Welded all-steel piston and manufacturing method thereof

Abstract

The invention discloses a welded all-steel piston and a manufacturing method thereof.The manufacturing method of the welded all-steel piston comprises the following operation steps that S1, a piston head and a piston skirt are preprocessed; s2, friction welding is conducted, specifically, the preprocessed piston head and the piston skirt are connected into a whole in a friction welding mode, and a closed inner cooling oil cavity is formed in the piston head and the piston skirt; s3, vacuum tempering is conducted; s4, the inner cooling oil cavity is filled with a removable sealing medium, specifically, the inner cooling oil cavity is filled with a removable solid sealing medium, and the whole inner cooling oil cavity and the oil hole are filled and sealed with the solid sealing medium; s5, finish machining is conducted, specifically, the piston body filled with the solid sealing medium is subjected to finish machining; and S6, the sealing medium is removed, specifically, the piston body subjected to finish machining is heated, so that the solid sealing medium is melted or softened, and the solid sealing medium is discharged out of the inner cooling oil cavity. According to the welded all-steel piston and the manufacturing method thereof, the cleanliness of the inner cooling oil cavity can be effectively improved, and the technological process is simplified.

Description

Technical Field

[0001] This invention relates to the field of internal combustion engine piston technology, and in particular to a welded all-steel piston and its manufacturing method, which is especially suitable for high power density diesel engines, natural gas engines, etc. Background Technology

[0002] Welded steel pistons typically employ a split structure, where the piston head and piston skirt are machined separately and then joined together using methods such as friction welding, forming an internal cooling oil chamber. To introduce and remove coolant from this chamber, inlet and outlet ports are machined on the piston, communicating with the chamber. In existing manufacturing processes, after the piston blank is welded, subsequent finishing processes are required, including turning, drilling, and milling of pin holes and crescent grooves. During this process, cutting fluid can easily enter the hollow internal cooling oil chamber, leading to internal corrosion. Simultaneously, machining debris such as metal shavings can easily enter the internal cooling oil chamber through the oil holes or other gaps, and are difficult to clean thoroughly, severely impacting piston cleanliness and final product quality.

[0003] To address the aforementioned problems, the existing technology typically employs a method of sealing the inlet and outlet ports of the internal cooling oil cavity with specialized rubber or plastic plugs before finishing. However, this approach has the following drawbacks: First, the plugs are specialized components, resulting in higher costs, and they are prone to detachment during processing due to corrosion, aging, or vibration, leading to seal failure. Second, the plugs must be removed before processes such as milling the pin holes and crescent grooves, allowing steel shavings to easily fall into the internal cooling oil cavity. Although deburring and air-blowing cleaning processes are added subsequently, the steel shavings swirl within the cavity, making complete removal difficult. Furthermore, weld seams formed during welding can easily trap foreign objects. Overall, the existing process is lengthy, and the cleanliness of the internal cooling oil cavity is difficult to guarantee. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the present invention provides a welded all-steel piston and its manufacturing method, which can effectively improve the cleanliness of the internal cooling oil cavity and simplify the process flow.

[0005] The technical solution provided by this invention is as follows: A method for manufacturing a welded all-steel piston includes the following steps: S1. Pre-machining of piston head and piston skirt: The piston head and piston skirt are machined to the preset shape respectively, and an internal cooling oil cavity and an oil hole communicating with the internal cooling oil cavity are formed. The remaining parts are left with a finishing allowance. S2. Friction welding: The pre-processed piston head and piston skirt are connected together by friction welding to form a piston body, and the interior of the piston body forms a closed internal cooling oil cavity. S3, Vacuum tempering: Vacuum tempering treatment is performed on the welded piston body; S4. Filling the internal cooling oil cavity with a removable sealing medium: Filling the internal cooling oil cavity with a removable solid sealing medium, so that the solid sealing medium fills and seals the entire internal cooling oil cavity and the oil hole; S5. Finishing: Finishing the piston body filled with solid sealing medium, including turning, boring, drilling and / or milling; S6. Remove sealing medium: Heat the finished piston body to melt or soften the solid sealing medium and discharge it from the internal cooling oil chamber.

[0006] Preferably, the sealing medium that can be removed in step S4 is rust-preventive paraffin wax. The melting point of the rust-preventive paraffin is in the range of 55–60°C.

[0007] Preferably, step S4 specifically includes the following operation process: cooling the piston body after vacuum tempering to 70-80°C, then pouring solid anti-rust paraffin particles into the oil hole, using the residual heat of the piston body to melt and flow the anti-rust paraffin particles until they fill the entire internal cooling oil cavity and oil hole, and then cooling to solidify the anti-rust paraffin into a solid state.

[0008] Preferably, the particle size of the solid rust-preventive paraffin particles in step S4 is 0.5 to 2.0 mm.

[0009] Preferably, the rust-preventive paraffin in step S4 consists of the following components by mass percentage: Fully refined paraffin wax 70-85%, Stearic acid 8-15%, Barium petroleum sulfonate rust inhibitor 3-8%.

[0010] Preferably, in step S2, a welded horn is formed at the joint between the piston head and the piston skirt during friction welding; The root width d of the welded ram's horn is not less than 0.5 mm; The gap t of the welded ram's horn is 0 to 0.4 mm.

[0011] Preferably, the specific process parameters for vacuum tempering in step S3 are as follows: Tempering temperature 580~630℃, Insulation time: 2-4 hours After cooling in the furnace to 200-90°C, the product is removed from the furnace.

[0012] Preferably, during the finishing process in step S5, cutting fluid is used for cooling, and the temperature of the machining area is controlled to be below 45°C.

[0013] Preferably, in step S6, the piston body is placed upside down in flowing hot water. The temperature of the hot water is 70-100℃. Heat is used to melt the rust-preventive paraffin wax and expel it through the oil pores. Then, the density difference between paraffin and water is used for physical stratification and recycling.

[0014] A welded all-steel piston, manufactured using the method described above.

[0015] The present invention has the following advantages over the prior art: 1. Significantly improves cleanliness: This invention achieves complete sealing of the oil cavity throughout the entire finishing process by filling the internal cooling oil cavity with a removable solid sealing medium (such as rust-preventive paraffin) before finishing. This effectively isolates the cutting fluid and air, preventing corrosion of the internal cooling oil cavity. At the same time, the solid medium also prevents any metal shavings or foreign objects from entering the oil cavity, thus solving the cleanliness problem at its source. 2. Simplified process and reduced cost: Compared with the existing technology which requires multiple processes such as "sandblasting, air blowing, rust prevention, plugging / removing, and deburring", the method of the present invention simplifies the process to two steps: "filling with sealing medium" and "removing sealing medium", which greatly shortens the process, improves production efficiency, and saves the cost of special plugs. 3. Improved processing quality: In processes such as milling pin holes and crescent grooves, the solid paraffin filling the oil cavity of this invention provides support for the inner cavity wall, which can effectively inhibit or reduce the formation of reverse burrs and improve processing quality. 4. Structural optimization to prevent foreign matter from hiding: This invention optimizes the welding process and controls the gap t of the welded horn to be between 0 and 0.4 mm, making it less likely for steel chips and other foreign matter to hide in the gap, making it easier to clean and further ensuring the cleanliness of the piston. 5. Environmental protection and energy saving: The rust-preventive paraffin used in this invention can be melted and recycled with hot water, which is in line with the concept of green manufacturing. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the welded all-steel piston in an embodiment of the present invention; Figure 2 for Figure 1Enlarged view of section I (structural schematic diagram of the location where the ram's horn is welded); Figure 3 This is a schematic diagram of the structure of the internal cooling oil cavity and oil hole filled with rust-preventive paraffin in an embodiment of the present invention; Figure 4 This is a flowchart illustrating the manufacturing method of welding an all-steel piston in an embodiment of the present invention.

[0018] Figure label: 1. Piston head; 2. Piston skirt; 3. Internal cooling oil chamber; 4. Welded ram's horn; 5. Oil hole; 6. Internal weld; 7. External weld. Detailed Implementation

[0019] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions in the embodiments of this invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0020] like Figure 1-4 As shown, this embodiment of the invention provides a method for manufacturing a welded all-steel piston, specifically including the following steps: S1. Pre-machining of piston head and piston skirt: Machining piston head 1 and piston skirt 2 respectively, completing the internal cooling oil cavity 3 and the oil hole 5 communicating with the internal cooling oil cavity 3 (e.g., Figure 1 The machining is shown in the figure. For other parts, such as the piston outer circle and ring groove, an appropriate amount of finishing allowance is left.

[0021] S2. Friction Welding: Using inertial friction welding equipment, the pre-machined piston head 1 and piston skirt 2 are welded under primary pressure, forming an inner weld 6 and an outer weld 7, which together create a closed inner cooling oil cavity 3. Figure 1 and Figure 2 As shown, during the welding process, welding horns 4 are formed at the outer weld 7 and the inner weld 6 respectively. By controlling the welding parameters, the root width d of the welding horn 4 is not less than 0.5mm to ensure the welding strength and avoid the formation of small gaps. At the same time, the gap t of the welding horn 4 is controlled within the range of 0 to 0.4mm. This narrow gap is not easy to hide foreign objects and is convenient for subsequent cleaning.

[0022] S3. Vacuum Tempering: The welded piston body is placed in a vacuum furnace for tempering. The tempering temperature is controlled between 580 and 630°C, and the holding time is 3 hours to eliminate welding stress. After the holding time, the piston is cooled in the furnace to 200–90°C before being removed from the furnace to prevent oxide scale formation due to air cooling. This step ensures that the surface of the internal cooling oil cavity 3 is smooth and free of oxide scale.

[0023] S4. Filling the internal cooling oil cavity with rust-preventive paraffin wax: First, prepare the rust-preventive paraffin wax. Weigh the raw materials according to the following percentages: 75% fully refined paraffin wax (56# or 58#), 12% stearic acid, and 5% barium petroleum sulfonate rust inhibitor. Mix and melt the raw materials to form solid particles with a diameter of approximately 0.5–2.0 mm for easy filling. Then, allow the piston body from step S3 to cool naturally to 70–80°C (the piston will still have residual heat). Pour the prepared solid rust-preventive paraffin wax particles into the oil holes. Utilizing the residual heat of the piston body, the paraffin wax particles quickly melt and flow to all corners of the internal cooling oil cavity 3 until the liquid paraffin wax completely fills the internal cooling oil cavity 3 and all oil holes 5. Figure 3 As shown. Subsequently, as the piston temperature continues to decrease, the rust-preventive paraffin cools and solidifies, completely sealing the internal cooling oil chamber 3.

[0024] S5. Finishing: Perform all subsequent finishing processes on the piston body, including but not limited to finish turning the outer diameter, finish turning the ring groove, drilling, boring the pin hole, and milling the crescent groove of the pin hole. Cutting fluid is used for cooling and lubrication throughout the finishing process. The temperature of the machining area must be strictly controlled to avoid local temperatures exceeding 45°C, preventing the rust-preventive paraffin filling from melting and losing its sealing effect. Due to the sealing and supporting effect of the solid paraffin, the cutting fluid and metal chips are completely isolated from the internal cooling oil cavity 3, and burrs are less likely to form on the inner cavity wall when milling the crescent groove.

[0025] S6. Rust-preventive paraffin wax recycling: After all finishing processes are completed, the piston body is placed upside down in a flowing hot water tank. The temperature of the hot water is controlled between 70 and 100°C. Heat is transferred through the piston body to the internal rust-preventive paraffin wax, causing it to melt. Under the influence of gravity, the melted rust-preventive paraffin wax automatically flows out from the oil hole and floats on the surface of the hot water. Utilizing the difference in density and incompatibility between paraffin wax and water, the paraffin wax is separated and collected from the water surface through physical methods (such as overflow, skimming, etc.), achieving the recycling and reuse of the rust-preventive paraffin wax. After the paraffin wax is emptied, the internal cooling oil chamber 3 is clean, dry, and free of rust.

[0026] S7. Surface treatment and finished product packaging: After the pistons have been finished and paraffin has been recovered, subsequent surface treatments (such as phosphating, graphitization, etc.) and final inspection and packaging are carried out to obtain the finished product.

[0027] A welded all-steel piston, manufactured by the above-described method, has the following structure: Figure 1 and Figure 2As shown, the piston comprises a piston head 1 and a piston skirt 2 connected by friction welding, forming an internal cooling oil chamber 3 and an oil hole 5 between them. A welded horn 4 is formed at the weld joint, with a root width d of not less than 0.5 mm and a gap t of 0-0.4 mm. The internal cooling oil chamber 3 of the piston has high cleanliness, free from rust and foreign matter residue.

[0028] While rust-inhibiting paraffin wax is preferably used as a removable sealing medium in this embodiment, the invention is not limited thereto. Any medium that is solid at room temperature, can fill and seal the internal cooling oil cavity, remains stable during finishing (does not melt, decompose, or react with the cutting fluid), and can be easily and thoroughly removed from the internal cooling oil cavity after finishing by heating (such as hot water, hot oil, or hot air), without damaging the piston substrate, can replace rust-inhibiting paraffin wax. Examples include certain low-melting-point polymers or alloys.

[0029] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for manufacturing a welded all-steel piston, characterized in that, The following steps are included: S1. Pre-machining of piston head and piston skirt: The piston head and piston skirt are machined to the preset shape respectively, and an internal cooling oil cavity and an oil hole communicating with the internal cooling oil cavity are formed. The remaining parts are left with a finishing allowance. S2. Friction welding: The pre-processed piston head and piston skirt are connected together by friction welding to form a piston body, and the interior of the piston body forms a closed internal cooling oil cavity. S3, Vacuum tempering: Vacuum tempering treatment is performed on the welded piston body; S4. Filling the internal cooling oil cavity with a removable sealing medium: Filling the internal cooling oil cavity with a removable solid sealing medium, so that the solid sealing medium fills and seals the entire internal cooling oil cavity and the oil hole; S5. Finishing: Finishing the piston body filled with solid sealing medium, including turning, boring, drilling and / or milling; S6. Remove sealing medium: Heat the finished piston body to melt or soften the solid sealing medium and discharge it from the internal cooling oil chamber.

2. The manufacturing method of the welded all-steel piston according to claim 1, characterized in that, In step S4, the sealant that can be removed is rust-preventive paraffin wax. The melting point of the rust-preventive paraffin is in the range of 55–60°C.

3. The manufacturing method of the welded all-steel piston according to claim 2, characterized in that, Step S4 specifically includes the following operation process: cooling the piston body after vacuum tempering to 70-80°C, then pouring solid anti-rust paraffin particles into the oil hole, using the residual heat of the piston body to melt and flow the anti-rust paraffin particles until they fill the entire internal cooling oil cavity and oil hole, and then cooling to solidify the anti-rust paraffin into a solid state.

4. The manufacturing method of the welded all-steel piston according to claim 3, characterized in that, The particle size of the solid rust-preventive paraffin particles in step S4 is 0.5 to 2.0 mm.

5. The manufacturing method of the welded all-steel piston according to claim 2, characterized in that, The rust-preventive paraffin in step S4 consists of the following components by mass percentage: Fully refined paraffin wax 70-85%, Stearic acid 8-15%, Barium petroleum sulfonate rust inhibitor 3-8%.

6. The method for manufacturing a welded all-steel piston according to any one of claims 1-5, characterized in that, In step S2, a welded horn is formed at the joint between the piston head and the piston skirt during friction welding. The root width d of the welded ram's horn is not less than 0.5 mm; The gap t of the welded ram's horn is 0 to 0.4 mm.

7. The method for manufacturing a welded all-steel piston according to any one of claims 1-5, characterized in that, The specific process parameters for vacuum tempering in step S3 are as follows: Tempering temperature 580~630℃, Insulation time: 2-4 hours After cooling in the furnace to 200-90°C, the product is removed from the furnace.

8. The method for manufacturing a welded all-steel piston according to any one of claims 1-5, characterized in that, During the finishing process in step S5, cutting fluid is used for cooling, and the temperature of the machining area is controlled to be below 45°C.

9. The method for manufacturing a welded all-steel piston according to any one of claims 1-5, characterized in that, In step S6, the piston body is placed upside down in flowing hot water. The temperature of the hot water is 70-100℃. Heat is used to melt the rust-preventive paraffin wax and expel it through the oil pores. Then, the density difference between paraffin and water is used for physical stratification and recycling.

10. A welded all-steel piston, characterized in that, It is manufactured using the manufacturing method described in any one of claims 1-9.

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