Article having diffuser holes and method of making same

Abstract

The diffusion opening in the cooling hole of an airfoil is formed by an EDM process in which the outwardly flaring sidewalls of the opening, rather then having surfaces that are approximated to be smooth by having many small ribs formed therein, are formed with a relatively few ribs with both longitudinally extending and radially extending surfaces that are substantially greater in dimension than those as normally formed. In this manner, the machining process is simplified and expedited, while at the same time, the cooling efficiency is increased.

1 . A method of forming a shaped hole in a structure comprising the steps of:
 providing an electrical discharge machining electrode with associated power pulsing capability;   advancing in incremental steps, said electrode along a longitudinal access toward a structure;   at each step, moving said electrode transversely and in a reciprocating pattern between boundaries defining a trapezoid with an included angle of θ to remove material from the structure,   wherein the number of incremental steps in which the electrode is advanced during the entire forming process is limited to a range of 4 to 12.   
     
     
         2 . A method as set forth in  claim 1  wherein said structure is an airfoil. 
     
     
         3 . A method as set forth in  claim 2  wherein said shaped hole fluidly communicates with a cylindrical hole passing through a wall of said airfoil. 
     
     
         4 . A method as set forth in  claim 1  wherein said included angle θ is greater than 10 degrees. 
     
     
         5 . A method as set forth in  claim 1  wherein said incremental steps result in said shaped hole having a plurality of ribs with the longitudinal depth of each rib being in the range of 0.002 inches to 0.010 inches. 
     
     
         6 . A method as set forth in  claim 1  wherein said ribs have a transverse dimension in the range of 0.000 inches to 0.006 inches. 
     
     
         7 . A method as set forth in  claim 1  wherein said incremental steps result in a shaped hole having a plurality of ribs with the ratio of their longitudinal depth to their transverse dimensions being in the range of 1.7 to 12. 
     
     
         8 . A method as set forth in  claim 1  wherein said electrode is of the wire type. 
     
     
         9 . A method of producing an electrical discharge machined cooling hole in the diffuser section of a gas turbine engine component comprising the steps of:
 providing a wire EDM electrode and means for supplying pulsed current thereto;   placing said electrode in close proximity to a surface of the component and pulsing current thereto while moving said electrode transversely between boundaries generally defining a trapezoid shape to remove material from the component;   and advancing said electrode longitudinally in incremental steps toward the component and repeating said material removing step for each incremental step,   wherein the longitudinal spacing of the incremental steps is such that the total number of incremental steps over the entire longitudinal length of the cooling hole is in the range of 4-12.   
     
     
         10 . A method as set forth in  claim 9  wherein said component is an airfoil. 
     
     
         11 . A method as set forth in  claim 10  wherein said cooling hole fluidly communicates with a cylindrical hole passing through the wall of said airfoil. 
     
     
         12 . A method as set forth in  claim 9  wherein the boundaries of said trapezoidal shape form an included angle .theta. with the longitudinal axes thereof, and the angle θ is greater than 10 degrees. 
     
     
         13 . A method as set forth in  claim 9  wherein the boundaries of said trapezoidal shape have a plurality of ribs formed therein, and the longitudinal depth of each of said ribs is in the range of 0.002 inches to 0.010 inches. 
     
     
         14 . A method as set forth in  claim 9  wherein the transverse dimension of each of said ribs is in the range of 0.000 inches to 0.006 inches. 
     
     
         15 . A method as set forth in  claim 9  wherein the boundaries of said trapezoidal shape have a plurality of ribs formed therein, and the ratio of the rib longitudinal depth to the rib transverse dimension is in the range of 1.7 to 12. 
     
     
         16 . A method of forming a diffuser hole in an airfoil comprising the steps of:
 forming a cylindrical hole extending from an inner end through an outer wall of the airfoil to an outer end;   advancing an electrode longitudinally toward said cylindrical hole outer end and pulsing current thereto to erode material;   advancing said electrode laterally and continuing to pulse current thereto to form a segment of a diffuser opening leading from said cylindrical hole outer end to a point longitudinally downstream thereof;   continuing to advance the electrode longitudinally in a plurality of steps toward said cylindrical hole outer end and repeating the lateral advancement and pulsing at each step, with the extent of lateral advancement being decreased as the steps approach the cylindrical hole,   wherein the total number of steps of advancement in the longitudinal direction is in the range of 4-12.