Laser welding method for thin-wall titanium alloy gas cylinder

Abstract

The invention discloses a laser welding method for titanium alloy. The laser welding method comprises pre-welding cleaning (acid pickling, polishing, laser cleaning and the like) of a titanium alloy part. By setting reasonable laser swing amplitude and frequency, laser power, defocusing amount, shielding gas flow and welding speed, the problems of deep penetration welding and pinhole effect of laser welding are solved, the porosity of a titanium alloy welding seam is reduced, and the mechanical property is improved. And the welding quality meets the requirements of QJ 20465-2016 I level.

Description

Technical Field

[0001] The invention relates to the technical field of laser welding, and in particular to a laser welding method for a thin-wall titanium alloy gas cylinder. Background Art

[0002] With the development of science and technology, aerospace fuel system cylinders are moving towards lightweight, from steel liner composite gas cylinders to lighter titanium alloy liner composite gas cylinders. Welding and forming of titanium alloy gas cylinder liner is one of the core technologies for composite gas cylinder processing. Laser welding of thin-walled titanium alloy gas cylinders is difficult, and there are problems such as weld penetration, weld pits, excessive weld oxidation, and spatter on the back of the weld. Prior art CN110280900B discloses a beam swing welding method for titanium alloys, wherein the titanium alloy materials are TC31 and TA15, the material structure is 3mm plate, the welding speed is a high speed of 0.02m / s, and the laser power is a high power of more than 1500W. The prior art uses a high-speed, high-power welding method, which cannot provide good protection for the weld and is prone to dents and burn-through. Summary of the invention

[0003] The invention relates to a laser welding method for a titanium alloy thin-wall gas cylinder. Appropriate welding parameters and reasonable welding gas protection measures are adopted to ensure that the weld seam of the thin-wall titanium alloy cylinder after laser welding meets the requirements of QJ 20465-2016 Level I and meets the airtightness requirements.

[0004] The technical solution adopted by the present invention is a laser welding method for thin-walled titanium alloy gas cylinders, comprising the following steps: Step 1: Position welding the rear head and pipe joint by argon arc welding, and position 4 points symmetrically in the circumferential direction; Step 2, welding, the fourth weld is welded using a 6kW continuous laser welder, and the welding parameters are as follows: laser output power: 400W, argon gas flow: 25L / min on the front, 10L / min on the back, defocus: 0, welding speed 13° / s, spot swing: circular, radius 1.0mm, 8Hz; Step 3: Use a 300W pulse laser cleaning machine for laser cleaning. The cleaning parameters are as follows: spot swing: 8, defocus: 4mm, output power: 45W; Step 4: Use an alloy scraper to scrape out the metal color of the welding end surface, and wipe the weld to be welded with a dust-free cloth dipped in anhydrous ethanol; Step 5, assemble the front head, cylinder, and rear head using the gas cylinder positioning fixture; Step 6, in a clamped state, the first weld, the second weld, and the third weld are positioned by argon arc welding, and each weld is positioned symmetrically at 8 points in the circumferential direction, and the positioning fixture is removed after positioning; Step 7, load the gas cylinder assembly into the welding fixture and start laser welding. The welding parameters are as follows: laser output power: 600W, argon gas flow: 25L / min on the front, 10L / min on the back, defocus: 1mm, welding speed 13° / s, spot swing: circular, radius 0.8mm, 90Hz; Step 8: Perform visual inspection and radiographic inspection on the above four welds according to QJ 20465-2016 Level I standard; Step 9, annealing the gas cylinder to relieve stress, requiring that the tensile strength of the welded test piece in the same furnace after heat treatment is ≥895MPa, and the surface bending angle is not less than 40°; Step 10, perform a hydraulic strength test on the gas cylinder, requiring 5MPa and no leakage for 6min; Step 11, conduct an airtightness test on the gas cylinder, requiring 3.5MPa and no leakage for 6 minutes.

[0005] Preferably, the rear head and the pipe joint are of plug-in structure, and the weld thickness is 2 mm.

[0006] Preferably, the front head, cylinder and rear head are butt-jointed structures, the joint structure is a cylinder with an outer diameter of φ106, and the weld thickness is 1 mm.

[0007] The beneficial effects of the present invention are as follows: the gas cylinder material is TC4 titanium alloy, the gas cylinder structure is a rotating body, the thin-walled girth weld is 1mm thick, the welding speed is a low speed of 0.013m / s, and the laser power is a low power of less than 1000W. In terms of technical effects: the low power and low welding speed used in the present invention have a better effect on the protection of the weld, and it is completely silver-white after welding; the welding parameters used are easier to control the weld formation, and a special welding positioning fixture is used, and the weld has no dents or burn-through. By adopting this laser welding method, the ability of thin-walled titanium alloy gas cylinders to withstand high pressure can be achieved, which is safe and reliable, and the lightweight requirements of the gas cylinders are achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is a structural diagram of the titanium alloy thin-walled gas cylinder of the present invention.

[0009] Figure 2 This is a plug-in structure diagram of the rear end cap and the joint of the present invention.

[0010] Figure 3 This is a structural diagram of a positioning fixture specifically for the gas cylinder of the present invention.

[0011] Markings in the figure: 1-front head, 2-cylinder, 3-rear head, 4-first weld, 5-second weld, 6-third weld, 7-fourth weld, 8-pipe joint. DETAILED DESCRIPTION

[0012] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0013] The titanium alloy thin-walled gas cylinder is composed of 4 titanium alloy parts, namely, the front head 1, the rear head 3, the cylinder 2 (2 pieces), and the pipe joint 8 (attached Figure 1 ), the titanium alloy grade is TC4, the above 4 parts are all machined, among which the front head 1, the rear head 3, and the tube 2 are butt joint structures, the joint structure is a tube with an outer diameter of φ106, and the weld thickness is 1mm; the rear head 3 and the pipe joint 8 are plug-in structures (attached Figure 2 ), the weld thickness is 2mm; it is welded and formed in the combination of front head 1 - cylinder 2 - rear head 3 - pipe joint 8, and finally forms a titanium alloy gas cylinder. The gas cylinder is subsequently fiber wound, filled with high-pressure helium, and packaged into a lightweight high-pressure gas cylinder.

[0014] The specific steps for implementing laser welding are as follows: Step 1: Position welding the rear end cap 3 and the pipe joint 8 by argon arc welding, and position four points symmetrically in the circumferential direction.

[0015] Step 2, welding, for the fourth weld 7 (attached Figure 2 )Use laser welding. Equipment used: 6kW continuous laser welder. Welding parameters are as follows: Laser output power: 400W Argon flow rate: front 25L / min, back 10L / min Defocus Amount: 0 Welding speed 13° / s Light spot swing: circular, radius 1.0mm, 8Hz Step 3: Laser cleaning. Equipment used: 300W pulse laser cleaning machine. Cleaning parameters are as follows: Light spot swing: 8 figures Defocus: 4mm Output power: 45W Step 4: Use an alloy scraper to scrape out the original metal color of the welding end face, and wipe the weld to be welded with a dust-free cloth dipped in anhydrous ethanol.

[0016] Step 5: Design a special positioning fixture for the gas cylinder (attached Figure 3 ), use the positioning fixture to assemble the front head 1, the tube 2, and the rear head 3.

[0017] Step 6: In the clamping state, the first weld 4 to the third weld 6 (attached Figure 1 ) for positioning welding, the welding method is argon arc welding, and each weld is symmetrically positioned at 8 points around the circumference. After positioning, remove the positioning fixture.

[0018] Step 7: Load the gas cylinder assembly into the welding tool and start laser welding. The welding parameters are as follows: Laser output power: 600W Argon flow rate: front 25L / min, back 10L / min Defocus: 1mm Welding speed 13° / s Light spot swing: circular, radius 0.8mm, 90Hz Step 8: Perform visual inspection and radiographic inspection on the above four welds according to QJ 20465-2016 Level I standard.

[0019] Step 9: Anneal the gas cylinder to relieve stress. The tensile strength of the welded test piece in the same furnace after heat treatment is required to be ≥895MPa, and the surface bending angle is not less than 40°.

[0020] Step 10, conduct a hydraulic strength test on the gas cylinder, requiring 5MPa and no leakage for 6min.

[0021] Step 11, conduct an airtightness test on the gas cylinder, requiring 3.5MPa and no leakage for 6 minutes.

[0022] The gas cylinder of the present invention is made of TC4 titanium alloy, and the gas cylinder structure is a rotating body, with a 1mm thick thin-walled ring weld, a low welding speed of 0.013m / s, and a low laser power of less than 1000W. In terms of technical effect: the low power and low welding speed used in the present invention have a better effect on protecting the weld, and the weld is completely silvery white after welding; the welding parameters used are easier to control the weld formation, and a special welding positioning fixture is used, so the weld has no dents or burn-through. By adopting this laser welding method, the ability of thin-walled titanium alloy gas cylinders to withstand high pressure can be achieved, which is safe and reliable, and the lightweight requirements of the gas cylinders are achieved.

[0023] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A laser welding method for thin-walled titanium alloy gas cylinders, characterized in that: The following steps are involved: Step 1, positioning welding is performed on the rear head (3) and the pipe joint (8), the welding method is argon arc welding, and four points are positioned symmetrically in the circumferential direction; Step 2: Welding: The fourth weld (7) is welded using a 6kW continuous laser welder with the following welding parameters: Laser output power: 400W, argon gas flow: 25L / min on the front, 10L / min on the back, defocus: 0, welding speed 13° / s, spot swing: circular, radius 1.0mm, 8Hz; Step 3: Use a 300W pulse laser cleaning machine for laser cleaning. The cleaning parameters are as follows: spot swing: 8, defocus: 4mm, output power: 45W; Step 4: Use an alloy scraper to scrape out the metal color of the welding end surface, and wipe the weld to be welded with a dust-free cloth dipped in anhydrous ethanol; Step 5, assemble the front head (1), the cylinder (2), and the rear head (3) using a gas cylinder positioning fixture; Step 6, in a clamped state, performing argon arc welding on the first weld (4), the second weld (5), and the third weld (6), positioning each weld at 8 points symmetrically around the circumference, and removing the positioning fixture after positioning; Step 7, load the gas cylinder assembly into the welding fixture and start laser welding. The welding parameters are as follows: laser output power: 600W, argon gas flow: 25L / min on the front, 10L / min on the back, defocus: 1mm, welding speed 13° / s, spot swing: circular, radius 0.8mm, 90Hz; Step 8: Perform visual inspection and radiographic inspection on the above four welds according to QJ 20465-2016 Level I standard; Step 9, annealing the gas cylinder to relieve stress, requiring that the tensile strength of the welded test piece in the same furnace after heat treatment is ≥895MPa, and the surface bending angle is not less than 40°; Step 10, perform a hydraulic strength test on the gas cylinder, requiring 5MPa and no leakage for 6min; Step 11, conduct an airtightness test on the gas cylinder, requiring 3.5MPa and no leakage for 6 minutes.

2. A thin-wall titanium alloy gas cylinder laser welding method according to claim 1, characterized in that: The rear end cap (3) and the pipe joint (8) are of plug-in structure, and the weld thickness is 2 mm.

3. A laser welding method for thin-walled titanium alloy gas cylinder according to claim 1, characterized in that: The front head (1), the cylinder (2) and the rear head (3) are butt-jointed structures, the joint structure is a cylinder with an outer diameter of φ106, and the weld thickness is 1 mm.

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