A precision assembly welding method for large-size titanium alloy thin-walled conical members

Abstract

The application provides a precision assembly welding method for large-size titanium alloy thin-wall conical members, which comprises the following steps: processing the front section and the rear section of the conical member according to the theoretical size; assembling the rear section, the middle section and the front section on a positioning mould, and determining the fitting allowance of the large end and the small end of the middle section; fitting and processing the large end and the small end of the middle section according to the determined fitting allowance until the butt joint gap and the wall deviation meet the requirements; performing surface cleaning on the to-be-welded parts of the middle section, the rear section and the front section, then assembling the to-be-welded parts on the positioning mould, and confirming that the butt joint gap and the wall deviation meet the requirements, then performing positioning welding by using argon arc welding; assembling the conical member after the positioning welding on a welding fixture, clamping the conical member on an electron beam welding machine turntable, and performing welding between the front section and the middle section and between the middle section and the rear section by using an electron beam welding process. The method can realize precision machining, assembly and electron beam welding of the multi-section conical titanium alloy member, and obtain a pure, reliable and dense connecting weld.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of assembly welding, and particularly relates to a precision assembly welding method for large-size titanium alloy thin-wall conical components. BACKGROUND

[0002] The nozzle of a liquid rocket engine thrust chamber is mostly a thin-wall conical component with a Laval surface, and welding is adopted to realize connection of segments, and the butt joint state between segments greatly influences the welding quality. For the large-size (the minimum diameter is greater than or equal to 1000 mm) titanium alloy thin-wall (the wall thickness is less than or equal to 1.5 mm) conical component, the requirements for the butt joint state of the parts before welding are higher, and generally the butt joint gap and the wall deviation are both required to be less than or equal to 0.1 mm. Therefore, for the large-size titanium alloy thin-wall conical component, a suitable machining process needs to be adopted to ensure that the gap and the wall deviation at the butt joint position meet the requirements, and then the product surface is continuous, and the electron beam welding quality is controlled. SUMMARY

[0003] In order to overcome the deficiencies in the prior art, the present application provides a precision assembly welding method for a large-size titanium alloy thin-wall conical component, realizes precision machining, assembly and electron beam welding of the multi-segment conical titanium alloy component, and obtains a pure, reliable and dense connection weld.

[0004] The technical scheme provided by the present application is as follows:

[0005] A precision assembly welding method for a large-size titanium alloy thin-wall conical component, comprising the following steps:

[0006] The front segment and the rear segment of the conical component are machined according to the theoretical size, the middle segment is formed, and the middle segment has a fitting allowance at both ends;

[0007] The rear segment, the middle segment and the front segment are sequentially assembled on a positioning jig, the rear segment and the front segment are positioned at the position where the positioning jig surface is fitted, the wall deviation of the butt joint position of the front segment and the middle segment and the middle segment and the rear segment is checked and confirmed, and the fitting allowance of the large end and the small end of the middle segment is determined;

[0008] The middle segment is hung on a machining jig, and the large end and the small end of the middle segment are respectively machined according to the determined fitting allowance;

[0009] The front segment, the rear segment and the middle segment after fitting are assembled on the positioning jig, and whether the butt joint gap and the wall deviation meet the requirements is checked and confirmed; if not, the fitting machining of the large end and the small end of the middle segment is re-performed until the butt joint gap and the wall deviation both meet the requirements;

[0010] The surface of the middle segment after fitting, the front segment and the rear segment to be welded is cleaned;

[0011] After cleaning, the front, middle and rear three sections are assembled on the positioning mold, the rear section and the front section are positioned at the matching position of the positioning mold profile, and after confirming that the butt joint gap and the wall offset meet the requirements, argon arc welding is used for positioning welding;

[0012] The positioning welded conical member is assembled on the welding fixture and clamped on the electron beam welding machine turntable, and electron beam welding process is used for welding the front section and the middle section and the middle section and the rear section.

[0013] According to the precision assembly welding method of the large-size titanium alloy thin-walled conical member provided by the application, the following beneficial effects are obtained:

[0014] (1) The precision assembly welding method of the large-size titanium alloy thin-walled conical member provided by the application, by designing reasonable turning molds, positioning molds and reasonable turning process flow, helps to ensure that the butt joint gap and the wall offset between the sections after processing meet the requirement of not more than 0.1mm;

[0015] (2) The precision assembly welding method of the large-size titanium alloy thin-walled conical member provided by the application, by designing a welding fixture and supporting the weld position by a support disc during welding, high-precision rotary welding of the sections of the conical member is realized;

[0016] (3) The precision assembly welding method of the large-size titanium alloy thin-walled conical member provided by the application, by adopting the welding process flow of sectional positioning welding→ large beam welding→ finishing welding, the weld penetration is ensured by large beam welding, and the undercut on the surface of the weld is eliminated by finishing welding, so that a pure, reliable and dense connecting joint is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The precision assembly welding method of the large-size titanium alloy thin-walled conical member provided by the application is implemented in the flowchart;

[0018] Figure 2 The conical member product structure diagram of the application is shown;

[0019] Figure 3 The positioning mold structure diagram of the preferred embodiment of the application is shown;

[0020] Figure 4 The turning mold structure diagram of the preferred embodiment of the application is shown;

[0021] Figure 5 The welding fixture structure diagram of the preferred embodiment of the application is shown.

[0022] EXPLANATION OF REFERENCE NUMBERS

[0023] 11-Support tire I; 12-Large end pull ring I; 13-Small end cap I; 14-Tightening nut I; 21-Support tire II; 22-Small end cap II; 23-Large end pull ring II; 24-Small end support plate; 25-Large end support plate; 31-Main support shaft; 32-Large end tension support plate; 33-Small end tension support plate; 34-Large end cap; 35-Small end cap III. Detailed Implementation

[0024] The features and advantages of the present invention will become clearer and more apparent from the following detailed description.

[0025] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments. Although various aspects of embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless specifically indicated otherwise.

[0026] This invention provides a precision assembly and welding method for large-size titanium alloy thin-walled conical components, such as... Figure 1 As shown, it includes the following steps:

[0027] Step S1, for large-sized titanium alloy thin-walled conical components ( Figure 2 The front and rear forgings are processed according to theoretical dimensions, while the middle section is a hot-formed sheet metal part. The middle section has a machining allowance to be used to match the large and small ends of the middle section with the front and rear sections for machining.

[0028] Step S2: The processed rear section, sheet metal middle section and front section are sequentially assembled onto the positioning jig, so that the rear section and front section are positioned at the matching point of the positioning jig surface. Check and confirm the misalignment of the front section and middle section, and the middle section and rear section docking parts, and determine the fitting allowance of the large end and small end of the middle section.

[0029] Positioning fixture structure such as Figure 3 As shown. The positioning fixture includes a support tire I11, a large-end pull ring I12, a small-end pressure cap I13, and a clamping nut I14. The support tire I11 is a tire body structure with an internal support shaft. The small end and large end of the tire body have a continuous profile consistent with the product within a certain range. The support shaft extending from the small end of the tire body is machined with external threads, which cooperate with the clamping nut I14 on the outside of the small-end pressure cap I13. The small-end pressure cap I13 is located on the outside of the small end of the support tire I11 and clamps the front section under the pressure of the clamping nut I14. The large-end pull ring I12 is sleeved on the outside of the large end of the rear section, and its maximum diameter is smaller than the maximum diameter of the rear section. It is connected to the large end of the support tire I11 through a threaded connector to tighten the rear section.

[0030] After the front section, the middle section and the rear section are respectively hung on the positioning mold, the rear section is pulled tight by the large end pull ring I12 and the front section is pressed tight by the small end gland I13, so that the butt joint parts of the front section and the middle section and the middle section and the rear section are fitted with the mold and are bulged to check and confirm the butt joint wall deviation state and determine the allowance of the butt joint parts of the front section and the middle section and the middle section and the rear section.

[0031] In step S3, the middle section is hung on the turning mold, the large end of the middle section is positioned at the turning mold profile matching position, and after confirming that the gap between the small end of the middle section and the turning mold profile is not greater than 0.1 mm, the small end is turned; the small end of the middle section is positioned at the turning mold profile matching position, and after confirming that the gap between the large end of the middle section and the turning mold profile is not greater than 0.1 mm, the large end is turned, and the welded surface after turning should be perpendicular to the product generatrix.

[0032] The turning mold structure is shown in Figure 4 . The turning mold includes a support mold II 21, a small end gland II 22 and a large end pull ring II 23; the support mold II 21 is a mold structure with a support shaft inside, and the large and small ends have the same profile as the large and small ends of the middle section, and the small end height is lower than the small end of the middle section; the support shaft is installed with support discs at both ends, the small end support disc 24 supports the small end of the middle section, and the large end support disc 25 supports the large end of the middle section.

[0033] The small end gland II 22 is installed outside the small end of the support mold II 21 and is fixedly connected with the small end support disc 24 through a fixed pin or a threaded connecting piece to press the small end of the middle section, and after confirming that the gap between the large end of the middle section and the mold is not greater than 0.1 mm, the large end of the middle section is turned.

[0034] The large end pull ring II 23 is sleeved outside the large end of the support mold II 21 and overlaps with the large end support disc 25 in height position, and the maximum diameter is smaller than the maximum diameter of the large end of the support mold II 21, and is fixedly connected with the large end of the support mold II 21 through a threaded connecting piece to pull the large end, and after confirming that the gap between the small end of the middle section and the mold is not greater than 0.1 mm, the small end of the middle section is turned.

[0035] In step S4, the front section, the rear section and the middle section after turning are assembled on the positioning mold shown in Figure 3 , the large end is pulled tight by the large end pull ring I12 and the small end is pressed tight by the small end gland I13, the rear section and the front section are positioned at the positioning mold profile matching position, and it is checked and confirmed whether the gap and wall deviation of the butt joint parts of the front section and the middle section and the middle section and the rear section meet the requirement of not greater than 0.1 mm.

[0036] If the requirements are not met, the vehicle matching allowance of the large and small ends of the middle section is re-determined according to the wall offset, and the middle section is re-matched and processed according to the requirements of step S3, and after the matching, the trial assembly is re-performed until the butt joint gap and the wall offset between the front section and the middle section and the middle section and the rear section are all not greater than 0.1 mm.

[0037] Step S5, the surface of the middle section, the front section and the rear section after the vehicle matching is cleaned, and oil stains, impurities and oxide films are removed.

[0038] Mechanical cleaning, laser cleaning and other means are used to clean the surface of the product to be welded, remove the surface oxide film and expose the base metal color; gasoline, alcohol and other cleaning agents are used to clean the surface of the product to be welded, remove the surface oil stains and impurities, and ensure the cleanliness of the butt joint.

[0039] Step S6, the cleaned front, middle and rear sections are respectively hung on the positioning fixtures shown in Figure 3 The rear section and the front section are positioned at the matching position of the positioning fixture profile, and the butt joint gap and the wall offset between the front section and the middle section and the middle section and the rear section are checked and confirmed to meet the requirement that they are all not greater than 0.1 mm.

[0040] After confirming that the butt joint state meets the requirements, the butt joint welds between the front section and the middle section and the middle section and the rear section are subjected to whole section positioning welding by argon arc welding without filling wire, the penetration depth of the positioning points should be controlled to be not greater than 0.5 mm, and the spacing between the positioning points is controlled to be between 50-100 mm.

[0041] The electron beam welding parameters selected for the section positioning welding are: focusing current 2000-2100 mA (surface focusing), electron beam current 20-25 mA, welding speed 1.0-1.5 m / min, positioning length 200-300 mm, and positioning point spacing 50-100 mm.

[0042] After positioning, the front-middle-rear three-section assembly positioned together is hung down from the positioning fixture, and the butt joint gap and the wall offset are checked and confirmed to meet the requirement that they are not greater than 0.1 mm.

[0043] Step S7, the front-middle-rear three-section assembly is hung on the welding fixture and fixed at both ends.

[0044] The welding fixture should be able to support the welds between the front section and the middle section and the welds between the middle section and the rear section during welding, and be designed with a welding leakage groove to prevent the product welds from being welded together with the mold body. For example Figure 5As shown, the welding fixture includes a main support shaft 31, a large end expansion support disc 32, a small end expansion support disc 33, a large end gland 34 and a small end gland III 35, the large end expansion support disc 32 and the small end expansion support disc 33 are located on the main support shaft 31, and support the structure on both sides of the front-middle weld and the middle-rear weld respectively, the large end expansion support disc 32 and the small end expansion support disc 33 are provided with welding leakage grooves on the circumferential profile, and the corresponding welds fall into the welding leakage groove area to prevent the product weld from being welded together with the tire body by welding leakage;

[0045] The large end gland 34 and the small end gland III 35 are sleeved on the main support shaft 31 and are arranged on the outside of the rear section and the front section respectively, and the components are clamped and fixed by the large end compression nut and the small end compression nut.

[0046] In step S8, the front-middle weld and the middle-rear weld of the front-middle-rear assembly are welded by using a vacuum electron beam welding process, and after the step S6 adopts the "sectional positioning welding", the step continues to adopt the sequence of "large beam formal welding → modification welding", the sectional positioning welding and the large beam welding are adopted by using the surface focusing and the electron beam scanning during the welding process to increase the weld width, and the modification welding is adopted by using the upper focusing and the smaller beam to eliminate the weld undercut, so that the full and reliable weld is obtained.

[0047] The electron beam welding parameters selected for the large beam formal welding are: focusing current 2000-2100 mA (surface focusing), electron beam current 35-40 mA, welding speed 1.0-1.5 m / min, scanning amplitude Vx=Vy=1.0-1.2 mm, and scanning frequency 300-350 HZ.

[0048] The electron beam welding parameters selected for the modification welding are: focusing current 2100-2200 mA (upper focusing), electron beam current 25-30 mA, welding speed 1.0-1.5 m / min, scanning amplitude Vx=Vy=1.0-1.2 mm, and scanning frequency 300-350 HZ.

[0049] Example 1

[0050] The titanium alloy thin-walled conical component is made of TC2, the front section and the rear section are machined from forgings, and the middle section is a hot-formed sheet metal part. The diameter of the butt joint between the front section and the middle section is φ1100mm, the butt joint thickness is δ1.5mm, the diameter of the butt joint between the middle section and the rear section is φ1740mm, the butt joint thickness is δ1.5mm, the front section and the rear section are processed according to the theoretical size, and the middle section has a certain allowance for processing.

[0051] Firstly, the titanium alloy thin-walled conical component rear section, middle section and front section are sequentially assembled on the positioning jig, the large end of the positioning jig is pulled tight by a large end pull ring, the small end is pressed tight by a small end gland, the wall thickness error of the abutting part between the front section and the middle section and the middle section and the rear section is checked, and the machining allowance of the large and small ends of the middle section is determined.

[0052] Secondly, the middle section is assembled on the machining jig, the small end of the middle section is first pressed tight by the small end gland, the gap between the large end and the jig is confirmed to be no more than 0.1 mm, the large end is machined, then the small end gland is removed, the large end of the middle section is pulled tight by the large end pull ring, the gap between the small end and the jig is confirmed to be no more than 0.1 mm, and the small end of the middle section is machined.

[0053] Thirdly, the rear section, the machined middle section and the front section are sequentially assembled on the positioning jig, and the abutting gap and the wall thickness error of the abutting part between the front section and the middle section and the middle section and the rear section are checked to confirm whether they meet the requirement of no more than 0.1 mm. If not, the machining allowance of the large and small ends of the middle section is determined again according to the wall thickness error, the middle section is machined again according to the second method, and the titanium alloy thin-walled conical component is reassembled after machining to confirm that the abutting gap and the wall thickness error of the abutting part between the front section and the middle section and the middle section and the rear section are all no more than 0.1 mm.

[0054] Fourthly, the abutting part of the front, middle and rear sections of the titanium alloy thin-walled conical component is cleaned, first, the surface is mechanically cleaned by sandpaper and polishing tools to remove the surface oxide film and expose the base metal color, then the surface is cleaned by gas phase cleaning with gasoline to remove surface oil stains and impurities, so as to ensure the cleanliness of the abutting surface and the surrounding area.

[0055] Fifthly, the cleaned rear section, middle section and front section are sequentially assembled on the positioning jig, the large end is pulled tight by the large end pull ring, the small end is pressed tight by the small end gland, and after confirming that the abutting gap and the wall thickness error of the abutting part between the front section and the middle section and the middle section and the rear section are all no more than 0.1 mm, the abutting part of the front section and the middle section and the middle section and the rear section is positioned and welded by manual argon arc welding, the argon arc welding without filler wire is used for positioning and welding, the penetration depth of the positioning point should be controlled to be no more than 0.5 mm, and the spacing between the positioning points is controlled to be between 50-100 mm.

[0056] The electron beam welding parameters selected for the sectional positioning welding are as follows: focusing current 2070 mA (surface focusing), electron beam current 20 mA, welding speed 1.2 m / min, positioning length 200-300 mm, and spacing between positioning points 50-100 mm.

[0057] Sixthly, the front-middle-rear three-section assembly positioned together is assembled on the welding jig, and the large and small ends are pressed and fixed by the gland.

[0058] The welding fixture with the product is hoisted to the electron beam welding machine, the large end is clamped by a chuck, the small end is tightly pressed by a tail top, and the round runout between the front section and the middle section and the middle section and the rear section is found and adjusted to be not more than 0.5 mm.

[0059] The electron beam welding gun is adjusted to a distance of 30 mm from the butting position, the welding gun angle is adjusted according to the butting angle, and the electron beam direction is ensured to be consistent with the butting direction.

[0060] In the seventh step, the electron beam welding is performed on the butting between the front section and the middle section and the middle section and the rear section, and the welding is continuously performed in the order of 'large beam current formal welding-modification welding'.

[0061] The electron beam welding parameters selected for the large beam current formal welding are as follows: focusing current 2070 mA (surface focusing), electron beam current 36 mA, welding speed 1.2 m / min, scanning amplitude Vx=Vy=1.0 mm, and scanning frequency 300 HZ.

[0062] The electron beam welding parameters selected for the modification welding are as follows: focusing current 2170 mA (upper focusing), electron beam current 25 mA, welding speed 1.2 m / min, scanning amplitude Vx=Vy=1.0 mm, and scanning frequency 300 HZ.

[0063] After welding, the surface of the weld is inspected, the weld surface quality should meet the requirements of the GJB1718A standard; the weld is subjected to X-ray detection, and the internal quality of the weld should meet the requirements of the GJB1718A standard.

[0064] The present application provides a precision assembly and electron beam welding method for large-size titanium alloy thin-walled conical components, a mature processing flow is formed through the design of special turning and positioning fixtures, and the gap and wall offset between the butt joints are ensured to be within a reasonable range, thereby meeting the requirements of electron beam welding.

[0065] The present application provides a precision assembly and electron beam welding method for large-size titanium alloy thin-walled conical components, a reasonable electron beam welding support tool is designed, which can support the weld joint during electron beam welding, prevent excessive welding deformation, and design a welding leakage groove on the welding fixture to avoid the phenomenon that the product and the tool are welded together due to excessive welding leakage.

[0066] The present application provides a large-size titanium alloy thin-walled conical component electron beam welding process flow, surface focusing large beam current welding is adopted to ensure that the butt joint part obtains a high-reliability penetration weld, and upper focusing small beam current welding is adopted to eliminate weld edge biting, so that a full and reliable weld is finally obtained.

[0067] The present application is described in detail above in connection with specific embodiments and exemplary examples, but the description is not to be construed to limit the present application. It will be understood by those skilled in the art that various equivalents, modifications and substitutions can be made to the present application and its embodiments without departing from the spirit and scope of the present application, and these are to be construed to fall within the scope of the present application. The scope of the present application is defined by the appended claims.

[0068] The contents not described in detail in the specification of the present application are known to those skilled in the art.

Claims

1. A precision assembly welding method of a large-sized titanium alloy thin-walled conical member, characterized by, It comprises the following steps: The front section and the rear section of the conical member are processed according to the theoretical size, and the middle section is formed with a fitting allowance at both ends; The rear section, the middle section and the front section are sequentially assembled on the positioning jig, the rear section and the front section are positioned at the joint of the positioning jig profile, the wall offset of the front section and the middle section and the wall offset of the middle section and the rear section are checked and confirmed, and the fitting allowance of the large end and the small end of the middle section is determined; The middle section is hoisted onto the turning jig, and the large end and the small end of the middle section are respectively processed according to the determined fitting allowance; specifically, the middle section is hoisted onto the turning jig, the large end of the middle section is positioned at the joint of the turning jig profile, and after it is confirmed that the gap between the small end of the middle section and the turning jig profile is not greater than 0.1mm, the small end is processed; the small end of the middle section is positioned at the joint of the turning jig profile, and after it is confirmed that the gap between the large end of the middle section and the turning jig profile is not greater than 0.1mm, the large end is processed, and the welding surface after turning should be perpendicular to the product generatrix; The front section, the rear section and the middle section after fitting are assembled on the positioning jig, and whether the joint gap and the wall offset meet the requirements are checked and confirmed; if not, the fitting of the large end and the small end of the middle section is reprocessed until the joint gap and the wall offset meet the requirements; The surface of the welded part of the middle section, the front section and the rear section after fitting is cleaned; The front section, the middle section and the rear section after cleaning are assembled on the positioning jig, the rear section and the front section are positioned at the joint of the positioning jig profile, and after it is confirmed that the joint gap and the wall offset meet the requirements, the positioning welding is performed by argon arc welding; The conical member after positioning welding is assembled on the welding fixture and clamped on the rotary table of the electron beam welding machine, and the welding of the front section and the middle section and the welding of the middle section and the rear section are respectively performed by electron beam welding process; the welding fixture comprises a main support shaft (31), a large end expansion support disc (32), a small end expansion support disc (33), a large end gland (34) and a small end gland III (35), the large end expansion support disc (32) and the small end expansion support disc (33) are located on the main support shaft (31) and support the structure on both sides of the middle section and the rear section weld, the front section and the middle section weld respectively, the large end expansion support disc (32) and the small end expansion support disc (33) are provided with a welding leakage groove on the circumferential profile, and the corresponding weld falls into the welding leakage groove area; the large end gland (34) and the small end gland III (35) are sleeved on the main support shaft (31) and arranged on the outside of the rear section and the front section respectively, and the component is clamped and fixed by the large end compression nut and the small end compression nut.

2. The precision fit welding method of large size titanium alloy thin-walled conical members according to claim 1, characterized by, The positioning mold comprises a support mold I (11), a large end pull ring I (12), a small end gland I (13) and a compression nut I (14), the support mold I (11) is a body structure with a support shaft inside, the small end and the large end have a continuous profile consistent with the product, the support shaft extending from the small end of the body is machined with external threads, and cooperates with the compression nut I (14) outside the small end gland I (13); the small end gland I (13) is located outside the small end of the support mold I and is compressed under the pressure of the compression nut I (14); the large end pull ring I (12) is sleeved outside the large end of the rear section, the maximum diameter is smaller than the maximum diameter of the rear section, and the large end pull ring I (12) is connected to the large end of the support mold I (11) through a connecting piece to pull the rear section.

3. The precision fit welding method of large size titanium alloy thin-walled conical members according to claim 1, characterized by, The vehicle machining mold comprises a support mold II (21), a small end gland II (22) and a large end pull ring II (23); the support mold II (21) is a body structure with a support shaft inside, the large end and the small end have a profile consistent with the large end and the small end of the middle section, and the small end height is lower than the small end end face of the middle section; the support shaft is provided with support discs at both ends, the small end support disc supports the small end of the middle section, and the large end support disc supports the large end of the middle section; The small end gland II (22) is mounted outside the small end of the support mold II (21) and is fixedly connected to the small end support disc through a connecting piece to compress the small end of the middle section, so that the large end of the middle section is machined and matched; The large end pull ring II (23) is sleeved outside the large end of the support mold II (21) and overlaps with the large end support disc in height position, the maximum diameter is smaller than the maximum diameter of the large end of the support mold II (21), and the large end pull ring II (23) is fixedly connected to the large end of the support mold II (21) through a connecting piece to pull the large end, so that the small end of the middle section is machined and matched.

4. The precision fit welding method of large size titanium alloy thin-walled conical members according to claim 1, characterized by, In the step of assembling the front section, the rear section and the middle section machined and matched to the positioning mold and checking whether the butt joint gap and the wall offset meet the requirements, the butt joint gap and the wall offset are not greater than 0.1 mm.

5. The precision fit welding method of large size titanium alloy thin-walled conical members according to claim 1, characterized by, In the step of cleaning the surface of the middle section machined and matched, the front section and the rear section to be welded, the surface of the product to be welded is cleaned by mechanical polishing, laser cleaning and organic solvent cleaning, so that the surface oxide film is removed, the base metal is exposed, the surface oil stain and impurities are removed, and the butt joint position is clean.

6. The precision fit welding method of large size titanium alloy thin-walled conical members according to claim 1, characterized by, In the step of positioning welding by argon arc welding, the butt joint weld between the front section and the middle section and between the middle section and the rear section is positioned and welded by argon arc welding without filling wire, the penetration depth of the positioning point is controlled to be not greater than 0.5 mm, and the spacing between the positioning points is controlled to be between 50 and 100 mm.

7. The precision fit welding method of large size titanium alloy thin-walled conical members according to claim 1, characterized by, After the step of positioning welding by argon arc welding, the front-middle-rear three-section assembly is separated from the positioning mold, and subsequent welding is performed after checking whether the butt joint gap and the wall offset meet the requirements.

8. The precision fit welding method of large size titanium alloy thin-walled conical members according to claim 1, characterized by, In the steps of welding the front section and the middle section and the middle section and the rear section by electron beam welding process, large beam current formal welding and modification welding are performed in sequence. The electron beam welding parameters for the large beam flow formal welding are: surface focusing current 2000-2100 mA, electron beam current 35-40 mA, welding speed 1.0-1.5 m / min, scanning amplitude Vx=Vy=1.0-1.2 mm, scanning frequency 300-350 HZ.

9. The precision fit welding method of large size titanium alloy thin-walled conical members according to claim 8, characterized by, The electron beam welding parameters for the modification welding are: focusing current 2100-2200 mA, electron beam current 25-30 mA, welding speed 1.0-1.5 m / min, scanning amplitude Vx=Vy=1.0-1.2 mm, scanning frequency 300-350 HZ.

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