MACHINE TOOL FOR MACHINING SEMI-FINISHED ALUMINUM OR TITANIUM ALLOY PRODUCTS

A machine tool for machining semi-finished aluminum or titanium alloy products has a supporting structure, an upright, a carriage and a working head. The supporting structure has a bench and a rear support rigidly connected to each other. The bench extends along a longitudinal direction, while the rear support extends both along the longitudinal direction and along a vertical direction. The supporting structure is provided with upright translation elements. The upright is connected to the supporting structure by the upright translation elements so as to translate along the longitudinal direction and is provided with carriage translation elements. The carriage is connected to the upright by the carriage translation elements so as to be translatable along the vertical direction. The machine tool has a first pair of carriage moving ratio motors and a second pair of carriage moving ratio motors positioned aboard the upright and engaging the carriage translation elements.

The present invention relates to the field of machine tools, and in particular to the technical field of large machine tools, such as a horizontal boring machine or a milling machine or a lathe. In particular, the present invention relates to a machine tool suitable to machine semi-finished aluminum alloy or titanium alloy products.

Such machine tools are used to carry out mechanical machining on large semi-finished products for the aeronautical, aerospace and naval industries.

Due to the criticality of such industrial applications, extremely low machining tolerances are generally required. Machine tool manufacturers are therefore constantly engaged in the research and development of solutions which may guarantee these tolerances.

In the case of semi-finished titanium alloy machining, it is observed that, during the chip removal operations, the tool develops vibrations with a frequency of between 12 and 18 Hz. Considering that the resonant frequency of machine tools according to the prior art is between 14 and 16 Hz, it is clear to those skilled in the art that the machining of titanium alloys produces vibrations in the resonance range of the machines, which in fact prevent the tolerances required by the industrial applications for which the finished piece is intended from being obtained.

On the other hand, in the case of machining of semi-finished aluminum alloy products, compliance with dimensional tolerances requires very long production times. It is clear that, by increasing the rigidity of the machine and increasing the value of the first resonant frequency, the dynamic performance of the machine tool would improve and consequently the production times could be reduced without compromising the respect of the required tolerances.

Therefore, in order to comply with tolerances and/or improve dynamic performance, machine tools should be rigid enough to guarantee a resonant frequency of between 23 and 30 Hz.

So far, the efforts made by manufacturers have been aimed at increasing the rigidity of the machines. While it is possible to improve the stiffness through an increase in the stiffness of the machine structures, this technical prejudice, however justified by structural science, has not so far produced any satisfactory results.

The object of the present invention is to provide a large-sized machine tool capable of obviating the drawbacks mentioned above.

Such object is achieved with a machine tool for machining semi-finished aluminum alloy or titanium alloy products according to the appended claim1. The claims dependent thereon identify additional advantageous embodiments of the invention.

In the following description, elements common to the various embodiments represented in the drawings are indicated with the same reference numerals.

With reference to the figures of the accompanying drawings, the reference numeral1generally indicates a machine tool suitable to machine semi-finished aluminum alloy or titanium alloy products.

In a general embodiment, the machine tool1for machining semi-finished aluminum alloy or titanium alloy products is designed to rest on a horizontal reference plane G, for example the ground plane. Such machine tool1comprises a supporting structure2, an upright4, a carriage6and a working head7.

The supporting structure2comprises a bench20and a rear support22. The bench20has a main extension along a longitudinal direction X, while the rear support22extends both along the longitudinal direction X and along a vertical direction Y.

The bench and the rear support are rigidly connected to each other, i.e. engaged and made integral. For example, the bench20and the rear support22are connected in such a way that the supporting structure2has an “L”-shaped cross section, where such cross section is meant to be obtained along a plane orthogonal to the longitudinal direction X.

The supporting structure2is also provided with upright translation means3oriented according to the longitudinal direction X.

The upright4is connected to the supporting structure2by means of the upright translation means3, so as to translate along the longitudinal direction X. Such upright4is further provided with carriage translation means5oriented according to the vertical direction Y.

The carriage6is connected to the upright4by means of the carriage translation means5so as to be translatable along the vertical direction Y.

The working head7is engaged with the carriage6and has a tool holder seat70suitable to house a tool for chip removal machining.

The machine tool1also comprises a first pair of carriage moving ratio motors61,62and a second pair of carriage moving ratio motors63,64. Said first61,62and second63,64pair of carriage moving ratio motors are positioned aboard the upright4and are engaged with the carriage translation means5.

In one embodiment, the carriage translation means5comprise a first ball screw5′ and a second ball screw5″.

According to an embodiment, the first ball screw5′ is actuated by the first pair of carriage moving ratio motors61,62whereas the second ball screw5″ is actuated by the second pair of carriage moving ratio motors63,64.

Preferably, the first ball screw5′ is provided with a first nut51and the second ball screw5″ is provided with a second nut52. In particular, these first51and second52nut are connected to opposite sides of the carriage6, respectively.

For example, considering that the working head7is engaged to the carriage6, the first51and the second52nut are connected to the carriage6so as to be arranged at the sides of the working head7.

According to an embodiment, the first pair of carriage moving ratio motors61,62comprises a first pair of electric motors610,620and a first gearbox615, where each electric motor of said first pair of electric motors is provided with a first moving shaft611;621which engages the first gearbox615. The second pair of carriage moving ratio motors63,64in turn comprises a second pair of electric motors630,640and a second gearbox635, where each electric motor of said second pair of electric motors is provided with a second moving shaft631;641which engages the second gearbox635.

Preferably, the first pair of carriage moving ratio motors61,62only comprises the first pair of electric motors610,620and the first gearbox615, while the second pair of carriage moving ratio motors63,64only comprises the second pair of electric motors630,640and the second gearbox635.

FIG.11illustrates the kinematic chain of engagement between the first (or second) pair of electric motors and the first (or second) gearbox.

According to an embodiment, a main electric motor630belonging to the first61,62or to the second pair of carriage moving ratio motors63,64is a master whereas the other three electric motors610,620,640of the first61,62and second pairs of carriage moving ratio motors63,64are slaves.

Therefore, the actuation of the translation of the carriage6along the vertical direction Y is guided by a master-slave architecture.

Preferably, the upright4also comprises a pair of vertical guides9on which the carriage6slides. For example, such pair of vertical guides9is a pair of vertical sliding tracks, that is, oriented along the vertical direction Y.

In one embodiment, the machine tool1further comprises a vertical position transducer90, e.g. an optical ruler, for detecting the position of the carriage6with respect to the upright4.

Preferably, the vertical position transducer90is associated with a vertical guide of the pair of vertical guides9.

According to an embodiment, the vertical position transducer90is positioned parallel to a vertical guide of the pair of vertical guides9. Furthermore, such vertical position transducer90is arranged along the vertical direction Y, so as to be substantially vertically aligned with the main electric motor630.

Preferably, both the first5′ and the second ball screw5″ comprise a lower support5aand an upper support5b. In this case, the lower support5ais represented inFIG.13, while the upper support5bis represented inFIG.12.

According to an embodiment, the machine tool1further comprises four pairs of ratio motors81,82,83,84which are positioned aboard the upright4and engage with the upright translation means3.

According to an embodiment shown in the accompanyingFIGS.6and7, the upright translation means3comprise a first pair of upright translation members31fixed to the bench20and a second pair of upright translation members32fixed to the rear support22.

According to an embodiment illustrated in the accompanyingFIGS.1and2, a first pair of ratio motors81and a second pair of ratio motors82of the four pairs of ratio motors81,82,83,84engage the first pair of upright translation members31.

Instead, a third pair of ratio motors83and a fourth pair of ratio motors84of such four pairs of ratio motors81,82,83,84engage the second pair of upright translation members32.

In one embodiment, the first81and the third pair of ratio motors83are positioned on a first side41of the upright4whereas the second82and the fourth pair of ratio motors84are positioned on a second side42of the upright4, opposite to the first side41.

Said first41and second side42are lateral with respect to the position of the carriage translation means5on which the carriage6translates.

According to an embodiment, a first main ratio motor831belonging to the first81or to the third pair of ratio motors83is a master, while the remaining three ratio motors of the first and third pair of ratio motors are slaves. Furthermore, a second main ratio motor842belonging to the second82or to the fourth pair of ratio motors84is a master, while the remaining three ratio motors of the second and fourth pair of ratio motors are slaves.

Preferably, the first main ratio motor831belongs to the third pair of ratio motors83and is positioned in proximity to an upper end22″ of the rear support22. The second main ratio motor842belongs to the fourth pair of ratio motors84and is positioned in proximity to the upper end22″.

In particular, both on the first side41and on the second side42of the upright4there is a master-slave architecture.

In one embodiment, each upright translation member of the first31and of the second pair of upright translation members32is a rack. Furthermore, each ratio motor of each of the four pairs of ratio motors81,82,83,84comprises an electric upright translation motor800and a gearbox802. The upright translation electric motor800has a motor axis M which is parallel to the vertical direction Y. The gearbox802has an inlet engaged with the upright translation electric motor800and an outlet engaged with the rack.

The accompanyingFIGS.5-8illustrate the kinematic chain, where each upright translation member is a rack fixed to the supporting structure and where each ratio motor is fixed aboard the upright4and engages with the rack.

Preferably, the inlet and outlet of the gearbox802are coaxial to the motor axis M and the outlet comprises a toothed wheel which engages with the rack.

According to an embodiment, a GANTRY control is provided between each master and the respective slaves.

Therefore, a GANTRY control is also provided on both the first side41and the second side42of the upright4. Furthermore, a GANTRY control is also provided between the first61,62and the second pair of carriage moving ratio motors63,64.

The GANTRY control is implemented on master-slave architectures where, by means of MIMO (Multiple-Input and Multiple-Output) communication, the slave ratio motors follow the positions controlled by the master and send their feedback data to the master, so as to obtain a closed-loop control.

In one embodiment, the working head7is rotatable about a pitching axis A and about a rolling axis C.

According to an embodiment illustrated inFIG.4, the tool holder seat70is rotatable about a tool axis T.

It should be noted that, by virtue of the type of machining to be carried out on the semi-finished product, the tool axis T may be collinear or incident with the rolling axis C.

In one embodiment, the bench20also comprises a first pair of guides201on which the upright4slides.

Furthermore, the rear support22extends between a lower end22′ connected to the bench20, and an upper end22″ where, at such upper end, the second pair of upright translation members32and a second guide202on which the upright4slides are positioned.

In an embodiment shown in the accompanyingFIGS.1and2, at least a third guide203which is fixed to the rear support22and on which the upright4slides is positioned in between the upper end22″ and the lower end22′.

Preferably, such third guide203is spaced vertically, i.e. along the vertical direction Y, from the second pair of upright translation members32.

In particular, the first pair of guides201, the second guide202and the third guide203are longitudinal sliding tracks, i.e. oriented along the longitudinal direction X.

According to an embodiment, both the first31and the second pair of upright translation members32extend along the longitudinal direction X between a first end3′ and a second end3″ opposite the first3′. A position transducer30, for example an optical ruler, is associated with such first3′ and second3″ ends.

Innovatively, the machine tool object of the present invention fulfills the intended purpose, as it achieves such a stiffness that the first resonance frequency is comprised in the range between 24 and 30 Hz.

Analytically, following software simulations for finite element analysis (FEA) of the machine tool object of the present invention, it has been calculated that the first resonance frequency is about 30 Hz. Considering that the value obtained is the result of a model that represents a simplification of reality, it was decided in favor of safety to consider 80% of the calculated value. Therefore, the first conservatively calculated resonance frequency is equal to 24 Hz, i.e. 80% of the result obtained through FEA simulations.

Advantageously, the machine tool object of the present invention is more rigid than the machine tools according to the prior art.

Contrary to the technical prejudice, which sought to improve the rigidity of the machines by only increasing the rigidity of the structures, in the present invention the degrees of constraint between the upright and the carriage translation means have been increased.

In addition, the degrees of constraint between the upright and the supporting structure have also been increased.

The increase in stiffness and in the value of the first resonant frequency were achieved when passing from the solution with only two ratio motors engaged with the carriage translation means, contemplated by the prior art, to the present invention in which a first and a second pair of carriage moving ratio motors engaged with the carriage translation means have been introduced. Therefore, the constraint between the upright and the carriage translation means has changed from two to four degrees.

Analytically, it has been observed that the increase in the degrees of constraint between the upright and the carriage translation means produces an increase in the resonance frequency such as to be able to machine the titanium alloys in absolute safety and in compliance with the required tolerances. In other words, it has been observed that by replacing each ratio motor of the prior art with a smaller pair of carriage moving ratio motors, the overall rigidity of the machine increases considerably and its dynamic performances improve.

According to an advantageous aspect, the machine tool object of the present invention is safe, since it operates on frequencies far from the resonant frequency of the machine itself.

According to a still further advantageous aspect, the machine tool object of the present invention has a lower manufacturing cost or comparable with the machine tools according to the prior art.

It is clear that those skilled in the art, in order to satisfy contingent needs, may make modifications to the machine tool described above, or replace elements with other functionally equivalent ones, without however departing from the scope of protection of the following claims. Each of the features described as belonging to a possible embodiment may be obtained independently in the other described embodiments.