Integral ceramic core used for casting automobile turbine shell and provided with gradually-changed hollowed-out holes

Abstract

The invention discloses an integral ceramic core used for casting an automobile turbine shell and provided with gradually-changed hollowed-out holes, and relates to the technical field of investment casting, the integral ceramic core is provided with a complex cavity matched with a spiral runner in the turbine shell in shape, and at least one hollowed-out hole is formed in a thick and large area, corresponding to the air inlet end of the turbine shell, of the ceramic core; the longitudinal section of each hollow hole is circular, the outline of the transverse section is a smooth gradient curve, and the transverse size is gradually increased from the interior of the ceramic core to the outer surface; an arc-shaped supporting rib extending in the axial direction of the hollowed-out hole is arranged in the hollowed-out hole. According to the structural design, the local volume shrinkage stress of the ceramic core is effectively reduced, the cracking risk in the sintering and pouring process is avoided, and meanwhile, the demolding performance of the mold and the forming consistency of the ceramic core are improved through the curve structure; therefore, the casting stability and runner quality of turbine shell castings are improved, high preparation yield and industrial controllability are achieved, and the technical problem that an existing ceramic core is unstable in formability and crack resistance is solved.

Description

Technical Field

[0001] This invention relates to the field of investment casting technology, and in particular to an integral ceramic core with gradually hollowed-out holes for casting automotive turbine housings. Background Technology

[0002] Automotive turbochargers are widely used in internal combustion engines to improve intake efficiency. As a key component, the turbine housing is typically designed with a spiral flow channel inside to achieve efficient airflow guidance. Currently, turbine housings are mostly manufactured using investment casting, which utilizes an integral ceramic core to form a complex internal flow channel structure during the metal pouring process. Furthermore, this ceramic core must withstand the impact of high-temperature metal flow during the casting process while ensuring geometric accuracy and structural integrity.

[0003] However, due to the significant change in the flow channel cross-section from the turbine housing inlet to the exhaust end, the overall structure of the ceramic core exhibits characteristics of localized thickening and localized thinning. The ceramic core located at the inlet end typically has a prominent wall thickness, which easily leads to stress concentration during injection molding cooling and subsequent firing, resulting in cracks or even overall fracture. To address the uneven volume shrinkage and thermal stress accumulation during sintering, existing technologies mainly employ methods such as adjusting the ceramic powder ratio, adding fiber reinforcement materials, or optimizing the sintering heating / cooling curves to improve crack resistance. However, the improvement effect of these process modifications is limited, especially when there are significant differences in wall thickness within the ceramic core geometry. Even with optimized sintering curves, cracking or warping due to uneven heat flow is still difficult to avoid.

[0004] To reduce shrinkage resistance in thick areas, some technologies attempt to create hollow holes in localized areas of the ceramic core to reduce weight and enhance heat conduction; however, if the hole shape is too sharp or the structure changes too drastically, stress concentration points can easily form at the hole edges, causing cracks to initiate.

[0005] In addition, the difficulty of matching the channel design with the core mold structure increases, and the surface of the ceramic core is easily scratched during demolding, resulting in a decrease in yield. At the same time, random hole configuration often fails to take into account the mechanical properties of the ceramic core and the accuracy of the flow channel formation, which has an adverse effect on the final inner surface quality of the turbine housing.

[0006] In summary, the existing technology has at least the following technical problems: Existing ceramic cores have technical problems such as easy cracking in thick areas, uncontrollable shape and location of local hollow holes, which can easily lead to structural damage of the ceramic core, and the structure of the holes is not conducive to mold forming and demolding, affecting the dimensional accuracy of the ceramic core and the quality of the casting, and making it difficult to stabilize the formability and crack resistance. Summary of the Invention

[0007] The purpose of this invention is to provide an integral ceramic core with gradually hollowed-out holes for casting automotive turbine housings, in order to solve the technical problems of existing ceramic cores, such as easy cracking in thick structural areas, uncontrollable shape and position of local hollowed-out holes, easy damage to the ceramic core structure, unfavorable hole structure for mold forming and demolding, affecting the dimensional accuracy of the ceramic core and the quality of the casting, and difficulty in stabilizing formability and crack resistance.

[0008] The preferred technical solutions among the many technical solutions provided by this invention can produce a variety of technical effects, which are described in detail below.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution: This invention provides an integral ceramic core with a gradually decreasing hollowed-out hole for casting automotive turbine housings. The integral ceramic core is formed with a complex cavity that matches the shape of the flow channel inside the turbine housing. At least one hollowed-out hole is provided in the thick area of ​​the integral ceramic core corresponding to the air intake end of the turbine housing. The longitudinal cross-sectional shape of the hollowed-out hole is circular, and the transverse cross-sectional profile is a smooth, gradually decreasing curve. The gradually decreasing curve causes the transverse dimension of the hollowed-out hole to gradually increase from the inside of the integral ceramic core to the outer surface. Furthermore, at least one supporting rib connected to the hole wall is provided inside the hollowed-out hole. The supporting rib adopts an arc-shaped structure extending along the axial direction of the hollowed-out hole to enhance the local strength of the hollowed-out hole area and release the internal stress during the sintering process.

[0010] In one embodiment, the gradient curve is an elliptic curve, a parabola, or a spline curve.

[0011] In one embodiment, the axial direction of the cavitation hole is parallel to the expected dominant direction of the airflow into the turbine housing.

[0012] In one embodiment, there are multiple hollow holes, which are evenly distributed around the air intake end of the turbine housing within the thick area of ​​the integral ceramic core.

[0013] In one embodiment, the inner surface of the hollowed-out hole is a smooth surface to reduce stress concentration and mold release resistance.

[0014] In one embodiment, the monolithic ceramic core has a buffer layer on the outer surface near the hollowed-out holes to buffer microscopic thermal expansion; the buffer layer includes multiple micropore structures with a size of 20-80μm, and the micropores are distributed along the surface of the monolithic ceramic core and transition into the interior of the monolithic ceramic core; the porosity of the buffer layer gradually decreases from the outside to the inside, which is used to slow down the release of local thermal stress generated during sintering and casting.

[0015] A mold for forming an integral ceramic core is also provided, including an upper mold and a lower mold. After the upper mold and the lower mold are closed, a cavity matching the shape of the integral ceramic core is formed. The upper mold or the lower mold is provided with a raised core that matches the shape of the hollow hole. The raised core has a groove on its surface at a position corresponding to the support rib inside the hollow hole, so as to form the support rib during injection molding. The demolding direction of the raised core is consistent with the axial direction of the hollow hole.

[0016] A method for investment casting of an automotive turbine housing is also provided, including an integral ceramic core and a mold, comprising the following steps: S1, making the integral ceramic core: using the mold, the integral ceramic core is obtained by injection molding; S2. Integral ceramic core sintering: The integral ceramic core is degreased and sintered. S3. Making a wax model: Place the sintered monolithic ceramic core into a wax mold and inject to form a wax model covering the ceramic core; S4. Making a ceramic shell: The wax model is dipped in slurry and sprinkled with sand multiple times to form a shell and then dewaxed to obtain a ceramic shell with the integral ceramic core inside. S5. Casting to form a casting: Melt the metal and pour it into the cavity between the ceramic shell and the integral ceramic core to form a turbine shell casting. S6. Casting cleaning: Clean the turbine housing casting to remove the ceramic shell and the integral ceramic core, and obtain the turbine housing blank.

[0017] The beneficial effects of this invention are as follows: (1) Significantly reduce the risk of ceramic core cracking and improve yield: The present invention adopts a gradually changing channel structure with the transverse size increasing from the inside to the outside, similar to a trumpet-shaped hole. The hollowed-out hole avoids the right angle transition or abrupt change of the hole wall, which greatly reduces the risk of stress concentration. At the same time, the introduction of hollowed-out hole effectively reduces the material accumulation in thick areas, optimizes the volume shrinkage and heat flow conduction of ceramic core during sintering from the structural level, and significantly improves the sintering stability of ceramic core.

[0018] (2) Support ribs enhance structural strength and release internal stress: By setting arc-shaped support ribs extending along the hole axis inside the hollow hole, an "elastic reinforcement structure at the corner of the hole" is formed; the combination structure of the arc-shaped support ribs and the hollow hole can provide lateral support during the sintering and casting of the integral ceramic core. At the same time, due to its arc-shaped characteristics, it can slowly guide the release of thermal stress, which not only retains the weight reduction effect of the hollow hole, but also ensures the overall bending strength and thermal shock resistance of the ceramic core.

[0019] (3) Demolding friendly and mold life extended: The hollow holes and support ribs adopt curved transition boundaries, which allows the mold core to adopt a "zero draft angle" structure, accelerating demolding while avoiding scratching the surface of the integral ceramic core. This helps to reduce layout stress, extend the mold life, and improve the yield of injection molding.

[0020] (4) Improvement of casting flow channel quality and aerodynamic performance: The axial direction of the hollow hole is preferably consistent with the airflow direction to reduce metal flow disturbance during casting and avoid adverse effects on the final forming quality of the turbine housing flow channel; at the same time, the presence of the support rib has no significant negative impact on the final flow performance of the flow channel, taking into account both lightweight, integral ceramic core structure and casting functional performance.

[0021] In summary, this invention solves the problems of easy cracking during sintering of thick areas and demolding of hollowed-out holes in integral ceramic cores from the source of the ceramic core structure. Through innovative integration of geometric structures, it improves the structural stability, manufacturability and casting consistency of integral ceramic cores. Attached Figure Description

[0022] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the integral ceramic core structure of the present invention; Figure 2 This is a cross-sectional structural schematic diagram of the integral ceramic core of the present invention; Figure 3 This is a cross-sectional structural diagram of the integral ceramic core and raised core combination of the present invention; Figure 4 This is a top view of the integral ceramic core and raised core of the present invention placed in the mold cavity; Figure 5 This is a side view of the mold assembly structure of the upper mold, lower mold, and protruding core of the present invention; Figure 6 This is a schematic diagram of the steps of the investment casting method of the present invention.

[0024] The accompanying figure is labeled as follows: 1. Integral ceramic core; 2. Hollowing out holes; 3. Supporting reinforcement; 4. Buffer layer; 5. Mold; 51. Upper mold; 52. Lower mold; 53. Cavity; 54. Protruding core; 55. Groove; 6. The intake end of the turbine housing. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0026] The specific implementation provides an integral ceramic core with gradually changing hollowed-out holes for casting automotive turbine housings. This integral ceramic core has a complex cavity that matches the shape of the spiral flow channel inside the turbine housing, and at least one hollowed-out hole is provided in the thick area of ​​the ceramic core corresponding to the turbine housing's air intake end. The longitudinal cross-section of the hollowed-out hole is circular, and the transverse cross-section profile is a smooth, gradually changing curve, with the transverse dimension gradually increasing from the inside of the ceramic core to the outer surface. Furthermore, an arc-shaped support rib extending axially along the hollowed-out hole is provided inside the hole. This structural design effectively reduces the local volume shrinkage stress of the ceramic core, avoids the risk of cracking during sintering and casting, and improves the mold release performance and consistency of the ceramic core forming through the curved structure. This improves the casting stability and flow channel quality of the turbine housing casting, resulting in a high production yield and industrial controllability. It effectively solves the technical problems of existing ceramic cores, such as easy cracking in thick structural areas, uncontrollable shape and position of local hollowed-out holes leading to structural damage, and the structure of the holes being unfavorable for mold forming and release, affecting the dimensional accuracy of the ceramic core and the quality of the casting, and making it difficult to stabilize formability and crack resistance.

[0027] The first implementation of the monolithic ceramic core, for example Figures 1 to 2 As shown, the integral ceramic core 1 is formed with a complex cavity that matches the shape of the flow channel inside the turbine housing; at least one hollow hole 2 is provided in the thick area of ​​the integral ceramic core 1 corresponding to the air inlet 6 of the turbine housing; the longitudinal cross-sectional shape of the hollow hole 2 is circular, and the transverse cross-sectional profile is a smooth gradient curve, which makes the transverse dimension of the hollow hole 2 gradually increase from the inside of the integral ceramic core 1 to the outer surface; and at least one support rib 3 connected to the hole wall is provided inside the hollow hole 2. The support rib 3 adopts an arc-shaped structure that extends along the axial direction of the hollow hole 2 to enhance the local strength of the hollow hole 2 area and release the internal stress during the sintering process.

[0028] Specifically, the integral ceramic core 1 for casting automotive turbine housings proposed in this invention achieves both structural optimization and thermodynamic stress relief by setting hollowed-out holes 2 with gradually changing cross-sectional shapes in the thick area of ​​the turbine housing intake end, and further setting axially extending arc-shaped support ribs 3 inside the holes; it has several technical advantages: Significantly reducing the risk of ceramic core cracking and improving yield: This invention adopts a gradually increasing channel structure with transverse dimensions from the inside to the outside. The hollow holes 2 formed by the funnel-shaped holes avoid right-angle transitions or abrupt changes in the hole walls, greatly reducing the risk of stress concentration. At the same time, the introduction of hollow holes 2 effectively reduces material accumulation in thick areas, optimizes the volume shrinkage and heat flow conduction of the ceramic core during sintering from a structural perspective, and significantly improves the sintering stability of the ceramic core.

[0029] Support rib 3 enhances structural strength and releases internal stress: By setting an arc-shaped support rib 3 extending along the hole axis inside the hollow hole 2, an "elastic reinforcement structure at the hole corner" is formed; the combination structure of the arc-shaped support rib 3 and the hollow hole 2 can provide lateral support during the sintering and casting process of the integral ceramic core 1. At the same time, due to its arc-shaped characteristics, it can slowly guide the release of thermal stress, which not only retains the weight reduction effect of the hollow hole 2, but also ensures the overall bending strength and thermal shock resistance of the ceramic core.

[0030] Demolding friendly and mold life extended: The hollow hole 2 and the support rib 3 both adopt curved transition boundaries, which allows the mold 5 to adopt a "zero draft angle" structure for the corresponding core, which accelerates demolding and avoids scratching the surface of the integral ceramic core 1. This helps to reduce layout stress, extend the service life of mold 5, and improve the yield of injection molding.

[0031] Improved casting flow channel quality and aerodynamic performance: The axial direction of the hollow hole 2 is preferably aligned with the airflow direction to reduce metal flow disturbance during casting and avoid adverse effects on the final forming quality of the turbine housing flow channel; at the same time, the presence of the support rib 3 has no significant negative impact on the final flow performance of the flow channel, taking into account both lightweight, integral ceramic core structure and casting functional performance.

[0032] In summary, this invention solves the problems of easy cracking during sintering of the thick area of ​​the integral ceramic core 1 and demolding of the hollow hole 2 from the source of the ceramic core structure. Through the innovative integration of geometric structure, it improves the structural stability, manufacturability and casting consistency of the integral ceramic core.

[0033] As one alternative implementation method: Regarding the specific type of gradient curve for the transverse cross-sectional profile of the aforementioned hollow hole 2, the gradient curve can be an elliptical curve, a parabola, or a spline curve.

[0034] When applied, a gradient curve composed of elliptic curves, parabolic curves, or spline curves is used as the transverse cross-sectional profile of the hollow hole 2. This facilitates the creation of a smooth, edge-free boundary shape within the channel structure, making demolding easier. The geometric characteristics of this type of curve ensure that the hole wall thickness decreases from the inside to the outside, significantly reducing local stress concentration during the sintering and cooling stages at the hole. Simultaneously, the curve shape matches the arc-shaped structure formed by the support ribs 3, allowing the support ribs 3 to extend smoothly through the channel, forming a stable elastic stress transmission path. This contributes to the uniform filling of the molten metal in the flow channel during the investment casting stage and the gradual release of pouring pressure, thereby achieving a high-strength, high-precision ceramic core design.

[0035] To further enhance the structural optimization effect, the gradient curve can be implemented using a free curve generated based on Bézier curves or hyperelliptic functions, allowing for differentiated orifice design for different flow channel cross-sections with varying pressure peak regions.

[0036] Regarding the extension direction of the aforementioned hollow hole 2, this embodiment is, for example... Figure 1 , Figure 4 and Figure 5 As shown, the axial direction of the cavitation hole 2 is parallel to the expected dominant direction of the airflow in the turbine housing.

[0037] When applied, the parallel arrangement of the axial direction of the hollow hole 2 with the dominant direction of the airflow in the turbine housing ensures a more uniform stress distribution in the integral ceramic core 1 and maintains the continuity and smoothness of the hollow hole 2. This axially consistent geometric structure, in conjunction with the complex internal cavity structure of the turbine housing formed by the outer surface of the integral ceramic core 1, can significantly reduce the risk of unstable eddies during casting. At the same time, this directional arrangement facilitates the alignment of the upper mold 51, lower mold 52 and other cores of the mold 5, reduces the effect of shear force during demolding, improves the molding success rate of the integral ceramic core 1 and extends the service life of the mold 5.

[0038] Regarding the surface structure of the aforementioned hollow hole 2, this embodiment is, for example... Figure 1 , Figure 4 and Figure 5 As shown, the inner surface of the hollow hole 2 is a smooth surface to reduce stress concentration and demolding resistance of the mold 5.

[0039] When applied, the inner surface of the hollow hole 2 is designed as a smooth surface, which helps to prevent the formation of stress concentration points. Especially during the sintering stage, the smooth surface avoids sharp geometric abrupt changes that could lead to crack initiation, thus improving the overall structural integrity of the monolithic ceramic core 1. Simultaneously, during injection molding, this smooth surface also reduces the frictional resistance between the protruding cores 54 embedded in the hollow hole 2, making the relative sliding process of the protruding cores 54 more stable during demolding, which is beneficial for improving the molding consistency and lifespan of the ceramic core.

[0040] A boron nitride isolation layer or a zirconium oxide film nanocoating is applied to the inner wall of the ceramic core to further improve the smoothness (Ra < 0.8 μm) and film formation enhancement of the inner surface of the hollow hole 2, thereby improving the demolding and anti-fouling ability of the ceramic core.

[0041] The second embodiment of the integral ceramic core differs from the first embodiment in that there are multiple hollow holes 2, which are evenly distributed around the axial direction of the air intake end 6 of the turbine housing within the thick area of ​​the integral ceramic core 1.

[0042] When applied, when there are multiple hollow holes 2, they can be evenly distributed or axially distributed around the turbine housing air inlet end to form a multi-point local weight reduction and stress relief mechanism, effectively avoiding excessive thermal stress or demolding pressure on a single hole position; the combined layout of multiple holes forms a mesh support structure for thick areas, which is conducive to improving the overall bending rigidity of the ceramic core. At the same time, with the setting of support ribs 3, uniform thermal coupling support is achieved, improving the synchronous cooling performance of thick and thin areas during sintering, avoiding local warping, and improving the forming accuracy of the integral ceramic core 1.

[0043] The third implementation of the monolithic ceramic core, for example Figure 2 and Figure 3 As shown, the difference between this embodiment and the first embodiment is that the integral ceramic core 1 has a buffer layer 4 on the outer surface near the hollow hole 2 to buffer microscopic thermal expansion; the buffer layer 4 includes multiple micropore structures with a size of 20-80μm, and the micropores are distributed along the surface of the integral ceramic core 1 and transition into the interior of the integral ceramic core 1; the porosity of the buffer layer 4 gradually decreases from the outside to the inside, which is used to slow down the release of local thermal stress generated during sintering and casting.

[0044] In application, a microporous buffer layer 4 is set on the outer surface of the integral ceramic core 1 near the hollow hole 2. The buffer layer 4 is composed of interconnected micropores of 20–80 μm, and the porosity gradually decreases from the outside to the inside. During sintering and molten casting, an "elastic pad" is simulated. The stress gradient is formed by the difference in pore density, so that the outer ceramic structure can absorb the shrinkage difference by slight deformation and avoid cracking.

[0045] Meanwhile, the density of the buffer layer 4 increases layer by layer, which, together with the support rib 3 structure of the hollow hole 2, is conducive to forming a continuous stress transition from surface micro-deformation to internal stable structure, which helps to significantly improve the overall thermal strain resistance and structural retention during casting.

[0046] Based on the above embodiments of the monolithic ceramic core, a mold for forming the monolithic ceramic core 1 is provided, such as... Figure 2 and Figure 5As shown, it includes an upper mold 51 and a lower mold 52. After the upper mold 51 and the lower mold 52 are closed, a cavity 53 is formed that matches the shape of the integral ceramic core 1. The upper mold 51 or the lower mold 52 is provided with a raised core 54 that matches the shape of the hollow hole 2. The raised core 54 has a groove 55 on its surface corresponding to the support rib 3 inside the hollow hole 2, so as to form the support rib 3 during the injection molding process. The demolding direction of the raised core 54 is consistent with the axial direction of the hollow hole 2.

[0047] In order to ensure that the raised core 54 can be smoothly demolded after the integral ceramic core 1 is formed, and to avoid being stuck by the support rib 3, the support rib 3 extends to the bottom of the hollow hole 2, and the corresponding matching groove 55 also extends to the end of the raised core 54 on the surface of the raised core 54.

[0048] When applied, since the thick area of ​​the integral ceramic core 1 has a gradually hollowed-out hole 2 structure with supporting ribs 3, a raised core 54 that precisely matches the shape of the hollowed-out hole 2 is used in the mold 5. At the same time, a groove 55 that perfectly matches the curve shape is opened at the corresponding position of the supporting rib 3 of the raised core 54. Thus, during the injection molding process, the clay is locally deformed and filled in the mold cavity at a predetermined position to form an arc-shaped supporting rib 3.

[0049] The geometric relationship between the support rib 3 and the hollow hole 2 is closely corresponding. Within the integral ceramic core 1, it not only supports the structure but also facilitates the dissipation of sintering thermal stress. By aligning the demolding direction of the raised core 54 with the axis of the hollow hole 2, structural damage or hole wall deformation caused by the dragging of the mold 5 is effectively avoided, fundamentally improving the geometric consistency of the ceramic core and the service life of the mold 5.

[0050] The raised core 54 is made of wear-resistant high-temperature steel or ceramic composite material. The outer surface of the core can be coated with a boron nitride or other isolation coating to further reduce clay adhesion and improve demolding quality. The groove 55 is realized by electrical discharge machining or five-axis CNC precision carving process according to the structural complexity of the support rib 3.

[0051] Based on the above embodiments of the integral ceramic core and the mold, a method for investment casting of an automotive turbine housing is provided, including the following steps S1 to S4 performed sequentially, as follows: Figure 6 As shown: S1, Making the integral ceramic core 1: Using mold 5, the integral ceramic core 1 is made by injection molding; S2, Sintering of integral ceramic core 1: Degreasing and sintering treatment is performed on integral ceramic core 1; S3. Making a wax model: Place the sintered monolithic ceramic core 1 into the wax mold 5 and inject to form a wax model covering the ceramic core. S4. Making ceramic shell: The wax model is dipped in slurry and sprinkled with sand multiple times to form a shell and then dewaxed to obtain a ceramic shell with an internal integral ceramic core 1. S5. Casting to form a casting: Melt the metal and pour it into the cavity 53 between the ceramic shell and the integral ceramic core 1 to form a turbine shell casting. S6. Casting cleaning: Clean the turbine housing casting, remove the ceramic shell and integral ceramic core 1, and obtain the turbine housing blank.

[0052] When applied, the use of the gradient hollowed-out holes 2 of the integral ceramic core 1 and the internal support ribs 3 structure can effectively balance the volume shrinkage difference during the sintering stage and improve the resistance to residual stress at the overlapping parts.

[0053] Meanwhile, because the channels of the hollow hole 2 form a volume-thinning structure in the thick area of ​​the integral ceramic core 1, the local heat conduction resistance is reduced, making the temperature gradient during the solidification process of the casting more controllable and avoiding local thermal shock damage to the ceramic core caused by the molten metal during pouring.

[0054] By applying the structure of integral ceramic core 1, in practical applications, the maximum wall thickness of the turbine housing ceramic core of a certain type of diesel engine reaches 50mm at the air inlet end of the turbine housing, while the sintering cracking rate of using traditional ceramic core structures exceeds 40%.

[0055] After applying the integral ceramic core 1 structure of the present invention, three axially distributed hollow holes 2 are designed in the thick area of ​​the air inlet of the turbine housing; the maximum diameter of a single hollow hole 2 is 10mm (circular cross section), the depth is 35mm, and the lateral contour adopts an elliptical gradient.

[0056] Results: The success rate of injection molding of the integral ceramic core 1 for this type of diesel engine turbine reached over 99%. After sintering, the cracking rate of the integral ceramic core 1 was reduced to about 2%. The turbine housing cast using the integral ceramic core 1 was inspected by sectioning, and the surface of the inner flow channel was smooth and flat, with no casting defects caused by the ceramic core structure. This proves that the integral ceramic core 1 has stable formability and crack resistance, thereby improving the casting quality of the turbine housing casting.

[0057] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described.

Claims

1. A monolithic ceramic core for casting a turbine shell with a tapered hollowing hole, the monolithic ceramic core is shaped with a complex cavity matching the shape of the turbine shell inner flow passage, characterized in that, at least one hollowing hole is provided in the thick region of the monolithic ceramic core corresponding to the turbine shell air inlet end; the longitudinal cross-sectional shape of the hollowing hole is circular, and the transverse cross-sectional profile is a smooth tapered curve, the tapered curve is such that the transverse dimension of the hollowing hole gradually increases from the inside of the monolithic ceramic core to the outer surface direction; and at least one support rib connected to the hole wall is provided inside the hollowing hole, the support rib adopts an arc-shaped structure extending along the axial direction of the hollowing hole to enhance the local strength of the hollowing hole region and release the internal stress during sintering.

2. The monolithic ceramic core according to claim 1, characterized in that, the tapered curve is an elliptical curve, a parabolic curve or a spline curve.

3. The monolithic ceramic core according to claim 2, characterized in that, the axial direction of the hollowing hole is parallel to the expected dominant direction of the turbine shell air inlet flow.

4. The monolithic ceramic core according to claim 1, characterized in that, the number of hollowing holes is multiple, and multiple hollowing holes are uniformly distributed around the axial direction of the turbine shell air inlet end in the thick region of the monolithic ceramic core.

5. The monolithic ceramic core according to claim 1, characterized in that, the inner surface of the hollowing hole is a smooth surface to reduce stress concentration and mold demolding resistance.

6. The monolithic ceramic core according to claim 1, characterized in that, a buffer layer is provided on the monolithic ceramic core near the outer surface of the hollowing hole to buffer the micro thermal expansion; the buffer layer includes a plurality of micro-pore structures with a size of 20-80 μm, and the micro-pores are distributed along the surface of the monolithic ceramic core and transition to the inside of the monolithic ceramic core; the porosity of the buffer layer gradually decreases from outside to inside to gradually release the local thermal stress generated during sintering and pouring.

7. A mold for forming the monolithic ceramic core according to any one of claims 1-6, comprising an upper mold and a lower mold, the upper mold and the lower mold form a cavity matching the shape of the monolithic ceramic core after closing, characterized in that: a raised core matching the shape of the hollowing hole is provided in the upper mold or the lower mold, and a groove is provided on the surface of the raised core corresponding to the support rib inside the hollowing hole to form the support rib during injection molding; the demolding direction of the raised core is consistent with the axial direction of the hollowing hole.

8. A method of investment casting an automotive turbine housing comprising the monolithic ceramic core of any one of claims 1-6, the mold of claim 7, characterized in that, it comprises the following steps: S1, making a monolithic ceramic core: using the mold, the monolithic ceramic core is made by injection molding; S2, sintering of the monolithic ceramic core: the monolithic ceramic core is subjected to debinding and sintering treatment; S3, making a wax mold: the sintered monolithic ceramic core is placed in a wax pressing mold to form a wax mold covering the ceramic core; S4, making a ceramic mold shell: the wax mold is coated with slurry and coated with sand several times to form a mold shell and is dewaxed to obtain a ceramic mold shell with the monolithic ceramic core inside. S5, pouring to form a casting: smelting metal and pouring, filling the molten metal obtained by smelting into the cavity between the ceramic shell and the integral ceramic core to form a turbine shell casting; S6, cleaning of the casting: cleaning the turbine shell casting to remove the ceramic shell and the integral ceramic core to obtain a turbine shell blank.

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