WO2010041945A2

WO2010041945A2 - Friction stir welding with heated supply material

Info

Publication number: WO2010041945A2
Application number: PCT/NL2009/050612
Authority: WO
Inventors: Teunis Cornelis Bor; Laurent Louis Warnet
Original assignee: Stichting Materials Innovation Institute (M2I)
Priority date: 2008-10-10
Filing date: 2009-10-09
Publication date: 2010-04-15
Also published as: WO2010041945A3

Abstract

Device and method for friction stir welding. Therein, a rotating shoulder generates heat on the interface of two workpieces to be joined together, material being supplied to the connecting region thus obtained. The invention proposes supplying this material under elevated temperature, thus allowing the generated amount of frictional heat to be limited. This allows the extent of the heat affected zone by the heating to remain limited and the quality of the connection to be improved. According to a particular variant of the invention, melted material is placed under pressure and extruded outward, through a hollow pin at the centre of the shoulder, into the melting bath.

Description

Friction stir welding with heated supply material

The present invention relates to a device for friction stir welding according to the preamble of Claim 1.

A device of this type is known from EP 1 510 280 Al, in which a friction shoulder is provided with a central passage through which a consumable pin can be moved. After contact with the surface to be machined, this pin is melted. Pressure may be applied to the pin from the back.

US 2003/0042292 discloses a friction stir welding device which operates with a wire supply. A device for preheating the supply material is present at a certain distance from the actual friction stir welding device, that is to say the construction with the friction shoulder and rotation mechanism.

Friction stir welding is possible both with the supply of material and without the supply of material. The former case gives rise to the problem that the rotating construction consisting of the shoulder and hollow supply pin has to deliver material which generally originates from a stationary source. In this way, it is necessary to apply in some manner a rotational movement to the material or to uncouple the rotational movement of the rotating shoulder with the hollow pin from the displacement of the supply material. Friction stir welding with the supply of material is used for example for attaching protective layers. The surrounding material may or may not be welded using the same method.

Furthermore, not only is it necessary to heat the end edges of two parts to be joined together, or another position where the melting must be carried out, to a sufficiently high temperature to obtain melting, it is also necessary to heat the supply material. In the prior art, the heating of the supply material to the desired deformability is also carried out using frictional heat. The additional frictional heat that is necessary for this purpose means that the shoulder in its entirety must be brought to a higher temperature, necessitating either a larger area of friction with the workpiece or more intensive friction. In both cases, the area of the workpiece parts that is heated or the degree of heating of the material of the workpiece is increased.

In certain applications, this may be undesirable in view of the loss of desired mechanical properties.

The object of the present invention is to provide a device allowing the structure of the material that is deposited by friction stir welding to be improved.

This object is achieved with a device having the features of Claim 1.

The fact that the holder is both provided with the pressure application means and comprises a heating vessel allows material to be added with sufficient force to the friction stir welding at elevated temperature. This is not possible in the construction as known from US 2003/0042292 because in that case the temperature can be elevated only to a limited degree because otherwise it is not possible to exert sufficient force on the wire used there in order to allow the wire to participate in the friction stir welding process. In particular as a result of allowing, in accordance with the invention, the material to soften, "upstream" of the application of pressure, as a result of the elevating of the temperature, such transportation of material can be carried out at elevated temperature. This makes it possible to improve the thermal conditions, as the added material issues from the tool, in such a way as to produce a more fine structure of the deposited material, allowing the mechanical properties thereof to be significantly improved.

The rotatable attaching of the holder, which is provided with pressure application means for pressing out the content thereof, which is attached in a rotating manner, allows a compact, reliable construction to be obtained.

If a considerable pressure has to be applied for the pressing-out of material, that is to say, a large amount of work has to be performed, this means that the material will become heated as a result of the pressing-out treatment. Furthermore, such a high pressure of this type is necessary to allow material to be brought outward into/onto the workpiece. After all, the tool will be pressed at high pressure into/onto the workpiece and this pressure must be overcome by the added material.

According to the present invention, the supply material is preheated before it is brought into/onto the workpiece. This preheating is carried out by a separate heater, i.e. the heat necessary for preheating the supply material does not (in part) originate from the heat generated by friction. As a result, the heat generated by friction may be used exclusively for locally bringing the workpiece to the correct operating temperature. Furthermore, if sufficient heat is present in the supply material, for example in the soft and/or kneadable state, heat can be supplied to the weld even using this external heating. However, it is also possible to supply the supply material in a harder state. However, as a result of the elevated temperature thereof, the supply material will have properties making it suitable for extrusion from the holder. These measures allow to reduce the heat affected zone; this promotes the later mechanical properties in proximity to the weld. This applies in particular to the variant wherein heat generated by friction can be limited as a result of the heat of the supply material. According to a further variant of the present invention, it is possible to supply the supply material without special preheating. This may for example be important if it is necessary to operate at higher production speed. In this case, the tool will be rotated at a higher rotational speed, thus producing more factional heat and, if the workpiece material is comparatively soft (low melting point), it is not necessary to separately heat the added material. It is possible to introduce the supply material into the operating region through one or more openings in the shoulder that may or may not coincide with the axis of rotation.

According to an advantageous embodiment of the invention, the shoulder is provided with a pin which is attached at the centre thereof, protrudes therefrom, is hollow in its embodiment and through which supply material is (also) passed.

Of course, it is also possible to provide the shoulder with a number of passages which may be formed, for example, in a circle, supply material being passed in each case via each of the passages. It is also possible to provide in the shoulder a single passage which is not formed at the centre thereof. According to an advantageous embodiment, a combination of elevated temperature and elevated pressure is used to bring the supply material into the operating region. More particularly, the supply material is moved out of the cavity in the shoulder or pin with hydraulic pressure. According to a particular embodiment of the invention, the temperature and pressure are selected in such a way that material is extruded through the hollow pin or cavity in the shoulder. In this case, according to an advantageous embodiment, the holder, which is located above said supply passage in the hollow pin, is embodied as a melting vessel and a pressure is exerted (hydraulically) on the melting bath from above. The storage material that has to be supplied originates from this vessel, so that complicated constructions, in which either the supply material must be made to rotate or the rotating movement of the shoulder must be separated from that of the supply material, may be dispensed with. Of course, it is also possible to press in any other conceivable manner the supply material from the cavity in either the shoulder or the pin. Mechanically functioning systems with (screw) jacks and the like may be used for this purpose. Furthermore, air or another gas may be used instead of a hydraulic fluid.

If the pressure has to be applied hydraulically, it is easily possible to proceed from a stationary piston/cylinder combination and, for example, to isolate, as far as rotation is concerned, the piston from the device described hereinbefore via a bearing, which is axially loaded, pressure being applied to the supply material.

The supply material may be heated in any conceivable manner. The simplest heater is an electrical resistance heater which rotates with the device. However, it is also possible to externally provide heating in a stationary manner. This is possible in a very simple manner by employing a heated gas stream or by using a stationary induction coil. Other designs using the rotation of the holder containing the supply material may also be applied.

The invention also relates to the processing by friction stir welding of two parts, including the generating, during the common boundary of said parts, of frictional heat by a shoulder, which rotates with respect to said two parts, at the adding of supply material through a passage which is formed in said shoulder and extends up to the processing region which is generated by said frictional heat, the supply material being preheated, using a separate heating, up to a temperature of at least 300 ⁰C during the moving through said passage prior to the entering at the boundary, hi this case, said machining of said parts may include both the connecting thereof and the attaching of a surface layer consisting of that supply material (a combination of both).

According to a further embodiment of the present invention, the invention relates to a device for friction stir welding comprising a rotatable tool with a friction shoulder, which comprises an internal channel for supplying a welding material, wherein welding material supply means are present, the opening of that internal channel being spaced, at the workpiece side, from the axis of rotation of that tool, the longitudinal axis of the mouth of that opening forming, at the workpiece side, an angle with the plane defined by the axis of rotation and a line perpendicular to said axis of rotation.

More particularly, this angle is approximately 90°. Furthermore, the mouth of the channel forms with the exit plane preferably an angle of from 0-45° and in particular 0- 20°. That is to say, if the supply material is attached to the workpiece at a distance from the axis of rotation of the friction shoulder, the opening of the internal channel describes a circular path and the axis of said opening lies in the extension of said circular path, that is to say, it is, according to a particular embodiment of the invention, tangential thereto.

By rotating, in accordance with a particular embodiment of the invention, the friction shoulder in the appropriate direction, that is to say, in a direction wherein the more upstream part of the internal channel is positioned more upstream with respect to the axis of rotation during rotation, a tensile force or under pressure will be exerted on the deposited material, drawing or sucking the material out of the opening of the internal channel. This is in contrast to constructions according to the prior art wherein, although the opening of the internal channel forms an angle with the axis of rotation, the internal channel is positioned in a plane defined by the axis of rotation and a line perpendicular to said axis of rotation.

The device described hereinbefore, with particular orientation of the internal channel, may be used both in combination with that which has been described hereinbefore, that is to say the subject-matter according to Claim 1, and independently thereof. In the latter case, no external pressure and/or temperature elevation will be used during the application of said external pressure.

The invention will be described in greater detail hereinafter based on an exemplary embodiment illustrated in the drawings, in which:

Fig. 1 is a schematic view of the device according to the present invention;

Fig. 2 is a partially exploded view of a detail of the tool according to the present invention; and

Fig. 3a-c are detailed views of a variant of the rotating shoulder.

In Fig. 1, reference numeral 1 denotes the device according to the present invention. The device consists of a rotating tool 20 which is attached above a workpiece carrier 2 on which two sheet material parts to be joined together, such as sheet material parts made of an aluminium alloy, are located. The tool 20 has a shoulder 4 (see Fig. 2) which is embodied to enter into contact with the upper surface of the sheet material parts during rotation thereof in the direction of arrow 19. This will generate frictional heat to an extent such that the end edges of the workpiece parts 3 become forgeable. A hollow pin 5, the cavity of which, which is embodied as an extrusion nozzle, is denoted by reference numeral 6, is present at the centre of the holder.

A holder or vessel 7, which delimits a chamber 9 for receiving supply material therein, is located above the shoulder 4. A resistance heater 8 is present and a piston 10 is located on the upper side of the chamber 9. This piston 10 is connected to a piston rod 12 which is connected to the outgoing piston (not indicated in greater detail) of a hydraulic piston/cylinder combination 16 via a bearing 13. A pressure, which in the drawings is a downward pressure, may be generated with lines 17, 18. Attached around the piston rod 12 is a sleeve 11 which is provided with a gear wheel 14 which is in engagement with a gear wheel of a motor 15, allowing the sleeve to be rotated in the direction of arrow 19. The tool 20 can be moved, in a manner not illustrated in greater detail, toward and away from the workpiece in the direction of arrow 21.

The construction described hereinbefore operates as follows. For friction stir welding, the chamber 9 is filled with supply material. Subsequently, the chamber 9 is closed by attaching the piston 10 and the heating element 8 is switched on. In the closed environment, the supply material in the chamber 9 is heated to at least 300 ⁰C and preferably to melting. However, it is also possible for the supply material to be in a plastic condition such that the material passes outward through the extrusion nozzle 5 as a result of the application of pressure on the piston 10. If the desired temperature has been reached, the tool 20 is brought onto the workpiece and the motor 15 is switched on and heat is generated at the site of the parts to be connected. If the desired operating level has been reached, material 6 is extruded from the hollow pin 5 for increasing the pressure via activation of lines 17, 18. As a result of the supplying of material 6 which has already been heated, less heat has to be generated by friction during the supplying of material. As a result, the welding process can be speeded up, the size of the heat affected zone being reduced and the structure of the weld may be influenced in a positive manner. Furthermore, concentrating the supply of material in the space above the hollow pin eliminates the need for the separate external supply of material; this promotes the simplicity and the operational safety of the device. The supply material may both form part of the material of the connection of the two parts to be joined together and be attached as a separate layer to parts (coatings) which may or may not have to be joined together.

Fig. 3a-c are schematic, partially exploded views of a modified embodiment of the friction shoulder. The friction shoulder is denoted in its entirety by reference numeral 36. The friction shoulder may or may not, in the foregoing manner, be provided with a central pin. The connection to the upper plate 37 is indicated highly schematically.

This variant differs from the embodiment described hereinbefore in that the channel of the supply wire is attached not centrically with respect to the direction of rotation 35 but more to the circumference of the friction shoulder. Furthermore, the passage 38 is formed at an inclination with respect to the plane perpendicular to the axis of rotation 40. As a result of this positioning, pull is exerted from the surface to be machined onto the supply wire which moves through the channel 38; this further promotes transportation.

The mechanism which has been described with reference to Fig. 3a-c may be used in combination with the device described hereinbefore with reference to Fig. 1-2. However, it is also possible to apply this variant in any other device wherein material is supplied in a different manner, that is to say without the pressure application means and/or heating.

After reading the foregoing description, a person skilled in the art will immediately think of variants which are under the scope of the appended claims and are obvious in view of the foregoing. It is also possible to embody the displacement mechanism of the piston in a mechanical rather than a hydraulic manner, hi this case, a variant is conceivable with a screw construction or with a rack-and-pinion coupling, supporting/engagement taking place on the surroundings.

Claims

1. Device (1) for friction stir welding, comprising a workpiece carrier (2), a tool (20) which can be moved toward the workpiece carrier, said tool comprising, at the side facing the workpiece carrier, a sleeve (7) with a shoulder (4) functioning as a friction face, the sleeve (7) and said workpiece carrier (2) being rotatable with respect to each other, said shoulder being embodied so as to be hollow (6) for transportation of supply material originating from a store in the tool at the side remote from the workpiece side, pressure application means (16) being present in order to drive material in the cavity of said shoulder outward by pressure, said store comprising a rotatable holder (7), which is connected to the tool, for supply material provided by said pressure application means (16), characterized in that said holder comprises a heating vessel.

2. Device according to Claim 1, wherein said shoulder comprises a pin (5) protruding therefrom, said pin being embodied for the transportation of said material.

3. Device according to one of the preceding claims, wherein said pressure application means comprise hydraulic pressure application means.

4. Device according to one of the preceding claims, wherein said pressure application means (10) act on the interior of the holder (7).

5. Device according to one of the preceding claims, wherein said heater is stationarily provided directly adjoining the rotatable holder.

6. Device according to one of the preceding claims, wherein said hollow pin (5) is embodied as an extrusion nozzle.

7. Device according to one of the preceding claims, wherein a heater (8) is present to heat the content of said holder to a temperature of above 300 ⁰C and wherein the outlet of said holder is connected to the cavity in said pin.

8. Device (1) for friction stir welding comprising a rotatable tool (4) with a friction shoulder (6), which comprises an internal channel (8, 38) for supplying a welding material (9), wherein welding material supply means (18) are present, the opening of said internal channel (38) being spaced, at the workpiece side, from the axis of rotation (40) of said tool, the longitudinal axis of the opening of said channel (38) forming, at the workpiece side, an angle with the plane defined by the axis of rotation and a line perpendicular to said axis of rotation.

9. Method for the processing by friction stir welding of two parts (3), including the generating, at the common boundary of said parts, of frictional heat by a shoulder (4), which rotates with respect to said two parts, during the pressurized adding of supply material through a passage (5) which is provided in said shoulder and extends up to the processing region which is generated by said frictional heat, characterized in that the supply material is preheated, using a separate heater, up to a temperature of at least 300 ⁰C during the moving through said passage prior to the entering at said boundary.

10. Method according to Claim 9, wherein the processing of said two parts includes the connecting thereof.

11. Method according to Claim 9 or 10, wherein the processing of said two parts includes the provision thereto of a lining.

12. Method according to one of the preceding Claims 9-11, wherein that supply material is driven under pressure through said hollow pin.

13. Method according to one of Claims 9-12, wherein that supply material is melted in a vessel above said hollow pin and an excess pressure prevails in that vessel.

14. Method according to one of Claims 9-13, wherein that vessel rotates with said passage for supply material.

15. Method according to one of Claims 9-14, wherein the heating energy is supplied from a source which is stationary with respect to the vessel.