A precision welding fixture and processing method for titanium alloy thin-diameter thin-wall straight tube assembly

Abstract

A precision welding fixture and processing method for a titanium alloy thin-diameter thin-walled straight tube assembly. The welding fixture includes a base, a support rod, a lower support plate, a column, an upper support plate, a straight tube limit sleeve and an elbow limit mechanism. The upper support plate, the column, the lower support plate and the support rod are arranged on the base from top to bottom, the straight tube limit sleeve is arranged on the upper support plate, the elbow limit mechanism is arranged on the lower support plate, the assembly is clamped between the elbow limit mechanism and the straight tube limit sleeve, and an argon gas introduction structure is arranged in the elbow limit mechanism. The processing method steps are: cleaning the elbow and straight tube of the titanium alloy thin-diameter thin-walled straight tube assembly; combining and clamping the elbow and straight tube of the assembly by using a welding fixture; introducing argon gas into the elbow limit mechanism; welding the elbow and straight tube of the assembly; vacuum heat treating the welded assembly; lathing the assembly after vacuum heat treatment until the parts to be processed on the assembly meet the design requirements of the drawings.

Description

Technical Field

[0001] The invention belongs to the technical field of manufacturing parts of aviation engines, and in particular relates to a precision welding fixture for titanium alloy thin-diameter and thin-wall straight pipe assemblies and a processing method thereof. Background Art

[0002] In order to meet the requirements of reducing the weight of aircraft engines, many parts in aircraft engines are increasingly made of lightweight metal materials, including titanium alloy thin-diameter thin-walled straight tube assemblies, such as Figure 1 As shown, the assembly consists of a straight pipe and an elbow, the straight pipe is made of TA16 and the elbow is made of TC4.

[0003] In addition, the assembly has particularly high requirements for processing accuracy, such as Figure 2 As shown, the tolerance range of the length dimension L1 from the lower end face of the flange of the elbow to the end of the straight pipe is -0.5mm to 0mm, the coaxiality and verticality requirements within the length dimension L2 of the straight pipe are both 0.1mm, and the tolerance range of the outer circle dimension φD is -0.05mm to -0.11mm.

[0004] At present, when the traditional method is used to process this assembly, there is a problem of low product processing qualification rate. The main restricting factors are: 1. The difficulty of titanium alloy welding; 2. The complex welding process; 3. The unsatisfactory argon protection effect; 4. The welding porosity problem of straight pipes and elbows; 5. The problem of excessive welding deformation. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a precision welding fixture and processing method for a titanium alloy thin-diameter, thin-walled straight tube assembly, which can effectively reduce the difficulty of titanium alloy welding, simplify the welding process, effectively improve the argon protection effect, avoid welding porosity in straight tubes and elbows, greatly reduce welding deformation, and further improve the product processing qualification rate.

[0006] In order to achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a precision welding fixture for a titanium alloy thin-diameter thin-walled straight tube assembly, comprising a base, a support rod, a lower support plate, a column, an upper support plate, a straight tube limit sleeve and an elbow limit mechanism; the base is horizontally arranged, and a threaded hole is opened in the center of the base; the support rod is vertically arranged, and external threads are arranged on the rod body surfaces at the upper and lower ends of the support rod, and limit stop rings are arranged at the stroke boundaries of the external threads; the lower support plate is horizontally arranged, and a transfer circular hole is opened at one end of the lower support plate, and the lower support plate is connected to the upper end rod body of the support rod through the transfer circular hole set, and the lower support plate is clamped with the limit stop ring at the upper end of the support rod. The upper support plate is horizontally arranged, one end of the upper support plate is fixedly connected to the flange structure at the upper end of the column, and a limiting sleeve insertion hole is provided at the other end of the upper support plate, and the straight tube limiting sleeve is vertically inserted into the limiting sleeve insertion hole; the elbow of the titanium alloy thin-diameter and thin-walled straight tube assembly is clamped in the elbow limiting mechanism, and the straight tube of the titanium alloy thin-diameter and thin-walled straight tube assembly is installed in the straight tube limiting sleeve.

[0007] The elbow limiting mechanism includes an elbow support platform, an elbow flange gasket and an elbow clamping block; the elbow support platform adopts a cylindrical low platform structure, and the elbow support platform is horizontally fixed on the upper surface of the lower support plate; a U-shaped notch is radially opened on the elbow support platform, and the elbow of the titanium alloy thin-diameter thin-walled straight pipe assembly is located in the U-shaped notch 13; the elbow flange gasket is fixed at the center of the upper surface of the elbow support platform, and the elbow flange of the titanium alloy thin-diameter thin-walled straight pipe assembly is blocked and limited by the elbow flange gasket; the elbow clamping block is located above the elbow flange of the titanium alloy thin-diameter thin-walled straight pipe assembly, and the elbow clamping block is fastened and limited with the elbow flange.

[0008] An argon gas buffer groove is provided on the upper surface of the lower support plate below the elbow support platform, and an argon gas access hole is provided on the lower support plate on the side of the argon gas buffer groove; a copper argon gas protection cover is fixedly mounted on the outer peripheral side of the elbow support platform, and a copper argon gas protection annular cover plate is fixedly installed on the top of the annular gap between the argon gas protection cover and the elbow support platform; an argon gas discharge annular gap is left between the argon gas protection annular cover plate and the elbow clamping block.

[0009] The vertical distance between the center point of the straight tube limiting sleeve and the upper surface of the elbow clamping block is 2 / 3 of the straight tube length of the titanium alloy thin-diameter thin-wall straight tube assembly.

[0010] The base adopts a cross-shaped structure, and each arm of the base is provided with a process weight-reducing hole; the support rod and the column both adopt a hollow tube weight-reducing structure; and a process weight-reducing hole is provided on the plate body of the upper support plate.

[0011] A method for precision machining a titanium alloy thin-diameter thin-wall straight tube assembly, using the titanium alloy thin-diameter thin-wall straight tube assembly precision welding fixture, comprises the following steps:

[0012] Step 1: Clean the elbows and straight tubes of the titanium alloy thin-diameter thin-walled straight tube assembly before welding. First, use sandpaper or a wire brush to grind and polish the surfaces of the elbows and straight tubes to be welded to remove the oxide layer. Then, pickle the polished surfaces of the elbows and straight tubes to be welded. Finally, use alcohol or acetone to wipe and clean the pickled surfaces of the elbows and straight tubes to be welded. Among them, the interval time between the grinding and polishing process and the pickling process shall not exceed 24 hours, and the interval time between the pickling process and the subsequent welding process shall not exceed 120 hours.

[0013] Step 2: Install the elbow and straight pipe that have been cleaned before welding into the precision welding fixture of titanium alloy thin-diameter thin-walled straight pipe assembly for assembly and assemble. First, rotate the column to adjust the threaded connection length between the column and the support rod, and then adjust the upward exploration height of the column to achieve the height of the upper support plate and the straight pipe limit sleeve thereon to adapt to the installation limit of straight pipes of different lengths; then put the elbow into the U-shaped notch of the elbow support platform, so that the elbow flange is blocked and limited on the elbow flange pad, and then fix the elbow clamping block above the elbow flange, and the elbow is pressed and fixed by the elbow clamping block, and then the argon protection annular cover plate is installed in place; then the straight pipe is inserted into the straight pipe limit sleeve from above the straight pipe limit sleeve until the lower end of the straight pipe is accurately connected with the upper end of the fixed elbow, and the weld to be welded is formed at the same time;

[0014] Step 3: Connect the gas outlet of the argon gas bottle with the argon gas access hole on the lower support plate through a conduit, then open the valve of the argon gas bottle, and the argon gas in the argon gas bottle enters the argon gas buffer groove through the conduit and the argon gas access hole in turn, and then flows in two ways from the argon gas buffer groove, the first way of argon gas flows into the inside of the elbow from the U-shaped notch, and flows from the inside of the elbow to the weld, forming argon gas protection for the back of the weld; the second way of argon gas flows into the annular space between the elbow support platform and the argon gas protection cover through the U-shaped notch, and then flows upward through the argon gas discharge annular gap between the argon gas protection annular cover plate and the elbow clamping block to the outer space of the weld; the argon gas is in a low temperature state when it enters the argon gas buffer groove from the argon gas access hole, and when it flows through the annular space between the elbow support platform and the argon gas protection cover, it will be assisted in heat dissipation by the copper argon gas protection cover and the argon gas protection annular cover plate to increase the heat dissipation efficiency during welding;

[0015] Step 4: Start the welding process and perform circumferential welding on the weld using a flat welding posture of the welding gun. The welding current is controlled at 40A to 50A, the argon flow rate of the welding gun is controlled at 15L / min, and the argon flow rate of the argon access hole is controlled at 6L / min.

[0016] Step 5: After the welding is completed, the elbow and the straight pipe form a titanium alloy thin-diameter thin-walled straight pipe assembly, and the titanium alloy thin-diameter thin-walled straight pipe assembly is first sent to a vacuum furnace for heat treatment to remove the weld and surrounding residual stress; wherein the interval time between the welding process and the vacuum heat treatment process shall not exceed 144 hours;

[0017] Step 6: After the vacuum heat treatment is completed, the titanium alloy thin-diameter thin-walled straight tube assembly is subjected to a turning process until the parts to be processed on the titanium alloy thin-diameter thin-walled straight tube assembly meet the design requirements of the drawings.

[0018] Beneficial effects of the present invention:

[0019] The titanium alloy fine-diameter thin-wall straight tube assembly precision welding fixture and processing method of the present invention can effectively reduce the difficulty of titanium alloy welding, simplify the welding process, effectively improve the argon protection effect, avoid the occurrence of welding pores in straight tubes and elbows, greatly reduce welding deformation, and further improve the product processing qualification rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the structure of the titanium alloy thin-walled straight tube assembly in the embodiment;

[0021] Figure 2 is a dimensional tolerance diagram of a titanium alloy thin-diameter thin-wall straight tube assembly in an embodiment;

[0022] Figure 3 A three-dimensional diagram of a precision welding fixture for a titanium alloy thin-diameter, thin-walled straight tube assembly according to the present invention;

[0023] Figure 4 It is a cross-sectional view of a precision welding fixture for a titanium alloy thin-diameter thin-wall straight tube assembly of the present invention;

[0024] Figure 5 This is the argon gas flow route diagram when argon protection is performed;

[0025] In the figure, 1—base, 2—support rod, 3—lower support plate, 4—column, 5—upper support plate, 6—straight pipe limiting sleeve, 7—elbow limiting mechanism, 8—elbow, 9—straight pipe, 10—elbow supporting platform, 11—elbow flange gasket, 12—elbow clamping block, 13—U-shaped notch, 14—argon buffer groove, 15—argon access hole, 16—argon protection cover, 17—argon protection annular cover plate, 18—weld. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] like Figure 3 , 4 As shown, a precision welding fixture for a titanium alloy thin-diameter thin-walled straight tube assembly comprises a base 1, a support rod 2, a lower support plate 3, a column 4, an upper support plate 5, a straight tube limiting sleeve 6 and an elbow limiting mechanism 7; the base 1 is horizontally arranged, and a threaded hole is opened in the center of the base 1; the support rod 2 is vertically arranged, and external threads are arranged on the rod body surfaces at the upper and lower ends of the support rod 2, and limiting retaining rings are arranged at the travel boundaries of the external threads; the lower support plate 3 is horizontally arranged, and a transfer circular hole is opened at one end of the lower support plate 3, and the lower support plate 3 is connected to the upper end rod body of the support rod 2 through the transfer circular hole sleeve, and the lower support plate 3 and the limiting retaining ring at the upper end of the support rod 2 are engaged in a blocking and limiting manner; the The elbow limiting mechanism 7 is arranged on the upper surface of the other end of the lower support plate 3; the column 4 is arranged vertically, and flange structures are provided at both ends of the column 4, and threaded holes are opened inside the column body at both ends of the column 4, and the lower end of the column 4 is threadedly matched with the external thread at the upper end of the support rod 2 through the threaded hole; the upper support plate 5 is arranged horizontally, and one end of the upper support plate 5 is fixedly connected to the flange structure at the upper end of the column 4, and a limiting sleeve insertion hole is opened at the other end of the upper support plate 5, and the straight pipe limiting sleeve 6 is vertically inserted in the limiting sleeve insertion hole; the elbow 8 of the titanium alloy thin-diameter thin-walled straight pipe assembly is clamped in the elbow limiting mechanism 7, and the straight pipe 9 of the titanium alloy thin-diameter thin-walled straight pipe assembly is inserted into the straight pipe limiting sleeve 6.

[0028] The elbow limiting mechanism 7 includes an elbow support platform 10, an elbow flange gasket 11 and an elbow clamping block 12; the elbow support platform 10 adopts a cylindrical low platform structure, and the elbow support platform 10 is horizontally fixed on the upper surface of the lower support plate 3; a U-shaped notch 13 is radially opened on the elbow support platform 10, and the elbow 8 of the titanium alloy thin-diameter thin-walled straight tube assembly is located in the U-shaped notch 13; the elbow flange gasket 11 is fixed at the center of the upper surface of the elbow support platform 10, and the flange of the elbow 8 of the titanium alloy thin-diameter thin-walled straight tube assembly is blocked and limited by the elbow flange gasket 11; the elbow clamping block 12 is located above the flange of the elbow 8 of the titanium alloy thin-diameter thin-walled straight tube assembly, and the elbow clamping block 12 is fastened and limited with the flange of the elbow 8.

[0029] An argon gas buffer groove 14 is provided on the upper surface of the lower support plate 3 below the elbow support platform 10, and an argon gas access hole 15 is provided on the lower support plate 3 on the side of the argon gas buffer groove 14; a copper argon gas protective cover 16 is fixedly mounted on the outer peripheral side of the elbow support platform 10, and a copper argon gas protective annular cover plate 17 is fixedly installed on the top of the annular gap between the argon gas protective cover 16 and the elbow support platform 10; an argon gas discharge annular gap is left between the argon gas protective annular cover plate 17 and the elbow clamping block 12. The purpose of adopting the above structure is to better perform argon gas protection on the back of the weld 18, and to further improve the efficiency of welding heat dissipation through the copper argon gas protective cover 16 and the argon gas protective annular cover plate 17.

[0030] The vertical distance between the center point of the straight tube limiting sleeve 6 and the upper surface of the elbow clamping block 12 is 2 / 3 of the length of the straight tube 9 of the titanium alloy thin-diameter thin-walled straight tube assembly. The purpose of adopting the above distance relationship is to maximize the clamping rigidity of the straight tube 9, improve the deformation resistance of the straight tube 9, and improve the coaxiality and verticality of the straight tube 9 after welding.

[0031] The base 1 adopts a cross-shaped structure, and each arm of the base 1 is provided with a process weight reduction hole; the support rod 2 and the column 4 both adopt a hollow tube weight reduction structure; and a process weight reduction hole is provided on the plate body of the upper support plate 5. The purpose of adopting the above structures is to achieve the maximum weight reduction of the welding fixture, and the total weight of the welding fixture in this embodiment can be controlled within 30 kg.

[0032] A method for precision machining a titanium alloy thin-diameter thin-wall straight tube assembly, using the titanium alloy thin-diameter thin-wall straight tube assembly precision welding fixture, comprises the following steps:

[0033] Step 1: Clean the elbow 8 and the straight tube 9 of the titanium alloy thin-diameter thin-walled straight tube assembly before welding. First, use sandpaper or a wire brush to grind and polish the surfaces of the elbow 8 and the straight tube 9 to be welded to remove the oxide layer, then pickle the polished surfaces of the elbow 8 and the straight tube 9 to be welded, and finally wipe and clean the pickled surfaces of the elbow 8 and the straight tube 9 with alcohol or acetone; wherein, the interval between the grinding and polishing process and the pickling process shall not exceed 24 hours, and the interval between the pickling process and the subsequent welding process shall not exceed 120 hours;

[0034] Step 2: Install the elbow 8 and straight tube 9 cleaned before welding into the precision welding fixture of titanium alloy thin-diameter thin-walled straight tube assembly for assembly and assembly. First, rotate the column 4 to adjust the threaded connection length between the column 4 and the support rod 2, and then adjust the upward exploration height of the column 4 to achieve the height of the upper support plate 5 and the straight tube limit sleeve 6 thereon to adapt to the installation limit of straight tubes 9 of different lengths; then put the elbow 8 into the U-shaped notch 13 of the elbow support platform 10, so that the flange of the elbow 8 is blocked and limited on the elbow flange pad 11, and then fix the elbow clamping block 12 above the flange of the elbow 8, and the elbow 8 is pressed and fixed by the elbow clamping block 12, and then the argon protection annular cover plate 17 is installed in place; then the straight tube 9 is inserted into the straight tube limit sleeve 6 from above the straight tube limit sleeve 6 until the lower end of the straight tube 9 is accurately connected with the upper end of the fixed elbow 8, and the weld 18 to be welded is formed at the same time;

[0035] Step 3: Connect the gas outlet of the argon gas bottle with the argon gas access hole 1 on the lower support plate 3 through a conduit, then open the valve of the argon gas bottle, and the argon gas in the argon gas bottle enters the argon gas buffer groove 14 through the conduit and the argon gas access hole 1 in turn, and then flows in two ways from the argon gas buffer groove 14, such as Figure 5 As shown; the first path of argon gas flows into the interior of the elbow 8 from the U-shaped notch 13, and flows from the interior of the elbow 8 to the weld 18, forming argon protection for the back of the weld 18; the second path of argon gas flows into the annular space between the elbow support platform 10 and the argon protective cover 16 through the U-shaped notch 13, and then flows upward through the argon gas discharge annular gap between the argon protective annular cover plate 17 and the elbow clamping block 12 to the outer space of the weld 18; when the argon gas enters the argon buffer groove 14 from the argon access hole 1, it is in a low temperature state, and when it flows through the annular space between the elbow support platform 10 and the argon protective cover 16, it will be assisted in heat dissipation by the copper argon protective cover 16 and the argon protective annular cover plate 17 to increase the heat dissipation efficiency during welding;

[0036] Step 4: Start the welding process, and use the welding gun to perform circumferential welding on the weld 18, the welding current is controlled at 40A-50A, the argon flow rate of the welding gun is controlled at 15L / min, and the argon flow rate of the argon access hole 1 is controlled at 6L / min; in this embodiment, the welding gun nozzle uses a large-size nozzle of 24mm, and the welding wire uses TA1 welding wire;

[0037] Step 5: After the welding is completed, the elbow 8 and the straight tube 9 form a titanium alloy thin-diameter thin-walled straight tube assembly, and the titanium alloy thin-diameter thin-walled straight tube assembly is first sent to a vacuum furnace for heat treatment to remove the weld 18 and the surrounding residual stress; wherein the interval time between the welding process and the vacuum heat treatment process does not exceed 144 hours;

[0038] Step six: After the vacuum heat treatment is completed, the titanium alloy thin-diameter thin-walled straight tube assembly is subjected to a turning process until the parts to be processed on the titanium alloy thin-diameter thin-walled straight tube assembly meet the design requirements of the drawings; in this embodiment, the length dimension L1 from the flange lower end face of the elbow 8 to the tube end of the straight tube is 386.6 mm, and the tolerance of L1 is -0.3 mm, which meets the requirement of a tolerance range of -0.5 mm to 0 mm; the length dimension L2 of the straight tube 9 is 35 mm, and the coaxiality and verticality within the range of L2 are both 0.08 mm, which meets the requirement of 0.1 mm; the tolerance of the outer circle dimension φD is -0.08 mm, which meets the requirement of a tolerance range of -0.05 mm to -0.11 mm.

[0039] The solutions in the embodiments are not intended to limit the patent protection scope of the present invention. All equivalent implementations or changes that do not deviate from the present invention are included in the patent scope of this case.

Claims

1. A precision welding fixture for titanium alloy thin-diameter thin-wall straight tube assembly, characterized in that: The cam is provided with a threaded hole at the center of the bottom end of the support rod, and an external thread is formed on the rod body surface at the upper and lower ends of the support rod, and a limit stop ring is provided at the stroke boundary of the external thread; the lower support plate is provided with a transfer circular hole at one end of the lower support plate, and the lower support plate is connected to the rod body of the upper end of the support rod through the transfer circular hole set, and the lower support plate and the limit stop ring at the upper end of the support rod are engaged in blocking and limiting cooperation; the elbow limit mechanism is arranged on the upper surface of the other end of the lower support plate; the column is arranged vertically, and flange structures are provided at the upper and lower ends of the column, and threaded holes are provided inside the column at the upper and lower ends of the column, and the lower end of the column is screwed and cooperated with the external thread on the upper end of the support rod through the threaded hole; the upper support plate is arranged horizontally, and one end of the upper support plate is connected to the flange at the upper end of the column The upper support plate is fixedly connected with the elbow limit mechanism, and a limit sleeve insertion hole is provided at the other end of the upper support plate, and the straight pipe limit sleeve is vertically inserted into the limit sleeve insertion hole; the elbow of the titanium alloy thin-diameter thin-walled straight pipe assembly is clamped in the elbow limit mechanism, and the straight pipe of the titanium alloy thin-diameter thin-walled straight pipe assembly is installed in the straight pipe limit sleeve; the elbow limit mechanism includes an elbow support platform, an elbow flange pad and an elbow clamping block; the elbow support platform adopts a cylindrical short platform structure, and the elbow support platform is horizontally fixed on the lower The upper surface of the support plate; a U-shaped notch is radially opened on the elbow support platform, and the elbow of the titanium alloy thin-diameter thin-walled straight pipe assembly is located in the U-shaped notch; the elbow flange gasket is fixedly installed at the center of the upper surface of the elbow support platform, and the elbow flange of the titanium alloy thin-diameter thin-walled straight pipe assembly is blocked and limited by the elbow flange gasket; the elbow clamping block is located above the elbow flange of the titanium alloy thin-diameter thin-walled straight pipe assembly, and the elbow clamping block is fastened and limited by the elbow flange.

2. A precision welding fixture for titanium alloy thin-diameter thin-wall straight tube assembly according to claim 1, characterized in that: An argon gas buffer groove is provided on the upper surface of the lower support plate below the elbow support platform, and an argon gas access hole is provided on the lower support plate on the side of the argon gas buffer groove; a copper argon gas protection cover is fixedly mounted on the outer peripheral side of the elbow support platform, and a copper argon gas protection annular cover plate is fixedly installed on the top of the annular gap between the argon gas protection cover and the elbow support platform; an argon gas discharge annular gap is left between the argon gas protection annular cover plate and the elbow clamping block.

3. The precision welding fixture for titanium alloy thin-diameter thin-wall straight tube assembly according to claim 1, characterized in that: The vertical distance between the center point of the straight tube limiting sleeve and the upper surface of the elbow clamping block is 2 / 3 of the straight tube length of the titanium alloy thin-diameter thin-wall straight tube assembly.

4. A precision welding fixture for titanium alloy thin-walled straight tube assembly according to claim 1, characterized in that: The base adopts a cross-shaped structure, and each arm of the base is provided with a process weight-reducing hole; the support rod and the column both adopt a hollow tube weight-reducing structure; and a process weight-reducing hole is provided on the plate body of the upper support plate.

5. A method for precision machining of titanium alloy thin-diameter thin-wall straight tube assemblies, using the titanium alloy thin-diameter thin-wall straight tube assemblies precision welding fixture as claimed in claim 2, characterized in that The steps include: Step 1: Clean the elbows and straight tubes of the titanium alloy thin-diameter thin-walled straight tube assembly before welding. First, use sandpaper or a wire brush to grind and polish the surfaces of the elbows and straight tubes to be welded to remove the oxide layer. Then, pickle the polished surfaces of the elbows and straight tubes to be welded. Finally, use alcohol or acetone to wipe and clean the pickled surfaces of the elbows and straight tubes to be welded. Among them, the interval time between the grinding and polishing process and the pickling process shall not exceed 24 hours, and the interval time between the pickling process and the subsequent welding process shall not exceed 120 hours. Step 2: Install the elbow and straight pipe that have been cleaned before welding into the precision welding fixture of titanium alloy thin-diameter thin-walled straight pipe assembly for assembly and assemble. First, rotate the column to adjust the threaded connection length between the column and the support rod, and then adjust the upward exploration height of the column to achieve the height of the upper support plate and the straight pipe limit sleeve thereon to adapt to the installation limit of straight pipes of different lengths; then put the elbow into the U-shaped notch of the elbow support platform, so that the elbow flange is blocked and limited on the elbow flange pad, and then fix the elbow clamping block above the elbow flange, and the elbow is pressed and fixed by the elbow clamping block, and then the argon protection annular cover plate is installed in place; then the straight pipe is inserted into the straight pipe limit sleeve from above the straight pipe limit sleeve until the lower end of the straight pipe is accurately connected with the upper end of the fixed elbow, and the weld to be welded is formed at the same time; Step 3: Connect the gas outlet of the argon gas bottle with the argon gas access hole on the lower support plate through a conduit, then open the valve of the argon gas bottle, and the argon gas in the argon gas bottle enters the argon gas buffer groove through the conduit and the argon gas access hole in turn, and then flows in two ways from the argon gas buffer groove, the first way of argon gas flows into the inside of the elbow from the U-shaped notch, and flows from the inside of the elbow to the weld, forming argon gas protection for the back of the weld; the second way of argon gas flows into the annular space between the elbow support platform and the argon gas protection cover through the U-shaped notch, and then flows upward through the argon gas discharge annular gap between the argon gas protection annular cover plate and the elbow clamping block to the outer space of the weld; the argon gas is in a low temperature state when it enters the argon gas buffer groove from the argon gas access hole, and when it flows through the annular space between the elbow support platform and the argon gas protection cover, it will be assisted in heat dissipation by the copper argon gas protection cover and the argon gas protection annular cover plate to increase the heat dissipation efficiency during welding; Step 4: Start the welding process and perform circumferential welding on the weld using a flat welding posture of the welding gun. The welding current is controlled at 40A to 50A, the argon flow rate of the welding gun is controlled at 15L / min, and the argon flow rate of the argon access hole is controlled at 6L / min. Step 5: After the welding is completed, the elbow and the straight pipe form a titanium alloy thin-diameter thin-walled straight pipe assembly, and the titanium alloy thin-diameter thin-walled straight pipe assembly is first sent to a vacuum furnace for heat treatment to remove the weld and surrounding residual stress; wherein the interval time between the welding process and the vacuum heat treatment process shall not exceed 144 hours; Step 6: After the vacuum heat treatment is completed, the titanium alloy thin-diameter thin-walled straight tube assembly is subjected to a turning process until the parts to be processed on the titanium alloy thin-diameter thin-walled straight tube assembly meet the design requirements of the drawings.

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