CASTING INSERT AND PRODUCTION METHOD

Abstract

A casting insert includes a casting insert wall formed substantially of a liquid-phase-sintered refractory metal alloy, a cavity formed by the casting insert wall, and at least one cooling duct, which is different from the cavity and which is formed at least partly within the cavity and/or which is formed at least partly within the casting insert wall. The casting insert wall has a wall thickness which can be defined as a normal distance between a point of the casting insert wall which faces the cavity and a point on an outer surface of the casting insert wall. The wall thickness is, at least in sections, less than 25% of a diameter of the casting insert.

Claims

1-15. (canceled)

16. A casting insert, comprising: a casting insert wall having an outer surface, said casting insert wall formed at least partially from a liquid-phase-sintered refractory metal alloy; said casting insert wall forming a cavity; at least one cooling duct being different from said cavity, said at least one cooling duct being at least one of configured at least in sections within said cavity or configured at least in sections within said casting insert wall; said casting insert wall having a wall thickness, said wall thickness being definable as a normal distance between a point of said casting insert wall facing said cavity and a point on said outer surface of said casting insert wall, and said wall thickness, at least in sections, being less than 25% of a diameter of the casting insert.

17. The casting insert according to claim 16, which further comprises a support structure interconnecting said casting insert wall and said at least one cooling duct.

18. The casting insert according to claim 17, wherein said support structure is configured as at least one of discrete crosspieces or discrete ribs.

19. The casting insert according to claim 17, wherein said support structure and said casting insert wall are formed of the same material.

20. The casting insert according to claim 16, wherein said at least one cooling duct and said casting insert wall are formed of the same material.

21. The casting insert according to claim 16, wherein said at least one cooling duct has a spiral-shaped profile at least in sections.

22. The casting insert according to claim 16, wherein said at least one cooling duct has cross-sectional variations at least in sections.

23. The casting insert according to claim 16, which further comprises a filling formed of a fill material differing from a material of said casting insert wall, said cavity between said casting insert wall and said at least one cooling duct at least partially containing said filling.

24. The casting insert according to claim 23, wherein said fill material is selected from the group including copper and copper alloys.

25. The casting insert according to claim 16, wherein said casting insert wall has at least one section having characteristics of having been produced by an additive manufacturing process.

26. The casting insert according to claim 16, wherein said casting insert wall and said at least one cooling duct have characteristics of having been produced in one piece by an additive manufacturing process.

27. A method for producing a casting insert, the method comprising steps of: producing the casting insert according to claim 16 by: providing a powder of a liquid-phase-sinterable refractory metal alloy and at least one organic binder constituent; producing a green body by additively constructing at least one section of the casting insert wall from the powder treated with the at least one organic binder constituent; debindering the produced green body to obtain a brown body; sintering the brown body in an at least temporary presence of liquid phase to yield a metallic blank of the casting insert; and optionally performing finishing of the blank to obtain the casting insert.

28. The method according to claim 27, which further comprises producing at least one section of the at least one cooling duct by additive construction, simultaneously with the construction of the at least one section of the casting insert wall.

29. The method according to claim 27, which further comprises simultaneously producing a support structure interconnecting the casting insert wall and the at least one cooling duct at least in sections, by additive construction.

30. The method according to claim 27, which further comprises at least partially filling the cavity with a fill material differing from a material of the casting insert wall.

Description

[0153] Further advantages and utilities of the invention emerge from the following description of exemplary embodiments with reference to the attached figures.

[0154] In the figures:

[0155] FIG. 1: shows a casting insert according to a first exemplary embodiment;

[0156] FIG. 2: shows a casting insert according to a further exemplary embodiment;

[0157] FIG. 3: shows a casting insert according to a further exemplary embodiment;

[0158] FIG. 4: shows a casting insert according to a further exemplary embodiment;

[0159] FIG. 5a-5b: show photos of a casting insert (specimen component)

[0160] FIG. 6a-6c show schematic illustrations of a casting insert

[0161] FIG. 7a-7c show sectional illustrations of a casting insert

[0162] FIG. 8a-8c show scanning electron microscope (SEM) images of surfaces at 50-fold magnification

[0163] FIG. 9a-9c show scanning electron microscope (SEM) images of surfaces at 100-fold magnification

[0164] FIG. 10a-10c show scanning electron microscope (SEM) images of surfaces at 250-fold magnification

[0165] FIG. 1 schematically shows a casting insert in cross section according to a first exemplary embodiment.

[0166] The casting insert 1 comprises a casting insert wall 2 formed by a liquid-phase-sintered refractory metal alloy, this wall forming a kind of shell and enclosing a cavity 3. Configured within this volume circumscribed by the casting insert wall 2—the cavity 3—is a cooling duct 4. The cooling duct 4 is thus a different unit from the cavity 3.

[0167] The cooling duct 4 is a conducting device for a cooling medium. The term “cooling duct” in connection with this application designates, depending on the case, the free conduit cross section of the conducting device for the cooling medium (in the case of a course within the casting insert wall 2) or the entire physical conducting device, that is to say the cooling duct wall thereof with a wall thickness together with the conduit cross section delimited by the cooling duct wall.

[0168] The cooling duct 4 is in this exemplary embodiment configured as a tubular conducting device. Block arrows indicate an inflow direction and an outflow direction of a cooling medium. Of course, two or more cooling ducts 4 may also be configured. The at least one cooling duct 4 may protrude from the cavity 3, as illustrated in the present example, or terminate flush with an open side of the casting insert 1.

[0169] The free conduit cross section of the cooling duct 4 is formed here by a wall of the cooling duct 4, compared to exemplary embodiments in which the cooling duct 4 runs at least in sections in the casting insert wall 2. In the latter case, the free conduit cross section is configured at least partially in the casting insert wall 2.

[0170] The cooling duct 4 is in this example retained by a support structure 5 and connected via the latter to the casting insert wall 2. The support structure 5 is preferably in the form of a lattice structure comprising crosspieces and/or ribs.

[0171] The support structure 5 has the task of holding and stabilizing the cooling duct in the desired position. It is advantageous for the support structure 5 to be of open design such that the support structure 5, more precisely the network of hollow spaces formed by the support structure 5, can be fully infiltrated.

[0172] In this exemplary embodiment, the optional, preferred variant is illustrated, according to which the casting insert 1 is filled at least partially with a filling 6 of a fill material that differs from the casting insert wall material. The filling 6 consists in particular of a material having a higher thermal conductivity than that of the casting insert wall material. Of particular suitability is a filling 6 formed of copper or of a copper alloy. The filling 6 can in this case be easily produced by back-casting.

[0173] The casting insert 1 is particularly preferably monolithic, i.e. one-piece. That means that the casting insert wall 2, the cooling duct 4 and the support structure 5 materially transition into one another. The casting insert wall 2, cooling duct 4 and support structure 5 are in particular formed from the same material, the casting insert wall material, and have been produced together in an additive manufacturing process.

[0174] In particular, the casting insert 1 has been produced via the method of filament printing (fused deposition modeling or fused filament fabrication) of a feedstock filament. The method enables the production of complex component geometries with hollow spaces and undercuts. Binder-based additive manufacturing processes are particularly advantageous for liquid-phase-sinterable refractory metal alloys.

[0175] When the casting insert 1 is in use, the casting insert protrudes into a casting mold 9 (not illustrated here in more detail). Optionally, a shoulder or a flange 8 may be formed on the casting insert 1, in order to create a bearing surface, sealing surface and/or mounting possibility for the casting mold 9. Preferably, the shoulder or flange 8 has been configured from the casting insert wall material in one piece with the casting insert 1.

[0176] In a use, the casting insert 1 is exposed to a melt M at an outer surface A. A surface of the casting insert 1 thus generally represents an outer contour of a workpiece. By way of the casting insert 1, heat can be extracted from a melt M located in the casting mold 9 in an intensified fashion. By way of this, properties of a component produced in the casting mold 9 can be influenced in a positive manner. Particularly favorable is a near-net-surface-shape profile of the cooling ducts 4. As a result of a variable spacing of the cooling duct 4 from the outer surface A of the casting insert 1, a local cooling action can be influenced.

[0177] There may be provision, in a region of the casting insert 1 that protrudes far into the casting mold 9 in use, in other words in a region averted from the inlet of the cooling medium, for a spacing of the cooling duct 4 from the outer surface A to be less than in a region close to the inlet of the cooling medium.

[0178] It is also possible in a particularly elegant fashion, via the discussed additive manufacturing process, to configure cross-sectional variations in cooling ducts 4, in order thus to influence the heat transfer.

[0179] The casting insert 1 shown here is cylindrical. Any other desired shapes are also producible. The casting insert 1 has a diameter D and a wall thickness t of the casting insert wall 2. The casting insert 1 has a thin-walled configuration. In the present example, the wall thickness t is approximately 1/12 of the diameter D, i.e. around 8%.

[0180] The wall thickness t is definable as a normal distance between a point of the casting insert wall 2 facing the cavity 3 and a point on an outer surface A of the casting insert wall 2.

[0181] There is provision in accordance with the invention for the wall thickness t to be at least in sections less than 25% of a diameter D of the casting insert 1.

[0182] It is preferable for the casting insert 1 of the invention for the wall thickness t to be on average less than 25% of the diameter D. More preferably, the wall thickness t is on average less than 20%, more preferably less than 10%, of the diameter D. For evaluation of the wall thickness t, those sections of the casting insert wall 2 are considered that protrude into a casting mold in use. Sections that predominantly serve a fastening purpose, such as a shoulder 8, are not to be counted.

[0183] The thin-walled nature means that casting insert wall material, the refractory metal alloy, can be saved. Besides economic considerations, this can also be advantageous for, in the case of the variant with a filling 6, accommodating more of the fill material and disposing the latter particularly close to an outer surface A of the casting insert 1 that is exposed to the melt. A thin-walled nature can also be advantageous for the case in which the casting insert 1 is intended to exhibit, in whole or in sections, a low thermal mass. It may for example be desired for the casting insert 1 to have a minimal thermal inertia, for example in the case of short cycle times.

[0184] This may advantageously be achieved by configuring the casting insert 1 to be thin-walled and/or at least partially hollow. The phrase “at least partially hollow” means that the casting insert 1 at least in part does not contain material filling. This can be achieved advantageously and in a defined manner via the additive manufacturing process.

[0185] In the case of deviation from a cylindrical basic shape, equivalent characteristic variables to the wall thickness t and diameter D can be defined for classifying the thin-walled nature.

[0186] To define a characteristic wall thickness t, use is made of an average of wall thicknesses of the casting insert wall 2 of those regions that are actually exposed to a melt when the casting insert 1 is being used.

[0187] A characteristic diameter D can be defined by a diameter of a smallest enclosing cylinder that surrounds that section of the casting insert 1 that is actually exposed to a melt when the casting insert 1 is being used. The ratio of wall thickness t to diameter D can therefore also be specified for shapes of the casting insert 1 that deviate from a cylinder.

[0188] It should be reiterated that a thin-walled nature does not mean that the casting insert 1 needs to be hollow. It may contain a filling 6 throughout. Rather, a thin-walled nature means that the casting insert wall 2 formed from refractory metal alloy is only as thick as is required for leak-tightness and resistance to the melt in question.

[0189] FIG. 2 shows a further exemplary embodiment of a casting insert 1 in cross section. The reference signs are assigned as in FIG. 1 and are therefore not explained again.

[0190] The exemplary embodiment shown here differs, inter alia, in that the cooling duct 4 runs in sections in the casting insert wall 2.

[0191] The cooling duct 4 can as a result be guided in a particularly near-net-surface-shape manner. This measure, which is also referred to as “conformal cooling”, promotes a homogeneous removal of heat via the casting insert 1.

[0192] FIG. 3 shows a further exemplary embodiment of a casting insert 1 in cross section. Here, in contrast to the example of FIG. 2, no support structure 5 is configured and instead the cooling duct 4 is configured partially within the casting insert wall 2 and runs in sections within the cavity 3.

[0193] The cooling duct 4 here is configured in one piece with the casting insert wall 2. The optional filling 6 is also shown in this example.

[0194] FIG. 4 shows a further exemplary embodiment of a casting insert 1 in cross section. Here, the cooling duct 4 runs within the cavity 3 without support structure 5. The cooling duct 4 may also be produced separately from the casting insert wall 2.

[0195] It is conceivable to provide the cooling duct 4 for example as a pipe and to connect it to the casting insert wall 2 via suitable means and/or a filling 6. The cooling duct 4 here is thus not configured in one piece with the casting insert wall 2.

[0196] As explained further above, however, preference is given to a one-piece production of the casting insert wall 2 with the at least one cooling duct 4 via an additive manufacturing process.

[0197] FIG. 5a shows a photograph of a casting insert 1 in the form of a specimen component. The viewing direction is directed onto inlet and outlet openings of the cooling duct 4. In the interior of the casting insert 1, lattice-like support structures 5 configured in the cavity 3 can be seen, these positioning the cooling duct 4. The casting insert 1 was produced via filament printing with feedstock filaments formed from a tungsten-heavy metal alloy. The casting insert wall 2, the support structures 5 and the cooling duct 4 are accordingly of one-piece configuration.

[0198] FIG. 5b shows a photograph of the casting insert 1 of FIG. 5a, in which here a majority of the cavity 3 contains a filling 6 of a fill material that differs from the material of the casting insert wall 2. The filling 6 consists here of copper, which has been introduced into the casting insert 1 via back-casting. This variant has particularly favorable properties in terms of the achievable heat removal. In addition, the filling 6 also forms a mechanical support for the cooling ducts 4 and the thin-walled casting insert wall 2.

[0199] FIGS. 6a to 6c show perspective illustrations of a casting insert 1 in various views, in each case with semi-transparent visualization. The cooling duct 4 runs in a spiral-shaped manner, with a spacing of the cooling duct 4 from an outer surface A of the casting insert 1 decreasing as the distance from a region of an inlet for a cooling medium increases (in FIG. 6a this region corresponds to the lower edge of the image). In other words, the cooling duct runs, in a section of the casting insert 1 that during use of the casting insert protrudes further into a casting mold 9 (not illustrated here), closer to the outer surface A than in the region of the inlet for the cooling medium.

[0200] FIG. 6b shows the casting insert 1 in another viewing direction. The support structure 5 configured in the form of ribs can be seen. Also sketched is a sectional plane P, the plane normal of which runs perpendicularly to a longitudinal axis L of the casting insert 1 and which contains the longitudinal axis L.

[0201] FIG. 6c shows the casting insert 1, with a viewing direction onto that face side of the casting insert 1 that in use protrudes into a casting mold (not illustrated here). The thin-walled configuration of the casting insert wall 3 can be seen in the illustration.

[0202] FIGS. 7a to 7c show schematic longitudinal cross sections through the casting insert 1 illustrated in FIGS. 6a to 6c, which longitudinal cross sections are produced by rotating the sectional plane P about the longitudinal axis L.

[0203] In FIG. 7a the sectional plane P is positioned so as to run through the support structure 5.

[0204] In FIG. 7b, the sectional plane is positioned so as to run between support structures 5, as a result of which the cavity 3 formed by the casting insert wall can be seen.

[0205] FIG. 7c schematically shows the profile of the cooling duct 4 (no cross-sectional illustration).

[0206] FIGS. 8a-8c, 9a-9c, and 10a-10c show scanning electron microscope images of various surfaces of tungsten-heavy metal specimens. Each series is taken with the same magnification.

[0207] In the first column (FIGS. 8a, 9a, 10a), ground surfaces of tungsten-heavy metal are shown with increasing magnification. These surfaces can for example be observed in conventionally produced casting inserts.

[0208] In the second column (FIGS. 8b, 9b, 10b), surfaces of tungsten-heavy metal are illustrated with increasing magnification, produced via selective laser sintering (SLS) of feedstock granules. The surfaces are as sintered. A slightly hilly characteristic of the surface can be seen, originating from the grains of the feedstock granules.

[0209] In the third column (FIGS. 8c, 9c, 10c), surfaces of tungsten-heavy metal are illustrated with increasing magnification, produced via filament printing with feedstock filaments.

[0210] The surfaces are as sintered. A slightly wavy characteristic of the surface can be seen, originating from the deposited feedstock filaments.

[0211] FIGS. 8b, 9b, 10b and 8c, 9c, 10c thus show surfaces as can be observed on an unprocessed casting insert 1 produced in accordance with the invention.

[0212] A person skilled in the art on the basis of the surface characteristic of as-sintered surfaces obtains indications of the production method.

[0213] In particular, a conclusion regarding the production route is possible at those sections of the casting insert 1 according to the invention that have not undergone any subsequent surface processing.

[0214] FIG. 11a shows a cross section of a ground surface of a body formed from tungsten-heavy metal. The cut tungsten grains in a matrix of metallic binder phase can be seen. By way of example, cut grains are identified with block arrows.

[0215] FIG. 11b shows a cross section of an unprocessed sinter surface of a body formed from tungsten-heavy metal. Coalesced, flattened tungsten grains in a matrix of metallic binder phase can be seen.

[0216] Surfaces without cut grains as illustrated in FIG. 11b can be observed on a casting insert 1 produced according to the invention, provided that no subsequent processing is carried out.

[0217] FIG. 12 schematically shows the method sequence for producing a casting insert 1 according to the variant of filament printing with feedstock filaments.

[0218] Here, in a first step (I) metal powder—P—of a liquid-phase-sinterable refractory metal alloy is processed with a binder—Bi—and also further organic constituents to give a plastically processable feedstock F and further processed to give a feedstock filament—FF.

[0219] A feedstock filament is a thin thread, usually produced by extrusion, formed from the feedstock mass, which is usually flexible and for example can be wound onto a spool.

[0220] In a following step (II), the feedstock filament is extruded through a heatable nozzle onto a movable table. The (filament) printing process takes place layer-by-layer according to a previously generated layer model to form the green body to be produced—G—and is conducted such that the feedstock tracks applied fuse with one another.

[0221] The green body produced, of the later casting insert 1, is overscaled in the X, Y and Z direction by the shrinkage factors expected during the sintering and any necessary finishing measures.

[0222] A green body—G—of the later casting insert 1 is obtained.

[0223] In a debindering step (III), the majority of the organic binder is removed. A chemical debindering is shown here. Alternatively, thermal or catalytic debindering is also possible.

[0224] The brown body—B—thus obtained is then sintered in the at least temporary presence of liquid phase, step IV.

[0225] A metallic blank—R—of the casting insert 1 is obtained, step V.

[0226] Finishing may optionally be effected.