GB2077639A

GB2077639A - Machining of the internal surface of a conical radome

Info

Publication number: GB2077639A
Application number: GB8015089A
Authority: GB
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1980-05-12
Filing date: 1980-05-12
Publication date: 1981-12-23
Also published as: GB2077639B

Abstract

In machining the inner core of a radome (4) according to a given ogival curve, a conical grinding head associated with a template follower (6) and a template (3) having a profile corresponding to the curve is employed in the final forming of the said inner cone, the grinding head being so shaped that its curvature at any common point of contact along the curve is greater than the curvature of the curve at that point. Preferably the grinding head incorporates a coolant manifold and spreader orifices toward the apex thereof. <IMAGE>

Description

SPECIFICATION Improvements relating to machining equipment This invention relates to the machining of a curved surface and in particular to the machining of the internal surface of a conical radome.

A radome is a precision component made of ceramic material which must be machined using diamond plated grinding heads. Normally the machining of the internal cone of a radome is a two stage process necessitating the use of two forms of grinding head. In the first stage material is machined from the mouth of the inner cone for approximately three quarters of the radome length using a disc shaped grinding head. Several passes are made over the stated length in accordance with a template until the curve of the cone matches the profile of the template. The remaining vertex portion of the internal cone is machined using a domed grinding head the dimensions of which correspond to those desired for the inner cone.

A problem arises in the machining of the vertex portion of the inner cone in that large reaction forces are generated as a result of the full form contact of the domed grinding head.

These forces lead to an unacceptable vibration of the grinding head. Also an overheating problem is incurred because the full form of the head makes the vertex portion inaccessible to coolant.

It is an object of the present invention to reduce the high reaction forces generated by the domed grinding head, and to provide a means of improving head dissipation when machining the vertex portion of the inner cone.

The present invention is an apparatus for machining the inner cone of a radome according to a given ogival curve, the apparatus comprises a template having a profile corresponding to the curve, a template follower, and a conical grinding head associated with the follower and arranged to trace the curve as the follower traverses the template profile, the grinding head being so shaped that its curvature at any common point of contact along the curve is greater than the curvature of the curve at that point. Preferably the follower has a profile which corresponds to the cutting profile of the conical grinding head.

According to a feature of the present invention the grinding head has a chamber therein adapted to receive coolant, and at least one capillary leading from the chamber to the exterior of the head. Preferably an even number of capillaries are used with outlets which are circumferentially equi-spaced. The capillaries may be sloped outwardly from the chamber and towards the forward end of the conical grinding head.

A radome machining apparatus in accordance with the invention will now be described by way of example with reference to the following figures of which: Figure 1 is a plan view of the apparatus with a radome shown in section; and Figure 2 is a sectional view through a conical grinding grinding head.

Referring to Fig. 1 the apparatus comprises a saddle assembly 1 forming part of a lathe 2, and a template 3 rigidly attached to the lathe bed. A radome 4 is fixed to rotate with the spindle of the lathe 2.

The saddle assembly 1 includes a crossslide 5 having mounted thereon a template follower 6 and a motor drive unit 7. The motor drive unit is geared to drive a projecting mandril 8 at high speed, and the mandril is adapted to conduct coolant delivered to a gland 9.

The template follower 6 is selected to correspond in form to the shape of the tool being used. The follower is connected to a sensing unit 10 such that the pressure generated between the follower and the template 3 activates a hydraulic drive unit 11 which translates the cross-slide 5 to the required position.

The template 3 has a profile 12 which corresponds to a desired curve 13 of the radome 4.

The grinding of the inner surface 14 of the radome 4 is a two stage process requiring the use of two forms of grinding head, one for each stage. In the first stage a conventional disc shaped grinding head 15 (not shown) is used, the periphery of which is diamond plated.

In the second stage a conical grinding head 20, as shown in Fig. 2, having a stem 21 is used. The stem is adapted to be held in the mandril 8 and has a bore 22 therein leading to a chamber 23 in the grinding head 20.

Four forwardly sloping capillaries 24, with outlets which are equi-spaced circumferentially, lead from the chamber 23 to the exterior of the head 20. The profile of the head 20 is such that when used to machine the radome 4 its curvature at any point of contact along the curve of the radome 4 is smaller than the curvature of the radome at that point.

In the first machining stage the disc shaped grinding head is secured in the mandril 8 and an appropriate template is used (not shown).

The radome 4 is then rotated and the motor drive unit 7 activated for rotation of the grinding head. The saddle assembly 1 is traversed towards the radome 4 and the follower makes contact with the profile 12 of the template 3 to activate the hydraulic drive unit 11 so that the grinding head moves along the required cutting path. The apparatus is set such that the disc-shaped grinding head 15 takes a cut from the inner surface of the radome for approximately three quarters of the radome length. This process is repeated until the internal dimensions of the radome 4 are marginally under-size.

The disc-shaped grinding head is then replaced by the conical grinding head 20 and the template follower 6 is fitted which has a profile equivalent to that of the conical grinding head.

The grinding head 20 is fed into the ra dome 4 to make point contact with the inner surface which is then machined in accordance with the template profile, the point contact ensures that the cutting forces are considerably less than they would have been had the grinding head been of the full form type, and as a result tool vibration is reduced to an acceptable level. When the grinding head 20 moves into the vertex portion of the inner cone 14 coolant is supplied to the gland 9 and reaches the chamber 23 via the bore of the mandril 8. The coolant in the chamber is then fed to the exterior of the grinding head to be supplied to the cutting surface of the head. Generated heat is thus dissipated from the radome until the machining of the inner cone is complete.

It will be appreciated that the invention can take several forms, for instance the template may be in the form of a cam. Alternatively the follower may comprise a microprocessor system which traverses the tool along the required profile.

Claims

1. Apparatus for machining the inner cone of a radome according to a given ogival curve, and comprising a template having a profile corresponding to the curve, a template follower, and a conical grinding head associated with the follower, and arranged to traces the curve as the follower traverses the template profile.

2. Apparatus as claimed in claim 1 and wherein the follower has a profile which corresponds to the cutting profile of the conical grinding head.

3. Apparatus as claimed in claim 1 or claim 2 and wherein the grinding head has a chamber therein adapted to receive coolant, and at least one capillary leading from the chamber to the exterior of the head.

4. Apparatus as claiimed in claim 3 and wherein an even number of capillaries is used with outlets which are circumferentially equispaced.

5. Apparatus as claimed in claim 3 or claim 4 and wherein the capillaries are sloped outwardly from the chamber and towards the forward end of the conical grinding head.

6. A process of machining the inner cone of a radome according to a given ogival curve and including the step of grinding at least part of the said inner cone with a conical grinding head linked to a template follower following a template which has a profile corresponding to the curve, the grinding head being so shaped that its curvature at any common point of contact along the curve is greater than the curvature of the curve at that point.

7. A process as claimed in claim 6 and wherein, the grinding head having a chamber therein adapted to receive coolant, and at least one capillary leading from the chamber to the exterior of the head, coolant is pumped through the grinding head.

8. A process as claimed in claim 6 or claim 7 and wherein the said step is a step subsequent to one in which a disc-shaped grinding wheel is used to form at least part of the cone interior almost to the required dimensions.

9. Apparatus for machining the inner cone of a radome according to a given ogival curve, substantially as hereinbefore described with reference to the accompanying drawings.

10. A process of machining the inner cone of a radome according to a given ogival curve, substantially as hereinbefore described with reference to the accompanying drawings.