US2996101A - Bending mandrel - Google Patents

Description

5, 1961 R. I. GILL 2,996,101

BENDING MANDREL Filed Nov. 28, 1958 2 511 9 11 1; 1

INVENTO'R Ron/F114) kwuvs GLL Aug. 96 R. l. GILL 2,996,101

BENDING MANDREL .Filed Nov. 28, 1958 2 Sheets-Sheet 2 Patented Aug. 15, 1961 2,996,101 BENDING MANDREL Ronald 'Irwine Gill, Harrow, England, assignor to The General Electric Company Limited, Kingsway, London, England Filed Nov. 28, 1958, Ser. No. 776,854 Claims priority, application Great Britain Dec. 2, 1957 Claims. (Cl. 153-63) The present invention relates to waveguides and methods of bending waveguides.

It has been suggested that waveguides formed, for example, of rectangular aluminum or brass tubing may be bent, while maintaining the internal dimensions of the original waveguide, by substantially filling the waveguide, prior to bending, with a mandrel comprising a number of flat strips of metal such as spring steel which are riveted together at one end. The waveguide is then bent on a suitable machine with the mandrel in place. It has been found however that there is a tendency, with this arrangement, for the outer strips of metal to break.

One object of the present invention is to provide a method of bending waveguides in which this undesirable tendency is reduced.

According to the present invention a method of bending a waveguide comprises the Steps of: substantially filling the waveguide, at least over that length of the waveguide which is to be bent, with a mandrel, said mandrel comprising a stack of substantially flat metal strips having, at least over that part of their length which lies within the length of the waveguide which is to be bent, a width slightly less than the dimension of the internal crosssection of the wave guide parallel to which the said strips are arranged to lie, while the said stack of strips includes a first group of strips which are clamped or otherwise attached together at a point beyond one end of the waveguide and a second group of strips which are clamped or otherwise attached together at a point beyond the opposite end of the waveguide, and all the strips of said second group lie between two adjacent strips of said first group at least over that length of the waveguide which is to be bent; bending the said waveguide; and removing the said mandrel.

The said strips may be formed of a resilient metal such as steel.

Preferably said first and second groups are each formed by a stack of strips which has been doubled back on itself, to double the effective thickness of the original stack, and then clamped at a point adjacent the loop so formed.

Two methods of bending a waveguide in accordance with the present invention will now be described by way of example with referecene to the accompanying drawings in which:

FIGURE 1 shows a perspective view of a mandrel being loaded into a waveguide,

FIGURE 2 shows a partly cut-away side elevation of an arrangement used in the first method of bending a waveguide, and

FIGURE 3 shows a plan view of an arrangement used in the second method of bending a waveguide.

In both the methods to be described the waveguide which it is required to bend is a length of waveguide formed of cartridge brass, that is to say an alloy of copper containing approximately 30% of zinc, having an internal cross-section of approximately 0.4 inch by 0.9 inch.

Prior to bending, the waveguide is cut to a length of say ten inches, care being taken to ensure that the plane of the cut at each end of the waveguide is at right angles to the longitudinal axis of the waveguide. The waveguide is deburred and a small hole is drilled near one end for ease of handling during the subsequent heat treatments.

As the material of the waveguide is normally too brittle to be satisfactorily cold worked it is annealed in an air circulating furnace. The furnace is brought to a temperature of 600 C. and a number of waveguides then loaded in. The waveguides are hung vertically, from the small hole previously mentioned, to minimise bowing at the elevated temperature. The temperature of the furnace is maintained steady at 600 C. for fifteen minutes and the waveguides are then quickly removed and quenched in water, this being followed by a dip in an acid bath to re move scale.

Referring now to FIGURE 1 of the drawings, a mandrel is then drawn into one of the lengths of waveguide 1. This mandrel is made up of a plurality of flat strips of spring steel, the strips having substantially uniform crosssections along their lengths. The width of the strips is some two to four thousandths of an inch less than the dimension of the internal cross-section of the waveguide 1 which is at right angles to a wall of the waveguide 1, the plane of which is to be the same both before and after the waveguide has been bent. The total thickness of the strips making up the mandrel is some one to two thousandths of an inch less than the other dimension of the internal cross-section of the waveguide 1.

The strips forming the mandrel are made up of one single strip 2 and two groups of strips 3 and 4. These two groups 3 and 4 are similar, and each group 3 or 4 comprises a number of strips formed into a stack which is then doubled back on itself and held with a clamp 5 or 6 respectively near the point where it has been bent. The group of strips 3 or 4 thus has a loop 7 or 8 respectively formed at one end and this loop 7 or 8 is arranged to be around part of the circumference of a bobbin 9 or 10 respectively, which has a rectangular channel -11 or 12 respectively around its circumference. The group of strips 3 or 4 lies within this channel 11 or 12 and the clamps 5 and 6 are drawn up close to the respective bobbin 9 or 10 so that it is not able to fall out during the subsequent operations.

The mandrel and the waveguide 1 are lubricated With tallow and the mandrel is then loaded into the waveguide 1 as follows. The group of strips 3 is loaded first and pushed through the waveguide 1 as far as the clamp 5 will allow. The single strip 2 is then doubled back on itself and loaded into the waveguide 1 so that the two parts of the strip 2 lie one between each of the outer strips of the first group 3 and the adjacent Waveguide wall. The loop in the single strip 2 should be at the same end of the waveguide l as the bobbin 9 of the first group 3.

The strips of the group 3 projecting from the opposite end of the waveguide 1 are then divided into two equal groups and the ends of the strips of the group 4 remote from the bobbin 10 are inserted in the gap so made. When the group 4 has been pushed as far as possible to wards the waveguide 1 by hand, the waveguide 1 is mounted on a hydraulically operated drawn bench 13 and the mandrel is drawn into the waveguide 1 by a draw-bar 114 exerting a pullon a rod 15 passed through an axial hole in the bobbin 9 of the first group of strips 3, in the J direction of the arrow. This pull is maintained until the mandrel substantially fills the waveguide 1 over the length which is to be bent.

To prevent the inner wall of the waveguide being scored by the edges of the strips during the loading operation, a hardened steel shoe 16 is arranged to abut the waveguide 1 at the opposite end to the drawbar 14 so that the strips are aligned with one another prior to entering the waveguide 1.

Two methods of actually forming the bend in the wtvegaide will now be described, the foregoing description of the loading of the mandrel being common to both these methods.

Referring now to FIGURE 2 of the drawings for the first method, the waveguide 1, complete with the mandrel, is bent in a press tool which comprises a hydraulically operated ram 17 arranged to bear on one wall of the waveguide 1 and so to force the waveguide 1 to conform to the shape of a recess 18 formed in the corresponding part 19 of the press tool. In FIGURE 2 one half of the part 19 has been removed so that the recess 13 may clearly be seen. The ram 17 is triangular in shape, the pressure being applied to the base 20 of the triangle in the direction of the arrow, and the opposite apex 21 corresponding to the required curvature of the wall of the waveguide 1 which is to be on the inside of the bend. The recess 18 is also triangular, the apex 22 of this triangle corresponding to the required curvature of the wall of the waveguide 1 which is to be on the outside of the bend. On completion of the press stroke of the ram 17, which should be continuous, the waveguide 1 will be constrained between the sides and bottom of the recess 18 and the lower surface of the ram 17.

In order to avoid corrugation of the wall of the waveguide 1 on which the ram 17 bears one or two strips 23 of metal similar to the strips making up the mandrel may be interposed between the ram 17 and the waveguide 1. There will naturally be some degree of spring-back of the waveguide 1 when the pressure of the ram 17 is released and during the subsequent operations. It is therefore necessary to bend the waveguide 1 slightly more at this stage than is required in the final product, the amount of extra bending required being small and being found by trial.

After bending, the waveguide '1 is removed from the press tool and the mandrel is removed on the draw bench shown in FIGURE 1 of the drawings. This is done by pulling the first group of strips 3 out of the waveguide 1, in the same direction as that in which the mandrel was pulled in, until the bulk of the group of strips 3 has passed through the waveguide 1. The single strip 2 and Lhe second group of strips 4 may then be removed by and.

If necessary the waveguide 1 is then deburred and it is degreased prior to stress relieving in an air circulating furnace for a period of one hour at 250 C. to 270 C. After removal from the furnace the waveguide 1 is allowed to cool in air.

When the waveguide 1 has been stress relieved, it is returned to the press tool shown in FIGURE 2 of the drawings and the ram 17 is locked in its closed position by means of an eccentric cam lever operating in the hole 24 in the ram 17. The Waveguide 1 is then finally sized by forcing through it a series of highly polished hardened steel rollers, tallow again being used as a lubricant. The rollers are fed through the waveguide 1 by inserting them in sequence at one end and urging them through the waveguide 1 by means of pressure exerted on the most recently inserted roller. The first roller of the series, which is hereinafter referred to as the first working roller, is some two thousandths of an inch smaller than the required internal cross-section of the waveguide 1 on each dimension, this is followed by four rollers hereinafter referred to as slave rollers, which are slightly smaller than the first working roller and there follows in sequence a second working roller which is half a thousandth of an inch larger than the first working roller on each dimension, four slave rollers, a third working roller, etc. until the fifth working roller which conforms to the required internal cross-section of the waveguide 1.

The waveguide "1 is then removed from the press tool, is dcgreased and finally bright acid dipped.

In the second method to be described it is required to provide the waveguide 1 with two adjacent bends in the sarne plane, the two ends of the waveguide 1 being parallel or approximately parallel to one another when the two bends are completed, so that the finished shape of the waveguide 1 approximates to a letter S, the type of mandrel which has been previously described is again used.

in such a case the waveguide is bent in a jig instead of the press tool previously described. Referring to FIG- URE 3 of the drawing, the jig comprises a first shoe 25 rigidly mounted on a base plate 26, one face of the shoe 25 having a. recess 27 the dimensions of which correspond to the dimensions of the waveguide 1. With one end of the waveguide 1 in position in the recess 27, the open side of the recess 27 is closed by a clamping member 28 so that the waveguide 1 is rigidly held in place. The other end of the waveguide 1 is clamped in a second shoe 2 which is similar to the shoe 25 and which includes a recess 3% One end of a threaded shaft 31, which engages with an internally threaded member 32 rigidly attached to the base plate 26, bears on one side of a plate 33 on which the shoe 29' is mounted. Rotation of the shaft 31 causes the plate 33 and, therefore, the shoe 29 to be urged in a direction at right angles to the longitudinal axis of the waveguide 1. The direction of this movement is controlled by projections 34 on the underside of the plate 33,

the projections 34 being free to slide in slots 35 in the baseplate 26.

The shoe 29 is mounted on the plate 33 by means of a projection 36 on the underside of the shoe 29, the projection 36 being free to slide in a groove 37 formed in the plate 33, so that, as the plate 33 is urged forward by the shaft 31, the shoe 29 is free to slide in a direction parallel to the longitudinal axis of the waveguide 1 in order to allow for the fact that as the waveguide 1 is bent it will also be foreshortened. At the adjacent ends of the shoes 25 and 29 the recesses 27 and 30 respectively are curved to correspond to the required final curvature of the waveguide 1 with the previously mentioned allowance for spring-back.

With the exception of this step, the manufacture of the waveguide 1 with two bends is the same as the first method described.

It will be realised that the invention is equally applicable to waveguides formed of other metals, for example, aluminum, and that it may be used for a wide range of waveguide sizes and shapes of bend.

I claim:

1. A waveguide-bending mandrel comprising a stack of substantially flat elongated resilient metal strips, said stack including first and second groups of strips, each said group being longitudinally doubled back on itself and including means slidable on the strips for holding the strips together adjacent the loop so formed, the first and second groups of strips, when brought together to form the mans drel, being arranged with their respective loops at opposite ends of the mandrel and with all the strips of the second group lying between two adjacent strips of the first group at least over that part of the length of the mandrel which, when it is in use, is to be within that part of the waveguide which is to be bent, the cross-section of at least said part of the length of the mandrel being such that it is a close fit in the waveguide.

2. A waveguide-bending mandrel according to claim 1 wherein said metal is steel.

3. A waveguide-bending mandrel according to claim 1 wherein at least said part of the length of the mandrel is References Cited in the file of this patent of rectangular cross-secti0n. 4

4. A waveguide-bending mandrel according to claim 3 UNITED STATHO PATENTS including tWO additional strips similar to the strips form- 2- W g t M 11 7, 1 111g said first and second groups of strips, said additional 5 3,324,945 rflih EC- 1 1 1 strips being arranged, when the mandrel is in use, to lie 1,554,697 u ll r t a1- Jan. 3, 1928 one between each of the outer strips of said first group of 2,117,724 IbbeiSOIl al y 17, 1938 strips and the adjacent wall of the waveguide. 2,390,274 Rose et a1. Dec. 4, 1945 5. A waveguide-bending mandrel according to claim 4 2,672,224 Horwitz Mar. 16, 1954 wherein said additional strips are the two parts of a single 10 2,825,386 Fuchs Mar. 4, 1958 strip doubled back on itself. 2,882,951 Fuchs et a1. Apr. 21, 1959

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