Patent Publication Number: US-2016222796-A1

Title: Manufacturing method for a baffle-containing blade

Description:
BACKGROUND 
     Dual wall airfoils have the potential to offer improved cooling to blades used in gas turbine engines. Turbine blades in particular are exposed to extremely high temperature during engine operation. Dual wall airfoils have sets of outer walls and sets of inner walls. The outer walls and the inner walls are separated by “skin cavities” and the inner walls are separated from one another by a central cavity. Cooling fluid flows through the skin cavities and the central cavity to provide impingement cooling to the inner and outer walls and/or form a cooling film along the outer surface of the outer walls. 
     SUMMARY 
     A blade includes a platform and a monolithic airfoil extending from the platform to a tip. The airfoil includes a first wall extending from a leading edge to a trailing edge, a second wall extending from the leading edge to the trailing edge and joined to the first wall at the leading edge, and at least one rib extending from the first wall to the second wall. The at least one rib and the first and second walls define a cavity. The blade also includes a baffle positioned within the cavity. The baffle has walls that are separate and distinct from and not attached to the at least one rib and the first and second walls of the airfoil. 
     A method for forming a blade includes forming a platform and forming an airfoil on a layer-by-layer basis using additive manufacturing. The airfoil includes a first wall that extends radially from the platform to a blade tip and extends axially from a leading edge to a trailing edge, a second wall that extends radially from the platform to the blade tip and extends axially from the leading edge to the trailing edge, and at least one rib that extends from the first wall to the second wall. The first wall and the second wall are joined at the leading edge, and the at least one rib and the first and second walls define a cavity. The airfoil further includes forming a baffle within the cavity on a layer-by-layer basis using additive manufacturing. The baffle has walls that are separate and distinct from the at least one rib and the first and second walls. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a blade. 
         FIG. 2A  is a cross section view of one embodiment of a blade containing a baffle taken along the line A-A shown in  FIG. 1 . 
         FIG. 2B  is a cross section view of one embodiment of a blade containing a baffle taken along the line B-B shown in  FIG. 1 . 
         FIG. 3A  is a cross section view of another embodiment of a blade containing a baffle taken along the line A-A shown in  FIG. 1 . 
         FIG. 3B  is a cross section view of another embodiment of a blade containing a baffle taken along the line B-B shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The present invention provides a baffle-containing blade and a method of manufacturing such a blade using additive manufacturing. The baffle acts as a substitute for the inner walls within the blade airfoil by separating skin cavities from the central cavities. However, because the baffle is a separate element and is not attached to the outer wall, the stresses caused by connected inner and outer walls are eliminated. Additionally, the baffle dampens vibrations within the blade, removing or reducing the need for additional damping features. 
       FIG. 1  is a side view of a blade. Blade  10  includes root section  12 , platform  14 , airfoil  16  and tip section  18 . Blade  10  extends from root section  12  to tip section  18  along a radial axis. Airfoil  16  extends radially from platform  14 . Airfoil  16  includes pressure side wall  20  and suction side wall  22 . Pressure side wall  20  and suction side wall  22  are joined at leading edge  24  and each extends downstream from leading edge  24  to trailing edge  26 . In some embodiments, airfoil  16  is monolithic. For the purposes of this patent application, a monolithic airfoil  16  is formed from a single piece of material (i.e. the airfoil is not composed of two or more separate pieces of material that are welded, brazed or otherwise connected together to form a single component). 
       FIG. 2A  illustrates a cross section view of one embodiment of baffle-containing blade  10  taken along the line A-A shown in  FIG. 1 . Pressure side wall  20  forms a first outer wall, and suction side wall  22  forms a second outer wall, the two walls meeting at leading edge  24 . Pressure side wall  20  includes outer surface  28  and inner surface  30 , and suction side wall  22  includes outer surface  32  and inner surface  34 . One or more cavities  36  separate pressure side wall  20  and suction side wall  22 . As shown in  FIG. 2A , five cavities  36 A- 36 E are present between pressure side wall  20  and suction side wall  22 . Cavities  36  are separated from one another by ribs  38 . Ribs  38 A- 38 D extend from inner surface  30  of pressure side wall  20  to inner surface  34  of suction side wall  22 . Each cavity  36  is defined by inner surface  30  of pressure side wall  20 , inner surface  34  of suction side wall  22  and two ribs  38  (an upstream rib and a downstream rib). For example, according to the embodiment shown in  FIG. 2A , cavity  36 B is defined by inner surface  30 , inner surface  34  and ribs  38 A and  38 B. 
     Baffles  40  are positioned within one or more cavities  36  of blade  10 . Baffle  40  is an insert sized to fit within a cavity  36 . Each baffle  40  includes upstream wall  42 , downstream wall  44 , pressure side baffle wall  46  and suction side baffle wall  48 . Upstream wall  42 , downstream wall  44 , pressure side baffle wall  46  and suction side baffle wall  48  define central cavity  50  within baffle  40 . As described below in greater detail, cooling fluid is delivered through central cavity  50  of baffle  40  to provide cooling to airfoil  16  and blade  10 . In some embodiments, central cavity  50  of one baffle  40  is connected to central cavity  50  of another baffle  40  within blade  10  to form a serpentine cooling circuit. 
     The walls of baffle  40  are separate and distinct from and not attached to inner surface  30  of pressure side wall  20 , inner surface  34  of suction side wall  22  and ribs  38  (i.e. the inner surfaces of airfoil  16 ). As shown in  FIG. 2A , upstream wall  42  is positioned near upstream rib  38 A and downstream wall  44  is positioned near downstream rib  38 B. Pressure side baffle wall  46  has a shape complementary to pressure side wall  20  and is located proximate pressure side wall  20 . Suction side baffle wall  48  has a shape complementary to suction side wall  22  and is located proximate suction side wall  22 . While pressure side baffle wall  46  is located near pressure side wall  20 , it is spaced from inner surface  30  of pressure side wall  20  to form cavity  52  therebetween. Similarly, while suction side baffle wall  48  is located near suction side wall  22 , it is spaced from inner surface  34  of suction side wall  22  to form cavity  54  therebetween. Like central cavity  50 , cooling fluid is delivered through cavities  52  and  54  of baffle  40  to provide cooling to airfoil  16  and blade  10 . Cavities  52  and  54  are sometimes referred to as “skin cavities” as they are cavities located near the skin (outer wall) of the airfoil. In some embodiments, passages  68  are formed in pressure side wall  20  so that cooling fluid can flow from cavities  52  and form a cooling film along outer surface  28  of pressure side wall  20 . Likewise, passages can be formed in suction side wall  22  so that cooling fluid can flow from cavities  54  and form a cooling film along outer surface  32  of suction side wall  22 . 
     One or more standoffs or standoff ribs can be present within cavities  52  and  54  to prevent contact between pressure side baffle wall  46  and pressure side wall  20  and suction side baffle wall  48  and suction side wall  22 , respectively. As shown in  FIG. 2A , standoff rib  56  extends from inner surface  30  of pressure side wall  20  towards pressure side baffle wall  46  of baffle  40 . In some embodiments, standoff rib  56  contacts pressure side baffle wall  46  at ambient temperature (approximately 25° C.). In other embodiments, standoff rib  56  approaches but does not contact pressure side baffle wall  46  at ambient temperature. In these embodiments, the distance between standoff rib  56  and pressure side baffle wall  46  is between about 0.001 inches (0.025 mm) and about 0.005 inches (0.13 mm) In some embodiments, standoff rib  56  is a longitudinal rib that spans substantially the entire length of inner surface  30  and/or baffle  40 . In these embodiments, standoff rib  56  serves to separate cavity  52  into two substantially distinct subcavities (labeled  52 A and  52 B in  FIG. 2A ). In those embodiments in which standoff rib  56  contacts pressure side baffle wall  46 , cavities  52 A and  52 B are separate and distinct. Where standoff rib  56  approaches but does not contact pressure side baffle wall  46 , fluid flowing through cavities  52 A and  52 B is able to cross between cavities near pressure side baffle wall  46 . In other embodiments, standoff rib  56  is a pedestal-type structure and does not separate cavity  52  into subcavities but can serve to increase turbulence of fluid flowing through cavity  52 . 
     Standoff ribs  58  extend from inner surface  34  of suction side wall  22  towards suction side baffle wall  48  of baffle  40 . Standoff ribs  58  are structured and function similarly to standoff rib  56 . As shown in  FIG. 2A , two standoff ribs  58  extend from inner surface  34  towards suction side baffle wall  48 . In some embodiments, standoff ribs  58  contact suction side baffle wall  48  at ambient temperature. In other embodiments, standoff ribs  58  approach but do not contact suction side baffle wall  48  at ambient temperature. In these embodiments, the distance between standoff rib  56  and pressure side baffle wall  46  is between about 0.001 inches (0.025 mm) and about 0.005 inches (0.13 mm) In some embodiments, standoff ribs  58  are longitudinal ribs that span substantially the entire length of inner surface  34  and/or baffle  40 . In these embodiments, standoff ribs  58  serve to separate cavity  54  into three substantially distinct subcavities (labeled  54 A- 54 C in  FIG. 2A ). In other embodiments, standoff ribs  58  are pedestal-type structures and do not separate cavity  54  into subcavities. 
       FIG. 2B  illustrates a cross section view of blade  10  taken along the line B-B shown in  FIG. 1 , showing pressure side wall  20 , suction side wall  22 , baffle  40  and cavities  50 ,  52  and  54 . As shown in  FIG. 2B , baffle extends from a region near platform  14  to a region near tip section  18 . As shown by arrows A I , cooling fluid enters cavity  36  from root section  12 . Just before cooling fluid A I  reaches baffle  40  it passes through feed openings  64  and  66 . Feed opening  64  communicates with cavity  52  and feed opening  66  communicates with cavity  54 , allowing some of the cooling fluid to reach cavities  52  and  54  instead of entering central cavity  50  of baffle  40 . In the embodiment shown in  FIG. 2B , cooling fluid exits airfoil  16  through film passages  68  within pressure side wall  20  and tip section  18  as shown by arrows A O . In some embodiments, cooling fluid A O  can also exit airfoil  16  through film passages  68  within suction side wall  22 . 
     Standoff ribs can also extend from baffle  40  towards inner surface  30  of pressure side wall  20  and/or inner surface  34  of suction side wall  22 .  FIG. 3A  illustrates a cross section view of another embodiment of baffle-containing blade  10 A taken along the line A-A shown in  FIG. 1 . Blade  10 A is similar to blade  10  but shows different standoff orientations. For example, with respect to baffle  40 A, standoff rib  60  extends from pressure side baffle wall  46  towards pressure side wall  20 . Similar to standoff rib  56 , standoff rib  60  can contact inner surface  30  of pressure side wall  20  at ambient temperature or approach but not contact inner surface  30  at ambient temperature (i.e. 0.001 inches to 0.005 inches). Standoff rib  60  can be a longitudinal rib that spans substantially the entire length of baffle  40 . In these embodiments, standoff rib  60  can separate cavity  52  into two substantially distinct subcavities. Alternatively, standoff rib  60  can be a pedestal-type structure that does not separate cavity  52  into subcavities but can serve to increase turbulence of fluid flowing through cavity  52 . Standoff ribs  62  extend from suction side baffle wall  48  towards suction side wall  22 . Similar to standoff rib  58 , standoff ribs  62  can contact inner surface  34  of suction side wall  22  at ambient temperature or approach but not contact inner surface  34  at ambient temperature. Standoff ribs  62  can be longitudinal ribs that span substantially the entire length of baffle  40  or pedestal-type structures. 
       FIG. 3A  also shows other possible standoff/baffle configurations. With respect to baffle  40 B, standoff rib  56 A extends from inner surface  30  of pressure side wall towards baffle  40 B while standoff ribs  62 A and  62 B extend from suction side baffle wall  48  towards suction side wall  22 . With respect to baffle  40 C, standoff rib  56 C extends from inner surface  30  of pressure side wall towards baffle  40 C, standoff rib  58 C extends from inner surface  30  of pressure side wall towards baffle  40 C, standoff rib  60 C extends from pressure side baffle wall  46  towards pressure side wall  20 , and standoff rib  62 C extends from suction side baffle wall  48  towards suction side wall  22 . 
       FIG. 3A  also illustrates impingement passages  70  within the walls of baffles  40 A- 40 C. Impingement passages  70  allow cooling fluid to flow from central cavity  50  through the walls of baffle  40  and into skin cavities  52  and  54  to provide additional cooling to pressure side wall  20  and suction side wall  22 .  FIG. 3B  illustrates a cross section view of blade  10 A taken along the line B-B shown in  FIG. 1 , showing cooling fluid (arrows A T ) crossing the walls of baffle  40  to flow from cavity  50  within baffle  40  to cavities  52  and  54  outside baffle  40 . 
     The design of blade  10  with baffle  40  described herein offers high durability and protection from harmful vibratory responses. For example, airfoil  16  and baffle  40  are separate and distinct pieces of material that are not connected to one another. As airfoil  16  heats up (e.g., during takeoff where fuel bum is high), pressure side wall  20  and suction side wall  22  are exposed to extremely high temperatures. Baffle  40  is comparatively cooler because it is insulated from the hot gas path by pressure side wall  20 , suction side wall  22  and cooling fluid within cavities  50 ,  52  and  54 . As the temperatures of pressure side wall  20  and suction side wall  22  increase, pressure side wall  20  and suction side wall  22  expand radially (from root to tip) and axially (away from each other). Because baffle  40  is comparatively cooler than pressure side wall  20  and suction side wall  22 , baffle  40  does not expand to the same degree. Since airfoil  16  and baffle  40  are separate and distinct pieces of material that are not connected to one another, pressure side wall  20  and suction side wall  22  are free to expand as their temperatures increase without causing strain or fatigue relative to baffle  40 . As airfoil  16  cools, the opposite effect is observed with pressure side wall  20  and suction side wall  22  shrinking or compressing. As airfoil  16  and baffle  40  are separate and distinct and not connected to one another, pressure side wall  20  and suction side wall  22  are free to shrink or compress as their temperatures decrease without causing strain or fatigue relative to baffle  40 . 
     Baffle  40  also provides a damping effect to blade  10 . Blade vibration is generally not desired during operation. Various components in a gas turbine engine vibrate at different responses. A component&#39;s mass, stiffness and temperature determine at what response (frequency) vibrations will occur. Because pressure side wall  20  and suction side wall  22  have different mass, stiffness and temperature than baffle  40  during operation, pressure side wall  20  and suction side wall  22  vibrate at a different response than baffle  40 . When airfoil  16  of blade  10  vibrates, airfoil  16  rubs against baffle  40 , which vibrates at a different response. Depending on the embodiment, pressure side wall  20  and suction side wall  22  rub against standoff ribs  60  and/or  62  and/or baffle  40  rubs against standoff ribs  56  and  58  on pressure side wall  20  and suction side wall  22 , respectively. The contact or rubbing between baffle  40  and airfoil  16  provides a damping effect to airfoil  16 , reducing its vibratory response. 
     Manufacturing blade  10  with baffle  40  is difficult. Due to the curvature of airfoil  16 , baffle  40  cannot merely be inserted within blade  10  from root section  12  or from tip section  18 . In order to insert baffle  40  within blade  10 , blade  10  must be manufactured as two or more separate pieces that fit around baffle  40 . These pieces of blade  10  are positioned around baffle  40  and welded or brazed together to form blade  10  around baffle  40 . Monolithic blades  10  cannot be formed in this way. In order to form a monolithic blade  10 , other techniques must be used. In one embodiment of the present invention, additive manufacturing is used to form blade  10  and baffle  40 . 
     Forming blade  10  using additive manufacturing removes the need to split blade  10  into separate pieces and assemble it around baffle  40 . Pressure side wall  20 , suction side wall  22 , ribs  38 , baffles  40  and standoff ribs  56 ,  58 ,  60  and/or  62  of blade  10  are formed using additive manufacturing. In additive manufacturing, a three-dimensional computer model of blade  10  is formed and “sliced” into layers. Material is then added layer by layer to form blade  10 . In some embodiments, blade  10  is formed starting at root section  12  or platform  14  and built layer by layer to tip section  18 . When present in baffle  40 , impingement passages  70  can also be formed during the additive manufacturing process. Film passages  68  in pressure side wall  20  and/or suction side wall  22  can also be formed during the additive manufacturing process or drilled following additive manufacturing. 
     Various additive manufacturing techniques can be used to form walls  20  and  22 , ribs  38 , baffles  40  and standoff ribs  56 ,  58 ,  60  and/or  62 . In one embodiment, direct metal laser sintering is the additive manufacturing technique used to form the walls, ribs and baffles of blade  10 . Direct metal laser sintering is an additive metal fabrication process often used with metal alloys. A layer of metal powder is positioned on a substrate or preceding metal layer according to the three-dimensional computer model of the part. A high-powered laser is then used to locally melt the layer of metal powder. This process of adding a layer of metal powder and locally melting the layer is repeated until the part is complete. In another embodiment, electron beam melting is the additive manufacturing technique used to form the walls and ribs of blade  10 . Electron beam melting is similar to direct metal laser sintering, but possesses some differences. Electron beam melting is often used with titanium alloys and instead of melting the material with a laser, an electron beam in a high vacuum is used to melt each metal powder layer. 
     Walls  20  and  22  and ribs  38  can be formed of the same material as baffles  40  or of a different material. Manufacturing walls  20  and  22 , ribs  38  and baffles  40  with the same material simplifies the manufacturing process. In one embodiment, walls  20  and  22 , ribs  38  and baffles  40  are formed of a directionally solidified material. Directionally solidified materials possess grains that have been grown in a particular direction. The grain boundaries (defects in the crystal or crystallite structure) of directionally solidified materials extend predominantly in a single direction. Suitable directionally solidified materials include, but are not limited to, nickel, cobalt and titanium. In another embodiment, walls  20  and  22 , ribs  38  and baffles  40  are formed of an equiaxed material. For equiaxed materials, the grains or crystals that make up the material have roughly the same properties in all directions (e.g., axes of approximately the same length). The grain boundaries of equiaxed materials can extend in multiple directions. Suitable equiaxed materials include, but are not limited to, nickel, cobalt and titanium. 
     Additive manufacturing allows the manufacture of a blade containing a baffle. The baffle provides the blade airfoil with a central cavity within the baffle and skin cavities between the baffle and the pressure and suction side walls. The baffle forms a dual wall component that can take advantage of improved cooling capabilities. The baffle also provides a damping effect to the blade. Additionally, the presence of baffles within the airfoil cavities does not increase the stress on the blade due to thermal expansion and shrinkage. 
     DISCUSSION OF POSSIBLE EMBODIMENTS 
     The following are non-exclusive descriptions of possible embodiments of the present invention. 
     A blade can include a platform and a monolithic airfoil extending from the platform to a tip. The airfoil can include a first wall extending from a leading edge to a trailing edge, a second wall extending from the leading edge to the trailing edge and joined to the first wall at the leading edge, and at least one rib extending from the first wall to the second wall where the at least one rib and the first and second walls define a cavity. The blade can further include a baffle positioned within the cavity, the baffle having walls that are all separate and distinct from and not attached to the at least one rib and the first and second walls of the airfoil. 
     The blade of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     A further embodiment of the foregoing blade can further include at least one standoff rib positioned between the baffle walls and the first wall where the standoff rib dampens vibration within the blade. 
     A further embodiment of any of the foregoing blades can further include that the at least one standoff rib is attached to only one of the first wall and the baffle. 
     A further embodiment of any of the foregoing blades can further include that the first wall has a first standoff rib that extends from the first wall towards the baffle, and the second wall has a second standoff rib that extends from the second wall towards the baffle. 
     A further embodiment of any of the foregoing blades can further include that the baffle has a third standoff rib that extends from the baffle towards the first wall or the second wall. 
     A further embodiment of any of the foregoing blades can further include that the baffle has a standoff rib that extends from the baffle towards the first wall or the second wall. 
     A further embodiment of any of the foregoing blades can further include that the platform has at least one feed opening that allows cooling air to pass through the platform and flow between the baffle and at least one of the first and second walls. 
     A further embodiment of any of the foregoing blades can further include that at least one impingement passage is formed in a baffle wall. 
     A further embodiment of any of the foregoing blades can further include that at least one film passage is formed in one of the first and second walls. 
     A further embodiment of any of the foregoing blades can further include that the airfoil and the baffle are made up of directionally solidified materials. 
     A further embodiment of any of the foregoing blades can further include that the airfoil and the baffle are made up of equiaxed materials. 
     A further embodiment of any of the foregoing blades can further include that the airfoil and the baffle are manufactured from a single material. 
     A method for forming a blade can include forming a platform and forming an airfoil on a layer-by-layer basis using additive manufacturing. The airfoil can include a first wall that extends radially from the platform to a blade tip and extends axially from a leading edge to a trailing edge, a second wall that extends radially from the platform to the blade tip and extends axially from the leading edge to the trailing edge where the first wall and the second wall are joined at the leading edge, and at least one rib that extends from the first wall to the second wall where the at least one rib and the first and second walls define a cavity. The method can also include forming a baffle within the cavity on a layer-by-layer basis using additive manufacturing where the baffle has walls that are separate and distinct from the at least one rib and the first and second walls. 
     The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     A further embodiment of the foregoing method can further include that at least one impingement passage is formed in a baffle wall. 
     A further embodiment of any of the foregoing methods can further include that at least one film passage is formed in one of the first and second walls. 
     A further embodiment of any of the foregoing methods can further include that the at least one film passage is formed by additive manufacturing. 
     A further embodiment of any of the foregoing methods can further include that the at least one film passage is formed by drilling. 
     A further embodiment of any of the foregoing methods can further include that forming the first wall, forming the second wall, forming the at least one rib and forming the baffle are carried out using direct metal laser sintering. 
     A further embodiment of any of the foregoing methods can further include that forming the first wall, forming the second wall, forming the at least one rib and forming the baffle are carried out using electron beam melting. 
     A further embodiment of any of the foregoing methods can further include forming the airfoil on a layer-by-layer basis using additive manufacturing progresses from the platform to the blade tip. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.