Corresponding application

The present application claims priority to the earlier European application N°15202168.9 filed on December 22, 2015 in the name of Ecole Polytechnique Federale de Lausanne (EPFL), the content of this earlier application being incorporated by reference in its entirety in the present application. Background of the invention

Selective Laser Melting (SLM), also known as Direct Metal Laser Sintering (DMLS), Laser Metal Fusion (LMF), Laser Cusing or Selective Laser Sintering (SLS) is an Additive Manufacturing (AM) process in which a part is built layer by layer out of a metallic, ceramic or polymer powder. An example of a prior art publication is disclosed in US 5,155,324. Since then, many patents in the field of SLM have been filed focusing mostly on improvements in the accuracy of the powder deposition system, scanning optics, preheating of the substrate, control of the chamber atmosphere etc.

As an example, figure 1 illustrates a standard SLM process of the art. At each step, a powder bed is deposited on a substrate 3 and selectively melted by a laser beam 1 piloted by the CAM system through a scanning head 2. After solidification, the material gets consolidated, the building platform (substrate) 3 is lowered for the value of the wanted next layer height and a new powder layer is deposited by the deposition system 4 containing fresh powder 5. The operation sequence is repeated until completion of the part 6. At the end the unused powder 7 is removed and recycled.

One of the biggest advantages of the SLM process is the ability to manufacture parts with an exceptionally complex geometry out of materials that are difficult to process with conventional methods. This gives rise to new approaches in the part design and also to new applications in different fields. Recent technological breakthroughs (e.g. in the laser technology and related optics), are enabling development and implementation of compact hybrid machines that are able to use a single laser for different production steps (e.g. laser cutting and welding on a single machine - workstation), thus lowering both the equipment (machine) and the production costs.

Detailed description of embodiments of the invention

Embodiments of the invention are defined by the appended claims.

In an embodiment, the invention concerns a method of manufacturing objects with a primary material and at least one secondary material, wherein said primary material is a powder, wherein said secondary material is a solid material. At least a layer of the object is made by selective laser melting (SLM) of the primary material, and the method comprises the addition of at least the secondary material different from the primary material to form the object, the secondary material being selectively welded to the previously solidified SLM layer of primary material and excess material of the secondary material being removed or cut after welding to the primary material.

Preferably, the primary material comprises metallic and/or ceramic and/or polymer materials.

In an embodiment, the primary material is in a powder form and the secondary material is in a sheet or a roll or a wire form.

In an embodiment, the object is made by selectively laser melting a first layer of primary material and then adding layers of primary material and/or secondary material.

In an embodiment, the object is made by placing a first layer of secondary material and then adding layers of primary material and/or secondary material. In an embodiment, both the SLM step, the welding step and the cutting step are done with a same laser. In an embodiment, these steps are done with a different laser.

In an embodiment, the secondary material is brought in form of sheets or rolls or wire coils.

In an embodiment, a confining overlay is used to increase contact pressure between the primary and secondary material prior to welding.

In an embodiment, a suction (vacuum) device is used to remove the excess material left in the inner holes of the secondary material when such holes are formed by a laser.

In an embodiment, at least two different primary materials are used.

In an embodiment, at least two different secondary materials are used.

In an embodiment, the secondary material is used as a first layer, the primary material is added to said layer and solidified, and wherein both layers are then selectively welded.

In an embodiment, the invention concerns a product or an object manufactured by a method as defined in the present application.

Figure 1 illustrates in a schematical way an SLM process and station according to the prior art;

Figure 2 illustrates in a schematical way an SLM process and station according to an embodiment of the present invention;

Figure 3 illustrates in a schematical way an SLM process and station according to an embodiment of the present invention. Figure 4 illustrates in a schematical way an SLM process and station according to an embodiment of the present invention.

Figure 5 illustrates in a schematical way an SLM process and station according to an embodiment of the present invention.

The present invention concerns a device and method for fabrication of 3D multi-material (or composite) parts by Selective laser melting (SLM) combined with laser cutting and welding. As mentioned, SLM is used for production of parts with complex geometry using ceramic, polymer and metallic powders. The growth of applications and the ability to process materials that are difficult to shape into complex parts (e.g. ceramic powders) together with certain technological advancements in laser and optics technology is leading to the ability to combine different materials during the process itself and produce new and exotic composites that could not be easily produced with the known technologies.

However, since the purity and full recyclability of powders used during an SLM process is one of the most important priorities, adding powders of different materials during the process is not an effective solution. Besides powder contamination, mixing different material in a powder form would limit the application of that powder to a whole layer due to the inability to deposit another powder material at the given layer. This would not give the ability to produce a 3D architectured composite with a combination of different (multiple) materials, even within a single layer.

The objective of the present invention is to provide an effective and economical method for producing new composites and objects made of a combination of ceramic, metallic and/or polymer materials and selectively tailoring them both on the surface and in the bulk of the part that is being produced. The produced parts can have a very complicated 3D composite structure. In order to be able to achieve this objective, a method and device for combining Selective Laser Melting (SLM) with laser welding and cutting on a single workstation (machine) as described herein are implemented. According to the present invention, a standard SLM process (as for example described above and figure 1) is modified with the introduction of an additional device (see references 10-12,fig 2.) allowing to add a different material to the part being fabricated. More precisely, the SLM process is used to introduce a primary material 6, 7 in a powder form (for example a metal, a composite, a ceramic or a polymer) and the said additional device is used to introduce a single secondary material 10 or multiple additional secondary materials 10 in the form of a roll (figure 2), or sheet (figure 4), or a wire (figure 5), which all can also be metal, composite, ceramic or polymer. The secondary material may also be a mix of different materials/products.

In a more detailed manner, during the SLM process after a certain number of layers (that is at least one layer) have been produced out of the primary material, the device with a secondary material is activated and it is moved on top of the building platform. The secondary material in the form of a roll (or sheet, wire) is then brought into contact with the previously solidified primary material (SLM) layer. Specifically, figure 2. A (l-l l) illustrates an embodiment of a realization of a close contact between the primary and the secondary material (the material is brought from position I to position I I), and figure 2.B shows the device in working position where the secondary material is placed on top of the object 6 being built. A laser source 1 is used to selectively weld areas of the secondary material 8 to the primary material 6. After welding, laser cutting is applied to the contours of the welded secondary material 10, so that the excess material 9 of the roll (sheet, wire) can be removed along with the device. I n variants, it is of course possible to add several secondary materials 10 according to the present invention. These materials can be placed in slots A as shown in figures 2-5. The material 10 may be different for each added layer or not, or even for the different parts of the same layer being added different materials 10 can be used, depending on circumstances.

After the welding and cutting operation of a single secondary material 10 or multiple secondary material are done, the device is lifted (Fig 2. A - 1), brought back to its starting position and a fresh section of the secondary material (or materials) is (are) prepared for future application. Then the SLM process is reactivated and a new powder layer of primary material 7 is deposited introducing again the primary material 6,7. By the regulation of the height of this powder layer, it can be applied either just besides the previously welded secondary material (if we want combination of a primary - secondary material (or materials) in the same layer) or also on top of it (if the secondary material covers the whole surface of the layer).

Figure 2 illustrates the principle of the invention. A secondary material 10 or one of the different materials placed in slots is brought in the laser welding/cutting position. A (right hand side of figure 2): transition from a starting position (I) to a position of close contact with the primary material (II), B (left hand side of figure 2): a working position with the secondary material 10 on the primary material 6.

In another embodiment, the sequence of the process described above is inverted, so that the SLM process takes place after having welded a roll (or a sheet as in figure 4, or a wire as in figure 5) of material on a substrate. In other words, one starts the production of the object with the secondary material 10 and then applies the primary material 6, 7 on the secondary material 10. Thus, according to the present invention, it is therefore possible to manufacture objects or parts with any succession of materials (primary and secondary) using the principles described herein. In embodiments of the invention, the secondary material 10 may be different in different layers of the produced object. In other words, the object 6 produced may comprise several layers of secondary material 10, each layer of secondary material 10 from a different material, or some layers of secondary material 10 may use the same secondary material 10 and other layers may use another secondary material 10. Similarly, the object may be made alternatively of primary material 6 and secondary material 10, or not, meaning some layers maybe made of several sublayers of primary material and/or secondary material. Also, certain layers may have sections of the same layer made of different secondary materials. Any combination is of course possible in accordance with the circumstances and depending on the materials to be used to form the object. In further embodiments, an initial primary material and an initial secondary material may be changed during the manufacturing process of a part, i.e. different primary materials (in powder form) and different secondary materials (in roll, sheet or wire form - figures 2-5) may be used in a same part/object. While the secondary material may be introduced in the same machine (as illustrated in figure 2 -5 for example), a different primary material may preferably be applied in a different machine or station to avoid the powder contamination problem mentioned above. In some circumstances, the use of a different primary material may be easily added in the manufacturing process, for example if it forms the first or the last layer of the part/object, so that it may be carried out in a different module of the machine or workstation or even a different machine or workstation in order to limit the loss of production time and complexity. Accordingly, parts of the object may be produced in different machines or stations (for example using different powders) then the formed parts are joined in another machine or station in accordance with the principles of the present invention. In a preferred embodiment, the same laser source 1 is used for different operations such as SLM (for the primary material), laser welding and cutting (for the secondary material), just by 4 changing the power density needed for each application. This can be accomplished by varying the power output or by changing the spot size during the process itself. The latter is notably possible due to recent technology advances in laser optics and the possible introduction of a 3 axis scanning head 2. This scanning head 2 can be used for a dynamic change of laser spot size on a same working plane (e.g. a decrease of the spot size used for laser cutting and thus increasing the power density). The said device with the secondary material can be comprised out of multiple positions (slots) A with different rolls (sheets, wires) of different secondary materials as shown in figures 2 -5. Also, a mixture of slots with rolls and wires/sheets might be advantageous. Different positions can be called upon during the building process in a way similar to, for example, an automated tool changer used in a CNC cutting machine. This is giving the possibility of introducing multiple materials to the production process and thus producing a complicated multi-material 3D structured part. Some of these materials may be used as transition materials such as to improve or allow welding between two dissimilar materials. An embodiment of the device according to the invention is shown in figure 2. It comprises at least one roll (sheet, wire) system. As mentioned, multiple rolls A with different secondary materials 10 may be utilized (figures 2-5). The secondary material 10 is brought on rolls (coils) 11 and placed on shafts 12. After each application of the secondary material 10, a new section of the material is unrolled from the coil and prepared for the application. In an alternative embodiment, a similar solution could use flat sheets instead of rolls as shown in figure 4. In an alternative embodiment, if smaller amount of secondary material is needed, a similar solution could use wire coils instead of rolls as in figure 5. An advantage of such a solution is that laser cutting would be needed just to cut through the diameter of the wire, thus decreasing the needed laser requirements for such a process.

If additional pressure is needed to achieve a good contact between the previously solidified primary material and the secondary material before the welding phase, a transparent confining overlay 13 may be applied, see figure 3. The confining layer 13 may be produced out of different materials, but they should not interfere with the laser 1 beam. Possible materials for the confining layer 13 include for example quartz, or different types of glass (glass, quartz glass, Pb glass, glass K7, glass K9), Perspex, silicon rubber, sodium silicate, fused silica, potassium chloride, sodium chloride, polyethylene, fluoroplastic (nitrocellulose or mixture thereof), PETN (pentaerythritol tetranitrate), PMMA, PTFE, Nylon and other types of polymer, etc. Other equivalent materials may be envisaged as confining layer 13, and the list given herein is only a non-limiting example of possible materials which have the necessary properties (i.e. a solid material that does not interfere with the laser beam). This confining layer may be constructed out of one or more materials in a layered fashion, where the top layer would increase its rigidity and the bottom one would be a consumable layer which could be exchanged when needed. This approach can be applied also to embodiments using sheets (figure 4).

In the case of materials that have a significantly different melting temperature and/or shrinkage rates, preheating might be beneficial to the bonding process. The preheating might be achieved by substrate preheating, or preheating of the surface of the last solidified layer (e.g. with a laser). These methods are known in the art and are applied in the processing of different materials with the SLM.

In a complicated case, the secondary material 10 might be selectively welded in a shape that requires an inner hole. For such cases, an embodiment with a suction (vacuum) device might be used to retrieve the inner portion of the material that is left separated from the rest of the roll (or sheet). Other options for such cases might include welding of the outer contour in two zones (steps), so that the inner material can be extracted in the usual way, i.e. together with the rest of the excess material of the roll. Another possibility, when the hole is small enough, is to further increase the laser power and ablate (evaporate) the excess material left inside.

The embodiments of the invention described in the present application are only illustrative examples and should not be construed in a limiting manner. The present invention may also use equivalent means and method steps to the ones described therein with corresponding results.

All suitable materials may be used as primary and secondary materials and they may be chosen according to the circumstances or the part to be fabricated as described herein.

Preferably, a single machine or workstation is used to form the parts in which machine both processes as described herein may be carried out. Alternatively, different

machines/workstations may be used in the manufacturing process as described herein to optimize the production process.