Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/06—Surface hardening
  • C21D1/09—Surface hardening by direct application of electrical or wave energy; by particle radiation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/08—Devices involving relative movement between laser beam and workpiece
  • B23K26/082—Scanning systems, i.e. devices involving movement of the laser beam relative to the laser head
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/34—Methods of heating
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/34—Methods of heating
  • C21D1/38—Heating by cathodic discharges
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/62—Quenching devices
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
  • C21D1/773—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material under reduced pressure or vacuum
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/0006—Details, accessories not peculiar to any of the following furnaces
  • C21D9/0025—Supports; Baskets; Containers; Covers
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
  • F27D7/00—Forming, maintaining or circulating atmospheres in heating chambers
  • F27D7/06—Forming or maintaining special atmospheres or vacuum within heating chambers
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
  • F27D7/00—Forming, maintaining or circulating atmospheres in heating chambers
  • F27D7/06—Forming or maintaining special atmospheres or vacuum within heating chambers
  • F27D2007/066—Vacuum
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/25—Process efficiency

Definitions

• the invention relates to a heat treatment process by volume. According to a second aspect, the invention relates to a system for the volume heat treatment of parts.
• the heat treatment by volume is a metallurgical operation which is known to a person skilled in the art.
• a heat treatment by volume consists in heating a part to a heating temperature and then cooling it at a predefined speed in order to maintain, for example at room temperature, the metallurgical structure of the part obtained at the heating temperature.
• a volume heat treatment essentially the entire volume of the part and preferably the entire volume of the part undergoes such a heat treatment.
• volume quenching heat treatment reduces hardness but improves mechanical properties.
• the heat treatment by volume is generally carried out by heating a part in an oven and by keeping it long enough in the oven in order to reach a predetermined temperature in essentially the entire room (or in essentially its entire volume) and which allows to obtain a structural modification of the material constituting the part or a relaxation of the stresses present in the part. Then, the latter is generally cooled, for example rapidly by exposing it to a liquid or gaseous fluid, often by immersing it therein.
• the fluids are, for example, water, oil or a gas. Rapid cooling is often necessary in order to keep the material in the induced structure at room temperature. by temperature rise.
• such a heat treatment has various drawbacks such as, for example: need to provide a system allowing relative movement between the part to be heated and the heat source, risk of inhomogeneous heating.
• induction heat treatments are industrially effective for certain materials only, such as for example ferromagnetic materials.
• one of the aims of the present invention is to provide a volume heat treatment process that is simpler to implement and faster to perform.
• the inventors propose a method of heat treatment by volume of a part having an external surface delimiting its volume, the method comprising the following steps: a. providing a laser source; b. provide the part; vs. providing support means for supporting the part; d. placing the part so that it is held in position by the support means; e. irradiating with the laser source at least a portion of the external surface of the workpiece with laser power and duration of exposure to achieve a temperature rise in substantially the entire volume of the workpiece.
• the support means have a degree of thermal insulation between them and the part.
• the inventors suggest having such a fairly large degree of thermal insulation, so that the heat (or thermal energy) generated by the laser source at the level of the outer surface portion of the part which is irradiated has a greater tendency to diffuse into the material constituting the part than into the support means.
• the inventors have observed, against all expectations, that it was possible to apply a heat treatment in volume to a part, to harden it for example, with the sole use of a laser source.
• the method of the invention makes it possible to carry out heat treatments without apparent deformation of the part.
• said temperature rise is greater than 200 ° C, more preferably greater than 400 ° C, even more preferably greater than 700 ° C, and even more preferably greater than 850 ° C.
• the method of the invention is particularly effective, because it allows, thanks to the laser source, to heat a room in volume without however heating its external environment.
• the laser source for heating the room, it is possible to heat only the room and not to heat its direct external environment.
• This is in particular possible thanks to the high surface radiative power of the laser source compared to conventional heating techniques by direct flame, by radiant tube, or by electric resistances for example.
• An advantage of the invention over an induction heating technique is that it allows the heat treatment of non-ferromagnetic materials.
• the combination of the laser source for heating and the support means with a degree of thermal insulation between them and the part makes it possible to confine in the part the heat supplied by the laser source and to reach temperatures of modification. of structure.
• This same combination of a laser source and support means with a degree of thermal insulation between them and the part allows, as soon as the laser beam coming from the source is extinguished, to initiate a sufficiently rapid cooling to freeze the material constituting the part in the structure obtained during the heating step (step e.).
• the process according to the invention can be qualified as more efficient compared to the known volume heat treatment methods.
• the heat supplied to the room generates very little heating of its direct external environment.
• This stems in particular, where appropriate, from the support means which have a degree of thermal insulation between them and the part, and from the fact that it is possible to confine a laser beam only on the part to be heated or on a part of it. this one.
• the absence of significant heating of the environment outside the room allows it to quickly absorb heat from the room since the thermal energy supplied by the laser source only has to heat the room and not its environment.
• the method of the invention is therefore particularly advantageous in comparison with the methods of the state of the art when it is desired to reduce the energy consumption associated with the heat treatment of parts.
• the laser exposure power is preferably chosen to be substantially equal to the thermal losses of the part at a given temperature.
• the laser exposure power to maintain the workpiece at a predetermined temperature will directly depend on the predetermined temperature chosen.
• a preferred embodiment of the invention provides for reducing the laser power supplied during step e. in order to obtain temperature stabilization in essentially the entire volume of the room and to maintain this temperature for a predetermined time at a temperature below the temperature reached during step e. ; such a temperature is typically that of an isothermal bearing.
• Such an isothermal bearing is known to those skilled in the art and is intended to adapt the heat treatment as a function of the metallurgical phases desired at the end of the heat treatment and of the materials treated.
• the method and the system of the invention are particularly advantageous for implementing such an isothermal bearing during a heat treatment; in particular, the invention makes it possible to have a rapid transition between the initial heat treatment temperature and the isothermal bearing temperature.
• the isothermal bearing has an isothermal bearing duration of between 10 minutes and 5 hours, preferably between 30 minutes and 2 hours. For parts of small volumes as defined by a preferred embodiment of the invention, it could be envisaged to have an isothermal bearing with a duration of less than 10 minutes.
• the entire volume of the room means in at least 80% of the volume of the room, preferably in at least 90% of the volume of the room, more preferably in at least 95% of the volume of the room and even more preferably in at least 99% of the volume of the room.
• the part or sample has a certain volume which can be expressed in mm 3 and an external surface which can be expressed in mm 2 . However, it is possible to use other units for volume and external surface.
• the heat treatment process of the invention can be used for the following applications:
• medical implants for example, dental implants, joint prostheses, ...;
• Another advantage of the method according to the invention is that it is very easy to implement, requiring only control means relatively simple.
• the programming of the heat treatment according to the invention requires, in most cases, a control of the electric power supplied to the laser source as a function of time by the control means.
• the control means thus make it possible to adapt the power of the laser source as a function of the physical and geometric characteristics of the part to be heat treated and as a function of the desired heat treatment (slope, level, etc.).
• the control means define a laser power to be delivered as a function of time in order to heat treat the part according to the slopes and levels corresponding to the heat treatment programmed by the operator.
• the method of the invention further comprising, after step e., The following step: f. stop the irradiation of step e. to cool the room.
• a step is added to allow the part to cool after it has been heated by the laser source.
• this preferred embodiment is simpler. Indeed, this method does not require movement or manipulation of the sample (or part) between the step of raising the temperature and the cooling step.
• step f. cooling system does not require immersing the part in a liquid. For this reason also the method according to the invention is simpler. The absence of these manipulations also makes it possible to obtain a volume heat treatment process with a faster cooling phase.
• the cooling rates known from the state of the art vary between 10 and 100 ° C / s. The method and the system of the invention make it possible to achieve during step f.
• a heat treatment process is volume quenching which consists in heating a part to a heating temperature and then cooling it at a sufficiently high speed to maintain, for example at room temperature, the metallurgical structure of the part obtained at the heating temperature. During volume quenching, essentially the entire volume of the part and preferably the entire volume of the part undergoes such a heat treatment.
• the mechanical properties of a part having undergone such a volume quenching process are generally much higher than those of an unhardened part (we generally speak of a part hardened by volume quenching, but if for certain materials such as for example aluminum alloys the quenching operation can have the effect of reducing the hardness but nevertheless improving its mechanical properties).
• Volume quenching is generally carried out by heating the part in an oven and maintaining it long enough to reach a predetermined temperature in essentially the entire room (or in essentially its entire volume), which makes it possible to obtain a structural modification of the material constituting the part. Then, the latter is cooled rapidly by exposing it to a liquid or gaseous fluid, often by immersing it.
• the fluids are, for example, water, oil or a gas. The rapid cooling allows the material to freeze in the structure induced by the temperature rise.
• one of the aims of the present invention is to provide a volume quenching process that is simpler to implement and faster to perform. Quenching is a term known to those skilled in the art.
• the process of the invention is a process for quenching the part by volume, step e. makes it possible to induce a modification of the structure of the material constituting the part, and, step f. is capable of freezing the material constituting the part in a structure different from that which it exhibited before the irradiation of step e.
• the modification of the structure of the material constituting the part is a phase change, or else a change in metallurgical structure. This is known to a person skilled in the art.
• a phase change is an allotropic transformation.
• a phase change can occur when, for a phase diagram of the material constituting the part, a phase change line is crossed during the rise in temperature of the part induced by the irradiation by the laser source.
• the material is frozen in the structure obtained in step e.
• the cooling in step f. should generally be fairly fast, although this will depend on the type of material.
• the volume quenching process proposed by the inventors is quite surprising. They observed, against all odds, that it was possible to apply volume quenching to a part to harden it with the sole use of a laser source.
• the method of the invention makes it possible to perform the quenching without apparent deformation of the part.
• the inventors have found that the absence of apparent deformation of the part is due to the fact that the quenching process allows the entire volume of the part to be treated in a very short time.
• the method of the invention allows the volume quenching of a part in a simple way because the method does not require movement or manipulation of the sample between the step of raising the temperature and the step of cooling. Step f.
• step e. cooling freezing the material constituting the part in a new structure, for example that obtained during heating (step e.) does not require immersing the part in a liquid. For this reason also the method according to the invention is simpler. The absence of these manipulations also allows for a faster volume quenching process.
• the method of the invention is particularly effective, because it allows thanks to the laser source to heat the room effectively without heating the environment outside the room.
• step f. when step f. is initiated so as to have a rapid cooling of the whole room, it is then necessary to dissipate only the heat stored in the room.
• Thanks to the use of the laser source for heating the room it is possible to heat only the room and not to heat its direct external environment. This is in particular possible thanks to the high surface radiative power of the laser source compared to conventional heating techniques by direct flame, by radiant tube, by electric resistances or else by induction.
• the combination of the laser source for heating and the support means with a degree of thermal insulation between them and the part makes it possible to confine in the part the heat supplied by the laser source and to reach temperatures of modification. of structure.
• This same combination of a laser source and support means with a degree of thermal insulation between them and the part allows, as soon as the laser beam coming from the source is extinguished, to initiate a sufficiently rapid cooling to freeze the material. constituting the part in a new structure, for example that obtained during the heating step (step e.).
• the heat in the room is very quickly evacuated to the environment outside the room, for example by radiation, convection, or any other heat exchange means. .
• the process according to the invention can be qualified as more efficient compared to known volume quenching methods.
• the heat supplied to the part When the volume quenching process of the invention is implemented, the heat supplied to the part generates very little heating of its direct external environment. This stems in particular, where appropriate, from the support means which have a degree of thermal insulation between them and the part, and from the fact that it is possible to confine a laser beam only on the part to be heated or on a part of it. this one. The absence of significant heating of the environment outside the part then allows it to rapidly dissipate heat from the part during the cooling step, step f, which is important for having a quenching process. efficient where the material constituting the part is fixed in a given structure.
• the quenching temperature of a steel part is very often between 700 ° C and 950 ° C.
• the quenching temperature is very often between 440 ° C and 535 ° C.
• the quenching temperature is between 300 ° C and 600 ° C.
• the entire volume of the room means in at least 80% of the volume of the room, preferably in at least 90% of the volume of the room, more preferably in at least 95% of the volume of the room and even more preferably in at least 99% of the volume of the room.
• the part comprises a material having a thermal conductivity greater than 15 W.nv 1. ° C ⁇ 1. , So that the part can preferably be affected by the heat treatment of the invention in 100% of its volume. .
• the irradiation of step e. is able to impose an essentially homogeneous temperature in essentially the entire volume of the room.
• the inventors have indeed observed, with surprise, that it is possible to choose such laser power and duration of exposure in step e. to achieve a substantially uniform temperature throughout the volume of a room, using laser irradiation. This ultimately allows for an efficient and good quality volume quenching process because the different regions of the part volume undergo essentially the same temperature increase in step e.
• An essentially homogeneous temperature means that the maximum relative temperature difference between two points of the volume of the room is at most equal to 20%, preferably at most equal to 10%, and even more preferably at most equal to 1% .
• a longitudinal or transverse section here means a section made parallel to the direction of the laser beam coming from the laser source.
• the laser source is configured to emit a collimated light beam, and to irradiate during step e. said at least a portion of the external surface of the part with the collimated light beam.
• the collimated laser beam allows the irradiation of a part during step e. whatever the profile of the external surface of the part (profile with several heights).
• the collimated laser beam makes it possible to irradiate a portion of the external surface of the part having a non-plane profile in a more homogeneous manner because the collimated laser beam makes it possible to irradiate simultaneously with the most homogeneous possible power density, portions of pieces having different heights.
• the use of a collimated laser beam therefore makes it possible to have a heat treatment suitable for parts having more complex surface geometries in comparison with a heat treatment with a focused laser beam.
• the laser beam is homogenized and then focused in the direction of the part.
• step f. further includes an action of directing a fluid toward the workpiece to cool it by convection.
• the fluid can be a gas or a liquid.
• the method further comprises the action of exposing the part to a treatment gas to modify its external surface.
• the gas is nitrogen, so that during heat treatment nitriding of the outer surface of the part occurs.
• the support means have a flat support surface for supporting the part. This increases the mechanical stability of the part, by minimizing high temperature stress on the part to prevent material from creeping, when the part has at least a portion of a flat outer surface.
• the support means comprise a refractory material.
• the inventors have observed that the process of the invention, and in particular the preferred embodiment corresponding to a volume quenching process, is all the more effective when the support means have a large degree of thermal insulation between them and the room. This makes it possible to minimize any heat transfer from the part to the support means, during step e. and ultimately to have a temperature rise with great homogeneity in the volume of the room because the heat tends to diffuse more inside the room rather than outside.
• the inventors propose to preferably use support means made of thermally insulating material and more preferably of refractory material, a term known to a person skilled in the art.
• the term refractory is known to a person skilled in the art.
• the support means comprise a material having a thermal conductivity of less than 20 W.nr 1. ° C 1 , more preferably less than 10 W.nr 1. ° C 1 , even more preferably less than 5 W.nr 1. ° C 1 .
• a unit equivalent to Wm 1 .K 1 is W.nr 1. ° C 1 .
• Thermal conductivity is a term known to those skilled in the art. Preferred thermal conductivity values are given for a temperature of 25 ° C. Thanks to this preferred variant, it is possible to have a relatively high thermal conductivity of the part to be quenched in comparison with the thermal conductivity of the support means, for a wide range of possible materials of the part, in particular for a wide range. of metals.
• support means having a thermal conductivity of less than 20 Wm-1 ° C-1, preferably less than 10 Wm-1. ° C-1, even more preferably less than 5 Wm-1 ° C-1, without necessarily using a refractory material for them. This constitutes another preferred embodiment of the method of the invention.
• the contact surface there is a contact surface between the workpiece and the support means, the contact surface having an area less than 10% of the area of the outer surface, more preferably the latter is less than 2%, even more preferably this is less than 1%.
• a heat exchange between the part and the support means will be lower when the contact surface between the part and the support means is smaller.
• the heat treatment method of the invention is particularly well suited to support means having low thermal conductivity and a contact surface between part and reduced support means.
• the part is made of a material having a thermal conductivity greater than 10 W.nr 1. ° C 1 , more preferably this is greater than 35 W.nr 1. ° C ⁇ 1 and even more preferably this is greater than 50 W.nv 1. ° C ⁇ 1 .
• the process of the invention and in particular the preferred embodiment corresponding to a volume quenching process is all the more efficient when the heat transfer generated by the heat transfer. level of the external surface of the part takes place above all within the volume of the part itself, rather than towards the outside, as for example towards the support means.
• the inventors propose to preferably use a part made of a material having a sufficiently high thermal conductivity.
• the volume of the part is between 0.01 mm 3 and 5 cm 3 , more preferably the latter is between 0.1 mm 3 and 500 mm 3 , and even more preferably between 1 mm 3 and 100 mm 3 .
• the inventors have surprisingly noticed that parts of small volume, that is to say less than one cm 3 (and therefore also having a fairly small mass), make it possible to have a method according to the invention that is particularly effective. This is also true for the preferred embodiment corresponding to a volume quenching process. This is quite surprising. A plausible explanation would be the following.
• the part to be thermally treated (to be soaked) has a small volume, that is to say less than cm 3 for example, there is little material allowing the heat generated at the external surface to be removed and therefore the the entire volume of the room tends to heat up very quickly.
• the mass of a part having a small volume is not sufficient to produce a high thermal gradient in the part due to the rise in temperature at its external surface.
• the process is therefore different from a surface hardening where the volume of the part makes it possible to absorb a heating on the surface without heating up in a homogeneous manner and reaching a temperature close to that of the irradiated surface.
• the volume of the part is less than 5 cm 3 for an aluminum or brass part.
• the volume of the part is less than 2 cm 3 for a part made of steel or titanium.
• the mass of small parts for the process of the invention are between 1 and 100 grams, preferably between 10 and 50 grams and more preferably between 15 and 30 grams. It is also possible to provide parts having a mass less than 1 gram, for example parts having a mass between 0.005 and 0.1 gram.
• the part has a specific surface area of between 0.01 mm -1 and 150 mm -1 , more preferably between 0.1 mm -1 and 100 mm -1 , even more preferably between between 1 mm -1 and 10 mnr 1 .
• the specific surface area of a part is equal to the area of its external surface divided by the volume of the part.
• said external surface consists of a first and a second external surface portions
• step e. consists in irradiating only the first outer surface portion with a laser power and duration of exposure to have a substantially equal temperature between the first and second outer surface portions.
• a substantially equal temperature between the first and second external surface portions of the part means that they have a temperature difference of less than 50 ° C, preferably less than 25 ° C, preferably less than 10 ° C, preferably less than 5 ° C, and even more preferably less than 2 ° C.
• This preferred embodiment makes it possible to have a method which is particularly easy to implement because it requires irradiating only a portion of the external surface of the part. In particular, one can imagine irradiating the room from only one side.
• the external surface comprises a first and a second external surface portions
• step e. consists in irradiating the first and second external surface portions.
• the inventors propose to irradiate at least two different portions of the external surface of the part. It is for example possible to irradiate the part from two of its faces which are for example opposite: for example irradiate a right side and a left side of the part. This helps to induce a rise in temperature from two different ends of the part, which can be particularly useful for thicker parts.
• step e. consists in irradiating at least a portion of the external surface of the part for an exposure time less than or equal to 10 s, more preferably less than or equal to 8 s, even more preferably less than or equal to 5 s.
• the inventors have found that particularly good results are obtained using such laser exposure times.
• such exposure times make it possible to have a temperature rise in essentially the entire volume of the irradiated part and in many cases to have a uniform temperature rise throughout the volume of the room.
• the laser source is a continuous laser source or with pulses of durations greater than 1 ms or with pulses of durations between 20 and 30 ms.
• the inventors have found that it is possible to have very good results using inexpensive continuous laser sources. Good results are also obtained with laser sources with relatively long pulses, that is to say greater than 1 ms.
• Laser sources continuous or with such pulse durations are inexpensive, but also very common and easy to implement in the context of the method of the invention. Such laser sources are available with a wide choice of wavelengths. This can be useful in order to have a wavelength adapted to the material constituting the part and thus maximize the absorption of radiation by the part and its conversion into heat for the rise in temperature thereof.
• the polarization of the radiation in order to maximize the absorption of the radiation by the part.
• the polarization of the laser beam on the part can be linear s or p, elliptical or circular.
• the reflection coefficients may change depending on the angle of incidence of the laser beam (angle between the direction of propagation of the laser beam and the normal to the surface at the point of irradiation).
• the laser beam has an angle of incidence with a portion of the part greater than 10 °
• a specific linear polarization preferably p
• the use of a specific linear polarization can lead to a better homogeneity of absorption of the laser beam by the irradiated portion of the external surface.
• step e. consists in irradiating at least a portion of the external surface of the part with a laser beam of a power less than 100 W, more preferably less than 50 W, even more preferably less than 10 W.
• a laser beam of a power less than 100 W, more preferably less than 50 W, even more preferably less than 10 W.
• the inventors have found that it was possible to have very good results, and in particular very good quenching results when the method of the invention is a volume quenching method, even with low power laser sources.
• the inventors have observed that a natural cooling of the part to ambient temperature (about 20 ° C), that is to say without forced cooling such as for example by convection, took less than 35 s.
• the laser source is able to provide an intensity modulated laser beam and step e. consists in irradiating at least a portion of the external surface of the part with an irradiation power which decreases over time during step e. Thanks to this preferred embodiment, it is possible to reduce the risk, or even avoid too much overheating of a part of the part, in particular too much overheating of the portion of the external surface irradiated by the laser source. Too much overheating is generally unacceptable and induces local or total melting of the part. By virtue of this preferred embodiment of the invention, this risk is reduced because the intensity of the laser beam is reduced during the heating step e.
• the laser source comprises:
• beam control means configured to modulate the intensity profile of the laser beam emitted by the laser beam generator.
• the laser beam generator is optically coupled with the laser beam control means.
• the laser beam control means are laser beam shaping means.
• the laser beam control means make it possible to model the intensity profile of the laser beam which is determined according to a plane perpendicular to its direction of propagation.
• the beam control means make it possible to obtain a beam having a more uniform intensity distribution and therefore make it possible to irradiate a part with more uniformity in terms of power density.
• the beam control means comprise:
• an optical fiber comprising an input and an output, capable of conveying a laser beam emitted by the laser beam generator between the input and the output, more preferably, the optical fiber is multimode;
• a laser beam projection device configured to project on the part, an image of the laser beam at its exit from the optical fiber.
• the laser beam generator is optically coupled with the input of the multimode optical fiber so that essentially the entire laser beam is conveyed by the multimode optical fiber to its exit.
• the laser beam generator is a multimode laser beam generator
• the multimode laser beam conveyed by the multimode optical fiber is mixed as it travels through the multimode optical fiber, so as to illuminate the exit face (the exit) of the fiber with homogeneous laser beam intensity.
• a better mixing of the modes and therefore a better homogeneity of beam intensity on the exit face is obtained when the multimode optical fiber is bent.
• the multimode optical fiber is bent forming an "8".
• the multimode optical fiber has a length greater than 2 m, and more preferably a length between 6 m and 10 m, for example 8 m in order to allow good mixing of the modes and therefore good uniformity of the intensity profile in multimode optical fiber output.
• the laser beam projection device makes it possible to project the image of the exit (of the exit face) of the multimode optical fiber on the part to be heat treated.
• This laser source embodiment makes it possible to modify the intensity profile of the laser beam, so that at the input of the multimode optical fiber, the laser beam (multimode) has an essentially Gaussian intensity profile as emitted by the laser beam generator, and, at the output, the laser beam has a uniform intensity profile over essentially the entire output face that it illuminates.
• the laser beam projection device then makes it possible to form an image of the exit face of the multimode optical fiber illuminated with uniform intensity, on the part to be heat treated.
• the laser beam projection device is configured to project the image of the laser beam onto the workpiece with a collimated laser beam.
• Another advantage of this embodiment of the laser source is that it allows the part to be irradiated with a collimated laser beam. This is all the more advantageous (as already described above) as it allows a simplification of the method by not requiring an additional step of adjusting the distance of the part relative to the laser source. Moreover, such a collimated laser beam of uniform intensity makes it possible to irradiate with more homogeneity in terms of power density of parts having complex geometries characterized by high form factors, or having curved surfaces.
• the laser beam projection device is able to adjust a magnification between the predetermined section of multimode optical fiber taken at the output and the image of the laser beam when the latter is projected onto the workpiece.
• the laser beam projection device preferably comprises a first and a second converging lenses, so as to project the laser beam at the output of the multimode optical fiber (which is then divergent) in one laser beam image on the workpiece to be heat treated with a laser beam which is collimated.
• the first and second lenses can be moved relatively relative to each other in a translation parallel to an optical axis defined by a main direction of propagation of the laser beam at the output of the multimode optical fiber.
• the first lens is movable with respect to the exit of the multimode optical fiber in order to adjust the distance of the first lens - the exit of the multimode optical fiber.
• an increase in the distance between the first and second lenses allows an increase in the magnification.
• the laser beam projection device makes it possible to adapt the size of the laser beam on the part to be heat treated as a function of the size of the latter.
• the multimode optical fiber has a section of 400 ⁇ m and the image of the laser beam at the output thereof projected onto the part has a diameter of 6 mm. Thanks to this preferred embodiment of the laser source of the invention, it is possible to obtain an irradiation of the part with a uniform laser intensity and adjustable in size.
• the uniform beam intensity on the part makes it possible to carry out a heat treatment with a high quality because the increase in temperature of the part is then generated with a thermal gradient at the level of the surface of the part which is almost zero or even zero .
• Another advantage of the laser beam projection device is that it allows modulation of the diameter of the image of the laser beam exiting it on the part without altering its uniformity in intensity.
• the beam control means comprise: a meniscus lens configured to modify the diameter of the laser beam emitted by the laser beam generator into a modified collimated laser beam.
• the beam control means comprise a plurality of meniscus lenses aligned along their respective optical axes. For example, at least one side of each of the meniscus lenses is aspherical so as to limit aberrations due to the use of meniscus lenses.
• the beam control means comprise: an optical element having an aspherical optical surface or an optical surface capable of inducing a phase shift.
• the beam control means comprise:
• the laser source further comprises beam focusing means positioned between the beam control means and the part.
• the process of the invention is a quenching process followed by tempering and it further comprises the following additional steps, after step f. : i. irradiating with the laser source at least a portion of the outer surface of the workpiece with a tempering laser exposure power that is less than the laser exposure power used in step e. for quenching.
• the part is tempered by maintaining the part at a tempering temperature (below the quenching temperature) for a predetermined time.
• the part is then subjected to appropriate cooling to room temperature.
• Tempering makes it possible to attenuate the effects of quenching by generally making the part more ductile and more tenacious.
• Such tempering can advantageously be carried out after quenching without modifying the position of the part, which greatly simplifies the implementation of the method and of the system making it possible to implement such a tempering step.
• a tempering temperature for a steel part is included between 200 ° C and 450 ° C.
• the tempering temperature of an aluminum part is between 150 ° C and 200 ° C, for example 170 ° C.
• the method of the invention is a quenching process preceded by annealing and it further comprises the following additional steps before step a. : g. irradiating with the laser source at least a portion of the outer surface of the workpiece with an annealing laser exposure power that is less than the laser exposure power used in step e. ; h. cool the part after heating it to an annealing temperature in the previous step to a temperature below 100 ° C, preferably at room temperature.
• Annealing consists in heating the part to a predetermined temperature (called the annealing temperature), in maintaining the part at this annealing temperature for a predetermined time, then in cooling the part with a predetermined cooling rate in order to obtain, after returning to ambient temperature a structural state of the material constituting the part close to the state of stable equilibrium.
• the purpose of this operation is to eliminate or reduce the residual stresses linked, for example, to a previous heat treatment, or to obtain the formation of a structure favorable to a subsequent action without fracturing (deformation, machining, heat treatment, etc. ).
• Such annealing can advantageously be carried out before quenching without modifying the position of the part on the support means, which greatly simplifies the implementation of the method and of the system making it possible to implement such an annealing step.
• annealing then quenching, then income.
• the method of the invention further comprises the following additional steps: j. provide a vacuum chamber and insert the part inside the vacuum chamber; k. achieve a partial vacuum in the vacuum chamber enclosing the part of less than 50,000 Pa, preferably less than 10,000 Pa and even more preferably less than 5,000 Pa.
• the method of the invention further comprises the following additional steps:
• L. provide a heat exchanger; mr. contacting the part with the heat exchanger during step f .. Such a preferred embodiment allows the part to be cooled faster and more efficiently.
• the method of the invention further comprises the following additional steps: n. provide a liquid bath; o. partially immerse the part in the liquid bath during step f., more preferably, fully immerse the part.
• Such a preferred embodiment allows the room to be cooled faster and more efficiently.
• the material constituting at least partially the part is a metallic material.
• the method of the invention is indeed particularly suitable for this type of material (metals).
• the metallic material constituting at least partially the part is a carbon steel, preferably a steel comprising 1% carbon by weight.
• a carbon steel is a term known to those skilled in the art. It generally designates a steel whose main component of alloy is carbon, in portions of, for example, between 0.02% and 2% by mass.
• the inventors also propose a system for the heat treatment by volume of a part having an external surface delimiting its volume, the system comprising:
• a laser source configured to irradiate at least a portion of the external surface of the part with a laser power and duration of exposure to obtain a temperature rise in essentially the entire volume of the part to induce a structural modification the material constituting the part;
• the system of the invention is used for volume quenching of a part.
• the support means have a degree of thermal insulation between them and the part.
• the laser source is a continuous laser source, or with pulses of durations greater than 1 ms, or with pulses of durations between 20 and 30 ms.
• the temperature rise is a temperature rise greater than 200 ° C, preferably greater than 400 ° C, more preferably greater than 700 ° C, even more preferably greater than 850 ° vs.
• the temperature rise in substantially the entire volume of the room is a temperature rise in at least 80%, more preferably at least 90%, more preferably 95%, still more. most preferred 99% of room volume.
• the support means have a support surface for coming into contact with the part, the support surface having an area less than 10% of the external surface of the part, preferably less than 5%, even more preferably less than 1% of the external surface of the part.
• the contact between the part to be quenched and the support means is reduced, reducing the possibility of heat transfer by conduction from the part to the support means.
• This makes it possible to further increase the temperature within the part during heating by laser irradiation because the heat generated on the external surface portion of the part to be quenched has little other solution than to diffuse within the volume. of the room.
• the heat transfer from the part to the support means is all the more reduced when they include a refractory material.
• the support means have a thermal conductivity of less than 20 W.nr 1. ° C 1 at 25 ° C.
• the support means have a flat support surface for supporting the part.
• the part to be quenched remains in position easily. There is then no need, in general, to have means such as clamps which hold the part in position.
• the support means have a thermal conductivity of less than 20 W.nr 1. ° C 1 , more preferably less than 10 W.nr 1. ° C 1 , even more preferably at 5 W .nr 1. ° C 1 .
• the part is made of a material having a thermal conductivity greater than 15 W.nr 1 . 0 C ⁇ 1 , more preferably greater than 35 W.nr 1. ° C ⁇ 1 and even more preferably greater than 50 W.nr 1. ° C 1 .
• the volume of the part is between 0.01 mm 3 and 1 cm 3 , more preferably between 0.1 mm 3 and 500 mm 3 , and even more preferably between 1 mm 3 and 100 mm 3 .
• the laser source is configured to irradiate the outer surface portion of a workpiece with a laser beam of a power less than 100 W, more preferably less than 50 W, even more preferably less. at 10 W.
• the system further comprises an optical fiber and it is designed so that a laser beam from the laser source is able to reach through the optical fiber at least one external surface portion of a part supported by the support means.
• optical fiber makes it possible to guide a laser beam coming from the laser source. This provides greater flexibility to the system. In particular, it is possible to move the laser source away from the part to be quenched. For certain applications, such a configuration may be preferred.
• the laser source comprises:
• - Beam control means configured to modulate the intensity profile of the laser beam emitted by the laser beam generator.
• the beam control means comprise:
• an optical fiber of predetermined section comprising an input and an output, capable of transporting a laser beam emitted by the laser beam generator between its input and its output, more preferably, the optical fiber is multimode;
• a laser beam projection device capable of projecting onto the part an image of the laser beam at its exit from the optical fiber, more preferably from the multimode optical fiber.
• the laser beam projection device is configured to project the image of the laser beam onto the workpiece with a collimated laser beam.
• the laser beam projection device is able to adjust a magnification between the predetermined section of multimode optical fiber taken at the output and the image of the laser beam when the latter is projected onto said part.
• the beam control means comprise:
• a meniscus lens configured to modify the diameter of the laser beam emitted by the laser beam generator into a modified collimated laser beam.
• the beam control means comprise:
• an optical element having an aspherical optical surface or an optical surface capable of inducing a phase shift.
• the beam control means comprise:
• the laser source further comprises beam focusing means positioned between the beam control means and the part.
• the multimode optical fiber has a length of between 1 m and 12 m, more preferably a length of between 2 m and 8 m.
• the system further comprises a scanner to be able to direct a laser beam from the laser source on different parts to be quenched in volume.
• a scanner to be able to direct a laser beam from the laser source on different parts to be quenched in volume.
• the system further comprises a temperature sensor, preferably a pyrometer, for measuring a room temperature.
• a temperature sensor preferably a pyrometer
• the system further comprises a temperature sensor, preferably a pyrometer, for measuring a room temperature.
• a regulation loop to adjust the power of the laser source as a function of the temperature measured by the temperature sensor.
• a pyrometer which is an example of a temperature sensor measures the temperature of the portion of the external surface of the part which is irradiated by the laser source.
• the inventors also propose an assembly comprising the system as described above with all its preferred embodiments and the part to be quenched.
• multiple beams could strike the entire casing (or external surface) of the part to further reduce the temperature gradient between the core of the part and the portion. of irradiated external surface.
• the laser of predetermined power P illuminates the portion of the external surface of the part with a diameter D, for example for a laser spot having a circular section. Study of the heat balance in the irradiated part
• the heat transfer between the part and its external environment is governed by three phenomena: conduction, convection, radiation.
• the physical properties to take into account are the following:
• k the coefficient of thermal conductivity k (or thermal conductivity) measures the propensity of a body to develop a heat flow when it experiences a difference in T °
• - specific heat c measures the rate of change of internal energy with T °; this quantity reflects the ability of a material to accumulate energy in thermal form as its temperature increases;
• the calorific capacity C measures the capacity of a medium to accumulate (or release) heat. Conversely, this quantity measures the energy that must be transferred to it to increase its temperature by one Kelvin.
• thermal diffusivity a k / (pc) which measures the ease of heat propagation in the material of the part.
• Table 1 shows an estimate of the thermal gradient by estimating a penetration depth for some known metals.
• Qin P x (irradiated surface / beam surface) x (1-R) where R is the reflectivity of the material constituting the part, preferably constituting the external surface of the part.
• the support means comprise very small contact surfaces and / or ceramic to minimize the extent of the transfer zone and the interstitial conduction coefficient.
• the loss by radiation is maximized during the implementation of the method of the invention compared to the use of an oven since the external environment remains at a moderate temperature, generally at room temperature (between 15 and 25 ° C, preferably at 20 ° C). As the radiation loss varies with T 4 , it must be taken into account at the end of the room temperature rise phase, when the difference between the temperature of the environment is large (significant) compared to that of the room. room.
• the losses by convection will be of the order of 2 to 10% of the heat input Qin
• the losses by radiation will be of the order of 1 to 2% of the heat input Qin
• the losses by convection will be of the order of 4 to 20% of the heat input Qin
• the losses by radiation will be of the order of 5 to 15% of the heat input Qin.
• an aluminum part held by support means, to 420 ° C in 4s, (starting from an ambient temperature of 20 ° C), ie a temperature difference DT of 400 ° C requiring a rise time of 100 ° C / s.
• the part is a rod of 2 x 2 mm section by 6 mm long:
• the losses by convection will be of the order of 5 to 15% of the heat input Qin
• the losses by radiation will be of the order of 1 to 2% of the heat input Qin ;
• the losses by convection will be of the order of 15 to 30% of the heat input Qin
• the losses by radiation will be of the order of 5 to 10% of the heat input Qin heat.
• a wall plug efficiency of 40% means that 100W of electrical power is converted into 40W of laser power.
• the powers available to carry out the heat treatment (quenching, for example) at the heart of small-volume parts correspond perfectly to the order of magnitude of power required for the heat treatment (quenching) of at least one part.
• the use of much more powerful laser sources would make it possible to carry out heat treatment (quenching for example) according to the method and system of the invention in parallel on many parts. So,
• insulating support means ceramic
• a small contact surface example cylinder deposited on a plate, plate on spikes
• thermoly conductive surface (heat exchanger).
• step B After raising the temperature of the room by laser (Power P), according to step e., Under partial vacuum (to avoid oxidation or decarbonization), a cooled neutral gas is injected to increase the losses by convection .
• step C After raising the temperature of the part by laser (Power P), according to step e., Under partial vacuum (to avoid oxidation or decarbonization), the part is lowered to bring it into contact with a thermally conductive surface (heat exchanger) which will facilitate conduction losses.
• Power P laser
• step e Under partial vacuum (to avoid oxidation or decarbonization)
• the part is lowered to bring it into contact with a thermally conductive surface (heat exchanger) which will facilitate conduction losses.
• the part After the temperature of the part has been raised by laser (Power P), the part is immersed (immersed) by means of a jack in a liquid bath (molten salt, oil, etc.) to make a hyperquenching.
• a liquid bath molten salt, oil, etc.
• the cooling means used depend, for example, on the desired cooling rate but also on the geometry of the part. For example, a part having a large external surface in the same plane could be effectively cooled by bringing it into contact with a thermally conductive surface (heat exchanger).
• the laser power P is very easily controlled via its interface converting the electric current into light power P.
• the gas supply and the control of its pressure are carried out via the control of a pneumatic island, for example.
• the descent of a jack for the movement of the part on a thermally conductive surface (heat exchanger) or in a bath is carried out for example by transmitting an electric signal to the control means of a pneumatic or electric cylinder.
• a control of the temperature of the room can be carried out:
• non-contact measuring means which will not disturb the thermal treatment cycles (quenching): thermal camera, pyrometer.
• - Fig.1a shows an embodiment of the system according to the invention
• FIG. 1 b and 1 c show other embodiments of the system according to the invention.
• Figs. 3a, 3b and 3c show different examples of part that can be quenched in volume with the process of the invention
• FIG. 4a, 4b show another possible embodiment of the method and the system according to the invention.
• FIG. 5a, 5b show another possible embodiment of the method and the system according to the invention.
• Figs. 6a, 6b, and 6c illustrate a temperature simulation when carrying out a process according to the invention
• - Fig. 7 shows an example of a thermal cycle that can be carried out in part or in its entirety by the method or the system according to the invention
• FIG. 8a, 8b and 8c show preferred embodiments of a laser source according to the invention
• - Fig. 9 shows an intensity profile of the laser beam projected onto a part according to a preferred embodiment of the invention
• - Figs. 10a and 10b represent preferred embodiments of the system according to the invention.
• FIG. 1 a shows an exemplary embodiment of the system for the heat treatment by volume of a part 2 according to the invention.
• the heat treatment corresponds to volume quenching.
• the system according to the invention comprises a laser source 3 which can be continuous or pulsed.
• Support means 4 make it possible to support the part 2, to be soaked for example.
• these support means have an essentially flat upper surface to support and hold in position the part 2 to be quenched, the lower face 28 of which is in contact with the support means 4.
• the method of the invention consists in irradiating with the laser source 3 at least a portion 23 of the external surface 22 of the part 2.
• the laser source 3 emits a collimated light beam so as to limit the settings concerning the position of a focusing distance of the collimated light beam with respect to the external surface 22 of the part 2.
• the laser source 3 emits a diverging light beam in order to be able to irradiate a large portion 23 of the external surface 22 of the part 2.
• FIG. 1 a the laser source 3 emits a diverging light beam in order to be able to irradiate a large portion 23 of the external surface 22 of the part 2.
• the laser source 3 emits a converging light beam in order to be able to direct the light beam onto a selected portion 23 of the external surface 22 of the part 2.
• FIG. 1 .c illustrates for example the use of a light beam that is homogenized and then focused.
• This external surface 22 delimits the volume of the part 2 to be quenched.
• This irradiation by the laser source 3 can be direct or indirect.
• the part 2 is irradiated from its upper surface only. Following this laser irradiation, the temperature of the room 2 will increase from the portion 23 of the surface illuminated by the laser source 3.
• the support means 4 have a certain degree of thermal insulation between them and the part 2 or, in an equivalent manner, a certain thermal insulation capacity between them and the part 2.
• a degree of thermal insulation can be defined by an ability to limit heat exchange between the part 2 and the support means 4. It is possible to have such a technical effect in different ways. Thus, it is possible to use support means 4 having a low thermal conductivity limiting heat exchange by conduction following contact between the part 2 and the support means 4. It is also conceivable to limit the contact areas between. the part 2 and the support means 4. Limited contact areas between the part 2 and the support means 4 also make it possible to limit any heat exchange by conduction between the part 2 and the support means 4.
• a heat exchange between the part 2 and the support means 4 will be lower when the contact surface (the contact areas) between the part 2 and the support means 4 is smaller.
• the heat generated at the level of the surface portion 23 illuminated by the laser source 3 tends to diffuse throughout the entire volume of the part 2.
• the inventors have noticed that 'it is possible to have a rise in temperature throughout the volume of the part 2 (and therefore not only at the level of the illuminated portion 23) inducing a modification of the structure of the material constituting the part 2.
• the invention preferably consists in stopping the laser irradiation used for heating.
• this allows the material to be fixed in a structure other than that present before the heating.
• certain parts for example of small size (that is to say, the volume of which is less than 1 cm 3 )
• This provides a huge advantage over known volume quenching processes where the use of a fluid is often required to cool part 2 and freeze it in a new crystallographic structure.
• the inventors have surprisingly noticed that it was not necessary to have very powerful laser sources 3 in order to carry out volume quenching of parts 2 using the method of the invention.
• volume quenching with continuous laser sources 3 having powers of the order of or less than 50 W, for example 20W or 6W. This is all the more true as part 2 has a small volume, that is to say less than cm 3 . It is then possible to obtain temperature rises of the order of 3000 K on the irradiated portion 23.
• FIG. 2 shows another embodiment of the invention for which part 2 is irradiated by two laser sources so as to have an irradiated portion 23 of part 2 that is larger than with a laser source.
• This is advantageous in order to obtain a rise in temperature throughout the volume of the room as quickly as possible.
• This embodiment is particularly advantageous for parts 2 that are thick and / or having complex geometries in order to have heat inputs distributed around the part 2.
• This embodiment can be implemented either from of embodiments comprising different examples of support means 4.
• the heat generated at the level of the irradiated portion 23 reaches the opposite lower surface 28 after a shorter time. than for the embodiment of Figure 1.
• This embodiment of FIG. 2 can be implemented without distinction from the embodiments of FIGS. 1a, 1b and 1c.
• Figures 3a-c show various examples of part 2 which can be quenched by volume with the method of the invention.
• Figures 3a-c illustrate the heart 27 of parts 2 of different geometries. The heart is often located in the volume of the part 2 at an equidistant position relative to the external surface 22. The method of the invention makes it possible to quench the entire volume of the part 2 including the quenching of the part. heart 27 of part 2.
• FIGS. 4a and 4b illustrate a particular embodiment of the invention.
• the support means 4 here have the shape of points so as to minimize the contact surface between them and the part 2.
• the inventors also propose for this particular embodiment a heat exchanger 18. positioned at a certain distance from the external surface 22 (preferably from the opposite lower surface 28) of the part 2.
• cooling of the part 2 is initiated (for example during step f. for embodiments comprising such a step).
• the laser radiation is stopped. Almost simultaneously, the part 2 is placed in physical contact with the heat exchanger 18 via its opposite lower surface 28.
• the heat exchanger 18 has a thermal conductivity (much) greater than that of the support means 4.
• the heat exchanger 18 is preferably able to undergo a relative movement with respect to the part 2.
• it can for example be mounted on an electric or pneumatic cylinder which allows it to describe a relative movement with respect to part 2.
• FIG. 5a and 5b illustrate another particular embodiment of the invention.
• the support means 4 also have the shape of points so as to minimize the contact surface between the part 2 and the support means 4 and thus reduce heat transfer by conduction between them and the part 2.
• the inventors propose to use a liquid bath 19, the upper surface of which is positioned at a certain distance from the external surface 22 (preferably from the opposite lower surface 28) of the part 2.
• cooling is initiated (and for example step f. for embodiments comprising such a step).
• FIG. 5b where it can be seen that the laser source 3 has been switched off. Almost simultaneously, the part 2 is immersed (partially or completely) in the liquid bath 19.
• Figures 6a, 6b, and 6c illustrate the results of a finite element simulation.
• Fig. 6a shows a half longitudinal sectional portion of a 1mm 3 steel cylinder 90 having an axial length of 4mm and a cross section of 0.6mm in diameter.
• Points 91, 92, 93 represent the center of cylinder 90.
• Points 91 and 93 are located on the outer face of the part, point 92 is located at the heart of the part, equidistant between points 91 and 93.
• the points points 94, 95, 96 represent a side face of cylinder 90. Points 94 and 96 are located on the outer face of the part, point 95 is located in the center of the side face of the part, equidistant between points 94 and 96.
• the following assumptions are used for the simulation, the results of which are presented in figure 6b and 6c:
• FIG. 6b illustrates the evolution of the temperature as a function of time for each of the points 91 to 96 of the simulated part.
• the various curves are superimposed: thus, one deduces an absence of significant temperature gradient between the various points: the evolution of the temperature at each of the points 91 to 96 is approximately the same.
• Figure 6c shows a zoom as the laser irradiation is terminated. At a given moment, thermal gradients are observed between the different points not exceeding 10 ° C. The irradiation by the laser beam is centered on the point 91, in the direction 91 - 93. This illustrates that the method of the invention is very well suited to the heat treatment (for example quenching) of (metal) parts having volumes. of the order of cm 3 .
• FIG. 7 shows a thermal cycle which can be implemented in part or in its entirety by the method according to the invention. Such a thermal cycle shows:
• the laser source 3 is switched off during these drops in temperature or cooling.
• the temperature rises and falls can be:
• the KLMN thermal cycle portion is often associated with annealing.
• the ABCDEF thermal cycle portion is often associated with quenching.
• point D is at a temperature close to the temperature of point A and points E and F are omitted.
• the GHIJ heat cycle portion is often associated with income.
• a hardening process according to the invention was implemented with a continuous laser source 3 with an output laser beam power of 0.7 W directed towards a portion of the external surface 22 of a part 2 made of steel. .
• the part is held by support means.
• the part is at room temperature (20 ° C); according to step e., after 2 s of irradiation with a laser power of 0.7 W, the part reaches a temperature of 750 ° C, after 3 s, the temperature is 950 ° C, between 4 s and 5 s the room temperature reaches 1300 ° C, which corresponds to a target temperature for the desired heat treatment.
• the laser source 3 is then turned off.
• Figures 8a, 8b and 8c show preferred embodiments of a laser source 3 of the invention.
• the example of the embodiment of Figure 8a shows a laser source 3 comprising a laser beam generator 31 and control means.
• beam 35 configured to modulate the intensity profile of the laser beam emitted by the laser beam generator 31.
• the example of the embodiment of Figure 8b shows a laser source 3 comprising a laser beam generator 31 and beam control means 35 configured to modulate the intensity profile of the laser beam emitted by the laser beam generator 31.
• the beam control means 35 comprise a multimode optical fiber 32, and a laser beam projection device 33.
• the multimode optical fiber 32 comprises an input and an output.
• Multimode optical fiber 32 is configured to carry a laser beam emitted by laser beam generator 31 from the input of multimode optical fiber 32 to its exit.
• Multimode optical fiber 32 has a predetermined section which is constant between its input and its output.
• the laser beam projection device 33 is configured to project onto the part 2, an image of the output of said multimode optical fiber 32, and consequently, an image of the laser beam transported by the multimode optical fiber 32 whose contour is defined.
• FIG. 8c shows a laser source 3 comprising a laser beam generator 31, beam control means 35 configured to modulate the intensity profile the laser beam emitted by the laser beam generator 31 and the focusing means 36.
• FIG. 9 shows a graph representing a distribution of the intensity of a laser beam transported by the multimode optical fiber 32 and projected by the laser beam projection device 33 on an external surface 22 of the flat part 2 and perpendicular to the main direction of propagation of the collimated light beam.
• This graph shows an intensity distribution at diameter 39 of the laser beam image on workpiece 2.
• the diameter 39 of the laser beam image on workpiece 2 is approximately 5mm.
• the laser beam image exhibits uniform irradiation over almost the entire irradiated surface 23 of part 2.
• FIG. 10a shows a preferred embodiment of the system for the heat treatment by volume of a part 2 comprising the laser source 3 shown in FIG. 8.
• the laser source 3 shown in FIG. 8 comprises a laser beam generator 31 , a multimode optical fiber 32, and a device laser beam projection device 33, wherein the laser beam projection device 33 comprises a first converging optical element 37 and a second converging optical element 38.
• the first 37 and the second 38 converging optical elements are preferably converging lenses, of more preferably lenses of the plane convex type. Even more preferably, the convex face of the first converging plane convex lens 37 faces the convex side of the second converging plane convex lens 38.
• the laser beam projection device 33 makes it possible to form an image having a diameter 39 on it. the part 2 supported by the support means 4.
• the diameter 39 is defined by the configuration of the laser beam projection device 33 (power of the lenses 37, 38 and their relative positions with each other and with respect to the output of the optical fiber multimode 32) and by the section of multimode optical fiber 32 (at its exit).
• the output of the multimode optical fiber 32 is imaged by the laser beam projection device 33, and the laser beam generator 31 emits a laser beam which is carried by the multimode optical fiber 32, then the image of the output of the multimode optical fiber corresponds to a light spot of diameter 39.
• FIG. 10b shows the embodiment of FIG. 10a for a part 2 of larger size for which it is necessary to increase the diameter 39 of the image of the multimode optical fiber output 32 on part 2 in order to be able to carry out a heat treatment with thermal gradients on the surface 22 of the part 2 as small as possible.
• the laser beam projection device 33 makes it possible to modulate such a diameter 39 of the image of the output of multimode optical fiber 32 on the part 2 by modifying the relative position of the first converging lens 37 with respect to the output of the fiber. multimode optics 32 and / or the position of the second converging lens 38 relative to the first converging lens 37. Such a modulation makes it possible to obtain magnifications allowing adaptation to parts having sizes that can vary greatly.
• the first converging lens 37 is driven into position between the output of the multimode optical fiber 32 and the second converging lens 38 so as to adjust the size of the laser beam on the part 2.
• the temperature rise in a room in step e. is carried out by a single step of irradiating the part, which has the advantage of offering a homogeneous heat treatment of the part.
• the present invention applies in particular to parts which have a longest dimension less than 10 mm, preferably equal to or less than 8 mm.
• a method of heat treatment by volume of a part 2 having an external surface 22 delimiting its volume comprising the following steps: a. providing a laser source 3; b. provide Exhibit 2; vs. providing support means 4 for supporting the part 2; d. placing said part 2 so that it is held in position by said support means 4; e. irradiating with said laser source 3 at least a portion 23 of the external surface 22 of said part 2 with a laser power and duration of exposure to obtain a temperature rise in essentially the entire volume of the room 2.
• the support means 4 for supporting the part 2 has a degree of thermal insulation between them and said part 2.
• the invention can also be described as follows.
• a system for the heat treatment by volume of a part having an external surface delimiting its volume comprising:
• a laser source configured to irradiate at least a portion of the external surface of the part with a laser power and duration of exposure to obtain a temperature rise in essentially the entire volume of the part to induce a structural modification the material constituting the part;
• the support means have a degree of thermal insulation between them and the part.

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• Optics & Photonics (AREA)
• General Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• Heat Treatment Of Articles (AREA)
• Recrystallisation Techniques (AREA)
• Heating, Cooling, Or Curing Plastics Or The Like In General (AREA)
• Waste-Gas Treatment And Other Accessory Devices For Furnaces (AREA)
• Control Of Heat Treatment Processes (AREA)

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• 2020
  • 2020-01-22 BE BE20205041A patent/BE1027475B1/fr active IP Right Grant
• 2021
  • 2021-01-22 WO PCT/EP2021/051442 patent/WO2021148600A1/fr not_active Ceased
  • 2021-01-22 CA CA3165012A patent/CA3165012A1/fr active Pending
  • 2021-01-22 AU AU2021209391A patent/AU2021209391A1/en active Pending
  • 2021-01-22 MX MX2022008882A patent/MX2022008882A/es unknown
  • 2021-01-22 US US17/794,483 patent/US20230078751A1/en active Pending
  • 2021-01-22 EP EP21702881.0A patent/EP4093888A1/de active Pending
  • 2021-01-22 JP JP2022543644A patent/JP2023511329A/ja active Pending

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