Patent Grant
10189086
The present invention relates to a method and an apparatus for manufacturing a three-dimensional article with porosity.
Additive manufacturing is a method for forming three-dimensional articles through successive fusion of chosen parts of powder layers applied to a worktable.
Such an apparatus may comprise a work table on which said three-dimensional article is to be formed, a powder dispenser, arranged to lay down a thin layer of powder on the work table for the formation of a powder bed, an energy beam source for delivering energy to the powder whereby fusion of the powder takes place, elements for control of the energy given off by the energy beam source over said powder bed for the formation of a cross section of said three-dimensional article through fusion of parts of said powder bed, and a controlling computer, in which information is stored concerning consecutive cross sections of the three-dimensional article. A three-dimensional article is formed through consecutive fusions of consecutively formed cross sections of powder layers, successively laid down by the powder dispenser.
Three-dimensional network structures may be used in body implant articles such as bone replacements. In recent years artificial bone implants may have a solid core with a surface layer having a network structure. Said network structure improves the bone/tissue in-growth capability and thereby strengthens the connection between the human bone and the artificial bone implant. The material used in said network structures may for instance be Titanium, which is a well proven material to be compatible with the human body tissue. Titanium is a relatively light and strong material. An implant may efficiently aggregate to the human body if the network structure is as human like as possible.
One way of enhancing the effectiveness of an orthopedic implant may be to randomize the porous structure of an implant so it better simulates trabecular structures in which it is implanted. One way of doing so is disclosed in WO 2011/060312 relating to a controlled randomized porous structures and methods for making the same. In said document it is disclosed a method for randomizing the network structure in order to meet the above mentioned needs. WO 2011/060312 discloses a method for seamlessly joining randomized units with improved porosity without sacrificing the strength of the final implant article.
One problem with said solution is that the manufacturing process is relatively CPU and memory consuming. Another problem with said solution is that there is some degree of periodicity in the porosity of the final article which may cause mechanical strength limitations.
An object of the invention is to provide a method for an additive manufacturing process for manufacturing three dimensional articles with improved randomized porosity while minimizing the CPU and memory usage.
The above mentioned object is achieved by the features in the method according to claim 1.
In a first aspect of the invention it is provided a method for manufacturing a porous three-dimensional article. Said method comprising the steps of creating a model of a non-porous three-dimensional article comprising a predetermined number of two-dimensional layers with a predetermined thickness, creating a model of a porous structure comprising the steps of:
An advantage of the present invention is that a final porous three-dimensional article can be manufactured which has a porous structure which is randomized in every direction, i.e., the porosity lacks periodicity meaning that the mechanical strength of the porosity is equal in all directions.
In another example embodiment said randomized pattern is defined by moving a predetermined number of nodes in a regular pattern of tetrahedrons, cubes or dodecahedrons a randomized distance, which distance is less than a predetermined value and in a randomized direction.
In an example embodiment said predetermined number of nodes is all nodes.
In still another example embodiment said randomized pattern is defined by the steps of:
In yet another example embodiment said randomized pattern is defined by the steps of:
An advantage with these embodiments is that the randomized patterns are relatively quickly to produce with a relatively small amount of computer power.
In another example embodiment of the present invention said manufacturing step comprising the steps of:
An advantage with this embodiment is that the model and manufacturing process are connected to each other resulting in a more precisely manufactured three-dimensional articles. In an example embodiment there may not be an exact correspondence between the thickness of the model layer and the thickness of the powder layer. There might be a scaling factor between the model layer and powder layer depending inter alia on the dimension of the powder particles and/or the type of powder used.
In another aspect of the present invention it is provided an apparatus for manufacturing a three-dimensional article with porosity comprising:
An advantage of the present inventive apparatus is that a final porous three-dimensional article can be manufactured which has a porous structure which is randomized in every direction, i.e., the porousity lacks periodicity meaning that the mechanical strength of the porousity is equal in all directions.
The invention will be further described in the following, in a non-limiting way with reference to the accompanying drawings. Same characters of reference are employed to indicate corresponding similar parts throughout the several figures of the drawings:
To facilitate the understanding of this invention, a number of terms are defined below. Terms defined herein have meanings as commonly understood by a person of ordinary skill in the areas relevant to the present invention. Terms such as “a”, “an” and “the” are not intended to refer to only a singular entity, but include the general class of which a specific example may be used for illustration. The terminology herein is used to describe specific embodiments of the invention, but their usage does not delimit the invention, except as outlined in the claims.
The term “three-dimensional structures” and the like as used herein refer generally to intended or actually fabricated three-dimensional configurations (e.g. of structural material or materials) that are intended to be used for a particular purpose. Such structures, etc. may, for example, be designed with the aid of a three-dimensional CAD system.
The term “electron beam” as used herein in various embodiments refers to any charged particle beam. The sources of charged particle beam can include an electron gun, a linear accelerator and so on.
Said apparatus 21 comprising an electron beam gun 6; deflection coils 7; two powder hoppers 4, 14; a build platform 2; a build tank 10; a powder distributor 28; a powder bed 5; and a vacuum chamber 20.
The vacuum chamber 20 is capable of maintaining a vacuum environment by means of a vacuum system, which system may comprise a turbomolecular pump, a scroll pump, an ion pump and one or more valves which are well known to a skilled person in the art and therefore need no further explanation in this context. The vacuum system is controlled by a control unit 8.
The electron beam gun 6 is generating an electron beam which is used for melting or fusing together powder material provided on the build platform 2. At least a portion of the electron beam gun 6 may be provided in the vacuum chamber 20. The control unit 8 may be used for controlling and managing the electron beam emitted from the electron beam gun 6. At least one focusing coil (not shown), at least one deflection coil 7 and an electron beam power supply (not shown) may be electrically connected to said control unit 8. In an example embodiment of the invention said electron beam gun 6 generates a focusable electron beam with an accelerating voltage of about 15-60 kV and with a beam power in the range of 3-10 Kw. The pressure in the vacuum chamber may be 10−3 mBar or lower when building the three-dimensional article by fusing the powder layer by layer with the energy beam.
The powder hoppers 4, 14 comprise the powder material to be provided on the build platform 2 in the build tank 10. The powder material may for instance be pure metals or metal alloys such as titanium, titanium alloys, aluminum, aluminum alloys, stainless steel, Co—Cr—W alloy, etc.
The powder distributor 28 is arranged to lay down a thin layer of the powder material on the build platform 2. During a work cycle the build platform 2 will be lowered successively in relation to the ray gun after each added layer of powder material. In order to make this movement possible, the build platform 2 is in one embodiment of the invention arranged movably in vertical direction, i.e., in the direction indicated by arrow P. This means that the build platform 2 starts in an initial position, in which a first powder material layer of necessary thickness has been laid down. Means for lowering the build platform 2 may for instance be through a servo engine equipped with a gear, adjusting screws etc.
An energy beam may be directed over said build platform 2 causing said first powder layer to fuse in selected locations to form a first cross section of said three-dimensional article. The energy beam may be an electron beam or a particle beam. The beam is directed over said build platform 2 from instructions given by the control unit 8. In the control unit 8 instructions for how to control the beam gun for each layer of the three-dimensional article is stored.
After a first layer is finished, i.e., the fusion of powder material for making a first layer of the three-dimensional article, a second powder layer is provided on said build platform 2. The second powder layer is preferably distributed according to the same manner as the previous layer. However, there might be alternative methods in the same additive manufacturing machine for distributing powder onto the work table. For instance, a first layer may be provided by means of a first powder distributor 28, a second layer may be provided by another powder distributor. The design of the powder distributor is automatically changed according to instructions from the control unit 8. A powder distributor 28 in the form of a single rake system, i.e., where one rake is catching powder fallen down from both a left powder hopper 4 and a right powder hopper 14, the rake as such can change design.
After having distributed the second powder layer on the build platform 2, the energy beam is directed over said work table causing said second powder layer to fuse in selected locations to form a second cross section of said three-dimensional article. Fused portions in the second layer may be bonded to fused portions of said first layer. The fused portions in the first and second layer may be melted together by melting not only the powder in the uppermost layer but also remelting at least a fraction of a thickness of a layer directly below said uppermost layer.
In the case where an electron beam is used, it is necessary to consider the charge distribution that is created in the powder as the electrons hit the powder bed 5. The invention is, at least partly, based on the realization that the charge distribution density depends on the following parameters: beam current, electron velocity (which is given by the accelerating voltage), beam scanning velocity, powder material and electrical conductivity of the powder, i.e. mainly the electrical conductivity between the powder grains. The latter is in turn a function of several parameters, such as temperature, degree of sintering and powder grain size/size distribution.
Thus, for a given powder, i.e. a powder of a certain material with a certain grain size distribution, and a given accelerating voltage, it is possible, by varying the beam current (and thus the beam power) and the beam scanning velocity, to affect the charge distribution.
By varying these parameters in a controlled way, the electrical conductivity of the powder can gradually be increased by increasing the temperature of the powder. A powder that has a high temperature obtains a considerably higher conductivity which results in a lower density of the charge distribution since the charges quickly can diffuse over a large region. This effect is enhanced if the powder is allowed to be slightly sintered during the pre-heating process. When the conductivity has become sufficiently high, the powder can be fused together, i.e. melted or fully sintered, with predetermined values of the beam current and beam scanning velocity.
In a first embodiment of a method for manufacturing a porous three-dimensional article, a model is created of a non-porous three-dimensional article comprising a predetermined number of two-dimensional layers with a predetermined thickness. This non-porous model may for instance be made in a computer aided design (CAD) tool. The two-dimensional layers in said three-dimensional article may be made by slicing said three-dimensional article by a slicing tool, for instance Magics or Infinity Slicer. The non-porous three dimensional article has an outer boundary which is the same as an outer boundary of the porous final three-dimensional article, i.e., the only difference between the porous article to be manufactured and the non-porous three dimensional article lies in the porosity. It is relatively easy to make a three-dimensional design of an article which is solid in a CAD program. However, it is more difficult to make the same three-dimensional article with a randomized porosity in the same CAD program.
In a next step a model is created of a porous structure. Said modelling comprising a first step of defining a three-dimensional space comprising a randomized pattern of nodes, wherein said nodes are connected together in a predetermined manner with struts.
In a first example embodiment said three-dimensional space is defined by providing a regular three-dimensional pattern of nodes. Said regular pattern of nodes may for instance be made of tetrahedrons, cubes or dodecahedrons, where the nodes are provided in corners and connected together in a predetermined way by struts to form regular three-dimensional structures. A distance between two nodes in the regular pattern of nodes is predetermined and can be chosen arbitrarily by an operator.
The network structure in
Each and every node 330 is thereafter moved a randomized distance, which distance is less than a predetermined value and in a randomized direction. This will destroy the regularity of the original structure. In
In a second example embodiment said three-dimensional space is defined by firstly providing a predetermined number of nodes randomly in a 3-dimensional space of a predetermined size.
Secondly a maximum number of neighbor nodes to a specific node is determined. This maximum number may be any positive integer between 1-∞.
Thirdly a number x of closest neighbors to said specific node is skipped. X may be a random positive integer number being ≥0. Being skipped should here be interpreted as ignoring those x nodes which is/are closest to a given node.
Fourthly, each of said maximum neighbor nodes, except those nodes that might have been skipped, are connected to said specific node with a strut. Step a-d is repeated for each node in the 3-dimensional space.
In a third example embodiment said three-dimensional space is defined by firstly providing a predetermined number of nodes randomly in a 3-dimensional space of a predetermined size.
Secondly said nodes are provided in a Delauney-triangulation giving a predetermined number of Delauney-tetrahedrons. In an example embodiment said tetrahedrons are provided with smallest angles connecting the nodes, i.e., the first derivative of two struts connected together via a node is continuous.
Thirdly a Voronoi diagram is provided by for each Delauny-tetrahedron connecting the centre of the circumsphere of the Delanuney-tetrahedron with the centres of the circumspheres for all the neighbors of the Delauney-tetrahedron. The method of constructing a randomized network according to this principle is well known in the art and could be studied in for instance “Randomized incremental construction of Delaunay and Voronoi diagrams” by Leonidas J. Guibas, Donald E. Knuth and Micha Sharir.
In a second step said three-dimensional space is sliced into a predetermined number of two-dimensional layers with a predetermined thickness. The two dimensional layers could be sliced at an arbitrarily plane in said three-dimensional space. The number of two-dimensional planes building up said three-dimensional space is depending on the thickness of said two dimensional planes, the smaller the thickness of said planes the larger the number of planes it takes to build the complete three-dimensional space.
In a third step one two-dimensional layer of said model of non-porous three-dimensional article is applied on one two-dimensional layer of said porous structure resulting in a porous two-dimensional layer of said article. An example embodiment of this is illustrated in
The meaning of applying one two-dimensional layer of said model of non-porous three-dimensional article on one two-dimensional layer of said porous structure resulting in a porous two-dimensional layer of said article is to use a Boolean operation resulting in deletion of the porous structure outside the model of said non porous two-dimensional layer 620 and a creation of a porous structure inside the model of said non porous two-dimensional layer 620, i.e., the two-dimensional layer of said model of non-porous three-dimensional article has become a porous two-dimensional layer of said three-dimensional article denoted by 630 in
In a fourth step said applying step is repeated for all two-dimensional layers of said article in order to create a complete porous 3-dimensional model of the article to be manufactured.
The porous three-dimensional article is manufactured by exposing fusible material to an energy source, so that a layer of fused material is corresponding to a porous two-dimensional layer of said article.
In another example embodiment a layer of powder material is provided on a build platform 2. The thickness of the powder material layer is adapted to the thickness of the predetermined thickness of the two-dimensional layer of said article. When deciding upon the thickness of the two-dimensional layers in said model, said thickness is corresponding to the thickness of the actual powder layer out of which said final three-dimensional article is to be made of.
Said powder material may be made of metal for instance titanium, titanium alloys, Co—Cr alloys, nickel based superalloys, aluminium, aluminium alloys, etc.
Said energy source may be an electron beam source, a laser source or a particle beam source.
A first derivative of at least one connection between two struts may be continuous. This is illustrated in a 2-dimensional case in
In an example embodiment of the present invention an approximated Voronoi diagram may be used instead of the above mentioned Voronoi diagram.
In an example embodiment of the present invention a randomized pattern of point may be generated inside a volume of the porous three-dimensional object to be manufactured. This may be useful if the outer shape of the manufactured three-dimensional article need not to be identical with the model of said porous three-dimensional article. Since the randomized pattern is generated inside the volume of the three-dimensional object, it is highly likely that the outer surface in said actual manufactured article is lying inside the model of said porous three-dimensional article. The reason for this is that the very few of the randomized pattern of points may be provided exactly on the boarder of said three-dimensional article.
In an example embodiment the struts which may connect the points may be a volume element, an area element or a linear element. An area element may be flat and the linear element may be a one dimensional line.
In the fusion process such lines or points are melted as lines or points or as a 2-dimensional figure around the point or line, e.g., like small circles or ovals.
In an example embodiment a linear element may be inclined with an angle α with respect to a slicing surface, where 15°≤α≤165°. In an example embodiment a linear element may be inclined with an angle α with respect to a slicing surface, where 10°≤α≤170°. If a line which may connect two points lying in two different and adjacent layers is horizontal or almost horizontal, such a line may not connect said two points in said two layers after the slicing procedure and/or the manufacturing procedure.
In still another example embodiment a maximum and minimum value of said angle α may be dependent on the thickness of the slicing layer.
In an example embodiment of the present invention it is provided a method for manufacturing a porous three-dimensional article comprising the steps of: creating a model of a non-porous three-dimensional article comprising a predetermined number of two-dimensional layers with a predetermined thickness, creating a model of a porous structure comprising the steps of: defining a three-dimensional space, larger or equal to the non-porous three-dimensional space, comprising a randomized pattern of nodes, wherein said nodes are connected together in a predetermined manner with struts. Slicing said three-dimensional space into a predetermined number of two-dimensional layers with a predetermined thickness, and if necessary applying one two-dimensional layer of said model of non-porous three-dimensional article on one two-dimensional layer of said porous structure resulting in a porous two-dimensional layer of said article. Repeating said applying step for all non-porous two-dimensional layers of said article, manufacturing the porous three-dimensional article by exposing fusible material to an energy source, so that a layer of fused material is corresponding to a porous two-dimensional layer of said article.
In still another example embodiment of the present invention said struts may either be described by volume, area or line elements or by any combination of these elements.
In still another example embodiment of the present invention said porous two-dimensional layers of said article may be described by either the 2D polygon data created from slicing the volume elements or of 2D line data created from slicing the area elements or of 2D point data created from slicing line elements or by any combination of these three sets of data.
In yet another example embodiment of the present invention said 2D line data and 2D point data in the porous two-dimensional layers of said article may be expanded to a predetermined 2D polygon data located at a predetermined position relative to the 2D line data or to the 2D point data.
The invention is not limited to the above-described embodiments and many modifications are possible within the scope of the following claims. Such modifications may, for example, involve using a different source of ray gun than the exemplified electron beam such as laser beam. Other materials than metallic powder may be used such as powder of polymers or powder of ceramics.
This application is a national stage application, filed under 35 U.S.C. § 371, of International Application No. PCT/EP2012/076025, filed Dec. 18, 2012, which claims priority to U.S. Provisional Application No. 61/580,775, filed Dec. 28, 2011, the contents of both which are hereby incorporated by reference in their entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2012/076025 | 12/18/2012 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2013/098135 | 7/4/2013 | WO | A |
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