CA1167628A - Method and apparatus for forming conical surfaces having curved longitudinal axes - Google Patents

Abstract

ABSTRACT
A method for representing or producing externally convex or internally concave conical surfaces is disclosed, whereby an instrument rotates about an axis in relation to a workpiece, while the workpiece is moved along a curved path parallel with the curved longitudinal axis of a body to be represented or produced. An apparatus for representing or producing an article by such a method, has a frame equipped with a curved guide, a mount for securing a workpiece being positioned to travel along the guide. An instrument carrier is mounted on the frame for rotation about an axis which is formed at a tangent with the curved longitudinal axis of the body to be represented or produced. Means are provided for simultaneously rotating the instrument carrier, adjusting the radius of the instrument path, and moving the mount along the guide.

Description

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This invention relates to the representation and reproduction of irregular conical surfaces.
In particular, it relates to a method and an apparatus for measuring or producing externally convex ~r internally CQnca`Ve conical surfaces in tubular bodies.
Methods of this kind are used to draw, produce and measure the shapes and dimensions of geometrical bodies to a high level of accuracy.
German Patent No. 619,187 describes an apparatus for machining of non-circular ingot moulds. The apparatus may be used for maching non-parallel internal surfaces by means of a transversely controlled bar carrying a cutting tool which is displaceable along the longitudinal axis of the workpiece, the bar being held in transversely displaceable brackets. The brackets may be attached to a common straight edge which is spaced from the surfaces to be formed through tie rods connec-ted to rockers. Using this apparatus only regular co*es can be produced.
In certain applications, however, it is necessary to draw, produce and measure conical surfaces and conical bodies whose longitudinal axes are curved. It should be borne in mind in connection with the present invention that the limiting case of straight line, i.e. a curve of infinite radius, does not arise and is therefore excluded from the invention. On the other hand, radii of curvature of several metres may be desired.
The present invention covers radii of curvature preferably of the order of about 2 to 20 meters.
This is a range suitable, for example, for use in the production of curved continuous-casting moulds used in the casting of molten ste,el or non-ferrous metals. The use of continuous-casting moulds oscillating upon a curved track requires a continuous-casting mould having a curved longitudinal axis.

It is also known to produce continuous-casting moulds ~,~ ., ;'7ti;~
from straight copper tube whereby the copper tube is positioned on a curved mandrel, and the final form of a curved hollow cone is shaped by explosive shaping. This process is in current use.
However, the difficulty with this process is that the accuracy of the outcome depends entirely upon the precision of the mandrel.
Mandrels of this kind can be produced only by a copying process using a planing tool or a milling tool which reproduces the mandrel to the required size from a pattern, a process which leads to inaccuracies. Even the pattern cannot as yet be produced with geometrical accuracy on a machine tool, but must be produced manually by pattern-making technology. Thus the problem of producing a curved mandrel of sufficient accuracy remains unsolved.
Basically, the present invention employs a method in which the workpiece or body to be machined moves in a curve relative to a generatrix which rotates while the radius thereof is continuously adjusted as a function of the motion of the workpiece. In this way, a three-dimensional task is reduced to two-dimensional components.
The present invention provides a method for producing a tapered internal surface on a workpiece the workpiece tapering from one end to the other and having an arcuately curved reference axis, comprising moving the workpiece on which the sur-face is to be produced along an arc of a circle, moving a cutting tool in rotation about an axis which is tangential to said arc at a point lying in the plane in which the tool rotates, and moving a control rod to progressively vary the distance between the cutting edge of the tool and the centre of rotation of the tool, thereby to cause the cutting edge to follow a helical-spiral path relative to the workpiece and form on the workpiece a surface 3~ with an axis of symmetry curved about the centre of said circle.
By the use of this invention it is possible to represent or to produce geometrical~y ideal solids of revolution which are - internally or externally conical and have a curved longitudinal 6Z~3 dXiS. One particular advantage of this method is that additional reproductions are produced more accurately and less expensively than by the previously known method.
The invention may be advantageously employed to produce ~ ' : : :
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cross-sectionally circular, axially curved conical bodies and cross-sectionally polygonal, axially curved, conical bodies.
In the case of bodies of polygonal cross-section provision is ma~de for the body to be formed by a stepwise rotation of the tool around the periphery of the convex or concave surface to be produced, wherein the workpiece is moved along the curved path against the tip of the cutting tool to produce cuts in the longitudinal direction of the cone.
In the case of bodies of circular or oval cross-section the generatrix preferably comprises at least one cutting tool which rotates in a fixed plane and having an adjustable radius.
The ratio between the radial distance travelled by the tool and the workpiece per unit of time can suitably be 1:1 or less.
Provision is also made in the invention for selecting a circular configuration for the longitudinal axis.
The method according to the invention may also be used as a measuring procedure in checking the body for deviations relative to a prescribed geometrical shape or prescribed dimen-sions.
The present invention also provides an apparatus forproducing an internal surface on a workpiece, the surface tapering from one end of the workpiece to the other, comprising a machine frame supporting a work holder displaceable along an arcuately curved guide, a rotary tool holder having an axis of rotation which is a tangent or parallel to a tangent to an arc, the centre of which coincides with the centre of curvature of the guide, the tool holder bearing a cutting tool or measuring instrument which extends perpendicularly to the axis of rotation of the tool holder and is adjustable relative to the workpiece by means of a movable control rod.
The apparatus according to the invention opens up the '7~8 possibility of producing in a single operation a particular spherical, hollow body which is geometrically accurate to tolerance permissible by the limitations of the apparatus.
The essence of the apparatus is that it is capable of carrying out three movement simultaneous; ~a~ rotating the tool about its longitudinal axis; (b~ advancing the workpiece in the mount along the curved guide; ~c~ advancing the tool radially in order to produce the cone.
The tool carrier is preferably a shaft which rotates with the tool and has attached thereto means for changing the radius of the cutting tool. Simple means are provided at each end of the shaft to allow it to rotate so that the method according to the invention may be carried out with suitably modified conventional machines such as boring mills.
In one em~odiment of the invention the means for changing the radius of the cutting tool is in the form of a control rod positioned within a hollow shaft and adapted to move hack and forth as a function of the movement of the mount. The rod is cone-shaped corresponding to the prescribed conicity of the body to be formed and the cutting tool rests on the wall of the cone.
In order to produce conical bodies having external conical surfaces the apparatus according to the invention can be suitably equipped with means for changing the radius of the cutting tool comprising an external guide surrounding the body, the mount and the shaft and having the cutting tool bearing upon the conical internal surface of the guide which is mounted to be displaceable in the direction of the axis of movement.
The quality of the surfaces to be produced can be further improved when the cutting tool consists of multiple bits arranged consecutively in the cutting direction and adjusted to various depths of cut.
In order to absorb the forces arising during the machining of a metal body, provision is made for the cutting , - 4 -.

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tool to bear against the control rod or guide ~y means of a support.
The absorption of cutting forces of high magnitude produced by deep cuts and high cutting speeds can ~e further improved when such a support comprises one or more rollers, the axes of which are at right angles to the direction of mot;on of the control rod, or a flat sliding element on the control rod, having its bearing surface conforming to the surface of t~e rod.
The tool carrier and the control rod can suitably be driven in synchronism If the method according to the invention is to be used for measurement the cutting tool is replaced by a measuring device, preferably one having a dial indicator sensing lever which bears upon the control bar or the external guide.
Several exemplary em~odiments of the present invention are illustrated in the accompanying drawings, in which:
Fig. 1 is a plan view of an apparatus according to the invention for producing a body having a curved longitudinal axis, an internally conical surface, and a circular cross-section;
Fig. 2 is a sectional side view of the method according to the invention as used for measurement.
Fig. 3 is a plan view of an apparatus according to the invention for producing a hody having a curved longitudinal axis, an externally conical surface, and a circular cross-section;
Fig. 4 is a cross-section through a control rod of circular cross-section and with a supported cutting tool;
Fig. 5 is a cross-section through a polygonal control rod with support for the cutting tool.
Referring to the drawings in detail, Fig. 1 illustrates a machine stand 1 which may suitably be a boring mill stand, supporting a mount 2, for a body 3 which is to be measured or machined. The mount 2 slides in a curved guide 4 which describes an arc having a curvature 4a. The centre of the arc 4a may lie .

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~ ternally of the machine stand 1. A longltudinal axis 5 of the body 3 forms at a point 5a a tangent to an axis 4b of the guide 4.
The axis 4b need not necessarily coincide with the central axis of the guide 4, but it generally coincides with the longitudinal axis 5 of the body 3. A tool carrier 6 is equipped with a cutting tool 7, the cutting direction of which is at right angles to an axis 8 of the tool carrier 6.
According to Figs. 1 and 3, a shaft 6a comprises a hollow shaft 6b. In Fig. la, a control rod 10 is positioned in the interior of the shaft 6b. The ends of the control rod 10, not visible in the drawing, are mounted in rotating bearings at least one end engaging with a rotating or sliding drive. The control rod 10 may be displaced longitudinally in a direction lOa from the initial position shown. The shaft 6b on the other hand is fixed axially with the tool 7. When the mount 2 is slid along the guide 4 to a point exceeding the length of the body 3 the sliding drive (not shown~ changes over to a position corres-pond ing to the starting position shown. The speed of the body 3 along the axis 4b is a function of the speed of the control rod 10. The control rod 10 has a conically shaped side wall lab and an inner wall 3a of the body 3 thus acquires a shape which is a function of the shape of the side wall lOb.
According to Fig. 3 control means are arranged externally of the hollow shaft 6b corresponding to the body 3 to be produced having external conical surfaces 3a. A guide 11 has a conical internal surface 12, against which the cutting - tool 7 bears. The guide 11 is positioned to slide along the path of the axis 4b in such a manner that an axis 8 is always tangential to the axis 4b at the point 5a where the cutting tool 7 is attached perpendicularly to the axis 8. Thus the guide 11 moves together with the mount 2 which carries the body

3 by means of holders on end faces 3b, 3c (not shown~.

The cutting tool 7 is shown in Figs. 1, 3, 4 and 5 a5 a bit ~a which by means of a supporting element 13 bears against the control rod 10 (Fig. 1) or the guide 11 tFig~ 3).
Since the cutting forces acting on the bit 7a vary from one type of operation to another, the structure of the support element 13 can be altered accordingly.
Referring to Fig. 4 the control rod 10 has a circular cross-section and may b~ rotated. The bit 7a is supported on a spherical roller 14 having an axis 14a which runs parallel with the axis 8. This type of support is used when the cross-sectionally circular control rod 10 moves longitudinally in a direction lOa (see Fig. 1) and the tool carrier 6 is longitu-dinally stationary but rotates in synchronization with the control rod 10 during the production of surfaces such as those of body 3 in Fig. 1. For such a body, the support as shown in Fig. 5 may also be used. A cross-sectionally polygonal control bar 10 moves longitudinally in the direction lOa (Fig. 1) and rotates simultaneously with the longitudinally fixed tool carrier 6.
If the body 3 to be produced is of polygonal, for example, rectangular cross-section, the polygonal control rod 10 moves longitudinally in the direction lOa, while the tool carrier 6 remains longitudinally stationary and is moved stepwise laterally together with the control rod 10 over the polygonal profile in relation to the body 3 and in a direction opposite to the direction of movement thereof. Particularly heavy cutting forces can be absorbed by a structure such as shown in Fig. 5 wherein a roller 15 is mounted to rotate on a bit 7a about an axis l5a which is perpendicular to an axis 8.
In Fig. 2 the cutting tool 7 is replaced by a measuring gauge 16 with a dial indicator 17 and a sensing lever 17a which bears upon the control rod 10 or, in the case of Fig. 3, on the outer guide 11.
The apparatus described is employed to effect the method ~ i'7ti2~ ~
of the invention in the following manner. While the body 3 and ' its mount ~ travel along the path at the curved guide 4, in a direction opposite to the direction lOa, the tool carrier 6 with the cutting tool 7 is rotated about the axis 8 (Figs. 1 and 3) while the control rod 10 is simultaneously advanced in the direction lOa. This results in the tool 7 producing the irregular surface 3a (in Fig. 1 an internal concaYe cone, in ~ig. 3 an external convex cone).
Internal or external polygonal conicities are produced by a method in which the cutting tool 7 is a linearly moving tool in the form of a planing bit. The latter (not shown) is moved stepwise around the periphery of the polygon and at each stop location is moved in a direction opposite to the linear movement of the body 3 and parallel to that of the axis 4b.

Claims (14)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of producing a tapered internal surface on a workpiece the workpiece tapering from one end to the other and having an arcuately curved reference axis, comprising moving the workpiece on which the surface is to be produced along an arc of a circle, moving a cutting tool in rotation about an axis which is tangential to said arc at a point lying in the plane in which the tool rotates, and moving a control rod to progressively vary the distance between the cutting edge of the tool and the centre of rotation of the tool, thereby to cause the cutting edge to follow a helical-spiral path relative to the workpiece and form on the workpiece a surface with an axis of symmetry curved about the centre of said circle.

2. A method according to claim 1, wherein the generatrix is defined by a rotational movement.

3. A method according to claim 1, wherein the generatrix is defined by a linear movement taking place stepwise across the surface and opposed to an individual curved movement of the workpiece.

4. A method according to claim 1, wherein the generatrix is formed by at least one rotary cutting tool which is axially stationary and is adjusted radially of the axis.

5. A method according to claim 3, wherein the distance by which the tool and workpiece are displaced per unit time are in the ratio of 1:1 or less than 1:1.

6. A method according to any one of claims 1, 2 and 3, wherein the workpiece is moved along an arc of a circle during the machining or measuring operation.

7. An apparatus for producing an internal surface on a workpiece, the surface tapering from one end of the workpiece to the other, comprising a machine frame supporting a work holder displaceable along an arcuately curved guide, a rotary tool holder having an axis of rotation which is a tangent or parallel to a tangent to an arc, the centre of which coincides with the centre of curvature of the guide, the tool holder bearing a cutting tool or measuring instrument which extends perpendicularly to the axis of rotation of the tool holder and is adjustable relative to the workpiece by means of a movable control rod.

8. An apparatus according to claim 7, wherein the tool holder comprises a shaft, the control rod being provided internally or externally of the shaft.

9. An apparatus according to claim 8, wherein the control rod is arranged within the shaft and is movable axially as a function of movement of the work holder.

10. Apparatus according to claim 9, wherein the control rod has a tapered guide portion, the angle of said taper corresponding to that to be formed or measured on the workpiece, the cutting tool bearing directly or indirectly against the guide portion on the control rod.

11. An apparatus according to claim 8, wherein the control means comprises a guide in surrounding relationship to the workpiece, work holder and tool holder, the guide having a tapered internal guide surface against which the cutting tool or measuring instrument is supported, the guide being movable in the direction of the axis of movement of the work holder.

12. An apparatus according to any one of claims 7, 8 and 9, wherein the cutting tool comprises a plurality of cutting chisels arranged to follow each other in the cutting direction and disposed for various cutting depths.

13. An apparatus according to claim 7, wherein the cutting tool bears against control means through the intermediary of a support element.

14. An apparatus according to claim 13, wherein the cutting tool is supported by means of at least one roller whose axis extends transversely to the direction of movement of the control means or a plane sliding body on the control means, the cross-sectional shape of the control means corresponding to that of the surface to be produced, and the tool holder and control means being drivable synchronously.