Patent Application
20080127891
The present invention relates to a device for resurfacing a part by supplying resurfacing material containing hard refractory particles and metal alloy particles.
More particularly, the invention relates to a device for resurfacing a concave face of a tubular part by supplying resurfacing material in powder form and by supplying energy by a laser.
Tubular parts having a hard refractory or metal alloy layer on their concave face are commonly used so as to be cut up into sections of variable length in order to produce bearings for the guiding of rotating shafts. Such tubular parts may also constitute cylinders for guiding the pistons in an internal combustion engine.
Various methods are already known for resurfacing the concave face of a tubular part.
Among these, the resurfacing of a concave face of a tubular part by supplying resurfacing material and energy by a laser proves to be particularly effective. This is because using a laser means that only a very localised and shallow heat-affected zone is formed on the concave face of the tubular part. The use of a laser thus prevents deterioration of the properties of the constituent material of the tubular part which has undergone, prior to the resurfacing, an important heat treatment for the purpose of giving it particular mechanical and chemical properties suitable for its subsequent conditions of use.
In document WO 00/23718 A1, there is a description of a concave face of a tubular part being resurfaced by supplying resurfacing material and energy by a laser.
That document describes a laser source that generates a laser beam directed onto a local zone of the concave face of the tubular part. Resurfacing material is delivered into this local zone and is heated by the energy of the laser beam. The laser source is placed radially facing the face to be resurfaced, i.e. inside the tubular part. This means that only tubular parts having a diameter sufficient to contain the laser source can be resurfaced. Thus, the diameter of the tubular parts on which it is possible to carry out resurfacing is very restrictively limited.
It has already been imagined to use a laser source associated with means for conducting the energy of the laser beam right to a zone to be treated inside a tube, the laser source then being able to remain outside the tube. The difficulty is then to ensure that the laser energy is produced and conducted effectively, reliably and inexpensively.
For example, document US 2002/0164436 A1 describes a method and a device for laser-resurfacing tubular parts, such as internal combustion engine cylinders. A diode laser generates a laser beam, and an optical system conducts the laser beam into the tube and makes it exit therefrom radially in order to strike a treatment zone. Resurfacing material delivery means carry a powdered resurfacing material, based on an alloy powder, into the resurfacing zone.
In this way, the laser source may be on the outside of the tubular part, and the optical system is engaged axially in the tubular part in order to deliver the laser energy into the treatment zone inside the tubular part.
The document provides no precise description of the optical system and the resurfacing material delivery means.
At the very most,
One problem, mentioned moreover by the above document, is the heating produced by the energy of the laser striking the treatment zone. This heating may impair the effectiveness of the laser and may disturb the progress of the pulverulent resurfacing material into the treatment zone. To remedy this, the document proposes delivering the pulverulent material by a vibrating conveyor or a screw.
However, this heating also affects the optical laser-conducting device and may damage it, in particular in small-diameter tubular parts in which the atmosphere is confined.
This heating problem is all the more crucial when it is desired to resurface a tubular part with a material containing refractory particles, used for their high hardness. This is because a large amount of energy has to be supplied to produce an effective hard resurfacing layer.
Also known, from document JP 2000-153382 A, is a laser beam machine capable of laser machining an object when the latter is placed under water.
The document describes a device for machining a tube, which includes an optical fibre conducting a laser beam to a first lens unit which converts the laser beam into parallel rays. Two successive mirrors then direct the laser beam onto a second lens unit, which makes the laser beam converge on a zone to be machined.
In that document, neither resurfacing nor a diode laser are mentioned, and the presence of water itself provides cooling and avoids the heating problems, which are not mentioned in that document.
Document EP 1 247 878 A1 describes a device for resurfacing a concave face of a tubular part, comprising a diode laser source and means for delivering resurfacing material via pipes. A lightguide or optical fibre conducts the laser beam over an axial penetration length in the tubular part. The resurfacing material is a silicon-based powder. On leaving the optical device, the laser beam is oblique.
It appears that none of these known devices is actually appropriate for reliably and inexpensively conducting the laser energy from an external laser source of the diode type right to a resurfacing zone placed inside a tubular part.
In particular, the conduction of the laser beam by an optical fibre inside a small-diameter tubular part does not appear to be very reliable, because of the excessive heating of the optical fibre, which furthermore does not allow the laser beam to be effectively directed perpendicularly to the resurfacing zone.
The optical lens devices described in the above documents are not satisfactory either, and they incur considerable risks of degrading the optical components during use at high temperature.
Thus, the present invention is aimed at devising a device for resurfacing the concave face of a tubular part that consists of inexpensive optical elements, the device having to be free of any risk of degrading or lowering the effectiveness resulting from heating the inside of a tubular part to be resurfaced, so as to be able to use resurfacing materials containing refractory powders.
To achieve this, the idea at the basis of the invention is to produce the laser beam by a diode laser source and to conduct the laser beam into the part to be resurfaced with a reduced surface energy density by means of commonplace and inexpensive optical components.
The diode laser source is effective and inexpensive but it does have the drawback of producing a divergent laser beam, which is of course incapable of suitably propagating along the penetration direction right to the resurfacing zone. The aim of the invention is also to solve this difficulty, using appropriate optical means.
To achieve these objects and other ones, the invention provides a device for resurfacing a concave face of a tubular part by supplying resurfacing material and energy by a laser, comprising:
Thanks to this arrangement, the laser beam is initially concentrated at the entry of the optical device, downstream of the optical insert, and then becomes a parallel-ray beam after it has passed through the first convergent lens. The laser beam then strikes the mirror on a maximized surface, avoiding heating and altering it, and then is concentrated by the second convergent lens.
The optical means are simple and inexpensive, and their arrangement optimises their operation by making them largely insensitive to the heating.
In particular, the relatively little heating caused by the laser beam passing through the optical lenses and onto the mirror is that there is no risk of degrading them, even in the presence of the surrounding heating produced by the impact of the laser beam on the zone to be resurfaced inside the tubular part.
One advantage is that it is possible to produce a low-cost device for resurfacing a concave face of a tubular part by supplying resurfacing material and energy by a laser using commonplace components, and ensuring effective confinement of the laser beam.
The use of a diode laser as laser source proves to be particularly advantageous owing to its compactness, its ease of high-frequency modulation, its low operating voltage and its low power consumption thanks to excellent efficiency.
Furthermore, a diode laser emits a slightly divergent laser beam. As a result, the laser beam may have energy concentration per unit area that is lower than that of conventional gas laser sources, so that it is easier to convey said beam without running the risk of damaging the transmission members, such as mirrors or lenses.
The laser beam delivery means and the directing means are simple and inexpensive, produced using standard, inexpensive and compact optical components.
The lenses and the mirror are also perfectly capable of withstanding the surface energy density of the laser beam from a diode laser.
The presence of the optical insert primarily makes it possible to extend the length of penetration along which the laser beam from the diode laser is delivered.
Furthermore, owing to the fact that the optical insert makes the laser beam coming from the diode laser converge near the object focal point of the first convergent lens, the first convergent lens transmits the laser beam in the form of substantially parallel rays. This is a good compromise between the fact of preserving all of the energy of the laser beam without any loss and the fact of delivering the laser beam with the lowest possible surface energy density so as to heat the optical components (convergent lenses, mirror, etc.) as little as possible.
Advantageously, the optical insert may comprise a third convergent lens making the laser beam coming from the diode laser converge near the object focal point of the first convergent lens.
Thus, a simple optical insert is produced for collecting the divergent laser beam at the output of the diode laser and for delivering it along the penetration direction right to the object focal point of the first convergent lens.
Preferably, arrangements may be provided such that:
By using a fourth convergent lens, the length of penetration over which the laser beam is delivered can be further extended. A person skilled in the art will readily understand that the length of penetration will depend on the focal lengths of the various convergent lenses used in the laser beam delivery means and in the optical insert.
Preferably, the optical insert may include an optical fibre that collects the laser beam coming from the diode laser and delivers it close to the object focal point of the first, third or fourth convergent lens, depending on the embodiment in question.
The optical fibre allows the laser beam to be delivered over a great length while minimising energy losses. The use of an optical fibre also means that the laser beam delivery means and the directing means can penetrate into the tubular part without the laser source having to be moved, it being possible for the optical fibre to be provided with slack.
Preferably, arrangements may be provided such that:
Advantageously, arrangements may be provided such that the optical insert, the first convergent lens and the mirror are contained within a double-walled hollow confinement tube, a coolant circulating between the walls.
The hollow confinement tube is used for holding the constituent components of the laser beam delivery means and to keep them in relative position, while still ensuring sure and reliable confinement of the laser beam.
The double-walled hollow confinement tube makes it possible for the components that it confines to be effectively cooled so as to avoid any deterioration caused by heating when the device is being used.
Preferably, arrangements are provided such that:
If the direction of penetration is substantially horizontal, the radial direction is thus vertical. This enables the resurfacing material to flow under gravity to the point where the laser beam strikes the face to be resurfaced.
Preferably, the device may comprise:
Complementarily, the device may include second displacement means for providing a relative displacement along a radial direction between, on the one hand, the tubular part to be resurfaced and, on the other hand, the subassembly comprising the laser beam delivery means and the directing means.
Other objects, features and advantages of the present invention will become apparent from the following description of particular embodiments, in conjunction with the appended figures in which:
The resurfacing device includes a laser source, which is a diode laser 4. Although the diode laser 4 is shown here as being very compact, it should be understood that the means for supplying and controlling the diode laser 4 are not shown and that these may take up a very considerable amount of space, and larger than the inside diameter D of the tubular part 1, so that it is not possible for the diode laser 4 and its supply and control means to penetrate inside the tubular part 1.
The resurfacing device includes resurfacing material delivery means 5, the resurfacing material being based on hard refractory particles and metal alloy particles. The resurfacing material delivery means 5 deliver the resurfacing material close to a resurfacing zone 6 on the concave face 2 of the tubular part 1 to be resurfaced.
The resurfacing device includes a subassembly 3 comprising laser beam delivery means 7 and directing means 8 for directing the laser beam 9 into the resurfacing zone 6.
The laser beam delivery means 7 conduct the laser beam 9 generated by the diode laser 4 over a penetration length L along a penetration direction which may coincide with the longitudinal axis I-I of the tubular part 1. The directing means 8 deflect the laser beam 9 along a radial direction II-II away from the penetration direction.
The diode laser 4 lies outside the tubular part 1, and the laser beam delivery means 7 may be axially engaged, completely or partly, in the tubular part 1.
During use of the resurfacing device, resurfacing material based on hard refractory particles and metal alloy particles is delivered by the resurfacing material delivery means 5 which comprise, as shown in
The resurfacing material delivery means 5 comprise a nozzle 5c with a generally conical internal wall with its point oriented towards the outlet and the apex of which is pierced, thus forming an outlet orifice 10. The outlet orifice 10 of the nozzle 5c is substantially coaxial with the radial direction II-II.
The nozzle 5c used may advantageously be in accordance with the teachings of document U.S. Pat. No. 5,418,350 included as reference. Such a nozzle allows the resurfacing material to be effectively directed to the only resurfacing zone 6, avoiding any loss of material. Furthermore, such a nozzle preheats the resurfacing material that passes through it, making it possible to reduce the laser power needed to melt the alloy and the resurfacing zone, and thus further reducing the heating of the optical laser beam delivery means 7.
The resurfacing material delivery means 5 thus deliver the resurfacing material close to the outlet orifice 10 where the resurfacing material is further heated by the laser beam 9 until the metal alloy particles melt. The heated resurfacing material is then deposited on the resurfacing zone 6 of the concave face 2 of the tubular part 1, where the metal alloy cools and solidifies again, to produce the resurfaced layer of the concave face 2.
In the embodiment illustrated in
A mandrel 11 is used to hold and rotate the tubular part 1 to be resurfaced. First displacement means 12 provide relative displacement along the penetration direction between, on the one hand, the tubular part 1 to be resurfaced and, on the other hand, the subassembly 3 comprising the laser beam delivery means 7 and the directing means 8, in order to make this subassembly 3 penetrate into the tubular part 1 to be resurfaced. Second displacement means 12a provide relative displacement along the radial direction II-II between, on the one hand, the tubular part 1 to be resurfaced and, on the other hand, the subassembly 3 comprising the laser beam delivery means 7 and the directing means 8.
The combination of the mandrel 11 and the first displacement means 12 allows the entire concave face 2 of the tubular part 1 to be resurfaced.
The combination of the mandrel 11 and the second displacement means 12a allows, for its part, the distance between the outlet orifice 10 and the resurfacing zone 6 to be adjusted, and to do so whatever the diameter D of the tubular part 1. Thus, it is possible for the laser beam 9 to strike the resurfacing zone 6 as a light spot of larger or smaller radius, and with a greater or lesser surface energy density.
In the embodiment shown in
In the embodiment illustrated in
The laser beam delivery means 7 and the directing means 8 are thus produced simply and inexpensively using compact inexpensive standard optical components. It has thus been possible to carry out the resurfacing in tubes having an inside diameter of less than 100 mm.
Furthermore, the lenses 13 and 15 and the mirror 14 are capable of withstanding the surface energy density of the diode laser 4.
Finally, it is advantageous to use a diode laser 4 whose wavelength permits good absorption of the energy by the tubular part 1. The laser beam delivery means 7 and the directing means 8 will thus be less subject to heating, the energy reflected by the tubular part 1 being less. This is because lenses and mirrors used in optics have characteristics that vary when being heated, which could impair the efficiency of the device.
The laser beam 9 emanates from the diode laser 4 as substantially divergent rays in the form of a cone having an apex angle equal to the angle α.
In the case of
A person skilled in the art will understand that the second convergent lens 15 may be replaced equivalently by another lens or a set of several other lenses so as to adjust the convergence distance d of the laser beam 9. However, it is judicious to choose the second convergent lens 15 so as to make the laser beam 9 converge close to the outlet orifice 10 of the nozzle 5c. The laser beam 9 thus strikes the resurfacing zone 6 with substantially maximum energy for heating the resurfacing material sufficiently and thus guaranteeing the quality of the resurfacing. Furthermore, by making the laser beam 9 converge close to the outlet orifice 10 it is possible to position the nozzle 5c in close proximity to the concave face 2, thereby making it possible to carry out resurfacing in tubular parts of very small inside diameter.
The fact of placing the diode laser 4 at the object focal point 13a of the first convergent lens 13 allows the laser beam 9 to be delivered in the form of a beam of parallel rays over the entire optical path going from the first convergent lens 13 to the second convergent lens 15. Thus, along the optical path going from the first convergent lens 13 to the second convergent lens 15, there is a good compromise between the fact of maintaining the energy of the laser beam 9 without any loss and the fact of delivering the laser beam 9 with the lowest surface energy density. In particular, this allows the optical components, namely the convergent lenses 13 and 15 and the mirror 14, to be heated as little as possible during use of the resurfacing device, for the purpose of preventing them from being damaged and of minimising the energy losses of the laser beam 9.
In the embodiments illustrated in
In the case of the embodiment illustrated in
The penetration length L may thus be substantially increased relative to the embodiment illustrated in
In the embodiments illustrated in
The first convergent lens 13, the second convergent lens 15, the mirror 14 and the optical insert 16 (in the case of the embodiments shown in
In the embodiments illustrated in
It is advantageous to provide such cooling means as delivering the laser beam 9 over a long penetration length L cannot be accomplished without loss, especially owing to the imperfections in the convergent lenses 13 and 15, the mirror 14 and the optical insert 16, owing to their approximate relative arrangements and owing to the diffusion of the energy from the laser beam 9 into the gas and dust present in the tubes 18 and 19.
Rays of the laser beam 9 may thus strike the confinement tubes 18 and 19 and heat them. The circulation of the coolant allows the damage caused by heating the confinement tubes 18 and 19 to be minimised and allows to cool all the components of the laser beam delivery means 7 and the directing means for directing the laser beam 9.
In the embodiments illustrated in
In the embodiment illustrated in
Again, the penetration length L over which the laser beam 9 is delivered is substantially extended. This makes it possible to resurface the concave face 2 of a longer tubular part 1.
In the embodiment shown in
Between the convergent lenses 22 and 17, the rays of the laser beam 9 are thus closer to the walls of the confinement tube 18. Because of the manufacturing imperfections in the convergent lenses 22 and 17, it is possible that some of the rays of the laser beam 9 will thus strike the walls of the confinement tube 18 and cause it to heat up.
A person skilled in the art will thus readily understand that the most opportune way of increasing the penetration length L is to provide convergent lenses 17 and 13 having matched focal lengths and to place them substantially in the particular manner illustrated in the embodiments shown in
However, the way in which the laser beam 9 is delivered between the convergent lenses 22 and 17 remains very effective in the case of high-quality convergent lenses 22 and 17.
As an alternative to the optical insert 16 of
In the embodiment illustrated in
By using the optical fibre 23 it is possible to deliver the laser beam 9 coming from the diode laser 4 over a long length with very few energy losses.
Close to the object focal point 22a, the laser beam 9 emerges from the optical fibre 23 in the form of divergent rays in the form of a cone with an apex angle of β. The laser beam 9 is then treated in the same way as in the embodiment illustrated in
The same effects are obtained by the embodiments shown in
To do this, optical fibres 23 collect the laser beam 9 coming from the diode laser 4 and deliver it close to the object focal point 13a of the first convergent lens 13 (
The fifth embodiment shown in
The entire optical fibre 23 is thus arranged so as to be wound over a winding device 26 above the resurfacing device, so that there is no risk of said fibre impeding the operations being carried out below. This also avoids the risk of damaging the optical fibre 23 by the various actions of the operators, an optical fibre being relatively fragile and having to be handled delicately.
The winding device 26 comprises several pulleys or cylinders 29a-29c. The radius of the pulleys or cylinders 29a-29c is such that the optical fibre 23 is not bent beyond a limit above which the laser beam 9 would suffer losses in the optical fibre 23, and beyond which the optical fibre 23 would be damaged.
The pulley or cylinder 29a is attached to the resurfacing device. The diode laser 4 is fixed, as is the pulley or cylinder 29b. The pulley or cylinder 29c can move translationally with respect to the diode laser 4 and to the pulley or cylinder 29b by means of a spring 28 or other equivalent device, such as a cylinder actuator or a counterweight.
During the displacement of the resurfacing device along the penetration direction by movements illustrated by the double arrow 27, the pulley or cylinder 29c will undergo the movements illustrated by the arrow 27a thanks to the stretching or shortening of the spring 28. The available length of optical fibre 23 thus varies automatically so as to accompany the displacements of the resurfacing device along the penetration direction. The spring 28 is chosen to exert a sufficiently small tensile force on the optical fibre 23 so as not to risk damaging it. The winding device 26 described above must be considered as a simple non-limiting example and may be adapted to the embodiments shown in
As an alternative to the winding device 26 described above, it is possible to use a winding device comprising a cableway in the form of a gutter comprising a plurality of interconnected sections so as to permit relative rotational movement of limited amplitude between two successive sections. The optical fibre is then fixed to the cableway and follows its movements. The amplitude of the relative rotational movement between two successive sections is such that the optical fibre is not bent beyond a limit above which the laser beam would suffer losses in the optical fibre and beyond which the optical fibre would be damaged.
In practice, in this embodiment shown in
The present invention is not limited to the embodiments that have been explicitly described, rather it includes the various alternative forms and generalisations thereof that are contained within the field of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 06 55286 | Dec 2006 | FR | national |
