WO2016024069A1

WO2016024069A1 - Device for laser beam machining a precisely tapered hole with a movable afocal module

Info

Publication number: WO2016024069A1
Application number: PCT/FR2015/052202
Authority: WO
Inventors: Bruno Chassagne; Benoît APPERT-COLLIN
Original assignee: Centre Technologique Alphanov
Priority date: 2014-08-14
Filing date: 2015-08-13
Publication date: 2016-02-18
Also published as: FR3024843B1; FR3024843A1

Abstract

The invention relates to a laser beam machining device for creating a precisely tapered hole (13). Said device includes: - a laser source (11) capable of emitting a laser beam; and - an optical focusing unit (17) for focusing the laser beam onto a surface of the part (12) to be machined. Said optical focusing unit (17) has an optical axis (14). The device also includes: - an afocal module (15) inserted between the laser source (11) and the optical focusing unit (17) so as to direct the laser beam onto the optical focusing unit (17); - means for controlling, in a precise manner, movement of said afocal module (15) in an orthogonal direction relative to the optical axis (14) between a first position, wherein the optical centers (0', 0") of the afocal module (15) are aligned with the optical axis (14), and a second position, wherein the optical centers (0', 0") of the afocal module are moved from a distance E relative to the optical axis (14) such that the beam is directed onto the part (12) to be machined at an angle Φ relative to the optical axis (14), the angle Φ being predetermined by said movement; and - a means for controlling rotation of the afocal module about the optical axis (14) such that said beam, angled at an angle Φ, follows a circular precessional movement on the part (12) to be machined.

Description

LASER BEAM MACHINING DEVICE OF A CONICIT HOLES CONTROLLED WITH A DISPLACABLE AFOCAL MODULE

The present invention relates to a laser beam machining device for making a conically controlled hole in a mechanical part.

It is known to use drilling and laser cutting techniques to perform machining in parts. In known manner, these techniques implement two types of operations, which are percussion and trepanation.

A percussion operation involves using a fixed laser beam to penetrate the thickness of the material. The laser beam therefore has a fixed impact on the piercing point. This results in a hole whose diameter is determined by the diameter of the laser beam and the power level of the laser source.

A trephination operation involves cutting the contour of a hole by moving the laser beam over the surface of a workpiece by drawing a substantially circular path instead of piercing it at one time. This results in a hole whose diameter is greater than the diameter of the laser beam.

In both cases, the incident laser beam arrives on the workpiece with a zero angle of incidence.

Although the percussion technique is faster, it is often preferred trepanation because of a lower thermal influence in the machined area. In addition, the diameter of the hole is no longer limited to that of the laser beam.

The technical field of the present invention relates more particularly to the technique of trephination.

The device for implementing the trepanation technique generally comprises a laser source that emits a laser beam. This beam is transformed and focused by an optical system at a focal point on the surface of the workpiece. In addition, a deflector system is placed between the source and the optical system to deflect the laser beam. Figure 1A schematically illustrates a hole 3 obtained in a workpiece 2 with a known trephination technique. A laser beam 6 emitted by a laser source and emerging from an optical system (not shown in FIG. 1A) is contained in a conical volume. The displacement of the laser beam is materialized by a double circular arrow. The hole 3 has an incoming diameter Di corresponding to the diameter of the hole located on the impact side laser beam on the workpiece and the outgoing diameter D ₂ corresponding to the diameter of the hole on the side opposite the impact of the laser beam.

FIG. 1A illustrates a conventional trepanation technique in which the beam arrives on the surface of the part with a zero angle φ, the beam transmission axis 5 extending parallel to the axis of the hole 4. The hole thus produced necessarily has an incoming diameter Di larger than the diameter D ₂ . This shape characteristic is inherent in the conventional trephination operation and the intensity profile of the laser beam.

When the hole must have a specific or complex shape, the conventional trephination technique as described above is no longer suitable. In general, it is important to be able to control the taper of the hole made according to the need of the industrial application.

A known solution consists in interposing between the laser source and the focusing optical system an optical deflection system which makes it possible to introduce an angle of inclination between the laser beam which arrives on the surface of the workpiece and the axis of the workpiece. hole 4.

The laser beam is then in the form of a cone with an angle inclined relative to the axis of the hole 4. In addition to this inclination, the laser beam is displaced to describe a substantially circular precessional movement on the workpiece. machined. By controlling the angle φ, it is therefore possible to make a hole of zero conicity (Figure 1B) or with a negative conicity (Figure 1C).

In the prior art, an optical system known for controlling the direction of a laser beam generally comprises a set comprising at least two rotating prisms separated from each other by a variable distance, which can rotate independently of one another. the other, to direct the laser beam in a cone with an angle inclined to the optical axis. Such a system is also known as the "diasporameter". By varying the distance separating the two rotating prisms or by moving all the prisms relative to the focusing system, or by varying their orientation, it is possible to drill convergent, divergent or cylindrical conical holes.

Nevertheless, existing systems involve complex assemblies of optical elements, expensive and fragile.

An object of the present invention is to provide a new device for machining a hole in a workpiece that is simple to implement, that is inexpensive, and is robust while allowing control of the taper of the hole. Another goal of this The invention is to integrate an optical means in the new drilling and cutting device for moving the impact of the beam on the workpiece.

For this purpose, the subject of the invention is a laser beam machining device for producing a hole with a controlled conicity, said device comprising a laser source capable of emitting a laser beam, an optical focusing unit for focusing the laser beam. on a surface of the workpiece, said optical focusing unit having an optical axis, the device being characterized in that it further comprises:

an afocal module interposed between the laser source and the optical focusing unit for directing the laser beam on the focusing optical unit,

means for controlling in a controlled manner a displacement of said afocal module in a direction orthogonal to the optical axis between a first position in which the optical centers (Ο ', 0 ") of the afocal module are aligned with the optical axis and a second position in which the optical centers (Ο ', O ") of the afocal module are displaced by a distance E with respect to the optical axis so that the beam is directed at the workpiece at an angle φ relative to the optical axis, the angle φ being predetermined by said displacement,

- Means for controlling a rotation of the afocal module around the optical axis so that said beam inclined at an angle φ describes a circular precession movement on the workpiece.

According to one embodiment of the invention, the machining device comprises a deflection unit for directing the laser beam on the optical focusing unit at a predetermined angle of field so that the laser beam is focused at a point. located on the piece off the optical axis.

According to one variant, said deflection unit is placed between the laser source and the afocal module.

According to another variant, said deflection unit is placed between the afocal module and the optical focusing unit, this deflector may or may not be placed at the objective focal length of the focusing lens.

According to one embodiment, the afocal module is in the form of two lenses. The invention will now be described in more detail with reference to the appended figures, given solely by way of example and in which: FIGS. 1A, 1B and 1C respectively illustrate three forms of holes with a positive, zero and negative conicity made with machining devices of the prior art;

FIG. 2A is a schematic view of a machining device according to a first embodiment of the invention, comprising an afocal module placed in a configuration to produce a zero angle φ;

FIG. 2B is an enlarged view of the impact zone of the laser beam on the workpiece of FIG. 2A,

FIG. 3A is a schematic view of the machining device of FIG. 2A, comprising an afocal module placed in a configuration to produce a non-zero angle φ on the workpiece,

FIG. 3B is an enlarged view of the impact zone of the laser beam on the workpiece of FIG. 3A with the afocal module illustrated in an initial angular position and a second position of the afocal module in which it has rotated from ° with respect to the initial angular position,

FIG. 4 is a schematic view of a machining device according to a second embodiment of the invention, comprising a deflection unit interposed between the laser source and the afocal module in order to displace the impact of the laser beam on the workpiece,

FIG. 5 is a variant of the machining device of FIG. 4 with the deflection unit placed between the afocal module and the optical focusing unit.

Figures 2 and 3 illustrate a machining device 10 according to a first embodiment of the invention for making a hole 13 with a controlled conicity in a workpiece 12. The device comprises a laser source 11 for generating a laser beam 16 The beam is then focused, by a focusing lens 17, at a focal point 18 on the surface of the workpiece 12.

The focusing lens is placed at a distance f from the workpiece and its optical axis is aligned with the longitudinal transmission axis 14 of the laser beam as it leaves the source. For the rest of the description, the machining device is placed in a reference (X, Y, Z), the Z axis corresponding to the transmission axis of the laser beam 16, oriented parallel to the optical axis 14. For the following description, the piece 12 to be machined is disposed in an orthogonal plane (X, Y) oriented perpendicularly to the optical axis 14 so that the axis of the hole 13 is substantially aligned with the optical axis 14.

An afocal module 15, magnified unitarily or not, consists of two lenses 15 ', 15 "is placed in the path of the laser beam between the laser source 11 and the focusing lens 17. According to an essential aspect of the invention, the machining device comprises means for moving this afocal module linearly with respect to the optical axis 14 in a plane orthogonal to the optical axis 14 so that the lenses 15 ', 15 "are off-center by a distance E relative to to the optical axis 14. Thus, the afocal module, being eccentric with respect to the optical axis 14, directs the laser beam 16 eccentrically with respect to the optical axis 14 and parallel thereto. The laser beam is then deflected by the focusing lens 17 and hits the workpiece at point 18, at a non-zero angle φ, where φ is the angle formed between the axis of propagation of the laser beam and the optical axis 14. .

FIG. 2A illustrates the machining device with the afocal module 15 placed in a first position in which the optical centers Ο ', O "of the lenses 15', 15" are aligned with the optical axis 14 of the focusing lens 17 The rays of the laser beam emanating from the laser source are parallel to each other and to the optical axis 14. They pass successively through the two lenses 15 ', 15 "of the afocal module 15 and the focusing lens 17 to converge towards a focal point 18 located at a distance f from the optical center of the focusing lens 17, the point 18 being located on the surface of the workpiece The assembly of Fig. 2A is placed in a configuration in which the laser beam 16 strikes the workpiece to be machined with a zero angle Fig. 2B is an enlarged view of the focusing area of the laser beam on the workpiece with the afocal module 15 aligned with the optical axis of the focusing lens (E = 0), the beam lase r 16 is directed parallel to the optical axis 14 of the focusing lens and passes through the focusing lens 17 at its center. The beam that is focused on the piece arrives with a tilt angle φ zero.

FIG. 3A illustrates the device of FIG. 2A placed in a configuration for introducing an angle of inclination φ between the laser beam and the optical axis. To do this, the afocal module 15 is moved in a direction orthogonal to the optical axis 14 by a distance E. The displacement of the afocal module is indicated by an arrow. More precisely, the optical centers O ', O "of the two lenses 15', 15" are displaced with respect to the optical axis 14 of the focusing lens by a distance E. The eccentricity of the two lenses relative to axis The optical system makes it possible to off-center the laser beam in the entrance pupil of the focusing lens so that the laser beam is deflected by this lens 17 and thus focuses on the workpiece at an angle φ. In the case where the eccentric afocal module is unit optical magnification, the angle φ is defined by the relation: tan φ = E / f, where E is the eccentricity distance between the optical centers of the two lenses of the afocal module and the optical axis 14, f being the focal length of the focusing lens.

Preferably, the device comprises a motor enabling the movement of the afocal module 15 to be controlled in a controlled manner.

According to an essential aspect of the invention, the device further comprises means for rotating the lenses 15 ', 15 "around the optical axis 14 of the focusing lens 17. The rotational movement of each of the two lenses is shown schematically by an arrow in FIG 3B, the beam can therefore rotate about the optical axis 14 at least forming part of the surface of a cone, by causing the afocal module to rotate 360 degrees around the 14, a complete trepanation is obtained Thus the laser beam which arrives on the surface of the workpiece describes a circular precession movement with an angle φ.

In FIG. 3B is illustrated this circular precession movement. The laser beam 16 which arrives on the focusing lens 17 is here represented arbitrarily at two different places P1, P2 on the focusing lens. PI corresponds to an initial angular position of the two lenses of the afocal module and P2 corresponds to an angular position in which the two lenses 15 ', 15 "have rotated 180 degrees with respect to the initial position. a rotation of 360 ° around the optical axis 14, so we obtain a complete trepanning movement.

Thus, the machining device, according to this first embodiment of the invention, by controlling the angle of inclination φ of the laser beam that arrives on the workpiece through the control of the transverse eccentricity E of the two lenses 15 ', 15 "with respect to the optical axis 14, therefore makes it possible to control the taper of the hole to be made in a part, In particular, with the device of the invention, it is possible to make a hole with a zero conicity (Figure 1B) or a negative conicity (Figure 1C) by controlling the angle of inclination φ.

To linearly move the two lenses of the afocal module in a direction orthogonal to the optical axis, it is intended to fix the two lenses on a support which is driven by a vertical movement controlled by a motor (not shown in Figure 3A). The support can also rotate around the optical axis through a bearing (not shown). The rotation of the support is controlled for example by a second motor.

In a variant (not shown) of the device of FIG. 3A, the two lenses constituting the afocal module are positive-positive or negative-positive spherical symmetry lenses. This latter embodiment avoids having a hot spot that could lead to deterioration of the device.

Another particularly advantageous variant consists in using cylindrical lenses instead of spherically symmetrical lenses in the afocal module. Thus a 180 ° rotation of the afocal module, and therefore of the two cylindrical lenses, produces a complete 360 ° rotation of the laser beam at the output of the afocal module. The cylindrical lenses that introduce an optical rotation of the beam, thus simplify the specifications of the motor that controls the rotation of the lenses.

According to a preferred embodiment of the invention, the laser beam emitted at the output of the source is able to be driven in a rotational movement about itself around its own transmission axis, thus making it possible to improve the quality of the machining by homogenization of the beam.

In the present invention, the term "focusing lens" designates a focusing lens of all shapes or a focusing unit composed of a combination of several lenses having the function of focusing without optical aberration the beam on the surface of the piece to machined.

Similarly, the afocal module 15 may be in the form of a combination of non-aberrant lenses successively arranged in the path of the beam, between the laser source 11 and the focusing lens 17.

FIGS. 4 and 5 illustrate a machining device 10 'according to a second embodiment of the invention in which a deflection unit 19 is integrated in the assembly of FIG. 3A in order to be able to displace the impact of the laser beam on the surface of the workpiece at predetermined positions along the two X and Y directions outside the optical axis 14 of the focusing lens.

FIG. 4 illustrates a first variant of the embodiment in which the deflection unit 19 is arranged between the laser source 11 and the afocal module 15. In order to highlight the operating mode of the deflection unit 19, the beam laser is drawn in continuous line 16 in the case where the laser beam is not deflected by the deflection unit 19 and dashed 16 'when deflected by the deflection unit 19. The laser source 11 emits a laser beam 16 directed in a direction of transmission oriented parallel to the optical axis 14 of the focusing lens. The laser beam incident on the deflection unit is deflected at an angle α with respect to the transmission axis towards the first lens 15 'of the afocal module. The spokes, passing through the ecocalced module 15 eccentric distance E relative to the optical axis, out parallel to each other and oriented at an angle. This angle is a if the afocal module is of unit optical magnification and different from a if the afocal module is magnification is different from one. By crossing the focusing lens 17, the rays converge towards a point 18 ', located in the image focal plane of the focusing lens but out of the optical axis. In this way, the deflection unit 19 has made it possible to move the focusing point to a new position 18 'of the workpiece which is offset from the focusing point 18 obtained when the angle a is zero. This new position 18 'is located outside the optical axis 14. By rotating the two lenses 15', 15 "of the afocal module around the optical axis 14, the beam 16 'can therefore describe at least a portion of the inner surface of a conical hole in the room 12. By turning the afocal module one full turn, a complete trepanning movement is achieved.

Preferably and in known manner, the deflection unit 19 is in the form of one or more mirrors driven by galvanometers. The galvanometer is controlled for example by a program for moving the mirror to predetermined positions in each of which it directs the rays of the laser beam to the first lens 15 'with a corresponding angle of incidence a. The mirror driven by the galvanometer generates a displacement of the laser beam on the surface of the workpiece in the two directions X and Y.

Thus, thanks to the deflection unit 19 placed between the laser source 11 and the afocal module 15, it is possible to define a beam displacement distance on the workpiece as a function of the angle of incidence a.

Preferably, the focusing lens 17 of the machining device comprises optical correction elements for reducing and / or eliminating the optical aberrations of the entire system. In this variant, however, the angle a must remain relatively small in order to not generate excessive aberrations, which leads to a limitation of the displacement of the laser beam on the object to be machined.

According to a second preferred variant of the second embodiment of the invention which is illustrated in FIG. 5, it is possible to increase this displacement distance with respect to the optical axis without increasing the aberrations or the vignetting.

To do this, the deflection unit 19 is placed between the afocal module 15 and the focusing lens 17. The laser beam 16 coming from the source passes firstly by the two lenses 15 ', 15 "eccentric with respect to the optical axis 14. The eccentricity of the lenses is carried out identically to that illustrated in FIG. 3A and its function is to direct the beam eccentrically with respect to the optical axis 14 and parallel thereto in the direction of the deflection unit 19. The laser beam is deflected at an angle α with respect to the optical axis 14 by the deflection unit 19 which then directs it towards the focusing lens 17. While crossing the focusing lens 17, the rays of the laser beam 16 'converge towards a point 18', situated in the image focal plane of the focusing lens but out of the optical axis 14.

The lenses 15 ', 15 "of the afocal module can rotate about the optical axis 14 which is also the axis of the hole to be machined.The beam 16' can therefore rotate around the axis of the hole 13 'to producing a trephination movement, thereby drawing the inner surface of a conical hole at a predetermined angle in the workpiece.

By positioning the deflection unit 19 after the afocal module, it is therefore easier to optically increase the angle a without increasing the aberrations or the vignetting, and thus produce a greater offset distance with respect to the optical axis.

In a preferred variant not illustrated, it is possible to place a second afocal module, of optical magnification higher than the unit, in the assemblies illustrated in FIGS. 3, 4 and 5, between the rotating afocal module 15 and the focusing lens. 17. This second afocal module is static. It thus makes it possible to increase the eccentricity introduced by the first afocal module. Consequently, it is possible to introduce only a small eccentricity of the first afocal module while maintaining a significant angle of inclination φ. This facilitates the rotation of the rotating afocal module by limiting the unbalance problem, due to the eccentricity of the center of gravity of the rotary afocal module.

The machining device according to the invention therefore makes it possible on the one hand to make holes with a well-defined profile by controlling the angle of inclination φ according to which the beam strikes the surface of the workpiece, and secondly to move the machining position on the surface of the workpiece.

Claims

1. A laser beam machining device for producing a hole (12) with a controlled conicity, said device comprising a laser source (11) capable of emitting a laser beam, an optical focusing unit (17) for focusing the laser beam on a surface of the workpiece (12), said focusing optical unit having an optical axis (14), characterized by further comprising:

an afocal module (15) interposed between the laser source (11) and the optical focusing unit (17) for directing the laser beam on the focusing optical unit,

means for controlling in a controlled manner a displacement of said afocal module in a direction orthogonal to the optical axis (14) between a first position in which the optical centers (Ο ', 0 ") of the afocal module (15) are aligned with the optical axis (14) and a second position in which the optical centers (Ο ', O ") of the afocal module are displaced by a distance E with respect to the optical axis (14) so that the beam is directed on the workpiece at an angle φ with respect to the optical axis, the angle φ being predetermined by said displacement,

- Means for controlling a rotation of the afocal module around the optical axis (14) so that said beam inclined at an angle φ describes a circular precession movement on the workpiece.

2. Machining device according to claim 1, characterized in that it comprises an optical deflection unit (19) for directing the laser beam on the optical focusing unit (17) at a predetermined angle of field of view so that the laser beam is focused at a point on the workpiece off the optical axis (14).

3. Machining device according to claim 2, characterized in that said deflection unit (19) comprises a mirror controlled by moving means.

4. Machining device according to claim 2 or 3, characterized in that said deflection unit (19) is placed between the laser source (11) and the afocal module (15).

5. Machining device according to claim 2 or 3, characterized in that said deflection unit (19) is placed between the afocal module (15) and the optical focusing unit (17).

6. Machining device according to one of claims 1 to 5, characterized in that the afocal module (15) is in the form of two lenses (15 ', 15 ") or a set of non-aberrant lenses .

7. Machining device according to claim 6, characterized in that the two lenses (15 ', 15 ") are positive-positive or negative-positive spherical symmetry lenses.

8. Machining device according to claim 6, characterized in that the two lenses (15 ', 15 ") are cylindrical lenses.

9. Machining device according to one of claims 1 to 8, characterized in that the optical focusing unit (17) is in the form of a focusing lens having a focal length f.

10. Machining device according to claim 9, characterized in that the optical focusing unit (17) further comprises optical correction elements to compensate for optical aberrations.