Process and apparatus for the cold extrusion of metal bushings, in particular, for tracks of track-laying tractors and the like

Abstract

 Process and apparatus for the cold extrusion of bushings (2) from cylindrical metal pieces or slabs, carried out by means of a single extrusion step, performed into an apparatus comprising a press body with a reciprocating punch (4), cooperating with a coaxial press die (8), including a coaxial seat adapted to receive the metal slab to be transformed in a bushing as well as a upper sleeve (6), slidably mounted about said punch and acting as guiding means for correctly centering said punch with regard of said piece during the extrusion step.

Description

[0001] The present invention relates to an improved process for the cold extrusion of metal bushings, in particular, for tracks of track-laying tractors or other intended purposes. According to this process the conventional preforming operation is eliminated, which is necessary in order to obtain a shallow axial dead hole on one end of the workpiece to be transformed in a bushing, said hole serving as guiding means for the punch employed to form the axial hole of said bushing.

[0002] The invention also relates to an improved apparatus for carryng out said process.

[0003] In the common practice relating to the cold extrusion of the metal bushings for the tracks of the track-laying tractors or other similar purposes a process is employed which comprises the following main operations:

1) - the cutting of slabs or sections of a predetermined length from a cylindrical metal rod;

2) - the phosphating or line coating of eachrodsection;

3) - a preforming of said rod section by means of a first passage through a press, using a particular or tooling arrangement so as to obtain a shallow axial dead hole for the punch at one of the ends of this piece, then performing a second passage through a press in order to obtain a bush by an extrusion step;

4) - spheroidal annealing;

5) - the blasting of the side surface;

6) - a second phosphating or line coating; and

7) - the extrusion by a press, of a body having a lower closed bottom and the knockout of said body out of said press.

[0004] The bottom of the extruded body is then bored and the outer and inner surfaces thereof are gauged according to the predetermined tolerances. Thus according to the conventional process before the final extrusion step six operations have to be performed and it is necessary to use two different press apparatus, each comprising a punch and a pressing die.

[0005] On the contrary, according to the present invention an improved process is provided which permits to shorten the operative cycle, eliminating the aforementioned steps 2) to 5) of the conventional process, i.e. performing a direct extrusion, without any preforming of the piece to be processed and using a single, duly improved apparatus. Of course, in. order to attain said purpose, it is necessary to ensure the correct centering between the axis of the hole of the finished bushing and that of the outer surface thereof within a tolerance range from 2/10 to 3/10 mm. It is also necessary to promote the metal flow during the extrusion, so as to prevent the risk of seizure between the extruded piece and the die surface during the extrusion and knockout steps.

[0006] By the use of the conventional process these two conditions are ensured by the preforming operation of a shallow axial dead hole. This hole serves for guiding the punch in order to ensure a correct centering of said punch during the final extrusion step. During this step, which is carried out, employing an apparatus comprising a die greater in the diameter than that of the preformed piece, it happens that the portion of the material which is sorrounding the dead hole does not deform and therefore it cannot contact the die surface, this retaining the lubricant applied on said surface and thus promoting a metal flow upwardly as well as making easier the knockout of the piece. In the fact, while the punch of the second press is guided by the guiding dead hole arranged in the upper end portion of the piece during the preforming step and therefore is avoided any uncorrect centering, in the first portion of the piece around said hole a modest increase of the diameter of the piece takes place which enables an annular gap to be created where the phosphating agent is retained, thus promoting the flow of the metal. According to the present invention the bushing is obtained by the use of an apparatus in which the punch will be guided by a floating sleeve mounted thereabout, and bound therewith, said sleeve being designed to be received into a seat arranged about the orifice of the inner forming chamber or cavity of the die, said sleeve preventing any lateral displacement of the punch, thus ensuring the correct centering thereof during the operative stroke of said punch. For the purpose of promoting the flow upwardly of the metal, thus avoiding the seizing-up, subst-antially at the level of the upper end of the block or piece to be extruded, the axial hole arranged in the die widens so as to form a section of a diameter greater than that of the preceding one, said hole section defining the seat to receive and to retain the guiding sleeve during the operative phase.

[0007] These and other characteristics and advantages of this invention will become more apparent from the following specification of an embodiment of the invention taken in consideration together with the accompanying drawings, in which:

Figures 1 to 3 show the axial section of a metal piece or block to be transformed in a bushing, these figures showing the three subsequent shapes which said block takes when it is subjected to the conventional extrusion process, up to the final extrusion step; Figures 4 and 5 show the axial section of the punch of the forming chamber of the press die as well as of the piece, before the extrusion phase and after said phase of the process according to the present invention respectively.

[0008] Referring to Figures 1 to 3, at 1 is indicated a block or slab cut away from a cylindrical metal rod having the predetermined diameter adapted to obtain a bushing, while at 2 is indicated in Figures 3 and 5 the bushing after the final extrusion step. The bushing is not shown, as appears after the conventional operations of the opening of its bottom and of the gauging thereof, since said operations are "per se" well known.

[0009] For comparison purpose, in Figure 2 is shown a block or piece la, afterwards a shallow dead guiding hole has been obtained i.e. so as it appears after the preforming step according to the conventional process, which operation has been eliminated by the present invention.

[0010] Now referring to the Figures 4 and 5, at 4 is indicated the pressing punch, mounted in the press 5, of which only the lower head has been shown, said press being neither entirely illustrated nor described, since it is well known in the art. The press 5 will include means to force the punch 4 downwardly or to raise it upwardly. The punch 4 has a slightly outwardly anlarged lower end portion 4a, while according to the present invention a guiding sleeve 6 is slidably mounted about said punch 4.. The upper portion of the outer surface of said sleeve 6 has a conical shoulder 6a so as to form a slightly outwardly extending upper peripheral retaining edge. Between the head of the press and the sleeve 6.may be mounted a helical expansion spring 7 which tends to urge the sleeve 6 downwards in cooperation with the effect of the force of gravity acting on the sleeve 6. Said spring 7 is not absolutely necessary, since the weight of the sleeve 6 normally is sufficient in order to maintain the sleeve 6 pressed against the enlarged end 4a of the punch 4. For assembly purpose, the sleeve 6 is constructed in two halves connected one to another by suitable means.

[0011] At 8 is indicated the press die body, in which the forming space or cavity for receiving the centering sleeve 6 as well as the guiding hole for the kick-off member or stripper 9 are arranged. Starting from below said cavity comprises a cylindrical section 10 for guiding the kick-off member or stripper 9, said section then widening so as to form an annular groove 11 of a small radial depth and positioned just at the level of the upper end of the knick-off member 9 which constitutes the lower closure means of the die cavity in the rest condition thereof. Above the section 12 the cavity widens with an annular conical shoulder 13, then forming a cylindrical section 14 of a diameter greater than that of the section 12. In order to make easier the insertion of the sleeve 6 into the first portion of the cavity of the press die 8, radiused by a conical portion 15, the section 14 extends upwards with a cylindrical section 16 ending with a flared end portion 17 designed to receive the outwardly extending peripheral edge 6a of the guiding sleeve 6.

[0012] At the beginning of the process the punch 4 together with the guiding sleeve 6 is raised and pushed off the press die 8, while the kick-off member 9 is positioned as shown in Figures 4 and 5 so as to flush the lower plane of the annular groove 11 so as to constitute the bottom of the forming chamber.

[0013] The piece or slab 1 is inserted inside said cavity or chamber and it will be received into the section 12 thereof. Then the punch 4 is lowered, said punch moving in the direction of the arrow in Figure 4 together with the sleeve 6 under the effect of the weight of this latter, and optionally with the co-operation of the action of the spring 7. The sleeve 6 enters into the section 16 and stops therein, as its outwardly extending peripheral edge 6a abuts against the flared orifice 17 thereof, so that the sleeve 6 will be positioned and remain in such a way as to constitute a guiding and centering means for the punch 4 during the operative downward stroke thereof (Figure 4). Then as

[0014] the punch continues its travel downwards, it reachs the piece 1 and penetrates this latter, compressing the material, which at first fills up the annular groove 11 and then, on account of the fact that it cannot flow downwardly, it is pushed upwardly in contact with the inner surface of the section 12. But above the upper end of the section 12 the material meets no more resistance, since the section 14 has a greater diameter and that promotes the flow of the material upwardly, thus preventing any seizing-up of the bushing 2 to the forming surface of the die so that the expulsion of the piece 2 after the removal of the punch 4 together with the guiding sleeve 6 can take place without difficulty and without any possibily that the extruded bushing 2 can be subjected to any deformation. The subsequent steps of the boring of the bushing bottom and of the gauging of the bushing surfaces are conventional.

Claims

1-An improved process for the cold extrusion of metal bushings comprising the cutting of a length of a rod of a predetermined diameter, the phosphating or spheroidal annealing of said metal piece, and further including the step of:

subjecting said phosphated piece to a single extrusion process performed inside a forming seat by means of a press punch associated with means for guiding along and centering said punch on the axis of said seat which is so shaped to include a first lowermost section having a aoss section mating the cross section of said piece to be transformed in a bush, a second section following said first section and coaxially thereto and having a slightly greater diameter and of such a height to be able to receive in combination with said first section the guiding means and the extruded bushing, this bushing being then subjected to boring and gauging operations.

2-Apparatus for carrying out the process according to claim 1, comprising a press body (5), including means for giving to a punch (4) reciprocating motion along a vertical path and co-operating with a press die (8) which includes a forming chamber or seat having upper and-lower ends, said lower end being closed by the upper head of a kick-off member (9) connected to control means, characterized by the fact that the punch (4) has an enlarged lower head (4a), and wherein about said punch (4) is axially slidably mounted a sleeve (6) having a peripheral upper outwardly extending edge (6a), while the forming chamber or seat comprises, beginning from its lower end, a first cylindrical section (10) of such a diameter to slidably receive the kick-off member (9), an annular groove (11) of a very small radial depth, a second cylindrical section (12) of a diameter equal to that of the bushing (2) which has to be obtained and of a height equal to that of the piece (1) to be processed, and a third section (14) of a diameter slightly greater than that of the section (12) and radiused thereto by a conical shoulder (13), the section (14) enlarging in an upper end portion (16) shaped so as to receive the guiding sleeve (6, 6a) for the punch (4).

3-An apparatus according to claim 2, wherein between the lower head of the press (5) and the guiding sleeve (6) a helical expansion spring (7) is mounted about said punch (6).

Drawing