GB2089260A - Tool for forming blanks - Google Patents

Abstract

A tool, e.g. for rolling external teeth or threads on a metal blank, has a working profile defined by separate sections. The tool may form a shaft or axle, and may be provided with an oscillating movement. In order to reduce the cost of manufacture of such a tool, and to facilitate repair and replacement, the sections, e.g. teeth (5), are removably clamped to a base (3) or holder. In a preferred embodiment, the tool is formed from two halves for working opposite sides of the blank. <IMAGE>

Description

SPECIFICATION Tool for forming blanks This invention relates to a tool for forming blanks, particularly metallic blanks.

The tool is provided with a geometry to be forced on the blank to be shaped. This geometry is transferred to the blank by impressing the tool thereon, where the geometry is being produced by profiling a form-locking and/or force-locking configuration and/or a smooth tread, and this geometry is held by a tool base and this base is attached to a tool holder.

It is known to provide blanks, such as blanks of plastics or deformable metals, with various types of profiles, such as gear teeth, screw threads, smooth and/or curved surfaces and to impose these profile shapes on the blank, typically without heating thue blank, by cold-forming, e.g. by rolling. For this purpose, the blankto be formed is moved between at least one tool having a geometry required to transfer the profile form to the blank and a supporting surface taking up the force exerted on the blank, so that the profile form of the tool is progressively reproduced on the blank. Depending on the type of profile and on the ability of the blank to undergo deformation, the tool is applied to the blank and its profile is produced by the material of the blank flowing up along the surface of the tool profile penetrating therein.Forming of the blank by means of a tool of this type will continue until the geometry of the tool has penetrated or been impressed into the blank. The tools used for such forming are constructed as so-called hard metal tools which, on the side facing the blank to be formed, are formed with the desired geometry having the profile to be formed into the blank and, on the side facing away from the blank have a tool base which is integral with the profiled part and which, simultaneously may be formed as a tool holder.

A known type of tool for making products of this kind especially, with external gear teeth, such as spur gears, is formed by two tool halves of which each is formed on its side facing the blank to be worked with the geometry of the tool in the form of a profile and, on its side opposite the profile is formed with a tool base which is integral with the profiled side. The tool base with the integral profile of each tool half is inserted in a tool holder and this tool holder is connected to drive means which provide an, e.g. oscillating, motion of the tool holder and tool.

The geometry of the tool is provided on the tool halves. Each tool base is machined by an eroding and/or cutting process until the required profile form has been produced on the base. Since the profile face has to be hardened, particularly for penetrating into metallic blanks, the profiled face together with the tool base is subjected to a hardening process and, where distortion occurs, is also subjected to additional machining. As a result of the method of profiling, the manufacture of such tools is extremely costly and, during the hardening and the additional machining which is frequently necessary, involves considerable difficulties. It is not always possible to avoid the risk of a loss of the tool, for instance, by unsatisfactory machining or inevitable distortion of the metallic parts.Furthermore, it has been found that, for instance, where manufacture of one half of the tool is unsatisfactory, the other half will be useless because the two halves are formed as mirror images and it is not possible to manufacture the one half along retroactively with the specified accuracy of the geometry of the tool. There is the further risk that, when one half of the tool is damaged, the second half can no longer be used, so that even a small defect, such as chipping of part of the profiled face, e.g. a segment tooth, will involve the loss of the complete tool (see for example German Patent Application No. 19 05 949).

An object of the present invention is to provide a tool for such forming processes so that not only will manufacture be easier and cheaper but the parts will be interchangeable, thus avoiding the loss of both halves in the case of damage to, say, one half.

Furthermore, it is to be possible for the tool to be constructed so that, depending on the type of forming process to be effected, part or parts of the profiled face will act upon the blank at different times during the forming process.

The invention provides a tool for forming a workpiece, wherein the tool has a profile made up of a plurality of individual sections forming the geometry of the tool and being clamped to a tool base and/or tool holder so that the tool geometry may be imparted to the workpiece by being pressed thereagainst.

Thus, not only is the above-described object achieved, but thus is the further advantage that other profiles can be produced at minimum cost and only by changing the sections formed with the profile, while retaining the tool base and/or tool holder.

Thus, the range of application of the tool is extended.

Another advantage is that, even in the event of breakage and/or wear of one section of the profiled face, the tool will not be unserviceable but can be reconditioned at very low cost be inserting a new section. It is also possible to keep individual sections in stock without any high inventory costs so that spares are available promptly if the tool should suffer damage. Another advantage is that the individual sections, where they are not individually made, can be cut off from pre-machined bar stock which makes machining both easier and more accurate and, consequently, permits production with less inaccuracy, for instance, tooth errors.

Owing to the absence of a large bulky metal part conventionally used to form the tool base, heat treatment hardly affects the individual sections of the tool and, consequently, its geometry. Thus, the tool can be made with closer tolerances, which is a most important factor for the toothing of e.g. gears because of the low noise level called for in such applications. The possibility of maintaining close tolerances clears the path to the wide use of cold forming for a great number of driving and moving parts, in particular in automotive engineering.

Where tools of this type are used, parts will only require additional finishing in very rare cases, not even in applications where specified tolerances are in the micrometer range. This is a substantial advantage for the toothing of gears which, when made by conventional methods, necessitate several machining operations and a cutting operation alone will fail to produce the surface finish of a rolled surface.

Furthermore, dividing the tool geometry into individual sections makes it possible to match it to the specific plastic properties of the blank to be formed or its material, which cannot be done with conventional tools or only at very high cost. This conclusion is based on the discovery that, for instance, in the case of a tool with internal toothing, not all teeth will be uniformly loaded during the forming of the blank so that, as investigations have shown, it is a good plane to make the teeth or sections subjected to heavier stressing of a different material than the sections subjected to lower stresses and to make the former sections with a different profile which is better matched to the material of the blankto be formed.

Embodiments of the invention will now be described with reference to the accompanying drawings, wherein: Figure lisa diagrammatic view showing a forming process for a spur gear using an internallytoothed too, Figure2 is a side elevation of a tool consisting of two halves and having a geometry formed with internal teeth for making an externally-toothed gear, Figure 3 is a section taken along the plane Ill-Ill of Figure 2, one half showing tooth segments clamped in a force-locking manner and the other half showing tooth segments clamped in a form-locking manner in the circumferential direction with an end plate shown partly broken, Figure 4 is a view of the tool base of Figure 3, but with the toothed segments removed, and the cover plates and clamping parts retaining the tooth segments in the base, Figure 5 is a view of a detached toothed segment having a flat base in the circumferential direction of the clamping arrangement as for Figure 3 and turned through 90 , designed for predominantiy force locking clamping of the segments, Figure 6 is a view of a detached toothed segment having a flat base in the circumferential direction of the clamping arrangement of Figure 3, designed for predominantlyform-locking clamping of the seg ment, the base supporting it being shown in section, Figure 7 is a perspective view of a prepared tooth bar for which individual toothed segments are cut to length, the toothed segments being formed with a flat base, Figure 8 is a perspective view of a prepared tooth bar from which individual toothed segments are cut to length, the toothed segments being formed with a convexly curved base, Figure 9 is a longitudinal centre section through a tooth segment with integral zones formed on it to impress them on a blank or workpiece, here a starting zone, impressing zone and finishing zone, Figure 10 shows a series of tooth segments for making spur gearing with staggered toothed segments, Figure 11 shows a series of toothed segments for making spur gearing with staggered toothed segments, Figure 12 shows a series of toothed segments for making helical gearing with non-staggered toothed segments, Figure 13 shows a series of toothed segments for making helical gearing with staggered toothed segments, and Figure 14 shows a series of toothed segments for making helical gearing with staggered toothed segments in a sandwich construction.

A tool 1 in accordance with the invention for the shaping of, typically, metallic blanks or objects 2, made of steel, brass etc. essentially comprises a tool base 3 and a plurality of arcuate sections 4 each forming part of the geometry of the tool, each arcuate section having part of the profile shape to be transferred to the blank.

The profile, which in the embodiment illustrated is a toothed profile, is made up of a series of individual sections 4 which in their entirety form the geometry of the tool 1 to be impressed on the blank 2.

Impressing the geometry of such a tool 1 on the blank 2 is effected by pressing the tool against the blank and by moving the tool additionally in relation to the blank, preferably in an oscillating fashion while it is pressed against the blank. This pressing and movement of the tool 1 on the blank 2 cause the profile of the tool to penetrate progressively into the blank. The desired profile is produced by the material of the blank flowing along the flanks of the tool, i.e. the respective section 4, and progressively moving outwards as the respective section 4 penetrates into the blankto achieve the desired profil. In other words, the geometry of the tool is transferred to the blank.

In order to ensure that, firstly, the geometry of the tool 1 is transferred to the blank 2 in a minimum of time and, secondly, the geometry is reproduced on the blank with a minimum of error, the blank is worked on simultaneously bytwo mirror-image tool halves. The profiles on the halves actually penetrate simultaneously at the respective points of attack into the blank. While the profile of the one tool half penetrates into the blank 2, the profile of the other tool half acting in the opposite direction in the plane of forces simultaneously penetrates into the blank so that the profiles positioned in the plane of forces X in action at a time are in direct opposition, for instance tooth against tooth, but with the blank in between.

Furthermore, the oscillating motions of the tool halves are coordinated so that the contours impressing the profiles on the blank 2 are invariably in the same plane X and thus penetrate into the blank simultaneously. The motion cycle of the tool half is schematically shown in Figure 1, for which it is apparent that the tool 1, due to its particular type of motion, produces a "generating" rolling motion on the blank 2.

The tool 1 itself, which is provided with the desired geometry to be transferred to the blank 2, is preferably formed by two mirror-image tool halves of which each consists of the tool base 3 with toothed segments 5 attached, both tool halves being at least pre-shaped together and, subsequently, separated from each other. The toothed segments 5, of which where the tool 1 is formed with internal teeth, are wedge-shaped, are preferably supported by means of intermediate members 6 (Figure 2) on the tool base 3 and are located in the circumferential direction by means of clamping means 7.

The clamping means 7, which are preferably wedge-shaped, are connectable to the tool base 3 and can be adjusted, e.g. by screw means 8, so as to clamp the tooth segments 5 in the circumferential direction. Special versions of tool 1 may, for the purpose of clamping the tooth segments 5, be provided with end plates 9 or yokes on the tool base 3 to provide additional abutments for the clamping means 7. In such constructions, it is an advantage to provide the clamping means 7 with a wedge-shape, moving it from the tool base 3 towards the centre of the circle M of the tool 1 until the clamping means 7 bearing against the end plate 9 and the toothed segments 5 produces the clamping of the tooth segments in the circumferential direction.The intermediate members 6, which are also clamped in the circumferential direction in a manner similar to the toothed segments 5, from a solid unit with the toothed segments so that they assist in transmitting the forming forces from the tool base 3 to the toothed segments. The intermediate members 6 may be omitted, especially where the tool 1 is used for forming blanks 2 of a smaller size and where the use of these intermediate members would unnecessarily enhance the cost of the forming geometry of the tool. In the case of such small tools 1, it is recommended, therefore, that each toothed segment 5 be made with a somewhat greater depth and that it be supported with its base 10 (Figure 7) directly on the tool base 3.

So that the toothed segments can also be clamped in an axial direction, the tool base 3 is provided on one side with an annular flange 11 (Figure 3) and on its other side with a cover plate 12. The flange 11 and cover plate 12 are secured, e.g. by means of screws 13 to the tool base 3, after the toothed segments 5 have been inserted in the tool base 3 and, by their action, assist the axial clamping of the tooth segments and also the intermediate members 6, if provided. The attachment of the cover plate 12 and/or the end plates 9 may be effected by means of screws 13 or other equivalent fastening means, such as clamping bolts. In certain constructions, it may be an advantage to provide the individual toothed segments 5 or their intermediate members 6 with roots 15 and to provide key-ways 16 in the tool base 3 for these roots (see Figures 3 and 6).Such key-ways 16 may take the form of dove-tail key-ways in which correspondingly-profiled roots 15 may form a sliding fit. Securing the toothed segments 5 by means of roots 15 in the key-ways 16 would afford simple alignment of the individual toothed segments and, moreover, provide a better hold in the tool base 3. Thus, if a toothed segment failed, it would be prevented from dropping out thereby preventing the otherwise severe consequences for the complete tool 1.

The toothed segments 5 may take various forms in accordance with the configuration required to obtain the geometry of the tool 1, such as simple spur toothing as shown for example in Figures 5 and 6 or staggered spur toothing as in Figure 11 or helical toothing according to Figures 12 to 14. In deciding on the profile shape of the toothed segments 5, the only factor will frequently be the geometry of the tool 1 and not the ease of making the tool and its function. Consequently, various configurations can be adopted for specified geometries of the tool 1, the overall geometry being reflected in the individual profile shapes and the overall geometry being sectionalized accordingly.

Extensive tests have shown that, considering the motion cycle of the tool 1 and also the different degrees of penetration of the profiles impressed on the blank 2, it is not necessary, for instance, to make all toothed segments 5 of the same hardened material, because individual toothed segments will not be impressed in an unformed material zone of the blank, but into an already preformed zone. It is on this surpsiring discovery that the staggering 10 of the toothed segments 5 as shown in Figures 11 and 14 is based, namely that the toothed segments are provided with a working surface that is divided into a starting zone 18, a forming zone 19 and a finishing zone 20 as shown also in Figure 9.

The method of making individual spur-type gear segments 5 is first to machine a bar 21 (Figures 7 and 8) with external toothing having the profile of the geometry of the desired tool 1 over its full length.

This bar 21, which while being machined in the manner of external toothing, has the profile of internal toothing which will later be transferred to the blank 2 to be formed. On completion of this externally-toothed bar 21, the individual toothed segments 5 are cut off this bar, these segments being formed with exactly the same profile shape that will result in the overall geometry of the tool 1.

Depending on the method selected to insert the toothed segments 5 in the tooth base 3, i.e. with or without intermediate members 6, the toothed segments may be constructed with a flat underside 10 as shown in Figure 7 or a curved underside 22 as shown in Figure 8.

Where intermediate members 6 are used, the curved underside 22 required for inserting the toothed segment 5 in the tool base 3 will be formed on the intermediate member itself. The intermediate members 6, which may be constructed as polygons, may be cut off a prepared bar in the same way as the toothed segments 5, it being possible to machine their form and heat-treat the bars beforehand to suit the quality of the intermediate members.

This prior forming or machining of the bars 21 for the toothed segments 5 and, where applicable, the intermediate members 6 offers an advantage, especially where heat treatment is applied, in that any thermal distortion occurring can be compensated for by simply regrinding the profile contour. For this method of separately making the toothed segments 5 and, whee applicable, the intermediate members 6, the tool base 3 and its cover and end plates 12, 9 as well as the clamping means 7 are made only by machining and are not subjected to a heat treatment.

The toothed segments 5 themselves may, where the accuracy of the geometry on the blank 2 makes this necessary, be clamped together after the cutting off operation and finished together to the dimensions of the desired profile shape by grinding.

The method of making helical tooth segments is analogous to the making of spur-type toothed segments 5 so that it is not necessary to describe this method in detail. Only the method of machining would differ in as much as, contrary to the spur toothing where, for instance, a wire eroding machine can be used, a die sinking electrode will be preferred where the machining of the toothing is not made by a cutting process in line with general practice.

As regards the stagger or offset 17 (Figures 11, 13 and 14) and, consequently, the degree of offset AX of the individual toothed segments 5 in the axial direction, allowance is made for the different amounts of penetration of the individual flanks of the toothed segments on the circumference of the blank or workpiece 2 to be formed. The amount of offset 17, i.e. AX, results from the diameter ratio "pitch circle 23 of the workpiece (blank 2) - pitch circle 24 of tool 1" (Figure 1). This same definition applies both to spur-type and helical type toothed segments 5, as is shown specifically in Figures 12 to 13.

As explained above, the geometry of each toothed segment 5 is subdivided into a starting zone 18, a forming zone 19 and a finishing zone 20. The plastic-flow properties of a specific material may make it necessary, for instance, to provide the starting zone 18 with a special geometry or profile.

The same may apply to the forming and/or finishing zones 19, 20. In orderto take this into account, in one embodiment of the invention the individual complete toothed segment 5 is divided into three individual parts, namely, starting zone 18, forming zone 19 and finishing zone 20 which are separated from each other by cutting. This enables each toothed segment 5 to satisfy more closely the specific requirements it has to meet. This construction of the individual toothed segments is referred to as the "sandwich construction" for short. In cases where an axial offset 17 (AX) is called for, too, this can be easily provided for by this type of sandwich construction.This configuration of tool lends itself well to applications where extreme flexibility is required in coping with varying flow-ability of different materials dr where more readily adaptable tools 1 have to be provided for a variety of applications.

In a similar way to the method described above for making toothing on blanks 2 or workpieces, it is possible in a similar manner to design and make tools 1 for forming, typically, cylindrical journals or treads, such as on axles, shafts, etc. Such tools 1 are specially suitable where journals or treads of different diameters and/or geometry have to be formed on a blank or object 2 and where these journals or treads are required to be made in one pass of the blank through the tool. The subdivision of the geometry of the tool 1 into individual profile sections 4 also involves the use of straight tools in place of the curved tools described here and arrangements where the sections and/or individual profiled parts serving forthe forming of the material are lined up in one plane.

Claims (10)

1. A tool for forming a workpiece, wherein the tool has a profile made up of a plurality of individual sections forming the geometry of the tool and being clamped to a tool base and/or tool holder so that the tool geometry may be imparted to the workpiece by being pressed thereagainst.

2. A tool as claimed in claim 1, wherein the tool has a face for acting on the workpiece which face is concavely curved, the profile of the tool being formed by a plurality of arcuate sections forming the overall geometry of the tool.

3. A tool as claimed in claim 2, wherein the arcuate sections are convexly curved on a rear surface opposite their face and bear via this convex curvature against concavely curved surfaces of the tool base and/or the tool holder.

4. A tool as claimed in any one of claims 1 to 3, wherein the geometry of the tool is toothed and each section out of the circumference of this toothing forms part of the profile.

5. A tool as claimed in claim 4, wherein the profile shape each section is formed on its face for acting on the blank with a starting zone a forming zone and a finishing zone, these zones being arranged in line on the tool in the direction in which, in use, forces are exerted by the tool on the blank.

6. A tool as claimed in claim 4 or 5, wherein each toothed segment of each section is formed with a root on its underside facing the tool base, a key-way being provided in the tool base for this root.

7. A tool as claimed in claim 5 or 6, wherein the starting zone, the forming zone and the finishing zone of each section each forms a separate part and that these parts are capable of being assembled to form a toothed segment.

8. A tool as claimed in any one of the preceding claims, wherein the individual sections are placed in the tool base are offset staggered in space in accordance with their timed displacement for acting on the blank, the offset corresponding to the degree of their successive action.

9. A tool substantially as herein described with reference to any one of the embodiments shown in the accompanying drawings.

10. A workpiece worked by a tool as claimed in any one of the preceding claims.