WO2006081819A1

WO2006081819A1 - A device for friction stir welding and a method of welding

Info

Publication number: WO2006081819A1
Application number: PCT/DK2006/000046
Authority: WO
Inventors: Torben Lorentzen
Original assignee: Dan Stir Aps
Priority date: 2005-02-01
Filing date: 2006-01-30
Publication date: 2006-08-10

Abstract

A device for friction stir welding along a line between butt arranged elements (10, 11) having opposite surfaces, said device comprising: a main tool body (8) to be rotated about a longitudinal axis. The main tool body (8) has a first end and a second end, said first end configured for connection to a rotating member and said second end having a probe (2) for engaging said elements (10,11) and thereby providing frictional heat for plasticizing said elements (10,11) when said probe (2) is rotated. The device has a first shoulder (3) for engaging of one surface of said elements (10, 11) and a second shoulder (4) for the engaging of the opposite surface of said elements (10, 11), said sec ond shoulder being connected to the probe (2) and clamping means for mov ing said shoulders (3, 4) towards each other. The first and the second shoul ders are connected such that a torque applied to the second shoulder (4) provides axial displacement of said first shoulder (3) or said second shoulder (4).

Description

A device for friction stir welding and a method of welding.

This invention relates to a device for friction stir welding along a line between butt arranged elements, said device comprising: a main tool body to be ro- tated about a longitudinal axis, said main tool body having a first end and a second end, said first end configured for connection to a rotating member and said second end having a probe for engaging said elements and thereby providing frictional heat for plasticizing said elements when said probe is rotated and a first shoulder for the engagement of one surface of said ele- ments; a second shoulder for the engaging of the opposite surface of said elements, said second shoulder being connected to the probe and clamping means for moving said shoulders towards each other.

Originally, linear friction welding was performed in such a way that two plates which were to be joined were moved relative to each other in the area in which they were to be joined while they were pressed against each other with a predetermined adjustable force. As a result of the heat generated by the friction, the material was finally plasticized in the area of joints. Upon sufficient plasticization, the materials of the two plates intermix sufficiently so that, upon cooling, the desired weld connection between the two plates was formed.

An apparatus for friction stir welding is known from EP 0 615 480. In the apparatus described in EP 0615 480 a cylindrical, shouldered tool with a pro- filed probe harder than the material to be welded is rotated and slowly plunged into the joint line between two pieces of sheet or plate material, which are butted together. With sufficient heating a layer of plasticized material is formed around the probe generally composed of a mixture of the materials of the two elements to be joined. The plasticized material is transferred from the leading edge of the tool to the trailing edge of the tool probe and is mixed by the intimate contact of the tool shoulder and the probe profile. It leaves a solid phase bond between the two pieces. The process is regarded as a solid phase keyhole welding technique since a hole to accommodate the probe is generated, then filled during the welding sequence.

It has further proposed in EP 0615 480 that the apparatus may comprise a lower shoulder physically connected to the upper shoulder through said welding probe. To accommodate variation in materials thickness it has, moreover, proposed that the lower shoulder may be connected to the upper part of the tool body via a spline, thereby facilitating a linear axially move- ment of the lower shoulder relative to the upper shoulder.

This represents a considerable disadvantage because the severe torque and side forces on the lower shoulder and on the welding probe tend to lock the welding probe in its spline, and any linear movement is thereby inhibited, with the result that the gap between the lower and upper shoulder becomes fixed. Therefore, this welding tool is not capable of accommodating variations in materials thickness and of accommodating thermal expansions of the tool parts and of the materials being welded.

To overcome this deficiency an actuated pin was proposed in the patent US5893507, and this actuated pin was further proposed to drive a lower shoulder in the patent US6758382. Both inventions concern the mechanical driving of the lower shoulder by an actuator thereby necessitating an external unit to control the force on, and the position of the lower shoulder, such that it is kept engaged upon the lower surface of the material being welded.

It is a general object of the invention to provide a device for stir welding where the shoulders are kept engaged without the necessity for an externally controlled actuation mechanism. It is a further object of the invention to provide a stir welding device by means of which the force applied to the materials by the shoulders is generated by the rotational forces.

The object of the invention is achieved by a device for friction stir welding having first and said second shoulders being connected such that a torque applied to the second shoulder provides axial displacement of said first shoulder or said second shoulder the clamping means comprising two threaded parts: a female part being connected to the main tool body and a male part being connected to the second shoulder by the probe.

This entails a movement of both the probe and the lower shoulder towards the upper shoulder when a torque is applied to the lower shoulder.

Preferable said threaded parts having Acme thread form or square threads with parallel sides. The Acme thread form is a strong thread which allows for use in translational applications such as those involving moving heavy machine loads as found on machine tools. However, the square thread form is stronger than the Acme thread.

In an embodiment of the invention, the device having means for restriction movement of said second shoulder towards said first shoulder and said means may further allowing for an adjustable restriction of said movement.

In another embodiment of the invention, the device having means for restrict- ing the pressure applied to opposite surface of the material situated between said first and said second shoulder. The pressure applied to the opposite surfaces of the material in the area in which the welding seam is to be formed may be adjusted by a flexible member generating a movement of said second shoulder away from said first shoulder.

The invention in another aspect provides a method of friction stir welding, said method comprising the steps of: rotating the main tool body about its longitudinal axis; locating the first and second shoulder on opposite surfaces of said elements without touching the elements; touching the elements with either the probe or the second shoulder and thereby drive the shoulders into contact with the surfaces of the material to be welded and moving the device in a direction along the joint line while the butt arranged elements are held against lateral movement away from the probe.

The invention will be described in greater detail on the basis of the accompanying drawings.

fig 1 is a perspective drawing of a device for stir welding according to an em- bodiment of the invention, fig 2 is a perspective drawing illustrating a device for stir welding according to an embodiment of the invention when welding, fig 3 is a schematic cross-sectional view of a device for stir welding according to an embodiment of the invention showing the operating principle of the device and its main components, fig 4 is a schematic cross-sectional view of a device for stir welding according to and embodiment of the invention showing the operating principle of the device and its main components when welding. Fig. 1 is a perspective drawing of a device 1 for stir welding according to a embodiment of the invention. The welding device comprises: a main tool body 8 to be rotated about a longitudinal axis L, said main tool body 8 having a first end 5 and a second end 6, said first end 5 configured for connection to a rotating member and said second end 6 having a probe 2 for engaging/contacting two plate-like elements 10,11 and thereby providing frictional heat for plasticizing said elements 10,11 when said probe 2 is rotated and a first upper shoulder 3 for the engaging one surface of the elements 10, 11 ; a second lower shoulder 4 for engaging the opposite lower surface of the elements 10, 11 , said second shoulder being connected to the probe 2 and clamping means for moving said shoulders 3, 4 towards each other.

A non-consumable probe 2 of preferably steel is positioned between upper shoulder 3 and lower shoulder 4 and applied for welding the two butt ar- ranged elements 10,11. The upper shoulder of the device 1 functions like that of a regular friction stir welding shoulder rigidly connected to the main tool body 8. This shoulder may have a variety of features providing pressure, friction and materials flow such as a concave dome or a scroll feature. The two but arranged elements 10,11 are not normally urged towards each other during welding, but are simply restrained against movement away from the joint region during passage of the probe.

The welding probe 2 is preferable adapted to have a material auging effect by means of welding probe features (e.g. threads), which, under rotation, en- tails a material flow; an auging effect. The materials flow generates a reaction force directed along an axis parallel to the axis of the device. For left hand welding probe features (like a left hand thread) rotated clock-wise, the reaction force of the materials auging is directed towards the main tool body 8 requiring a counteracting force — the down force. The friction between the welding probe 2 and the semi-molten weld material surrounding the welding probe 8 provide a reaction moment opposing to the moment driving the device. As a result of the reaction moment generated by friction between the welding probe and the weld metal, the welding probe, and the attached lower shoulder of the device, will act to resist following the rotational movement of the device. At the same time, and by design of the auging features of the welding probe, the reaction force may be directed towards the main tool body 8 of the device (or the upper shoulder 3). In combination the effect of the welding process itself on the welding probe, is a reaction force opposing to the auging effect, and a reaction moment opposing the moment driving the device. Moreover; as the lower shoulder engages with the lower surface of the materials being welded, a further reaction moment opposing the moment driving the device, is generated by the friction between the lower shoulder and the lower surface of the material being welded. In the event that the lower shoulder has features enforcing a material flow, like a (already known) scroll feature, this will further ad to the reaction moment. In summary any friction between the weld material and the lower shoulder and between the weld material and the welding probe, generate a reaction moment opposing the moment driving the device while the auging effect of the welding probe generate a reaction force directed towards the main tool body 8. These three inherent forces and moments are converted into an axial movement of the welding probe by incorporation of a screw mechanism according to the invention.

Turning now to figure 2, the stir welding device 1 with probe 2, is rotated by a motor (not shown) while the welding device is moved in a direction along the joint line with the butt arranged elements 10,11 held against lateral movement away from the probe 2. The rotating welding device 1 produces sufficient friction heating to achieve a local region of plasticized material around the probe 2, while top and bottom pressure is provided by the shoulders 3, 4. Upon passage of the probe, the plasticized stirred regions (indicated by the spotted area) will immediately coalesce and solidify. On cooling, the plasti- cized material bonds the plates 10,11 together. The method generally results in a mix of the two abutting surfaces 10,11 , often at mixing temperatures below the normal melting point of the materials to be joined.

Figure 3 and 4 shows an embodiment of a stir welding device according to an embodiment of the invention. The stir welding device comprises: a main tool body 8, an upper shoulder 3, a lower shoulder 4 and a welding probe 2. The main tool body 8 of the welding device 1 is provided with a hollow sec- tion containing a female part 20 of a screw mechanism while a male part 21 of the screw mechanism 20, 21 is rigidly connected to the probe 2 by a shaft 23 being slideable and rotateable arranged in a bearing in the upper shoulder 3. The shaft 23 may advantageously be releasably connected to the male part 21 by a pin 30 threadably engaging a mating apertured portion in the male part 21.

The lower shoulder 4 is attached to the probe 2 by a shaft 23a which is fastened by a lock nut 26. By coordinating the direction and pitch of these treads 20, 21 along with the direction of rotation of the main tool body 8, the lower shoulder 4 will be driven against the upper shoulder 3 by male part 21 in figure 3 when the lower shoulder and probe under use engages material being disposed between the shoulders 3, 4.

The pressure applied on the opposite surfaces of the material disposed be- tween the upper shoulder 3 and lower shoulder 4 in the area in which the welding seam is to be formed is generated by the screw mechanism 20, 21 and is in the shown embodiment only limited by a (stop) surface 28 provided proximate to a end surface 27 on the male part of the screw mechanism 21. Advantageously, the stir welding devices is adapted for the insertion of means (like e.g. washers) between surface 27 and surface 28 thereby facilitating adjustment of the distance between upper 3 and lower shoulder 4 (when engaged).

The pressure applied to the opposite surfaces of the material in the area in which the welding seam is to be formed may be adjusted by flexible means as e.g. Belleville spring washer (s) being disposed between surface 27 and surface 28. The provision of Belleville springs (or other spring mechanisms) between surface 27 and 28 also facilitates the ejection of shoulder 4 after use.

To facilitate maintenance of the stir welding device, the upper shoulder 3 is releasable connected to the main tool body 8. Advantageously, the screw mechanism 20,21 and main tool body are releasably connected but prevented from mutual displacement by e.g a locking screw 24 preferably engaging a recess 25 in the female part of the screw mechanism. However, any conventional connection means could be used e.g. a female 20 part comprising a multangular or quadrangular outside being received in a corre- sponding shaped opening in the main tool body thereby preventing mutual rotation between the female part 20 and the main tool body 8.

By modifying the screw mechanism 20,21 parameters, for instance the pitch, the length of the thread, the thread type or the ratio between these parame- ters is it possible to design a screw mechanism 20,21 suitable for particular tasks and the locking screw 24 makes it possible to select and mount the screw mechanism most suited for the actual welding task. As an alternative to the locking screw 24 being received in a recess 25, the locking against mutual axially displacement of the main tool body 8 and the female part 20 could be made as e.g. snap engaging means comprising a pin which penetrates and fits openings in both the main tool body 8 and the female part 20. However the locking of the female part 20 in the main tool body 8 can be obtained in many other ways.

When a friction stir welding device according to the invention is used, there will initially (before contact with material 10,11) be no frictional forces on the welding probe and therefore no force or moment (torque) to drive the lower shoulder 3 towards the upper shoulder 4 and the lower shoulder will remain freely spinning underneath the upper shoulder. The welding process is preferable initiated by the rotating welding probe gently touching the weld material (ie. at the edge of a pilot hole), thereby providing friction between the ma- terial and the welding probe which causes the internal screw mechanism 20,21 to drive the lower shoulder into contact with the lower surface of the material to be welded. As soon as the welding probe meets friction, a process is initiated where further friction is made available as the translational movement of the device along the weld line moves the welding probe further into the weld material. Still further friction arises as the welding probe is driven so far into the main tool body that the lower shoulder 4 engages with the lower surface of the material to be welded and the clamping forces between the shoulders will increase almost momentary until prevented by physical limits - as stop or spring as described above - or limited by the torque capacity of the host machine.

Although the invention has been discussed in relation to a friction stir device having a screw mechanism 20,21 situated in the main tool body 8 of the device, the device in another embodiment may instead have the screw mecha- nism situated inside the lower shoulder. Accordingly, the clamping force be- tween the shoulders in this embodiment is generated by relative rotation between the lower shoulder 4 and the probe 2. Therefore it is not (in this embodiment) possible to follow the above described welding method involving the initial step of touching the weld material with the probe because this would not cause the necessary mutual rotation between the members in the screw mechanism. Welding with a friction stir device having a screw mechanism situated in the lower shoulder therefore has to be initiated with the upper side of the lower shoulder gently touching the underside of the material to be welded thereby providing a torque pulling the shoulders 3, 4 towards each other.

The device for friction stir welding according to the invention is especially suitable for e.g. repair operations because not only are the forces required for the engagement of the element to be welded generated internally in the device such that no support structure is needed but the device is also self- contained ( the engagement forces are generated within the device by the rotation) and therefore independent of any external units to control or move the shoulders. As a result, a welding seem e.g. following a crack can be made (virtual any places) without the need for any support or any external unit to control or supply the clamping force between the shoulders.

Claims

1. A device for friction stir welding along a line between butt arranged elements (10, 11) having opposite surfaces, said device comprising: - a main tool body (8) to be rotated about a longitudinal axis, said main tool body (8) having a first end and a second end, said first end configured for connection to a rotating member and said second end having a probe (2) for engaging said elements (10,11 ) and thereby providing frictional heat for plasticizing said elements (10,11) when said probe (2) is rotated and a first shoulder (3) for engaging of one surface of said elements (10, 11 );

- a second shoulder (4) for the engaging of the opposite surface of said elements (10, 11), said second shoulder being connected to the probe (2) and - clamping means for moving said shoulders (3, 4) towards each other characterized by said first and said second shoulders being connected such that a torque applied to the second shoulder (4) provides axial displacement of said first shoulder (3) or said second shoulder (4) said clamping means comprising two threaded parts: a female part (20) being connected to the main tool body (8) and a male part (21) being connected to the second shoulder (4) by the probe (2).

2. A device for friction stir welding according to claim 1 characterized by said threaded parts having Acme thread form.

3. A device for friction stir welding according to claim 1 or 2 characterized by having means (27, 28) for restricting movement of said second shoulder (4) towards said first shoulder (3).

4. A device for friction stir welding according to any of the claims 1-3 characterized by a flexible member generating a movement of said second shoulder away from said first shoulder.

5. A device for friction stir welding according to any of the claims 1-4 characterized by said means allowing for an adjustable restriction of said movement.

6. A method for welding butt arranged elements (10, 11) with a device for friction stir welding according to any of the preceding claims, said method comprising the steps of:

— rotating the main tool body (8) about its longitudinal axis (L);

— locating the first and second shoulder on opposite surfaces of said elements (10,11 ) without touching the elements (10,11 ); — touching the elements (10,11) with either the probe (2) or the second shoulder (4) and thereby drive the shoulders into contact with the surfaces of the material to be welded and

— moving the device in a direction along the joint line while the butt arranged elements (10,11 ) are held against lateral movement away from the probe (2).