GB2246580A

GB2246580A - Metal components

Info

Publication number: GB2246580A
Application number: GB8920765A
Authority: GB
Inventors: Brian Lynch
Original assignee: British Aerospace PLC
Current assignee: BAE Systems PLC
Priority date: 1989-09-13
Filing date: 1989-09-13
Publication date: 1992-02-05
Also published as: GB8920765D0

Abstract

The component, for electronic or optical equipment, is made by forming a metal e.g. aluminium mandrel having portions shaped to match the component. The component is formed on the mandrel by electro-deposition of nickel, copper or nickel on copper and then the mandrel is dissolved using a suitable etchant e.g. potassium hydroxide or hydrochloric acid which does not attack the metal of the component. The component may be a W band radar reflector dish, Fig 1 (mandrel Figs 2-4) or flexible waveguide (Fig 5). Selective covering during electro-deposition allows formation of different thicknesses. <IMAGE>

Description

METAL COMPONENTS FOR ELECTRONIC AND/OR OPTICAL EQUIPMENT This invention relates to metal components for electronic and or optical equipment, more particularly but not exclusively for W-band radio frequency equipment such as radar homing heads for missiles.

For this application, metal components such as sub-reflector dishes, waveguides and such are quite small and have to be made and positioned very accurately. The known manufacturing methods, eg normal machining of parts which are then assembled into components, may not be able to achieve the desired specification.

According to the invention, there is provided a method of making a metal component, for example a three-dimensional component for electronic or optical equipment, in which method there is made a metal mandrel having portions shaped to match the component and then the component is formed on the mandrel by electro-deposition and then the mandrel is dissolved using a suitable etchant which does not attack the metal of the component for electronic and/or optical equipment in which method there is made a metal mandrel having portions shaped to match the component and then the component is formed on the mandrel by electro-deposition and then the mandrel is dissolved using a suitable etchant which does not attack the metal of the component.

Reference will now be made, by way of example, to the accompanying drawings, in which:- Figure 1 is a perspective view of a one-piece sub-reflector) support component for use in a radar homing head (not shown) of a guided projectile (also not shown), Figures 2 and 3 are a sectional elevation and an end view of a mandrel used for making the figure 1 component, Figure 4 is a sectional elevation of the mandrel with the partly-made component on it, and Figure 5 is a sectional elevation of a flexible wave guide and a mandrel for making the waveguide.

The sub-reflectorjsupport component comprises a cylindrical mounting collar 1 and an RF reflector dish 2 connected to the collar 1 by way of four straight support legs 3. The legs 3 extend from equi-spaced positions around one end of the collar 1 to similarly equi-spaced positions around the periphery of dish 2. The dish 2 has a diameter greater than that of the collar 1 so that, with increasing distance from the collar, the distance between each two opposite ones of the legs 3 increases up to the dish diameter.

The dish 2 has a complex cross-sectional profile designed to give the desired reflection and abberation-reduction characteristics appropriate to its situation - the profile illustrated is by way of example only.

To ensure positional accuracy of the dish 2 relative to the collar 1, and to give lightness of construction while achieving the strength necessary to withstand acceleration forces experienced during launch of the projectile, the sub-reflector/support component is made in one piece by electro-forming on an aluminium mandrel shown in figures 2 and 3.

The mandrel 4 comprises two turned parts 5 and 6.

The part 5 is cylindrical and has a larger outer diameter at one end 7 than at the other end 8, the surface of the part stepping down from the larger to the smaller diameter at a position 9 about half way along the part 5 from the larger diameter end 7.

Leading into this larger diameter end 7, there is an axial bore 10 which, near the position 9, steps down in diameter and then continues through to the other end 8 of the part 5. A portion 11 of the narrower diameter section of the bore 10, leading in from the end 8, is threaded for engagement with a workpiece holder of a machine tool (not shown).

The part 6 of the mandrel is generally conical and has four slots 12 with radiused floors 20 milled into its curved outer surface at equi-spaced positions around the central axis of the part. The slots extend, in planes containing the central axis, from one end of the part 6 to the other end. The larger diameter end face of the part 6 is machined for this face to define a dish shaped space 13 matching the desired cross-sectional profile of the dish 2 while, near the other end, a portion 14 of the part 6 is turned down to a cylindrical shape for fitting into the larger diameter section of the bore 10 in mandrel part 5. Further slots 15 are machined into the periphery of the larger diameter end face of the part 6 in alignment with and, at one end, connected to respective ones of the slots 12 while opening into the dish shaped space 13 at their other ends.

After making the two mandrel parts 5 and 6, the portion 14 of part 6 is engaged within the bore 10 as shown in figure 2 and, with a quantity of electrically conductive adhesive 16, for example silver loaded epoxy resin, interposed to fix the two parts together. The machining of the dish shaped space in the larger end face of part 6 could be done after the two parts have been fixed together if required.

The reason for making the mandrel in two parts is to allow easy machining of the slots 12 in the part 6 without cutting into the outer surface of the larger diameter end of the part 5.

Having made and assembled the mandrel, the part 6 and the larger diameter portion of part 5 of the mandrel is immersed in a bath of electrolyte and a deposit of nickel built up thereon.

The section 17 of the mandrel part 5 which is not to receive any deposit of nickel (see figure 4), is masked as appropriate. In addition, once the required thickness of the dish 2 has been deposited, the end face of the part 6 is also masked off so that the dish retains that thickness while the rest of the component continues to be made. Eventually, the deposits in the slots 12 and on the curved surface of part 6 and the unmasked surface of part 5 will have been built up to greater than the thicknesses required and then the mandrel with its nickel covering is removed from the bath and machined down so as to leave only the deposits within slots 12, which will form the legs 3, and the collar 1 along with the dish 2. The aluminium mandrel is then dissolved away by immersion in a suitable etchant, say strong potassium hydroxide or sodium hydroxide at 80 to 900C.The component is agitated during the removal process and is also periodically removed, washed and subjected to an ultrasonic cleaning process.

The same mandrel removal process could be used if the reflectorlsupport component had been made of electroformed copper rather than nickel although, for more speed, it would also then be possible to use concentrated hydrochloric acid as the aluminium etchant.

To reduce the time required to remove the mandrel, the mandrel could be hollowed out for example by providing a wide axial bore extending into the part 6 from its narrow end.

The manufacturing process described could also be used for making components for optical equipment, for example instead of being an RF sub-reflector, the dish 2 could comprise a suitable material or be suitably treated to make it optically reflective and then the component would form say a sub-reflector for an infra-red sensitive homing head.

The illustrated shape of the reflector! support component could be changed. For example, it could have two or three legs 3 instead of four or it could have more than four legs. As will have been appreciated by those skilled in the art, the collar 1 constitutes a mounting by which the component is fixed into a radar homing head, the collar being engaged in a fixed predetermined relationship to an item with which the reflector dish 2 interacts, eg an output waveguide, main antenna dish, detector or the like.Using the described method of making the component and taking appropriate care in so doing, the fixed component very accurately matches the dimensions of the mandrel and, provided the mandrel is made very accurately, ie to so-called "optical limits" which can be achieved using modern machine tools, it is possible to make the component with cylindrical and concentricity tolerances also to optical limits. If that is achieved, then there follows the very major cost reducing advantage that final assembly of the homing head does not involve a lot of customisation and adjustment to give accurate collimation of the reflector with its interacting item.

Figure 5 shows a turned elongate mandrel 50 made of aluminium and having a series of radiused ribs 51 closely spaced along its axis. A deposit of copper is formed by electrolysis on the mandrel and then a thicker deposit of nickel, again by electrolysis, up to a total thickness equal to that required for the eventual component, namely a flexible waveguide for W-band RF equipment. Before the electrolytic plating of the copper and nickel, the mandrel is ultrasonically cleaned and chemically polished to ensure a good surface for the plating. After the electrolytic plating, the mandrel is dissolved as before, again with periodic ultrasonic cleaning, so as to leave just the copper! nickel component.

Claims

CLAIM

1. A method of making a metal component, for example a three-dimensional component for electronic or optical equipment, in which method there is made a metal mandrel having portions shaped to match the component and then the component is formed on the mandrel by electro-deposition and then the mandrel is dissolved using a suitable etchant which does not attack the metal of the component.