FIELD OF THE INVENTION

The present invention relates to the sector of machine tools and, in greater detail, the sector of broaching systems which, owing to the swinging motion impressed by the cutting tool, enable realisation of shapes, typically lobulated or polygonal or substantially polygonal figures, internally of blind or through-hollows. In particular, the invention relates to a kit to be applied to a machine tool, the components of the kit and a method.

DESCRIPTION OF THE PRIOR ART

In the sector the term broaching is also used to identify machining operations using a tool, constituted by a series of cutting tools and known as a pin or broach, which is pulled or pushed by broaching machines. The common denomination does not correspond to a technical similarity as the two applications work in different ways and have different work objectives. The two types of broaching are generally distinguished as linear and rotary broaching.

Document FR1533594A describes a kit for transforming a machine tool into a rotary broaching machine which comprises a broach or a broaching head with a broach-bearing axle and bearings. The broaching head comprises, at a first end, a shank which is predisposed for fixing a machine tool and, at a second end, a cavity for accommodating the bearings that house the axle, which comprises a seat for housing the broach which has cutting edges over the whole edge of the free end.

The kit can be used in a wide range of machine tools for realising lobulated or polygonal figures, or the like, starting from blind or through-holes generally having a circular section. With the kit, this operation can be carried out within a work cycle on a same machine tool, without requiring collecting manoeuvres on the piece, or a change of machine tool. Usually, before making the shape, a pre-hole is made that, when dealing with polygonal figures, has a slightly larger diameter. Once the piece to be machined comprises a blind or through-cavity, the broach is neared to the cavity with the piece and the broach in relative rotation with respect to one another, generally, though not necessarily, between 500 and 1800 revolutions per minute, mainly according to the material to be machined. Upon contact, the broach and the piece take on the same rotation velocity and owing to the swinging oscillating motion given to the broach by the broaching head and to the advancement provided, usually by the machine tool, the desired shape is obtained. In fact the axle is mounted in the broaching head with an inclined axis with respect to the rotation axis of the broaching head.

By way of example the kit can be applied on lathes, work centres, millers and drills both traditional and with numerical control, with both horizontal and vertical machining. For this reason several versions of the same broaching head are generally available, with different shanks.

The most common shapes realised have hexagonal, square section, Torx (registered mark) or Torx Plus (registered mark), as well as various geometric shapes with various coggings. The machinings can be particularly small, for example, inside pre-holes having diameter of lower than 3 millimetres. The typical dimensions of the profiles varies from 1 to 25 millimetres, in the case of square sections, and from 1 to 40 millimetres in the case of hexagonal sections.

During the machining the cutting blades of the broach, arranged frontally, machine the material during the movement according to the axial direction, thus cutting away the material which tends to flow to the bottom on the cavity. The quality of the machining is particularly sensitive to the type of the material which, as well as heating up, can tend to collect together in a paste or form burrs that are particularly small. Both in the case of short burrs and pasty material, a successive drilling or milling may be necessary, following the broaching, to free the compacted material from the bottom of the cavity, which in each case makes the advancement of the broach more difficult. For example, particularly obstinate materials are polyvinyl chloride, PVC, some types of cast iron and zinc alloys, known as Zamak.

The broach exits the cavity by returning through it in the opposite direction to the entry direction: in the case of heat dilations or burrs that have remained in proximity of the machined surface, interactions may arise which damage the shape obtained, for example by scratching the surface and/or the broach.

These critical events take place especially in the case of more complex shapes to be realised, an example being that of involute splines or serration splines.

The aim of the present invention is to obviate the drawbacks of the prior art. SUMMARY OF THE INVENTION

A first aim is to be able easily to arrange a rotary broaching machine the broach of which has a longer working life and/or with ensures better surface finishings.

A further aim is to be able easily to have available a rotary broaching machine which can work on less workable materials, typically because they are plastics and/or paste and/or powdery products and/or have particularly complex shapes with respect to the typical characteristics of rotary broaching.

These and other aims, which will be obvious to the expert in the sector from a reading of the following text, are attained by means of a kit for transforming a machine tool into a rotary broaching machine, a method for realising a shape internally of a cavity, a broaching head or a broach according to the claims. In accordance with the teachings of the present document, the kit comprises a broach and a broaching head and is predisposed for a machine tool with a toolbearing part and with a piece-bearing part that rotate with respect to one another about a first rotation axis during the machining of the piece.

The broaching head comprises an attachment part predisposed to engage the tool-bearing part, an axle configured to bear the broach, at least a bearing and a hollow part which has a first chamber which houses the at least a bearing which is interposed between the hollow part and the axle so that the axle is rotatable with respect to the hollow part about a second rotation axis.

The attachment part is integrally connected to or forms a single piece with the hollow part so that the hollow part rotates with respect to piece-bearing part about the first rotation axis, during the relative rotation between the tool-bearing part and the piece-bearing part.

The attachment part has a first channel predisposed to receive a lubricating- coolant fluid. The axle comprises a seat, for housing the broach, which faces on the side of the hollow part opposite the side of the attachment part. The broach comprises a cutting part and an engaging part, to engage the seat. The cutting part has a free end with the whole cutting edge and is tapered towards the engaging part. The first rotation axis and the second rotation axis being inclined with respect to one another so as to place successive portions of the edge at a greater distance from the broaching head, during the relative rotation between the tool-bearing part and the piece-bearing part.

The axle advantageously comprises a second channel for the lubricating-coolant fluid which opens on the seat and the broach comprises a third channel for the lubricating-coolant fluid which extends to the free end and which is predisposed to receive the lubricating-coolant fluid from the second channel when the broach is in the seat.

The broaching head has a second chamber which is in communication with the first channel so as to receive the lubricating-coolant fluid and which is in communication with the second channel so that the lubricating-coolant fluid flows towards the second channel.

The broaching head further comprises at least a seal which separates the first chamber from the second chamber so that the lubricating-coolant fluid flow is directed towards the second channel without crossing the first chamber.

The invention advantageously enables cooling and removing material from the machining area using lubricating-coolant fluids comprising water or air under pressure, i.e. at a greater pressure than the machining environment pressure. BRIEF DESCRIPTION OF THE DRAWINGS

Specific embodiments of the invention will be described in the following part of the present description, according to what is set down in the claims and with the aid of the accompanying figures, in which:

- figure 1 is an axonometric view of a first embodiment of a kit according to the invention;

- figure 2 is an axonometric view of the broach of figure 1 ;

- figure 3 and figure 4 are respectively a lateral view and a view from above of a further embodiment of a broach according to the invention;

- figure 5 is a section view of the kit of figure 1 while machining a piece;

- figure 6 is a view from above of the kit of figure 1 while machining a piece and shows the trace line of the cutting plane of the preceding figure;

- figure 7 is a section view of a further embodiment of the kit of the invention while machining a piece; - figure 8 is a view from above of the kit of figure 8 and shows the trace line of the cutting plane;

- figure 9 is a schematic lateral view of the kit of figure 1 applied to a tool-bearing part of a turret;

- figure 10 shows a frontal view of figure 9 without a piece and a piece-bearing part;

- figure 11 and figure 12 are larger-scale photographs of a broach, respectively according to the invention and of a traditional type.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the appended figures, reference numeral (100) relates to a kit for transforming a machine tool into a rotary broaching machine, with a tool-bearing part (A) and with a piece-bearing part (B) predisposed to rotate with respect to one another about a first rotation axis (X) during the machining of the piece (C), in a rotary broaching machine for realising shapes internally of cavities (CC) of the piece. Generally the tool-bearing part (A) is provided with a passage (P) for a lubricating-coolant fluid, but the latter, in general terms, might be made available via alternative connections.

The invention is especially advantageous in applications with lubricating-coolant fluids that are mixable with water or are transported with air or other gases, i.e. with lubricating-coolant fluids typically used in the sector of machine tools which do not use whole fluids, for example: mineral, or semi-synthetic or synthetic and mixable with water or minimum quantity lubrication, known as minimum quantity lubrication.

An embodiment of the kit (100) comprises a broach (6) and a broaching head (10). The broaching head (10) comprises an attachment part (1 ) predisposed to engage the tool-bearing part (A), an axle (2) configured to bear the broach (6), at least a bearing (3) and a hollow part (4). The attachment part (1 ) is usually connected to the tool-bearing part (A) so as to be integral with it.

The hollow part (4) has a first chamber (41 ) which houses the at least a bearing (3), which is interposed between the hollow part (4) and the axle (2) so that the axle (2) is rotatable with respect to the hollow part (4) about a second rotation axis (Y). For example, in the embodiment of figure 5 two opposite roller bearings can be observed. Typically the at least a bearing (3) is a rolling bearing.

The attachment part (1 ) is connected to the hollow part (4) so that the hollow part rotates with respect to the piece-bearing part (B) about the first rotation axis (X), during the relative rotation between the tool-bearing part (A) and the piece-bearing part (B). The attachment part (1 ) can be connected to the hollow part (4), for example by means of screws as in figure 5, or can form a single piece with the hollow part (4). As will be described in the following the way in which the attachment part (1 ) and the hollow part (4) are joined to one another influences some advantages of preferred embodiments of the invention.

The attachment part (1 ) has a first channel (13) predisposed to receive a lubricating-coolant fluid. Figure 5 and figure 7 show two of the possible terminal connections of the first channel (13), respectively to receive a fluid mixable in water or a fluid that uses compressed air as a vector.

The axle (2) comprises a seat (21 ) for housing the broach (6). The seat (21 ) faces onto the side of the hollow part (4) opposite the side of the attachment part (1 ), so as to be facing towards the piece-bearing part (B) when the attachment part (1 ) engages the tool-bearing part (A).

The broach (6) comprises, at opposite ends thereof, a cutting part (7) and an engaging part (8), to engage the seat (21 ). The cutting part (7) has a free end (71 ) with the whole cutting edge (72) and is tapered towards the engaging part (8); the engaging part (8), once in the seat (21 ), moves the cutting part (7) in rotation. The tapering, i.e. the slimming towards the engaging part (8), defines the rake angle of the broach (6).

The first rotation axis (X) and the second rotation axis (Y) are inclined with respect to one another so as to place successive portions of the edge (72) at a greater distance from the broaching head (10), during the relative rotation between the tool-bearing part (A) and the piece-bearing part (B). In other words the angle formed between the first rotation axis (X) and the second rotation axis (Y), visible for example in figure 5, guarantees the oscillating motion that enables tearing successive areas of the cavity (CC). This characteristic enables carrying out this machining even when using machine tools not predisposed to axially exert on the tool significant drawing or compression forces, as instead happens with broacher or shaper cutter machines.

The first rotation axis (X) and the second rotation axis (Y) are incident with respect to one another at the cutting part (7), preferably in proximity of the free end (71 ). Typically, the angle formed between the first rotation axis (X) and the second rotation axis (Y) is one sexagesimal degree.

The axle (2) advantageously comprises a second channel (22) for the lubricating- coolant fluid which opens on the seat (21 ) and the broach (6) comprises a third channel (60) for the lubricating-coolant fluid which extends to the free end (71 ) and which is predisposed to receive the lubricating-coolant fluid from the second channel (22), when the broach (6) is in the seat (21 ).

Further, the broaching head (10) has a second chamber (42) which is in communication with the first channel (13) so as to receive the lubricating-coolant fluid and which is in communication with the second channel (22) so that the lubricating-coolant fluid flows towards the second channel (22). The broaching head (10) further comprises at least a seal which separates the first chamber (41 ) from the second chamber (42) so that the lubricating-coolant fluid flow is directed towards the second channel (22) without crossing the first chamber (41 ).

The kit (100) of the invention enables using lubricating-coolant fluids with water or air and even at high working pressures for example greater than 0,15 MPa, or even greater than 0,3 MPa, without impacting the functionality and the duration of the broaching head (10).

The second chamber (42) creates a suitable volume both for receiving the lubricating-coolant fluid and for receiving the axle (2) in rotation. The positioning of the at least a seal advantageously separates the first chamber (41 ) from the second chamber (42) simply and reliably.

The lubricating-coolant fluid can therefore flow up to the free end (71 ) of the broach (6) so as to cool and carry away the processed material, typically between the interstices present between the pre-perforated cavity (CC) and the broach (6). The pressure and the vector of the lubricating-coolant fluid enable obtaining multiple advantages with respect to the simple application of oil at the cavity (CC) prior to the work machining operation. Among other things, according to the material of the piece (C), the broach (6) used and the dimensions of the cavity (CC), some of the following advantages may exist.

The lowering of the temperatures increases the working life of the broach (6) and improves the surface roughness of the obtained shape, further preventing the risk of undesirable machining during the exit of the broach (6).

The advantages become even more evident in the case of machining cavities (CC) having a small diameter, for example with a diameter of less than 5 mm or even 3 mm. As known to the technical expert, the diameter is usually slightly greater than the typical dimension of the shape of the broach, for example can be the same as the distance between parallel sides of broaches (6) having a square or regular hexagonal shape.

The lubricant on the surface of the realised shape limits rubbing with the broach (6), especially in exiting the cavity, thus being able to improve the surface finishing and preventing the formation of furrows due to the machine material or the deformations or breakages of the broach (6) during the course of its extraction.

The presence of the vector facilitates the cleaning of the machining area and the extraction of the material out of the cavity during the course of the machining, thus preventing accumulation inside and the consequent disadvantages in terms of advancement and the need to remove the accumulation on completion of work.

By way of example, figures 11 and 12 illustrate photographic details that show the state of the surfaces of two broaches, respectively according to the invention and of a traditional type, after machining 100 very hard pieces, i.e. steel, with K100 tools and 30 HRC hardness. The cutting part of figure 11 , relative to the broach (6) provided with a third channel (60), visible in the photograph, is less worn while the other is in need of at least sharpening. Other advantages have been found in regard to the view of the roughness: the average roughness (Ra) detected on some pieces of the 100 pieces machined with the broach (6) according to the invention was 0,5 micrometres while the average roughness of some machined pieces using the traditional broach was 0,8 micrometres.

As previously mentioned, the advantages of the kit (100) according to the invention are not limited to particularly hard pieces (C) but extend also to pieces made of short chip board materials, including plastic and/or paste, such as for example PVC or copper-based alloys. The cooling and the thrust of the vector prevent or reduce the recompacting of the material.

Among other things, in the event that the attachment part (1 ) is predisposed for minimum quantity lubrication, as for example in figure 7, it is possible to machine materials that exclude the use of water such as, for example, magnesium. In this case, it is preferable that the kit (100) comprises an air attachment part (9) which, more preferably, comprises a threaded connection so as to be connected removably from the attachment part (1 ).

The kit (100) preferably comprises a third seal (24) which is interposed between the axle (2) and the broach (6), once arranged in the seat (21 ), for example an elastomer ring as can be observed in figure 5.

In general the attachment part (1 ) is configured for the specific machine tool to which the kit (100) is destined, for example it can be adapted for a cylindrical attachment, morse taper, ISO (BT), VDI, HSK or CAPTO.

A first seal (5) of the at least a seal is preferably positioned between the axle (2) and the lateral walls (43) of the second chamber (42), i.e. the walls of the second chamber (42) which extend along the direction of the second rotation axis (Y). This arrangement guarantees the seal between the second chamber (42) and the first chamber (41 ) notwithstanding the relative rotation between the axle (2) and the hollow part (4) or the attachment part (1 ).

By way of example, figure 5 illustrates a piston seal with the outer lip of the first seal (5) which guarantees the seal on the walls of the second chamber (42), in particular of the hollow part (4).

More preferably, the lateral walls (43) comprise a contact portion which contacts the first seal (5) and which is axial symmetric with respect to the second rotation axis (Y). This conformation limits the variations of deformation of the first seal (5) due to the inclination of the axle (2) with respect to the hollow part (4) or the attachment part (1 ).

More preferably the end part of the axle (2) facing the second chamber (42) has an axial symmetric external surface (23) and on which a housing is made which houses the first seal (5). Further, the diameter of the external surface (23) of the end part is reduced at the housing. The conformation and the reduction of diameter of the external surface (23) at the second chamber (42) enables reducing the volume thereof and to allows the first seal (5) to work optimally between two axial symmetric surfaces.

In general it is also preferable for the first seal (5) to guarantee a piston seal, with the part near the housing being more rigid and with a more flexible lip seal (51 ), being configured to contact the lateral walls (43) so as to guarantee the seal. This configuration facilitates the seal of the first seal (5) in the typical working conditions of the kit (100), i.e. with the stresses on the broach (6) unloading onto the axle (2). The lateral walls (43) can be made exclusively on the hollow part (4), exclusively on the attachment part (1 ) or on both the hollow part (4) and the attachment part (1 ). If the attachment part (1 ) is connected to the hollow part (4), generally a second seal (12) is included internally of a seal seat (11 ) which, in figure 5, is made on the attachment part (1 ), by way of example. The second seal (12), for example an elastomer ring in figure 5, prevents undesired leakage.

Since the attachment part (1 ) is connected to the specific machine tool while the type of broaching head (10) can depend on the desired machining, the attachment part (1 ) is preferably connected to the hollow part (4), i.e. is not in a single piece, so that the attachment part (1 ) can serve a plurality of broaching heads (10). It is therefore preferable for the lateral walls (43) to be part of the hollow part (4) and for the second seal (12) to be positioned between the attachment part (1 ) and the hollow part (4), as shown by way of example in figure 5.

The broach (6) of the invention, especially in the case that the third channel (60) comprises at least a second branch (63, 64) as described herein below, facilitates undesired inlet of fluids into the first chamber (41 ), also on the side of the hollow part (4) opposite the attachment part (1 ). The broaching head (10) preferably comprises a fourth seal (45) which is interposed between the hollow part (4) and the axle (2), for example a double lip seal ring as can be observed in figure 7. The fourth seal (45) further preserves the at least a bearing (3) and improves the working life of the broaching head (10).

Owing to construction and maintenance issues it is preferable for the broaching head (10) to comprise a cover (44), which closes the first chamber (41 ) on the side opposite the side of the attachment part (1 ) and which is connected removably to the hollow part (4), for example with threaded connections, such as in the case of the flange visible in figure 5.

More preferably, the second channel (22), at the end facing the second chamber (42), has a countersink that is useful for directing the lubricating-coolant fluid.

With respect to a third channel (60) which opens centrally, or axially, greater benefits are obtained with angled branches which open at the lateral surfaces of the cavity (CC). The following contains some preferred embodiments of the broach (6) as an element of the kit (100) according to the invention, which can also be advantageously applied in other kits.

The broach (6) preferably comprises a third channel (60) which comprises at least two first branches (61 , 62) which are angled with respect to the rotation axis of the broach (6), therefore with respect to the second rotation axis (Y), and which exit from the free end (71 ) internally of the edge (72), so that the lubricating-coolant fluid flows towards the cavity (CC) directed laterally. Figure 2 illustrates a third channel (60) with two first branches (61 , 62) and with a central opening. The central opening is not strictly necessary, as shown by way of example in figure 4. By directing the lubricating-coolant fluid it is possible to target the areas directly involved in the machining and facilitate the removal of the machined material from among the spaces that remain between the broach (6) and the shape already obtained.

The third channel (60) preferably comprises at least a second branch (63, 64) between the engaging part (8) and the cutting part (7) so as to unload the lubricating-coolant fluid before it reaches the free end (71 ). This feature is particularly useful in the case of blind cavities (CC) and more modern machines; generally, with machine tools having high working pressures of the lubricating- coolant fluid, for example greater than 0,3 MPa. In fact an excessive pressure internally of the blind cavity (CC) can compromise the advancing of the broach (6) or cause it to be unstable. Owing to the at least a second branch (63, 64) the quantity of lubricating-coolant fluid internally of the cavity (CC) is limited without having to make further interventions.

The invention also relates to a method for realising a shape, preferably lobulated or polygonal, internally of a cavity (CC) using a machine tool, with a tool-bearing part (A) and with a to-be-machined piece-bearing part (B) which can be set in mutual rotation about a first rotation axis (X) and with the tool-bearing part (A) provided with a passage (P) for a lubricating-coolant fluid. An embodiment of the method comprises steps of:

- predisposing a piece (C) to be machined on the piece-bearing part (B);

- making a cavity (CC);

- providing a kit (100) according to any one of claims from 1 to 7;

- providing a lubricating-coolant fluid comprising water or air;

- coupling the attachment part (1 ) to the tool-bearing part (A) so that the toolbearing part (A) transfers, to the attachment part (1 ), a relative rotation with respect to the piece-bearing part (B) an such as to place the passage (P) in communication with the first channel (13);

- engaging the seat (21 ) of the axle (2) with the engaging part (8) of the broach (6);

- injecting the lubricating-coolant fluid into the passage (P);

- advancing the broach (6) along the first rotation axis (X) with the tool-bearing part (A) and the piece-bearing part (B) in relative rotation so as to enter the cavity (CC);

- injecting the lubricating-coolant fluid into the passage (P);

- extracting the broach (6).

At least the step of advancing the broach (6), more preferably also the step of extracting the broach (6), advantageously takes place during the step of injecting the lubricating-coolant fluid.

Generally the step of engaging the seat (21 ) can be successive to or can precede the step of engaging the attachment part (1 ).

The invention also relates to a broaching head (10) or a broach (6) of a kit (100) according to the invention the characteristics of which are clearly derivable from the foregoing description and which might each be advantageously applied in various kits.

By way of example an embodiment of the broaching head (10) comprises:

- an attachment part (1 ) predisposed to engage the tool-bearing part (A);

- an axle (2) configured to bear the broach (6);

- at least a bearing (3);

- a hollow part (4) which has a first chamber (41 ) which houses the at least a bearing (3) which is interposed between the hollow part (4) and the axle (2) so that the axle (2) is rotatable with respect to the hollow part (4) about a second rotation axis (Y).

The attachment part (1 ) is integrally connected to, or forms a single piece with, the hollow part (4) so that the hollow part (4) rotates with respect to the piece-bearing part (B) about the first rotation axis (X), during the relative rotation between the tool-bearing part (A) and the piece-bearing part (B). Further, the attachment part (1 ) has a first channel (13) predisposed to receive a lubricating-coolant fluid.

The axle (2) further comprises a seat (21 ), for housing the broach (6), which faces on the side of the hollow part (4) opposite the side of the attachment part (1 ) and the first rotation axis (X) and the second rotation axis (Y) are inclined with respect to one another.

The axle (2) advantageously comprises a second channel (22) for the lubricating- coolant fluid which opens on the seat (21 ) and the broaching head (10):

- has a second chamber (42) which is in communication with the first channel (13) so as to receive the lubricating-coolant fluid and which is in communication with the second channel (22) so that the lubricating-coolant fluid flows towards the second channel (22);

- comprises at least a seal which separates the first chamber (41 ) from the second chamber (42) so that the lubricating-coolant fluid flow is directed towards the second channel (22) without crossing the first chamber (41 ).

A first seal (5) of the at least a seal is preferably positioned between the axle (2) and the lateral walls (43) of the second chamber (42). More preferably, the lateral walls (43) comprise a contact portion which contacts the first seal (5) and which is axial symmetric with respect to the second rotation axis (Y).

The end part of the axle (2) facing towards the second chamber (42) preferably has an external surface (23) which is axial symmetric and on which a housing is made which houses the first seal (5), wherein the diameter of the external surface (23) is reduced at the housing and wherein the first seal (5) comprises a lip seal (51 ) which contacts the lateral walls (43).

The broaching head (10) preferably comprises a second seal (12); the lateral walls (43) are part of the hollow part (4) and the second seal (12) is interposed between the attachment part (1 ) and the hollow part (4).

An embodiment of the broach (6) comprises:

- a cutting part (7);

- an engaging part (8), for engaging a seat (21 ), the cutting part (7) having a free end (71 ) with the whole cutting edge (72) and being tapered towards the engaging part (8);

- a third channel (60) for the lubricating-coolant fluid which extends to the free end (71 ) and which is predisposed to receive the lubricating-coolant fluid when the broach (6) is in the seat (21 ).

The third channel (60) preferably comprises at least two first angled branches (61 , 62) which exit from the free end (71 ) internally of the edge (72), so that the lubricating-coolant fluid flows towards the cavity (CC) directed laterally. It is also preferable for the third channel (60) to comprise at least a second branch (63, 64) between the engaging part (8) and the cutting part (7) so as to unload the lubricating-coolant fluid before it reaches the free end (71 ).

Figures 9 and 10 enable observation, in a schematic illustration, of a typical application of a kit (100) according to the invention on a machine tool which, in this case, comprises a turret (AA). Figure 9 illustrates the passage (P) internally of the tool-bearing part (A) and a portion of a piece-bearing part (B).

It is understood that the above has been described by way of non-limiting example and that any constructional variants are considered to fall within the protective scope of the present technical solution, as claimed in the following.