Undercut Internal Surface

This invention relates to manufacture of a hollo article having an internal surface of which at least part i undercut.

The invention is particularly applicable to the tnanu facture of an outer member of a constant velocity rati universal joint, the joint comprising an outer member, having a closed end and affording an internal cavity wit the internal circumferential surface thereof having axiall.* extending grooves formed therein; an inner joint member disposed within the outer joint member and having an external suface having grooves therein which face the grooves in the outer member; a plurality of balls disposed one in each pair of grooves in the joint members for torque transmission therebetween; and a cage of annular form disposed between the joint members and having apertures in which the balls are located. The internal circumf rential surface of the outer joint member between the grooves thereof is part-spherical, as is the external surface of the inner joint member, and the cage has external and internal part-spherical surfaces which engage the part-spherical surfaces of the joint members, and the shape of the grooves and/or the part-spherical surfaces of the cage and joint members is such that when the joint is articulated the balls are caused to occupy a plane which bisects the angle between the rotational axes of the joint members.

In such a universal joint, the grooves in the outer joint member 2ay be undercut, by which we mean that the base of each groove is, at a position away from the free open end of the joinc member, a grsacer radial distance from the rotational .axis of the joint member than it is at the end of

the member. The part-spherical internal surface of the outer joint member is undercut.

^' 3ecause of the undercut of the part-spherical interior surface of the outer joint member, and possibly of the grooves, the joint member cannot be completely formed by a forging or extrusion process involving a forming tool inserted axially into the joint member, if the tool is in one piece. T-his is because a one piece forming tool cannot be withdrawn once the undercut configuration has been established. A one piece tool can be used to form the internal shape of the joint member adjacent the closed end thereof, but it is then necessary to produce the undercut; shape by removal of material, usually by milling followed b a grinding process to give the required surface finish. It is also known to produce the undercut shape in a cold, war or hot forming operation, not involving removal of material, by use of a forming tool which is made of many components and is collapsible for removal from the joint member afte the undercut surfaces have been shaped. Ideally the oute joint member would then require no further treatmen whatsoever, but in practice grinding is usually stil required to produce the necessary surface finish.

Such collapsible forming tools as proposed hithert have been made of a relatively large number of components This means that the manner in which the tool collapses an is reassembled is complex, and it is difficult to ensur consistantiy repeatable dimensional accuracy in th assembled tool and the resulting components. Wear in us adds to these di ficulties.

t has also been proposed, for example in Ξ? 0C135-5A to use a tool which has relatively few parts, but does no define an external surface corresponding to the complet internal surface of the outer joint member. Gaps exis between the parts of the tool, into which material :ar. flo

during the extrusion process. Such material then has to removed subsequently.

It is an object of the present invention to overcome reduce such problems.

According to one aspect of the invention, we provide tool for use in manufacture of a hollow article having internal surface at least part of which is undercut, sai tool comprising a plurality of elements having portio together adapted to define a substantially complete externa surface having a con iguration corresponding to tha required in said internal surface, said elements includin first elements and second elements interposed between them and the arrangement being such that said first elements ca be withdrawn from said article to leave a space or spaces t permit said second elements subsequently to be move inwardly to dis-engage them from said undercut interna surface part and withdrawn from said article.

By a substantially complete surface, we mean one i which there are no gaps or discontinuities sufficient fo the material of the article to enter during the extrusio process, and which material would have to be removed, e.g. by machining, subsequently. By use of the tool according t the invention, the requirement for finish grinding of th internal surface of the article, including the ball groove in a joint outer member, can be reduced or eliminated.

By providing for the first elements of the tool to b withdrawn from the article to leave space to permit th second elements of the tool subsequently to be move inwardly and withdrawn, the tool can be designed to hav relatively few component parts and yet still define th entire shape of the internal surface of the hollow article

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Preferably said elements of the tool together define a internal cavity into which an expander member is movable t hold said elements in their positions in which they defin said external surface, and from which the expander membe can be withdrawn to permit said first elements of the too to be moved inwardly into said cavity prior to their with drawal.

Inward movement of the first elements of the tool prio to their withdrawal enables both the first and secon elements of the tool to have an external con iguration whic defines an undercut part of the internal surface of th article.

To enable the first elements of the tool to be move inwardly after withdrawal of the expander member, the sid faces of the first elements, which contact the secon elements, must be parallel to one another or convergen towards the outside of the tool.

The expander member may have a tapered portion whic enters said internal cavity defined by said elements of th tool, to facilitate withdrawal of the expander member afte a forming operation.

The second elements of the tool may include ca surfaces which are engaged by the expander member, to hol the elements in engagement with the article, after th expander member has been at least partially withdrawn fro said cavity, out which cam surfaces are dis-engaged upo further withdrawal of the expander member. This ensure that there is no hindrance to withdrawal of the firs elements of the tool from the article after the expande member has been withdrawn from the cavity of the tool However, even without such cam surfaces, the second element of the tool will tend to remain in contact with the articl

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after withdrawal of the expander member while the firs elements of the tool are withdrawn.

The tool may comprise a holder member which holds sai first elements to allow for said inward movement thereof said holder member being mounted for movement relative t said expander member, abutment means engaging said holde member when said expander member is withdrawn from sai cavity, to withdraw said first elements from said article and further abutment means engaging said second element after further withdrawal of said expander member and dis engagement thereof from said cam surfaces, to withdraw sai second elements from said article, and spring mean operative between said expander member and said first an second elements to return said elements to their operativ positions and said expander member to said cavity.

Further details of the tool according to the inventio are described hereaf e .

The invention also provides a press fitted with a too according to the invention, and further comprising a di through which a hollow blank having the tool inside it ca be pressed to form the article, and means for holding sai article during withdrawal of the tool.

The invention will now be described by way of exampl with reference to the accompaning drawings, of which

Figure 1 is a section through a blank for making universal joint outer member by use of the invention.

Figure 2 is a section through a press according to th invention, in a first stage of operation.

Figure 3 is a diagrammatic section of part of the too

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of the invention, in a first stage of operation corres¬ ponding to that of Figure 2.

Figure 4 and 5 correspond to Figures 2 and 3, but showing a second stage of operation.

Figures 6 and 7 correspond to Figures 2 and 3. out showing a third stage of operation.

Referring firstly to Figure 1 of the drawings, this shows a blank for use in making the outer member of a constant velocity ratio universal joint, by use of the invention. The blank comprises a hollow cup-shaped portion 10, and a spigot 11, the latter of which will, ultimately be provided with splines for torque transmission with another drive line component, eg. a motor vehicle hub. The internal shape of the cup-shaped portion 10 of the blank includes a part-spherical surface portion 12 which runs into a cylin¬ drical surface 13, and in the surfaces 12, 13 are formed axially extending circu erentially spaced grooves 14, aach with an arcuate portion 15 and straight portion 1δ in it's base. The blank includes no undercut portions, and hence can be made by a conventional cold, warm or hot forging or back extrusion process using a one piece forming tool to give the internal shape to the blank, withdrawal of such a tool being possible because there is no undercut.

In the finished joint outer member, the shape of the internal surface of the member is as shown in broken lines at 17, ie. a continuation of the part-spherical surface 12, and the shape of the bottom of the grooves is entirely arcuate as shown in broken Lines at 18. Although th undercut present in the finished joint member is exaggerate in Figure 1 , it will be appreciated that a one piece formin tool cannot be used to make the article because it cannot b withdrawn from the finished article.

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Referring now to Figures 2 and 3 of the drawings, the is shown a ram 20 of a press to which is secured, by a scre threaded connection ring 21, a mandrel 22. The lower end mandrel 22 has secured to it an elongate cylindric expander member 23- A sleeve 24 is slidable longitudina of mandrel 22, between limits determined by a peg 25 exten ing inwardly from sleeve 24 into a longitudinaly extendi slot 26 in mandrel 22. Towards the lower end of sleeve 2 there is a circumfersntially extending flange 27, and sli able on sleeve 24 below the flange 27 is a collar 28. T collar 28 Is spring biased upwardly by a plurality tension springs 29 spaced around the collar, only one which springs is shown in the drawing. The springs engage pins 30 extending into the mandrel 22.

Within flange 27, the sleeve 24 is provided with thr equally circum erentially spaced radial apertures 31- Ea aperture 31 receives a ball end of a peg 32 extendi outwardly from the upper end of an element 33 having a he 34 at its lower end. Circum erentially spaced about slee 24, between the apertures 31. re three slots 35 whi extend downwardly from flange 27. Each slot 35 receives peg 36 extending outwardly from the upper end of an eleme 37 having a head 38 at its lower end. The pegs 36 are lo enough to be engaged by collar 28. The head portions 34, of elements 33, 37 together define an internal cavity which is cylindrical and in which the expander member 23 a close fit. The elements 37 have cam surfaces 39, exten ing above their parts defining the cavity 40.

The shapes of the head portions 34, 38 of elements 3 37 are shown diagrammatically in Figure 3 of the drawings It will be noted that head portions 34 have parallel sice while head portions 38 interposed therebetween are wed shaped. The external shape of the head portions of t elements corresponds to the required internal configurati of the universal joint outer member, and thus eacn of t

elements includes a protuberance which corresponds to one of the grooves of the finished joint member. The remainder of the exterior of the head portions of the elements 33, 37 define the part-spherical surface which is to be present in the finished joint member.

In use of the apparatus,the assembly of elements 33 _. 37, with the expander member 23 therein, is introduced into a blank as shown in Figure 1. The lowermost end portions of the elements 33, 37 will fit closely within the already formed part-spherical surface 12 and grooves 14 of the blank. The press is then used to force the blank with the tool within it through a die 41. This has the effect of deforming inwardly the wall of the blank adjacent its free end, to conform to the surface shape of the assembled tool elements, as shown at 42.

The tool must then be withdrawn from the formed joint outer member, and the first stags in such withdrawal is shown in Figures 4 and 5.

Initially, the open end of the joint outer member is engaged by gripper members 43 to prevent its upwar movement. Thereafter, mandrel 22 is raised by operation o the press. Since the elements 33, 37 cannot be withdraw from the joint outer member because of the undercut config uration it now possesses, the sleeve 24 remains in a fixe position as the mandrel is raised, until peg 25 abuts th lower end of slot 26. During this, springs 29 have bee tensioned, while the expander member, fast with mandrel 22, has been withdrawn clear of the internal cavity of the hea portions of elements 33, 37.

he elements 33 are now free to tilt inwardly, so tha their head portions 34 adopt the positions shown in Figur 5- This tilting is possible by virtue of the ball ends o pegs 32 engaging in apertures 3 * Such tilting permits th

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head portions to be withdrawn from the joint outer membe with continued upward movement of mandrel 22. The he portions 38 of elements 37 at this stage, however, cannot withdrawn because the expander member 23 remains in engag ment with their cam surfaces 39 to prevent them bei displaced inwardly.

On continued upward movement of mandrel 22, springs are tensioned further as pegs 36 on elements 37 move do slots 35, taking collar 28 down the sleeve 24 with the Ultimately a position as shown in Figure 6 is reached, which pegs 36 have reached the lower ends of slots tensioning springs 29 to their fullest extent and t expander member 23 reaching the ends of cam surfaces within the elements 37. The elements 37 can then displa inwardly so that their head portions 38 reach the positio shown in Figure 7.

The condition shown in Figure 6 will not exist mor than momentarily, since as soon as the expander member 23 i clear of cam surfaces 39 there will be a tendency for th elements 37 to move inwardly. However, as a consequence o the deformation of the material of the joint outer member the elements 37 and indeed, elements 33 at an earlier stage may adhere thereto so that an appreciable force needs to b exerted, by pegs 36 engaging bottoms of slots 35, before th elements 37 will remove from the joint outer member. Thi is why the joint outer member must be engaged by gripper 43- As soon as the elements 37 are clear of the joint oute member, springs 29 will bring collar 28 upwardly and return firstly, the elements 37 to their starting position. There after springs 29 will bring sleeve 24 along with collar 2 upwardly to its original position relative to mandrel 22 and the parts will then regain their relative position illustrated in Figure 2.

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Because of the tendency of the head portions 38 o elements 37 to adhere to the joint outer member, th provision of cam surfaces 39 thereon to maintain them i position while elements 33 are moved inwardly and withdraw may not be required.

Although as described the apparatus is used for th manufacture of the outer member of a constant velocity rati universal joint, it will be appreciated that it is suitabl for manufacture of other components of the same genera configuration, having an internal undercut surface. Ther may be other numbers of elements such as elements 33, 37 according to the shape of the component to be manufactured

In the embodiment described above, the expander membe 23 is cylindrical, and the cavity defined by the hea portions of elements 33, 37 of the tool also Is cylindrica In practice, the expander member and the cavity may requi to be of tapering configuration, to facilitate withdrawal the expander member after a forming operation. If during forming operation very high forces are developed be treer. t contacting surfaces of the expander member and the elemen of tool withdrawal of the expander member is facilitated it is tapered. Further, for the same reason, the he portions 3 of the elements 33 of the tool may require have sides which converge outwardly, rather than bei parallel.

In one form of constant velocity ratio universal join the grooves in the outer joint member are not unde cut. T part spherical surface between the grooves is, howeve still undercut. The tool can be used to make a joint of th typ .

Although as described above the tool assembly mounted on the ram of the press and the die is fixed on t base of the oress , it would be Dossible for the die rath

than the tool assembly to be moved by the press ram. T relative movements occuring between the parts of the to assembly and the die would be the same.

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