WO1995004623A1

WO1995004623A1 - Improved autoforcing face carrier utilizable on lathes and similar machine tools

Info

Publication number: WO1995004623A1
Application number: PCT/IT1994/000134
Authority: WO
Inventors: Gabriele Vetrala; Marco Manetti
Original assignee: Gabriele Vetrala; Marco Manetti
Priority date: 1993-08-10
Filing date: 1994-08-09
Publication date: 1995-02-16
Also published as: ITSP930005U1; ITSP930005V0; IT233777Y1

Abstract

Improved face carrier suited to be mounted at the spindle of a machine tool to support the piece being machined and contemporaneously set it in rotation. It comprises a head (2) equipped with claws (5) slidingly mounted on a body (1) for attachment to a spindle, said head (2) having an elastically retractable center (6) suited to be engaged on said piece (40) to be machined in correspondence with its rotational axis. More precisely the head (2) engages against a plurality of spheres (7) housed in seats (28) formed in the body (1). The spheres (7) engage against an autoforcing disc (3) on which, in turn, a ring (4) engages, in such a way that it can be oriented, in contact with shanks (35) of claws (5) for gripping the piece (40), said shanks (35) being slidindly engaged in said head (20) which, in turn, slidingly engages in said body (1). The carrier, besides being autoforced on said piece in variation with the loads to which it is submitted, is suited to grip the face of the piece even when it is not flat and orthogonal to the rotational axis. Furthermore, it allows pieces of different diameter to be set in rotation and makes the changing of the gripping claws and the center easy.

Description

XI £

IMPROVED AUTQFQRCING FACE CARRIER UTILIZABLE QN LATHES AND

STMTT.AR MACHINE TOOLS. DESCRIPTION Field of the invention

The present invention generally relates to the field of machine tools and more precisely it relates to an improved autoforcing face carrier, that can be engaged on a parallel lathe or similar machine-tool to sustain the piece and set it in rotation for the machining.

Description of the prior art

As is known, the pieces being machined on the lathe are subject to radial loads, i.e. orthogonal to the rotational axis, axial loads and tangential loads, due to the action of the tool which provokes the cutting away of the shavings. The intensity of the radial and tangential loads is proportional to the cutting depth, the hardness of the material rotated, the cutting speed and the other machining parameters. To make the piece withstand the radial and tangential loads, it is axially forced by a tailstock on a motorised spindle which supports it by means of a self- centering chuck or a face carrier. The self-centering chuck holds the piece by means of jaws which grip it radially, whereas the face carrier holds the piece by means of acuminate claws which wedge themselves in the face of the piece that is turned towards the carrier itself.

To allow the piece to withstand strong radial and tangential loads, it is thus necessary that a strong axial load be exercised on it by the tailstock, a load which transmits itself entirely on the spindle. Also the face carrier or the self-centering chuck are strongly pressed and are sized appropriately to resist the great stress transmitted by the piece.

Face carriers are normally subject to the following inconveniences:

- they do not allow for the machining of workpieces with a high cutting depth;

- they have to be changed according to the diameter of the piece to be carried, or in any case, it is at least necessary to substitute the interchangeable facing heads which must, therefore, be provided in a vast assortment; - the claws must be changed when passing from clockwise to counterclockwise rotation;

- in any case, they require a very strong axial load by the tailstock, which, with time, causes grave damage to the spindle of the machine on which the carrier is mounted.

This last inconvenience is caused by the fact that the face carrier supports the piece only by effect of the axial loads transmitted by the tailstock, and that the forces transmitted on the spindle are, in this case, much greater than in the case in which a self-centering chuck is used. To avoid pressing the spindle too much, when machining must be carried out with heavy radial loads, it is advisable to hold the piece by means of a self- centering chuck. The use of such a chuck is nevertheless disadvantageous when pieces must be machined along_, their lateral surface, since a portion of that surface is covered by the jaws of the self-centering chuck and cannot be machined by the tools without turning the workpiece.

A type of face carrier is known which is capable of overcoming, in part, the above-mentioned inconveniences, described in the Italian utility model no. 0218067, in the name of one of the present applicants.

This type of face carrier comprises a head equipped with claws slidingly mounted on a body for attachment to the spindle. The claws are fixed to a claw head separable from the head, and coaxial to the claw head, an elastically retractable center is present, suited to be engaged on the piece in correspondence with its rotational axis. The head is in contact with the body through a plurality of spheres housed in spherical seats formed in it. The spheres rollingly engage in radial grooves having a triangular cross-section. Therefore, the greater the twisting effect on the piece due to the cutting away of the shavings, the greater the axial force with which the carrier pushes its claws against the piece.

This type of carrier, nevertheless, is limited by its scarce capacity for adaptation of the claws to the face of the piece when the latter is rough or is not orthogonal to the rotational axis. The claw head that holds the claws, although it can be oriented, has a very limited angular range and is subject to becoming caught between the center and the head. Further limitations consist in a less than optimum capacity for gripping the piece in the presence of heavy radial loads and in a scarce flexibility of the claw head to adopt to different diameters of the pieces being machined.

Summary of the invention

The object of the present invention is to provide an improved face carrier able to overcome the above-mentioned inconveniences, and in particular suited to grip the face of the piece even when it is not flat and orthogonal to the rotational axis.

A further object of the present invention is to provide an improved face carrier that is autoforcing on the piece in varying degrees according to the loads to which the piece is subjected, with a high reliability, safety and precision even in the presence of strong axial and radial pressures. Yet another object of the present invention is to provide an improved face carrier that allows pieces of different diameters comprised within a certain range of variability to be set in rotation with the possibility of easily changing the gripping claws when necessary.

These and other objects are accomplished by the improved face carrier according to the present invention, characterized in that said head comprises an autoforcing element which pulls the claws against the pieces with a force which varies with the machining loads. Engaged on the autoforcing element, in such a way that it can be oriented, is a ring on which the shanks of the claws for gripping the piece slidingly engage. These shanks slidingly engage in said head to which they are preferably secured by means of stop dowels. The head engages slidingly both on an annular enlargement and on a neck of the body of the carrier.

Brief description of the drawings

Further characteristics and advantages of the autoforcing face carrier according to the present invention will become more apparent in the description which follows of one of its embodiments, given as an example, but not limitative, with reference to the attached drawings in which: - figures 1 and 2 are respectively a longitudinal sectional view and an exploded partial sectional view of an improved face carrier according to the present invention;

- figures 3 and 4 are partial sectional views of the head of the carrier in figure 1 in two different operative positions;

- figures 5 and 6 are two different embodiments, respectively of a center and a claw of the carrier of figure 1. Description of the preferred embodiment

With reference to figures 1 and 2, a substantially cylindrical body is indicated with 1, having an axial cavity 21 and an annular enlargement 22 from which a neck 23 extends. Body 1 is tapered towards end la, opposite neck 23, and on which a setting cap 14 of a spring 13 housed in cavity 21 engages. Also in cavity 21, at the height of neck 23, a cylindrical center 6 with a conical end 6a is slidingly housed, and though its sliding is allowed, its slipping is prevented by a dowel 12 which fits inside neck 23 protruding into cavity 6b of center 6. From the opposite side of end 6a, center 6 abuts spring 13.

On two external cylindrical faces 22a and 23a respectively of enlargement 22 and neck 23 of body 1, a head 2 slidingly engages, having an axial cavity 24 for neck 23 in which it engages forcing against an O-ring 8 housed in reliefs 26 and 27 formed respectively in head 2 and neck 23. Relief 26 is axially elongated to allow a certain axial movement of head 2 with respect to body 1. This axial movement is regulated by a plurality of spheres 7 housed in recesses 28 formed in annular enlargement 22. Spheres 7 engage against the inclined faces of an equal number of radial grooves 29 having a triangular profile and being formed on a autoforcing disc 3 made integral with head 2 by means of a screw 11. At the opposite side of grooves 29, disc 3 has a spherical seat 30 in which spherical surface 4a of a ring 4 engages. The flat face 4b of the ring serves as a rest for shanks 35 of claws 5 having extremities in the form of knives 36 having straight blades. Shanks 35 slidingly engage in seats 31 formed in head 2 and their slipping is prevented by dowels 9 which protrude into recesses 37 formed in shanks 35 themselves. With reference to figure 3, when the carrier is in contact with surface 40 of a piece to be machined, knives 36 of claws 5 sink into the metal along with center 6a, which draws back elastically. As an effect of the tangential forces on the piece impressed by the machining, spheres 7 roll on one of the inclined faces of grooves 29 of autoforcing disc 4 causing the translation towards the piece of the whole head 2, and, in particular, of claws 5 whose shanks 35 having rounded ends axially force the piece with an intensity proportional to the radial and tangential forces in play. These axial forces release themselves on the spindle and the tailstock (not shown) for the duration of the machining at those particular operative parameters. As soon as the forces on the piece vary, the position of the head adapts itself by modifying the conditions of axial forcing.

As shown in figure 4, in the case in which surface 40 of the piece is not orthogonal to the rotational axis R, claws 5 move, adapting to said surface irregularity even before beginning the autoforcing, and even better after this has begun in the manner illustrated in figure 3. More precisely, the different pressure exercised on knives 36, transmits a rotation to ring 4 through shanks 35, making it so that their sliding in seats 31 of head 2 makes ring 4 move with respect to spherical seat- 29 of disc 3.

The combination of the movement of figures 3 and 4 makes, therefore, the face carrier according to the present invention very reliable, given that the capacity of the claws to adapt to surface 40 increases considerably the value of the torque T that they can support, and, therefore, raises greatly the values of the radial and tangential loads that can be placed on the piece during machining. At the same time, the carrier, thus improved, allows for the adaptability of the claws while maintaining the characteristic of autoforcing, which, as stated above, allows for the limitation of the duration of axial loads of greater intensity to the duration of the heaviest machining, above-all, making it possible to release the forces on the spindle during the lighter machining.

A further advantage of the carrier according to the present invention consists in the facility of disassembly of head 2 and in the consequent possibility of rapidly substituting claws 5 and center 6. More precisely, when not in contact with the piece to be machined, head 2 can be slipped from body 1 easily overcoming the resistance offered by 0-ring 8. Claws 5 and center 6 can therefore be extracted loosening respectively the dowels 9 and 12 thus freeing grooves 37 and 6b respectively. It is worth noting how claw 5 of figures 1 and 2 has double grooves 37 formed on two opposite faces. In this way, knife 36 can be rotated to the two positions of figure 2, adapting to larger or smaller diameters of face 40 of the piece. In order to allow a correct positioning of claws 5, head 2 has face grooves 38 radially crossing one another and in the same number as claws 5. In this way, knives 36 partially sink into grooves 38 preventing shanks 35 from rotating inside holes 31 of head 2, thus preventing them from forcing against screws 9.

Given the extreme facility of substitution of claws 5 and center 6, respectively in figures 5 and 6, given as examples, two possible embodiments are illustrated. Claw 5 of figure 5 is, in particular, appropriate for pieces of small diameter, and to allow knife 36 to place itself as close as possible to the rotational axis R of the piece, center 6 of figure 6 has a portion 6c of decreased diameter. Each set of claws 5 however, adopts to a certain range of diameters of workpieces 40. In a preferred embodiment, for example, three sets of claws respectively for diameters ranges from 16 to 140, from 60 to 210, from 100 to 380 mm are provided.

Claims

C AIMS

1. Improved face carrier comprising a head (2) equipped with claws (5) slidingly mounted on a body (1) for attachment to a spindle, said head (2) having an elastically retractable center (6) suited to be engaged on a piece (40) to be machined in correspondence to its rotational axis and engaging against a plurality of rolling elements (7) housed in seats (28) formed in said body (1) , characterized in that said rolling elements (7) engage against an autoforcing element (3) on which is engaged, in a way in which it can be oriented, a ring (4) against which the shanks (35) of said claws (5) for gripping said piece (40) are in contact, said shanks (35) being slidingly engaged in said head (2) which in turn engages slidingly on said body (1) .

2. Face carrier according to claim 1, wherein said rolling elements are spheres (7) .

3. Face carrier according to claim 1, wherein said autoforcing element (3) has radial grooves (29) having inclined faces for the engagement of said spheres (7) and a spherical seat (30) opposite said grooves (29) wherein said ring (4) engages having a face with a spherical surface (4a) .

4. Face carrier according to claim 1, wherein the shanks (35) of said claws (5) and said center (6) slidingly engage in said head (2), stop dowels (9,12) being provided suited to engage in cavities (37,6b) provided respectively in said shanks (35) and center (6) to prevent the complete slipping.

5. Face carrier according to claim 4 wherein said claws (5) have said shank (35) with a rounded end and a knife (36) on the opposite part of said shank (35) .

6. Face carrier according to claim 1, wherein said claws have said knife (36) which extends asymmetrically from said shank (35) to adapt to the diameter of said piece (40) .

7. Face carrier according to claim 6 wherein said head (2) has face grooves (38) radially crossing one another and in which said knives (36) of said claws (5) partially engage.

8. Face carrier according to claim 1, wherein said body (1) has an annular enlargement (22) wherein said seats (28) are formed for said spheres (7) , said head (2) slidingly engaging on said enlargement (22) and on a cylindrical neck (23) extending from it.

9. Face carrier according to claim 7, wherein, between said head (2) and said neck (23) , an annular elastic element (8) is engaged.

10. Face carrier according to claim 1, wherein said body (1) has, opposite said neck (23) , a cylindrical surface tapered toward the end for the engagement of a cap (14) for setting the tensioning of a spring (13) housed in a cavity (21) coaxial to said body (1) and engaging against said center (6) .