GB2077152A

GB2077152A - Machining or measuring tapering surfaces

Info

Publication number: GB2077152A
Application number: GB8115500A
Authority: GB
Original assignee: Mannesmann AG
Current assignee: Vodafone GmbH
Priority date: 1980-05-31
Filing date: 1981-05-20
Publication date: 1981-12-16
Also published as: JPS5754005A; DE3020795A1; GB2077152B; FR2483294B1; DE3020795C2; FR2483294A1

Abstract

A workpiece 3 is formed with an internal or external surface 3a which tapers frusto-conically from one end of the workpiece to the other and has an arcuate axis of symmetry 5, by moving the workpiece along an arcuate path 4b relative to a rotary cutting tool 7a having an axis of rotation 8 which is tangential to the arcuate axis 4b at a point 5a constituted by the centre of rotation of the cutting edge of the tool. The tool is radially expanded or controlled by relative movement of a tapered shaft 10 or a tapered bore tool support. A planing tool may used to form a polygonal cross-section surface, again with a radial variation and having a curved axis. The already machined surface may be measured for divergences by a clock gauge constructing analogous to this tool. <IMAGE>

Description

SPECIFICATION Improvements in operations concerning tapering surfaces In various industries, it is necessary to produce or measure tapering internal or external workpiece surfaces with a high degree of accuracy. Thus, German Patent Specification No. 619 187, for example, proposes an apparatus for the manufacture of a mould or similar workpiece but which, by its construction, is incapable of forming a tapering surface other than a right, circular conical surface. However, in some industries, use is made of components having frusto-conical surfaces, the axes of which are curved lines.

An example of such a component is a mould for the continuous casting of strands of steel and non-ferrous metals. A mould of this type consists of a body through which extends a passage, the surface of which tapers conically or otherwise, and has an axis of symmetry with a radius of curvature measured in metres. Consequently, there is a need for a method and apparatus capable of producing frusto-conical and other tapering surfaces having axes with curvatures in the approximate range of radii from 2 to 20 metres or more, and of measuring the accuracy of such surfaces. The theoretical limiting case of an infinite radius of curvature does not occur in connection with this type of product, and is excluded from consideration, references herein to a curved axis meaning a curve of finite radius.

It is known to make a mould for this purpose from a length of copper tube which is shaped around a curved mandrel and given hollow frusto-conical form with a curved axis by explosion forming. However, the dimensional precision of a mould made in this way depends upon the accuracy with which the mandrel is itself produced and at the present time the problem of forming the mandrel with adequate precision has not yet been solved.

To overcome this problem, there is proposed herein a method of producing or measuring a surface of a workpiece, the surface tapering from one end of the workpiece towards the other and having a curved axis (referred to herein as the reference axis), wherein the workpiece is moved along a path having a defined centre of curvature, and a measuring or machining means is moved along a generatrix, the distance of which from the reference axis is adjusted during the machining or measuring operation. Although the present proposal is particularly concerned with the production and measuring of internal surfaces, such as the surface of a bore or passage through a workpiece, it is also relevant to tapering external surfaces, and within the scope of the present proposal, a workpiece may be simultaneously operated upon internally and externally.The proposed method is based upon the splitting of a spherical geometric object into two geometric objects having a functional relationship to each other and it permits, for example, surfaces of revolution to be described ideally geometrically or to be produced internally and/or externally with curved reference axes. A particular advantage of the proposed method is that it may be used repetitively to produce workpieces which are far more accurate than those which could hitherto be produced individually.

The proposed method may be used to generate or measure tapering surfaces which are circular or elliptical in cross-section, i.e. conical and frusto-conical surfaces, as well as tapering surfaces which are polygonal in cross-section i.e. pyramidal and frusto-pyramidal surfaces, the reference axes of which sur faces are curved. In order to machine such a conical or frusto-conical surface, it is proposed that the generatrix be preferably formed by at least one cutting tool which rotates in a stationary plane, the cutting edge being adjusted in position relative to its centre of rotation.On the other hand, for maching a pyramidal or frusto-pyramidal surface, it is proposed that the generatrix be preferably formed from a linear movement step-wise over the periphery of the external or internal surface to be generated or measured in an opposite direction to the respective individual curved movement of the surface. Machining of a smooth surface is facilitated by arranging for the displacement per unit time of tool and workpiece to be in a ratio of 1:1 or less than 1:1, both for conical and pyramidal machines.

For use in measuring a surface to test for deviations of the surface from a pre-determined geometrical shape and/or predetermined dimensions, the cutting tool used for machining a surface may be replaced by a feeler or sensor of a gauge and the method carried out as if the surface were to be machined.

Apparatus for carrying out the proposed method of machining a conical or frustoconical surface may include a machine frame on which a work holder is supported for movement along a curved guide, a rotatable holder for a cutting tool, the axis of rotation of which is tangential to a curved axis, the centre of curvature of which coincides with that of the guide, the tool being adjustable radially of its axis of rotation. With a workpiece set up in the work holder, the said curved axis coincides with the reference axis of the surface to be machined upon the workpiece. It should be noted that it is the distance between the workpiece or its holder and the centre of curvature which is decisive in the machining of the surface to be produced and not the distance between the curved guide and the centre of curvature.

The proposed apparatus makes it possible for a spherical surface to be described in one operation with geometric exactness within a tolerance specific to the apparaus. The essence of the apparatus accordingly lies in its ability to perform three movements simultaneously, namely: (a) To rotate a tool about a longitudinal axis, (b) to advance the workpiece along a curved axis, and (c) to adjust the tool radially of the longitudinal axis to generate the conical or frustoconical surface.

One construction of apparatus given by way of example makes use of a tool holder including a rotary shaft and control means located internally or externally of the shaft for adjusting the cutting tool relative to the shaft. The shaft may be supported in bearings either at both ends, or at one end if the shaft is to have an overhung arrangement, so that conventional commercial machines, such as, for example, boring machines may be used for carrying out the proposed method after suitable modification.

The shaft may be hollow and the control means may consist of a control rod formed with a cam surface which controls the position of the tool relative to the shaft in the radial sense, or carrying a plane sliding body.

During operation, the control rod is displaced axially relative to the shaft to adjust the tool in position, such displacement taking place as a function of the movement of the work holder. The cam surface of the rod may be formed by a frusto-conical surface, the cone angle of which depends upon the desired cone angle of the surface to be machined and in the case in which the speed of advance of the control rod and work holder are equal, the cone angle of the rod is equal to the desired cone angle of the surface to be machined.

For the machining of external surfaces the control means may be arranged outside the shaft of the work holder and consist of an outer hollow guide surrounding the workpiece, the work holder and the shaft, the guide having a frusto-conical internal surface against which the cutting tool is supported, the guide being mounted for movement in the direction of the axis of movement of the work holder.

In any construction of apparatus, the quality of the surface to be machined may be improved by making use of a cutting tool which includes a plurality of chisels which succeed each other in the cutting direction and act at respective cutting depths. In order to absorb the forces occurring during the machining of a metallic body, it is preferred that the cutting tool should bear against a control rod, or the guide by way of an intermediate support element, especially in the form of a roller having an axis of rotation extending transversely to the direction of advance of the control rod or guide in order to absorb the greater cutting forces corresponding to greater machining depths or high machining speeds.

Advantageously, it is arranged that the tool holder and control rod are driven synchronously.

The apparatus described above for machining a surface may be modified to allow for measurement of an existing surface by replacing the cutting tool with a measuring instrument, conveniently in the form of a dial gauge, a feeler of which engages the surface and is adjusted in position under the action of the control rod for the measurement of internal surfaces or an outer guide for the measurement of external surfaces, whereby deviations of the surface to be measured from the position of the feeler are indicated.

In the drawings: Figure 1 is a diagrammatic longitudinal section through apparatus in accordance with the present proposal to illustrate the machining of a passage through a workpiece, Figure 2 is a cross-section through the apparatus shown in Fig. 1 illustrating a modification for measuring the accuracy of the surface of a passage through a workpiece, Figure 3 is a longitudinal section through apparatus for machining an external surface of a workpiece, Figure 4 is a cross-section through Fig. 1, and Figure 5 is a view similar to Fig. 4, but showing a modification for machining an internal surface of polygonal cross-section.

Referring to the drawings, each of the constructions of apparatus shown therein is arranged to perform an operation in connection with a tapering surface which has a reference axis 5 with a finite radius of curvature 4a.

Each construction of apparatus comprises a machine frame or bed 1 provided with a guideway 4, the centre of curvature of which coincides with that of a curved axis 4b coinciding with the reference axis 5. As illustrated, the axis 4b is the centreline of the guideway 4, although the axis and centreline need not coincide. The bed 1 may take the form of a clamping table of a machine, for example a boring table, and the centre of curvature of axis 4b is located externally of the confines of the bed, although it may lie within its confines. Supported on the bed for sliding movement in operating direction 7 along the guideway 4 in a curved path about the centre of curvature of the axis 4b is a work support 2 provided with clamping means for supporting a workpiece in or on which a surface is to be machined or measured for accuracy.

The bed also supports a tool holder 6 in the form of a hollow shaft or tube 6a equipped or associated with means 9 for adjusting a tool 7a radially relative to the tool holder. The hollow shaft 6a is carried in bearings (not shown) either at both ends of the tube or at the left hand end as viewed in Fig. 1 or Fig.

3, and associated with drive means likewise not shown, for causing the tube to rotate about a longitudinal axis 8 which is tangential to the curved axis 4e at the point 5a which forms the centre of rotation of the tool.

Depending upon the construction of apparatus under consideration, the tool holder may carry a tool for machining an internal or an external surface of conical or pyramidal form or, alternatively, carry a feeler for testing the accuracy of a previously machined surface of either type.

Referring now specifically to Figs. 1 and 4, the work holder 2 is set up with a workpiece 3, possibly of copper, which has been cast with an internal bore or passage which is to be finished to an accurate frusto-conical form of circular cross-section, symmetrical about a reference axis which coincides with the axis 4e.

Arranged within the hollow shaft 6b is a control rod 10 supported at each of its ends permitting the rod to rotate about the longitudinal axis 8 synchronously withe the shaft 6b under the action of a rotary drive at one or both ends of the rod, and to move longitudinally in the direction 1 0a from the start position illustrated under the action of suitable linear displacement means, for example a lead screw drivably connected with means driving the work support. The control rod 10 has a frusto-conically tapering guide or cam portion 1 0b with a cone angle equal to that of the frusto-conical surface 3a to be machined in the workpiece 3, assuming that the rate of movement of the control rod is equal to that of the work holder.The tool includes a chisellike cutter and a support 13 provided with a follower in the form of a roller 14 which bears on the guide portion 1 Ob of the control rod and rotates about an axis of rotation 14a parallel to the axis 8. The tool is movable radially of the tool holder 6 in response to adjustment of the guide rod and is constrained to rotate with the tool holder within a plane normal to the axis 8 and including the point 5a. In the initial working position of the machine, the plane including point 5a intersects the smaller diameter end of the roughedout bore in the workpiece and the smaller diameter end of the guide portion of the control rod.From these positions, with the tool holder 6 and control rod 10 in synchronous rotation, the control rod is caused to advance continuously in the direction 1 0a while the work holder 2 carrying the workpiece 3 is moved continuously in the opposite direction following the guideway 4 at the same speed. With the tool holder rotating about the longitudinal axis 8, the cutting edge of the tool follows a path centred on the point 5a, the diameter of the path increasing as the guide portion of the control rod moves in direction 1 0a so that, relative to the workpiece, the cutting edge of the tool describes a spiral-helix as it fine machines the passage or bore through the workpiece.Adjustments in position of the workpiece relative to the axis 8 as the work holder follows the axis 4b result in the machining of the workpiece to form an internal surface of frusto-conical form with a reference axis of symmetry coinciding with the axis 4b. The radius of the path about the axis 8 followed by the cutting edge of the tool is determined by the radius of that part of the control rod 10 instantaneously in contact with the roller 14. The machining operation finishes when the control rod and work holder reach an end position in which the larger diameter end of the guide portion 1 Ob and larger diameter end of bore 3a lie in the plane normal to axis 8 and including the point 5a.

Clearly, modifications may be made to the arrangement and method of working described above, and these changes may be incorporated in the other embodiments to be described hereinafter. Thus, for example, the control rod may be reversed in position so that the larger diameter end of the guide portion 1 0b is at the right as viewed in Fig. 1, whereby the rod and work holder both move to the left during the machining operation.

Provided that the tube 6a and the control rod rotate synchronously, it is not essential for the control rod to be of circular cross-section as shown in Fig. 4, and it may consist of a flat bar with a tapered guide portion. Alternatively, the control rod may remain rotationally stationary, or it may rotate in the direction opposite to that of the tool holder. Finally, the superimposition of the curved movement of the work holder and rotational movement of the tool in a fixed plane may be achieved in other ways, for example by a linear movement of the work holder, coupled with adjustment of the tool holder about a suitable axis.

The apparatus set up as shown in Fig. 1 may be modified to indicate divergencies between the surface 3a and an ideal imaginary conical surface by replacing the cutting tool with the measuring instrument 16 shown in Fig. 2. Referring to this Figure in conjunction with Fig. 1, the measuring instrument 16 comprises a dial gauge 17 mounted on a carrier 1 7a having adjusting means 9 consisting of a roller 15 or contact with the guide portion of the control rod 10. The carrier 1 7a receives a feeler which is biased radially outwards by a spring and is coupled with the point of the dial gauge in a known manner, so as to indicate positive or negative deviations from an optimum position.In operation, the control rod and work holder are displaced as described above with reference to Figs. 1 and 4, and the feeler pressed into contact with the surface 3a, the position of the support 1 7a varying in dependence upon the diameter of the control rod at the point at which it is contacted by the roller 15. Variations of the diameter of the surface 3a from the optimum will be indicated by divergences of the feeler relative to the support and indicated by move ment of the pointer of the dial gauge from the zero position.

Referring now to Fig. 3, the apparatus may be set up for machining a frusto-conical exter nal surface 3a on a workpiece 3 by omitting the control rod 10 and mounting on the bed a hollow guide 11 having a frusto-conical internal guide surface 12 symmetrical about a linear axis, the guide being linked with means for displacing it along the bed in the direction 7. The cutting tool is reversed relative to the position shown in Fig. 1, so that the support 13 of the adjustment means 9 engages the internal guide surface 12 2 of the hollow guide 11. The workpiece is supported on the workpiece holder 2 by clamping means not shown engaging the plane end faces 3b and 3c of the workpiece.In operation, the tool holder rotates about axis 8 so that the cutting edge of the tool follows a path centred on the point 5a, the diameter of the path decreasing as the guide moves in direction 7 so that relative to the workpiece the cutting edge describes a spiral-helix of progressively decreasing diameter. Adjustments in position of the workpiece caused by the work holder following the axis 4b result in the machining on the workpiece of a frusto-conical external surface with a curved reference axis.

The apparatus may be adapted to machine or measure an internal or external surface of pyramidal form having a curved reference axis of symmetry by making use of a control rod or hollow guide with a guide surface portion of suitable pyramidal form. Thus, Fig. 5 shows the arrangement for producing a frustopyramidal surface with square cross-section.

The control rod 10 moves in the direction 1 0a and the tool holder 6 remains stationary in the axial sense but is advanced and retracted step-wise together with the control rod 10 over the polygonal profile relative to the body 3 against the direction of movement thereof.

According to Fig. 5, particularly large cutting forces are absorbed by arranging the roller axis 1 5a transversely to the axis 8 and about which the roller 15 is rotatably mounted on the cutting chisel 7a. Pyramidal surfaces are thus produced internally and/or externally according to this modified method which proposes the rectilinearly moved cutting chisel in the form of a planing tool as generatrix and not the rotating cutting chisel. The planing tool (not shown) is moved step-wise over the periphery of the polygon and, at each standstill position is moved relatively against the rectilinear movement of the body 3 parallel to the axis of movement 4b.

Reference is to be made to the disclosure contained in the specification of our Federal German application No. P 30 20 795.5, a copy and translation of which are on the file of this application, the disclosure of which German specification is to be taken to be incorporated herein to the extent that the subject matter thereof differs from the forego ing.

Claims

1. A method of machining or measuring a surface of a workpiece, the surface tapering from one end of the workpiece towards the other and having an arcuately curved refer ence axis, wherein the workpiece is moved along a path having a defined centre of curvature, and a machining or measuring means is moved along a generatrix, the distance of which generatrix from the surface is adjusted during the machining or measuring operation.

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 step-wise 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 distances 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 preceding claim, wherein the workpiece is moved along an arc of a circle during the machining or measuring operation.

7. An apparatus for machining or measuring a surface of a workpiece, 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.

8. An apparatus according to claim 7, wherein the tool holder comprises a shaft, control means for adjustment of the cutting tool or measuring instrument being provided internally or externally of the shaft.

9. An apparatus according to claim 8, wherein the control means comprises a control rod arranged within the shaft and moveable 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 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 of claims 7 to 11, 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 any of claims 7 to 12, 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.

15. A method of machining a tapered surface having an arcuately curved reference axis, comprising moving a workpiece on which the surface is to be machined 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 progressively varying 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 helicalspiral path relative to the workpiece and form on the workpiece a surface with an axis of symmetry curved about the centre of said circle.

16. A method substantially as hereinbefore described with reference to the accompanying drawings.

17. An apparatus substantially as hereinbefore described with reference to and as illustrated in Figs. 1 and 4, considered alone or as modified by Fig. 2 or Fig. 5, or as illustrated in Fig. 3 of the drawings.

18. A method for the description or generation of externally conical and/or internally conical generated or cavity surfaces, in particular on tubular bodies of defined length, whose reference axis or central longitudinal axis respectively has a curved path, characterised in that the conical path of the generated or cavity surface is described, during and as a function of a curved movement of the body to be provided with a curved cone, about a defined centre of curvature based on a generatrix formed from a rotational movement, by continuous adjustment of the distance between the generatrix and the curved reference axis or central longitudinal axis.