US 3,936,920 A · Aerodynamic shell structure with fittings and method for fabricating same

Abstract

The present invention is a lightweight, internally stiffened aerodynamic shell structure with local fittings and a method for fabricating the same. Two typical type structures are the blades and vanes of a turbo fan engine. The invented structure exhibits heretofore unattainable strength and stiffness to weight ratios and a high degree of structural integrity. It is, therefore, particularly advantageous in applications such as the rotating blades in airborne or ground power conversion equipment. It is an aerodynamically shaped structure comprising metallic stiffening material interposed between, and joined to, a pair of relatively thin corresponding metallic face sheets which form the shell skin of the structure. As a function of design requirements, a root fitting, shroud fitting, and tip rib or fitting are solid-state diffusion bonded to the shell structure. In addition, the leading and trailing edges of the shell structure are formed by the solid-state diffusion bonding of the edges of the corresponding face sheets. The invented method for diffusion bonding the shell structure to the required fittings and the edges of the face sheets to form the leading and trailing edges achieves a homogeneous joint having parent material strength and properties while achieving a high degree of filleting in multiple directions. The invented method for fabricating the invented aerodynamic shell structure includes the use of (i) flow volumes of excess material located on the parts to be joined, the respective geometry and location of such flow volumes being determined as a function of the geometry of the parts and the juncture to be achieved, as well as the required filleting, and (ii) a specially designed die assembly which applies high localized pressure at an elevated temperature for a suitable period of time to achieve the desired plastic flow diffusion bond. Typical metals used to construct the invented shell structure are the wrought alloys such as titanium, aluminum, stainless steel, nickel base alloys, cobalt base alloys and columbium base alloys, etc. The invention also contemplates many variations of the internal stiffening material used to achieve the required shear and bending stiffness, and the placement of such material.

Claims43

Dependent claims

A method for fabricating a thin skin, internally stiffened, aerodynamic shaped shell structure having homogeneous leading and trailing edges with parent material properties comprising the steps of:

a. fabricating a panel blank comprised of metallic stiffening material disposed between and joined to first and second planar metallic face sheets, said face sheets each having a thickness dimension substantially less than its surface dimensions, the edges of each of said face sheets having in their longitudinal direction a sufficient volume of flow material thereon to achieve the required solidity of said leading and trailing edges, said volume of flow material being about 5-10 percent oversized, and said stiffening material giving to said structure the required strength and stiffness to weight ratios;
b. forming said panel blank into a basic aerodynamic shape by imparting thereto aerodynamic contours;
c. providing a die assembly including a die ram, said die assembly being installed within means for applying pressure and said die ram being configured to achieve the desired contours for said aerodynamic structure;
d. disposing said panel blank in said die assembly;
and
e. applying a forming and joining force to said panel blank by the action of said die ram in said die assembly as pressure is applied to said die assembly in an inert atmosphere at a temperature below the transformation temperature of the metal of said panel blank for a sufficient duration to form said aerodynamic structure and to acheive solid state diffusion bonding of said edges of said face sheets into said leading and trailing edges, said forming and joining force being determined from the volumes of said flow material and the plastic flow and creep characteristics of said metal whereby said oversized flow material on said face sheet edges allows said edges to fit within said die assembly with a positive fill, thereby substantially eliminating the necessity of very close tolerances.

3 more elements

A method for fabricating a thin skin, internally stiffened, aerodynamic shaped shell structure having leading and trailing edges and having joined thereto at least one fitting, said leading and trailing edges and the juncture with said fitting each having homogeneous joints with parent material properties, comprising the steps of:

a. fabricating a panel blank comprised of metallic stiffening material disposed between and joined to first and second planar metallic face sheets, said face sheets each having a thickness dimension substantially less than its surface dimensions, the edges of each of said face sheets having in their longitudinal direction a sufficient volume of flow material thereon to achieve the required solidity of said leading and trailing edges, said volume of flow material being about 5-10% oversized, and said stiffening material giving to said structure the required strength and stiffness to weight ratios;
b. fabricating a fitting blank of the same metal alloy group as said panel blank, said fitting blank being adapted to engage said panel blank along the corresponding surfaces to be joined, said fitting blank having a sufficient volume of flow material in the vicinity of said surfaces to be joined to achieve said homogeneous joint and required blending geometry, said volume of flow material of said surfaces being about 5-10 percent oversized;
c. forming said panel blank into a basic aerodynamic shape by imparting thereto aerodynamic contours;
d. position attaching said fitting blank to said panel blank;
e. providing a die assembly including a die ram, said die assembly being installed within means for applying pressure and said die ram being configured to achieve the desired contours of said aerodynamic structure;
f. disposing said panel blank and said fitting blank in said die assembly, and
g. applying a forming and joining force to said panel blank and said fitting blank by the action of said die ram in said die assembly as pressure is applied to said die assembly in an inert atmosphere at a temperature below the transformation temperature of said metal for a sufficient duration to form said aerodynamic structure, to achieve solid state diffusion bonding of said edges of said face sheets into said leading and trailing edges, and to achieve solid state diffusion bonding between said forming and joining force being determined from the volumes of said flow material and the plastic flow and creep characteristics of said metal whereby said oversized flow material on said face sheet edges allows said edges and said fitting blank to fit within said die assembly with a positive fill and the engagement of said fitting blank and said panel blank is made with a positive fill, thereby eliminating the necessity of very close tolerances.

4 more elements

A method for fabricating a thin skin, internally stiffened, aerodynamic shaped shell structure, having homogeneous leading and trailing edges with parent material properties comprising the steps of:

a. fabricating first and second planar, metallic face sheets, each having a thickness dimension substantially less than its planar dimension, the thickness thereof being initially greater than that required;
b. reducing the thickness of said face sheets in at least one step in the transverse direction away from the longitudinal edges of said face sheets, thereby leaving on said edges of said face sheets a sufficient volume of flow material to achieve the required solidity of said leading and trailing edges;
c. fabricating a panel blank comprised of crushable metallic stiffening material disposed between said face sheets equidistantly spaced, said stiffening material being partially diffusion bonded to said face sheets so as to maintain them in intimate contact, complete diffusion bonding thereof taking place subsequently during the application of a forming and joining force thereto, said stiffening material giving to said structure the required strengh and stiffness to weight ratios;
d. rough trimming said panel blank and providing reference control means;
e. crush forming said panel blank within a crush die set, thereby imparting to it the basic aerodynamic contours and causing said longitudinal edges of said face sheets to be in contacting engagement along their entire length;
f. cleaning the to-be-joined surfaces of said panel blank;
g. installing said panel blank into a die assembly comprised of a restraining die body, a die ram, a ram base, load distribution plates and means for holding said panel blank securely in position, the shape of said die ram being configured to achieve the desired contours of said aerodynamic structure, said parts of said die assembly being first cleaned, said die assembly in turn being enclosed in metallic members to form a retort envelope;
h. purging said die assembly with an inert gas and evacuating the same a sufficient number of times to remove air enclosed during assembly;
i. heating said die assembly and said panel blank to approximately 1000.degree.F for sufficient time to remove remaining contaminants by vacuum hot out-gassing;
j. evacuating said die assembly to a vacuum of at least approximately 10.sup.-.sup.4 Torr.
k. soaking said die assembly and said panel blank at a temperature approximately 50.degree.-100.degree.F below the transformation temperature of the metal of said panel blank for sufficient time to achieve a uniform temperature distribution;
l. placing said die assembly into an insulation box to retain the heat, said insulation box in turn being placed into an hydraulic press;
m. applying pressure to said die ram, through said insulation box, for a sufficient duration to form said aerodynamic structure, to cause said flow material on said edges of said face sheets to plastic flow to the required shape while achieving intimate surface contact at the joint and to achieve thereby solid state diffusion bonding of said edges into said leading and trailing edges, said pressure causing said die ram to apply a forming and joining force upon said panel blank, said forming and joining force and its duration being determined from the volumes of said flow material, the distance of said flow, the travel of said die ram, the plastic flow and creep deformation characteristics of said metal and the force required to achieve final sizing and contour forming of said panel blank;
n. cooling said die assembly and removing therefrom said aerodynamic structure;
o. removing flashing from said leading and trailing edges;
and
p. removing said reference control means and final machining any unnecessary remaining material.

14 more elements

Dependencies are inferred from the claim text.

Aerodynamic shell structure with fittings and method for fabricating same

Life of this patent

Aerodynamic shell structure with fittings and method for fabricating same

Life of this patent

Abstract

Claims43