GB2035152A

GB2035152A - Method of fabricating a split case for a gas turbine engine

Info

Publication number: GB2035152A
Application number: GB7938364A
Authority: GB
Original assignee: United Technologies Corp
Current assignee: Raytheon Technologies Corp
Priority date: 1978-11-27
Filing date: 1979-11-06
Publication date: 1980-06-18
Also published as: SE7909696L; GB2035152B; DE2947355A1; FR2442339B1; FR2442339A1

Abstract

The split case is formed from a cylinder 10 in whose outer surface at least two axially extending grooves 14 are cut. A pair of mating elements 16, 18 are placed in each slot and are respectively welded to the adjoining parts of the cylinder. The inner diameter of the cylinder is turned to at least the inner edge of the mating elements so that the cylinder separates into at least two portions. The cylinder may be formed with circumferentially extending ribs 12 and/or rails and the mating elements may be machined to form matching ribs and/ or rails, the interfaces being electron welded. <IMAGE>

Description

SPECIFICATION Method of fabricating a split case for a gas turbine engine This invention relates to the method of fabricating the split case of a gas turbine engine.

It has become advantageous in certain jet engine models to make the engine case into halves which not only facilitate assembly, it facilites the maintenance of the engine. Typically the split engine case was manufactured by machining the cylindrical blank to the required dimension and then splitting the case as by sawing it axially through the center.

We have found a more satisfactory way of fabricating a split case by machining the outer diameter of a cylindrical blank, axially grooving two diametrically located slots, inserting two mating half flanges in each slot and turning the inner diameter to expose the inner edges of the flanges, thereby splitting the case.

In certain engine models it is desirable to incorporate rails that extend radially and circumferentially around the outer diameter of the case. Additionally radial structural circumferential ribs are formed on the outer diameter of the case. Inasmuch as it is necessary to weld the flanges into place and because of the material selected, say titanium or an alloy thereof, electron beam welding has become essential to the construction thereof. The flanges and rails however present welding problems that are solved by the present invention.

A feature of this invention is the split case for a turbine type power plant and its construction where the outer diameter of a blank cylinder is machined, diametrically opposed axial grooves are slotted, a pair of mating flanges are fitted into the slots, joined and the inner diameter of the cylinder is turned to remove sufficient material to expose the inner edges of said mating flanges. The outer diameter of the casing can be either machined finished at the initial machining operation or it can be partially machined then and machine finished at a subsequent stage. Said construction being characterized as being simpler and less costly than other heretofore methods of making a split case.

According to one embodiment the mating flanges are electron beam welded to the case and each half of the flange is constructed with a base, extending rib and rail that allow for constant metal exposure to the electron beam as it travels along the surfaces. The 'L' shaped rails adjacent the flange are cut away to allow exposure to the welding surface and to avoid having the electron beam penetrating the vertical leg of the 'L'. The slot or groove is undercut so that the flanges extending into the groove sets below the cutting surface. In this manner the inner diameter and the inner edge of the flange are turned con-concomitantly to assure an integral and uniform internal surface of the cylinder.

The discrete shape of the mating flanges allows for constant and uniform contact of the electron beam welding the surfaces between the cylinder and flange halves. When 'L' shaped rails are included on the cylinder, they are sufficiently cut back away from the flange to allow the unimpeded travel of the beam as it translates along the welding surface.

Other features and advantages will be apparent from the specification and claims and from the accompanying drawings which illustrate an embodiment of the invention.

In the drawings: Figure 1 illustrates in perspective the four steps (A, B, C, and D) for fabricating turbine engine split case according to this invention; Figure 2 is a perspective view of half of the split case; Figure 3 is a partial view in perspective showing another embodiment split case of a gas turbine engine prior to the step of splitting the case; Figure 4 is an exploded view in perspective illustrating the details of the flange/cylinder of Fig. 3.

The invention can best be understood by referring to the steps A, B, C and D depicted in Fig. 1 which shows the cylindrical blank 10 as being the first step in the process. The cylinder may be either a flash butt welded forging or rolled plate of a suitable high temperature resistance material, such as titanium. The outer circumference is machined as depicted by step B to incorporate radial circumferential ribs 1 2 for structural integrity.

As noted in step C, the outer diameter at diametric locations is slotted to define channel 14 along the axial expanse of the case and a pair of mating flanges or flat plates 1 6 and 1 8 are mounted edgewise and welded in position. A plurality of axial spaced holes 20 are drilled therein and doweled work bolts 22 are fastened therein to secure the unit in the next operation.

The inner diameter in the next step of fabricating casing 10 is turned to remove sufficient metal to expose the inner edges of plates 16 and 18. From the foregoing it is apparent that the casing is split and after removing the doweled work bolts 22 each half of the case is removable as depicted in Fig. 2. It may be preferable to machine finish the outer casing at this stage of the operation.

As shown in Figs. 3 and 4 the cylindrical case 1 10 is formed either by forging or bending flat plates of suitable metal such as titanium or alloy thereof and butt welding the edges (weldment not shown). The outer ribs 11 2 are formed for structural purposes and the 'L' shaped rails 114 are machined on the outer diameter of cylinder 11 0. Corresponding ribs 11 2a and 'L' shaped rails 11 4a are machined as the outer surface or top surface of flange 116. Flange 116 is formed into two complementary halves and carry a plurality of matching holes for accepting bolt assemblies 11 8 serving to bolt the two halves together.

Located on the inner edge or mating edges 1 20 and 1 20a are the rib or flange faces 1 22 and 1 22a which are discretely spaced from the weld interface 1 24. After securing the two halves of flange 1 16 it is inserted into the axial slot 1 30 formed in the cylinder 11 0. As noted from Fig. 3 the rails 114 adjacent the corresponding rails 1 14a are machined back slightly so as not to impede the flow of electrons in the process of electron beam welding the flange into the slot 1 30.

Slot 1 30 is cut deeper into cylinder 110 than would otherwise be necessary so that the step of machining the inner diameter of the cylinder splits the case. The inner edge of flange 11 6 is also bored in this operation to ensure aiignment of the inner diameter of the cylinder. Obviously, by removing that amount of metal from the inner diameter of the cylinder 110, the case will split along the parting plane defined by the mating faces of both halves of each of the flanges.

The space formed by machining back the 'L' shaped rails can be welded by say a tungsten inert gas welding technique.

While a two piece split case is described as the preferred embodiment it may be desirable to split the case into multiple pieces and such designs are contemplated within the scope of this invention.

It should be understood that the invention is not limited to the particular embodiments shown and described herein, but that various changes and modifications may be made without departing from the spirit or scope of this novel concept as defined by the following

Claims

claims. CLAIMS

1. The method of fabricating a split case for a gas turbine engine including the steps of: forming a cylinder; cutting at least two axially extending slots into the outer diameter of said cylinder; inserting two mating elements into said slots and each pair of mating elements extending radially from the outer diameter of the cylinder; welding each of said mating elements to the cylinder; and cutting by turning the inner diameter of said cylinder to at least the inner edge of said mating elements so that the cylinder separates into two halves at the mating surface of each pair of said elements.

2. The method as claimed in claim 1 comprising the step of forming the cylinder from a forged or flat plate and butt welding the joining edges.

3. The method as claimed in claim 1 or 2 comprising the step of cutting the outer diameter of the cylinder by turning, prior to cutting the slots, to form upstanding circumferential, axially spaced rib-like elements.

4. The method as claimed in claim 1 or 2 comprising the steps of forming a cylinder having a plurality of circumferentially extending axially spaced ribs and L-shaped rails, machining the outer surface of said mating member to form radially extending ribs and Lshaped rails corresponding to the ribs and Lshaped rails of the cylinder and electron beam welding each of the mating member to the cylinder at the interface of the wall of the slot by moving the stream of electrons axially along the welding surface.

5. The method as claimed in claim 4 including the step of machining back an edge portion of the L-shaped rail at the location adjacent the welding surface.

6. The method as claimed in any one of claims 1 to 5 including the step of drilling a plurality of holes spaced axially along each pair of mating elements and securing each of the mating elements constituting each pair thereof prior to the step of welding.

7. The method as claimed in anyone of claims 1 to 6 said cylinder is fabricated from titanium or an alloy thereof.

8. The method substantially as hereinbefore described with reference to the accompanying drawings.