WO2024175289A1

WO2024175289A1 - Laser head for wire deposition

Info

Publication number: WO2024175289A1
Application number: PCT/EP2024/051556
Authority: WO
Inventors: Roberto OCAÑA PEREZ; Asier CUEVAS ETTCHETO
Original assignee: Fundación Tekniker
Priority date: 2023-02-23
Filing date: 2024-01-23
Publication date: 2024-08-29

Abstract

The invention relates to a laser head for wire deposition, preferably for omnidirectional wire deposition. The laser head (1) comprises: a nozzle (2) having an opening (3) defining an axis X, a wire guiding tube (4) disposed in the nozzle's opening (3) and extending along the axis X, for guiding a wire along the axis X. The wire guiding tube (4) has an output (5) placed outside the nozzle (2), and laser beam sources (6a, 6b, 6c) are arranged to emit respective laser beams converging towards the output (5) of the wire guiding tube (4) and intersecting with the axis X. Force sensors (9a, 9b, 9c, 9d) are installed in the laser head to sense forces exerted on the wire guiding tube (4) in a transversal direction to the axis X, during a wire deposing process. The laser head (1) assures a homogeneous or constant material deposition rate, that is, a constant wire melting rate, such that the number of failures or defective pieces produced by wire deposition are significantly reduced.

Description

LASER HEAD FOR WIRE DEPOSITION

DESCRIPTION

TECHNICAL FIELD

The present invention relates to a laser head for wire deposition, preferably for omnidirectional or 360° wire deposition works, such as: laser welding or 3D manufacturing.

An object of the invention is the provision of a laser head for wire deposition, that assures a homogenous or constant material deposition rate, such that the number of failures or defective pieces produced by wire deposition are significantly reduced.

STATE OF THE ART

Currently, there are several techniques in laser heads for omnidirectional wire deposition, in which the wire is melted by means of a circular laser beam that converges on the wire or by an array of focused beams symmetrically arranged around the wire.

Omnidirectional wire deposition means that the wire is melted and deposited on a surface with the same characteristics regardless of the direction of movement of the laser head. This symmetry in the deposition is crucial when it comes to generating a layer on a surface in a homogeneous way or manufacturing 3D parts.

It is also important in laser welding processes to generate weld seams with the same characteristics regardless of the deposition direction. In all cases, the laser beam is projected at an angle with respect to the wire. The wire exits the head through a nozzle of an automatic wire supply system embedded in the head. Generally, it is desirable that the wire be melted at a point not too far from the nozzle, so that the melt point coincides with the position designed for the wire to meet the circular laser beam or array of symmetrical beams. If the wire is melted at a distant point, two effects may occur: (1) the wire is melted at a slower rate and increasing forces opposite to the movement direction of the head start acting on the wire bringing it to a non-optimal position, (2) the wire is not melted at all.

Existing wire deposition heads use working distances (distance between the outlet of the wire's conductive nozzle and the point where it meets the laser radiation and melts) of 9-10 mm. This has the advantage that the angles of incidence of the laser beam or beams with the wire are not very pronounced and therefore the heads can be designed with reduced dimensions. However, such a large working distance makes the wire more susceptible to bending due to the forces involved in the process. For example, in MIG welding, the recommended working distance is just 5 mm. Making a head where the wire is less susceptible to bending due to process forces means that the angle of incidence of the laser has to be higher.

In general, once the wire comes out of the nozzle, it is exposed to the forces generated in the process tending to deflect it. If this deviation is pronounced, the wire will not melt correctly, and the deposition process will fail. In some cases, these failures force to discard the manufactured parts and start over. In other cases, the ability of the operator to start the process again at the point where the failure occurred is decisive.

Heads designed with a small angle between the laser beam and the wire are compact but they are more prone to deviations since the point where the laser beam or beams meet the wire is further away from the nozzle than in larger head designs.

DESCRIPTION OF THE INVENTION

The invention is defined in the attached independent claim, and satisfactorily solves the above-described drawbacks of the prior art, by the provision of a laser head that features a homogenous or constant material deposition rate, regardless of the transversal forces exerted on the wire during the deposition process.

The laser head of the invention integrates force sensors which reports forces exerted on the wire during the wire deposition process, in order to monitor the process and to control the process.

Therefore, an aspect of the invention refers to a laser head for wire deposition, that comprises a nozzle having an opening and a wire guiding tube disposed in the nozzle's opening and extending long an axis X, for guiding a wire along the axis X.

The wire guiding tube has an output placed outside the nozzle, and the laser head further comprises at least three laser beam sources equidistantly arranged to emit respective laser beams converging towards the output of the wire guiding tube and intersecting with the axis X. Preferably, the laser beam sources are arranged such that, when they are emitting respective laser beams, the laser beams intersect the axis X at a point distanced around 5 mm from the output of the wire guiding tube.

This larger angle of incidence of the laser on the wire compared with prior art laser heads, results in that the distance in which the wire comes out (from the nozzle to the point where the laser beam or beams are focused) is shorter. This has the benefic that the laser head is less sensitive to deviations from the optimal position due to transverse forces operating on the wire during the deposition process.

Additionally, the laser head comprises at least three force sensors installed in the laser head to sense forces (direction and module of the forces) exerted on the wire guiding tube in a transversal direction relative to the axis X, during a wire deposing process in which the wire is melted by the laser beams and deposited on a working surface either for welding or for forming a 3D piece.

Alternatively, springs are used in the X and Y directions, then, only one sensor per Cartesian axis is required. Since as transverse forces (X-Y plane) are monitored, only two sensors are used to sense forces, one sensor in the X direction and another sensor in the Y direction.

In a preferred embodiment, the laser head has four force sensors, that is, two sensors for each axis (X,Y) of a Cartesian system to achieve more accurate measurements.

The processing of the measurements is as follows: two sensors are adjusted in one direction by touching both sides of the wire. One tightens in the +X direction and one in the -X direction. The two forces add up to zero at the optimum position of the wire in the X-direction. If the wire sees a force in the -X direction, the -X sensor will measure an increase in force while the +X will measure a relaxation of force. The difference from the previous position produces the magnitude of the force that has originated on the wire. If we do the same for the Y direction then we have a system that gives us the magnitude and direction of the forces acting on the wire in the entire XY plane.

A gap is formed all around the wire guiding tube and between the nozzle and the wire guiding tube, such that the radial position of the wire guiding tube can be adjusted. The laser head is fitted with threaded pins displaceable in a transverse direction relative to the axis X, and configured to contact with the wire guiding tube for adjusting the radial position of the wire guiding tube within the nozzle's opening, so that the wire is perfectly dispensed along the axis X.

Each force sensor is attached to a free end of a threaded pin, for contacting with the wire guiding tube. Preferably, the force sensors are piezoelectric sensors attached to the nozzle adjustment threaded pins or screws, that allow not only to adjust the wire at the point where the three beams are focused, but also offer in-situ monitoring of the transverse forces operating on the wire during the deposition process.

Another aspect of the invention refers to a laser system that includes the laser head previously described, and control means communicated with the force sensors and adapted for receiving and processing data generated by the force sensors, and a wire feeding system adapted for dispensing a wire along the axis X. The control means and the wire feeding system, are configured such that the operation of the wire feeding system is controlled by the control means depending on the data generated by the force sensors.

The control means are adapted such the wire feeding system stop feeding wire, when any one of the force sensors detect a force applied on the wire feeding tube above a predefined force threshold, so that, so less failures or defective pieces are produced.

As a very large transverse force will deflect the wire from its optimum point causing it to melt at a different rate, these transverse forces are counteracted by controlling wire deposition parameters such as wire feed speed, head movement speed, laser power etc., which are set appropriately in such a way that the deposition rate is homogeneous. The in-situ reading of the transverse forces not only serves to detect deviations but also to correct them within the framework of an automatic or manual control strategy.

The way of controlling a wire feeding system is well-known for a skilled person in the art, thus, it is not considered necessary to describe that control process any further.

BRIEF DESCRIPTION OF THE DRAWINGS

To complete the description and in order to provide a better understanding of the invention, a set of drawings is provided. These drawings form an integral part of the description and illustrate embodiments of the invention, which should not be interpreted as restricting the scope of the invention, but just as examples of how the invention can be carried out. The drawings comprise the following figures:

Figure 1.- shows a perspective view from below of a laser head according to the invention. The sphere represents the point where the laser beams converge together.

Figure 2.- shows a front elevational view of the laser head of Figure 1.

Figure 3.- shows a perspective view of a detail of the wire guiding tube inside the nozzle.

Figure 4.- shows in Figure 4A a threaded pin with a force sensor coupled at one of its ends, and in Figure 4B another representation of the nozzle including four threaded pins equidistantly arranged.

Figure 5.- shows a front elevational view of the laser head of the previous figures, including a wire feeding system and a main laser source.

DESCRIPTION OF WAYS OF CARRYING OUT THE INVENTION

Figure 1 shows a preferred implementation of a laser head (1) for wire deposition according to the invention, wherein the laser head (1) comprises a nozzle (2) having an opening (3), and a wire guiding tube (4) disposed in the nozzle's opening (3) and extending long an axis (X) for guiding a wire (not shown) along the axis (X). The wire guiding tube (4) has an output (5) placed outside the nozzle (2).

The laser head (1) is fitted with three laser beam sources (6a, 6b, 6c) arranged to emit respective laser beams converging towards the output (5) of the wire guiding tube (4) and intersecting with the axis (X) at a point (P), as better shown in Figure 2. In this preferred implementation, the point (P) is distanced 5 mm from the output (5) of the wire guiding tube (4).

The laser head (1) in this embodiment incorporates four threaded pins (7a, 7b, 7c, 7d) displaceable in an orthogonal direction relative to the axis (X), and configured to contact with the wire guiding tube (4) for adjusting the radial position of the wire guiding tube (4) within the nozzle's opening (3). The four threaded pins (7a, 7b, 7c, 7d) are equidistantly arranged on a plane orthogonal to the axis (X). As represented in Figure 3, a gap (8) is formed between the nozzle (2) with the wire guiding tube (4) and the part that holds the threaded pins (7a, 7b, 7c, 7d). This gap (8) extends all around the wire guiding tube (4), such that the radial position of the wire guiding tube (4) can be adjusted, for aligning a wire (not shown) with the axis (X).

As represented in Figure 4, each threaded pin (7a, 7b, 7c, 7d) has a force sensor (9a, 9b, 9c, 9d), for example piezoelectric sensors, coupled to its free end, for contacting with the wire guiding tube (4), for sensing transversal forces applied to the wire guiding tube (4) and for adjusting the radial position of the wire guiding tube (4). The force sensor (9a, 9b, 9c, 9d) does not rotate when the threated pin (7a, 7b, 7c, 7d) is rotated, but exerts a force on the wire guiding tube (4) to position the wire and leave it in its fixed position with an initial force.

Figure 5 shows a laser system (12) including the laser head (1) previously described, and a wire feeding system (10) adapted for dispensing a wire along the axis (X), a main laser source (11), and a control unit (13) communicated with the force sensors (9a, 9b, 9c, 9d) and adapted for receiving and processing data generated by the force sensors.

In practise, the control unit (13) is located outside the laser head (1), and the laser head (1) integrates the necessary electronics for conditioning the sensor signals so that they can transmit the information to the control unit (13) via communication protocol or similar communication means, so that data would not deteriorate if it has to be transmitted over long cables.

Claims

1.- Laser head (1) for wire deposition, comprising: a nozzle (2) having an opening (3), a wire guiding tube (4) disposed in the nozzle's opening (3) and extending long an axis (X) for guiding a wire along the axis (X), the wire guiding tube (4) having an output (5) placed outside the nozzle (2), at least three laser beam sources (6a, 6b, 6c) arranged to emit respective laser beams converging towards the output (5) of the wire guiding tube (4) and intersecting with the axis (X), and at least two force sensors (9a, 9b, 9c, 9d) installed in the laser head to sense forces exerted on the wire guiding tube (4) in a transversal direction relative to the axis (X) during a wire deposing process.

2.- Laser head according to claim 1 , having a gap (8) formed between the nozzle (2) and the wire guiding tube (4), the gap (8) extending all around the wire guiding tube (4), such that the radial position of the wire guiding tube (4) can be adjusted.

3.- Laser head according to claim 2, further comprising at least three threaded pins (7a, 7b, 7c, 7d) displaceable in a transverse direction relative to the axis (X), and configured to contact with the wire guiding tube (4) for adjusting the radial position of the wire guiding tube (4) within the nozzle's opening (3).

4.- Laser head according to claim 3, wherein each force sensor (9a, 9b, 9c, 9d) is attached to a free end of a threaded pin (7a, 7b, 7c, 7d), for contacting with the wire guiding tube (4).

5.- Laser head according to any of the preceding claims, wherein the force sensors (9a, 9b, 9c, 9d) are piezoelectric sensors.

6.- Laser head according to any of the preceding claims, wherein the laser beam sources (6a, 6b, 6c) are arranged such that, when they are emitting respective laser beams, the laser beams intersect the axis X at point P distanced 5 mm from the output of the wire guiding tube (4).

7.- Laser head according to claim 3, comprising four threaded pins (7a, 7b, 7c, 7d) equidistantly arranged on a plane orthogonal to the axis (X), and displaceable in an orthogonal direction relative to the axis X, and configured to contact with the wire guiding tube (4) for adjusting the radial position of the wire guiding tube (4) within the nozzle's opening (3).

8.- A laser system (12) including the laser head (1) defined in any of the preceding claims, comprising control means (13) communicated with the force sensors (9a, 9b, 9c, 9d) and adapted for receiving and processing data generated by the force sensors.

9.- Laser system according to claim 8, further comprising a wire feeding system (10) adapted for dispensing a wire along the axis (X).

10.- Laser system according to claims 8 and 9, wherein the control means (13) and the wire feeding system (10), are configured such that the operation of the wire feeding system (10) is controlled by the control unit (13) depending on data received from the force sensors (9a, 9b, 9c, 9d).

11.- Laser system according to claim 8, wherein the control unit (13) and the wire feeding system (10) are configured to control wire feed speed and laser head movement speed, depending on data received from the force sensors (9a, 9b, 9c, 9d).

12.- Laser system according to claim 8, wherein the control unit (13) are adapted such the wire feeding system (10) stop feeding wire, when any one of the force sensors (9a, 9b, 9c, 9d) detect a force applied on the wire feeding tube (4) above a predefined force threshold.