CN113245703A

CN113245703A - Laser welding process for improving sheet titanium alloy tailor-welding assembly margin

Info

Publication number: CN113245703A
Application number: CN202110610923.9A
Authority: CN
Inventors: 陈纪城; 杜心伟; 孔斌; 陈小梅; 魏艳红; 刘学军
Original assignee: Nanjing University of Aeronautics and Astronautics
Current assignee: Nanjing University of Aeronautics and Astronautics
Priority date: 2021-06-01
Filing date: 2021-06-01
Publication date: 2021-08-13
Anticipated expiration: 2041-06-01
Also published as: CN113245703B

Abstract

The invention discloses a laser welding process for improving the tailor welding assembly margin of a thin titanium alloy, and belongs to the technical field of high-energy beam welding. Aiming at the problems of welding deviation, welding leakage and the like caused by unstable groove gaps due to factors such as machining burrs, assembly errors, thermal deformation and the like in the sheet laser tailor-welding process, the process adopts low-frequency pulse laser as a welding heat source and is matched with a larger focal spot size, so that the sufficient gap filling metal amount is obtained, the welding spot cooling rate is improved, the wire-filling-free laser welding of 1.2 mm-thick sheet titanium alloy under the condition of 0.2-0.3mm tailor-welding assembly gaps is realized, the continuity and the uniformity of welding seams are good, no obvious welding defects exist, and the effective assembly gap reaches 25% of the sheet thickness. The process can obviously reduce the sensitivity of the laser welding gap of the sheet metal and improve the forming quality of the welding seam. The invention has important significance for promoting the application and development of the laser welding process in the field of sheet tailor-welding.

Description

Laser welding process for improving sheet titanium alloy tailor-welding assembly margin

Technical Field

The invention provides a laser welding process for improving the assembling margin of sheet titanium alloy splice welding, belongs to the technical field of high-energy beam welding, and is suitable for the splice welding of sheet titanium alloy under the condition of plane assembling clearance or unstable clearance.

Background

The titanium alloy has high strength-to-weight ratio and good corrosion resistance and creep resistance, and is widely applied to the industrial fields of aerospace, nuclear energy, transportation, biomedicine and the like. The laser deep fusion welding has the advantages of small heat input, small welding deformation, narrow heat affected zone, refined grain structure and the like, and is particularly suitable for the tailor welding of the thin-plate titanium alloy component.

However, in the actual welding production, the welding assembly gap of the titanium alloy sheet is unstable and the local gap is enlarged due to the machining burr, the tooling error and the welding thermal deformation, and the problems of welding deviation, welding leakage and the like are easily caused by the adoption of the conventional laser welding process and parameters, so that the welding quality is seriously weakened, and the reject ratio of the product is greatly improved.

Aiming at the problems, at present, a laser wire filling welding process is mainly adopted at home and abroad, and a liquid bridge is formed by utilizing the gap filling effect of welding wire molten drops, so that better welding seam forming quality and mechanical property are obtained, and the gap sensitivity is effectively reduced. However, in the production occasions with strict requirements on the weight reduction of the components and the welding process, the weight increase of the components and the machining after welding caused by wire filling are not allowed; in addition, the laser wire filling process additionally increases equipment investment and improves production cost.

At present, the problem of the assembly margin of the sheet titanium alloy under the pure laser welding process condition is not well solved, and the development of the laser tailor-welding technology is restricted to a certain extent.

Disclosure of Invention

In view of the limitation of the background technology, the invention provides a laser welding process for improving the welding assembly margin of the thin titanium alloy, which can greatly reduce the problems of welding deviation and welding leakage of the thin titanium alloy caused by the welding gap under the condition of no wire filling, obtain effective, continuous and uniform weld joint forming, and has the advantages of high reliability, good flexibility, low cost and the like.

The technical scheme of the invention is as follows:

a laser welding process for improving the splicing welding assembly margin of a thin titanium alloy plate adopts a Ti6Al4V titanium alloy thin plate with the thickness of 1.2mm as a welding parent metal; adopting an I-shaped butt joint form, wherein the assembly gap of the tailor-welded joint is 0.2-0.3 mm; the method adopts low-frequency pulse laser as a welding heat source, the laser power is 2.2-2.4kW, the welding speed is 1.8m/min, the pulse frequency is 20Hz, the duty ratio is 0.6, the defocusing amount is 0, the diameter of a focus spot is 700 mu m, the shielding gas is pure Ar, the surface flow is 30L/min, and the back flow is 15L/min.

Furthermore, the sheet titanium alloy assembly gap is set by a feeler gauge so as to simulate the gap change caused by the factors of workpiece machining burr, assembly error, thermal deformation and the like in the actual welding process.

Further, the adopted laser welding equipment is a Trumpf Trudisc 4001 disc laser, the maximum output power is 4kW, the wavelength is 1030nm, the maximum modulation frequency is 5010Hz, and the beam quality is 4mm multiplied by mard.

Further, the diameter of the focal spot is directly adjusted by adjusting a built-in optical path lens of the laser welding torch. For a laser without the function, the spot diameter of the surface of the workpiece can be increased by changing the defocusing amount.

Further, the spot diameter needs to be enlarged while the laser power needs to be adjusted appropriately to ensure sufficient laser power density.

And further, after welding is finished, carrying out sample preparation and shooting on the weld macroscopic forming and the cross section metallographic morphology.

The invention has the beneficial effects that: firstly, the larger laser spot can compensate the heat input loss caused by the assembly clearance, and enough metal melting amount is ensured to form a liquid bridge in the welding process. Secondly, the cooling rate of the molten pool is obviously improved by the pulse mode laser, and the phenomenon that a large-area liquid bridge is greatly shrunk to form discontinuous Button holes in the slow cooling process is prevented. Therefore, the process can effectively reduce the laser tailor-welding gap sensitivity of the titanium alloy sheet and obviously improve the weld forming quality.

Drawings

Fig. 1 is a schematic laser welding of a thin titanium alloy plate.

Fig. 2 a pulse laser waveform.

FIG. 3 example 1-2 weld surface and backside macroscopical topography

FIG. 4 metallographic morphology of cross section of weld in examples 1-2

Detailed Description

The present invention is further illustrated by the following specific examples.

Example 1

Adopting a 1.2mm Ti6A14V titanium alloy thin plate as a welding parent metal, processing the specification of a sample to 100mm multiplied by 50mm by linear cutting, wherein the groove is I-shaped, and the joint is in a planar butt joint mode; and cleaning the workpiece before welding by adopting alcohol, and setting the assembly gap to be 0.2mm by means of a clearance gauge in the tooling process.

The welding adopts a Trumpf Trudisc 4001 disc laser, the laser power is 2.2kW, the welding speed is 1.8m/min, the pulse frequency is 20Hz, the duty ratio is 0.6, the defocusing amount is 0, the diameter of a focus spot is 700 mu m, and the pulse waveform is the default waveform of the laser, as shown in figure 2; the protective gas is pure Ar, the surface flow is 30L/min, and the back flow is 15L/min.

Shooting the formation of the surface and the root of the welding seam after welding; and preparing a weld metallographic specimen through the processes of wire cutting, inlaying, grinding, polishing, corroding and the like, and shooting the metallographic appearance of the cross section.

Example 2

Adopting a 1.2mm Ti6A14V titanium alloy thin plate as a welding parent metal, processing the specification of a sample to 100mm multiplied by 50mm by linear cutting, wherein the groove is I-shaped, and the joint is in a planar butt joint mode; and cleaning the workpiece before welding by adopting alcohol, and setting the assembly gap to be 0.3mm by means of a clearance gauge in the tooling process.

The welding adopts a Trumpf Trudisc 4001 disc laser, the laser power is 2.4kW, the welding speed is 1.8m/min, the pulse frequency is 20Hz, the duty ratio is 0.6, the defocusing amount is 0, the diameter of a focus spot is 700 mu m, and the pulse waveform is the default waveform of the laser, as shown in figure 2; the protective gas is pure Ar, the surface flow is 30L/min, and the back flow is 15L/min.

The surface and back surface morphologies of the welded joints obtained in examples 1-2 are shown in FIG. 3, and the cross-sectional metallographic morphology is shown in FIG. 4. It can be seen that under the condition of a butt joint gap of 0.2mm, the surfaces of welding seams are high in continuity and uniformity, the back surfaces are completely melted through, the fusion between adjacent welding toes is good, and phenomena such as welding deviation, welding leakage, button holes and splashing do not occur; from the cross section appearance, a small amount of recesses appear on the surface and the root of the welding seam, and the weld surface fusion width is slightly larger than the root fusion width as a result of liquid metal gap filling, and no obvious internal defects such as pores, cracks, unfused fusion and the like are observed. When the butt joint clearance is increased to 0.3mm, the appearance and defect control of the welding seam are still maintained at a high level.

The analysis of the results of the embodiment shows that the laser welding process and parameters based on the large-spot pulse mode can solve the problem of sensitivity of the assembly gap of the laser tailor-welding of the titanium alloy sheet, improve the assembly margin and simultaneously obtain good weld forming quality, and the ratio of the effective assembly gap to the sheet thickness reaches 25%. The invention provides an important technical reference for promoting the development of a laser welding process and promoting the wide application of laser welding in the field of sheet tailor-welding, and has potential economic and social benefits.

The foregoing is only a few embodiments of the present invention, which is not intended to be limiting in any way. Any simple modification, equivalent replacement, and improvement made to the above embodiments by those skilled in the art without departing from the technical scope of the present invention still fall within the protection scope of the claims of the present invention.

Claims

1. A laser welding process for improving the assembling margin of the titanium alloy tailor-welding of a thin plate is characterized in that: the welding parent metal is a Ti6Al4V titanium alloy thin plate with the thickness of 1.2mm, an I-shaped butt joint mode is adopted, and the tailor-welding assembly gap is 0.2-0.3 mm; the method adopts large-spot low-frequency pulse laser as a welding heat source, the laser power is 2.2-2.4kW, the welding speed is 1.8m/min, the pulse frequency is 20Hz, the duty ratio is 0.6, the defocusing amount is 0, the diameter of a focus spot is 700 mu m, the shielding gas is pure Ar, the surface flow is 30L/min, and the back flow is 15L/min.

2. The laser welding process for improving the tailor welding assembly margin of the thin titanium alloy plate according to claim 1, wherein: the pulse laser waveform is the default waveform of the Trumpf Trudisc 4001 disc laser, and the size of a focal spot is adjusted and amplified by adjusting a light path lens built in a laser welding torch.