Date of A pplication and filing Complete Specification: November 16, 1954.
769,466 No 33182/54 P A I D Application made in United States of America on December 30 1953 Complete Specification Published: March 6, 1957
Index at acceptance:-Classes 40 ( 8), WG; and 82 ( 2), Fi G 1, F 2 (H:M:P:T:Y:Z 3), F 4 (E:J:K:M:N:W).
International Classification:-C 23 c, H Oib.
Improvements relating to the Making of Precision Articles by Spray Processes We GENERAL ELECTRIC COMPANY, a Corporation of the State of New York United States of America having its office at Schenectady 5 State of New York United States of America do hereby declare the invention.
for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement:-
This invention relates to the manufacture of hollow or dished precision articles of great strength and requiring sharp and well-defined surfaces, such for instance as wave-guides for radar systems precision moulds and precision punches and dies.
Wave guides of the type used in radar "plumbing" systems must have sharp and well-defined inside surfaces Also it is frequently desriable that such radar wave guides have sharp curvatures with short radii Because of these requirements it has been the practice in the past to make wave guides from wrought metal However in many instances special technique and expensive equipment must be used in order to twist and shape the metal to meet the precise requirements needed in the finished product.
Precision moulds for castings have often in the past required expensive and complicated equipment for their fabrication The problems of economy and durability have been aggravated when the moulds are used for high temperature castings.
In the making of precision punches and dies for press-forming production parts, high strength materials, such as steel alloys, have proved to be the most durable However.
for many operations the cost and length of time required to make steel punches and dies prohibits their use and an inferior substitute material has been used.
It is accordingly an object of the invention to provide a simple and economical process for making precision articles in the form of consolidated spray metal structures which may if desired also incorporate ducts to lPrice facilitate cooling of the article during its use.
In accordance with the invention, a matrix or core of shape conforming to that of the desired precision article, is formed from a 50 suitable disposable material A thin coating of suitable metal is then applied to the core by metal spraying Reinforcing members, for example piano wire or other material having high tensile strength, are placed on 55 the coating and a filler or backing material, which may also be metal, is sprayed over the coating and reinforcing members so as to consolidate the same into an integral shell structure which is of sufficient thickness to 60 be self-supporting When it is desirable, cooling coils for circulation of a coolant may also be incorporated into the integral shell structure The disposable matrix or core may then be removed from the integral shell 65 structure.
The invention will be better understood from the following description taken in connection with the accompanying drawing in which: 70 Fig 1 which is a part elevation, part sectional view, illustrates the manufacture of a portion of a wave guide and a wave guide termination according to the invention; Fig 2 is a view showing a section taken 75 along line 2-2 of Fig 1; Fig 3 illustrates the manufacture of a precision mould in accordance with the invention; Fig 4 illustrates the manufacture of a pre 80 cision punch in accordance with the invention; Fig 5 is an elevation, partly in section, of the finished punch.
Referring more particularly to the draw 85 ings, a wave guide 10 and a wave guide termination 11 may be seen in Figs 1 and 2 as formed by spraying metal on a disposable core 12 The disposable core 12 is made from a disposable material, such as Wood's 90 metal, wood or plastic into a shape conforming to the desired internal shape of the wave I i I 2 769,466 guide and termination The core 12 is preferably carefully cleaned immediately prior to spraying for example, by very light blast cleaning or vapour-degreasing A thin coating of molten metal is then sprayed directly onto the disposable core to a thickness sufficient to make a conductive coating 13 This thickness may be as little as 00001 inch or even less That such thickness is satisfactory :0 is believed to be due to the nature of the conductivity along the coating surface which is according to the well-known skin effect This spraying may be accomplished by the use of a suitable spray gun The metal sprayed on the core should be electrically conductive and may be steel or its alloys, or non-ferrous materials, depending on the service intended and the melting point of the molten metal.
Silver is an admirable metal for use in the making of a wave guide since silver is a good conductor and since it is well-suited for the metal spraying process.
The termination 11 in its use for testing purposes and also portions of the wave guide itself, may be subjected to considerable stresses and also to hiah temperatures This is true because in testing operations the termination and the end portions of the wave guide must absorb all the energy normally transmitted through the wax'e guide and out through a lens in radar systems such energy is partly electrical, partly mechanical an ' pardy heat energy hence the stresses and high temperatures To strengthen the wave guide and termination, reinforcing members having high tensile strength are placed on the coating 13 The melting point of the reinforcing members 20 is preferably higher than that of the spray metal because otherwise the reinforcing members may melt entirely or in part and lose their strengthening characteristics However, the spray metal is not necessarily in an entirely molten condition and reinforcing members may be used which do not substantially melt upon contact with the spray metal even though the melting point of the reinforcing member is close to or even less than that of the spray metal Piano wire, for example has been found to be one suitable type of reinforcing member.
In order to provide for the dissipation of the high temperatures which may be generated within the wave guide and termination.
cooling coils may be built in Such a cooling coil 21 may be placed on the coating 13 in a suitable fashion, for example, by winding it around the coating leaving inlet and outlet portions of the coil exposed for the circulation of a suitable coolant Additional layers are then built up to form a strengthening backing 15 for the coating and to secure the reinforcing members 20 and the cooling coil 21 to the coating 13 by metal spraying.
e g by the use of a spray gun 14 These additional layers complete an integral self-supporting spray metal structure and may be of a relatively inexpensive backing material, for example, copper, zinc, or ferrous alloys The thickness of the backing 15 may be as much 70 as one-eighth of an inch using presently known spraying technique and metals However, as these techniques are improved, greater thicknesses may be practical.
After the spray metal structure of the wave 75 guide 10 and the wave guide termination II has been built up as described above to the desired thickness which is a thickness enabling the structure to be strong and self-supporting the disposable core is removed In 80 the event Wood's metal has been used as the disposable material the structure may be placed in boiling water and the Wood's metal melted out If wood has been used as the disposable material it may be chipped 85 out and if a plastic material has been used, it may be dissolved by solvents or warmed and removed Upon removal of the disposable core an inside facing is left which with a minimum co grinding provides a very ac 90 curate economical, and serviceable wave guide and wave guide termination surface.
Fi- 3 illustrates another embodiment of this intention as used in the making of high strenbth moulds for use in high temperature 95 castiwnrs As described in connection with Figs I and 2 a disposable core or matrix 30 mnay be formed of a disposable material and having a shape conforming to the shape of the desired cast product A thin spray metal 100 coating 31 may be built up by metal spraying onto the matrix 30 The melting point of the metal used in spraying must be higher than that of the casting material to be cast.
Molybdenum and tungsten are examples of 105 high temperature metals which are suitable for spraying This coating 31 need be only as thick as is required to withstand the high temperatures of the molten cast metal and since it is usually sprayed with a relatively 110 expensive metal it is preferably extremely thin Reinforcing members 20 and a cooling coil 21 may then be placed on the spray metal coating as described hereinabove and additional layers of a relatively inexpensive 115 backing metal may then be sprayed over the structure 31 the reinforcing members 20, and the cooling coil 21 to secure the members and coils to the coating and form an integral self-supporting spray metal structure 32 120 Upon removal of the disposable core, a high strength mould is left capable of handling high temperature castings as they may be cooled by circulating cooling fluid such as water through coil 21 125 Figs 4 and 5 illustrate a further embodiment of this invention as used in making punches A matrix or negative 40 is made up from an existing mock-up This matrix again may be made of a disposable material, 130 769,466 769,466 3 such as metal, plastic, wood, or plaster The matrix is then metal sprayed with a wear or abrasion resistant metal, such as high carbon steel or molybdenum, to form a thin coating 41 This coating 41 need be only thick enough to withstand the wear to which the punch is subjected, and for many purposes may be quite thin For example, where a punch will be used for only a few hundred punchings, an extremely thin coating of the more expensive, wear resistant metal will satisfactorily withstand the wear and impact stresses Reinforcing members 20 may be placed on the coating 41 as in previously described embodiments or may be tacked for temporary holding purposes, and additional layers of relatively inexpensive backing metal may be sprayed on the coating 41 covering the reinforcing members and securing them to the coating to form an integral self-supporting spray metal structure 42 The cavity thus formed may then be filled up with a material 43 (see Fig 5) having sufficient compressive strength, for example, metal.
concrete, plastic, or plaster, as the application may require Upon removal of the structure thus formed from the disposable matrix 40 and with a minimum of finishing, a high strength, economical punch is formed.