locked to a bottom plate through first pressing pieces, welding is not needed, and fixation is convenient and rapid; and after the first round of machining is conducted on the impeller, a second concave part is arranged to position the second circular face of the impeller, fastening is conducted through second pressing pieces, machining is conducted on the impeller in order, the situation that some faces are not machined due to clamps or other reasons is avoided, and the surface precision of the impeller is improved.

[0010] JP5728589B2 discloses an impeller in which a plurality of vanes are provided so as to overlap each other back and forth as viewed in the direction of axis has a first impeller part on a front side and a second impeller part on a rear side. A method for manufacturing impeller includes a step of molding a first impeller part, a step of molding a second impeller part and a step of combining together the first impeller part and the second impeller part.

[0011] ES2792034T3 discloses An impeller (8) includes main plate-side welded portions (8a, 8b) between main plate-side blade axial ends (71) and a main plate (60) and includes shroud-side welded portions (8c) between shroud-side blade axial ends (72) and a shroud (80). Main plate-side welding holes (8d) that are recesses extending through the main plate (60) to portions of the main plate-side blade axial ends (71) are provided on the main plate welded portions (8a, 8b), while shroud-side welding holes (8e) that are recesses extending through the shroud (80) to the shroud-side blade axial ends (72) are provided on the shroud-side blade axial ends (8c).

[0012] The above-referred patents describe the manufacturing of 3D impeller using electron beam welding (EBM) process, additive manufacturing process, die casting method using a magnesium alloy, by providing special cooling plates in the casting process, molding process (for large thin wall impeller), joining by brazing, etc..

[0013] None of the patents described the machining of weld grooves on shroud part using 5 axis CNC milling method and joining them using the arc welding process.

[0014] In view of the above, the present invention has been introduced.

OBJECTS OF THE INVENTION:

[0015] The main objective of the invention is to provide a method for manufacturing a smaller diameter three-dimensional (3D) impeller of a centrifugal compressor by 5 Axis CNC machining techniques and robotic work cell for external TIG welding methods.

[0016] Another object of the invention is to make high efficiency and robust 3D impeller for usage in the Centrifugal Compressor.

[0017] Still another object is to provide a method for manufacturing a smaller diameter three-dimensional (3D) impeller of a centrifugal compressor by a Robotic TIG welding work cell for conducting external welding, which is simple.

[0018] These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.

SUMMARY OF THE INVENTION :

[0019] One or more drawbacks of conventional systems and process are overcome, and additional advantages are provided through the apparatus/composition and a method as claimed in the present disclosure. Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be part of the claimed disclosure.

[0020] According to this invention, there is provided a method for manufacturing a smaller diameter three-dimensional (3D) impeller of a centrifugal compressor by a Robotic TIG welding work cell for conducting external welding.

[0021] The present invention involves machining vanes and weld grooves on the hub and the shroud respectively and joining them both using an automatic external TIG welding method, where the complete vanes on the hub are welded to the shroud. This eliminates welding access restriction.

[0022] In the present invention, weld grooves are machined on the shroud part of the impeller. The profile of the weld groove is similar to the twisted vane profile. Then the shroud is assembled to the hub using locating pins. Thereafter the shroud is welded to the hub using an automatic robotic TIG welding work cell. This new method of manufacturing giving a way to produce smaller diameter 3D impellers, which are otherwise difficult to manufacture using conventional methods.

[0023] A special fixture developed helps in creating robot trajectory paths offline, which makes the welding torch always normal to the weld groove across the vane length, by matching the coordinate system of the 3D impeller with the coordinate system of the two-axis positioner.
[0024] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

[0025] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.

[0026] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS :

[0027] The illustrated embodiments of the subject matter will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and processes that are consistent with the subject matter as claimed herein, wherein:-

Figure 1 shows the Hub, indicating Vanes on hub (1a) and flow path (1b).

Figure 2 shows the Shroud.

Figure 3 shows the 3D impeller indicating the channel width (C).

Figure 4 shows the Weld grooves on Shroud indicating Weld grooves (4a) and Outer periphery of Shroud (4b).
Figure 5 shows the Hub and shroud assembly.

Figure 6 shows the Cross-section of Hub (H) and shroud (S) after assembly.

Figure 7 shows the location of the holes on the weld grooves indicating the locating holes (O).

Figure 8 shows the Fixture developed to mount the 3D impeller indicated the base/disc (8a); a longitudinal member/rod (8b), Outer holes (8c) and inner holes (8d).

Figure 9 shows the Robotic TIG welding work cell for conducting external welding indicates a six-axis articulated industrial robot (9.1), TIG torch (9.2) mounted at the robot flange, Filler wire feeding mechanism (9.3), TIG welding power source (9.4), 2 axis tilt and turn positioner (9.5), work holding fixture (9.6) and 3D impeller (9.7).

[0028] The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAIL DESCRIPTION OF THE PRESENT INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS OF PREFERRED EMBODIMENTS :

[0029] While the embodiments of the disclosure are subject to various modifications and alternative forms, specific embodiment thereof have been shown by way of example in the figures and will be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.

[0030] The present invention makes a disclosure regarding a technology pertaining to a method for manufacturing a smaller diameter three-dimensional (3D) impeller of a centrifugal compressor by a Robotic TIG welding work cell for conducting external welding.

[0031] The impeller is a very important component of any centrifugal compressor. It is classified into two-dimensional (2D) impellers and three-dimensional (3D) impellers. It comprises of two parts i.e., hub (which is having vanes) and shroud. In a 2D impeller, the vanes on the hub are not twisted, whereas in a 3D impeller the vane profile is complicated aerofoil shape and twisted. As the vanes create a flow path of the fluid, 3D impellers are more efficient than 2D impellers.

[0032] In general, special purpose centrifugal compressors are custom designed. Hence, the profile of the impeller vanes is not unique and changes as per the design requirement. Therefore, machining of vane profile on the hub using a CNC milling machine and welding the hub with shroud is only the best available manufacturing method, as the impeller sizes are ranging up to 1000mm in diameter. Other conventional manufacturing methods are not commercially viable.

[0033] The vanes on the hub are welded to shroud using an arc welding process. The welder inserts the electrode between the bottom surface of the shroud and the upper surface of the vane and carries out welding. This welding process is known as the internal welding process as the welding is done inside the shroud portion. However, for a smaller diameter impeller (450mm) the access of the welding electrode for complete vane length is not possible. So the welding is done till access is available. This is making the strength of the impeller low. For 3D impellers whose diameter is less than 450mm, there is no access for doing internal welding. So, this is becoming a manufacturing constraint for the designer even to design lesser diameter 3D impellers.

[0034] To address the above issue, a new manufacturing method has been devised and successfully implemented. In this, weld grooves are machined on the shroud (Fig 4) using a 5 axis CNC milling machine. The profile of the weld grooves is exactly similar to the profile of the vanes i.e. the profile of the weld grooves corresponds to profile of the vanes.

[0035] The vanes are machined on the hub (H). The hub (H) and shroud (Fig 4) are assembled by matching locating holes (O, Fig 7) which are machined exactly at a similar location on both hub and shroud. Blue matching is carried out between hub (H) and shroud (S) so that the contact area between the vane top surface and shroud bottom surface is intact. The centreline (CL) of vane and groove should be collinear while assembling (Fig 6). Thereafter tack welding is carried out around the outer periphery (4b) of the shroud so that the hub and shroud part cannot be disturbed.

[0036] The profile of the weld grooves (4a) machined on the shroud is exactly similar to the vane profile and V-type butt joint cross-section. The path is twisted. To get a quality weld joint, the welding torch should always be normal to the weld groove across its length while welding. Maintaining the torch always normal to the weld groove is not consistent in the manual arc welding process. The welding process needs to be automated to achieve the desired weld quality and sound weld joint.

[0037] To address this a robotic TIG welding work cell is designed. For the same reference may be made to Fig 9. The developed robotic work cell comprises of a six-axis articulated industrial robot (9.1), TIG torch (9.2) mounted at the robot flange, Filler wire feeding mechanism (9.3). Wire feeding is carried out at torch (9.2) area. Here welding parameters are controlled by TIG welding power source (9.4) and the parameters are fed to said torch (9.2). 2 axis tilt and turn positioner (9.5) supports work holding fixture (9.6) for holding 3D impeller (9.7).

[0038] Now, reference may be made to Figure 8 indicating a special fixture designed and developed to firmly hold the 3D impeller on the 2 axis positioner (9.5). Locating holes are machined on both the fixture (Fig 8) and 3D impeller so that the impeller can be fitted concentric to the positioner turning axis.

[0039] The fixture as best seen in Figure 8 comprises a base (8a) such as disc having a plurality of through holes therein. The disc (8a) is mounted with a longitudinal member (8b) such as rod, which is used for clamping the impeller. Said base (8a) is having outer holes (8c) for positioner (9.5) and inner holes (8d) for the impeller.

[0040] This reference is also useful for matching the coordinate system of the 3D impeller with the coordinate system of the positioner (9.5). This helps to develop offline robot trajectory path programs, which are very precise and always keep the robot TIG torch normal to the weld groove across its length. It also eliminates manual robot path teaching.

[0041] With a valid welding procedure specification (WPS) and sequence of weld groove welding to control the distortion, the welding process is carried out for the joining of the hub and shroud. The welding is a multilayer, with an initial root pass without filler wire and subsequent layers with suitable filler wire. With this process, a sound quality weld joint is achieved. To achieve this the six-axis of the robot and 2 axes of the positioner i.e., a total of 8 axes have been synchronously moved.

[0042] The present invention creates a high strength and more efficient 3D impellers of lesser diameter. Also it eliminates welding access restriction.
[0043] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the “invention” may in some cases refer to certain specific embodiments only. In other cases, it will be recognized that references to the “invention” will refer to subject matter recited in one or more, but not necessarily all, of the claims.

[0044] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.

[0045] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particulars claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogues to “at least one of A, B and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B”.

[0046] The above description does not provide specific details of manufacture or design of the various components. Those of skill in the art are familiar with such details, and unless departures from those techniques are set out, techniques, known, related art or later developed designs and materials should be employed. Those in the art are capable of choosing suitable manufacturing and design details.

[0047] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.

[0048] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.

[0049] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

Claims:WE CLAIM :

1. A method for manufacturing a smaller diameter three-dimensional (3D) impeller of a centrifugal compressor by a Robotic TIG welding work cell for conducting external welding comprising steps of:
- Machining of grooves on shroud (S);
- Machining of vanes on hub (H);
- Assembling the hub (H) and shroud by matching locating holes (O) that the contact area between the vane top surface and shroud bottom surface is intact;
- Welding of the vanes on the hub (H) to the shroud(S);
- Tack welding around the outer periphery (4b) of the shroud.

2. The method as claimed in claim 1, wherein the profile of the weld grooves corresponds to profile of the vanes.

3. The method as claimed in claim 1 or 2, wherein the centreline (CL) of vane and groove should be collinear while assembling followed by tack welding.

4. The method as claimed in claims 1-3, wherein the profile of the weld grooves (4a) machined on the shroud is similar to the vane profile and V-type butt joint cross-section, in which the path is twisted.

5. The method as claimed in claims 1-4, wherein the welding torch should always be normal to the weld groove across its length while welding.

6. A robotic work cell comprises of a six-axis articulated industrial robot (9.1), TIG torch (9.2) mounted at the robot flange, Filler wire feeding mechanism (9.3), wherein Wire feeding is carried out at torch (9.2) area.
7. The robotic work cell as claimed in claim 6, wherein welding parameters are controlled by TIG welding power source (9.4) and the parameters are fed to said torch (9.2), in which 2 axis tilt and turn positioner (9.5) supports work holding fixture (9.6) for holding 3D impeller (9.7).

8. A fixture to hold the 3D impeller on the 2 axis positioner (9.5) comprises a base (8a) having a plurality of through holes therein, wherein the base (8a) is mounted with a longitudinal member, which is used for clamping the impeller, in which said base (8a) is having outer holes (8b) for positioner (9.5) and inner holes (8c) for the impeller.

9. The fixture as claimed in claim 8, wherein locating holes are machined on both the fixture and 3D impeller that the impeller can be fitted concentric to the positioner turning axis.

10. The method as claimed in claims 1-5 which creates a high strength and more efficient 3D impellers of lesser diameter and eliminates welding access restriction.