US3248918A

US3248918A - Method for forming reflectors

Info

Publication number: US3248918A
Application number: US310419A
Authority: US
Inventors: Louis E Brown
Original assignee: Decibel Products Inc
Current assignee: Decibel Products Inc
Priority date: 1963-09-20
Filing date: 1963-09-20
Publication date: 1966-05-03
Anticipated expiration: 1983-05-03
Also published as: GB1068965A

Description

y 1966 E. BROWN 3,248,918

METHOD FOR FORMING REFLECTORS Filed Sept ZO, 1963 4 SheetsSheet 1 FIG. I I0 INVENTOR. LOUIS E. BROWN A TTORNEYS,

y 1966 1.. E. BROWN 3,248,918

METHOD FOR FORMING REFLECTORS Filed Sept. 20, 1963 4 Sheets-Sheet 2 FIG.3 H 10 F|G.4

.Ililll m mm ilHllllIlHil INVENTOR. LOUIS E. BROWN A TTORNE Y5,

May 3, 1966 r L. E. BROWN 3,248,918

METHOD FOR FORMING REFLECTORS Filed Sept. 20, 1963 4 Sheets-Sheet a INVENTOR. LOUIS E. BROWN A TTORNE YS,

y 3, 1966 L E. BROWN 3,248,918

METHOD FOR FORMING REFLECTORS INVENTOR. LOUIS E. BROWN A TTORNEYS.

United States Patent 3,248,918 METHOD FOR FORMING REFLECTORS Louis E. Brown, Dallas, Tex., assignor to Decibel Products, Inc., Dallas, Tex., a corporation of Texas Filed Sept. 20, 1963, Ser. No. 310,419 3 Claims. (Cl. 728I) This invention relates to a metal forming process and apparatus and more particularly to the formation of antennas such as microwave radio reflectors, radar reflectors, radio astronomy reflectors and the like.

Methods of forming concave metallic elements have been known for some time. These earlier metal forming methods were used for the most part in the manufacture of dished heads for tanks, such as pressure water tanks and storage tanks for butane and similar other gaseous or liquid products. However, these prior arrangements have been found inadequate for the production of accurate reflectors for use as antennas in radar, microwave radio communications, and radio astronomy.

For reflecting surfaces of this type, the contour and the diameter of the reflector must be constant from one antenna to the next in order to provide a product manufiactured to desired specifications. For example, it is well known that when electromagnetic energy strikes a paraboloid'al surface, the energy will be directed away from the surface in parallel rays seeming to emanate from the focal point or focal region 'of the reflector. It is extremely important that this energy arrive at the aperture, that is the circular aperture of the reflector, in the proper phase relation. Any deviation in this phase front across the aperture results in a loss of antenna gain and efficiency, a widening of the beam width, and objectional increase of the minor lobe energy content. Further, unless the circular aperture formed by the paraboloid or hyperboloid or other spherical segment is of a constant diameter it becomes impractical to provide a weatherproof covering such as a fiberglass radome for the aperture since the radomes and other coverings are normally manufactured from different types of molds and will not adequately fit "and protect the reflector. Also, unless the diameters remain constant from one antenna reflector to the next during manufacture, the gain, beam width, the side lobe energy content, and other electrical parameters will vary from one antenna to the next; consequently, it becomes impractical to provide antennas meetig given desired specifications.

As a result, special manufacturing techniques have been developed for the manufacture of reflector antennas. Most often the reflectors, such as those of paraboloid contour, for example, are customarily manufactured by a spinning technique whereby a tool pressed by an operator against a metal disc is formed into the shape or contour of a mold or die in order to impart the desired paraboloid or *other contour to the sheet with the desired accuracy. This technique is not only time consuming,

but is subject to the skill or lack of skill of the operator, does not lend itself to eflicient mass production, and requires the use of expensive dies or molds. Very small reflectors have, in the past, been die pressed, but this process is diflicult for large size antennas and involves the high cost of expensive dies and machinery for reflectors of diflerent sizes and contours.

The present invention avoids the above mentioned difliculties by providing a novel method and apparatus for forming spherical type metal reflectors which completely eliminates the necessity for expensive dies While at the same time retaining the required accuracy for precision radio applications. The present invention substantially reduces the necessity for skilled technicians and substantially reduces the cost of manufacture of the product.

It is therefore one object of the present invention to provide a method for forming metallic antenna reflectors of conical sections of revolution such as are used in microwave radio communications, radar, and radio astron- 'omy antennas.

Another object of the present invention is to provide a metal forming process capable of forming conic sections of revolution such as paraboloid, hyperboloid, or ellipsoid, having maximum mechanical strength for forces in tension, compression, and shear.

Another object of the present invention is the provision of a stretch forming method utilizing a predetermined metal alloy temper such as half 'hard aluminum and work stretching the metal to full hard temper.

Another object of the present invention is to provide a metal forming apparatus for producing conic sections of revolution from a metallic sheet or plate blanks whereby the completed conic section of revolution is stressed in tension throughout the thickness contour of the section.

Another object of the invention is to provide a metal forming process and apparatus whereby the diameter of conic section is determined prior to work stretching of the metal and maintained constant throughout the stretching operation.

Another object of the present invention is to provide a process and apparatus for forming conical sections of revolution from metal blanks varying in thickness from a few millimeters up to many millimeters and varying in diameter from 'a few inches to in excess of 10 feet.

Another object of the present invention is to provide novel apparatus for forming conical sections of revolution.

These and further objects and advantages of the invention will be more apparent upon reference to the following specification, claims and appended drawings, wherein:

FIGURE 1 is a front elevation with parts in section showing the novel apparatus of the present invention.

FIGURE 2 is a plan view of a portion of the apparatus of FIGURE 1.

FIGURE 3 is an enlarged cross sectional view showing the mounting of the upper end of the contour template of FIGURES 1 and 2.

FIGURE 4 is an enlarged cross section taken along line 4-4 of FIGURE 1 showing the details of the carriage mount.

FIGURE 5 is an enlarged cross sectional view showing the mounting arrangement for the lower end of the contour template.

FIGURE 6 is a cross section taken along line 66 of FIGURE 5.

FIGURE 7 is an elevational view of part of the apparatus similar to that of FIGURE 1 showing a first step in the process of forming a metallic reflector according to the present invention.

FIGURES 8, 9 and 10 respectively show subsequent stages in the forming of a reflector, and

FIGURE 11 illustrates the configuration of the finished reflector.

Referring to the drawings, the novel device of the present invention generally indicated at 10 in FIGURE 1 comprises a table 12 of generally rectangular configuration and including four legs, two of which are illustrated at 14 and 16 supporting the four corners of a flat metal plate or table top 18. A pair of

channel members

20 and 22 are connected to the opposite ends of the table top 18 approximately midway of the legs by

suitable brackets

24 and 26.

Similar brackets

28 and 30 secure the upper ends of the

uprights

20 and 22 to the opposite ends of a pair of parallel spaced

horizontal channels

32 and 34.

Resting on a suitable support, such as a floor 34, beneath the table top 18 is a drive motor 36 which may be of the conventional electrical type, coupled by a drive shaft 38 to a variable gear train box 40. The output from the gear box 40 is by way of avertical rotary shaft 42 which passes through a suitable anti-friction bearing 44 carried in the table top 18 and which has rigidly secured to its upper end a circular rotating plate 46. Rigidly secured to the rotating plate 46 by brackets 48 are the lower ends of a plurality of circumferentially spaced and upwardly extending arms 50. The upper ends of these arms are in turn connected by suitable brackets 52 to the inner surface of a support ring 54.

Mounted on the parallel

horizontal channel members

32 and 34 is a contour template generally indicated at 56, comprising a curved track 58 along which moves a carriage 60. The curved track 58 is of a predetermined contoured shape of the desired conic section of revolution. As seen in FIGURES 1 and 4, the carriage is provided with a plurality of rollers such as 62 and 64 which engage the opposite sides of the track 58 so that the carriage is free to move along the track by the rotary engagement of the rollers. Dependent from the underside of the carriage is a forming roller 66 adapted to engage and press against a metal blank to be formed.

The top of carriage 60 carries an upwardly extending tab 68 provided with an aperture loosely receiving the end of a threaded rod 70. Tab 68 is retained between the spaced

washers

72 and 74 tightly secured to the rod by a suitable means, such as set screws or the like.

The upper end of threaded rod 70 is provided with a hand wheel 76 for manually rotating the rod to cause the carriage 60 to move along the track 58. As best seen in FIGURE 3, the upper end of the threaded rod 70 adjacent hand wheel 76 is threadedly received through a support block 78 provided with cavities which receive the narrowed ends or hearing portions 80 and 82 of

wing bolts

84 and 86. These wing bolts are threaded into

angle elements

88 and 90 welded or otherwise suitably secured to the respective

parallel channels

32 and 34. Bearings 80 and 82 also support the bifurcated ends '92 and 94 of the track 58. In this way both the threaded support block 78 and the upper end of the track 58 are free to pivot about the bearings 80 and 82.

As best seen in FIGURES 1, 5 and 6, the lower end of track 58 is supported from the

parallel channels

32 and 34 by means of a threaded shaft 96 also provided with a hand wheel 98 for manual rotation of the shaft 96 and the accompanying adjustment of the lower end of the track. A pair of pivot pins 100 and 102 is rotatably received through the

respective channels

32 and 34 and is rigidly secured as by welding or the like to a threaded block 104 which similar to the support block 78 threadedly engages shaft 96.

The lower end of shaft 96 is provided with a flange 188 which supports a yoke rotable with respect to the shaft 96 by means of a bronze bushing 112. Passing through the two

legs

114 and 116 of the yoke is a pivot 'pin in the form of a bolt 118. The lower end of the track 58 is provided with an enlarged rectangular portion illustrated at 120 in FIGURES 5 and 6 suitably apertured to receive bolt 118 and pivotally connected to the bolt by a bronze sleeve 122. Thus, shaft 96 may be rotated to raise and lower the yoke, is free to pivot about the bearing pins 100 and 102 received in

bronze bushings

124 and 126 secured to the

channel elements

32 and 34 and at the same time the lower end of the track 58 is free to pivot about the shank of bolt 118.

As best seen in FIGURES 1 and 7 the upper end 126 of the vertical drive shaft 44 passes through plate 46 which plate is mounted on shaft collar 124. A hollow vertical staflf 128 (FIGURE 7) is slidably received over the projecting end 126 and seats on the circular plate 46. The upper end of the staff 128 terminates in a flange 130 adapted to engage the under side of a flat circular metal blank indicated at 132 in FIGURE 7. Positioned above the metal blank 132 is a circular disc 134 preferably made of wood having a diameter equal to the outer diameter of the support ring 54. A removable clamp including clamp screw 136 is provided having a jaw 138 rotatably mounted on its lower end which cooperates which the support ring 54 to tightly clamp the wood form or disc 134 and the outer edges of the metal blank 132 to the top of the support ring 54. The engagement of the flange 5 130 with the under side of the metal blank is very light so as to be preferably only suflicient to support the center of the metal blank against any flexure of the disc 134 under the pressure of clamping jaw 138. The upper end of the clamping screw 136 is provided with a head 140 so that it may be engaged by a suitable tool and rotated. The screw threadedly passes through a nut and bracket 142 removably attached to the

parallel channels

32 and 34 by suitable clamps, such as the threaded clamping elements illustrated at 144 and 146 in FIGURE 7.

FIGURE 7 in conjunction with FIGURES 8, 9 and 10 illustrates various stages in the formation of a paraboloidal reflector in accordance with the present invention. In operation the metal blank 132, preferably of half-hard aluminum, is cut to size such that its outer edge slightly overlaps the outer edge of the support ring 54 as illustrated at 148 in FIGURE 7. The disc 134 is then placed over the blank and the clamp screw 136 tightened to press the disc 134 against the blank so as to tightly engage the outer edges of the blank between the disc and ring support. With the blank in this position, the support ring is rotated by motor 36 and the outer edge 148 is turned down as illustrated at 150 in FIGURE 7 by a suitable forming tool (not shown) to form a downwardly extending flange 152 completely around the blank as illustrated in FIGURE 11 showing the finished reflector.

The clamp screw 136 is then removed as is the disc 134 and a metallic clamping ring 154, illustrated in FIG- URE 8, is placed over the outer edge of the metal blank 132. This clamping ring may be suitably secured to the support ring by clamps, screws, or the like so as to tightly clamp the outer edge of the metal blank 132 to the support ring, thus establishing a fixed and accurately controlled diameter for the reflector.

As previously stated, the track 58 is of the desired contour of the finished reflector and its initial position is established by manual rotation of the threaded rods 96 and '70. Preferably these rods are adjusted so that the first pass of the forming roller 66 begins at approximately the position illustrated in FIGURE 8 with the carriage 60 travelling along the track from the periphery of the metal blank towards its center. Due to the rotation of the support ring 54 as it is driven by motor 36, the curvilinear motion of the carriage 60 along track 58 is 5 imparted to the metal blank to form a conical section of revolution. In ordinary operation, several inward passes of the carriage and forming roller 66 are preferred so that formation of the blank 132 occurs progressively in sequential steps with additional formation occurring dur- 55 ing each pass of the roller 66. Normally, three or four passes of the roller 66 from the periphery to the center of the blank are suflicient to form a completed reflector.

FIGURE 9 shows an intermediate stage of reflector formation which by way of example only may repre- 50 sent the third pass of the roller 66 along the track from the periphery to the center of the blank. After each such pass the shaft 70 is rotated in the opposite direction to draw the roller 66 back to the retracted position illustrated in FIGURE 8 and then shaft 96 is rotated 5 to cause it to move downwardly so as to lower the track and put it in position for the next pass.

FIGURE 10 illustrates the last pass of the roller 66 over the metal blank which is shown as having assumed the contour of the finished reflector. The final pass of 70 the roller resulting in the finished contour is readily determined by the fact that when the track 58 is in the proper position, such as illustrated in FIGURE 10 for the final pass, the shaft 96 will have assumed an exactly vertical position as illustrated. Any tilting of the shaft 75 96 from the vertical indicates that the track 58 is not in the proper position for forming the final contour of the metal blank.

After the forming operation, contour template 56 is removed along with the clamping ring 154 and the finished product is removed from the support ring 54. The apparatus is then made ready for the next metal blank to be formed.

FIGURE 11 illustrates the finished reflector formed from the blank 132 provided with the peripheral flange 152. In the example illustrated the reflector is of para bolic configuration with the curvature defined by the equation where the x coordinate is coincident with the axis of rotation of the blank during its formation and the y coordinate is perpendicular to the x coordinate. It is of course readily apparent that in addition to paraboloids, other conical sections of rotation, such as hy erboloids or ellipsoids may be formed according to the present invention.

As discussed above, an important feature of the present invention lies in the fact that the metal blank 132 is formed under tension because the forming operation of the roller 66 develops only tension stress in metal fibers completely throughout the surface from the outer edge to the center of the paraboloid. Since the paraboloid surface is completely under tension rather than compression or a combination of compression and tension, springback is eliminated in the finished shape.

The accuracy of the formed conic section such as depicted by the paraboloid of revolution in FIGURE 11 is determined solely by the predetermined contour of the template 56. This contour template can be simply and easily manufactured and shaped to the required accuracy. This means that the quality of control in both the work stressing of the metal and the accuracy of the finished shape is substantially independent of the operators skill.

Another important feature of the present invention is that the stretch forming operation disclosed permits the use of a predetermined alloy temper such as half hard aluminum and work stretching the metal to a full hard temper. This results in producing the desired conical section of revolution shape without any intermediate process of annealing or heat treating. Prior methods have almost uniformly required heat treatment of the metal after the spinning or work stretching process.

Reflectors of any size from 1 foot up to 20 feet in diameter may be made according to the present invention without the use of a back-up die. These reflectors are useful in areas of microwave communications,

radar, satellite tracking, and similar applications, where a high accuracy is required. Not only is a wide range of diameters possible to accurately reproduce, but the conical sections provided by the apparatus of this invention may be made from metal blanks of extremely thin material, for example, varying in thickness from a few millimeters up to many millimeters in thickness, depending on the metal and metal alloy of the blank. In addition to solid sheets or plates metal blanks of perforated sheet or plate metal may be used.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come Within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. A method of forming radiation reflectors comprising supporting a flat circular blank of radiation reflective material adjacent its outer edge on an annular support, aflixing first clamping means over said blank to clamp said flat blank to said annular support, rotating said blank and turning the outer edge of said blank over said annular support, removing said first clamping means, aflixing second clamping means over said blank to clamp the turned over edge of said blank to said annular support, rotating said clamped blank, causing a forming tool to move along a curved template radially inward of said rotating blank, and moving the inner end of said template toward said blank with each pass of said tool to cause increasingly greater deformatioin of said blank.

2. A method according to claim 1 wherein said forming tool is moved along a parabolic path.

3. A method according to claim 1 wherein said first clamping means includes a circular disc, and including the steps of placing the disc over said flat blank, andpressing the disc against said blank to tightly engage the outer edges of the blank between said disc and said annular support.

References Cited by the Examiner UNITED STATES PATENTS CHARLES W. LANHAM, Primary Examiner.

Claims

1. A METHOD OF FORMING RADIATION REFLECTORS COMPRISING SUPPORTING A FLAT CIRCUIT BLANK OF RADIATION REFLECTIVE MATERIAL ADJACENT ITS OUTER EDGE OF AN ANNULAR SUPPORT, AFFIXING FIRST CLAMPING MEANS OVER SAID BLANK TO CLAMP SAID FLAT BLANK TO SAID ANNULAR SUPPORT, ROTATING SAID BLANK AND TURNING THE OUTER EDGE OF SAID BLANK OVER SAID ANNULAR SUPPORT, REMOVING SAID FIRST CLAMPING MEANS, SAID ANNULAR SUPPORT, REMOVING SAID FIRST CLAMPING MEANS, THE TURNED OVER EDGE OF SAID BLANK TO SAID ANNULAR SUPPORT, ROTATING SAID CLAMP BLANK, CASING A FORMING TOOL TO MOVE ALONG A CURVED TEMPLATE RADIALLY INWARDLY OF SAID ROTATING BLANK, AND MOVING THE INNER END OF SAID TEMPLATE TOWARD SAID BLANK WITH EACH PASS OF SAID TOOL TO CAUSE INCREASINGLY GREATER DEFORMATION OF SAID BLANK.