US3341432A

US3341432A - Method of making wave guides

Info

Publication number: US3341432A
Application number: US349981A
Authority: US
Inventors: Kadner Woldemar
Original assignee: International Standard Electric Corp
Current assignee: International Standard Electric Corp
Priority date: 1963-03-14
Filing date: 1964-03-06
Publication date: 1967-09-12
Anticipated expiration: 1984-09-12
Also published as: DE1256505B; GB1033325A

Description

United States Patent 3,341,432 METHOD OF MAKING WAVE GUIDES Woldemar Kadner, Birkenfeld, Wurttemberg, Germany,

assignor to International Standard Electric Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Mar. 6, 1964, Ser. No. 349,981 Claims priority, application Germany, Mar. 14, 1963,

5 Claims. (Cl. 204-99) ABSTRACT OF THE DISCLOSURE A wave guide is electro-formed by depositing metal on a lost mandrel which is then melted away, leaving the deposited shell. The interior of the shell is flushed with aquaregia, and other chemicals. The mandrel is made in a negative pressure atmosphere to improve the fineness of its surface finish.

This invention relates to methods of making wave guides and more particularly to methods of electroforming wave guides.

Generally, wave guides may be made by any number of well known processes, one of which is herein termed electroforming. By this term, I mean that the wave guide is formed by depositing material upon a mandrel, as by a plating or galvanizing-like process. Then the deposited material is removed from the mandrel to leave the shell of plating-which is the wave guide.

One way of electroforming involves the use of a permanent, high grade, well made steel mandrel on which the wave guide may be deposited 'by the electroforming process. This permanent mandrel process is very good because it gives not only an excellent surface on the inside of the wave guide, but also insures a precise size and shape. Unfortunately, however, the shell of plating material must be slipped off the permanent mandrel. This is not too hard to do if the mandrel is in the form of a smooth and simple shape. However, if the mandrel is a complicated shape, full of undercuts, recesses, protrusions,

.and the like, it may not be possible to slip the shell of plating material off the mandrel.

Another Way of electroforming wave guides involves the use of a lost mandrel which is destroyed during the electroforming process. For example, if a mandrel is made from a material having an extremely low melting point, it may be used to support the shell of plating material during the electroforming process. Then the mandrel may be melted away, thereby leaving only the shell of plating, which is the wave guide. This way almost any complicated shape may be formed. The invention relates to this lost mandrel process.

In the past, lost mandrels have been made of a metal alloy which melts at an extremely low temperature, such as an alloy which consists of bismuth-lead-tin-indium. However, experiments show that satisfactory results are not always possible with such a mandrel material for the following reasons:

(1) The bismuth-lead-tin-indium alloy sometimes combines itself with the plating material. Therefore, the mandrel cannot be completely removed from the shell of plating material by a melting process. A mechanical cleaning of the inside of the plating shell is neither economioally nor technically practical. Also, it is difficult to use a preliminary treatment-such as applying a plastic coating to the mandrel-because this coating would unpredictably change the size and dimensions of the various components.

(2) The only practical way of making a lost mandrel is by a molding process. But, this process often causes bubbles, cavities, and other irregularities which form on the surface of the lost mandrel due to an insuflicient wetting of the mold resulting from the relatively high surface tension of the liquid metal alloy.

In keeping with one aspect of the invention, these and other disadvantages are eliminated by a method of manufacture which enables the use of a conventional bismuthlead-tin-indium a-lloy as a lost mandrel material. First, the mandrel is made by molding it under an atmosphere having a negative pressure. During the electroforming of a wave guide, several layers of different kinds of plating material are deposited onto the mandrel whereby the interior and the exterior layers are silver and an intermediate layer is a base metal. The lost mandrel is then melted and its residues are eliminated by flushing with aqua regia. Since aqua regia dissolves almost every metal except silver, the wave guide is freed of all traces of the lost mandrel without damage to surface conditions.

A pressure chamber or box represents any suitable way of providing a negative atmosphere pressure. While any suitable means may be provided, I use a simple closed chamber which is connected to a vacuum pump. In one embodiment, the pump is able to evacuate the pressure chamber to a negative pressure of about a 10 mm. mercury-column. Any suitable input is arranged to convey a molten alloy having a low melting point into the negative pressure chamber through a valve-like arrangement. The valve is any suitable device for allowing entry of the molten alloy without loss of the negative pressure.

Inside the negative pressure chamber is a mold for making the lost mandrel. The extremely simple mold comprises a cope and a drag, joined together by any suitable means. The cope contains a pair of small drilled holes (perhaps 5 mm. in diameter) forming an ingot and a riser gate. When the cope and drag are fastened together, they form a matrix in which the lost mandrel is formed. This matrix may have any geometrical shape.

The ingot is positioned adjacent the input in a manner such that the molten alloy flows through the input ingot, fills the matrix and raises into the riser. The negative atmospheric pressure in the chamber insures a smooth surface on the lost mandrel free of bubbles, cavities, and other irregularities.

The mold is made of brass. The inside surfaces of this mold must be prepared with sufficient care to meet the exacting requirements of a wave guide surface quality, size, and dimensions. Furthermore, the mold must consist of as many individual parts as is necessary for a proper removal of the lost mandrel after it has hardened in the mold. Brass is used as mold material because it is relatively simple to fabricate and does not combine chemically with the lost mandrel material. Thus, the mold does not require any protective coat which would make it difiicult to meet the extremely precise wave guide requirements as to size and dimension. A further advantage of brass is that it does not oxidize when the mold is cooled down.

Since the lost mandrel is made from an alloy having a very low melting point (below centigrade), the thermal, linear expansion or contraction of the brass mold is of minor importance. Moreover, when the mold is made, allowance may be provided to correct any small dimensional changes which do occur as a function of temperature.

After it has hardened in the matrix, the lost mandrel is removed from the mold by separating the cope and the drag. At this time the residue of the ingot and riser may be broken off the mandrel, and any resulting surface irregularities are removed from the mandrel, as by grinding or filing. Since the mandrel can be molded or dieeast in its final size, it can be used for electroforming of wave guide components without further treatment.

The wave guide component is electroformed onto the 3 lost mandrel in any well-known manner, as by plating, for example. To obtain a smooth surface, the lost mandrel is moved in its electrolytic plating bath toward and away from the plating electrode.

As already mentioned, the lost mandrel will be melted out of the shell of plating material, and the residues of the mandrel material remaining on the inside surface of the plating shell will be dissolved by aqua regia. However, since aqua regia dissolves nearly all metals, except silver, the entire shell of plating must be embedded in a thin silver layer. This layer is obtained by plating the shell in successive layers of different kinds of metal. Therefore, the lost mandrel is first plated in a bath with a suitable silver solution to provide an inside layer of silver. T hereafter, the wave guide component receives its prescribed wall thickness of about 1.7 mm. in a bath of base material, such as a suitable copper solution. Finally, the wave guide is again silver-coated in the silver solution bath. This way, the lost mandrel can be melted out of the wave guide, and its residues can be eliminated by flushing with aqua regia, heated up to approximately 50 centigrade. Since the base metal is entirely embedded in silver, the aqua regia bath may be used without damaging the wave guide component.

When producing smaller components withless metallic volume, the production costs caused by the multi-layer plating process may not be justified. Thus, a solid silver plating shell is recommended.

Due to the aqua regia treatment, an oxide layer is caused at the wave guide components. This layer is finally flushed oiT with hydrochlorid, heated up to 50 centigrade.

While the principles of the invention have been described above in connection with specific apparatus and applications, it is to be understood that thi description is made only by way of example and not as a limitation on the scope of the invention.

I claim:

1. The method of manufacturing wave guides comprising the steps of molding a lost mandrel under negative atmospheric pressure from a material having a low melting point, said material being soluble in aqua regia, electroforming a wave guide on the lost mandrel by first plating the mandrel with a layer of silver, then with a layer of base met-a1, and following with another layer of silver whereby said base metal is encased in silver, melting the lost mandrel out of the shell of plating metal to leave a wave guide, and flushing theinterior of the wave guide with aqua regia to eliminate all residue of the lost mandrel.

2. The method of claim 1 including a final step of cleaning the interior of the wave guide with concentrated hydrochloric acid.

3. The method of claim 1 wherein said aqua regia is heated to approximately centigrade.

4. The method of claim 2 wherein said hydrochloric acid is heated to approximately 50 centigrade.

.5. The method of claim 1 wherein said lost mandrel is made from an alloy of bismuth-lead-tin and indium.

References Cited UNITED STATES PATENTS 1,320,770 11/1919 Lougheed 26634 2,490,193 12/1949 Barr 266-34 2,592,614 4/1952 Stoddard 204-9 OTHER REFERENCES Publicationi Safranek, W. H. Schickner, W. C., and Faust, C. L., Electroforming Aluminum Wave Guides Using Organo-Aluminum Plating Baths, Journal of the Electrochemical Society, vol. 99, No. 2, February 1952,

JOHN H. MACK, Primary Examiner. HOWARD S. WILLIAMS, Examiner.

D. R. VALENTINE, Assistant Examiner.

Claims

1. THE METHOD OF MANUFACTURING WAVE GUIDES COMPRISING THE STEPS OF MOLDING A LOST MANDREL UNDER NEGATIVE ATMOSPHERIC PRESSURE FROM A MATERIAL HAVING A LOW MELTING POINT, SAID MATERIAL BEING SOLUBLE IN AQUA REGIA, ELECTROFORMING A WAVE GUIDE ON THE LOST MANDREL BY FIRST PLATING THE MANDREL WITH A LAYER OF SILVER, THEN WITH A LAYER OF BASE METAL, AND FOLLOWING WITH ANOTHER LAYER OF SILVER WHEREBY SAID BASE METAL IS ENCASED IN SILVER, MELTING THE LOST MANDREL OUT OF THE SHELL OF PLATING METAL TO LEAVE A WAVE GUIDE, AND FLUSHING THE INTERIOR OF THE WAVE GUIDE WITH AQUA REGIA TO ELIMINATE ALL RESIDUE OF THE LOST MANDREL.