Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
  • B22F10/30—Process control
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
  • B22F10/20—Direct sintering or melting
  • B22F10/25—Direct deposition of metal particles, e.g. direct metal deposition [DMD] or laser engineered net shaping [LENS]
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/10—Sintering only
  • B22F3/105—Sintering only by using electric current other than for infrared radiant energy, laser radiation or plasma ; by ultrasonic bonding
• • 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
  • B23K26/14—Working by laser beam, e.g. welding, cutting or boring using a fluid stream, e.g. a jet of gas, in conjunction with the laser beam; Nozzles therefor
  • B23K26/1462—Nozzles; Features related to nozzles
  • B23K26/1464—Supply to, or discharge from, nozzles of media, e.g. gas, powder, wire
• • 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
  • B23K26/34—Laser welding for purposes other than joining
  • B23K26/342—Build-up welding
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B28—WORKING CEMENT, CLAY, OR STONE
  • B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
  • B28B1/00—Producing shaped prefabricated articles from the material
  • B28B1/001—Rapid manufacturing of 3D objects by additive depositing, agglomerating or laminating of material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
  • B29C64/10—Processes of additive manufacturing
  • B29C64/141—Processes of additive manufacturing using only solid materials
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
  • B29C64/10—Processes of additive manufacturing
  • B29C64/141—Processes of additive manufacturing using only solid materials
  • B29C64/153—Processes of additive manufacturing using only solid materials using layers of powder being selectively joined, e.g. by selective laser sintering or melting
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C67/00—Shaping techniques not covered by groups B29C39/00 - B29C65/00, B29C70/00 or B29C73/00
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
  • B22F10/20—Direct sintering or melting
  • B22F10/28—Powder bed fusion, e.g. selective laser melting [SLM] or electron beam melting [EBM]
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
  • B29L2031/00—Other particular articles
  • B29L2031/772—Articles characterised by their shape and not otherwise provided for
• • 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 present invention relates to the field of manufacturing parts by melting powder by means of a high energy beam (laser beam, electron beam, etc.).
• a high energy beam laser beam, electron beam, etc.
• the invention more particularly relates to a method comprising the following steps:
• a material is provided in the form of powder particles forming a powder bundle
• a first quantity of this powder is heated to a temperature above the melting point T F of this powder using a high energy beam, and a first bath is formed on the surface of a support. comprising this melted powder and a portion of this support,
• step (d) repeating step (c) until forming a first layer of this part on this support
• step (g) repeating step (f) so as to form a second layer of the workpiece above said first layer, (h) Steps (e) to (g) are repeated for each layer above an already formed layer until the part is substantially in its final form.
• Methods that make it possible to obtain mechanical parts of complex three-dimensional (3D) shape. These methods construct a layer-by-layer piece to reconstruct the desired shape of that piece.
• the part can be reconstituted directly from the CAD / CAM file deduced from the data processing of its 3D CAD graphic file by means of a computer control of the machine which thus forms one on the other of the successive layers of melted then solidified, each layer consisting of juxtaposed cords having a size and a geometry defined from the CFAO file.
• the particles constituting the powder are, for example, metal, intermetallic, ceramic, or polymer.
• the melting temperature T F is a temperature between the liquidus temperature and the solidus temperature for the given composition of this alloy.
• the construction support may be a part of another room on which it is desired to add an additional function. Its composition may be different from that of the powder particles and thus have a different melting temperature.
• a first layer 10 of material is formed, under local protection or in a chamber under pressure or regulated depression of inert gas, by spraying particles of powder of this material on a support 80, through a nozzle 190.
• This nozzle 190 emits, simultaneously with the projection of particles 60 of powder, a beam laser 95 which comes from a generator 90.
• the first orifice 191 of the nozzle 190 through which the powder is projected onto the support 80 is coaxial with the second orifice 192 through which the laser beam 95 is emitted, so that the powder is projected in the laser beam 95.
• the powder forms a cone of particles, this cone being hollow and having a certain thickness (powder beam 94 in Figure 4), and the laser beam 95 is conical.
• the work plane P is defined as the plane containing the surface on which the layer is under construction / formation.
• this surface is the (free) upper face S 0 of the support 80.
• this surface is the (free) upper face of the [n + 1] layer. ] -th layer (with n integer, n ⁇ l).
• the laser beam 95 forms a bath 102 on the support 80 by melting the region of the support 80 exposed to the laser beam.
• the powder feeds the bath 102 in which it reaches the molten state, the powder having melted during its journey in the laser beam before arriving in the bath.
• the nozzle 190 and the laser focal point can be adjusted and / or positioned so that the given size distribution powder does not spend enough time, for example, in the laser beam 95 so that all of its particles of different sizes are completely melted, and melt on arriving in the bath 102 previously formed on the surface of the support 80 by melting the region of the support 80 exposed to the laser beam 95.
• the working distance WD is defined as the distance between the outlet of the nozzle 190 and the work plane P.
• the powder may also not be melted by the laser beam 95 or be only partially because the size of all or some of the particles constituting the powder is too important for them to be fondues.
• the lower the average diameter D p of the powder particles the greater their heating rate, but the shorter their maintenance at the melting stage and the faster their cooling.
• Figure 3 demonstrates that the smaller the size distribution, the more all the particles of the powder arrive melted in the bath for a given work configuration.
• the powder particles are heated by their passage in the laser beam 95 before feeding the bath.
• the bath 102 is maintained and solidifies step by step to form a bead of solidified material 105 on the support 80.
• the process is continued to form another cord solidified on the support 80, this other cord being for example juxtaposed to the first bead.
• a first layer 10 of material is deposited on the support 80 which solidifies a first element 15 in one piece with the geometry conforms to that defined by the CAD / CAM file.
• a second scan of the nozzle assembly 190 / laser beam 95 is then performed to similarly form a second layer 20 of material above the first element 15.
• This second layer 20 forms a second consolidated element 25, the entire of these two elements 15 and 25 forming a block in one piece.
• the baths 102 formed on the first element 15 during the construction of this second layer 20 generally comprise at least a portion of the first element 15 which has been melted by exposure to the laser beam 95, and the particles of the powder feed the baths 102. .
• the work plane P is not necessarily parallel to the surface S 0 .
• the Z axis defined as being perpendicular to the work plane P, is not necessarily parallel to the Z 0 axis.
• Figure 5 is a cross section of the liquid bath formed in part in the support, and shows the shape of this bath.
• the surface S 0 of the support 80 is the plane of zero height. Also, during the construction of the first layer, a plane parallel to So, a part of which is contained in this support or below this support (with reference to the axis Z 0 ) is of negative height, and a parallel plane at S 0 , a part of which is above the surface S 0 of the support (with reference to the axis Z 0 ) is of positive height.
• a given work plane P for the construction of one [n] -th layer will be above another worktop attached to a lower layer if it has a positive height, greater than the height of that other plan.
• the working plane of an upper layer may not be parallel to the working plane of the previous lower layer, in this case the Z axis of the upper layer makes a non-zero angle with the axis.
• Z of the working plane of the lower layer, and the distance ⁇ , measured along the latter axis Z above each point of the lower layer, is a mean value.
• This process of building the part layer by layer is then continued by adding additional layers above the already formed assembly.
• FIG. 4 which represents the prior art, shows in more detail the configuration of the laser beam 95 and the powder beam 94.
• the laser beam 95 leaves the nozzle 190 diverging at a 2 ⁇ angle from its focal point F L (located in the lower part of the nozzle 190) and illuminates a region of the support 80, thereby creating a bath 102.
• the powder bundle 94 leaves the nozzle 190 converging at an angle ⁇ 2 to its focal point F P which lies inside the laser beam 95, and just on (or above) the surface of the support 80 (P worktop), so that the powder particles 60 pass a maximum time in the laser beam 95 to be heated.
• the advantage of a wide laser / powder interaction upstream of the bath is to generate both a high deposition rate and a low dilution which are frequently sought in the case of reloading (surface repair of worn parts) and the coating of hard deposits.
• the theoretical melting efficiency is defined as the ratio of the diameter 0 L of the laser beam 95 to the diameter P of the powder bundle 94, these two diameters being determined at the right of the worktop P.
• 0 L can be replaced by the diameter of the liquid bath 0BL (see FIG. 4) in order to evaluate the yield, which depends inter alia on the parameterization chosen, in particular on the laser power, P L , on the scanning speed of the laser beam, V and the mass flow D m of powder.
• the working configuration according to the prior art requires logically that the laser beam either defocused (its focal point F L is above the work plane P) for a focused powder beam (its focal point Fp is located on the work plane P) or a defocused powder beam whose focal point F P is above the work plane P and below the focal point F L , failing to generate an unstable construction and moreover not guaranteeing an acceptable melting efficiency.
• the diameter of the laser beam 0 L measured at right of the plane P does not correspond to the diameter of the liquid bath 0 B L which is, meanwhile, approximated to the width (denoted e app ) the cord after solidification ( Figures 4 and 5).
• This diameter of the liquid bath 0 B L is supposed to be a function of 0 L and thus of 0 L o but also of the parametrium defined by the triplet (P L , V, D m ) and moreover of the size D p of the different particles of powder and their Vp speeds in addition to depend on their thermo-physical properties.
• the focal point F P of the powder beam 94 remains inside the laser beam 95, and just on (or above) the surface of the previously constructed layer (work plane P).
• each layer 190 / laser beam 95 makes it possible to give each layer a form independent of the adjacent layers.
• the lower layers of the room are annealed and cool as the top layers of the room are formed.
• melt mass efficiency R m i.e., the ratio of the amount of material forming the finished part to the amount of material projected by the nozzle to form this part.
• mass efficiency of recycled powder re cy that is to say the ratio of the amount of powder intact in morphology and agglomerates obtained for example after sieving the amount of material sprayed
• stability of the baths formed on the surface of the part and the material health of the fabricated part for a given non-exhaustive set of parameters (size distribution D P of the powder particles, nature of the powder material, mass flow rate D m of powder, speed of displacement V of the nozzle / laser beam assembly, power P L provided by the laser, distribution of the power density on the work plane P, type of laser source (solid or gas), mode (pulsed or continuous), coaxial nozzle, nature and gas flow po D gp powder particles, nature and flow rate of the protective gas D gl through the axis of the nozzle, the angles 2 ⁇ and 2 ⁇ and
• the aim of the invention is to propose a method and more particularly an optimized working configuration (defined by: Defoc L , defocus P , WD) for the DMD process which makes it possible firstly to improve the stability of the bath and in a second time to mass melting efficiency, the recycled powder mass yield, the material health and the construction speed (maximizing the Z-riser increment of the nozzle noted ⁇ ).
• This goal is achieved by virtue of the fact that the powder particles arrive in each bath at a cold temperature relative to the temperature of the bath.
• the mass yield of ⁇ ⁇ process defined as the sum of the mass of fusion yields (R m) and recycled fe re cy powder) is greater than the mass yield of the process in the case where the powder particles arrive hot partially or totally melted in the bath.
• the powder particles, arriving in the bath will temper the temperature of the liquid bath TBL (because they are much colder than this bath, the latter being substantially at room temperature before entering the bath), while by increasing the volume of the bath and in particular that above the plane P without increasing the width and the height of the diluted zone (volume of the bath which is below the plane P). This inevitably leads to a rapid increase in the liquid / vapor surface tension of the bath, and consequently generates a better stability of the bath.
• the focal point F L of the high energy beam is above the working plane P or on this plane, and the focal point F P of the powder bundle is below the working plane P, such that so that the powder particles do not intersect at any time the high energy beam between the outlet of the nozzle and the working plane P.
• the focal point F P of the powder bundle can be located inside the support , especially when depositing the first layers. After the deposition of a number of layers, the focal point F P of the powder bundle may lie within the previously deposited layers. Thus, a majority of powder particles arrive cold in the previously formed bath on part of the already constructed part.
• the powder bundle and the high energy beam may be substantially coaxial, that is to say that their axes form between them an angle of less than 30 °, preferably less than 20 °, more preferably less than 10 °, more preferably less than 5 °.
• the high energy beam can easily follow the powder beam when making parts with complex geometry. Tracking the shape of the part to be manufactured is much more difficult in the case of a remote projection or melting, that is to say when the powder beam and the high energy beam are not substantially coaxial.
• FIG. 1 is a diagram showing a possibility of positioning the high energy beam and the powder bundle in the case of the method according to the invention
• FIG. 2 already described, is an explanatory diagram of the method according to the prior art illustrating the device of the DMD method
• FIG. 3 already described, shows the effect of the diameter D P of the Ti-6Al-4V powder particles on their temperature from the outlet of the nozzle on arrival in the liquid bath
• FIG. 4 is a diagram showing the positioning of the high energy beam and the powder bundle in the case of the method according to the prior art
• FIG. 5 is a schematic representation of a cross section of the liquid bath formed in the support.
• the powder particles arrive cold in the bath formed on the surface of the previous layer (or support).
• the term "cold" means that the temperature of the particles is much lower than the temperature of the bath. Indeed, the temperature of the particles, before entering the bath, is substantially equal to the ambient temperature, for example of the order of 20 ° C.
• the temperature of the liquid bath T B L is greater than the melting temperature T F of the material constituting the powder but lower than the boiling point T e of this material.
• This melting temperature is greater than 550 ° C for aluminum alloys, 1300 ° C for nickel bases, 1450 ° C for steels and 1550 ° C for titanium alloys.
• Figure 1 illustrates an embodiment of the invention that allows the powder particles to arrive cold in the bath formed on the surface of the previous layer (or support). Such an embodiment also has the advantage of facilitating the coaxial vision of the bath by among other things a CCD (Charge Coupled Device) camera to allow control of the on-line process, useful for the industrialization of the process.
• CCD Charge Coupled Device
• FIG. 1 shows a sectional view of a support 80 and a first layer 10 of material already deposited on this support 80.
• a second layer 20 is then deposited on this first layer 10.
• a bead 105 of this second layer 20 is under construction, the progression of the cord 105 from left to right, from upstream to downstream (direction of advance of the cord 105, or, equivalently, the liquid bath 102).
• the bath 102 is thus located immediately downstream of the bead 105, under the nozzle 190 from which the laser beam 95 and the powder bundle 94 exit.
• the upper surface of the first layer 10 then constitutes the work plane P relative to the second layer under construction and from which defocus laser defocus L , defocus powder defocus P , working distance WD, laser beam diameter 0 L , and powder beam diameter 0 P are measured.
• the nozzle 190 emits, simultaneously with the projection of particles 60 of powder, a laser beam 95 which comes from a generator 90.
• the first orifice 191 of the nozzle 190 through which the powder is projected on the support 80 is coaxial with the second orifice 192 by which the laser beam 95 is emitted, so that the powder is projected into the laser beam 95.
• the powder forms a cone of particles, this hollow cone having a certain thickness (powder beam 94), and the laser beam is conical.
• the nozzle 190 is configured and positioned so that the focal point F L of the high energy beam 95 is above the working plane P or on this plane, and the focal point F P of the beam powder 94 is located below the working plane P, so that the powder particles 60 do not intersect at any time the high energy beam between the outlet of the nozzle and the work plane P.
• the focal point F P of the powder bundle may be located inside the support.
• Defoc P powder defocusing is smaller than that shown in FIG. 1.
• the diameter of the laser beam 0 L at the plane P is close to the diameter of the powder bundle 0 P at the plane P, for parameterization (P L / V, D m ) considered.
• the diameter of the laser beam 0 L in line with the plane P is slightly smaller than the diameter of the powder beam 0 P at the right plane P.
• Such a configuration is obtained, as represented in FIG. 1, by bringing the nozzle 190 closer to the working plane P of the configuration according to the prior art (FIG. 4), that is by decreasing the working distance WD.
• Such a working configuration is particularly suitable for producing large cords 105, that is cords 105 whose width is greater than the diameter 0 L o of the high energy beam 95 at the laser focal point.
• the diameter of the liquid bath 0 B L is then wider and more powder particles arrive cold in the liquid bath 102, which is beneficial as explained above.
• the focal point F L of the high energy beam (95) may alternatively be located on the working plane P, which is preferable in the production of thin cords whose width is smaller.
• the focal point F P of the powder bundle 94 can be located on the work plane P.
• the focal point F P of the powder bundle 94 can also be located below the work plane P.
• certain parameters can be adapted accordingly, in particular the laser power P L , the scanning speed V and / or the mass flow rate D m of powder.
• an (additional) cooling of the nozzle 190 may be necessary, since the nozzle 190 heats up by radiation due to its proximity to the liquid bath 102.
• Such cooling requires a expensive device.
• the inventors have developed an embodiment which advantageously consists either in to decrease the distance Defoq, or to decrease the divergence half-angle ⁇ of the laser beam 95 with respect to the Z axis, returning in both cases to decrease 0 L so that it is lower than 0 P.
• the defocus distance P of the powder beam 94 is increased in order to compensate for the decrease of 0 P in the event of an increase in WD and thus maintain 0 P greater than 0 L.
• the nozzle 190 is thus configured and positioned so that the powder particles 60 reach the working plane P just outside the area of the working plane P covered by the laser beam 95.
• the bath 102 is more thermally stable because the powder particles 60 rapidly cool the bath 102 (which results in an increase in the liquid / vapor surface tension of the bath, and certainly also a variation of the convective movements at the bath. in the bath because of the variation of the density of the liquid by the addition of "cold" powders and a change of the thermal gradient in the bath).
• An additional advantage of the process according to the invention is that the powder particles 60 which did not participate in the formation of the liquid bath (because fallen outside the bath 102) remained cold and are therefore recyclable almost completely. .
• the total mass yield of the process (melting + recycling) according to the invention is therefore much higher than the total mass yield of the process according to the prior art.
• the bath has an oblong shape defined by ⁇ ⁇ 90 °, H a pp / e at pp ⁇ 1 and H ZR / H app ⁇ 0.6, where ⁇ is the angle of the upper surface of the bath 102 with the worktop P, H ap p the apparent height of the bead (part of the bath 102 above worktop P), e app its width, and H Z R the height of the remelted zone or diluted zone (part of the bath below worktop P) (see Figure 5).
• the size distribution of the powder particles 60 is narrow (which corresponds to particles all having substantially the same size, which size is in agreement with the temperature and the volume of the liquid bath to be melted at any moment during the duration of the laser / bath interaction).
• the probability is high for all the powder particles 60 to have time to melt in the bath 102 before the laser beam 95 is moves (and therefore stops heating this bath 102).
• the process of feeding the bath of cold powder particles and of narrow size distribution will then be more effective in terms of stability and speed of construction because the temperature of the bath decreases more rapidly and the apparent height of the cords becomes larger. This apparent height is even greater than the particles are fine because the bath temperature will gradually decrease and then remain constant (solidification plateau reached) as the particles enter the bath 102.
• the powder particles 60 have sizes ranging from 25 to 75 ⁇ m (microns). Preferably, these sizes are between 25 and 45 ⁇ m.
• the positioning of the nozzle 190 is slaved to the spatial variations of the working plane P (variations in the height of consolidated material H app of a layer of the part to be constructed whereas the Z-rise increment ⁇ of the nozzle 190 is kept constant by pre-programming) so that, for each layer, the focal point F L of the laser beam 95 is at the same height above the work plane P and the focal point F P of the powder bundle 94 is at the same height below the work plane P.
• the increment ⁇ can be enslaved to changes in the height of consolidated matter H app of a layer.

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