Casting method for front end cover of helicopter engine

Abstract

The invention discloses a casting method for a front end cover of a helicopter engine. The casting method comprises the following steps: modeling the front end cover of the engine; designing a pouring system; determining a parting surface and designing a bottom mold, a cover mold, each detachable sand mold, a mold core and an oil path sand core; 3D printing is carried out on a bottom mold, a cover mold, a riser sand mold, each detachable sand mold, a mold core and an oil way sand core; the mold cores, the oil way sand cores and the detachable sand molds are loaded into the corresponding sand molds correspondingly; hoisting and stacking the bottom mold and the cover mold to form an integral sand mold; hoisting the combined integral sand mold into a sand box, carrying out sand filling molding, and hoisting the sand box above a sealing cover of a heat preservation furnace after the resin sand is cured; the upper port of the riser tube is in butt joint with the center sprue of the bottom mold; magnesium alloy liquid is smelted, low-pressure pouring is conducted, and under the air pressure effect, the magnesium alloy liquid is subjected to upward mold filling through a liquid rising pipe and a pressure adjusting sprue; and shakeout is performed after cooling and curing. The pouring requirements of thick and large parts and thin walls can be met at the same time, a slender oil way is internally integrated, sequential solidification is achieved, feeding is reliable, and the quality is high.

Description

Technical Field

[0001] The present invention relates to the casting of magnesium alloys, and particularly to a casting method for the front end cover of a helicopter engine, belonging to the technical field of casting processes for complex castings. Background Art

[0002] Currently in China, the vast majority of engine front end cover products are made of aluminum alloy, and there are few front end covers made of high-performance heat-resistant rare earth magnesium alloy. With the increasing requirements for aircraft lightweight, the application of magnesium alloy engine front end covers is also increasing. Therefore, it is urgent to study the casting process for large-sized high-performance heat-resistant rare earth magnesium alloy engine front end covers with thin walls, complex oil circuits, large planes, and special shapes.

[0003] The engine front end cover casting includes a central rotating shaft hole in the center of the large plane of the casting body, which is the thickest and largest part of the casting, difficult to feed and slow to solidify. On the left and right of the upper end of the central rotating shaft hole, there are two large mounting flanges and connecting shaft holes respectively. At the other end of the central rotating shaft hole, there is an integrally concave gear shaft housing. The overall contour length exceeds 1300 mm, the width exceeds 800 mm, and the thickness exceeds 250 mm; there is an observation port connecting flange on the side wall of the front end cover large plane.

[0004] The side walls on both sides of the engine front end cover are mainly thin walls. Due to the poor fluidity, low density, and low pouring temperature of magnesium alloy, it is very difficult to cast the thin wall parts into shape. The solidification speed is too fast, and casting defects such as porosity, looseness, inclusion, and misrun are likely to occur; when the pouring temperature is high, casting defects such as looseness, hot cracking, and shrinkage holes are likely to occur in the thin wall parts, and the yield rate is relatively low. In addition, too large a difference in the solidification time of the molten metal will cause thermal stress in the casting after solidification, resulting in casting deformation, cracks, and defects such as shrinkage holes and shrinkage porosity.

[0005] There are two oil circuits respectively around the central rotating shaft hole at the center of the bottom plane of the cover and the two large mounting flanges and connecting shaft holes connected to the left and right of the upper end. The oil circuit around the central rotating shaft hole is a 36 mm * 13 mm flat pipeline, with a length of more than 1.4 meters, high quality requirements, and great casting difficulty. The oil circuit around the large mounting flange and the connecting shaft hole is a φ12 oil circuit, with a length of more than 1.6 meters. Because the oil circuit is thin, long, and relatively tortuous, the strength is insufficient, and it is easy to deform or even be washed off during pouring. The two oil circuits have complex shapes, with a total length of more than 3 m. The wall thickness of the overall oil circuit is 4 - 6 mm. It is difficult to form the oil circuit structure and it is also difficult to clean the oil circuit. In short, the engine front end cover has high requirements for casting equipment and processes, and great casting difficulty. Summary of the Invention

[0006] The purpose of this part is to outline some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this part, as well as in the abstract and title of the present application, but such simplifications or omissions shall not be used to limit the scope of the present invention.

[0007] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0008] The purpose of the present invention is to overcome the problems existing in the prior art and provide a casting method for a front end cover of a helicopter engine, which can simultaneously meet the casting requirements of the thick and large parts and the thin-walled parts of the front end cover, generate a slender oil path inside the casting, realize sequential solidification of the casting, reliably compensate for shrinkage and avoid insufficient pouring, and improve the quality of the casting.

[0009] In order to solve the above technical problems, a method for casting a front cover of a helicopter engine of the present invention comprises the following steps in sequence:

[0010] S1, engine front cover modeling;

[0011] S2. Design the pouring system;

[0012] S3, determine the parting surface, and design the bottom mold 24, the cover mold 31, each dismantling sand mold, the core and the oil circuit sand core;

[0013] S4, 3D printed bottom mold 24, cover mold 31, riser sand mold, each disassembled sand mold, core and oil channel sand core;

[0014] S5, respectively placing each core, oil passage sand core and disassembled sand mold into the corresponding sand mold;

[0015] S6, hoisting the stacked bottom mold 24 and cover mold 31 from bottom to top in sequence to form an integral sand mold;

[0016] S7, hoisting the assembled integral sand mold into the sand box, filling sand for molding, covering the exhaust groove and exhaust hole above the cover mold with insulation cotton, and after the resin sand is solidified, hoisting the sand box above the sealing cover of the insulation furnace; a liquid riser is installed at the center of the sealing cover, and the upper port of the liquid riser is connected to the central gate of the bottom mold 24;

[0017] S8, melting the magnesium alloy liquid, performing low-pressure pouring, and under the action of gas pressure, the magnesium alloy liquid is filled upward through the liquid riser and the pressure regulating gate;

[0018] S9, after cooling and solidification, the sand is removed to obtain the engine front end cover blank.

[0019] Further, in step S1, the engine front cover includes a large flat surface of the casting body. A central rotating shaft hole 1a is provided on the large flat surface of the casting body. On the left side of the upper end of the central rotating shaft hole 1a, a left arm rotating shaft hole 1b1 and a large left arm mounting flange 1c1 are connected. On the right side of the upper end of the central rotating shaft hole 1a, a right arm rotating shaft hole 1b2 and a large right arm mounting flange 1c2 are connected. At the other end of the central rotating shaft hole 1a, a thin-walled area gear shaft housing 1d1 with an overall concave shape is connected. A gear shaft housing oil inlet 1d2 is provided at the central position of the gear shaft housing 1d1.

[0020] Further, a left suspension oil inlet 1e1 is provided between the large left arm mounting flange 1c1 and the gear shaft housing 1d1, and a right suspension oil inlet 1e2 is provided between the large right arm mounting flange 1c2 and the gear shaft housing 1d1. An observation port connecting flange 1f is provided on the outer side wall of the left suspension oil inlet 1e1. An oil passage 1g is provided on the outer circumference of the central rotating shaft hole 1a, and the oil passage 1g communicates the central rotating shaft hole 1a with the gear shaft housing oil inlet 1d2.

[0021] Further, the gating system in step S2 includes a central gate 2. A plurality of first-layer support cross gates 3 extending radially outward are connected to the outer circumference of the upper end of the central gate 2. The top of the first-layer support cross gate 3 near the outer end is connected to a second-layer water inlet cross gate 5 through a first-layer water inlet 4, forming a double-gate system. The second-layer water inlet cross gate 5 forms a ring shape below the areas of the left arm rotating shaft hole 1b1, the large left arm mounting flange 1c1, the right arm rotating shaft hole 1b2, and the large right arm mounting flange 1c2 and is connected to the bottom of the engine front cover through a plurality of second-layer water inlets 6.

[0022] Further, a side over-barrel 8 extending upward is connected to the outside of the second-layer water inlet cross gate 5. The side over-barrel 8 is connected to the second-layer water inlet cross gate 5 and is connected to the outside of the casting through a side water inlet 9.

[0023] A central over-barrel 14 extending upward is connected to the center of the second-layer water inlet cross gate 5. The outer circumference of the central over-barrel 14 is connected to the inner circumferential wall of the central rotating shaft hole 1a through a plurality of central water inlets.

[0024] Further, an exhaust groove 12 extending upward is provided at the center of the top of the central rotating shaft hole 1a. Flange risers 11 are provided at the upper openings of the thick and large parts of the left arm rotating shaft hole 1b1, the large left arm mounting flange 1c1, the right arm rotating shaft hole 1b2, and the large right arm mounting flange 1c2. A convex platform is provided on the outer wall of the central rotating shaft hole 1a, and the second-layer water inlet cross gate 5 fills the convex platform separately through a dot gate 7.

[0025] Furthermore, the molten magnesium alloy enters from the central gate 2 and then flows radially outward along each first-layer support runner 3. After the molten magnesium alloy fills the first-layer support runner 3, it reaches the second-layer inlet runner 5 through the first-layer water inlet 4. After the molten magnesium alloy evenly fills the second-layer inlet runner 5, it enters the cavity through the second-layer water inlet 6 and the dot gate 7 for filling from bottom to top, and also fills the side hole wall of the relatively thick central shaft hole 1a through the central barrel 14. The molten magnesium alloy entering the engine front cover cavity rises evenly from the bottom and fills the thick and large parts such as the left-arm large mounting flange 1c1 and the right-arm large mounting flange 1c2, and then continues to rise upward into the flange riser 11.

[0026] Furthermore, three upward-extending exhaust grooves 12 are evenly distributed at the top of the circumferential wall of the central shaft hole 1a to discharge the gas generated during the casting of the casting; the flange riser 11 compensates for the thick and large parts including the left-arm large mounting flange 1c1 and the right-arm large mounting flange 1c2; the top of the gear shaft housing 1d1 is compensated through each open riser 13, and the gas generated during the filling process is discharged through each open riser 13; upward-extending side barrels 8 are respectively provided on the outer side of the observation port connecting flange 1f, and the side barrels 8 are connected to the second-layer inlet runner 5. After the molten magnesium alloy fills the side barrels 8, it compensates for the observation port connecting flange 1f through two side water inlets 9; a plurality of upward-extending central risers 10 are respectively provided in the regions and bosses between the top of the gear shaft housing 1d1 and the left-arm shaft hole 1b1 and the right-arm shaft hole 1b2 for compensating for the top boss and the flange below it.

[0027] Furthermore, curved and slender oil passages are provided on the outer periphery of the left-arm large mounting flange 1c1 and the right-arm large mounting flange 1c2. The inner diameter of the curved and slender oil passages is 12 mm, the wall thickness is 4 - 6 mm, the length is more than 1.6 m, and it is fixed in the cover type 31; the head end of the curved and slender oil passage core 16 is connected to the oil holes on the side walls of the left-arm large mounting flange 1c1, the right-arm large mounting flange 1c2, the left-arm shaft hole 1b1, and the right-arm shaft hole 1b2; the tail end of the curved and slender oil passage core 16 is connected to the oil hole on the side wall of the central shaft hole 1a; the curved and slender oil passage core 16 is assembled from multiple segments, and the opposite ends of each segment are respectively connected by half-tenons 16a in a lap joint manner. An oil passage positioning gap 16b of 0.3 mm is respectively provided between each half-tenon 16a, and the length of each segment of the curved and slender oil passage core 16 is 300 - 400 mm.

[0028] Further, each oil port of the curved and slender oil passage core 16 serves as a support column, and an oil passage core positioning pin 23 is provided at the lower end of each support column. Each oil passage core positioning pin 23 is of a conical structure and is respectively embedded in the corresponding oil passage core positioning groove 24a of the bottom mold 24. A process hole positioning gap 24b of 0.3 mm is provided between each oil passage core positioning pin 23 and the corresponding oil passage core positioning groove 24a. After the oil passage assembly is completed, all gap positions are brushed and filled with paint.

[0029] Further, a through central vent hole is provided along the centerlines of the curved and slender oil passage core 16 and each support column.

[0030] Further, an annular flat long oil passage that surrounds most of the circumference of the central rotating shaft hole 1a is provided on the outer periphery of the central rotating shaft hole 1a. The cross-section of the annular flat long oil passage is 36 mm × 13 mm, and the length is more than 1.4 m and is fixed in the bottom mold 24. The head ends of the annular flat long oil passage cores 19 are respectively connected to the left suspension oil passage inlet 1e1 and the right suspension oil passage inlet 1e2, and the ends extend directly to the gear shaft box oil passage inlet 1d2 at the center of the gear shaft box 1d1.

[0031] Further, each oil port of the annular flat long oil passage core 19 serves as a support column, and an inner groove is provided in the ends of the two support columns at both ends. A cold iron groove 22 is placed in the inner groove for placing a cold iron. A central vent hole is provided along the axis of the annular flat long oil passage core 19 and penetrates through the center of the cold iron groove 22 to the outside.

[0032] Further, the bottom mold 24 is provided with five bottom mold removable cores, including two bottom mold side removable cores 25, two bottom mold front removable cores 26, and an integral rear side wall mounting seat sand mold 27. Among them, the two bottom mold side removable cores 25 are located in the grooves on the side walls of the bottom mold, which is convenient for brushing paint on the parts in contact with the side walls of the casting; the two bottom mold front removable cores 26 are respectively located in the front side grooves of the bottom mold, which is convenient for installing the inner cold iron; an integral rear side wall mounting seat sand mold 27 is located at the upper end of the base, which is convenient for installing the annular flat long oil passage core 19 and the cold iron; the five bottom mold removable cores are respectively located between the four base mounting holes and are respectively provided with tenons embedded in the grooves of the bottom mold 24 at the bottom.

[0033] Further, the integral left side wall mounting seat sand mold 28 is inserted into the upper-wide and lower-narrow dovetail groove 31a of the cover mold 31 from the left side of the cover mold 31, and the integral right side wall mounting seat sand mold 30 is inserted into the upper-wide and lower-narrow dovetail groove 31a of the cover mold 31 from the right side of the cover mold 31; after the cavity of the gear shaft box 1d1 is cleaned, the exhaust hole removable sand mold 29 is accessed from below to the cover mold 31.

[0034] Furthermore, the bottom of the integral right side wall mounting seat sand mold 30 is provided with an integral right side wall mounting seat sand mold positioning core head 30a, and an integral right side wall mounting seat sand mold positioning boss 30b is provided on the circumference of the integral right side wall mounting seat sand mold positioning core head 30a; chiller grooves 30c are provided at the thick hot spots of the integral right side wall mounting seat sand mold 30, and chillers are respectively inserted into each chiller groove 30c to enhance heat dissipation; the outer wall at the relatively thick hot spots of the integral right side wall mounting seat sand mold 30 is provided with grid-shaped and downwardly concave chill rib grooves 30d, which are polished off after molding.

[0035] Furthermore, step S5 includes the following sub-steps:

[0036] Step S5.1: Install the annular flat long oil passage sand core 19 in the cavity of the bottom mold 24;

[0037] Step S5.2: After placing chillers in the chiller grooves on the front side of the bottom mold 24 respectively, then insert the front split movable sand core 26 of the bottom mold into the front ports of the chiller grooves to position the chillers;

[0038] Step S5.3: Install the bottom mold side split movable sand core 25 and the integral rear side wall mounting seat sand mold 27 in the bottom mold;

[0039] Step S5.4: Insert the formed chiller into the chiller groove 30c of the integral right side wall mounting seat sand mold 30, and then insert the integral right side wall mounting seat sand mold positioning core head 30a into the corresponding positioning counterbore of the bottom mold to achieve central positioning and axial positioning of the integral right side wall mounting seat sand mold 30; at the same time, the integral right side wall mounting seat sand mold positioning boss 30b is embedded in the corresponding groove of the bottom mold 24 to achieve radial positioning of the integral right side wall mounting seat sand mold 30; finally, it is fixedly fitted on the cover mold 31 through the dovetail groove 31a; assemble the integral left side wall mounting seat sand mold 28 and the exhaust eye split movable sand mold 29 onto the cover mold 31 in the same way;

[0040] Step S5.5: Insert the chillers into the chiller grooves of the cover mold 31;

[0041] Step S5.6: Install the curved slender oil passage sand core 16 in the cavity of the cover mold.

[0042] Compared with the prior art, the present invention has achieved the following beneficial effects: 1. A low-pressure double-runner pouring process is set up, and the double runner can realize uniform distribution of the temperature field in the sand mold, avoid local overheating, and ensure smooth shrinkage compensation of the casting. After the first layer of supporting runner is filled with magnesium liquid, the oxidized slag generated during filling will remain at the end of the runner and will not flow into the second layer of water inlet runner. The magnesium liquid fills the mold evenly in the second layer of water inlet runner, and when the magnesium liquid enters the mold cavity, it is avoided that the area that first enters the water due to the long runner backflows into the runner, resulting in defects such as air entrainment and slag inclusions. During low-pressure pouring, the flow rate of the magnesium liquid is controllable, and it flows under pressure, and the filling capacity is improved. It can provide a stable and adjustable flow rate and pressure, and the internal structure is denser, without pores and shrinkage defects.

[0043] 2. The gear shaft box on the bottom plane of the end cover and the large mounting flanges on the left and right sides of the upper end and the connecting shaft area are thick parts, and are respectively provided with water inlets along their own circumferential walls for direct water inlet compensation to ensure the internal quality of the thick wall area. The double runner can directional fill different areas and optimize the compensation of the thick wall area. The water inlet along its own circumferential wall is set in the thick part. The lower end of each water inlet is connected to the corresponding horizontal runner, and the middle section of each horizontal runner is connected to the large mounting flange and the circumferential wall of the connecting shaft through multiple radial runners. Multiple water inlets can disperse heat and reduce defects caused by overheating; water is directly introduced through the second layer of water inlet horizontal runner for compensation to ensure the internal quality of the thick wall area.

[0044] 3. A tube connected to the second-layer water inlet runner is provided on the outside of the observation port connecting flange. The observation port connecting flange and the tube are connected through an entgate. The entgate directly fills the mold to improve the filling rate of the thin wall and prevent the thin wall area from solidifying too quickly and causing insufficient pouring. The point gate compensates for the shrinkage of local hot spots such as bosses and adjusts the temperature distribution and solidification sequence of the casting.

[0045] 4. The overall pouring system of the casting realizes sequential solidification, giving full play to the shrinkage-feeding effect of the pouring and riser, reducing the formation of loose shrinkage cavities, and improving the internal quality of the casting; at the same time, a chiller is also provided to chill the hot spot, thereby improving the shrinkage-feeding capacity of the hot spot and reducing the formation of loose shrinkage cavities.

[0046] 5. Set up removable sand cores, including removable sand cores on the bottom mold side, removable sand cores in front of the bottom mold and integral rear wall mounting seat sand mold, which is convenient for the installation of internal parts such as oil circuit sand cores and chillers, convenient for brushing paint and cleaning the inner wall of the cavity, and also convenient for embedding and fixing inside the bottom mold during assembly.

[0047] 6. In order to facilitate the installation of the integral left wall mounting seat sand mold and the integral right wall mounting seat sand mold, a dovetail groove is set on the cover mold. The inclination of the dovetail groove produces a mechanical self-locking effect and is not easy to move. The dovetail groove single-direction sliding assembly design can achieve rapid disassembly and assembly, and improve the efficiency of assembly.

[0048] 7. The slender oil passage core is disassembled into multiple short oil passage cores according to its structure. The length of each short oil passage core is 300 - 400 mm. Each oil passage core is positioned through the oil port, which can effectively reduce the structural deformation of the oil passage core during casting. A positioning is set between adjacent two sections of oil passage cores, and the oil passage positioning gap is 0.3 mm. A 0.3 mm process hole positioning gap is set between the positioning of the oil passage process hole and the sand mold positioning to ensure the accuracy of the oil passage assembly dimensions. After the oil passage assembly is completed, all gap positions are brushed and filled with coating to reduce the generation of redundant substances such as internal flash and casting tumors in the casting oil passage, reduce the runner resistance and facilitate sand cleaning. An internal oil passage connected to each lubrication point is integrated inside the casting, greatly reducing the external oil passage, improving the reliability of the engine and reducing the weight.

[0049] 8. Using 3D printing sand molds, the complex structure and oil passages of the engine front cover can be accurately printed according to the three-dimensional model of the product, and it is convenient for dimensional scanning inspection, eliminating the cycle of mold design and processing, thus greatly shortening the production cycle. The 3D printed slender oil passage sand mold can print tortuous vent holes inside to prevent the problem of air entrapment caused by the inability to exhaust due to the overly long oil passage. In addition, a large amount of chemical reagents and binders are not required during the 3D printing of sand molds, and less waste is generated, meeting the requirements of green environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for description in the embodiments will be briefly introduced below. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings. The drawings are only provided for reference and explanation, and are not used to limit the present invention. Among them:

[0051] Figure 1 It is a schematic structural diagram of the engine front cover casting in the present invention;

[0052] Figure 2 It is a three-dimensional view of the gating system in the present invention;

[0053] Figure 3 It is a bottom view of the gating system in the present invention;

[0054] Figure 4 It is a structural diagram of the casting after pouring and forming in the present invention;

[0055] Figure 5 It is an arrangement diagram of the chill in the present invention;

[0056] Figure 6 It is a sectional structural diagram of the curved slender oil passage core in the present invention;

[0057] Figure 7Schematic diagram of the segmented structure of the annular flat long oil passage core in the present invention;

[0058] Figure 8 Cross-sectional view of the curved slender oil passage core in the present invention;

[0059] Figure 9 Exploded view of each component during mold closing in the present invention;

[0060] Figure 10 Enlarged view of the integral right side wall mounting seat sand mold in the present invention;

[0061] Figure 11 Top view of the bottom mold in the present invention;

[0062] Figure 12 Front view of the bottom mold and the cover mold before mold closing in the present invention;

[0063] Figure 13 Front view of the bottom mold and the cover mold after mold closing in the present invention;

[0064] Figure 14 Stereogram of the bottom mold and the cover mold after mold closing in the present invention;

[0065] In the figure: Engine front cover casting: 1a. Central rotating shaft hole; 1b1. Left arm rotating shaft hole; 1b2. Right arm rotating shaft hole; 1c1. Left arm large mounting flange; 1c2. Right arm large mounting flange; 1d1. Gear shaft housing; 1d2. Gear shaft housing oil passage inlet; 1e1. Left suspension oil passage inlet; 1e2. Right suspension oil passage inlet; 1f. Observation port connecting flange; 1g. Oil passage;

[0066] 2. Central sprue; 3. First layer supporting cross-riser; 4. First layer water inlet; 5. Second layer water inlet cross-riser; 6. Second layer water inlet; 7. Spot sprue; 8. Side over-tube; 9. Side water inlet; 10. Central riser; 11. Flange riser; 12. Exhaust groove; 13. Open riser; 14. Central over-tube; 15. Chilled iron;

[0067] 16. Curved slender oil passage core; 16a. Half tenon; 16b. Oil passage positioning gap;

[0068] 17. Curved slender oil passage core support column; 18. Curved slender oil passage vent hole; 19. Annular flat long oil passage core; 20. Annular flat long oil passage core support column; 21. Annular flat long oil passage vent hole; 22. Chilled iron groove; 23. Oil passage core positioning pin;

[0069] 24. Bottom mold; 24a. Oil passage core positioning groove; 24b. Process hole positioning gap; 24c. Bottom mold lifting handle;

[0070] 25. Bottom-type side removable core; 26. Bottom-type front removable core; 27. Integral rear side wall mounting seat sand mold; 28. Integral left side wall mounting seat sand mold; 29. Exhaust hole removable sand mold;

[0071] 30. Integral right side wall mounting seat sand mold; 30a. Locating core head of integral right side wall mounting seat sand mold; 30b. Locating boss of integral right side wall mounting seat sand mold; 30c. Chilled iron groove; 30d. Chilling rib groove;

[0072] 31. Cover type; 31a. Dovetail groove; 31b. Lower convex tenon of cover type; 31c. Lifting handle of cover type; 31d. Exhaust riser of cover type; 31e. Exhaust hole of cover type;

[0073] 32. Positioning scale line. Detailed implementation mode

[0074] In the following description of the present invention, the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating that the device must have a specific orientation.

[0075] As Figures 1 to 5 shown, in the present invention, the front end cover of the engine includes a central rotating shaft hole 1a on the large flat surface of the casting body. On the left side above the central rotating shaft hole 1a, there are connected a left arm rotating shaft hole 1b1 and a large left arm mounting flange 1c1. On the right side above the central rotating shaft hole 1a, there are connected a right arm rotating shaft hole 1b2 and a large right arm mounting flange 1c2. At the other end of the central rotating shaft hole 1a, there is connected a thin-walled area gear shaft housing 1d1 with an overall concave shape. In the central position of the gear shaft housing 1d1, there is a gear shaft housing oil inlet 1d2. The left arm rotating shaft hole 1b1 and the large left arm mounting flange 1c1 are symmetrically arranged with the right arm rotating shaft hole 1b2 and the large right arm mounting flange 1c2 centered on the casting central axis.

[0076] Between the large left arm mounting flange 1c1 and the gear shaft housing 1d1, there is a left suspension oil inlet 1e1. Between the large right arm mounting flange 1c2 and the gear shaft housing 1d1, there is a right suspension oil inlet 1e2. The left suspension oil inlet 1e1 and the right suspension oil inlet 1e2 are symmetrically arranged with the casting central axis as the center. On the outer side wall of the left suspension oil inlet 1e1, there is an observation port connecting flange 1f; on the outer periphery of the central rotating shaft hole 1a, there is an oil passage 1g, which communicates the central rotating shaft hole 1a with the gear shaft housing oil inlet 1d2.

[0077] Below the central rotating shaft hole 1a, there is a center gate 2 coaxial with it. On the outer periphery of the upper end of the center gate 2, there are connected a plurality of first-layer support cross gates 3 extending radially outward. The top of the first-layer support cross gate 3 near the outer end is connected to the second-layer water inlet cross gate 5 through the first-layer water inlet 4, forming a double-gate system.

[0078] The second - layer inlet cross - runner 5 forms a ring shape below the regions of the left - arm rotating - shaft hole 1b1, the left - arm large mounting flange 1c1, the right - arm rotating - shaft hole 1b2, and the right - arm large mounting flange 1c2, and is connected to the bottom of the engine front cover through a plurality of second - layer inlet ports 6.

[0079] The outer side of the second - layer inlet cross - runner 5 is connected with a side - passing cylinder 8 extending upward. The side - passing cylinder 8 is connected to the second - layer inlet cross - runner 5 and is connected to the outside of the casting through a side - inlet port 9.

[0080] The center of the second - layer inlet cross - runner 5 is connected with a center - passing cylinder 14 extending upward. The outer periphery of the center - passing cylinder 14 is connected to the inner peripheral wall of the central rotating - shaft hole 1a through a plurality of center - inlet ports. At the top center of the central rotating - shaft hole 1a, there is an exhaust groove 12 extending upward, and flange risers 11 are provided at the upper openings of the thick - and - large parts of the left - arm rotating - shaft hole 1b1, the left - arm large mounting flange 1c1, the right - arm rotating - shaft hole 1b2, and the right - arm large mounting flange 1c2.

[0081] There is a boss on the outer wall of the central rotating - shaft hole 1a. Since it is close to the oil passage 1g, the second - layer inlet cross - runner 5 is connected to the boss through a dot - shaped gate 7, and the boss is filled separately through the dot - shaped gate 7.

[0082] The magnesium - alloy liquid enters from the center gate 2, then flows radially outward along each first - layer support cross - runner 3. After the magnesium - alloy liquid fills the first - layer support cross - runner 3, it reaches the second - layer inlet cross - runner 5 through the first - layer inlet port 4. After the first - layer support cross - runner 3 is filled, the oxidation slag generated during filling will remain at the end of the cross - runner and will not flow into the second - layer inlet cross - runner. The magnesium - alloy liquid evenly fills the second - layer inlet cross - runner 5 and enters the cavity through the second - layer inlet port 6 and the dot - shaped gate 7, filling the cavity of the engine front cover from bottom to top. Since the magnesium - alloy liquid fills the second - layer inlet runner evenly, when the magnesium - alloy liquid enters the cavity, it avoids the situation where the magnesium - alloy liquid, due to the too - long cross - runner, backflows into the cross - runner in the area where water enters first, resulting in defects such as gas entrapment and slag inclusion.

[0083] Since the thickness of the central rotating - shaft hole 1a is the thickest, the magnesium - alloy liquid also flows along the center - passing cylinder 14 and then fills the side - hole wall of the central rotating - shaft hole 1a through the center - inlet port. There are three exhaust grooves 12 extending upward evenly distributed on the top of the circumferential wall of the central rotating - shaft hole 1a, which are used to discharge the gas generated during the casting of the casting.

[0084] The magnesium - alloy liquid entering the cavity of the engine front cover rises evenly from the bottom, fills the thick - and - large parts such as the left - arm large mounting flange 1c1 and the right - arm large mounting flange 1c2, and then continues to rise into the flange riser 11. The flange riser 11 compensates for the shrinkage of the thick - and - large parts such as the left - arm large mounting flange 1c1 and the right - arm large mounting flange 1c2.

[0085] Since the gear shaft axle box 1d1 is mainly made of thin walls, defects such as incomplete filling are likely to occur during the filling process from bottom to top. Therefore, multiple second-layer water inlets 6 are provided on the side walls and bottom planes of the gear shaft axle box 1d1. The magnesium alloy liquid reaching the first-layer support runner 3 enters the second-layer water inlet runner 5 through the first-layer water inlet 4. After the magnesium alloy liquid fills the second-layer water inlet runner 5, it enters the cavity of the gear shaft axle box 1d1 upward along the second-layer water inlets 6. After the magnesium alloy liquid filling is completed, it enters the open riser 13, and the top of the gear shaft axle box 1d1 is compensated for shrinkage through each open riser 13. During the filling process, the water vapor generated by the reaction of the cold air in the sand mold and the gas generated by the protective agent to prevent the combustion of the magnesium alloy liquid are discharged through each open riser 13.

[0086] On the outer sides of the observation port connection flanges 1f, side over-tubes 8 extending upward are respectively provided. The side over-tubes 8 are connected to the second-layer water inlet runner 5. After the magnesium alloy liquid fills the side over-tubes 8, the observation port connection flanges 1f are compensated for shrinkage through two side water inlets 9.

[0087] In the areas and bosses between the top of the gear shaft axle box 1d1 and the left arm rotating shaft hole 1b1 and the right arm rotating shaft hole 1b2, multiple center risers 10 extending upward are respectively provided for compensating for shrinkage of the top boss and the flange below it.

[0088] Chills 15 are respectively placed at the thick and hot spots of the central rotating shaft hole 1a, the left arm rotating shaft hole 1b1, and the right arm rotating shaft hole 1b2 to accelerate the cooling rate of the thick and hot spots, make the solidification process more uniform, and reduce the stress concentration phenomenon caused by asynchronous solidification.

[0089] As Figures 6 to 8 shown, curved and slender oil passage sand cores 16 are provided on the outer perimeters of the left arm large mounting flange 1c1 and the right arm large mounting flange 1c2. The inner diameter of the curved and slender oil passage is 12 mm, the wall thickness is 4 - 6 mm, and the length is more than 1.6 m. The head ends of the curved and slender oil passage sand cores 16 are connected to the oil holes on the side walls of the left arm large mounting flange 1c1, the right arm large mounting flange 1c2, the left arm rotating shaft hole 1b1, and the right arm rotating shaft hole 1b2; the tail ends of the curved and slender oil passage sand cores 16 are connected to the oil holes on the side walls of the central rotating shaft hole 1a.

[0090] Around the outer perimeter of the central rotating shaft hole 1a, a ring-shaped flat and long oil passage that surrounds most of the circumference of the central rotating shaft hole 1a is provided. The cross-section of the ring-shaped flat and long oil passage is 36 mm * 13 mm, and the length is more than 1.4 m. The head ends of the ring-shaped flat and long oil passage sand core 19 are respectively connected to the left suspension oil inlet 1e1 and the right suspension oil inlet 1e2, and the tail end extends directly to the gear shaft axle box oil inlet 1d2 at the center of the gear shaft axle box 1d1.

[0091] The curved slender oil passage core 16 and the annular flat long oil passage core 19 are assembled in multiple sections along the length direction. Taking the assembly of the curved slender oil passage core 16 as an example, the opposite ends between the sections are respectively overlapped and connected with each other through half tenons 16a, and there are oil passage positioning gaps 16b respectively arranged between the half tenons 16a, and each oil passage positioning gap 16b is 0.3 mm. The length of each section of the curved slender oil passage core 16 and the annular flat long oil passage core 19 is 300 - 400 mm.

[0092] The curved slender oil passage core 16 and the annular flat long oil passage core 19 use each oil outlet as a support column, including the curved slender oil passage core support 17 and the annular flat long oil passage core support column 20. At the lower ends of the oil passage core support columns respectively, there are oil passage core positioning pins 23, and each oil passage core positioning pin 23 is of a conical structure and is respectively embedded in the corresponding oil passage core positioning grooves 24a of the bottom mold 24.

[0093] A plurality of vent holes are arranged along the length direction of the curved slender oil passage core 16 and the annular flat long oil passage core 19, including the curved slender oil passage vent holes 18 and the annular flat long oil passage vent holes 21. The 3D printed oil passage core can be provided with vent holes along its axis inside the core to prevent the problem of air congestion caused by the inability to exhaust air due to the overly long oil passage.

[0094] There are process hole positioning gaps 24b respectively arranged between each oil passage core positioning pin 23 and the corresponding oil passage core positioning groove 24a, and each process hole positioning gap 24b is 0.3 mm to ensure the accuracy of the oil passage assembly dimensions. After the oil passage assembly is completed, all gap positions are brushed and filled with coating.

[0095] A section of inner groove is arranged in the end heads of the annular flat long oil passage core support columns 20 at both ends, and a section of chill groove 22 is placed in the inner groove for placing chills. The vent hole extending along the axis of the annular flat long oil passage core 19 penetrates through the center of the chill groove 22 to the outside.

[0096] As Figures 9 to 14 shown, the pouring method of the engine front cover casting successively includes the following steps:

[0097] S1. Modeling of the engine front cover;

[0098] S2. Designing the gating system;

[0099] S3. Determining the parting surface, and designing the bottom mold 24, the cover mold 31 and each split mold; a plurality of bottom mold lifting handles 24c are symmetrically arranged on the outer wall of the bottom mold, and a plurality of cover mold lifting handles 31c are symmetrically arranged on the outer wall of the cover mold 31, which is convenient for lifting.

[0100] S4. 3D printing the bottom mold 24, the cover mold 31, the riser mold, each split mold, the core and the oil passage core;

[0101] S5, each core and the annular flat long oil path sand core 19 are respectively loaded into the bottom mold 24, and each disassembled sand mold is respectively loaded into the bottom mold 24 or the cover mold 31;

[0102] S6. Hoist and splice the curved and slender oil channel sand core 16 onto the cover type 31, and hoist and splice the cover type 31 onto the base type 24 through the cover type hoisting handle 31c. The cover type lower tenons 31b at the four corners of the lower port of the cover type 31 are embedded in the upper port grooves of the base type 24 and match each other; confirm that the positioning marks 32 on the outer walls of the cover type 31 and the base type 24 are aligned with each other.

[0103] S7, hoisting the assembled whole sand mold into the sand box, filling sand and molding, using insulation cotton to cover the exhaust groove and exhaust hole above the cover mold to prevent sand from falling into the mold cavity, and after the resin sand is solidified, hoisting the sand box above the sealing cover of the insulation furnace; a liquid riser is installed in the center of the sealing cover, and the upper port of the liquid riser is connected to the central gate of the bottom mold;

[0104] S8, melting the magnesium alloy liquid, and performing low-pressure pouring. Under the action of gas pressure, the magnesium alloy liquid fills the mold upward through the riser and the center gate;

[0105] S9, after cooling and solidification, the sand is removed to obtain the engine front end cover blank.

[0106] The four walls of the bottom mold 24 are respectively provided with cold iron grooves with open outer ends. After cold irons are placed in the cold iron grooves, the sand core 26 is removed and positioned before the bottom mold is inserted into the outer ends.

[0107] In step S4, the removable sand mold includes five bottom mold removable sand cores, including bottom mold side removable sand cores 25, bottom mold front removable sand cores 26 and an integral rear side wall mounting seat sand mold 27. Two bottom mold side removable sand cores 25 are located in the grooves of the bottom mold side wall, which is convenient for painting the parts in contact with the casting side wall; two bottom mold front removable sand cores 26 are respectively located in the front side grooves of the bottom mold, which is convenient for installing the inner side cold iron; an integral rear side wall mounting seat sand mold 27 is located at the upper end of the base, which is convenient for installing the annular flat long oil channel sand core (19) and the cold iron. The five bottom mold removable sand cores are respectively located between the four base mounting holes and the bottoms are respectively provided with tenons embedded in the bottom mold grooves.

[0108] like Figure 9 As shown, the bottom mold is provided with an annular flat long oil path sand core 19, the lower end of the vertical section of the annular flat long oil path sand core 19 is connected to the oil port in the bottom mold, and the horizontal section port is connected to the oil port of the side wall mounting seat in the bottom mold.

[0109] A plurality of cover-shaped exhaust risers 31d and cover-shaped exhaust holes 31e extending downward are provided on the top of the cover 31 for exhausting gas and skimming slag during the pouring process.

[0110] The curved and slender oil passage core 16 is assembled and connected to the cover type 31 from below. The integral left side wall mounting seat sand mold 28 is inserted from the left side of the cover type 31 and fixed through the dovetail groove 31a that is wider at the top and narrower at the bottom. The integral right side wall mounting seat sand mold 30 is inserted from the right side of the cover type 31 and is also fixed through the dovetail groove 31a that is wider at the top and narrower at the bottom. The exhaust eye removable sand mold 29 is connected to the cover type 31 from below.

[0111] As Figure 10 shown, the bottom of the integral right side wall mounting seat sand mold 30 is provided with an integral right side wall mounting seat sand mold positioning core head 30a, and an integral right side wall mounting seat sand mold positioning boss 30b is provided on the circumference of the integral right side wall mounting seat sand mold positioning core head 30a.

[0112] The thick hot spot position of the integral right side wall mounting seat sand mold 30 is provided with chiller grooves 30c, and chillers are respectively inserted into the chiller grooves 30c to enhance heat dissipation.

[0113] On the outer wall of the thick hot spot position of the integral right side wall mounting seat sand mold 30 where the formed chiller cannot be placed, there are grid-shaped and downwardly concave chill rib grooves 30d to increase the heat dissipation area and strengthen the local heat dissipation effect, and it will be polished off after forming.

[0114] Step S5 is assembled in the following sub-steps, which is the safest and most efficient:

[0115] Step S5.1, as Figure 11 shown, install the annular flat long oil passage core 19 in the cavity of the bottom mold 24;

[0116] Step S5.2, after respectively placing chillers in the chiller grooves on the front side of the bottom mold, then insert the bottom mold front removable sand core 26 into the front port of the chiller groove to position the chiller;

[0117] Step S5.3, install the bottom mold side removable sand core 25 and the integral rear side wall mounting seat sand mold 27 in the bottom mold;

[0118] Step S5.4, as Figure 12 shown, load the formed chiller into the chiller groove 30c of the integral right side wall mounting seat sand mold 30, and then insert the integral right side wall mounting seat sand mold positioning core head 30a into the corresponding positioning counterbore of the bottom mold to achieve central positioning and axial positioning of the integral right side wall mounting seat sand mold 30; at the same time, the integral right side wall mounting seat sand mold positioning boss 30b is embedded in the corresponding groove of the bottom mold 24 to achieve radial positioning of the integral right side wall mounting seat sand mold 30; finally, it is fixedly fitted on the cover type 31 through the dovetail groove 31a;

[0119] Assemble the integral left side wall mounting seat sand mold 28 and the exhaust eye removable sand mold 29 onto the cover type 31 in the same way;

[0120] Step S5.5: Load the chill into the chill groove of the cover type 31;

[0121] Step S5.6: Install the curved and slender oil passage core 16 in the cavity of the cover type.

Claims

1. A casting method for the front end cover of a helicopter engine, characterized in that, It successively includes the following steps: S1. Model the engine front cover; S2. Design the gating system; S3. Determine the parting surface, and design the bottom mold (24), cover mold (31), each split movable sand mold, core and oil passage core; S4. 3D print the bottom mold (24), cover mold (31), riser sand mold, each split movable sand mold, core and oil passage core; S5. Install each core, oil passage core and split movable sand mold into the corresponding sand mold respectively; S6. Hoist and stack the bottom mold (24) and cover mold (31) successively from bottom to top to form an integral sand mold; S7. Hoist the combined integral sand mold into the sand box, carry out sand filling and molding, cover the exhaust groove and exhaust hole above the cover mold with heat insulation cotton. After the resin sand is cured, hoist the sand box above the sealing cover of the heat insulation furnace; a lifting pipe is installed at the center of the sealing cover, and the upper port of the lifting pipe is butted against the center gate of the bottom mold (24); S8. Melt the magnesium alloy liquid, carry out low-pressure casting, and under the action of air pressure, the magnesium alloy liquid fills upward through the lifting pipe and the pressure-regulating gate; S9. Shake out the sand after cooling and solidification to obtain the blank of the engine front cover.

2. The casting method of the front end cover of a helicopter engine according to claim 1, characterized in that, In step S1, the engine front cover includes a large flat surface of the casting body, a central rotating shaft hole (1a) is provided on the large flat surface of the casting body, a left arm rotating shaft hole (1b1) and a left arm large mounting flange (1c1) are connected to the left side of the upper end of the central rotating shaft hole (1a), a right arm rotating shaft hole (1b2) and a right arm large mounting flange (1c2) are connected to the right side of the upper end of the central rotating shaft hole (1a), the other end of the central rotating shaft hole (1a) is connected to a thin-wall area gear shaft housing (1d1) with an overall concave shape, and a gear shaft housing oil passage inlet (1d2) is provided at the central position of the gear shaft housing (1d1).

3. The casting method of the front end cover of a helicopter engine according to claim 2, characterized in that, A left suspension oil passage inlet (1e1) is provided between the left arm large mounting flange (1c1) and the gear shaft housing (1d1), a right suspension oil passage inlet (1e2) is provided between the right arm large mounting flange (1c2) and the gear shaft housing (1d1), and an observation port connecting flange (1f) is provided on the outer side wall of the left suspension oil passage inlet (1e1); an oil passage (1g) is provided on the outer periphery of the central rotating shaft hole (1a), and the oil passage (1g) communicates the central rotating shaft hole (1a) with the gear shaft housing oil passage inlet (1d2).

4. The casting method of the front end cover of a helicopter engine according to claim 1, characterized in that, The gating system in step S2 includes a center gate (2), a plurality of first-layer support cross gates (3) extending radially outward are connected to the outer periphery of the upper end of the center gate (2), the top of the first-layer support cross gate (3) near the outer end is connected to a second-layer water inlet cross gate (5) through a first-layer water inlet (4) to form a double-gate system; the second-layer water inlet cross gate (5) forms a ring below the areas of the left arm rotating shaft hole (1b1), left arm large mounting flange (1c1), right arm rotating shaft hole (1b2), and right arm large mounting flange (1c2) and is connected to the bottom of the engine front cover through a plurality of second-layer water inlets (6).

5. The casting method of the front end cover of a helicopter engine according to claim 4, characterized in that, The outer side of the second-layer water inlet cross-riser (5) is connected with a side riser (8) extending upward. The side riser (8) is connected with the second-layer water inlet cross-riser (5) and is connected with the outside of the casting through a side water inlet (9). The center of the second-layer water inlet cross-riser (5) is connected with a center riser (14) extending upward. The outer circumference of the center riser (14) is connected with the inner circumferential wall of the central rotating shaft hole (1a) through a plurality of center water inlets.

6. The casting method of the front end cover of a helicopter engine according to claim 2, characterized in that, At the top center of the central rotating shaft hole (1a), there is an exhaust groove (12) extending upward. At the upper openings of the thick and large part left-arm rotating shaft hole (1b1), left-arm large mounting flange (1c1), right-arm rotating shaft hole (1b2), and right-arm large mounting flange (1c2), there are flange risers (11). On the outer wall of the central rotating shaft hole (1a), there is a boss. The second-layer water inlet cross-riser (5) fills the boss separately through a dot gate (7).

7. The casting method of the front end cover of a helicopter engine according to claim 6, characterized in that, The magnesium alloy liquid enters from the center gate (2), then flows radially outward along each first-layer support cross-riser (3). After the magnesium alloy liquid fills the first-layer support cross-riser (3), it reaches the second-layer water inlet cross-riser (5) through the first-layer water inlet (4). After the magnesium alloy liquid evenly fills the second-layer water inlet cross-riser (5), it enters the cavity through the second-layer water inlet (6) and the dot gate (7) for filling from bottom to top, and also fills the side wall of the thicker central rotating shaft hole (1a) through the center riser (14). The magnesium alloy liquid entering the engine front cover cavity rises evenly from the bottom, fills the thick and large parts such as the left-arm large mounting flange (1c1) and the right-arm large mounting flange (1c2), and then continues to rise into the flange riser (11).

8. The casting method of the front end cover of a helicopter engine according to claim 7, characterized in that, On the top of the circumferential wall of the central rotating shaft hole (1a), three exhaust grooves (12) extending upward are evenly distributed to discharge the gas generated during the casting of the casting. The flange riser (11) compensates for the shrinkage of the thick and large parts including the left-arm large mounting flange (1c1) and the right-arm large mounting flange (1c2). The top of the gear shaft housing (1d1) is compensated for shrinkage through each open riser (13), and the gas generated during the filling process is discharged through each open riser (13). On the outer side of the observation port connecting flange (1f), there are side risers (8) extending upward. The side risers (8) are connected with the second-layer water inlet cross-riser (5). After the magnesium alloy liquid fills the side risers (8), it compensates for the shrinkage of the observation port connecting flange (1f) through two side water inlets (9). In the areas between the top of the gear shaft housing (1d1) and the left-arm rotating shaft hole (1b1), the right-arm rotating shaft hole (1b2) and the boss, there are a plurality of center risers (10) extending upward, which are used to compensate for the shrinkage of the top boss and the flange below it.

9. The casting method of the front end cover of a helicopter engine according to claim 2, characterized in that, The outer peripheries of the left-arm large mounting flange (1c1) and the right-arm large mounting flange (1c2) are provided with curved slender oil passages. The inner diameter of the curved slender oil passages is 12 mm, the wall thickness is 4 - 6 mm, the length is more than 1.6 m, and they are fixed in the cover type (31); the head ends of the curved slender oil passage cores (16) are connected to the side wall oil holes of the left-arm large mounting flange (1c1), the right-arm large mounting flange (1c2), the left-arm rotating shaft hole (1b1), and the right-arm rotating shaft hole (1b2); the tail ends of the curved slender oil passage cores (16) are connected to the side wall oil hole of the central rotating shaft hole (1a); the curved slender oil passage cores (16) are assembled from multiple segments, and the facing ends between the segments are respectively lap-connected to each other through half-tenons (16a), and there is an oil passage positioning gap (16b) of 0.3 mm between each pair of half-tenons (16a), and the length of each segment of the curved slender oil passage core (16) is 300 - 400 mm.

10. The casting method of the front end cover of a helicopter engine according to claim 9, characterized in that, Each oil port of the curved slender oil passage core (16) serves as a support column respectively, and an oil passage core positioning pin (23) is provided at the lower end of each support column. Each oil passage core positioning pin (23) is of a conical structure and is respectively embedded in the corresponding oil passage core positioning groove (24a) of the bottom mold (24). There is a process hole positioning gap (24b) of 0.3 mm between each oil passage core positioning pin (23) and the corresponding oil passage core positioning groove (24a). After the oil passage assembly is completed, all the gap positions are brushed and filled with coating.

11. The casting method of the front end cover of a helicopter engine according to claim 10, characterized in that, A through central vent hole is provided along the centerlines of the curved slender oil passage core (16) and each support column.

12. The casting method of the front end cover of a helicopter engine according to claim 2, characterized in that, The outer periphery of the central rotating shaft hole (1a) is provided with an annular flat long oil passage that surrounds most of the circumference of the central rotating shaft hole (1a). The cross-section of the annular flat long oil passage is 36 mm × 13 mm, the length is more than 1.4 m, and it is fixed in the bottom mold (24). The head ends of the annular flat long oil passage core (19) are respectively connected to the left suspension oil passage inlet (1e1) and the right suspension oil passage inlet (1e2), and the tail end extends straight to the gear shaft box oil passage inlet (1d2) at the center of the gear shaft box (1d1).

13. The casting method of the front end cover of a helicopter engine according to claim 12, characterized in that, Each oil port of the annular flat long oil passage core (19) serves as a support column respectively. A section of inner groove is provided at the end of the two end support columns, and a section of chill groove (22) is placed in the inner groove for placing chills. A central vent hole is provided along the axis of the annular flat long oil passage core (19) and penetrates through the center of the chill groove (22) to the outside.

14. The casting method of the front end cover of a helicopter engine according to claim 1, characterized in that, The bottom mold (24) is provided with five bottom mold split cores, including bottom mold side split cores (25), bottom mold front split cores (26), and an integral rear side wall mounting seat sand mold (27). Among them, two bottom mold side split cores (25) are located in the grooves on the side walls of the bottom mold, which is convenient for brushing the coating on the parts in contact with the side walls of the casting; two bottom mold front split cores (26) are respectively located in the front side grooves of the bottom mold, which is convenient for installing the inner chills; an integral rear side wall mounting seat sand mold (27) is located at the upper end of the base, which is convenient for installing the annular flat long oil passage core (19) and the chills; the five bottom mold split cores are respectively located between the four base mounting holes and are respectively provided with tenons at the bottom that are embedded in the grooves of the bottom mold (24).

15. The casting method of the front end cover of a helicopter engine according to claim 1, characterized in that, The integral left wall mounting seat sand mold (28) is inserted into the dovetail groove (31a) that is wider at the top and narrower at the bottom in the cover mold (31) from the left side of the cover mold (31), and the integral right wall mounting seat sand mold (30) is inserted into the dovetail groove (31a) that is wider at the top and narrower at the bottom in the cover mold (31) from the right side of the cover mold (31); after the cavity of the gear shaft housing (1d1) is cleaned, the exhaust hole removable sand mold (29) is connected to the cover mold (31) from below.

16. The casting method of the front end cover of a helicopter engine according to claim 15, characterized in that, The bottom of the integral right wall mounting seat sand mold (30) is provided with an integral right wall mounting seat sand mold positioning core head (30a), and an integral right wall mounting seat sand mold positioning boss (30b) is provided on the circumference of the integral right wall mounting seat sand mold positioning core head (30a); chill grooves (30c) are provided at the thick hot spots of the integral right wall mounting seat sand mold (30), and chills are respectively inserted into each chill groove (30c) to enhance heat dissipation; a grid-shaped and downwardly concave chill rib groove (30d) is provided on the outer wall at the thicker hot spots of the integral right wall mounting seat sand mold (30), and it is polished off after molding.

17. The casting method of the front end cover of a helicopter engine according to claim 1, characterized in that, Step S5 includes the following sub-steps: Step S5.1: Install the annular flat long oil passage sand core (19) in the cavity of the bottom mold (24); Step S5.2: After placing chills in the chill grooves on the front side of the bottom mold (24) respectively, then insert the front removable sand core (26) of the bottom mold into the front ports of the chill grooves to position the chills; Step S5.3: Install the side removable sand core (25) of the bottom mold and the integral rear wall mounting seat sand mold (27) in the bottom mold; Step S5.4: Insert the formed chills into the chill grooves (30c) of the integral right wall mounting seat sand mold (30), and then insert the integral right wall mounting seat sand mold positioning core head (30a) into the corresponding positioning counterbores of the bottom mold to achieve central positioning and axial positioning of the integral right wall mounting seat sand mold (30); at the same time, the integral right wall mounting seat sand mold positioning boss (30b) is embedded in the corresponding grooves of the bottom mold (24) to achieve radial positioning of the integral right wall mounting seat sand mold (30); finally, it is fixedly engaged on the cover mold (31) through the dovetail groove (31a); assemble the integral left wall mounting seat sand mold (28) and the exhaust hole removable sand mold (29) onto the cover mold (31) in the same way; Step S5.5: Insert the chills into the chill grooves of the cover mold (31); Step S5.6: Install the curved slender oil passage sand core (16) in the cavity of the cover mold.

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