WELDED INTEGRAL FORGED STEEL PISTON AND MANUFACTURING PROCESS THEREOF

Abstract

Disclosed are a welded integral forged steel piston and a manufacturing process thereof. A piston head and a piston skirt are fixedly connected. A closed cooling oil cavity is formed between the piston head and the piston skirt. The cooling oil cavity is communicated with the outside through an oil inlet and an oil outlet. The bottom end of the piston head is concentrically provided with annular inner welding shoulder A and outer welding shoulder A. The top end of the piston skirt is concentrically provided with annular inner welding shoulder B and outer welding shoulder B which are respectively matched with the inner welding shoulder A and the outer welding shoulder A. The present invention provides a welded integral forged steel piston with reasonable structure, safety, reliability and high production efficiency, and a manufacturing process thereof.

Claims

1. A welded integral forged steel piston, comprising a piston head and a piston skirt which are forged, wherein the piston head and the piston skirt are fixedly connected; a closed cooling oil cavity is formed between the piston head and the piston skirt; the cooling oil cavity is communicated with the outside through an oil inlet and an oil outlet, wherein the bottom end of the piston head is concentrically provided with annular inner welding shoulder A and outer welding shoulder A; the top end of the piston skirt is concentrically provided with annular inner welding shoulder B and outer welding shoulder B which are respectively matched with the inner welding shoulder A and the outer welding shoulder A; the inner welding shoulder A and the inner welding shoulder B are welded through friction welding to form a main weld; and the outer welding shoulder A and the outer welding shoulder B are welded through melting welding to form an auxiliary weld.

2. The welded integral forged steel piston of claim 1, wherein the piston head and the piston skirt are forged by quenched and tempered steel or non-quenched and tempered steel; and the quenched and tempered steel is selected from 42CrMo, and the non-quenched and tempered steel is selected from 38MnVS6.

3. The welded integral forged steel piston of claim 2, wherein the oil inlet and the oil outlet are formed in the bottom of the cooling oil cavity on the piston skirt.

4. The welded integral forged steel piston of claim 1, wherein the auxiliary weld comprises a top auxiliary weld and an excircle auxiliary weld.

5. The welded integral forged steel piston according to claim 5, characterized in that the top auxiliary weld is welded by vacuum electron beam welding; welding speed is 300 mm/min; a welding technology is implemented twice at high voltage of 80 KV; in the first welding technology, preheating is conducted and welding beam current is 15 mA; and in the second welding technology, the welding beam current is determined according to welding depth.

6. The welded integral forged steel piston of claim 5, wherein the excircle auxiliary weld is welded by argon arc welding.

7. A manufacturing process of a welded integral forged steel piston, comprising the following steps: S1 material selection: selecting quenched and tempered steel or non-quenched and tempered steel bars with satisfactory diameter according to process requirements, and cutting and preparing the bars with a sawing machine; S2 hot processing: determining heating time according to the process requirements, and heating the cut bars with an electromagnetic induction furnace to 1120-1250 C.; S3 forging: conducting rough forging on the heated bars with a hydraulic press of 400 t; upsetting; removing oxide coatings on the surfaces of the bars; precision forging a piston head blank and a piston skirt blank after rough forging using an electric helical press of 1000 t; and determining precision forging number of times and the size of each precision forging pressure according to the process requirements to obtain the piston head blank and the piston skirt blank; S4: rough machining: processing the top surface of the cooling oil cavity, the annular inner welding shoulder A and the annular outer welding shoulder A in the piston head blank; processing the bottom surface of the cooling oil cavity, the annular inner welding shoulder B and the annular outer welding shoulder B in the piston skirt blank to obtain a piston head semi-finished product and a piston skirt semi-finished product; S5 welding: conducting friction welding on the piston head semi-finished product and the piston skirt semi-finished product after precision forging using a friction welding machine; welding the inner welding shoulder A and the inner welding shoulder B with a friction welding machine of 45 t to form a main weld, with the friction welding machine of 45 t having largest upsetting force of 390 KN and largest welding area of 4100 mm.sup.2; welding the outer welding shoulder A and the outer welding shoulder B through melting welding to form an auxiliary weld; the auxiliary weld comprising a top auxiliary weld and an excircle auxiliary weld, wherein the top auxiliary weld is welded by vacuum electron beam welding; welding speed is 300 mm/min; a welding technology is implemented twice at high voltage of 80 KV; in the first welding technology, preheating is conducted and welding beam current is 15 mA; and in the second welding technology, the welding beam current is determined according to welding depth; and S6 post processing: conducting heat treatment, finish machining and surface treatment on the welded piston to finally obtain a piston finished product.

8. The manufacturing process of the welded integral forged steel piston of claim 7, wherein in the heat treatment process, the piston forged by the quenched and tempered steel is firstly heated to 845-855 C., insulated for 2-3 hours, taken from a furnace and then oil-cooled; tempering temperature is 590-620 C. ; the piston is insulated for 3-4 hours; finally, the piston is taken from the furnace and air-cooled; and the piston forged by the non-quenched and tempered steel is only annealed to remove stress.

9. The manufacturing process of the welded integral forged steel piston of claim 7, wherein in the finish machining: the piston after heat treatment is processed into a ring groove, a pin hole and an excircle profile of the piston; and in the surface treatment, the piston surface after finish machining is phosphorized and graphitized.

Description

DESCRIPTION OF DRAWINGS

[0028] To more clearly describe the technical solution in the embodiments of the present invention or in the prior art, the drawings required to be used in the description of the embodiments or the prior art will be simply presented below. Apparently, the drawings in the following description are merely the embodiments of the present invention, and for those ordinary skilled in the art, other drawings can also be obtained according to the provided drawings without contributing creative labor.

[0029] FIG. 1 is a front sectional view of a welded integral forged steel piston;

[0030] FIG. 2 is a side sectional view of a welded integral forged steel piston;

[0031] FIG. 3 is a bottom view of a welded integral forged steel piston;

[0032] FIG. 4 is a stereogram of a welded integral forged steel piston; and

[0033] FIG. 5 is a flow chart of a manufacturing process of a welded integral forged steel piston.

DETAILED DESCRIPTION

[0034] The technical solution in the embodiments of the present invention will be clearly and fully described below in combination with the drawings in the embodiments of the present invention. Apparently, the described embodiments are merely part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those ordinary skilled in the art without contributing creative labor will belong to the protection scope of the present invention.

[0035] Embodiments of the present invention disclose a welded integral forged steel piston and a manufacturing process thereof. On one hand, a piston head blank and a piston skirt blank are forged separately, thereby simplifying the forging technology, reducing requirements for device tonnage and reducing investment of device cost. On the other hand, the piston head and the piston skirt are processed separately, which also reduces the requirements for devices and cutters. Meanwhile, only one inner weld of two welds of the piston head and the piston skirt is welded by friction welding, thereby reducing the requirements for the power of a friction welding machine. Thus, a piston with large cylinder diameter can be welded with a friction welding machine with low power, thereby reducing device investment and expanding the use range of the devices. The periphery of the piston head and the periphery of the piston skirt are welded by electron beam welding or argon arc welding to form auxiliary welds, so as to strengthen welding reliability.

[0036] By combining with FIGS. 1-4, the present invention discloses a welded integral forged steel piston, comprising a piston head 1 and a piston skirt 2 which are forged, wherein the piston head 1 and the piston skirt 2 are fixedly connected; a closed cooling oil cavity 3 is formed between the piston head 1 and the piston skirt 2; and the cooling oil cavity 3 is communicated with the outside through an oil inlet 4 and an oil outlet 5. The bottom end of the piston head 1 is concentrically provided with annular inner welding shoulder A6 and outer welding shoulder A7. The top end of the piston skirt 2 is concentrically provided with annular inner welding shoulder B8 and outer welding shoulder B9 which are respectively matched with the inner welding shoulder A6 and the outer welding shoulder A7. The inner welding shoulder A6 and the inner welding shoulder B8 are welded through friction welding to form a main weld 10. The outer welding shoulder A7 and the outer welding shoulder B9 are welded through melting welding to form an auxiliary weld.

[0037] To further optimize the above technical solution, the piston head 1 and the piston skirt 2 are forged by quenched and tempered steel or non-quenched and tempered steel; and the quenched and tempered steel is selected from 42CrMo, and the non-quenched and tempered steel is selected from 38MnVS6.

[0038] To further optimize the above technical solution, the oil inlet 4 and the oil outlet 5 are formed in the bottom of the cooling oil cavity 3 on the piston skirt 2, so that a cooling medium in the cooling oil cavity 3 can be in communication with a circulation cooling system of an engine so as to better cool the piston.

[0039] To further optimize the above technical solution, the main weld 10 is welded with a friction welding machine of 45 t. The friction welding machine of 45 t has largest upsetting force of 390 KN and largest welding area of 4100 mm.sup.2, thereby reducing the requirements for the power of the friction welding machine. Thus, a piston with large cylinder diameter can be welded with a friction welding machine with low power, thereby reducing device investment and expanding the use range of the devices.

[0040] To further optimize the above technical solution, the auxiliary weld comprises a top auxiliary weld 11 and an excircle auxiliary weld 12. The top auxiliary weld 11 is mainly used for strengthening the connecting quality between the piston head 1 and the piston skirt 2. The excircle auxiliary weld 12 plays the effect of supporting a piston ring.

[0041] To further optimize the above technical solution, the top auxiliary weld 11 is welded by vacuum electron beam welding; welding speed is 300 mm/min; a welding technology is implemented twice at high voltage of 80 KV; in the first welding technology, preheating is conducted and welding beam current is 15 mA; and in the second welding technology, the welding beam current is determined according to welding depth, thereby enhancing welding quality.

[0042] To further optimize the above technical solution, the excircle auxiliary weld 12 is welded by argon arc welding. Because the temperature at an excircle is low, the excircle auxiliary weld 12 only plays the effect of supporting the piston ring. Requirements for the weld are low, and argon arc welding is selected, thereby reducing device investment and reducing the cost.

[0043] By combing with FIG. 5, the present invention discloses a manufacturing process of a welded integral forged steel piston, comprising the following steps:

[0044] S1 material selection: selecting quenched and tempered steel or non-quenched and tempered steel bars with satisfactory diameter according to process requirements, and cutting and preparing the bars with a sawing machine, wherein the quenched and tempered steel is selected from 42CrMo, and the non-quenched and tempered steel is selected from 38MnVS6;

[0045] S2 hot processing: determining heating time according to the process requirements, and heating the cut bars with an electromagnetic induction furnace to 1120-1250 C.;

[0046] S3 forging: conducting rough forging on the heated bars with a hydraulic press of 400 t; upsetting; removing oxide coatings on the surfaces of the bars; precision forging a piston head blank and a piston skirt blank after rough forging using an electric helical press of 1000 t; and determining precision forging number of times and the size of each precision forging pressure according to the process requirements to obtain the piston head blank and the piston skirt blank;

[0047] S4: rough machining: processing the top surface of the cooling oil cavity, the annular inner welding shoulder A and the annular outer welding shoulder A in the piston head blank; processing the bottom surface of the cooling oil cavity, the annular inner welding shoulder B and the annular outer welding shoulder B in the piston skirt blank to obtain a piston head semi-finished product and a piston skirt semi-finished product;

[0048] S5 welding: conducting friction welding on the piston head semi-finished product and the piston skirt semi-finished product after precision forging using a friction welding machine; welding the inner welding shoulder A and the inner welding shoulder B with a friction welding machine of 45 t to form a main weld, with the friction welding machine of 45 t having largest upsetting force of 390 KN and largest welding area of 4100 mm.sup.2; welding the outer welding shoulder A and the outer welding shoulder B through melting welding to form an auxiliary weld; the auxiliary weld comprising a top auxiliary weld and an excircle auxiliary weld,wherein the top auxiliary weld is welded by vacuum electron beam welding; welding speed is 300 mm/min; a welding technology is implemented twice at high voltage of 80 KV; in the first welding technology, preheating is conducted and welding beam current is 15 mA; and in the second welding technology, the welding beam current is determined according to welding depth; and

[0049] S6 post processing: conducting heat treatment, finish machining and surface treatment on the welded piston to finally obtain a piston finished product.

[0050] To further optimize the above technical solution, in the heat treatment process, the piston forged by the quenched and tempered steel is firstly heated to 845-855 C., insulated for 2-3 hours, taken from a furnace and then oil-cooled; tempering temperature is 590-620 C.; the piston is insulated for 3-4 hours; and finally, the piston is taken from the furnace and air-cooled. The piston forged by the non-quenched and tempered steel is only annealed to remove stress.

[0051] To further optimize the above technical solution, in the finish machining: the piston after heat treatment is processed into a ring groove, a pin hole and an excircle profile of the piston; and in the surface treatment, the piston surface after finish machining is phosphorized and graphitized.

[0052] Each embodiment in the description is described in a progressive way. The difference of each embodiment from each other is the focus of explanation. The same and similar parts among all of the embodiments can be referred to each other. For a device disclosed by the embodiments, because the device corresponds to a method disclosed by the embodiments, the device is simply described. Refer to the description of the method part for the related part.

[0053] The above description of the disclosed embodiments enables those skilled in the art to realize or use the present invention. Many modifications to these embodiments will be apparent to those skilled in the art. The general principle defined herein can be realized in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principle and novel features disclosed herein.