Model for the creation of a mold for investment casting and method for investment casting of an object

Abstract

An investment casting model for the creation of a mold for investment casting of a plurality of objects, the investment casting model being realized in solidifiable resin, and includes: a base defining a Z axis; a plurality of wire-like elements all extending from the base, the wire-like elements intersecting each other to form a plurality of simple closed curves, which form a net around the Z axis. At least two of the simple closed curves of the plurality are identical to each other and the net includes: at least a first and a second sets of simple closed curves, each set forming a net sub-structure around the Z axis, the second set being adjacent to the first set along the Z axis; a plurality of object models; and a plurality of connecting branches joining the plurality of object models to the wire-like elements forming the net.

Claims

1. An investment casting model for the creation of a mold for investment casting of a plurality of objects, the investment casting model being realized in solidifiable resin, and comprises: a base defining a Z axis; a plurality of wire-like elements all extending from the base, the wire-like elements intersecting each other to form a plurality of simple closed curves, the plurality of simple closed curves forming a net around the Z axis; wherein at least two of the simple closed curves of the plurality are identical to each other and wherein the net comprises at least a first and a second sets of simple closed curves, each set forming a net sub-structure around the Z axis, the second set being adjacent to the first set along the Z axis; a plurality of object models; and a plurality of connecting branches joining the plurality of object models to the wire-like elements forming the net.

2. The investment casting model according to claim 1, wherein each of the simple closed curves comprises a plurality of sides, each side forming an angle different from 0 and 180 with the Z axis.

3. The investment casting model according to claim 1, wherein the net defines an inner volume including the Z axis internal to the net and an outer volume external to the net, and wherein the object models extend both in the inner and outer volume.

4. The investment casting model according to claim 1, wherein the plurality of simple closed curves comprise triangles, rectangles, rhombi or a combination thereof.

5. The investment casting model according to claim 1, wherein the net has an open end opposite to the base.

6. The investment casting model according to claim 1, wherein one of the plurality wire-like elements, in its extension along the Z axis, splits in more than one wire-like element.

7. The investment casting model according to claim 1, wherein an envelope of the net comprises a portion having a constant cross section.

8. The investment casting model according to claim 1, wherein a wire-like element of the plurality of wire-like elements includes a first portion connected to the base and forming an angle with the Z axis comprised between 80 and 90.

9. The investment casting model according to claim 1, wherein all the simple closed curves of the plurality of simple closed curves are identical to each other.

10. The investment casting model according to claim 1, wherein the wire-like elements have a variable cross section.

11. The investment casting model according to claim 10, wherein the wire-like elements define a first end and a second end, the first end being connected to the base, and wherein the dimension of the cross section of the wire-like element at the first end is bigger than the dimension of the cross section at the second end.

12. The investment casting model according to claim 1, wherein the Z axis is a symmetry axis for the net.

13. A method for investment casting of a plurality of objects, the method comprising: a. forming a tri-dimensional image of the object to be cast; b. forming a tri-dimensional image of an object model using the tri-dimensional image of the object; c. forming a tri-dimensional image of a sprue structure to support a plurality of object models, the sprue structure including: i. a base defining a Z axis; ii. a plurality of wire-like elements extending from the base, the wire-like elements intersecting each other to form a plurality of simple closed curves, the plurality of simple closed curves forming a net around the Z axis; iii. wherein at least two of the simple closed curves of the plurality are identical to each other and wherein the net comprises at least a first and a second sets of simple closed curves, each set forming a net sub-structure around the Z axis, the second set being adjacent to the first set along the Z axis; d. creating a tri-dimensional image of an investment casting model including a plurality of the tri-dimensional images of the object models connected to the tri-dimensional image of the sprue structure; e. realizing the investment casting model in solidifiable resin by 3D printing using the tri-dimensional image of the investment casting model; f. forming a mold by inserting the investment casting model in a bath of a shell-forming material and hardening the shell-forming material; g. removing the solidifiable resin forming the investment casting model from the mold; h. pouring a molten substance into the mold; i. solidifying the molten substance; and j. removing the solidified substance from the mold.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The following detailed description of the preferred embodiment of the present invention will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It is understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings:

(2) FIG. 1 is a perspective view of a first embodiment of a sprue structure realized according to the present invention;

(3) FIG. 2 is a perspective view of a second embodiment of a sprue structure realized according to the present invention;

(4) FIG. 3 is a perspective view of a third embodiment of a sprue structure realized according to the present invention;

(5) FIG. 4 is a perspective view of an investment casting model comprising the third embodiment of a sprue structure of FIG. 3 and a plurality of object models realized according to the present invention;

(6) FIG. 5 is a perspective view of a fourth embodiment of a sprue structure realized according to the present invention;

(7) FIG. 6 is a perspective view of an investment casting model comprising the fourth embodiment of a sprue structure of FIG. 5 and a plurality of object models realized according to the present invention;

(8) FIG. 7 is a top view of the investment casting model of FIG. 6;

(9) FIG. 8 is a perspective view of a fifth embodiment of a sprue structure realized according to the present invention;

(10) FIG. 9 is a perspective view of an investment casting model comprising the fifth embodiment of a sprue structure of FIG. 8 and a plurality of object models realized according to the present invention;

(11) FIG. 10 is a schematic representation of the steps of the method of the invention; and

(12) FIG. 11 is a lateral view of a 3D printer for the 3D printing of the sprue structures and/or investment casting models of FIGS. 1-9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(13) With initial reference to FIG. 1, a first embodiment of a sprue structure 1 realized according to the invention is shown.

(14) The sprue structure 1 comprises a base 2, substantially cylindrically shaped, which defines a Z axis. The Z axis is the axis of the cylinder. The sprue structure 1 further includes a plurality of wire-like elements 3, all having a first end 4 and a second end 5. The first ends 4 of the wire-like elements 3 are connected to the base 2. All wire-like elements 3 are identical to each other, simply angularly positioned differently around base 2.

(15) In this embodiment of sprue structure 1, each wire-like element comprises a second portion 11 extending predominantly along the Z axis and a first portion 12 substantially perpendicular to the Z axis, or slightly tilted to orthogonality. The first portions 12 of all the wire-like elements 3 are connected to the base 2 in a stellar manner, that is, they form a star configuration. The angular distance between two second portions of nearest neighbor wire-like elements is preferably the same among all wire-like elements.

(16) The first portion 12 of each wire-like element is substantially straight and substantially perpendicular to the Z axis, or forming an angle close to 90, preferably 85. The second portion 11 is connected to the first portion 12 by means of a bend 6. The second portion 11 extends substantially parallel to the Z axis.

(17) Further, each wire-like element 3, along the second portion 11, splits in several wire-like elements at regular spacing along the Z axis. For example, every few cm, the wire-like element 3 splits in two sub wire-like elements.

(18) The wire-like element therefore splits into a continuation of the second portion (still indicated with 11 in the drawings) and into a transversal bar 13 connecting parallel second portions 11 of nearest neighbor wire-like elements. From a single second portion 11, several transversal bars 13 depart, one parallel to the other. In each wire-like element 3, the transversal bars 13 are positioned one above the other at different coordinates along the Z direction and extends all on the same side of the first portion 15. The transversal bars are substantially horizontal, that is, substantially perpendicular to the Z axis. As a convention, a wire-like element 3 bifurcates forming transversal bars 13 only on its right side. The transversal bars 3 intersect the neighboring wire-like element 3. Thus the transversal bars 13 forms a plurality of intersection with the second portion 11 of the neighboring wire-like element 3.

(19) The plurality of wire-like elements 3 thus form simple closed curves 15, which in this case are rectangles. Each rectangle is formed by two parallel transversal bars 13, belonging to the same wire-like element, and by two parallel parts of two parallel first portions 11 belonging to nearest neighbor wire-like elements.

(20) The plurality of rectangles 15 forms a net 16. The envelope of the net forms a cylindroid surface. Cross sections of the envelope of the net 16 along planes perpendicular to the Z axis defines closed curve having the form of an octagon. All octagons have substantially the same size.

(21) With now reference to FIG. 2, a second embodiment of a sprue structure 10 realized according to the invention is depicted.

(22) The sprue structure 10 comprises a base 2, substantially cylindrically shaped, which defines a Z axis, which is the axis of the cylinder. The sprue structure 10 further includes a plurality of wire-like elements 3a, all having a first end 4 and two second ends 5a, 5b (only the two second ends of a single wire-like element are depicted). The first ends 4 of the wire-like elements 3a is connected to the base 2.

(23) In this embodiment of sprue structure 10, each wire-like element comprises two second portions 11a, 11b forming the net and a first portion 12 substantially perpendicular to the Z axis, or slightly tilted to orthogonality. This first portion is identical to the first portion of the first embodiment in FIG. 1. First portion 12 and second portions 11a, 11b are connected at the bend 6. The first portions 12 of all the wire-like elements 3a are connected to the base 2 in a stellar manner, that is, they form a star configuration. The angular distance between two second portions of nearest neighbor wire-like elements is preferably the same among all wire-like elements.

(24) The first portion 12 is substantially straight and substantially perpendicular to the Z axis. The first portion at the bend 6 bifurcates in the two second portions 11a, 11b. The second portions 11a, 1 lab are slightly tilted with respect to the Z axis and have a given curvature.

(25) The two second portions 11, 11a form an angle therebetween.

(26) Each second portion 11a, 11b intersects other second portions 11a, 11b of several other wire-like elements 3a in its extension. In addition, at every intersection, one of the two second portions which intersects branches off again creating a transversal bar 13 connecting parallel second portions of nearest neighbor wire-like elements. From a single second portion 11a, 11b several transversal bars 13 depart, one parallel to the other.

(27) The sprue structure 10 includes therefore a single type of wire-like element 3a (that is, all wire-like elements are identical to each other). The wire-like element includes two second portions 11a, 11b, and a first portion 12 which connects the first portions to the base 2. From the second portions 11a, 11b, at a regular spacing, substantially perpendicularly to the Z axis, a transversal bar 13 departs. The transversal bar is substantially horizontal, that is substantially perpendicular to the Z axis.

(28) All transversal bars 13 departing from one wire-like element 3 intersect the nearest neighbor wire-like element 3. The plurality of wire-like elements thus forms simple closed curves 15a, which in this case are triangles. Each triangle 15a is formed by one transversal bar 13 and by two second portions 11a, 11b of two different wire-like elements.

(29) The plurality of triangles 15a forms a net 16a. The net forms as an envelope a cylindroid surface. Cross sections of the envelope along planes perpendicular to the Z axis defines closed curve having the form of an octagon.

(30) With now reference to FIG. 3, a third embodiment of a sprue structure 20 is depicted realized according to the invention is shown.

(31) The sprue structure 20 comprises a base 2, substantially cylindrically shaped, which defines a Z axis, which is the axis of the cylinder. The sprue structure 20 further includes a plurality of wire-like elements 3b, all having a first end 4 and a second end 5c. The first ends 4 of the wire-like elements 3b is connected to the base 2.

(32) In this embodiment of sprue structure 20, each wire-like element comprises a first portion 12 identical to first portion described with reference to FIGS. 1 and 2. Further, each wire-like element comprises a second portion 11c connected to the first portion as in the previous examples.

(33) The second portion 11c is straight and it is slightly tilted with respect to the Z axis. All wire-like elements converge with their second ends 5c to the Z axis and intersect each other forming an apex 7 of the sprue structure.

(34) Further, along the second portions 11c, two nearest neighbor wire-like elements are connected by two bars 17 forming a cross. This two bars forming a cross 17 are positioned at regular spacing along the Z axis.

(35) The two bars forming a cross can be considered as branches of the wire-like element which splits in more components.

(36) The sprue structure 20 includes therefore a single type of wire-like element 3c (that is, all wire-like elements are identical to each other). From the second portion 12 of each wire-like element, at a regular spacing, two bars 17 forming a cross depart.

(37) All bars 17 departing from one wire-like element 3c intersect the nearest neighbor wire-like element 3c. The plurality of wire-like elements thus forms simple closed curves 15c, 15d, which in this case are of two types. A first type, 15d, is a triangle formed by two bars 17 and a part of the second portion 11c of the wire-like element. The second type is a polygon, a non regular hexagon, formed by the bars 17 and two parts of the second portion of two nearest neighbor wire-like elements.

(38) The plurality of triangles and hexagons forms a net 16b. Cross sections of the surface along planes perpendicular to the Z axis defines closed curve having the form of an hexagon. The cross section of the net 16b changes.

(39) With now reference to FIG. 5, a fourth embodiment of a sprue structure 30 realized according to the invention is depicted. This embodiment is similar to the embodiment of FIG. 2.

(40) The sprue structure 30 comprises a base 2, substantially cylindrically shaped, which defines a Z axis, which is the axis of the cylinder. The sprue structure 30 further includes a plurality of wire-like elements 3a, all having a first end 4 and two second ends 5a, 5b (only the two second ends of a single wire-like element are depicted). The first ends 4 of the wire-like elements 3a is connected to the base 2.

(41) In this embodiment of sprue structure 30, each wire-like element comprises two second portions 11a, 11b forming the net and a first portion 12 substantially perpendicular to the Z axis, or slightly tilted to orthogonality. This first portion is identical to the first portion of the first embodiment in FIG. 1. First portion 12 and second portions 11a, 11b are connected at the bend 6. The first portions 12 of all the wire-like elements 3a are connected to the base 2 in a stellar manner, that is, they form a star configuration. The angular distance between two second portions of nearest neighbor wire-like elements is preferably the same among all wire-like elements.

(42) The first portion 12 is substantially straight and substantially perpendicular to the Z axis. The first portion at the bend 6 bifurcates in the two second portions 11a, 11b. The second portions 11a, flab are slightly tilted with respect to the Z axis and have a given curvature. They are similar to the second portions of wire-like elements of FIG. 2.

(43) The two second portions 11, 11a form an angle therebetween.

(44) Each second portion 11a, 11b intersects other second portions 11a, 11b of several other wire-like elements 3a in its extension.

(45) The sprue structure 30 includes therefore a single type of wire-like element 3a (that is, all wire-like elements are identical to each other). The wire-like element includes two second portions 11a, 11b, and a first portion 12 which connects the first portions to the base 2.

(46) The plurality of wire-like elements thus forms simple closed curves 15b, which in this case are rhombi. Each rhombus 15b is formed by two parts of second portions 11a, 11b of two different wire-like elements.

(47) The plurality of rhombi 15b forms a net 16c. The net forms as an envelope a cylindroid surface. Cross sections of the envelope along planes perpendicular to the Z axis defines closed curve having the form of an octagon.

(48) With now reference to FIG. 8, a fifth embodiment of a sprue structure 40 realized according to the invention is depicted.

(49) The sprue structure 40 comprises a base 2, substantially cylindrically shaped, which defines a Z axis, which is the axis of the cylinder. The sprue structure 40 further includes a plurality of wire-like elements 3c, all having a first end 4 and a second ends 5c. The first ends 4 of the wire-like elements 3c is connected to the base 2.

(50) In this embodiment of sprue structure 40, each wire-like element comprises two second portions 11d, 11e forming the net and a first portion 12 substantially perpendicular to the Z axis, or slightly tilted to orthogonality. This first portion is identical to the first portion of the first embodiment in FIG. 1. The first portions 12 of all the wire-like elements 3c are connected to the base 2 in a stellar manner, that is, they form a star configuration. The angular distance between two second portions of nearest neighbor wire-like elements is preferably the same among all wire-like elements.

(51) The first portion 12 is substantially straight and substantially perpendicular to the Z axis. The first portion at the bend 6 bifurcates in the two second portions 11d, 11e. The second portions 11d, 11e then converge again and forms closed loops 15e. Closed loops 15e one on top of the other are thus formed, the wire-like element is splitting in two and merging again at regular intervals. Two closed loops of nearest neighbor wire-like elements 3c intersect.

(52) Each second portion 11d, 11e intersects other second portions 11d, 11e of several other wire-like elements 3c in its extension.

(53) The sprue structure 40 includes therefore a single type of wire-like element 3c (that is, all wire-like elements are identical to each other). The wire-like element includes two second portions 11d, 11e, and a first portion 12 which connects the first portions to the base 2.

(54) The plurality of wire-like elements thus forms simple closed curves 15e, which in this case are loops. Each loops 15e is formed by two parts of the second portions 11d and 11e of the same wire-like element.

(55) The plurality of loops 15e forms a net 16d. The net forms as an envelope a cylindroid surface. Cross sections of the envelope along planes perpendicular to the Z axis defines closed curve having the same form.

(56) FIG. 4 shows a first embodiment of investment casting model 220 using the sprue structure 20 of the embodiment of FIG. 3. The investment casting model 220 includes a plurality of object models 200. In this case, all object models 200 are identical.

(57) Each object model 200 is connected to either bars 17 or wire-like element 3b of the sprue structure 20. The connection is made via connecting branches 80. Each connecting branch 80 includes a first end 81 fixed to the wire-like element 3b or bar 17. The connecting branch 80 further includes three second ends 81a, 81b. 81c, each connected to a different object. The whole net formed by the sprue structure 20 is thus covered by object models 200.

(58) FIGS. 6 and 7 show a second embodiment of investment casting model 230 using the sprue structure 30 of the embodiment of FIG. 5. The investment casting model 230 includes a plurality of object models 200. In this case, all object models 200 are identical.

(59) Each object model 200 is connected to second portions 11a or 11b of wire-like element 3a of the sprue structure 30. The connection is made via connecting branches 80. Connecting branches 80 are identical as in the example of FIG. 4. The whole net formed by the sprue structure 30 is thus covered by object models 200.

(60) In the top view of FIG. 7, it is clear that the object models 200 can be connected on both sides of the net formed by the sprue structure 30.

(61) FIG. 9 shows a third embodiment of investment casting model 240 using the sprue structure 40 of the embodiment of FIG. 8. The investment casting model 200 includes a plurality of object models 200. In this case, all object models 200 are identical.

(62) Each object model 200 is connected to either second portions 11d, 11e of wire-like element 3c of the sprue structure 40. The connection is made via connecting branches 80, similar to those of FIGS. 4 and 6. The whole net formed by the sprue structure 40 is thus covered by object models 200.

(63) The investment casting models of the above FIGS. 4, 6, 9 and of the sprue structures of FIGS. 1, 2, 3, 5, 8 are made according to the method of the invention shown schematically in FIG. 10.

(64) In a first step 100 of the method of the invention a file 101 is created representing the investment casting model to be realized, be it the investment casting model of any of the above figures or any other investment casting model. Therefore, the file is a digital representation of the investment casting model then realized in resin.

(65) The file 101 is, in a suitably processed manner, sent to a stereolithography machine, such as for example the machine 60 of FIG. 11.

(66) The stereolithography machine 60 comprises a cartridge 63 containing a resin solidifiable by exposure to a predefined electromagnetic radiation. The cartridge 63 is in fluid communication with a tank 62 so that the substance can slide inside the tank 62. The solithfiable resin is in liquid form, it can be more or less dense and, when inserted inside the chamber, its upper surface assumes a substantially flat shape.

(67) The solidifiable resin is preferably a photosensitive liquid polymer.

(68) The machine 60 also includes an electromagnetic source (not visible) able to emit electromagnetic radiation. The source is capable of selectively radiating a layer of solidifiable resin having a predefined thickness and disposed adjacent to a bottom of the tank 62 so as to solidify it.

(69) The source is preferably arranged below the tank 62 and is configured to direct the electromagnetic radiation towards the bottom of the tank 62 which is preferably transparent to the electromagnetic radiation emitted by the source. Therefore, the solidifiable resin is irradiated from below. The electromagnetic radiation is selected so as to solidify the resin.

(70) Preferably, if the solidifying resin is a photosensitive resin, the source comprises a laser light emitter associated with an optic (not shown) suitable for directing the light beam towards any point of the aforementioned solidifying resin layer.

(71) The stereolithographic machine 60 further comprises a platform 68 having the function of supporting the model which is formed

(72) The machine 60 further includes a first actuator 69 connected to the platform 68 adapted to move it with respect to the bottom of the tank 62 according to a modelling direction Z preferably perpendicular to the same bottom. This Z direction is shown in FIG. 11 by an arrow. Preferably, this direction is parallel to the vertical axis (Z). In particular, the platform 68 is made in such a way that a layer of the solidifiable resin adheres to it once it has solidified.

(73) Moreover, the stereolithographic machine 60 includes or is connected to a processor 66 (schematically indicated in FIG. 11) which controls the machine 60 and which includes a user interface where parameters can be entered or modified.

(74) Given the processed file 101, for example sent to the processor 66, the parameters of the stereolithographic process are determined. These parameters can be entered via a user interface or can be determined automatically or present in file 101.

(75) The parameters may be one or more of the following: parameters related to the layers. Sectioning and shrinking. The dimensions of the layers may be variable; parameters related to the path that is scanned by a laser source (in case the electromagnetic source is a laser source). These parameters include filling, delimiting, z compensation, etc.; parameters of an electromagnetic source (power, size of the laser beam, etc.).

(76) Based on the parameters, the following 3D printing steps 102 are performed for each cycle, as shown in FIG. 10.

(77) The electromagnetic source radiates the tank 62 as a function of the determined pattern by the processed file 101 obtained in step 100. The layer of the solidifiable resin is selectively irradiated in order to obtain a solidified layer, which adheres to the platform 68.

(78) Subsequently, the platform 68 is moved by the actuator 69 so as to move the solidified layers away from the bottom of the tank 62 and the cycle is repeated for the next layer.

(79) Layer after layer, in the 3D printing step 102, the investment casting model 220, 230, 240 is made by 3D printing.

(80) The invested casting model in resin is then immersed in a bath of a solidifiable material, for example plaster, in step 103. The solidifying material solidifies and incorporates the investment casting resin model.

(81) The resin forming the investment casting model is then removed in step 104. In this way a mold is formed with a cavity (not shown in the figures), in which the cavity has a geometrical conformation dictated by the geometrical conformation of the resin investment casting model 220, 230, 240 and in particular by the conformation of its external surface.

(82) In the cavity thus created, a liquid metal or other molten substance is poured, in step 105. The metal is then allowed to cool until it is solidified. The geometry of the cavity allows the liquid to reach each part of the same as well as controlled cooling with good control of the temperature gradient. Eventually, the mold can be placed in rotation to favor the reaching of each part of the cavity by the metal. A vacuum pressure can also be applied.

(83) Once the cooling is achieved, the mold is broken or otherwise removed and a metal model of the resin investment casting model is obtained, in step 106.

(84) Therefore, the metal model is further processed in step 107, such as for example the separation of the desired objects (corresponding to the resin object models) and a possible finishing thereof.