WO1999008830A1

WO1999008830A1 - Method of laser welding of thin sheet metallic components

Info

Publication number: WO1999008830A1
Application number: PCT/RU1997/000264
Authority: WO
Inventors: Leonid Efimovich Fedorov
Original assignee: Zakrytoe Aktsionernoe Obschestvo 'firma Novye Sistemnye Tekhnologii'
Priority date: 1997-08-18
Filing date: 1997-08-18
Publication date: 1999-02-25
Also published as: AU5140998A

Abstract

A method of welding thin sheet metallic components such that a focused laser beam is used as a heat source with power sufficient to melt welded metallic components and directed to a weld pool to which a cooled inert shielding gas is supplied while the parts of welded components adjacent to the weld pool are cooled to the temperature ranging from approximately - 100 °C to approximately - 200 °C. In accordance with the invention a flow of liquid nitrogen is directed to the weld pool as an alloying material and the inert shielding gas is cooled to the temperature in the range from approximately - 170 °C to - 200 °C.

Description

METHOD OF LASER WELDING OF THIN SHEET METALLIC COMPONENTS

DESCRIPTION

This invention relates to the field of obtaining permanent joints of machine elements and structures by laser welding methods and particularly it relates to the method of laser welding of sheet metallic components with a thickness ranging from 0.02mm to 5.0mm.

At the present time there is an acute problem of obtaining quality permanent welding joints (without cracking and recrystallization regions) of thin and ultrathin metallic components made of heterogeneous difficult- to- weld materials such as, for example, stainless steel and heat-resistant steel or carbon steel and alloyed steel. Other combinations of heterogeneous difficult- to- weld materials are also possible.

Many investigations in the field of laser welding have been carried out to solve this problem, for example, well known US patent 4,990,741 defining a thin sheet component welding technique to be accomplished with the help of a concentrated laser beam having sufficient power to melt welded metallic components and directed into a weld pool around which a low turbulent flow of an inert shielding gas is supplied. In this case a laser beam in the weld region is focussed such that the beam energy is linearly distributed along the weld. Such laser beam energy distribution and supply of an inert shielding gas into the weld pool allowed to achieve maximum efficiency of the laser beam energy to protect melted metal from interaction with the atmospheric air thereby improving the weld quality. However, this method does not eliminate formation of a noticeable dendritic structure of the weld as well as formation of a recrystallization region of the metal to be welded. It is conditioned by delivery of a considerable amount of heat within a short period of time which is the cause of formation of both a recrystallization region and a dendritic structure.

Patent No. 2047446 of the Russian Federation is also known. It provides a welding technique of thin sheet metallic components in which a focussed laser beam is used as a heat source having sufficient power to melt welded metallic components and directed into a weld pool to which a cooled inert gas is supplied, in this case argon, while the parts of welded components adjacent to the weld pool are cooled to the temperature ranging from approximately -100° C to approximately - 200 C. A characteristic feature of the method described in Patent No. 2047446 of the Russian Federation is cooling of the components to be welded up to the temperature in the range o o from about - 100 C to about - 200 C. Cooling causes sharp heat removal from the weld pool which contributes to the formation of a fine-grain high-strength structure of the weld, prevents development of a noticeable dendritic structure and a recrysrallization region. It tend to decrease probability of cracking. Furthermore, it provides a possibility to weld thin sheet components (thickness of welded components is in the range from 0.02 mm to 5.0 mm).

However, application of this method has not been successful in welding components made of heterogeneous difficult-to-weld metals. Among difficult-to-weld combinations of heterogeneous metals are, for example, carbon and alloyed steel, stainless austenitic and heat resistant steel and other combinations well known to specialists in this technical field.

Besides, implementation of this technique has revealed that probability of cracking in the weld cannot be avoided completely with this method.

The basic objective of this invention is to create a method of welding metallic components under which by alloying the weld to increase its strength, corrosion resistance, to prevent cracking and formation of a recrystallization region, thereby to improve quality of the weld and the welded joint as a whole.

This objective is solved such that under the method of welding thin sheet metallic components wherein a focussed laser beam is used as a heat source having sufficient power to melt welded metallic components and directed into the weld pool to where an inert shielding gas is supplied while the parts of the welded components adjacent to the

O O weld pool are cooled to the temperature ranging from about - 100 C to - 200 C, according to this invention a flow of liquid nitrogen is injected into the weld pool as an alloying material and the inert shielding gas is cooled to the temperature in the range from o o approximately - 170 C to approximately - 200 C. By supplying a flow of liquid nitrogen to the weld pool and as a result of its dissosiation into the melt of the weld pool there occurs formation of microparticles of metal nitrides, i.e. alloying of the weld metal with nitrogen. In case of extremely rapid and deep cooling of the melt which is ensured by preliminary cooling of the parts of the welded components nitride microparticles generate multitude of additional crystallization centres to result in formation of quazi-amorphous metal structure of nitride-clustered type. By changing the amount of nitrides it is possible to control properties of the weld metal and to weld components made of difficult- to- -weld metal combinations by a high quality weld. Practical investigations have proved that an attempt to alloy a weld with liquid nitrogen without an inert shielding gas results in formation of a weld with a porous structure which considerably lowers its quality. An inert shielding gas helps to avoid the above-mentioned phenomenon and therefore its presence in the process is imperative.

It would be advisable to use argon as an inert shielding gas to be cooled with liquid nitrogen prior to its supply to the weld pool.

Presence of argon prevents most effectively formation of a porous structure on the weld surface and its cooling with nitrogen around the weld pool by an optimal way helps to reach and hold during welding the temperature close to the boiling point of liquid nitrogen (-196 C), i.e. the temperature ranging from - 170 C to - 200 C.

It is not less advisable to add acetone to a flow of liquid nitrogen in the ratio by volume of acetone to liquid nitrogen from 1 : 100 to 1 :10.

It allows to obtain a quazi-amorphous nitride-diamond clustered structure which additionally extends possibilities to control the weld properties.

It would be wise to add alcohol to a flow of liquid nitrogen in the ratio by volume of alcohol to liquid nitrogen from 1 :100 to 1 :10.

It allows to obtain a quazi-amorphous nitride-cement clustered structure in the weld metal which also extends possibilities to control the weld properties. When welding components made of non-ferrous metals such as brass, bronze, copper, etc. it would be advisable to add welding flux to acetone or alcohol in the ratio by weight of flux to acetone or alcohol from approximately 1:10 to approximately 1:30. Borax or boric acid may be used as the above-mentioned fluxes.

Other objectives and advantages of this invention will be enumerated in more detail in further description of the examples of this invention implementation.

EXAMPLE No.1

To implement this method a solid state laser with an active element of alumo-yttrium garnet with the wave length of 1.64 nm and power of 500W-700W was used. Two metallic plates 0.5 mm thick were welded with its help. The first component was made of heat resistant steel XH65MBTK) with a composition by weight of 0.03% of C, 0.15% of Si, 1% of Mn, 14.5-16.5% of Cr, 3-4.5 of W, 15-17% of Mo, 1% Ti, 1% Al and the balance Ni. The second component was made of austenitic stainless steel 08X18H10T with a composition by weight of 0.08% of C, 18% of Cr, 1% of Ti, 10% of Ni and the balance Fe. In the course of welding the laser power was 550W. A flow of liquid nitrogen was preliminary directed on the parts of the components to be welded to cool them. In this

0 particular case the welded components were cooled to the temperature of - 190 C with the consumption of liquid nitrogen equal to 100 g/min. When liquid nitrogen stopped to boil on the surface of the welded components a dosed flow of argon at the rate of 2 1/min was directed to the weld region. After that a focussed laser beam was guided to the weld region and it melted the edges of the welded components creating a weld pool. Liquid nitrogen holding the temperature of the welded components at the temperature level close to the liquid nitrogen boiling point simulteneously dissosiating into the melt of the weld pool forms microparticles of metal nitrides, i.e. there happens alloying of the metal weld with nitrogen. It is clear for a specialist with an average skills in this technical field that this method may be used for both spot and linear welding. For linear welding of the above components welding speed may be up to 40 mm/sec. As it is seen from Fig. 1 showing a microstructure of the weld (cross section) which joins a plate of heat resistant steel and an angle plate made of austenitic stainless steel, the weld has a fine-crystalline

SUBSTITUTE SHEET ^RULE 26) high strength structure with high kenetics. It is seen from the picture that the weld microstructure is enriched to the maximum with metal nitrides, has no recrystallization regions and cracking. In other words the quality of the weld and the joint itself is high.

In addition to that in the course of welding acetone is added to the flow of liquid nitrogen with the acetone consumption of 6 g/min. As a result of acetone dissosiation ultradispersed diamond particles are formed in the weld and these particles , being a part of the melt structure, create a structure of higher hardness during the process of cooling. A specialist with an average skills in this technical field understands that it is possible to change the weld metal hardness, i.e. the quality of the weld joint by changing the relationship between the amoun of acetone and the amount of liquid nitrogen.

EXAMPLE No. 2

To implement this method a solid body laser with an active element of alumo-yttrium garnet with a wave length of 1.64 nra and power of 300W - 500W was used. Two metallic plates 0.19 mm thick were welded with its help. The first and second components were made of low carbon food tin plate widely used for manufacture of cans. In the course of welding the laser power was 400W. Prior to that a flow of liquid nitrogen was directed on the parts of components to be welded to preliminary cool them, in this particular case of implementation of the invention the welded components were cooled to - 170 C while the consumption of liquid nitrogen was 50 g/min. At the same time a dosed flow of argon with the consumption of 1 1/min was directed to the surface of the welded components in the weld region. After that a laser beam was focussed in the weld region. It melted the edges of the welded components creating a weld pool. Liquid nitrogen holding the temperature of the welded components at the temperature level close to the liquid nitrogen boiling point simulteneously dissosiating into the melt of the weld pool forms metal nitrides on the weld surface, i.e. alloying the weld metal with nitrogen raising its corrosion resistance. In case of a linear weldidng of the above components welding speed may be 50 mm/sec. As it is seen from Fig. 2 showing the microstructure of the weld face which joins the plates made of low carbon food tin plate, the weld has an enriched structure of higher strength and corrosion resistance to be especially important for domestic articles.

EXAMPLE No. 3

To implement this method a solid body laser with an active element made of alumo- yttrium garnet with the wave length of 1.64 nm and power of 500W - 700W was used. Two metallic plates 0.5 mm thick were welded with this laser. The first component was made of austenitic steel 12X18H10T with the composition by weight of 0.03% of C, 0.15% of Si, 1% of Mn, 14.5-16.5% of Cr, 3-4.5 of W, 15-17% of Mo, 1% Ti, 1% Al, 6.5% of Ni and the balance Fe The second component was made of cermet material, including by volume of near 15% of A1₂0₃ and of near 35 % of ZrO₂. In the course of welding the laser power was 650W. A flow of liquid nitrogen was supplied on the parts of the components to be welded to preliminary cool them. In this particular case of the invention implementation the welded components were cooled to the temperature - 180 C. Consumption of liquid nitrogen was 200 g/min. After liquid nitrogen stopped to boil on the surface of the welded components a dosed flow of argon with the consumption of 2 1/min was guided to the weld region. It was followed by focussing a laser beam in the weld region to melt the edges of the components to be welded thereby creating a weld pool. Liquid nitrogen holding the temperature of the welded components at the temperature level close to the liquid nitrogen boiling point simulteneously dissosiating into the melt of the weld pool forms microparticles of metal nitrides, i.e. alloying of the weld metal occurs. It is clear for a specialist with an average skills in this technical field that this method can be applied to both spot and linear welding. In case of linear welding of the above components the welding speed may be up to 30 mm sec. As it is seen from Fig. 3 showing the microstructure of the weld which joins a plug of austenitic steel with a pipe of cermet the weld has a high-strength structure. It is seen from the picture that the weld microstructure is enriched with metal nitrides, there is no recrystallization region and cracking. In other words the quality of the weld and the joint itself is high.

In addition to that in the course of welding alcohol is added to the flow of liquid nitrogen at the rate of 15 g/min. As a result of dissosiation of alcohol monatomic carbon is formed in the weld and both, being part of the melt structure, form metal cementites when cooled enhancing the weld hardness. It is clear for a specialist with an average skills in this technical field that by changing the ratio between alcohol and liquid nitrogen it is possible to change hardness of the weld metal, thereby the quality of the weld.

When welding components of non-ferrous metals such as brass, bronze, etc. by the method of this invention difficulties arise in fusing together the edges of welded components due to the presence of oxide films on their surfaces. To avoid this difficulty alcohol or acetone containing solution or suspension of weld flux are supplied to the weld pool. Examples of laser welding of non-ferrous metals according to this invention are given in the Table below.

Table

Although the description above contains many specificities, these should be not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention.

Thus the scope of the invention should be determined by the appended claims and their equivalents, rather than by the examples given.

Claims

CLAIMS:

1. A method of welding thin sheet metallic components such that a focussed laser beam is used as a heat source with power sufficient to melt welded metallic components and directed to a weld pool to which a cooled inert shielding gas is supplied while the parts of welded components adjacent to the weld pool are cooled to the temperature ranging from near -100 C to near -200 C wherein a flow of liquid nitrogen is directed to the weld pool as an alloying material and the inert shielding gas is cooled to the o temperature in the range from near -170 C to near -200 C.

2. The method of welding metallic components of claim 1, wherein argon is used as an inert shielding gas to be cooled with liquid nitrogen prior to its supply to a weld pool.

3. The method of welding metallic components of claim 1, wherein acetone is added to a flow of liquid nitrogen in the ratio by volume of acetone to liquid nitrogen from 1:100 to 1:10.

4. The method of welding metallic components of claim 1, wherein alcohol is added to a flow of liquid nitrogen in the ratio by volume of alcohol to liquid nitrogen from 1 : 100 to 1 :10.

5. The method of welding metallic components of claim 3, wherein welding flux is added to acetone in the ratio by weight of flux to acetone from 1 : 10 to 1 :30.

6. The method of welding metallic components of claim 4 wherein flux is added to alcohol in the ratio by weight of flux to alcohol from 1:10 to 1:30.

7. A method of welding thin sheet components with thickness from 0.02 mm to 1.0 mm, the first component is of heat resistant steel and the second one is of austenitic stainless steel wherein a focussed laser beam is used as a heat source with power in the range from about 500W to about 700W and directed to a weld pool to which cooled argon is supplied with the temperature approximately equal to the liquid nitrogen boiling point while the parts of welded components adjacent to the weld p ol are cooled to the temperature as approximately great as the boiling point of liquid nitrogen and a flow of liquid nitrogen is directed to the weld pool as an alloying material.

8. A method of welding thin sheet components made of low carbon food tin plate with thickness from 0.01 mm to 0.2 mm wherein a focussed laser beam is used as a heat source having power in the range from about 300W to about 500W and directed to a weld pool to which cooled argon is supplied with the temperature approximately equal to the liquid nitrogen boiling point while the parts of welded components adjacent to the weld pool are cooled to the temperature as approximately great as the boiling point of liquid nitrogen and a flow of liquid nitrogen is directed to the weld pool as an alloying material.

9. A method of welding thin sheet components with thickness from 0.02 mm to 1.0 mm, the first component is of austenitic steel and the second one is of cermet material wherein a focused laser beam is used as a heat source having power in the range from about 500W to about 700 W and directed to a weld pool to which cooled argon is supplied with the temperature approximately equal to the liquid nitrogen boiling point while the parts of welded components adjacent to the weld pool are cooled to the temperature as approximately great as the boiling point of liquid nitrogen and a flow of liquid nitrogen is directed to the weld pool as an alloying material.