A casting method of a high-compactness air-cooled diesel engine cylinder head

Abstract

The application discloses a casting method of a high-compactness air-cooled diesel engine cylinder cover, and comprises the following steps: step 1, melting RR350 aluminum alloy into a liquid and obtaining an aluminum alloy solution after deslagging and degassing; step 2, pouring the aluminum alloy solution into a preheated metal mold; step 3, connecting a collaborative vibration rod with a free end of an ultrasonic amplitude bar of an ultrasonic concentrator, then inserting the collaborative vibration rod into the metal mold through an oil injection hole of the metal mold, so that the aluminum alloy solution in the metal mold is vibrated under the driving of the ultrasonic amplitude bar and the collaborative vibration rod until the aluminum alloy solution is completely solidified, so that fine and uniform crystal grains are formed when the aluminum alloy solution is solidified and crystallized; the application realizes ultrasonic vibration mode solidification and shrinkage compensation at a difficult position of a thin wall of a casting, forms a multi-field auxiliary cylinder cover casting forming process of coupling of an ultrasonic field and a gravity field, promotes the shrinkage compensation, reduces the pinhole degree, refines the crystal grains, and improves the yield and performance of the casting.

Description

Technical Field

[0001] This invention belongs to the field of metal smelting and casting, and particularly relates to a casting method for a high-compactness air-cooled diesel engine cylinder head. Background Technology

[0002] With the development of equipment technology, the power output per liter of air-cooled diesel engines is constantly increasing, and their service conditions are becoming increasingly harsh. Under conditions of high compactness, high temperature, high pressure, high mechanical stress, high thermal load, high speed, and high friction, extremely high demands are placed on the heat dissipation performance and load-bearing capacity of the diesel engine cylinder head. With the increase in engine power density and the high compactness of the structural layout, the thermal and mechanical loads on the cylinder head are becoming more severe. This not only requires the cylinder head material to have good strength, toughness, and fatigue resistance, but also places higher demands on the casting and molding of high-compact air-cooled diesel engine cylinder heads. Therefore, based on improvements in cylinder head materials, the casting and molding process is optimized and improved to enhance the performance of high-compact air-cooled diesel engine cylinder head products and obtain high-quality, low-cost cylinder head castings.

[0003] The development of aluminum alloy cylinder head castings has progressed from initial sand casting to semi-metallic mold casting (forming the outer metal mold and inner sand core) and then to low-pressure casting. Gravity casting and low-pressure casting are the most commonly used casting processes for aluminum alloy cylinder heads. In the vast majority of aluminum alloy cylinder head production worldwide today, gravity casting is the most widely used casting process. Using a gravity casting machine, molten metal fills the metal mold through a gating system under its own gravity, thus obtaining the desired casting. During gravity casting, due to the high thermal conductivity of the metal mold and the effect of the mold water cooling system, the casting cools rapidly, resulting in a relatively fine grain structure and high mechanical properties. Furthermore, gravity casting equipment is simple and reliable in construction, and easy and flexible to operate and maintain. Compared to traditional pressure casting and vacuum casting, gravity casting machines do not require high-pressure or vacuum equipment, reducing complexity and energy consumption.

[0004] Currently, due to the trend of increasing compactness, refinement, and thinness in air-cooled diesel engine cylinder head castings, the performance requirements for castings are becoming increasingly stringent. In particular, there are issues such as insufficient filling of thin-walled cooling blades in air-cooled cylinder heads, coarsening of grains in thin-walled structures, localized thermal shrinkage, slow solidification in thick areas, and the tendency for coarse grains to appear, which in turn lead to low alloy performance. Summary of the Invention

[0005] The purpose of this invention is to provide a casting method for a highly compact air-cooled diesel engine cylinder head, in order to solve the problems of insufficient filling of thin-walled cylinder heads, grain coarsening at thin-walled structures, and localized thermal shrinkage caused by traditional gravity metal mold casting processes.

[0006] This invention adopts the following technical solution: a casting method for a highly compact air-cooled diesel engine cylinder head, comprising:

[0007] Step 1: Melt RR350 aluminum alloy into a liquid and remove slag and gas to obtain an aluminum alloy solution;

[0008] Step 2: Pour the molten aluminum alloy into the preheated metal mold;

[0009] Step 3: Connect the co-vibrating rod to the free end of the ultrasonic amplitude transformer of the ultrasonic energy concentrator, and then insert the co-vibrating rod through the oil spray hole of the metal mold into the metal mold. This allows the aluminum alloy solution in the metal mold to vibrate under the drive of the ultrasonic amplitude transformer and the co-vibrating rod until the aluminum alloy solution is completely solidified, so that the aluminum alloy solution forms fine and uniform grains during solidification.

[0010] Furthermore, the coordinated vibration rod includes:

[0011] The coordinating rod has a square cross-section. Its outer end is threaded to the free end of the ultrasonic amplitude transformer of the ultrasonic energy concentrator, and its inner end is beveled and used to fit against the outside of the oil spray hole of the metal mold.

[0012] The vibrating extension rod is cylindrical and fits the oil spray hole surface of the metal mold. The vibrating extension rod and the coaxial linkage are coaxially arranged. The fixed end of the vibrating extension rod is integrally connected to the inner end of the coaxial linkage. Its extension end is used to extend into the metal mold and make the aluminum alloy solution vibrate under the drive of the ultrasonic amplitude transformer and the coaxial linkage.

[0013] Furthermore, in step 3, the vibration frequency of the ultrasonic amplitude transformer is 20-30 kHz and the power is 2-3 kW.

[0014] Furthermore, in step 3, the insertion depth of the vibrating extension rod is 50–60 mm, and the insertion angle is 30°–60°.

[0015] Further, in step 1, the RR350 aluminum alloy is smelted twice at a temperature of 750±20℃. During the first refining, 0.3-0.5% inorganic salt and 4%-6% Al-5Ti-B are added; during the second refining, 1%-2% inorganic salt is added.

[0016] Furthermore, in step 2, the preheating temperature of the metal mold is 250–280°C.

[0017] Furthermore, step 2, in which the aluminum alloy solution is poured into the preheated metal mold, is completed in 8–10 seconds.

[0018] The beneficial effects of this invention are:

[0019] This invention introduces an ultrasonic field into the cylinder head casting mold, applies ultrasonic vibration during the solidification process of the casting, and designs a vibration extension rod according to the shape of the oil injection hole in the mold; thereby realizing the solidification and feeding of thin-walled and difficult-to-fill parts of the casting by ultrasonic vibration mode, forming a multi-field assisted cylinder head casting process coupled with ultrasonic field and gravity field, promoting feeding, reducing pinholes, refining grains, and improving the yield and performance of the casting;

[0020] This invention introduces ultrasound to refine the grain size during alloy solidification, resulting in a 15% increase in yield strength and a 73% increase in elongation compared to traditional gravity casting, thus reducing the risk of engine cylinder head cracking.

[0021] This invention utilizes a vibrating insert rod to drive the aluminum alloy solution in the metal mold to achieve ultrasonic vibration during the casting process under certain power parameters. This alters the original solidification characteristics of the alloy, resulting in finer, more uniform grains and optimized grain boundaries during crystallization. Consequently, it improves the strength and toughness of the cylinder head material and creates a certain residual stress field in typical structural parts of the cylinder head, enhancing the overall rigidity and stability of the cylinder head. It also provides a certain feeding function, reduces porosity, increases the cylinder head yield, and enables multi-field assisted casting of highly compact air-cooled diesel engine cylinder heads. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the collaborative vibration rod of the present invention;

[0023] Figure 2 These are tissue morphology diagrams of Comparative Example 1, Examples 1, 2, and 3 in this invention;

[0024] Figure 3 The mechanical properties of Comparative Example 1, Examples 1, 2, and 3 in this invention are shown in the diagram. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0026] This invention discloses a casting method for a highly compact air-cooled diesel engine cylinder head, comprising:

[0027] Step 1: Melt RR350 aluminum alloy into a liquid and remove slag and gas to obtain an aluminum alloy solution;

[0028] Step 2: Pour the molten aluminum alloy into the preheated metal mold;

[0029] Step 3: Connect the co-vibrating rod to the free end of the ultrasonic amplitude transformer of the ultrasonic energy concentrator, and then insert the co-vibrating rod through the oil spray hole of the metal mold into the metal mold. This allows the aluminum alloy solution in the metal mold to vibrate under the drive of the ultrasonic amplitude transformer and the co-vibrating rod until the aluminum alloy solution is completely solidified, so that the aluminum alloy solution forms fine and uniform grains during solidification.

[0030] Step 1 involves two melting processes of RR350 aluminum alloy, both at a temperature of 750±20℃. During the first refining process, 0.3-0.5% inorganic salt and 4%-6% Al-5Ti-B are added; during the second refining process, 1%-2% inorganic salt is added.

[0031] In step 2, the preheating temperature of the metal mold is 250–280°C. The pouring of the molten aluminum alloy into the preheated metal mold in step 2 is completed in 8–10 seconds.

[0032] In step 3, the vibration frequency of the ultrasonic amplitude transformer is 20–30 kHz, and the power is 2–3 kW. The insertion depth of the vibrating extension rod 2 in step 3 is 50–60 mm, and the insertion angle is 30°–60°. The vibration time of the ultrasonic amplitude transformer of the ultrasonic concentrator in step 3 is 3–5 minutes.

[0033] The coordinated vibration rod includes: coordinated rod 1 and vibration extension rod 2.

[0034] The cross-section of the coordinating rod 1 is square. The outer end of the coordinating rod 1 is threadedly connected to the free end of the ultrasonic amplitude transformer of the ultrasonic energy concentrator. The inner end of the coordinating rod 1 is beveled and is used to fit against the outside of the oil spray hole of the metal mold. The vibration extension rod 2 is cylindrical and fits against the surface of the oil spray hole of the metal mold. The vibration extension rod 2 is coaxially arranged with the coordinating rod 1. The fixed end of the vibration extension rod 2 is integrally connected to the inner end of the coordinating rod 1. The extension end of the vibration extension rod 2 is used to extend into the metal mold and make the aluminum alloy solution vibrate under the drive of the ultrasonic amplitude transformer and the coordinating rod 1.

[0035] Comparative Example 1

[0036] This comparative example uses the conventional gravity casting method, and the specific steps include:

[0037] Step 1: Melt RR350 aluminum alloy into a liquid and remove slag and gas to obtain an aluminum alloy solution.

[0038] The RR350 aluminum alloy, by atomic percentage, includes: Cu: 4.6%, Ni: 1.5%, Mn: 0.2%, Zr: 0.2%, Ti: 0.18%, Co: 0.3%, Sb: 0.3%, Fe≤0.50%, Si≤0.30%, Mg≤0.05%, with the remainder being Al.

[0039] Step 1 involves two melting processes, both at 760℃. During the initial refining, 0.4% inorganic salt and 5% Al-5Ti-B are added; during the second refining, 1.5% inorganic salt is added. High-purity argon is used for degassing in Step 1 at a flow rate of 0.5 L / min, and the slag removal settling time is 15 min.

[0040] Step 2: When the temperature of the aluminum alloy solution is 750℃, pour the aluminum alloy solution into the metal mold that has been preheated to 280℃. The pouring of the aluminum alloy solution into the preheated metal mold should be completed within 8 seconds.

[0041] Step 4: After casting and filling the mold, remove the blank cylinder head 4 minutes later and perform T6 heat treatment for solution aging. Solution treatment: hold at 545±5℃ for 8 hours, then raise the temperature to 555±5℃ with the furnace, hold for 7 hours, and then quench in water at 70-95℃. Aging treatment: hold at 160℃ for 24 hours, and then air cool after removal.

[0042] The cylinder head obtained in Comparative Example 1 was dissected to examine the grain size. Under conventional gravity casting conditions, the grain size of the aluminum alloy cylinder head was 98±15μm, and its microstructure was as follows. Figure 2 As shown in Comparative Example 1, the mechanical property results are shown in Table 1 and... Figure 3 As shown.

[0043] Example 1

[0044] Step 1: Melt RR350 heat-resistant aluminum alloy into a liquid and remove slag and gas to obtain an aluminum alloy solution.

[0045] The RR350 aluminum alloy, by atomic percentage, includes: Cu: 4.6%, Ni: 1.5%, Mn: 0.2%, Zr: 0.2%, Ti: 0.18%, Co: 0.3%, Sb: 0.3%, Fe≤0.50%, Si≤0.30%, Mg≤0.05%, with the remainder being Al.

[0046] Step 1 involves two melting processes, both at 750℃. During the initial refining, 0.3% inorganic salt and 4% Al-5Ti-B are added; during the second refining, 1% inorganic salt is added. High-purity argon is used for degassing in Step 1, with a flow rate of 0.6 L / min, and the slag removal settling time is 18 min.

[0047] Step 2: When the temperature of the aluminum alloy solution is 755℃, pour the aluminum alloy solution into the metal mold that has been preheated to 250℃. The pouring of the aluminum alloy solution into the preheated metal mold is completed in 8 seconds.

[0048] In step 3: the insertion depth of the synergistic vibration rod is 50mm, the insertion angle is 30°, the vibration frequency of the ultrasonic amplitude transformer is 20KHz, the power of the ultrasonic generator of the ultrasonic amplitude transformer is 2KW, and the ultrasonic vibration solidification time is 4min.

[0049] The cylinder head obtained in Example 1 was dissected to examine the grain size. The grain size of the aluminum alloy cylinder head in Example 1 was 75±8μm, and its microstructure was as follows. Figure 2 As shown in Example 1, the mechanical property results are shown in Table 1 and Figure 3 As shown.

[0050] Example 2

[0051] The specific steps in this embodiment are the same as in embodiment 2, except that:

[0052] In step 1, 0.45% inorganic salt and 5% Al-5Ti-B are added during the initial refining; 1.5% inorganic salt is added during the secondary refining.

[0053] In step 2, the aluminum alloy solution is poured into a metal mold that has been preheated to 260°C and the process is completed in 9 seconds.

[0054] In step 3, the insertion depth of the co-vibrating rod is 55mm, the insertion angle is 45°, the vibration frequency of the ultrasonic amplitude transformer is 25KHz, the power of the ultrasonic generator of the ultrasonic amplitude transformer is 2.5KW, and the ultrasonic vibration solidification time is 4min.

[0055] The cylinder head obtained in Example 2 was dissected to examine the grain size. The grain size of the aluminum alloy cylinder head in Example 2 was 56±10μm, and its microstructure was as follows. Figure 2 As shown in Example 2, the mechanical properties are shown in Table 1 and... Figure 3 As shown.

[0056] Example 3

[0057] The specific steps in this embodiment are the same as in embodiment 1, except that:

[0058] In step 1, 0.5% inorganic salt and 6% Al-5Ti-B are added during the initial refining; 2% inorganic salt is added during the secondary refining.

[0059] In step 2, the aluminum alloy solution is poured into a metal mold that has been preheated to 280°C and the process is completed in 10 seconds.

[0060] In step 3, the insertion depth of the co-vibrating rod is 60mm, the insertion angle is 60°, the vibration frequency of the ultrasonic amplitude transformer is 30KHz, the power of the ultrasonic generator of the ultrasonic amplitude transformer is 3.0KW, and the ultrasonic vibration solidification time is 4min.

[0061] The cylinder head obtained in Example 3 was dissected to examine the grain size. The grain size of the aluminum alloy cylinder head in Example 3 was 43±10μm, and its microstructure was as follows. Figure 2 As shown in Example 3, the mechanical properties are shown in Table 1 and... Figure 3 As shown.

[0062] Table 1

[0063] Tensile strength / MPa Yield strength / MPa Elongation / % Comparative Example 1 262 225 1.85 Example 1 276 234 2.21 Example 2 281 245 2.8 Example 3 298 260 3.2

[0064] Based on the results of the alloy microstructure and grain size of the cylinder heads prepared in Comparative Example 1 and Examples 1, 2 and 3, it can be seen that the grain size of the aluminum alloy in Examples 1, 2 and 3 is significantly reduced, with the grain size being refined from 98±15μm in Comparative Example 1 to 43±10μm. The number of precipitated strengthening phases increases by up to 8%, the tensile strength increases to 298MPa, the yield strength increases to 260MPa, and the elongation increases to 3.2%.

[0065] Anatomical analysis of the thin-walled region of the cylinder head reveals that, with the assistance of multi-field coupling of gravity and ultrasonic fields, the thin-walled structure achieves feeding compensation and microstructure refinement, reducing porosity and cracking, and improving the casting quality of the cylinder head. Figure 3 It can be seen that pores and cracks did not appear in the metallographic structure.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A casting method for a highly compact air-cooled diesel engine cylinder head, characterized in that, include: Step 1: Melt RR350 aluminum alloy into a liquid and remove slag and gas to obtain an aluminum alloy solution; Step 2: Pour the molten aluminum alloy into the preheated metal mold; Step 3: Connect the co-vibrating rod to the free end of the ultrasonic amplitude transformer of the ultrasonic energy concentrator, and then insert the co-vibrating rod through the oil spray hole of the metal mold into the metal mold. This allows the aluminum alloy solution in the metal mold to vibrate under the drive of the ultrasonic amplitude transformer and the co-vibrating rod until the aluminum alloy solution is completely solidified, so that the aluminum alloy solution forms fine and uniform grains during solidification. The coordinated vibration rod includes: The collaborative rod (1) has a square cross-section. Its outer end is threaded to the free end of the ultrasonic amplitude transformer of the ultrasonic energy concentrator, and its inner end is a bevel and is used to fit on the outside of the oil spray hole of the metal mold. The vibrating extension rod (2) is columnar and fits the oil spray hole surface of the metal mold. The vibrating extension rod (2) is coaxially arranged with the cooperating rod (1). The fixed end of the vibrating extension rod (2) is integrally connected with the inner end of the cooperating rod (1). Its extension end is used to extend into the metal mold and make the aluminum alloy solution vibrate under the drive of the ultrasonic amplitude rod and the cooperating rod (1).

2. The casting method for a high-compactness air-cooled diesel engine cylinder head according to claim 1, characterized in that, In step 3, the vibration frequency of the ultrasonic amplitude transformer is 20~30 KHz and the power is 2~3 KW.

3. The casting method for a high-compactness air-cooled diesel engine cylinder head according to claim 1, characterized in that, The insertion depth of the vibrating extension rod (2) in step 3 is 50~60 mm, and the insertion angle is 30°~60°.

4. The casting method for a high-compactness air-cooled diesel engine cylinder head according to claim 1, characterized in that, Step 1 involves two melting processes of RR350 aluminum alloy, both at a temperature of 750±20℃. During the first refining process, 0.3~0.5% inorganic salt and 4%~6% Al-5Ti-B are added; during the second refining process, 1%~2% inorganic salt is added.

5. The casting method for a high-compactness air-cooled diesel engine cylinder head according to claim 1, characterized in that, In step 2, the preheating temperature of the metal mold is 250~280℃.

6. The casting method for a high-compactness air-cooled diesel engine cylinder head according to claim 1, characterized in that, Step 2, pouring the aluminum alloy solution into the preheated metal mold, should be completed in 8-10 seconds.

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