Three-dimensional additive manufactured product and three-dimensional additive manufacturing method

Abstract

A three-dimensional additive manufactured product includes a body portion and a male screw portion integrally disposed on a surface of the body portion so as to protrude therefrom. The male screw portion includes a following side flank forming a first flank angle with respect to a vertical plane to an axis thereof. The first flank angle is not less than 45 degrees.

Claims

1. A fuel injector comprising: a three-dimensional additive manufactured product, comprising: a base portion having a base surface; a plurality of projections formed integrally with the base portion so as to protrude from the base surface and extend in an axial direction of each of the projections, the plurality of projections forming a plurality of respective fuel injection elements for injecting fuel, wherein each projection of the plurality of projections includes a male screw portion on an outer surface of the projection, the male screw portion including a following side flank forming a first flank angle with respect to a plane that is perpendicular to the axial direction; a porous plate for seeping the fuel to cool an injection surface of each of the fuel injection elements; and a plurality of nuts, each nut having a female screw portion screwed onto the male thread portion of a respective one of the fuel injection elements such that the porous plate is interposed between the plurality of nuts and the plurality of fuel injection elements, wherein the first flank angle is not less than 45 degrees.

2. The fuel injector according to claim 1, wherein the first flank angle is not more than 70 degrees.

3. The fuel injector according to claim 1, wherein the following side flank has surface roughness with arithmetic average roughness (Ra) of not more than 700 microinches.

4. The fuel injector according to claim 1, wherein the base portion forms a partition wall between a fuel chamber storing the fuel and an oxidant chamber storing oxidant used for combustion of the fuel.

5. The fuel injector according to claim 1, wherein the male screw portion of each projection of the plurality of projections includes a leading side flank forming a second flank angle with respect to the plane that is perpendicular to the axial direction, and wherein the second flank angle is smaller than the first flank angle.

6. The fuel injector according to claim 5, wherein the second flank angle is zero degrees.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a cross-sectional view showing the internal structure of a fuel injector of a liquid rocket engine for which a three-dimensional additive manufactured product is used according to at least one embodiment of the present invention.

(2) FIG. 2 is an enlarged perspective view showing a male screw portion in FIG. 1 separately from a nut.

(3) FIG. 3 is a cross-sectional view showing the cross-sectional structure of the male screw portion in FIG. 1 fitted to the nut.

(4) FIG. 4 is an explanatory view showing, in stages, a modeling process by a three-dimensional additive manufacturing method according to at least one embodiment of the present invention.

(5) FIG. 5 is a view showing another example of a three-dimensional additive manufactured product to be modeled by the three-dimensional additive manufacturing method of FIG. 4.

(6) FIG. 6 is a schematic view showing the cross-sectional shape of the male screw portion included in the conventional fuel injection element.

(7) FIG. 7 is a view showing a modified example of FIG. 6.

DETAILED DESCRIPTION

(8) Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It is intended, however, that unless particularly identified, dimensions, materials, shapes, relative positions and the like of components described in the embodiments shall be interpreted as illustrative only and not intended to limit the scope of the present invention.

(9) For instance, an expression of relative or absolute arrangement such as “in a direction”, “along a direction”, “parallel”, “orthogonal”, “centered”, “concentric” and “coaxial” shall not be construed as indicating only the arrangement in a strict literal sense, but also includes a state where the arrangement is relatively displaced by a tolerance, or by an angle or a distance whereby it is possible to achieve the same function.

(10) Further, for instance, an expression of a shape such as a rectangular shape or a cylindrical shape shall not be construed as only the geometrically strict shape, but also includes a shape with unevenness or chamfered corners within the range in which the same effect can be achieved.

(11) On the other hand, an expression such as “comprise”, “include”, “have”, “contain” and “constitute” are not intended to be exclusive of other components.

(12) FIG. 1 is a cross-sectional view showing the internal structure of a fuel injector 1 of a liquid rocket engine for which a three-dimensional additive manufactured product is used according to at least one embodiment of the present invention. Embodiments below will be described by taking, as an example, the fuel injection element 2 serving as one component used for the fuel injector 1 of the liquid rocket engine as one embodiment of the three-dimensional additive manufactured product according to the present invention. However, it goes without saying that another member may be used as an example.

(13) The liquid rocket engine includes a combustor which combusts an oxidant and fuel made from hydrogen or the like, a nozzle which generates a thrust force by expanding and accelerating a combustion gas generated by the combustor, and a propellant supply system which feeds a propellant in a tank to the combustor. The propellant supply system includes the fuel injector 1 which mixes the oxidant and the fuel accumulated in the propellant tank to inject the obtained mixture into the combustor.

(14) As shown in FIG. 1, the fuel injector 1 includes a housing 4 formed integrally with or separately from the fuel injection elements 2 each having a circular cross-section. The housing 4 defines hydrogen chambers 8 to which liquid hydrogen is supplied from the propellant tank via a hydrogen supply passage 6 and an oxygen chamber 12 to which liquid oxygen is supplied from the propellant tank via an oxygen supply passage 10. The plurality of fuel injection elements 2 are formed so as to protrude downward from a partition wall 14 arranged between the hydrogen chambers 8 and the oxygen chamber 12. On the tip side of each of the fuel injection elements 2, a face plate 18 is fixed, which partitions the hydrogen chamber 8 and a combustion chamber 16 defined in the combustor.

(15) The fuel injection elements 2 each include a body portion 20 extending along the axial direction and the male screw portion 22 formed integrally with the body portion 20 on the tip side of the body portion 20. The body portion 20 includes a liquid hydrogen post 24 and a liquid oxygen post 26. The liquid hydrogen post 24 forms a flow passage for making the hydrogen chamber 8 and the combustion chamber 16 communicate with each other, and supplying liquid hydrogen from the hydrogen chamber 8 to the combustion chamber 16. The liquid oxygen post 26 forms a flow passage for making the oxygen chamber 12 and the combustion chamber 16 communicate with each other, and supplying liquid oxygen from the oxygen chamber 12 to the combustion chamber 16. The liquid oxygen post 26 is formed so as to pass through the center of the fuel injection element 2 along the axis C. The liquid hydrogen post 24 is formed so as to communicate with the combustion chamber 16 through the periphery of the liquid oxygen post 26 from a slit 28 opened to the hydrogen chamber 8 in a side wall of the body portion 20.

(16) Moreover, the male screw portion 22 of each of the fuel injection elements 2 is arranged concentrically with the body portion 20 and extends downward from the body portion 20 along the axis C. The male screw portion 22 has a male screw structure with screw threads disposed at a predetermined pitch. The male screw portion 22 is fitted with a nut 30 having a corresponding female screw structure. The above-described face plate 18 is interposed between the nut 30 and the male screw portion 22.

(17) The face plate 18 interposed between the male screw portion 22 and the nut 30 is arranged so as to partially contact the liquid hydrogen stored in the hydrogen chamber 8. The face plate 18 is a functional member formed of a porous material and is configured to be able to cool an injection surface 32 of the fuel injection element 2 by partially transmitted (seeped) liquid hydrogen stored in the hydrogen chamber 8.

(18) FIG. 2 is an enlarged perspective view showing the male screw portion 22 in FIG. 1 separately from the nut 30. FIG. 3 is a cross-sectional view showing the cross-sectional structure of the male screw portion 22 in FIG. 1 fitted to the nut 30.

(19) The male screw portion 22 is a single-thread screw having a male screw structure with the outer diameter a, the root diameter b, the pitch p, and the effective diameter d, and has a shape corresponding to the female screw structure formed in the nut 30. The male screw portion 22 includes the leading side flank 34 facing the traveling direction when screwed into the nut 30 and the following side flank 36 on the opposite side of the leading side flank 34.

(20) As shown in FIG. 3, a first flank angle α1 and a second flank angle α2 (not shown in FIG. 3 because α2=0) are defined. The first flank angle α1 is an angle of the following side flank 36 with respect to a vertical plane P to the axis C of the male screw portion 22. The second flank angle α2 is an angle of the leading side flank 34 with respect to the vertical plane P to the axis C of the male screw portion 22. Moreover, as will be described later with reference to FIG. 4, the fuel injection element 2 is molded by additive manufacturing from the body portion 20 toward the male screw portion 22 along the vertical plane P. Thus, the overhang angle θ at the time of additive manufacturing is defined as the angle of the following side flank 36 with respect to the axis C and is equal to (90−α1) degrees.

(21) The first flank angle α1 is set to not less than 45 degrees, keeping the overhang angle θ (=90−α1) under 45 degrees. In the present embodiment, an example is shown in which the first flank angle α1 is set to 60 degrees. Therefore, the overhang angle θ is 30 degrees. Thus, surface roughness of the male screw portion 22 is kept within a practical range when formed by the 3D printer technology. According to a research by the present inventor, surface roughness of the following side flank 36 forming the overhang angle θ has arithmetic average roughness (Ra) of not more than 700 microinches.

(22) The first flank angle α1 is preferably not more than 70 degrees. It is advantageous that the overhang angle θ formed by the following side flank 36 with respect to the vertical plane P to the axis C can further be decreased as the first flank angle α1 increases. By contrast, however, durability to an axial force generated when the male screw portion 22 is engaged with the nut 30 is weakened. Considering the durability to the axial force, the first flank angle α1 is preferably not more than 70 degrees.

(23) Furthermore, the second flank angle α2 is set smaller than the first flank angle α1. Thus, it is possible to suppress the length L of the male screw portion 22 in the direction of the axis C. In the present embodiment, a case is exemplified in which the second flank angle α2 is set to zero degrees (in other words, the leading side flank 34 is formed to be the vertical plane P to the axis C). Thus, the leading side flank 36 of the male screw portion 22 is parallel to the vertical plane P to the axis C, and the length L of the male screw portion 22 along the direction of the axis C can be minimized, allowing a more compact configuration.

(24) Subsequently, a method of manufacturing the fuel injection element 2 having the above-described configuration will be described with reference to FIG. 4. FIG. 4 is an explanatory view showing, in stages, a modeling process by a three-dimensional additive manufacturing method according to at least one embodiment of the present invention.

(25) In the present embodiment, molding is started with the body portion 20 (upper side in FIGS. 2 and 3) of the fuel injection element 2 having a relatively large capacity, and then the male screw portion 22 having a relatively small capacity is molded. Molding in this order, it is possible to keep the overhang shape in the three-dimensional additive manufactured product small and to achieve high-quality molding. In (a) of FIG. 4, an intermediate state in which the body portion 20 of the fuel injection element 2 is molded halfway is shown as an initial state.

(26) As shown in (b) of FIG. 4, molding of the body portion 20 is performed through formation of a power bed 106 by laying, in layers, powder materials supplied from a recoater 104 to a modeling surface 102 on a base plate 100 serving as a base. Then, as shown in (c) of FIG. 4, the powder materials are selectively hardened by scanning on the modeling surface 102 while irradiating the power bed 106 with a beam 108 such as a light beam or an electronic beam from a beam emitting unit (not shown).

(27) The powder materials are powdery substances to be raw materials of the three-dimensional additive manufactured product. It is possible to widely adopt, for example, a metal material such as iron, copper, aluminum, or titanium, or a non-metal material such as ceramic.

(28) The base plate 100 is configured to be able to be lifted/lowered along the vertical direction. Molding of the body portion 20 is advanced by repeating a forming step of the power bed 106 shown in (b) of FIG. 4 and an irradiating step with the beam 108 shown in (c) of FIG. 4 while lifting/lowering the base plate 100.

(29) Upon completion of the body portion 20 as shown in (d) of FIG. 4, then, molding of the male screw portion 22 is performed sequentially from molding of the body portion 20. Similarly to the body portion 20, molding of the male screw portion 22 is basically performed by repeating formation of the power bed 106 and beam irradiation with respect to the modeling surface 102. As described above with reference to FIGS. 2 and 3, the male screw portion 22 has the overhang shape in the following side flank 36. Thus, in molding the male screw portion 22, formation of the power bed 106 and beam irradiation are repeated such that the first flank angle α1 is not less than 45 degrees, keeping the overhang angle θ not more than 45 degrees. Accordingly, surface roughness of the following side flank 36 has arithmetic average roughness (Ra) of not more than 700 microinches, making it possible to withstand practical use.

(30) It is preferable that durability to the axial force is sufficiently ensured by molding the male screw portion 22 such that the overhang angle θ is not more than 70 degrees, as described above. Moreover, it is preferable that the length L of the male screw portion 22 in the direction of the axis C is suppressed by molding the male screw portion 22 such that the second flank angle α2 is smaller than the first flank angle α1. Thus suppressing the length L, it is possible to shorten a molding time required for additive manufacturing, which is effective for a cost reduction. More preferably, the length L can be minimized by performing molding such that the second flank angle α2 is zero degrees.

(31) When molding of the male screw portion 22 is completed as shown in (e) of FIG. 4, the powder materials remaining around the molded fuel injection element 2 is removed, completing the fuel injection element 2 (see (f) of FIG. 4).

(32) FIG. 5 is a view showing another example of a three-dimensional additive manufactured product 110 to be modeled by the three-dimensional additive manufacturing method of FIG. 4. Similarly to the aforementioned fuel injection element 2, the male screw portions 22 of the three-dimensional additive manufactured product 110 are modeled integrally with a flange portion 112 on a body side, and in particular, the plurality of male screw portions 22 are disposed along the circumferential direction of the flange portion 112. Three-dimensional additive manufacturing is also performed on the three-dimensional additive manufactured product from the flange portion 112 on the body side toward the plurality of male screw portions 22 at the time of modeling. Each of the plurality of male screw portions 22 is modeled such that at least one of the first flank angle α1 and the second flank angle α2 has the aforementioned angular range, making it possible to suppress the overhang angle θ, as in the aforementioned embodiment.

(33) As described above, according to the present embodiment, it is possible to provide the three-dimensional additive manufactured product and the three-dimensional additive manufacturing method capable of effectively reducing the manufacturing cost while molding the male screw portion 22 integrally with the body portion 20 by using the 3D printer technology of the lamination type.

INDUSTRIAL APPLICABILITY

(34) At least one embodiment of the present invention can be utilized for a three-dimensional additive manufactured product manufacturable through additive manufacturing by irradiating laid powder with a beam such as a light beam or an electronic beam and a three-dimensional additive manufacturing method for manufacturing the three-dimensional additive manufactured product.

REFERENCE SIGNS LIST

(35) 1 Fuel injector 2 Fuel injection element 4 Housing 6 Hydrogen supply passage 8 Hydrogen chamber 10 Oxygen supply passage 12 Oxygen chamber 14 Partition wall 16 Combustion chamber 18 Face plate 20 Body portion 22 Male screw portion 24 Liquid hydrogen post 26 Liquid oxygen post 28 Slit 30 Nut 32 Injection surface 34 Leading side flank 36 Following side flank 100 Base plate 102 Modeling surface 104 Recoater 106 Powder bed 108 Beam 110 Three-dimensional additive manufactured product 112 Flange portion