Forming of intermetallic materials with conventional sheet metal equipment

Abstract: A method and apparatus for applying heat sufficient to permit plastic deformation of intermetallic material. The heat is applied to a fractional region of a workpiece, and then manipulations capable of causing the workpiece to deform are applied using conventional sheet metal forming equipment. The invention utilizes elevated forming temperatures to heat the fractional region of the intermetallic workpiece so that the fractional region has sufficient ductility to permit a plastic deformation required for the forming operation. The apparatus is a sheet metal-working machine which has been modified to provide the localized heating required to carry out the process of the present invention.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to methods for forming titanium alloy materials, and more particularly to a method of forming titanium aluminide materials using conventional sheet metal equipment and tooling to fabricate structural components and localized heating of the workpiece alone. 2. Background of the Invention In the family of intermetallic metals, titanium aluminide materials have become most useful in the design of structures requiring a high strength-to-weight ratio. Although unique in the class of titanium alloy compositions, titanium aluminide materials may, like the more typical titanium alloys, contain additions of one or more alloying agents such as tin, zirconium, molybdenum, vanadium, silicon, chromium, manganese and iron. Titanium aluminide materials find particular application in the field of aircraft and spacecraft design. While several important end uses exist for titanium aluminide materials, there still remain various difficulties in effecting deformation of these materials to achieve a final, desired useful shape. The most frequently encountered obstacle is the inability to manipulate these materials, for it has become well-known that titanium aluminides are relatively brittle and not amenable to forming with conventional techniques at or near room temperatures. One recent approach which has found widespread utility in the fashioning of structural components from such materials is superplastic forming, a process in which a superplastic material (eg., a titanium or aluminum alloy) is heated to a forming temperature, generally in the range of from 926°C to 1038°C (1700° F. to 1900° F.), and then formed in a die using positive or negative pressure on one side of the metal to force the metal to plastically "flow" against or into the die. Although the advantages of superplastic forming are numerous, the process has drawbacks. For one thing, it requires special equipment including a controlled environment within the heating and forming apparatus, the application of very high forming temperatures (on the order of 926°C to 1038°C (1700° F. to 1900° F.)), and specially designed tools for handling the materials and equipment while heated and before they are fully cooled. Additionally, the heating and cooling phases of the process take place over extended periods of time and require uniquely designed tool supports having appropriate thermal coefficients to accomodate the high forming temperatures. For these reasons, as well as the fact that this process requires thermal treatment of not only the whole workpiece, but also the heating and forming apparatus, efforts have been made to discover alternative techniques and/or equipment to achieve the same or similar end results, while reducing cost and time involved and increasing efficiency. OBJECTS AND SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a novel method of forming structure out of titanium aluminide, which facilitates the use of conventional sheet metal forming equipment while overcoming all the deficiencies and disadvantages of other forming methods of like kind. Another object of the present invention is to provide a novel forming method for fabricating a structural member from a workpiece of titanium aluminide, where localized heating of a predetermined portion of the workpiece to be formed is employed to overcome the brittle behavior of the material at room temperature. Attention is drawn to DE-C-877 617 which shows a method and an apparatus for forming sheet metal and metal plates. Said apparatus comprising upper and lower shaping elements, means for heating said sheet metal and means for moving the upper and lower shaping elements together to engage said sheet metal to be formed. In order to achieve the above objects, a method as set forth in claim 1 is provided. Preferred embodiments of the method are claimed in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 schematically illustrates a press brake forming machine which has been modified to include heating apparatus required to carry out the heating step of the method of the present invention; and Figure 2 illustrates a formed titanium aluminide workpiece following the teachings of the method of the present invention; DETAILED DESCRIPTION OF THE INVENTION The present invention comprises a method of forming titanium aluminide materials at elevated temperatures, and contemplates the use of conventional sheet metal equipment in the form of a press brake, as well as conventional tooling, to fabricate structural components. The process includes the application of heat to a small, fractional region of a workpiece to a temperature at which the material possesses sufficient ductility to undergo the desired deformation. Temperatures in the range of 204°C to 316°C (400°F to 600°F) have been experimentally demonstrated for the alpha-2 (Ti 3 Al) family of titanium aluminide alloys. The heat is applied using heat-applying apparatus which is secured to the conventional forming equipment. The invention contemplates modification of the conventional forming equipment so that the heat-applying apparatus can be moved into and out of accessibility with the fractional region of the workpiece about to be deformed. The present invention contemplates application of heat to just the fractional region of the workpiece to be manipulated. The process of this invention. therefore, does not require heating of the forming tools. Figure 1 illustrates one embodiment of a conventional sheet metal machine commonly known as a press brake, in which the machine has been modified to provide the localized heating capability required to carry out the process of the present invention. As shown, the press brake machine 100 comprises an upper, vertically movable, press brake die 110 and a lower, fixed, press brake die 120. The upper and lower dies are vertically aligned so that the convex forming face 112 of the upper die overlies the concave forming face 122 of the lower die. Typically, the convex forming face of the the upper die will conform in topographical shape to the concave forming face of the lower die. Attached to the upper press brake die is a heater assembly 200 which includes a supporting arm 202 pivotably mounted on the upper die at pivot 204 for movement between a first position in which the arm is substantially vertically arranged and a second position in which the arm is substantially horizontally arranged. A heater 206 is carried at the end of the arm located opposite the pivotably mounted end. A plurality of quartz lamp heating elements 208 are attached within the casing of the heater 206. A thermocouple 300 is positioned below the workpiece in a location relative to the lower die (eg., as seen in Figure 1, substantially centrally of the concave lower die forming face 122). In carrying out the method according to the present invention, a workpiece in the form of a sheet of titanium aluminide material is placed on a supporting bed 130 located just upstream of the press brake lower die 120, and is fed in a forward direction past the lower die. At each predetermined location where the sheet of metal is to be deformed by bending between the upper and the lower dies, that predetermined location of the sheet is positioned atop the concave forming face of the lower die. The heater assembly is then pivoted downwardly from its second position to the first position so that the heater 206 is positioned directly atop the sheet's predetermined location. The heating elements are then actuated for a period of time to attain a predetermined temperature appropriate for the deformation to take place, the thickness of the material to be shaped, and the physical properties which the final product is intended to possess. After this predetermined temperature has been achieved, the heating elements are deactivated and the heater assembly is pivoted out of its first position back to the second position so that the now-heated region of the sheet at the predetermined location can be deformed using the upper and lower dies of the press brake (i.e., by lowering the upper die toward the lower die and into deforming engagement with heated region of the sheet). The sheet is then advanced in the forward direction a distance which corresponds to the location where the next deformation of the sheet is to be imparted using this press brake machine. The steps of this process are repeated until the sheet presents the desired shape(s). An example of one structural element obtained following steps of the inventive process similar to those described above is shown in Figure 2. The invention contemplates performing the steps of the entire process manually as well as by automated machinery. In the latter case, one or more machines could be controlled by computer hardware and software which would facilitate forming several sheets of intermetallic material simultaneously, each on its own machine.

Claims: A method for transforming a substantially planar sheet of titanium aluminide material into a non-planar structural component using a conventional press brake machine, comprising: locating one region of said sheet material where a first deformation of said sheet material is to take place, heating said one region at one side thereof to a temperature of at least 200°C and no more than 400°C for a predetermined period of time, and deforming said heated region into a desired shape by pressing an upper die associated with said press brake machine against said region and toward a lower die associated with said press brake machine, whereby a substantially planar sheet of material is transformed into a non-planar structural component. The method of claim 1, where the step of locating comprises defining all of said regions of said sheet where deforming is to take place, and then performing each of said further steps of said process sequentially at each of said defined regions, whereby a plurality of deformations are imparted to said sheet of material to cause said sheet to be transformed into a corrugated structural component. The method of claim 1, wherein said step of applying a predetermined amount of heat to each of said regions comprises moving a heated source between a first position of non-use and a second actuatable position where the heat source is positioned in overlying correspondence with the identified region.

Inventors: BAKALYAR ALLAN D, LYDIA PETER, BAKALYAR, ALLAN D., LYDIA, PETER
Applicants: ROCKWELL INTERNATIONAL CORP, ROCKWELL INTERNATIONAL CORPORATION
Application year: 1993
Main classification: B21D13
IPC codes: B21D13, C22F1