Three dimensional printers are known as machines that automatically fabricate physical objects from computer files without additionally programming the machine with step-by-step instructions.
Three dimensional printers use several different technologies for building the objects and for supporting them in space. Almost all of the technologies build the objects by horizontal layering, and they differ in the way the layers are set in place and the way overhanging areas of the model are supported during the building process. The variety of materials used in three dimensional printers is currently limited by the chemical properties required by the printer instead of by the chemical properties desired by the user. For example, some build materials need to have a specific melting point, some need to be photopolymers, some need to be sinterable powders, and some need to be made of gluable sheets comprising a substrate sheet of one material and a glue of a different material.
Some of the most important and useful materials for building models, molds, and other products are aluminum alloys. Aluminum is light, conducts electricity and heat, is machinable, and can be welded. Unfortunately, known methods of aluminum-based three dimensional printing have significant disadvantages, such as the following: Sintering metal powder is a messy process, the fine powder used as raw material for the process is expensive, and the sintered end product tends to be porous. The powder also poses health hazards, such as danger from inhalation, and further the powder is explosive. Printing by welding also has low resolution, and it requires a great amount of power.
It would be very desirable to have a method of direct three dimensional printing of aluminum, using low cost raw material, and obtaining high resolution and full, bulk, non-porous materials.
The present inventors developed methods, systems, and materials for three dimensional printing of metals using low cost raw material and obtaining high resolution and full, bulk, non-porous materials.
The invention may be embodied as a method of building at least one three dimensional metal object. The method includes: setting in place a first foil having at least one structural layer and at least one melting layer; setting in place a second foil on the first foil, the second foil having at least one structural layer and at least one melting layer; designating as first areas regions of the first and second foils to remain unjoined to each other; compressing and heating the first and second foils so that second areas of the first and second foils, distinct from the first areas, become joined to each other by brazing; and removing the first areas to form at least one three dimensional object.
The invention may also be embodied as a three dimensional metal object. The three dimensional object has multiple metal sheets. The metal sheets are joined together by selective brazing.
The invention may further be embodied as a masked brazing foil. The masked brazing foil has: at least one structural layer; at least one melting layer; and at least masking layer.
Embodiments of the present invention are described in detail below with reference to the accompanying drawings, which are briefly described as follows:
The invention is described below in the appended claims, which are read in view of the accompanying description including the following drawings, wherein:
The figures are not necessarily drawing to scale.
The invention summarized above and defined by the claims below will be better understood by referring to the present detailed description of embodiments of the invention. This description is not intended to limit the scope of claims but instead to provide examples of the invention.
The present description uses the following terms presented with their definitions:
The present invention may be embodied as a method and system for building three dimensional objects of various shapes from metal foils, such as foils made of aluminum. While the present disclosure often uses the term “aluminum” to describe the raw material of some embodiments, it should be understood that the method and system described hereinbelow apply to any metal or metallic alloys that can be used in foils.
The basic raw material for some embodiments of the present invention is a thin foil (typically 10-200 microns thick) made of two or more layers of metal or metallic alloy. The metals/metallic alloys are selected such that (1) at least one of the outer layers has a melting temperature that is significantly lower than at least one of the other layers of the foil and (2) that one of the outer layers, when melted, has the ability to wet an outer layer of an adjacent foil.
A detailed description of the drawings is as follows:
In one implementation of the embodiment the two layers are supplied at least partially fused into each other such as a clad metal sheet as available from Alcoa under catalog number Alloy QQ-A-250/13, where a 7075 type aluminum alloy core is clad on both sides by 7072 type aluminum alloy. This type of sheet is conventional.
Attention is now called to
One method of removing excess layer material is etching using a chemical, such as sodium hydroxide, that dissolves the aluminum. The surface area of the unjoined material is much larger than the surface area of the joined body material, and the etching rate is dependent upon the contact surface between the etchant and the material. As the un-joined layers are not fused to each other, fluid can penetrate using capillary forces in between the layers until it reaches the bulk object where it slows down. By controlling the etching time, the user of this embodiment can cause all of the unjoined material to dissolve while the joined body preserves its shape and is only slightly etched, and the slight amount of etching may be the amount needed to smooth the “stair-like” surface resulting from the manufacturing process.
Another method of removing excess material is electrochemically dissolving the aluminum using electric current within an electrolyte bath. The electrolytic process works on the surface of the material and the surface area of the unjoined layers is much larger than that of the bulk material.
The shell is preferably built so that at least 2 intersections of the etchant tunnels 181 with the side walls and top of the shell are left open as cylindrical holes in the shell, preferably in the bottom of the shell. These two or more holes serve as input (180) and output (182) channels for the etchant to be pumped into and out of the shell.
The layout of the tunnels within the shell is preferably designed as a manifold, causing the etchant to split upon entrance into the input port of the shell (180) to a plurality of sub-tunnels that eventually converge back to a single tunnel coming to the out-port 182.
Preferably, the machine has the etchant flowing mechanism (container, pump, tubing) built into the machine and directed to the in-port 180 and the out-port 182, so that upon termination of the building process, the etchant can be pumped into the shell without a need to move and handle the work piece.
Alternatively, as shown in
The shell is built with a relatively thick wall of typically 5 mm, and has a weakened strip region (labeled 178 in
The step of ablation (
In all embodiments of this invention, a new layer is selectively joined to the previous layer, where the selectivity is created by enabling or disabling the wetting of one layer to another. Two layers will be joined to each other only in areas where a melting layer comes in contact under pressure with a structural or a melting layer in the absence of masking between them.
The mask can be selectively generated during the process. Alternatively, the mask can be pre-fabricated in the raw material and selectively removed during the manufacturing processes.
The mask can be generated during the process by causing a local chemical reaction between the foil material and its surrounding gases. For example, an aluminum foil such as the material of a structural layer or the surface of a melting layer, which is initially free of surface oxides, can be selectively oxidized by heating with a laser beam in the presence of oxygen. While oxide-free aluminum surface can generally be wetted by melted aluminum alloy such as 12% silicon aluminum alloy, an oxidized surface of the same aluminum has significantly lower ability to be wetted under the same conditions.
A pre-fabricated mask can be selectively removed during the process by causing local ablation of the mask using a suitable (typically pulsed) laser beam. A typical pre-fabricated mask can be created by anodizing the surface of an aluminum foil, or by coating with TiN (Titanium Nitride) compound.
The object built in this process is a solid body of material, typically aluminum, that is made of sheets of material joined to each other.
The joining is done by heating the top layer beyond the melting temperature of its melting layers, and compressing it onto the previous layer.
The joining can also be done placing the whole stack of layers, after the masking layers have been processed, under pressure and heat that will join the whole object as one body.
The geometry of the built object is obtained by causing the layer to join onto each other only in areas that are to become a part of the object.
The selective joining is obtained by maintaining at least one patterned masking layer between each pair of layers while heating and compressing.
The masking layers are either selectively generated during building, or are selectively removed from a pre-fabricated mask during building.
The selective masking can be done by heating and oxidizing the layer using a laser beam, and the selective mask removal can be done by heating and ablating a pre-fabricated mask using a laser beam.
The joining of the layers can be done layer by layer, or can be done in bulk after the layers have been stacked and their masking layers prepared.
Following the joining step, the excessive material has to be removed. One method of removing the excess material is by etching it away, using the fact that the excessive material is made of separate layers while the object is made of a joined material.
An alternative method of selectively joining metal sheets is to use a laser beam to selectively remove the melting layer by ablation. In the absence of the melting layer, no joining would occur when the material is compressed and heated.
The following preferred embodiments that are described and illustrated in this application: One preferred embodiment uses a method of building three dimensional metal objects in layers, by selectively masking layers against wetting and non-selectively compressing and heating them. In this embodiment, the top layer may be joined to the previous layer before being covered by a next layer. Alternatively, all the layers may be masked separately and joined as a single body. As another option, the masking is done by an additive process where material is added to the layer. As still a further option, the masking is done by a subtractive process where material is removed from the layer.
The above method may include a step of applying etchant to the built volume after all layers are selectively joined. The method may further include introducing holes in each layer so that the holes combine to inter-layer tunnels. The method may still further include pumping etchant through said tunnels. The method even further include building a joined shell around the models. The method may also include having at least some of the tunnels reach out through the sides of the shell. The method may include further the holes being at the bottom of the shell and the system being configured to pump etchant into and out of the model through the holes. The method may yet further include the tunnels reaching out through the sides of the shell and configured to accept a sealing insert. The method may even further include the inserts being interconnected with flexible tubing. The method may also include having a band of a significantly reduced wall thickness essentially close to the top of the shell.
Another preferred embodiment uses a multilayered metal foil comprising at least a structural layer, at least on melting layer, and at least one masking layer. The metal foil may have one structural layer and two melting layers on both of its sides. The metal foil may have one structural layer, one melting layer on one of its sides, and a masking layer on its other side. The metal foil may have at least one melting layer, at least one structural layer on one of its sides, and a masking layer on its other side. The metal foil may have one structural layer, one melting layer on one of its sides, and a masking layer on its other side. The metal foil may have one structural layer, two melting layers on both sides, and a masking layer on one of the two melting layers. The metal foil may have one structural layer, two melting layers on both sides and a masking layer on each of the two melting layers.
Another preferred embodiment is a three dimensional printing system using the above material as raw material.
Another preferred embodiment uses the method discussed above and adds the step of selective perforating the parts of the foil that do not belong to the built object prior to its application. The method could add the step of selectively ablating a pre-fabricated melting layer and non-selectively compressing and heating the treated layers.
Another preferred embodiment uses a model building machine that has means to place layers of sheet metal on top of each other, means to selectively coat each layer with wetting preventing material, means to heat and compress the layers to a level of brazing, and means to cause etchant fluid to flow between the non-wetted areas of the layers and dissolve them.
Having thus described exemplary embodiments of the invention, it will be apparent that various alterations, modifications, and improvements will readily occur to those skilled in the art. Alternations, modifications, and improvements of the disclosed invention, though not expressly described above, are nonetheless intended and implied to be within spirit and scope of the invention. Accordingly, the foregoing discussion is intended to be illustrative only; the invention is limited and defined only by the following claims and equivalents thereto.
This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 62/193,087, filed Jul. 16, 2015, which is hereby incorporated by reference in its entirety.
Number | Date | Country | |
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62193087 | Jul 2015 | US |