Clamp for machine tool

Abstract

The invention relates to a clamp for a machine tool, of the type making it possible to grip a workpiece from the inside, i.e. by being inserted into a cavity thereof. Such a clamp includes a hollow clamp body (1) that is elongate along a longitudinal central axis (X), a clamp head (2) intended to be removably mounted on one end of the clamp body (1) and a push rod (3) that is movable inside the clamp body (2) between a retracted position and an extracted position. The clamp head (2) includes a cylindrical portion (26) having slots (33) that extend at least along the longitudinal central axis (X), and a central hole (34) extending along the longitudinal central axis (X) from the side of the clamp head (2) facing the clamp body (1), the central hole (34) having a conical or frustoconical portion (37), the smallest diameter of which is on the side opposite to the clamp body (1). The push rod (3) includes a conical or frustoconical end (16) capable of being inserted into the central hole (34) of the clamp head (2) during the passage of the push rod (3) into the extracted position, the smallest diameter of the (frusto)conical end (16) then being on the side opposite to the clamp body (1). The clamp head (2) includes a groove (29) separating its cylindrical portion (26) from an attachment portion (27) which lacks any slots and with which the clamp head (2) can be removably mounted on the clamp body (1).

Description

[0001] CLAMP FOR MACHINE TOOL

[0002] Technical field

[0003] The invention relates to a clamp for a machine tool, of the type allowing a workpiece to be gripped from the inside, that is to say by inserting it into a cavity thereof.

[0004] State of the art

[0005] Machine tool collets of the above type generally consist of three main parts:

[0006] - a hollow and substantially cylindrical clamp body,

[0007] - a clamp head mounted on one end of the clamp body and having a central hole,

[0008] - a pusher movable inside the clamp body, between a retracted position and an extracted position, and comprising a conical end capable of penetrating into the central hole of the clamp head.

[0009] The end of the collet body opposite the collet head is intended to be inserted into the spindle of a machine tool and the pusher is intended to be actuated by a sliding sleeve of this machine tool which moves it from the retracted position to the extracted position.

[0010] When moving from the retracted position to the extracted position, the tapered end of the pusher cooperates with the central hole of the gripper head to increase the diameter of the gripper head, so that it exerts pressure on the walls of the cavity of the workpiece and thus holds it.

[0011] Such clamping pliers are described in the European, Swiss and international patent applications published respectively under the numbers EP 2383059, CH 719160 and WO 2013 / 037990. These known clamping pliers are able to hold a workpiece with sufficient firmness for so-called light machining operations, namely, chamfering, surfacing, polishing, drilling of small diameter holes, etc.

[0012] However, they do not allow the workpieces to be held with the firmness necessary to carry out so-called heavy operations, such as turning and milling, these operations involving higher cutting speeds and depths of cut and therefore involving higher forces.

[0013] Disclosure of the invention

[0014] The main aim of the invention is to propose a clamping pliers which overcomes the aforementioned drawback.

[0015] This object is achieved by a clamping pliers according to claim 1.

[0016] The clamping pliers according to the invention offer in particular the following advantages over known clamping pliers:

[0017] - its clamp body has increased resistance,

[0018] - its lifespan is longer,

[0019] - the positioning of the clamping head in the part is improved,

[0020] - the clamping force is applied as close as possible to the workpiece,

[0021] - the elimination of tightening inertia thanks to direct tightening,

[0022] - identical repositioning of the clamping head on the clamping body after disassembly / reassembly,

[0023] - superior rigidity,

[0024] - a simpler structure with a lower number of component parts, - the possibility of easily choosing the geometry of the clamping head to have a better distribution of the clamping force depending on the geometry of the part to be machined,

[0025] - greater ease and speed of assembly.

[0026] Brief description of the drawings

[0027] Other characteristics and advantages of the present invention will appear on reading the following detailed description of several embodiments of the invention, given as non-limiting examples, and made with reference to the appended drawings in which:

[0028] - figure 1 is an exploded view of a clamp according to the invention;

[0029] - Figures 2 to 4 show a clamp body of the clamp according to the invention, in perspective, in front view and in bottom view in section respectively;

[0030] - figures 5 and 6 represent a pusher used in the pliers according to the invention, in perspective and in top view in section respectively;

[0031] - figure 7 represents a detailed view of a shoe and the fixing means;

[0032] - figures 8 and 9 respectively represent a perspective view and a sectional view of a clamp body / pushbutton assembly of the clamp according to the invention;

[0033] - figures 10 to 15 respectively represent a clamp head according to an embodiment of the clamp according to the invention, in perspective view, in front view, in left view, in right view; in right view in section along line BB, in top view in section along AA;

[0034] - Figure 16 is a view of detail D of Figure 11; - Figures 17 to 20 represent a clamp head according to another embodiment of the clamp according to the invention, in perspective view, in front view, in left view and in top view in section along AA, respectively;

[0035] - figure 21 represents the clamp head of figure 17, after pivoting 180 degrees;

[0036] - Figure 22 represents a detail showing the mounting of the clamp head of Figures 17 to 21 on the clamp body of Figures 2 to 4 and the pusher of Figures 5 and 6, in the retracted position; and

[0037] - figure 23 represents a clamping pliers according to the invention, ready for use.

[0038] Embodiments of the invention

[0039] An example of an embodiment of a clamp according to the invention is shown in Figure 1.

[0040] As can be seen in this figure, the clamp is composed of three essential parts: a clamp body 1, a clamp head 2 and a pusher 3.

[0041] These three pieces and their accessories will now be described in relation to the other figures.

[0042] The terms "proximal end" and "distal end" refer respectively to the side of the clamp intended to be held by the machine tool spindle (left in Figure 1) and to the side of the clamp intended to hold the workpiece (right in Figure 1).

[0043] Clamp body

[0044] This clamp body is shown in Figures 2 to 4. It has a hollow and elongated shape and generally has a symmetry of revolution, because the clamp can be called upon to rotate on itself when carrying out machining operations on the workpiece that it holds.

[0045] The clamp body 1 therefore has substantially the shape of a hollow cylinder having a longitudinal central axis X. It comprises a proximal end 4 intended to cooperate with the spindle of a machine tool and a distal end 5 intended to support the clamp head 2.

[0046] The clamp body 1 comprises an axial hole 6 having a bore 7 of larger diameter forming a shoulder 8 at the distal end 5 (figure 4).

[0047] In the wall of the distal end 5 several holes 9 have been provided, in this case three in the figures, which are not necessarily tapped and are intended to receive fixing screws, as will be described in detail below.

[0048] As can be seen in particular in figures 2 and 3, the clamp body 1 comprises elongated slots 10 along the X axis, at the level of the bore 7, which pass through the entire thickness of the clamp body 1.

[0049] A collar 11 is also provided near the distal end 5.

[0050] Notches or recesses 24 visible in Figure 2 extend between the outer face 25 of the distal end 5 and the shoulder 8. They are preferably regularly arranged around the periphery of the end 5. The role of these notches 24 will be detailed below.

[0051] Pusher

[0052] This pusher 3 is visible in particular in figures 5 and 6. It has a substantially cylindrical shape, with a proximal end 12 and a distal end 13 provided with a bore 14 intended to receive an elastic element such as a helical spring, which will bear on the bottom 15 of the bore 14.

[0053] The distal end 13 has a truncated cone-shaped tip 16.

[0054] As can be seen in Figure 5, several flats 17, three in this case, are provided on the outer surface of the pusher 3. They preferably have an elongated shape along the longitudinal central axis X and are preferably located in the middle of the pusher 3. They each comprise a tapped radial hole 19 and possibly another non-tapped radial hole 18 which may have a diameter different from that of the hole 19.

[0055] Assembly of the pusher and the clamp body

[0056] The pusher 3 is sized to slide inside the axial hole 6 of the clamp body 1, as can be seen in particular in Figure 9.

[0057] Shoes 21, visible in Figure 7, are provided to cooperate with the spindle and the socket of the machine tool to advance the pusher 3, as well as to limit its axial movements. They each have a flat face intended to rest on the flats 17 of the pusher 3. They also each have a hole 22 crossed by a screw 23 which is screwed into a tapped hole 19 of the pusher 3. To facilitate the installation of the shoes 21, pins 50 can optionally be slid both into holes 20 (see Figure 1) provided on the flat faces of the shoes 21 and into any holes 18 located in correspondence on the flats 17.

[0058] As can be seen in Figure 8, once the pusher 3 is inserted into the clamp body 1 and the shoes 21 are in place, the latter limit the axial movements of the pusher 3 by coming into abutment against the proximal and distal longitudinal ends of the elongated slots 10. Clamp head

[0059] Figures 10 to 15 show a first embodiment of the clamp head 2. This clamp head 2 comprises a deformable cylindrical part 26 and a rigid assembly or fixing part 27, with which the clamp head 2 can be removably mounted on the clamp body 1.

[0060] According to the invention, the cylindrical part 26 and the fixing part J are separated by a cylindrical connecting part 28 of smaller diameter, so as to create a groove 29 between said cylindrical part 26 and fixing part 27.

[0061] The cylindrical part 26 is similar to a solid cylinder divided by several slots 33 extending radially from the longitudinal central axis X to the longitudinal face 30 of the cylindrical part 26 and then extending longitudinally from the distal transverse face 31 to the proximal transverse face 32 of the cylindrical part 26, face 32 which is in fact the distal wall of the groove 29.

[0062] In this embodiment, the slots 33 are in principle two in number and preferably perpendicular to each other. However, since each slot 33 is cut in two by a slot which makes an angle with it, as can be seen in Figure 13, four slots 33 are finally obtained, meeting at the longitudinal central axis X.

[0063] These four slots 33 divide the cylindrical part 26 into four identical parts which are in fact jaws 36 intended to be introduced into the cavity of a part to be machined, in order to hold it.

[0064] As can be seen in particular in Figure 15, the clamp head 2 has an axial central hole 34 extending along the longitudinal central axis X from the side of the clamp head 2 facing the clamp body 1 - i.e. the proximal face 35 of the clamp head 2 - towards the distal face 31 of the cylindrical part 26 which is also the distal face of the clamp head 2.

[0065] This central hole 34 has a conical or truncated part 37 whose smallest diameter is located on the side opposite the clamp body 1, that is to say on the side opposite the proximal face 35 of the clamp head 2.

[0066] Unlike the devices of the state of the art and in particular part 16 of the aforementioned international application No. WO 2013 / 037990 (see in particular Figures 2 and 4), according to the invention, the fixing part 27 is devoid of slots. It is therefore rigid, which advantageously allows it to be used to mount the clamp head 2 on the clamp body 1, without requiring an intermediate part.

[0067] In addition to this reduction in the number of parts, the absence of an intermediate part for assembly (like parts 40 and 60 in figure 7 of WO 2013 / 037990) has the advantage of allowing the groove 29 to be left clear.

[0068] This emptiness of the groove 29 has a particularly interesting effect: it makes it possible to absorb the deformations of the cylindrical part 26, namely, the spacing of the jaws 36 relative to each other. Thus, the clamp head 2 can open sufficiently by flaring and not in a uniform radial manner as in the device described in publication WO 2013 / 037990.

[0069] The groove 29 therefore gives more flexibility to the clamp head 2, which results in a sufficient opening at the distal end of the clamp, even if the diameter of the cylindrical part 26 is large.

[0070] The groove 29 may optionally be occupied by an element, but on the condition that it does not hinder the movements of the jaws. This must therefore be an element made of a deformable material, such as an O-ring which can easily be compressed. Preferably, the (truncated)conical part 37 of the central hole 34 of the clamp head 2 is located in the cylindrical part 26. Thus, the clamping force is applied in the clamping head and not in the clamping body. As a result, the force applied against the workpiece is greater.

[0071] The action of the pusher 3 on the cylindrical part 26 has no effect on the fixing part J and, therefore, on the mounting of the clamp head 2 on the clamp body 1.

[0072] Furthermore, the central hole 34 of the clamp head is blind, with the exception of the central capillary orifice 39 passing through the cylindrical part 26 and which is formed by the junction of the slots at the longitudinal axis X (see figure 13).

[0073] But in concrete terms, as the diameter of the capillary orifice 39 is tiny, in particular of the order of 0.3 mm, whereas the diameter of the bottom 40 of the central hole 34 is of the order of 12 mm, i.e. 30 times greater, it can be considered that the central capillary orifice is negligible and that the central hole 34 is blind.

[0074] Preferably, the central hole 34 of the clamp head 2 extends at most over half the length of the cylindrical part 26 of the clamp head 2. Even more preferably, the length of the central hole 34 is at most one third of the length of the cylindrical part 26 of the clamp head 2. In this way, the majority of the cylindrical part 26 is solid, without a central recess. Consequently, it is possible to have a cylindrical part 26 with a larger outer diameter than in the devices of the prior art, more resistant, but which remains sufficiently mobile to be able to deform from its proximal end, so as to move away sufficiently at its distal end to be able to hold the workpiece with force.

[0075] Thus, thanks to the empty groove 29, the diameter of the cylindrical part 26 can be increased even if the (truncated)conical part 37 does not extend to the distal end of the head, as is the case in the aforementioned state-of-the-art devices.

[0076] In general, the axial length of the (truncated)conical portion 37 represents less than a third and preferably less than a quarter of the length of the central hole 34.

[0077] According to a preferred embodiment of the invention, the deformability of the cylindrical part 26 is further increased by holes 38 provided in the connecting part 28. These holes 38 are radial, that is to say they start from the bottom of the groove 29 and open into the central hole 34 of the clamp head 2.

[0078] Preferably, the diameter of these radial holes 38 provided in the groove 29 is equal to the axial length of the groove 29.

[0079] Preferably, each radial hole 38 is positioned such that its center is at the same level as a slot 33, so that the proximal end of each slot 33 opens into a radial hole 38. This makes it possible to further increase the flexibility at the proximal end of the cylindrical part 26.

[0080] Figures 17 to 21 show a second embodiment of the clamp head 2, which differs from the first embodiment of Figures 10 to 16 only in that it comprises, instead of four slots, six slots forming an angle of 60 degrees with respect to each other.

[0081] Therefore, the second embodiment of the clamp head 2 comprises six jaws 36 which can be clearly seen in Figure 17.

[0082] As for the connecting part 28 of the clamp head 2, it is similar to a disc having in its center a part of the central hole 34.

[0083] As for the rigid fixing part J of the clamp head 2 to the clamp body 1, it comprises a discoid part 41 crossed by the central hole 34, like the connecting part 28, but it has a diameter greater than the latter and possibly identical to that of the cylindrical part 26, so as to form the groove 29.

[0084] On the proximal side of the fixing part 27, a cylinder 42 crossed by a part of the central hole 34 extends the discoid part 41.

[0085] The fixing part 27 comprises tabs 43 which project radially from the cylinder 42 and are preferably regularly arranged around this cylinder, preferably at its proximal end. Said tabs 43 are arranged to cooperate with the recesses 24 provided on the clamp body 1 to achieve a bayonet fixing.

[0086] Furthermore, holes 44, preferably tapped, are provided between the discoid part 41 and the legs 43.

[0087] Assembling the gripper head onto the gripper body / pusher assembly

[0088] Figure 22 shows the distal end 5 of the clamp body 1 on which the clamp head 2 partially shown in the figure has been mounted.

[0089] The tabs 43 of the clamp head 2 have been oriented so that they can be slid inside the recesses or notches 24 until the discoidal portion 41 abuts against the face 25, then the clamp head 2 has been slightly rotated so that the tabs 43 are adjacent to the shoulder 8 of the clamp body 1. This operation is typical of a bayonet attachment. However, it is desirable to lock this attachment. For this purpose, screws 46 are arranged to immobilize the clamp head 2 by screwing onto the clamp body 1. More particularly, the screws 46, passing radially through the proximal end of the clamp head 2 and the distal end 5 of the clamp body 1, are screwed into the holes 9 of the clamp body 1 until they penetrate into a hole 44 of the clamp head 2, but avoiding them passing through the latter and blocking the rotation of the pusher 3 by coming into contact with the distal end

[0090] 13 of this one.

[0091] It goes without saying that there are at least as many notches 24 as there are tabs 43 and that the dimensions of the tabs 43 are designed to allow the latter to pass through the notches 24. Similarly, the distance between the tabs 43 and the discoid part 41 must be at least equal to the distance between the shoulder 8 and the face 25 of the distal end 5 of the clamp body 1.

[0092] In this way, the end 5 of the clamp body 1 is wedged between the tabs 43 passed behind the shoulder 8 and the discoid part 41 of the fixing part 27.

[0093] Furthermore, the frustoconical part 37 of the central hole 34 of the clamp head 2 has substantially the same angle of inclination relative to the X axis as the frustoconical end 16 of the pusher 3. However, the axial length of the frustoconical part 37 is greater than that of the frustoconical end 16, preferably at least 1.7 times greater.

[0094] A helical spring 45 is arranged between the bottom 15 of the bore 14 of the pusher 3 and the bottom 40 of the frustoconical part 37 of the central hole 34.

[0095] It can therefore be seen that the assembly of the clamping pliers according to the invention is carried out quickly. It is further simplified by the fact that the clamp body 1 and the clamp head 2 are in one piece and that few accessories (screws, etc.) are required.

[0096] Once the clamp body 1, the pusher 3 and the clamp head 2 are assembled and locked, the clamp according to the invention is operational.

[0097] The dimensions of the pusher 3 and the central hole 34 are calculated so that the passage in the extracted position does not damage the cylindrical part 26. A deformable element such as an O-ring 48 can be introduced into the groove 29. This seal has the purpose of preventing dirt from entering the system through the radial holes 38 and obstructing the groove 29. It also prevents losses of lubricating fluid because this is injected from the socket of the machine tool.

[0098] We then obtain the clamp shown in figure 23.

[0099] Functioning

[0100] When the clamping pliers are at rest, the spring 45 keeps the pusher 3 in the retracted position, that is to say that its frustoconical end 16 is not in contact with the frustoconical part 37 of the clamp head 2.

[0101] When the socket of a machine tool moves the pusher 3 towards the clamp head 2 along the arrow F by means of the shoes 21, towards its extracted position (towards the right in figure 22), its truncated end 16 comes into contact with the truncated part 37 of the central hole 34 of the clamp head 2, then, if the movement continues, there is a separation of the jaws 36 from each other which exerts a clamping on the part to be machined, namely, on the interior walls of its cavity.

[0102] Because the central hole 34 of the clamp head 2 extends only over a portion of the cylindrical portion 26, the spacing of the jaws 36 is not uniform: their distal end moves further away from the longitudinal central axis X than their proximal end. In other words, the groove 29 therefore makes it possible to soften the clamp head 2 to have a sufficient opening at its distal end, so that the cylindrical portion 26 flares even if the diameter is large and the same if the pusher 3 does not go as far as the distal end of the clamp head 2.

Claims

Claims 1. Clamp comprising: - a hollow and elongated clamp body (1) along a longitudinal central axis (X), - a clamp head (2) intended to be removably mounted on one end of the clamp body (1) and comprising • a cylindrical part (26) having slots (33) extending at least along the longitudinal central axis (X), • a central hole (34) extending along the longitudinal central axis (X) from the side of the clamp head (2) facing the clamp body (1) and having a conical or frustoconical part (37) whose smaller diameter is on the side opposite the clamp body (1), and - a pusher (3) • movable inside the hollow of the clamp body (2) between a retracted position and an extracted position, and • comprising a conical or truncated end (16) capable of being inserted into the central hole (34) of the clamp head (2) when the pusher (3) passes into the extracted position, the smallest diameter of the (truncated) conical end (16) then being on the side opposite the clamp body (1), characterized in that the clamp head (2) comprises a groove (29) separating its cylindrical part (26) from a fixing part (27) without slots and with which a removable mounting of the clamp head (2) on the clamp body (1) can be carried out.

2. Clamping pliers according to claim 1, characterized in that the groove (29) is empty or contains a deformable element.

3. Clamping pliers according to one of the preceding claims, characterized in that the central hole (34) of the clamp head (2) is blind.

4. Clamping pliers according to one of the preceding claims, characterized in that the (truncated)conical part (37) of the central hole (34) of the clamp head (2) is located in its cylindrical part (26).

5. Clamping pliers according to claim 4, characterized in that the central hole (34) of the pliers head (2) extends at most over half the length of the cylindrical part (26) of the pliers head (2).

6. Clamping pliers according to claim 5, characterized in that the central hole (34) of the pliers head (2) extends at most over one third of the length of the cylindrical part of the pliers head (2).

7. Clamping pliers according to one of the preceding claims, characterized in that the groove (29) of the clamp head (2) comprises radial holes (38).

8. Clamping pliers according to claim 7, characterized in that the diameter of the radial holes (38) is equal to the axial length of the groove (29).

9. Clamping pliers according to one of claims 7 and 8, characterized in that each slot (33) opens into a radial hole (38).

10. Clamping pliers according to one of the preceding claims, characterized in that the clamp body (1) is in one piece.

11. Clamping pliers according to one of the preceding claims, characterized in that the pliers head (2) is in one piece.

12. Clamping pliers according to one of the preceding claims, characterized in that the fixing part (27) of the pliers head (2) comprises lugs (43) and in that the pliers body (1) comprises recesses (24) cooperating with said tabs (43) to provide a bayonet attachment.

13. Clamping pliers according to claim 12, characterized in that it further comprises screws (46) arranged to immobilize by screwing the clamp head (2) on the clamp body (1).

14. Clamping pliers according to one of the preceding claims, characterized in that the axial length of the (truncated)conical part (37) represents less than one third of the length of the central hole (34).

15. Clamping pliers according to claim 14, in which the axial length of the (truncated)conical part (37) represents less than a quarter of the length of the central hole (34).

16. Clamping pliers according to one of the preceding claims, characterized in that the (truncated)conical end (16) of the pusher (3) and the (truncated)conical part (37) of the central hole (34) have the same angle of inclination relative to the axis (X).

17. Clamping pliers according to one of the preceding claims, characterized in that the axial length of the (truncated)conical part (37) of the central hole (34) of the clamp head (2) is greater than that of the truncated conical end (16) of the pusher (3).

18. Clamping pliers according to claim 17, characterized in that the axial length of the (truncated)conical part (37) of the central hole (34) of the clamp head (2) is at least 1.7 times greater than that of the truncated conical end (16) of the pusher (3).

19. Clamping pliers according to one of the preceding claims, in which a deformable element is arranged in the groove (29).

20. A clamp according to claim 19, wherein the deformable element is an O-ring (48).

Images