A processing method for an electron beam welded piston with an insert ring

Abstract

This application discloses a method for machining an electron beam welded piston with a ring insert, comprising the following steps: S1: piston head → quenching → aging → rough boring → end face turning → boring → X-ray inspection → ultrasonic inspection → turning the lower ring insert boss → ultrasonic inspection → turning the weld surface; S2: piston skirt → quenching → aging → rough turning the outer diameter → flat riser → turning the stopper → boring the pin hole → semi-finish turning the outer diameter → turning the step surface → drilling the oil hole → turning the weld surface; S3: electron beam welding → annealing → rough turning the outer diameter → stopper positioning machining → milling the valve pit → ring groove machining → finish turning the outer diameter → turning the combustion chamber → finish boring the pin hole → inspection → finished product. This machining method can reduce the quality risks caused by welding stress during electron beam welding, reduce the possibility of cracking in the piston head, and improve the quality of piston welding and bonding.

Description

Technical Field

[0001] The present application relates to the technical field of piston processing methods, and in particular to a processing method of an electron beam welded piston with an insert ring. Background Art

[0002] The insert is an annular cast iron ring embedded in the first ring groove of the piston crown. Its primary function is to improve the wear and heat resistance of the piston crown groove, thereby enhancing the seal between the piston ring and the cylinder liner, increasing the piston's service life and engine reliability. Electron beam welding utilizes the high temperatures generated by the impact of an electron beam to melt the welded parts in specific areas, thus forming a single piece. Its primary function is to weld piston crowns and skirts made of different materials, thereby improving piston strength and the engine's combustion power.

[0003] Electron beam welded pistons are produced by electron beam welding the piston head and skirt, followed by machining. The piston head and skirt require machining to create the mating surfaces. The piston head and skirt are then assembled and pressed together before electron beam welding. After electron beam welding, the welded piston requires further machining to meet product requirements. The piston head blank is a casting, while the piston skirt blank is a forging. Both the piston head and skirt must be semi-finished before electron beam welding. Since the piston oil channel, ring insert and combustion chamber are all on the piston head, when processing the piston head, if the margin at the bottom of the combustion chamber becomes smaller, the distance from the oil channel will be reduced, resulting in a decrease in the wall thickness between the combustion chamber and the oil channel. In addition, during electron beam welding, a large welding stress will be generated. When the welding stress acts directly on the thin wall, it will cause cracks between the oil channel and the combustion chamber. At the same time, since the piston ring insert and the piston head are made of different materials, the tightness of their connection is mainly determined by the size of the bonding force. When the stress of electron beam welding is too large, the bonding force between the piston head and the ring insert will be unstable, affecting the bonding quality of the finished piston.

[0004] The technical problems existing in the prior art are as follows: During the actual operation of the existing electron beam welding, turning the lower ring boss is the first machining process after the piston is welded. During the machining process, the cutting stress when machining the ring boss is relatively high, which can easily cause the aluminum substrate to tear, resulting in insufficient adhesion between the piston ring and the piston head, and the scrap is not easy to detect. When the existing technology is rough turning the outer circle of the piston ring, due to the different materials of the piston ring and the piston head, the cutting process will generate shear force in the longitudinal direction of the piston. This shear force will form a tearing force at the piston ring bonding point. At the same time, when milling the valve, due to the processing using a one-step molding process, after the machining is completed, there will be large cutting stress on the piston head that cannot be released. Under the action of these cutting stresses, the adhesion quality of the piston ring is further deteriorated. In the prior art, when electron beam welding a piston to rough-turn the combustion chamber, the large machining allowance of the combustion chamber generates significant cutting stress during machining. Since the bottom of the combustion chamber is relatively close to the base of the ring insert, this longitudinal cutting force directly acts on the base of the ring insert, separating the back of the ring insert from the aluminum substrate and affecting the bonding quality. In the prior art, after electron beam welding, the entire piston is subjected to a quenching and aging treatment. During this heat treatment, the stress generated affects the bonding strength between the ring insert and the piston head. The aforementioned piston ring bonding quality issues caused by these factors are not easily discovered during machining and are often only detected during fine flaw detection. In particular, this can lead to a phenomenon where, due to the cutting stresses on some pistons during fine flaw detection, the bonding between the ring insert and the piston head reaches a critical point, making it impossible to detect the unqualified bonding quality. Quality defects only become apparent after the piston surface is treated, creating a significant quality risk. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a processing method for an electron beam welded piston with an insert ring, which can reduce the quality risks caused by welding stress during electron beam welding, reduce the possibility of cracking of the piston head, and improve the welding quality and bonding quality of the piston.

[0006] The technical solutions provided by the present invention are as follows:

[0007] A method for processing an electron beam welded piston with an insert ring comprises the following steps:

[0008] S1. Pre-weld machining of the piston head: piston head → quenching → aging → rough hole digging → end face turning → boring → X-ray flaw detection → ultrasonic flaw detection → turning the lower ring boss → ultrasonic flaw detection → turning the welding surface;

[0009] S2. Pre-weld machining of the piston skirt: Piston skirt → quenching → aging → rough turning of the outer diameter → flat riser → turning of the stopper → boring of the pin hole → semi-finishing turning of the outer diameter → turning of the step surface → drilling of the oil hole → turning of the welding surface;

[0010] S3. The piston head and piston skirt are electron beam welded and subsequently processed as follows: electron beam welding → annealing → rough turning of the outer diameter → stop positioning processing → milling of the valve pit → ring groove processing → fine turning of the outer diameter → turning of the combustion chamber → fine boring of the pin hole → inspection → finished product.

[0011] Preferably, in step S3, the welding surface of the piston head and the welding surface of the piston skirt are aligned and then placed in an electron beam welding machine for welding. Before shutting down the machine, the surface temperature of the piston is 160±10°C.

[0012] Preferably, the welding parameters in step S3 are: beam current of 50-63 mA, focusing current of 2.8-4.05 A, and arc closing angle of 30-60°.

[0013] Preferably, in step S1, the depth and inner diameter of the rough excavation process are controlled to shallowly turn the combustion chamber pit, thereby increasing the distance between the bottom of the combustion chamber pit and the oil channel and the insert ring.

[0014] Preferably, the specific operation of turning the lower ring boss in step S1 is: when processing the outer circle of the piston ring part, the outer circle of the piston ring and the piston head of different materials is processed in sections for multiple times, specifically: first, the outer circle of the piston head including the ring part is turned in multiple times, and then the outer circle of the piston head is turned, and finally the ring boss is cut separately for the ring segment, so that there is no boss structure on the outer side of the ring, and the outer cylindrical surface of the ring is lower than the outer circle of the piston head.

[0015] Preferably, the plane formed by the welding surfaces in steps S1 and S2 serves as the assembly surface of the piston assembly. After assembly, the piston is formed by the piston head and the piston skirt to form a combustion chamber pit.

[0016] Preferably, the piston head and the piston skirt are preheated before the electron beam welding in step S3. Specifically, the piston head and the piston skirt are preheated in an electric furnace at a temperature of 170±15°C for 2 to 4 hours.

[0017] This application has the following advantages over the prior art:

[0018] 1. In order to improve the quality of post-weld machining and reduce the labor intensity of employees, the present invention's processing method for an electron beam welded piston with an insert is to advance the machining of the insert boss to after ultrasonic flaw detection of the head. After the insert boss is processed, a second ultrasonic flaw detection is performed, and the flaw detection technical requirements are improved to ensure the quality of the head bonding.

[0019] 2. Regarding the phenomenon that the backside bonding quality of the piston head is seriously degraded after electron beam welding, it is believed that the temperature during electron beam welding has a significant impact on the bonding quality of the insert. Therefore, the processing method of the electron beam welded piston with an insert of the present invention adopts a method of lowering the welding temperature during welding to reduce the impact of the electron beam welding process on the bonding quality, thereby improving the welding quality;

[0020] 3. The present invention reduces the cutting stress of each process during the processing by appropriately adding and adjusting the process steps in the electron beam welded piston process, thereby reducing the defects of the electron beam welded piston ring bonding quality and the cracking of the piston head;

[0021] 4. The processing method of the electron beam welded piston with an insert of the present invention can effectively reduce the influence of electron beam welding on the adhesion of the insert and the possibility of electron beam welding cracking of the piston, thereby early detecting and reducing the influence caused by mechanical processing and improving product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 1 is a process flow chart of a method for processing an electron beam welded piston with an insert ring according to an embodiment of the present invention;

[0024] Figure 2 Schematic diagram of the piston structure obtained after electron beam welding in an embodiment of the present invention.

[0025] Reference numerals:

[0026] 1. Piston head; 2. Piston skirt; 3. Ring insert; 4. Piston oil channel. DETAILED DESCRIPTION

[0027] In order to help those skilled in the art better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without making any creative efforts shall fall within the scope of protection of this application.

[0028] like Figure 1 、 2As shown, an embodiment of the present invention provides a method for processing an electron beam welded piston with an insert ring, comprising the following steps:

[0029] S1. Pre-weld machining of piston head 1: piston head 1 → quenching → aging → rough hole digging → end face turning → boring → X-ray flaw detection → ultrasonic flaw detection → turning of lower ring boss → ultrasonic flaw detection → turning of welding surface;

[0030] S2. Pre-welding machining of piston skirt 2: piston skirt 2 → quenching → aging → rough turning of outer diameter → flat riser → turning of stopper → boring of pin hole → semi-finishing turning of outer diameter → turning of step surface → drilling of oil hole → turning of welding surface;

[0031] S3, the piston head 1 and the piston skirt 2 are electron beam welded and subsequently processed as follows: electron beam welding → annealing → rough turning of the outer diameter → stop positioning processing → milling of the valve pit → ring groove processing → fine turning of the outer diameter → turning of the combustion chamber → fine boring of the pin hole → inspection → finished product.

[0032] According to the existing process, when the piston head 1 is processed, if the distance between the bottom of the combustion chamber and the oil channel is too close, the welding stress generated during welding can easily cause cracks in the thin wall between the oil channel and the combustion chamber. Through continuous process tests, the processing method of the electron beam welded piston with an insert in this embodiment increases the distance between the bottom of the combustion chamber pit and the oil channel and the insert by shallow turning the combustion chamber pit, thereby improving the strength of the thin wall. Since the combustion chamber pit is formed after the electron beam welding is completed, the change of process parameters should be made from the piston head and piston skirt.

[0033] Turning the lower bezel boss is the first machining step after welding a welded piston. Because the bezel has a bulge, excessively fast cutting speeds can create cutting forces that could tear the bezel from the aluminum substrate, affecting the bonding quality and resulting in scrap. To improve post-weld machining quality and reduce labor intensity, the present method for machining an electron beam welded piston with a bezel advances the machining of the lower bezel boss to after ultrasonic testing of the head. A second ultrasonic testing is then performed after the bezel boss is machined, and stricter testing requirements are employed to ensure high-quality head bonding.

[0034] Regarding the phenomenon that the back bonding quality of the piston head is seriously reduced after electron beam welding, it is analyzed that the temperature during electron beam welding has a great influence on the bonding quality of the ring. Therefore, the processing method of the electron beam welded piston with a ring in this embodiment adopts the method of lowering the welding temperature during welding to reduce the impact of the electron beam welding process on the bonding quality, thereby improving the welding quality.

[0035] In this embodiment, in step S3, the welding surface of the piston head 1 and the welding surface of the piston skirt 2 are aligned and then placed in an electron beam welding machine for welding. Before closing the machine, the surface temperature of the piston is 160±10°C.

[0036] In this embodiment, the welding parameters in step S3 are: beam current of 50-63 mA, focus current of 2.8-4.05 A, and arc closing angle of 30-60°.

[0037] In this embodiment, in step S1, the depth and inner diameter of the rough excavation process are controlled to shallowly turn the combustion chamber pit, thereby increasing the distance between the bottom of the combustion chamber pit and the oil channel and the insert ring.

[0038] In this embodiment, the specific operation of turning the lower ring boss in step S1 is: when processing the outer circle of the piston ring part, the outer circle of the piston ring and the piston head 1 of different materials is processed in sections multiple times, specifically: first, the outer circle of the piston head 1 including the ring part is turned in multiple times, then the outer circle of the piston head 1 is turned as a whole, and finally the ring boss is cut separately on the ring segment, so that there is no boss structure on the outer side of the ring, and the outer cylindrical surface of the ring is lower than the outer circle of the piston head 1.

[0039] In this embodiment, the plane formed by the welding surfaces in steps S1 and S2 serves as the assembly surface of the piston assembly. After assembly, the piston is formed by the piston head 1 and the piston skirt 2 to form a combustion chamber pit.

[0040] In this embodiment, the piston head 1 and the piston skirt 2 are preheated before the electron beam welding in step S3. Specifically, the piston head 1 and the piston skirt 2 are preheated in an electric furnace at a temperature of 170±15°C for 3 hours.

[0041] The piston structure obtained by the processing method of the electron beam welding piston with a ring in this embodiment is as follows: Figure 2 As shown, from Figure 2 As can be seen from the figure, within the overall piston structure, the outer circumference of the piston head, including the ring insert, is free of bulges. The outer cylindrical surface of the ring insert is lower than the outer circumference of the piston head, and there is no boss structure on the outer side of the ring insert. This reduces the machining allowance during rough turning of the outer circumference in step S3 and reduces stress during machining of the outer circumference. The rough drilling process in step S1 controls the depth and diameter of the welding surface (assembly surface). After the piston head and piston skirt formed in steps S1 and S2 are assembled with the welding surface (assembly surface), the piston head and piston skirt form a combustion chamber recess, and the distance between the bottom surface of the combustion chamber recess and the oil passage and the ring insert is increased.

[0042] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one 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 present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for processing an electron beam welded piston with an insert ring, characterized in that: The steps are as follows: S1. Pre-weld machining of the piston head (1): piston head (1) → quenching → aging → rough digging → turning end face → boring → X-ray inspection → ultrasonic inspection → turning lower ring boss → ultrasonic inspection → turning welding surface. By controlling the depth and inner diameter of the rough digging process, the combustion chamber pit is shallowly turned to increase the distance between the bottom of the combustion chamber pit and the oil channel and the ring. The specific operation of turning the lower ring boss is as follows: when machining the outer circle of the piston ring part, the outer circle of the piston ring and the piston head (1) are machined in sections for multiple times. Specifically, first, the outer circle of the piston head (1) including the ring part is turned in multiple times, and then the outer circle of the piston head (1) is turned as a whole. Finally, the ring boss is cut separately for the ring segment. Finally, there is no boss structure on the outer side of the ring, and the outer cylindrical surface of the ring is lower than the outer circle of the piston head (1). S2. Pre-welding machining of the piston skirt (2): piston skirt (2) → quenching → aging → rough turning of the outer diameter → flat riser → turning of stopper → boring of pin hole → semi-finishing turning of the outer diameter → turning of step surface → drilling of oil hole → turning of welding surface; S3, the piston head (1) and the piston skirt (2) are subjected to electron beam welding and subsequent processing: electron beam welding → annealing → rough turning of the outer circle → stopper positioning processing → milling of the valve pit → ring groove processing → fine turning of the outer circle → turning of the combustion chamber → fine boring of the pin hole → inspection → finished product. The welding surface of the piston head (1) and the welding surface of the piston skirt (2) are aligned and placed in the electron beam welding machine for welding. Before turning off the machine, the piston surface temperature is 160±10℃; The plane formed by the welding surface in steps S1 and S2 serves as the assembly surface of the piston assembly. After assembly, the piston is formed by the piston head (1) and the piston skirt (2) together to form a combustion chamber pit.

2. The method for processing an electron beam welded piston with an insert according to claim 1, characterized in that: The welding parameters in step S3 are: beam current of 50-63 mA, focusing current of 2.8-4.05 A, and arc closing angle of 30-60°.

3. The method for processing an electron beam welded piston with an insert according to any one of claims 1 to 2, characterized in that: In step S3, the piston head (1) and the piston skirt (2) are preheated before the electron beam welding begins.

4. The method for processing an electron beam welded piston with an insert according to claim 3, characterized in that: In step S3, the piston head (1) and the piston skirt (2) are placed in an electric furnace for preheating. The preheating temperature is 170±15° C. and the heating time is 2 to 4 hours.

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