RU2126738C1 - Method of friction welding with mixing and permanent probe for use in friction welding - Google Patents

Abstract

FIELD: mechanical engineering; cold welding of structures with continuous longitudinal welds. SUBSTANCE: method of friction welding with mixing is based on increased flow of plasticized material in horizontal and vertical directions relative to adjoining assembly parts. Pressure is applied to forming plasticized material in direction perpendicular to surfaces of parts to be connected with simultaneous provision of material flow along probe pin in vertical direction. plasticized material hardens behind the probe. Permanent probe has concave lower part with interchangeable pin. Pin has thread-shaped outer surface. In preferred version it has two or more blades projecting across. EFFECT: provision of homogeneous welds without cavities and other defects in welds of different types. 7 cl, 9 dwg

Description

 The invention relates to a method of friction welding of connected (metal) elements or parts, and, in particular, to the so-called friction stir welding based on mutual polishing motion or movement between a probe of harder material and the parts to be joined. The present invention is also directed to an improved tool used in a friction welding process.

 Friction welding is based on the principle of "rubbing" or "polishing" the joined products in such a way as to generate a sufficient amount of heat, thus creating a plasticized or softened state of adjacent surfaces, which is well known and widely used in practice for several decades. Friction heat is generated only by two connected elements. However, the weld resulting from this suffers from all the disadvantages inherent in the process used. The main disadvantage, which significantly limits the applicability of friction welding, is that at least one of the elements to be welded must be axisymmetric. Therefore, this process is not applicable, for example, for structures requiring continuous longitudinal welds.

 An improved version of such welding, the so-called friction stir welding, is known from WO 93/10935. In the welding process, use a probe or probe (third body) of material harder than the workpiece. Friction welding is based on the mutual cyclic movement between the probe and the workpieces, causing the probe and the workpieces to create a plasticized or softened zone in the area of the workpiece due to the generated heat of friction, the cessation of mutual cyclic motion and the possibility of hardening of the softened plastic material. Thus, no heat is generated due to the mutual movement between the workpieces to be joined. The method is illustrated by several examples of blanks from various materials (plastics, metals), applications (crack repair, welding, sealing, joints) and the options for the probe used.

 None of the above methods and devices, when used to join stamped profiles in structures for critical use, can satisfy either the requirements for highly integrated welds that are free from voids and shells, the proper metallurgical connection of structural parts, or the need to provide weld overlaps.

 In order to ensure proper solidification of the weld metal, the lower or bottom part of the probe (nozzle) must be maintained in close contact with the surface of the parts to be joined during the entire welding operation. If the probe nozzle during this forward movement even temporarily “rises” from the surface, a small amount of plasticized material to be welded will be pushed out behind the probe, which will cause the appearance of shells and voids in the weld, since there is no material needed to fill the empty space after the material is pushed out .

 In addition, there is another limitation associated with the use of a “smooth” welding probe, known from the prior art, namely, to ensure sufficient frictional heating of the material (the contact time of the probe and the connected elements) and to ensure an adequate flow of plasticized material being welded, low welding speeds are required .

 Therefore, it is an object of the present invention to provide an improved friction stir welding method that guarantees highly integrated weld seams that are shell-free and have a smooth, even surface.

 Another objective of the present invention is the improvement of the now known method of friction welding with stirring the joint to obtain overlap welds and configuration of the connection of three or more components.

 Another objective of the present invention is the creation of a new type of probe, providing uniform homogeneous welds having a zone of reduced exposure to heat.

 The above and other objectives in accordance with the invention are achieved by a method of friction welding with stirring the joint and device (probe), as defined by the claims below.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of preferred embodiments with reference to the accompanying drawings, FIG. 1-5, where:
FIG. 1 is a schematic perspective view of a welding device / process used in the present invention;
FIG. 2 is an enlarged cross-sectional view (partial) of the arrangement of two probe elements;
FIG. 3 schematically depicts the principal features of a new friction stir welding;
FIG. 4 graphically shows the optimum relationship between welding and rotation speed and pressure applied to the probe, and
FIG. 5a - e are fragmentary schematic perspective views of various types of welds obtained.

 According to the drawings, in particular FIG. 1, the non-expendable probe 1 includes a rotating cylindrical body 2 having an upper part 22 connected to an energy source, for example, an engine (not shown in the drawing), and a lower part 23 having a separate pin 24, and is used to connect (welding) two elements (metal plates) 3, 4, located end to end. By introducing the probe 1 between the elements 3 and 4 under pressure and rotating it to ensure adequate frictional heating, a butt weld is obtained essentially during an intermediate movement along the ends of the elements.

 The special configuration of the two component parts of the probe 1, the lower part (23) (nozzle) of the probe and the outer shape (configuration) of the used finger 24 according to the invention are more clearly visible in FIG. 2, where the lower part 23 of the rotating cylindrical body 2 has a concave surface, while the outer surface of the finger 24 has alternately spaced protrusions and recesses along its longitudinal axis.

 Even if a conventional screw thread is used on the outer surface of the finger, the quality of the weld is improved, however, in the preferred embodiment of the probe finger, the surface configuration of the finger, as shown in FIG. 2 is preferably made with two or more separate blades 25 located vertically and protruding transversely from the central part of the finger.

 The microstructure of the welds provided by the new type of finger has strong bonds made up of mutually connected plasticized segments of connected elements with minimal material turbulence.

 The composite design of the used probe 1, containing a separate finger of the probe, in comparison with the monolithic design of the previously known probes, creates several advantages. Firstly, the tool (probe) is adapted to regulate the depth of finger insertion, thereby giving flexibility to the process. Secondly, the finger part can be easily interchanged for various tool blocks (nozzle / holder) and, therefore, adaptable for welding elements having different wall thicknesses.

New features of the new tool and an improved method of friction stir welding can be easily understood from the schematic sketch of the probe and the welding operating parameters shown in FIG. 3, where W denotes the thickness of the parts to be welded, ω denotes the welding speed, K is the radius of curvature of the concave nozzle of the probe, C is the downward force (pressure applied to the probe, r _s is the radius of the probe nozzle, and t represents the "undercut" of the nozzle in the welded the material.

 The concave bottom surface 23 of the probe 1 has a slight inclination relative to the normal to the surfaces to be welded and, in combination with the above-described screw configuration of the finger 24 (not shown), ensures that the plasticized softened material moves both vertically and in the transverse direction in the weld zone and, as a result, converts metal between different levels throughout the weld profile. The concave shape of the probe nozzle provides some asymmetric compression on the surface of the elements, leading to a vertical flow / transition of the material. This, in conjunction with the horizontal movement of the material due to the external configuration of the finger, results in high-quality, shell-free welds.

в Н/мм², приложенным к щупу, и фактической скоростью сварки ω (мм/мин) при различных скоростях вращения, гарантирующая прочный сварной шов, свободный от раковин и имеющий гладкую поверхность. Реальные значения оптимальных давления/скорости сварки зависят от нескольких факторов, т. е. используемого материала соединяемых элементов (Al-сплавы), геометрии насадки и т.п.In FIG. 4 schematically shows the optimal relationship between downward pressure

in N / mm ² applied to the probe and the actual welding speed ω (mm / min) at various rotational speeds, guaranteeing a durable weld, free from sinks and having a smooth surface. The actual values of the optimum pressure / welding speed depend on several factors, i.e., the material used for the connected elements (Al alloys), the geometry of the nozzle, etc.

 Several welding tests carried out with probes of various diameters have shown that reducing the probe tip diameter relative to the actual wall thickness of the elements being welded has a beneficial effect on the quality of joints / welds in addition to the possibility of increasing the welding speed.

 Therefore, reducing the probe tip diameter from 20 mm to 15 mm and then to 10 mm, used before joining flat stampings of alloy 6082.50 with a thickness of 3 mm, allows to increase the welding speed from 0.3 m / min to 0.8 m / min, providing high-quality, pore-free welds having a reduced HRT (heat exposure zone). This is the total result of reduced heat input and its focusing in the direction of the vicinity of the formed weld, which allows to increase the welding speed and reduce the downward force applied to the probe, which results in the deformation of freely welded structures.

Материал щупа более твердый чем материал обрабатываемых заготовок/соединяемых элементов. Обычно при сварке алюминиевых (сплавов) деталей или элементов материал должен иметь хорошую прочность при повышенных температурах, например, такой, как штамповая сталь, быстрорежущая инструментальная сталь или керметные материалы.The optimal relationship between the probe tip radius (r _s ) and the wall thickness of the elements to be welded W is expressed by a simple formula

The probe material is harder than the material of the workpieces / joining elements. Typically, when welding aluminum (alloys) of parts or elements, the material should have good strength at elevated temperatures, such as forged steel, high speed tool steel or cermet materials.

 In FIG. 5a - e are schematic fragmentary perspective views of various types of balls obtained by the method and probe according to the invention, where in FIG. 5a shows a butt weld; FIG. 5b shows a T-shaped connection of two elements, in FIG. 5c shows a lap weld; FIG. 5 shows another embodiment of a T-shaped connection of three elements, and finally in FIG. 5e shows the receipt of an angular welded joint of two elements located in planes perpendicular to each other.

 Thus, the use of a new improved tool design according to the present invention allows to increase the welding speed, while ensuring sufficient generation of frictional heat. This effect is achieved by increasing the contact / heating time per unit volume of the material being welded and closer localization of the generated heat along the welding line. In addition, more pressing forces (pressure) are applied to the material leaving the welding probe. The optimal combination of the above effects leads to high-quality welds both in terms of metallurgical and mechanical properties due to a homogeneous, homogenized weld that does not have porosity over the entire cross section of the weld.

Claims (7)

 1. A method of friction stir welding, in particular, for joining stamped assembly profiles, in which the elements to be welded are installed along the line of their joining, welding is performed by rotating the probe with a finger made of a material harder than the material of the elements to be welded, which generates frictional heat and provides the formation of a plasticized zone in the material of adjacent elements, characterized in that the outer surface of the finger of the probe is performed with a given configuration, providing the intensified flow of plasticized material in the horizontal and vertical direction by applying pressure to it, directed perpendicularly to the connected surfaces of the elements while ensuring the flow of plasticized material along the finger of the probe in the vertical direction and the possibility of solidification of the material behind the probe, while the resulting weld is homogenized.  2. The method according to claim 1, characterized in that the lower surface of the probe is meshed with the adjacent surfaces of the elements to be connected with a slight deviation from the normal to the surfaces to be welded.  3. The method according to claim 1 or 2, characterized in that they weld two or more elements to obtain a T-shaped weld.  4. The method according to p. 1 or 2, characterized in that the welding of two elements to obtain a lap joint.  5. The method according to p. 1 or 2, characterized in that they weld two elements located at any angle to each other to obtain an angular weld.  6. Non-consumable probe for welding friction with stirring, containing a cylindrical body, the upper part of which is connected to an energy source to ensure its rotation, and a finger is fixed on the lower end, characterized in that the lower end is made with a concave surface, and the finger is made with a thread-like configuration its outer surface and is installed with the possibility of replacement.  7. The probe according to claim 6, characterized in that at least a pair of blades are made on the finger, transversely protruding from its central part and placed perpendicular to the outer surface of the finger.

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