Patent Publication Number: US-2016237826-A1

Title: Method of processing unfinished surfaces

Description:
TECHNICAL FIELD 
     This disclosure generally relates to metal parts manufacturing and, more particularly, relates to methods for finishing surfaces of metal parts. 
     BACKGROUND 
     Metal parts are commonly manufactured to fulfill a variety of uses across many industries. Such parts, generally made from metals or metal alloys, can exhibit excellent thermal, electrical, insular and structural properties. Welding is a common method used to join or otherwise alter metal components. Casting is also often used to form parts by pouring molten material into molds. 
     Metal parts can be fabricated to serve in gas turbine engines. Specifically, such parts can be airfoils, blades or vanes. However, when a metal part is manufactured, raised surfaces may result on the part that must be addressed. These raised surfaces must be removed in order to ensure proper gas turbine engine operation, a process that may result in added time, costs and manual inputs. 
     Gas turbine engine parts are made from a variety of fabrication processes, including casting, welding, joining and additive machining, among others. The parts may be fabricated from a range of materials, including metals and specialty alloys due to varying thermal and mechanical operational stresses at different points in the gas turbine engine. 
     When fabricating a gas turbine engine part using such processes, the unfinished part may be left with a resulting surface deformation. Creating a finished part suitable for use requires removing the surface deformation and finishing the part. Currently, this involves separate steps of removing the surface deformation and then modifying the unfinished part into a finished part with another process. These distinct steps increase fabrication time and costs. Further, current manufacturing often requires significant manual input for one or both of these steps, hindering production speed and accuracy. 
     Accordingly, there is a need for an improved method of finishing a part. 
     SUMMARY OF THE DISCLOSURE 
     To meet the needs described above, the present disclosure provides a method of fabricating a finished part, that may comprise creating an unfinished part using a primary metal fabrication process, wherein the primary metal fabrication process leaves a surface deformation on the unfinished part, and removing the surface deformation from the unfinished part using a secondary metal fabrication process, wherein the secondary metal fabrication process further creates the finished part from the unfinished part. 
     The primary metal fabrication process may be casting, investment casting or may be selected from the group consisting of welding, joining and additive manufacturing. Further, the secondary metal fabrication process may expose one or more cores used in the primary metal fabrication process. Additionally, the secondary metal fabrication process may be an electrochemical machining process or a photochemical machining process, and the finished part may be a gas turbine engine airfoil. 
     The present disclosure also provides a method of fabricating a finished airfoil, that may comprise creating an unfinished airfoil using a primary metal fabrication process, wherein the primary metal fabrication process leaves a surface deformation on the unfinished airfoil, and removing the surface deformation from the unfinished airfoil using a secondary metal fabrication process, wherein the secondary metal fabrication process further creates the finished airfoil from the unfinished airfoil. 
     The primary metal fabrication process may be casting, investment casting or may be selected from the group consisting of welding, joining and additive manufacturing. Further, the secondary metal fabrication process may expose one or more cores used in the primary metal fabrication process. Additionally, the secondary metal fabrication process may be an electrochemical machining process or a photochemical machining process. 
     The present disclosure also provides a finished part prepared by a process that may comprise the steps of creating an unfinished part using a primary metal fabrication process, wherein the primary metal fabrication process leaves a surface deformation on the unfinished part, and removing the surface deformation from the unfinished part using a secondary metal fabrication process, wherein the secondary metal fabrication process further creates the finished part from the unfinished part. 
     The finished part may be a finished airfoil. Further, the primary metal fabrication process may be investment casting, and may expose one or more cores used in the primary metal fabrication process. Additionally, the secondary metal fabrication process may be an electrochemical machining process or a photochemical machining process. 
     These, and other aspects and features of the present disclosure, will be better understood upon reading the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For further understanding of the disclosed concepts and embodiments, reference may be made to the following detailed description, read in connection with the drawings, wherein like elements are numbered alike, and in which: 
         FIG. 1  is a sectional view of a gas turbine engine constructed in accordance with the present disclosure; 
         FIG. 2  is a sectional view of an unfinished part constructed in accordance with the present disclosure. 
         FIG. 3  is a schematic view of a primary metal fabrication process in accordance with the present disclosure. 
         FIG. 4  is a sectional view of an unfinished part with a surface deformation constructed in accordance with the present disclosure. 
         FIG. 5  is a sectional view of another embodiment of an unfinished part with a surface deformation constructed in accordance with the present disclosure. 
         FIG. 6  is a sectional view of a finished part constructed in accordance with the present disclosure. 
         FIG. 7  is a sectional view of another embodiment of a finished part constructed in accordance with the present disclosure. 
         FIG. 8  is a perspective view of a finished airfoil constructed in accordance with the present disclosure. 
         FIG. 9  is a schematic view of a secondary metal fabrication process in accordance with the present disclosure. 
         FIG. 10  is a schematic view of another embodiment of a secondary metal fabrication process in accordance with the present disclosure. 
         FIG. 11  is a flowchart depicting a sample sequence of steps which may be practiced using the teachings of the present disclosure. 
     
    
    
     It is to be noted that the appended drawings illustrate only typical embodiments and are therefore not to be considered limiting with respect to the scope of the disclosure or claims. Rather, the concepts of the present disclosure may apply within other equally effective embodiments. Moreover, the drawings are not necessarily to scale, emphasis generally being placed upon illustrating the principles of certain embodiments. 
     DETAILED DESCRIPTION 
     Turning now to the drawings, and with specific reference to  FIG. 1 , a gas turbine engine constructed in accordance with the present disclosure is generally referred to by reference numeral  10 . While the following detailed description will be made with specific reference to gas turbine engines  10 , and parts made therefore, it is to be understood that the teachings of this disclosure are not so limited. Rather, the casting and finishing processes disclosed herein are applicable to a wide range of metal part manufacturing areas including, but not limited to, the aerospace, automotive and medical industries as well. 
     However, by way of background with specific reference to aerospace, the gas turbine engine  10  is shown to include a compressor  11 , combustor  12  and turbine  13 , known as the engine core  14 , lying along a central longitudinal axis  15 , and surrounded by an engine core cowl  16 . The compressor  11  is connected to the turbine  13  via a central rotating shaft  17 . Additionally, in a typical multi-spool design, plural turbine  13  sections are connected to, and drive, corresponding plural sections of the compressor  11  and a fan  18  via the central rotating shaft  17 , enabling increased compression efficiency. 
     As is well known by those skilled in the art, ambient air enters the compressor  11  at an inlet  19 , is pressurized, and is then directed to the combustor  12 , mixed with fuel and combusted. This generates combustion gases that flow downstream to the turbine  13 , which extracts kinetic energy from the exhausted combustion gases. The turbine  13 , via central rotating shaft  17 , drives the compressor  11  and the fan  18 , which draws in ambient air. Thrust is produced both by ambient air accelerated aft by the fan  18  and by exhaust gasses exiting from the engine core  14 . 
     In operation, various parts of the gas turbine engine  10  may experience varying thermal and mechanical operational stresses at different points in the gas turbine engine  10 . In addition, such parts need to function under high stresses and extremely tight tolerances. Accordingly, the specifications to which the component parts are manufactured are exacting. Parts with any surface deformations must be finished so as to meet such specifications. However, as mentioned above, current metal fabrication processes require such finishing to be manual. This may add costs and time, while also leading to increased scrap metal. 
     It is in this regard that the present disclosure drastically improves over the prior art. For example, referring now to  FIG. 2 , a sample unfinished part  30 , which is to be finished according to the present disclosure, is shown as an unfinished airfoil  34 . As shown therein, the unfinished airfoil  34 , which may be defined as a blade, stator or vane, may initially include a surface deformation  38 . If not removed, the gas turbine engine  10  will not operate, or will operate at decreased efficiency. As defined herein, a “surface deformation” is a protrusion or undesired surface irregularity. Examples include parting lines, gates, and raised areas such as RMC (Refractory Metal Core) exit posts as described below. 
     In the embodiment of the unfinished part  30  shown in  FIG. 2 , the unfinished part  30  may include a removable core  42 . The core  42  may be used to help shape the unfinished part  30 , but then be removed in the finished part leaving behind a hollowed interior. The surface deformation  38  may be a byproduct of using such a core  42  and associated RMC exit post, or be otherwise formed. 
     According to the present disclosure, the unfinished part  30  may be formed by a primary metal fabrication process  46  as shown in exemplary fashion in  FIG. 3 . The primary metal fabrication process  46  is shown as a casting process  50  and, more specifically, as an investment casting process  54 . Although the primary metal fabrication process  46  is shown as the investment casting process  54 , it is to be understood that the “primary metal fabrication process” as defined herein includes, but is not limited to, casting, welding, joining, additive machining or a combinations thereof. Additive manufacturing is a process by which layers or sections of material are systematically and sequentially added to an existing part to modify the existing part. Alternatively, the additive manufacturing process can build a part from scratch by adding layers and sections of material. 
     Referring again to  FIG. 3 , the primary metal fabrication process  46  may begin by forming a pattern  58  constructed from wax  62 , or any number of easily liquefied substances including foams, and polymers. The pattern  58  may also be in variety of shapes, and a single wax structure may include a plurality of patterns  58  to expedite the production of metal parts, for example airfoils. The pattern  58  may then be coated in a slurry  66  comprising a refractory material  70  such as, but not limited to, plaster, silica, sand, clay or another ceramic. After the pattern  58  is coated in the slurry  66 , the slurry  66  may then dry and form an investment  74  around the pattern  58 . 
     Subsequently, the pattern  58  and investment  74  may then be heated, with the wax  62  melting and being removed from the investment  74 , as by heating upside down. Molten material  78  may then be poured into the now empty investment  74 . The molten material  78  may include, but is not limited to, metals, alloys, ceramics and polymers. In addition, while not shown in  FIG. 3 , if the desired part is to have an internal void or hollow, a core such as RMC core  42  may be used. In order to be ultimately removable, the core  42  may be made of materials such as ceramics or refractory metals having a lesser melting point than the part  30 . 
     Once poured, the molten material  78  is then allowed to solidify within the investment  74  to take the shape of the original pattern  58 . After solidification, the investment  74  may be removed from the solidified molten material  78 , as by hammering, sand blasting, vibration or the like. As used herein, this solidified molten material  78  is referred to as an unfinished part  30  with one or more surface deformations  38  needing to be removed before use, as will now be described. 
     Referring now to  FIG. 4 , an embodiment of the unfinished part  30  is shown, having the core  42  and surface deformation  38  shown along with a core exit  82 . The core exit  82  may be a section of the core  42  at or near the exterior of the unfinished part  30 . In  FIG. 4 , the core exit  82  is shown as being disposed within the surface deformation  38 . If the casting process  50  is used, the core  42  may be employed to shape the unfinished part  30  and form a hollow interior as mentioned above. After the molten material  78  has hardened, the core  42  is removed from the unfinished part  30  in order to isolate the unfinished part  30 . The core exit  82 , sometimes referred to as an RMC exit post, exposed to the exterior of the unfinished part  30  facilitates this removal. Further, the unfinished part  30  may include one or more core exits  82 . 
     An alternative embodiment of the unfinished part  30  is shown in  FIG. 5 . However, as opposed to  FIG. 4 , this embodiment does not include a core  42  or a core exit  82 . Instead, this embodiment may result from a primary metal fabrication process  46  that does not involve a core  42 , but nevertheless leaves a surface deformation to be removed. The teachings of the present disclosure can nonetheless be used to remove such surface deformations  38 . 
     While the foregoing completes the primary metal fabrication process  46  as defined herein, the present disclosure also includes a secondary metal fabrication process  84  to arrive at a finished part  86 . The finished part  86 , as shown in  FIG. 6 , is fit for use in that it is free of any unfinished surfaces, with the surface deformation  38  removed. While the finished part  86  shown in  FIG. 6  does not incorporate a core  42  or a core exit  82 , another embodiment of the finished part  86 , as shown in  FIG. 7 , may include a core  42  and a core exit  82 . 
     The finished part  86  may be any number of products, with one example being a finished airfoil  90 , as shown in  FIG. 8 . The finished airfoil  90  may produce an aerodynamic force when subjected to a fluid flow. Additionally, the finished airfoil  90  may be located in a compressor  11 , turbine  13 , fan  18  or inlet  19  of a gas turbine engine  10 , as well as in other locations as noted above. Further, the finished airfoil  90  may be a vane, blade, stator, fan blade or other airfoil within the gas turbine engine  10 . 
     The secondary metal fabrication process  84  will now be described in detail with reference to  FIGS. 9 and 10 . As defined herein, “secondary metal fabrication process” is defined as finishing an unfinished part, in order to make it suitable for use, including removing any surface deformation using one of electro-chemical machining and photo-chemical machining In so doing, the present disclosure drastically improves upon the prior art by avoiding the separate steps of removing the surface deformation  38  and then modifying and finishing the unfinished part  30 . Rather, these distinct steps are combined and performed by a single process as will now be described. This combination saves fabrication time and resources. The unfinished part  30  may also be finished by a process that does not cause fabrication components to wear, as described below, further reducing production costs. Additionally, current metal fabrication processes require significant manual labor inputs for one or both of these steps, hindering production speed and accuracy. The processes described below eliminate these hindrances. 
     An embodiment of a secondary metal fabrication process  84  is shown in  FIG. 9 . Specifically, the embodiment shown is an electrochemical machining process  98 , although other processes may be used. As shown therein, a finishing tool  102  is provided for finishing the unfinished part  30 . For example, the finishing tool  102  may include a channel  106  for communicating an electrolyte  110  to the unfinished part  30 , specifically the surface deformation of the unfinished part  30 . The electrolyte  110  is used to carry electrical charge to electrochemically remove or wash away machined material. In operation, the finishing tool  102  may travel in a feed direction  114 , which may be towards the unfinished part  30 . The finishing tool  102  may function as an anode while the unfinished part  30  may function as a cathode. However, the opposite arrangement is certainly possible. As the finishing tool  102  is fed towards the unfinished part  30 , material of the unfinished part  30  may be liquefied by the involved electrical forces, and may be washed away by the electrolyte  110 . Accordingly, the finishing tool  102  shape and travel may determine how the unfinished part  30  is machined. 
     Not only does the electrochemical machining process  98  described above machine the unfinished part  30 , but it also not produce finishing tool  102  wear, as the finishing tool  102  does not make direct contact with the unfinished part  30 . The electrochemical machining process  98  may also enable the manufacture of complex shapes, and save costs by completing a given task within less time with fewer passes. Additionally, the unfinished part  30  may be modified into a finished part  86 , while also removing a surface deformation  38  from an unfinished part  30 , in a single step using the electrochemical machining process  98 . 
     Another embodiment of a secondary metal fabrication process  94  is shown in  FIG. 10 . Specifically, the secondary metal fabrication process  94  is shown as a photochemical machining process  118 , as opposed to the aforementioned electrochemical process of  FIG. 9 . As shown herein, the secondary metal fabrication process  94  may begin by providing a mask  122  having one or more holes  126  therethrough. The mask  122  may be positioned adjacent to a photoresist  130 , and the photoresist  130  may be positioned adjacent to the unfinished part  30 . The photoresist  130  may be composed of a substance whose chemical properties change when exposed to radiation  134 , including, but not limited to, metals and polymers such as SU- 8  and poly(methyl methacrylate) (PMMA) or poly(methyl glutarimide) (PMGI) or phenol formaldehyde resin (DNQ/Novolac). The radiation  134  may pass through the holes  126  in the mask  122  and strike the exposed areas of the photoresist  130 . The exposed areas of the photoresist  130  may then change chemical properties. 
     Subsequently, a developing solution  138  may be used to wash away the parts of the photoresist  130  exposed to the radiation  134 . This process is known as developing. An etching solution  142  may then be used to etch a portion of the unfinished part  30  adjacent to the portion of the photoresist  130  washed away by the developing solution. In this manner, the pattern of the holes  126  may be transferred to the photoresist  130  and to the unfinished part  30 , and may finish the unfinished part  30 . The photochemical machining process  112  described above is referred to as a positive resist process. However, it is to be understood that the photochemical machining process  112  can also be a negative resist process, as well. 
     The photochemical machining process  118  described above also does not produce wear among any fabrication components involved, as there are no moving parts that make contact with the unfinished part  30 . The photochemical machining process  118  may also enable the manufacture of complex and delicate shapes, and save costs by completing a given task within less time with fewer passes. Additionally, the unfinished part  30  may be modified into a finished part  86 , while also removing a surface deformation  38  from an unfinished part  30 , in a single step using the photochemical machining process  118 . 
     A method for fabricating a finished part can best be understood by referencing the flowchart in  FIG. 11 . The method may comprise creating an unfinished part using a primary metal fabrication process, wherein the primary metal fabrication process leaves a surface deformation on the unfinished part, as shown in step  1100 . The method then removes the surface deformation from the unfinished part using a secondary metal fabrication process, wherein the secondary metal fabrication process further creates the finished part from the unfinished part, as shown in step  1104 . The secondary metal fabrication process may expose a core used in the primary metal fabrication process, as shown in step  1108 . Additionally, the secondary metal fabrication process may be an electrochemical machining process or a photochemical machining process, as shown in steps  1112  and  1116 , respectively. 
     INDUSTRIAL APPLICABILITY 
     In operation, the present disclosure sets forth a method of fabricating a finished part which can find industrial applicability in a variety of settings. For example, the disclosure may be advantageously employed in manufacturing various parts of a gas turbine engine  10 , such as but not limited to, blades and vanes. 
     The metal fabrication processes, as described herein, preclude separate steps of removing a surface deformation and then modifying such an unfinished part into a finished part with an additional process. The disclosed method increases process efficiency by completing two steps simultaneously, in less time. The unfinished part may also be finished by a secondary metal fabrication process that does not cause fabrication components to wear, further reducing production costs. Additionally, the disclosed method may eliminate manual inputs for one or both of these steps, increasing production speed and accuracy.