Milling machine for the aviation industry and working method

Abstract

A horizontal or vertical milling machine (10; 20; 30), in particular for machining aluminum pieces for the aviation industry, has a reference direction G, defined as the intersection of a first plane (a), orthogonal to a first axis of rotation (A), and a second plane (β), orthogonal to a second axis of rotation (B), inclined on the first plane (α) by a reference angle (δ) of between -5° and +20° (-5° < δ ≤ +20°) with respect to a third axis of translation (Z) of the machine.

Description

Milling machine for the aviation industry and working method" DESCRIPTIONField of the invention

[0001] The present invention is in the field of machine tools; in particular, the present invention relates to a numerically-controlled milling machine for machining aluminum pieces, for example for the aviation industry. The present invention furthermore relates to a milling machine working method.Background of the invention

[0002] In accordance with the international standard ISO 841, relating to "Industrial automation systems and integration — Numerical control of machines — Coordinate system and motion nomenclature", the coordinate system of a milling machine is an orthogonal right-handed system, wherein the three main axes of translation are called X, Y and Z; the axes of rotation about each of the axes of translation are called A, B and C, respectively. According to the standard, the Z axis is parallel to the main spindle of the machine and, if the main spindle is rotatable, the Z axis is parallel to the spindle axis when the spindle is in the zero angular position, wherein the spindle axis is perpendicular to the support surface of the workpiece.

[0003] Furthermore, according to established practice, a milling machine is defined as "horizontal" when the axis Z, as normalized above, is horizontal; a milling machine is defined as "vertical" when the axis Z, as normalized above, is vertical.

[0004] Fig. la and le depict a customary horizontal milling machine of the prior art, equipped with a two- axis milling head. Fig. lb, lc and Id depict only the milling head. Such milling head comprises a spindle, carrying a milling tool, rotatable about a working axis M for performing the milling machining operation. The spindle is supported by a first support, rotatable with respect to a first axis A, which is in a horizontal direction; in turn, the first support is supported by a second support rotatable about a second axis C. A first vertical plane is perpendicular to the first axis A and contains the axis C; a second vertical plane is perpendicular to the axis C and contains the axis A. Finally, a horizontal plane passes through the axis A. A direction G is defined at the intersection of the first vertical plane and the second vertical plane. In the horizontal milling machine of the prior art, the direction G is perpendicular to the axis Z.

[0005] Considering the above and the fact that in a horizontal machine the working plane is vertical (it maybe horizontal only for special needs) and that in a vertical machine the working plane is horizontal (it may be vertical only for special needs), the following conditions result:

[0006] In the position of the head as in Fig. la, the spindle may tilt only in the second vertical plane.

[0007] There is however a need to perform some machining operations wherein it is also necessary to be able to tilt the spindle in the horizontal plane. This is not immediately feasible by means of the customary heads of the prior art. For this purpose, in fact, a rotation of 90° of the second support about the axis C is required so as to bring the axis A in the vertical direction, and subsequently a rotation of the first support about the axis A, so that the spindle may be arranged inclined in the horizontal plane as required (Fig. le).

[0008] Fig. 2a to 2e show an example of machining a customary piece in aluminum for aviation applications.The milling tool has to machine the two inclined surfaces a and b, inclined by 30° with respect to a plane that is normal to the base plane c (Fig. 2a and 2b). The machining starts from the face a in position 0; the axis A inclines the milling tool by 30° (Fig. 2c). When the milling tool finishes machining the face a, it is in the position 1 (Fig. 2d). In order to machine the face b, it is necessary to rotate the second support about the axis C by 90° and then rotate the first support about the axis A by 30° (Fig. 2e). Only at this point is it possible to start machining the face b, up to point 2.

[0009] This obviously involves a loss of time, which may have a major impact upon the total cycle time, especially with the machining of aluminum pieces, which is usually performed at high cutting speeds.

[0010] In order to satisfy such requirement, some known milling heads provide for a third axis, obtained by means of various technical solutions.

[0011] For example (Fig. 3a to 3c), milling heads are known that are provided with a parallel kinematic (tripod) device, wherein the spindle is supported by a platform moved by three actuators. As a function of the relative movement imparted by the three actuators, the platform translates or rotates in such a way that the axis of the spindle may describe a cone. However, insofaras it is not possible to directly measure the axial and angular position of the spindle, these solutions have the drawback of poor stiffness and poor precision.

[0012] A further known milling head (Fig. 4a to 4c), equipped with a spindle, with the first support rotatable about the axis A, and the second support rotatable about the axis B, is further provided with a third support having a guiding device that engages with the second support in such a way that said second support may perform a rotation about a further axis B, orthogonal to the axis A and to the axis C. However, in such a solution, the second support may perform a very limited rotation, hardly greater than 15° in one direction or the other, while some special machining operations may require rotations of 45° in one direction or the other.

[0013] Some further polar axis milling machine solutions are shown, for example, in US2002 / 077233A1, EP3693129A1, US2020 / 276677A1, CN100349693C and EP2305418A1.Object of the invention

[0014] The object of the present invention is to meet the needs mentioned and at the same time to overcome the drawbacks of the solutions of the prior art. In particular, but not exclusively, the object of the present invention is to provide a milling machine formachining parts for the aviation industry, preferably made of aluminum. In such industry, inclinations of the milling tool between 10 and 20° with respect to the initial angular reference position are routinely required.

[0015] This object is achieved by a milling machine according to the independent claims. The claims respectively dependent thereon describe additional advantageous embodiments of the invention.Brief description of the figures

[0016] Fig. la and le show a horizontal milling machine of the prior art, equipped with a milling head. Fig. lb to Id show the milling head only.

[0017] Fig. 2a to 2e show an example of the machining of a workpiece.

[0018] Fig. 3a to 3c show a further milling head of the prior art.

[0019] Fig. 4a to 4c show a still further milling head of the prior art.

[0020] The features and advantages of the milling machine according to the present invention will become apparent from the following description, given by way of non-limiting example according to further figures in the accompanying drawings, wherein:- Fig. 5a and 5b show a horizontal milling machineequipped with a milling head, according to one embodiment of the present invention;- Fig 6a to 6d are orthogonal views of a milling head, according to one embodiment of the present invention;- Fig. 7a and 7b show second axis actuation means of the milling head, according to an embodiment of the present invention;- Fig. 8 shows first axis actuation means of the milling head, according to one embodiment of the present invention;- Fig. 9a shows an embodiment variant of the second axis actuation means of the milling head;- Fig. 9b shows an embodiment variant of the first axis actuation means of the milling head;- Fig. 10 schematically shows an embodiment variant of the milling head, according to a fork configuration;- Fig. 11a and lib schematically show a further embodiment variant of the milling head, according to a cantilevered configuration;- Fig. 12 schematically depicts a still further variant of the milling head;- Fig. 13a to 13c show the milling head according to one embodiment of the present invention, applied to a horizontal milling machine;- Fig. 14 shows the working methods of a horizontalmilling machine, equipped with a milling head according to one embodiment of the invention;- Fig. 15 show a vertical milling machine, equipped with a milling head according to one embodiment of the invention, and related working methods;- Fig. 16a to 16c show the milling head according to a further embodiment of the present invention, applied to a vertical milling machine;- Fig. 17a to 17c show a milling head according to a further embodiment of the present invention, having three axes of rotation;- Fig. 18 shows a portal milling machine provided with a milling head according to the embodiment with three axes of rotation.Detailed description of embodiments of the invention Horizontal milling machine

[0021] A horizontal milling machine 10 (Fig. 5a and 5b) rests on a working region defined by a reference ground plane T and comprises a fixed bench 12, having a main extension along a first horizontal axis of translation X with respect to the ground plane T, an upright 14 supported by the bench 12 by means of an upright carriage 15 translatable along the first axis of translation X, a ram carriage 16 applied to the upright 14 and translatable along a second vertical axis oftranslation Y, and a ram or structure 18 supported by the ram carriage 16 and translatable along a third axis of translation Z, orthogonal to the first axis of translation X and to the second axis of translation Y.

[0022] The milling machine 10 further comprises a milling head 100 supported from the front by the ram 18 and suitable for carrying at least one milling tool for performing a milling machining operation.

[0023] A workpiece is supported by a piece-holder table, applied to a work surface.

[0024] For the horizontal milling machine, the pieceholder table is arranged vertically (piece-holder table 20a); the work surface is therefore vertical. According to the standards, such configuration defines the axes of translation of the machine and the angular position 0.

[0025] The piece-holder table comprises fixing means for rigidly fixing the workpiece to the work surface and keeping it fixed thereto also during the execution of a machining operation.

[0026] In general, the third axis of translation Z is to be understood as the direction of the milling head either toward or away from the vertical work surface, for example in the case wherein it is the piece-holder table that is translatable.

[0027] The milling head 100 is described withreference to Fig. 6a to 12.

[0028] According to one embodiment (Fig. 6a to 6e and Fig. 7), the milling head 100 comprises a primary support 102, provided with an attachment plane 102a applied and fixed to the ram or structure 18 of the milling machine 10, and a secondary support 104, supported by the primary support 102 rotatably about a second axis of rotation B. The second axis of rotation B defines a second plane p, orthogonal to the second axis of rotation B.

[0029] The milling head 100 further comprises second axis actuating means 106 which may be controlled so as to rotate the secondary support 104 about the second axis of rotation B in a controlled manner. Said second axis actuation means 106 are motorized and arranged on board the primary support 102.

[0030] The milling head 100 further comprises a spindle 108 provided on board with spindle axis actuation means thereof, for example comprising an electric motor, adapted for rotating a milling tool about a spindle axis of rotation M. In other words, the spindle 108 is preferably an electro-spindle.

[0031] The spindle 108 is supported by the secondary support 104 in a rotatable manner about a first axis of rotation A; the first axis of rotation A defines a first plane a, orthogonal to the first axis of rotation A andthrough the intersection between the first axis of rotation A and the second axis of rotation B. The second plane p also passes by means of the intersection between the first axis of rotation A and the second axis of rotation B.

[0032] Furthermore a "pivot A" is defined as the distance between the first axis of rotation A and the front face of the spindle 108.

[0033] A reference direction G is further defined at the intersection of the first plane a and the second plane p. The reference direction G is orthogonal to a reference plane y, passing through the intersection of the first axis of rotation A and the second axis of rotation B.

[0034] The first axis of rotation A is preferably spaced apart from the second axis of rotation B, and is in particular arranged at an advanced position towards the working area with respect to the second axis of rotation B by a predefined offset distance s, for example approaching the vertical work surface of the pieceholder table 20a.

[0035] According to one aspect of the invention, the offset distance s of the first axis of rotation A with respect to the second axis of rotation B is less than the pivot of A.

[0036] According to an embodiment variant, the spindle axis of rotation M lies on the first plane a. According to a further embodiment variant, the spindle axis of rotation M lies on a plane parallel to the first plane a.

[0037] The milling head 100 further comprises first axis actuation means 110 controllable for rotating the spindle 108 about the first axis of rotation A in a controlled manner. Said first axis actuation means 110 are motorized and arranged on board the secondary support 104.

[0038] According to a preferred embodiment (Fig. 7a and 7b), the second axis actuation means 106 comprise at least one electric motor, preferably a plurality of electric motors, for example a pair of electric motors 106a, 106b, for example arranged symmetrically with respect to the first plane a.

[0039] Said electric motors 106a, 106b are predominantly arranged within a rear region, i.e., within the region opposite the working region with respect to the third plane y- For example, the respective rotor axes are parallel to the reference direction G.

[0040] According to a preferred embodiment, the electric motors 106a, 106b are arranged on the same side with respect to the second plane p.

[0041] The electric motors 106a, 106b are each preferably connected to a respective right-angle gear reducer 106c, 106d and, by means of, for example, a respective pinion 106e, 106f, engage with a gear wheel 106g, rotationally integral with the secondary support 104.

[0042] The secondary support 104 is preferably rotationally supported by the primary support 102 by means of at least one axial-radial bearing 106h coaxial to the second axis of rotation B.

[0043] According to a preferred embodiment (Fig. 8), the first axis actuation means 110 comprise at least one electric motor, preferably a plurality of electric motors, for example a pair of electric motors 110a, 110b, for example arranged symmetrically with respect to the first plane a.

[0044] Said electric motors 110a, 110b are predominantly arranged within a rear region, i.e., within the region opposite the working region with respect to the plane y- For example, the respective rotor axes are parallel to the reference direction G and, preferably, parallel to the rotor axes of the electric motors 106a, 106b of the second axis actuation means 106.

[0045] The electric motors 110a 110b are eachpreferably connected to a respective reducer 110c, llOd and, by means of, for example, a respective pinion llOe, llOf, engage with a gear wheel 110g, rotationally integral to a spindle support 112, which is fixed to the spindle body 108 and supports it.

[0046] The spindle support 112 is preferably rotationally supported by the secondary support 104 by means of at least one axial-radial bearing llOh, coaxial to the first axis of rotation A.

[0047] Advantageously, by virtue of such arrangement of the electric motors, and also of the respective reducers, the working area, where the spindle operates, is free from encumbrances, in such a way that the milling tool may work freely and the milling head may be arranged very close to the workpiece.

[0048] According to a further embodiment variant, the rotor axles of the electric motors 106a, 106b of the second axis actuation means 106 intersect the first plane a (Fig. 9a); according to a still further embodiment variant, the rotor axes of the electric motors 110a, 110b of the first axis actuation means 110 intersect the second plane p (Fig. 9b).

[0049] According to an embodiment variant, the secondary support 104 has a fork configuration (Fig. 10), i.e., it comprises two legs therebetween thespindle support 112 that carries the spindle 108 is arranged.

[0050] According to a further embodiment variant, the secondary support 104 has an asymmetrical configuration (Fig. 11a and lib), i.e., it comprises a single leg that laterally supports the spindle support 112 and the spindle 108 in a cantilevered manner.

[0051] According to a still further embodiment, the spindle 108 is configured in such a way that the spindle axis M is spaced apart from the first axis of rotation A (Fig. 12), i.e. the axis of rotation M does not intersect the axis of rotation A.

[0052] According to one aspect of the invention (Fig. 13a, 13b and 13c), the milling head 100 is configured in such a way that the reference direction G is inclined between -5° and +20° with respect to the third axis of translation Z of the horizontal milling machine 10 (the range is shown in Fig. 13c). For example, Fig. 13a shows the configuration wherein the reference direction G is parallel to the third axis of translation Z; Fig. 13b shows the configuration wherein the reference direction G is inclined by -5° with respect to the third axis of translation Z.

[0053] In particular, the reference direction G is inclined on the first plane a by a reference angle 5between -5° and +20° (-5° < 6 < +20°) with respect to the third axis of translation Z.

[0054] In the normal operation of the horizontal milling machine 10 (Fig. 14), in the angular position 0, the spindle axis of rotation M is orthogonal to the work surface of the vertical piece-holder table 20a.

[0055] By means of the controlled actuation of the first axis actuation means 110, the spindle axis of rotation M may be inclined, remaining in the first plane a. By means of the controlled actuation of the second axis actuation means 106, the first axis of rotation A may be inclined, remaining in the second plane p. Having fixed in space a predefined angular arrangement of the spindle axis of rotation M, depending on the angular position of the spindle axis of rotation M on the first plane a and the angular position of the first axis of rotation A in the second plane p, the actuation of the spindle axis of rotation M allows the desired milling machining operation to be performed. In particular, the milling head is configured in such a way that the spindle axis of rotation M is capable of describing a conical surface or parts of a conical surface in an "endless" mode (e.g., ±45° in amplitude with respect to the angular position 0), i.e., by means of an alternating oscillation with respect to the first axis of rotation A and thesecond axis of rotation B. This occurs without cables or fluid ducts becoming twisted.

[0056] Furthermore, in the angular position 90°, the spindle axis of rotation M is orthogonal to the work surface of the horizontal piece-holder table 20b and is capable of operating only in a traditional manner, for example reaching inclinations of ±45° with respect to the angular position 90°.Vertical milling machine

[0057] A vertical milling machine 20 (Fig. 15), for example a portal milling machine, comprises a ram 18 vertically translatable along a third axis of translation Z, whereto the milling head 100 is applied from the front. In one embodiment variant, the ram is fixed and the milling head is applied directly to a crosspiece 26 movable along the third axis of translation Z, which therefore acts as a support structure.

[0058] The piece-holder table is horizontal (pieceholder table 20b) and, according to the standards, in the angular reference position 0, the spindle axis M is orthogonal to the horizontal work surface of the horizontal piece-holder table 20b.

[0059] In general, the third axis of translation Z is to be understood as the direction of the milling head either toward or away from the horizontal work surface,for example in the case wherein it is the piece-holder table that is translatable.

[0060] The milling head 100 has been previously described with reference to Fig. 6a to 12.

[0061] According to the invention (Fig. 16a, 16b and 16c), the milling head 100 is configured in such a way that the reference direction G is inclined between -5° and +20° with respect to the third axis of translation Z of the vertical milling machine 20 (the range is shown in Fig. 16c). For example, Fig. 16a shows the configuration wherein the reference direction G is parallel to the third axis of translation Z; Fig. 16b shows the configuration wherein the reference direction G is inclined by -5° with respect to the third axis of translation Z.

[0062] In the normal operation of the vertical milling machine 20 (Fig. 15), in the angular position 0, the spindle axis of rotation M is orthogonal to the work surface of the horizontal piece-holder table 20b.

[0063] By means of the controlled actuation of the first axis actuation means 110 and the second axis actuation means 106, the spindle axis of rotation M is capable of describing a conical surface or parts of a conical surface in an "endless" mode (e.g., ±45° in amplitude with respect to the angular position 0).

[0064] Furthermore, in the angular position 90°, the spindle axis of rotation M is orthogonal to the work surface of the vertical piece-holder table 20a and is capable of operating only in a traditional manner, for example reaching inclinations of ±45° with respect to the angular position 90°.Three-axis milling head milling machine

[0065] According to a further embodiment of the invention (Fig. 17a to 17c), the primary support 102 is supported rotatably, directly or indirectly, by said structure 18 about a third axis of rotation C, parallel to the third axis of translation Z, and the milling head is provided with third axis actuation means controllable for rotating the primary support 102 about the third axis of rotation C in a controlled manner. Said third axis actuation means are motorized and preferably comprise at least one electric motor, preferably a plurality of electric motors.

[0066] In one embodiment of the invention (Fig. 18), a vertical milling machine 30 is provided with a milling head 100 with a first A, second B, and third axis of rotation C.

[0067] A piece-holder assembly 20c has a horizontal face 20c' and two opposite vertical faces 20c'', 20c'''.

[0068] In the angular position 0, the spindle axis Mis orthogonal to the horizontal face 20c', and the angular position of the head 100 with respect to the third axis of rotation C is predefined. In such working state (I), the milling machine 30 is capable of working on the horizontal face 20c'.

[0069] In a further configuration, the angular position of the head 100 with respect to the third axis of rotation C has not changed, and the spindle axis M is orthogonal to the first vertical face 20c''. In this working state (II), the milling machine 10c is capable of machining the first vertical face 20c''.

[0070] In a still further configuration, the head 100 has completed a predefined rotation about the third axis of rotation C, for example 180°, and the spindle axis M is orthogonal to the second vertical face 20c'''. In such working state (III), the milling machine 10c is capable of machining the second vertical face 20c''', which is opposite the first vertical face 20c''.

[0071] In other words, the milling machine 30 is adapted to machine a hypothetical cube on as many as five faces: the upper horizontal face and the four vertical lateral faces.Further embodiments

[0072] According to a further embodiment of the invention (not shown), the three rotation axes A, B, Care orthogonal therebetween, but do not intersect.

[0073] According to a still further embodiment (not shown), the three axes of rotation A, B, C are not orthogonal therebetween.

[0074] According to a still further embodiment, the actuation means comprise hydraulic or electric motors of the direct traction torque motor type.— 0—

[0075] Innovatively, for the milling machine according to the present invention, with reference to horizontal or vertical milling machine configurations and with reference to a vertical or horizontal pieceholder table, the following table applies:

[0076] The milling machine according to the present invention satisfies the aforesaid requirements and overcomes the drawbacks of the solutions of the prior art.

[0077] In fact, the milling machine allows the milling tool to be advantageously arranged in space according tothe machining requirements, and in particular such as to describe a cone oriented in space, especially in the case of parts for the aviation industry, typically made of aluminum.

[0078] Advantageously, in some working configurations, the machine according to the invention makes it possible to drastically reduce the cycle times for the execution of some particular processes.

[0079] According to a further advantageous aspect, moreover, the milling head is particularly rigid and is therefore capable, in an excellent manner, of limiting the occurrence of vibratory phenomena.

[0080] Furthermore, the combination of the horizontal milling machine and the vertical piece-holder table is particularly advantageous in the case of machining aluminum pieces insofar as it allows chips from the work area to fall away by gravity.

[0081] It is understood that those skilled in the art, in order to meet contingent needs, might make modifications to the milling head and to the milling machine described above, all of which are contained within the scope of protection as defined by the following claims.

Claims

CLAIMS1. An apparatus for machining aluminum parts for the aviation industry, comprising- a vertical piece-holder table (20a) having a vertical work surface for applying a workpiece, comprising fixing means for rigidly fixing the workpiece to the work surface during the machining operation;- a horizontal milling machine (10) with two polar axes, comprising : a) a structure (18) translatable along a third axis of translation (Z) either toward or away from the vertical work surface; b) a milling head (100) comprising: i. a primary support (102), applied to the structure (18) and fixed rotatably in relation to the third axis of translation (z); ii. a secondary support (104), supported by the primary support (102) in a rotatable manner about a second axis of rotation (B), which defines a second plane (p) orthogonal to the second axis of rotation (B); iii. a spindle (108) supported by the secondary support (104) in a rotatable manner about a first axis of rotation (A), orthogonal to the second axis of rotation (B) and defining a first plane (a) orthogonal to said first axis of rotation (A), said spindle (108) beingprovided on board with spindle axis actuation means thereof for rotating a milling tool about a spindle axis of rotation (M); iv. wherein the first plane (a) contains the second axis of rotation (B), the second plane (p) contains the first axis of rotation (A), and the intersection between the first plane (a) and the second plane (p) defines a reference direction (G); c) first axis actuation means (110) arranged on board the secondary support (104), adapted to rotate the spindle (108) about the first axis of rotation (A) in a controlled manner, comprising at least one motor (110a,110b); d) second axis actuation means (106) arranged on board the primary support (102), adapted to rotate the secondary support (104) about the second axis of rotation (B) in a controlled manner, comprising at least one motor (106a,106b);- wherein the reference direction (G) is inclined on the first plane (a) by a reference angle (5) between -5° and +20° (-5° < 6 < +20°) with respect to the third axis of translation (Z).

2. Apparatus according to claim 1, wherein the first axis of rotation (A) is spaced apart from the second axis of rotation (B) by an offset distance (s)approaching the vertical work surface of the pieceholder table (20a).

3. Apparatus according to claim 2, wherein a pivot A is the distance between the first axis of rotation (A) and a front face of the spindle (108) and said pivot A is less than the offset distance (s) (pivot A < s).

4. Apparatus according to claim 1, wherein the first axis of rotation (A) intersects the second axis of rotation (B).

5. Apparatus according to any of the preceding claims, wherein the motors (106a,106b) of the second axis actuation means (106) are arranged on the same side with respect to the second plane (p).

6. Apparatus according to any of the preceding claims, wherein the motors (106a,106b) of the second axis actuation means (106) are arranged in a rear region, opposite the working region with respect to the third plane (y)•7. Apparatus according to any of the preceding claims, wherein the secondary support (104) has a fork configuration wherein a spindle support (112) which carries the spindle (108) is arranged between two legs of said secondary support (104).

8. Apparatus according to any of claims 1 to 6, wherein the secondary support (104) has an asymmetricconfiguration, comprising a single leg which laterally supports in a cantilevered manner a spindle support (112) which carries the spindle (108).

9. Apparatus according to any of the preceding claims, wherein the spindle axis of rotation (M) intersects the first axis of rotation (A).

10. Apparatus according to any of claims 1 to 8, wherein the spindle axis of rotation (M) is spaced apart from the first axis of rotation (A), i.e., the axis of rotation (M) does not intersect the axis of rotation (A).

11. Apparatus according to any of the preceding claims, wherein the secondary support (104) is rotationally supported by the primary support (102) by means of at least one axial-radial bearing (106h) coaxial to the second axis of rotation (B).

12. Apparatus according to any of the preceding claims, wherein the spindle (108) is supported by a spindle body (112) which in turn is rotationally supported by the secondary support (104) by means of at least one axial- radial bearing (llOh), coaxial to the first axis of rotation (A).

13. Apparatus according to any of the preceding claims, wherein the primary support (102) is fixed with respect to the structure (18).

14. Method for machining aluminum parts for the aviation industry, comprising the following steps:- providing an apparatus according to any of claims 1 to 13;- during the performance of the machining operation: a) the piece is fixed to the vertical work surface; b) the first axis of rotation (A) and the second axis of rotation (B) are actuated.

15. Apparatus for machining aluminum parts for the aviation industry, comprising:- a horizontal piece-holder table (20b) having a horizontal work surface for applying the workpiece, comprising fixing means for rigidly fixing the workpiece to the work surface during the machining operation;- a vertical milling machine (20) with two polar axes comprising: a) a structure (18) translatable along a third axis of translation (Z) either toward or away from the horizontal work surface; b) a milling head (100) comprising: i. a primary support (102), applied to the structure (18) and fixed rotatably with respect to the third axis of translation (z); ii. a secondary support (104), supported by the primary support (102) in a rotatable manner about a second axisof rotation (B), which defines a second plane (p) orthogonal to the second axis of rotation (B); iii. a spindle (108) supported by the secondary support (104) in a rotatable manner about a first axis of rotation (A) orthogonal to the second axis of rotation (B) and defining a first plane (a) orthogonal to said first axis of rotation (A), said spindle (108) being provided on board with spindle axis actuation means thereof for rotating a milling tool about a spindle axis of rotation (M); iv. wherein the first plane (a) contains the second axis of rotation (B), the second plane (p) contains the first axis of rotation (A), and the intersection between the first plane (a) and the second plane (p) defines a reference direction (G); c) first axis actuation means (110) arranged on board the secondary support (104), adapted to rotate the spindle (108) about the first axis of rotation (A) in a controlled manner, comprising at least one motor (110a,110b); d) second axis actuation means (106) arranged on board the primary support (102), adapted to rotate the secondary support (104) about the second axis of rotation (B) in a controlled manner, comprising at least one motor (106a,106b);- wherein the reference direction (G) is inclined on the first plane (a) by a reference angle (5) between -5° and +20° (-5° < 6 < +20°) with respect to the third axis of translation (Z).

16. Method for machining aluminum parts for the aviation industry, comprising the following steps:- providing an apparatus according to claim 15;- during the performance of the machining operation: a) the piece is fixed to the horizontal work surface; b) the first axis of rotation (A) and the second axis of rotation (B) are actuated.

17. An apparatus for machining aluminum parts for the aviation industry, comprising:- a piece-holder table having a work surface for applying the workpiece, comprising fixing means for rigidly fixing the workpiece to the work surface during the machining operation;- a milling machine (10;20) with three polar axes comprising : a) a structure (18) translatable along a third axis of translation (Z) either toward or away from the work surface; b) a milling head (100) comprising: i. a primary support (102), applied to the structure(18);ii. a secondary support (104), supported by the primary support (102) in a rotatable manner about a second axis of rotation (B), which defines a second plane (p) orthogonal to the second axis of rotation (B); iii. a spindle (108) supported by the secondary support (104) in a rotatable manner about a first axis of rotation (A) orthogonal to the second axis of rotation (B) and defining a first plane (a) orthogonal to said first axis of rotation (A), said spindle (108) being provided on board with spindle axis actuation means thereof for rotating a milling tool about a spindle axis of rotation (M); iv. wherein the first plane (a) contains the second axis of rotation (B), the second plane (p) contains the first axis of rotation (A), and the intersection between the first plane (a) and the second plane (p) defines a reference direction (G); c) first axis actuation means (110) arranged on board the secondary support (104), adapted to rotate the spindle (108) about the first axis of rotation (A) in a controlled manner, comprising at least one motor (110a,110b); d) second axis actuation means (106) arranged on board the primary support (102), adapted to rotate the secondary support (104) about the second axis of rotation(B) in a controlled manner, comprising at least one motor (106a,106b);- wherein the reference direction (G) is inclined on the first plane (a) by a reference angle (5) between -5° and +20° (-5° < 6 < +20°) with respect to the third axis of translation (Z); and- wherein the primary support (102) is rotatably supported, directly or indirectly, by the structure (18) about a third axis of rotation (C) parallel to the reference direction (G).

18. Method for machining aluminum parts for the aviation industry, comprising the following steps:- providing an apparatus according to claim 17;- during the performance of the machining operation: a) the piece is fixed to the work surface; b) the first axis of rotation (A), the second axis of rotation (B) and the third axis of rotation (C) are actuated.

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