GB2606627A

GB2606627A - Friction stir welding tool insert

Info

Publication number: GB2606627A
Application number: GB2204254.3A
Authority: GB
Inventors: Ghosh Santonu; Åke Andersin Stig
Original assignee: Element Six UK Ltd
Current assignee: Element Six UK Ltd
Priority date: 2021-03-26
Filing date: 2022-03-25
Publication date: 2022-11-16
Also published as: WO2022200604A1; GB202204254D0; GB202104264D0

Abstract

A PCBN friction stir welding tool insert has a shoulder having concentric grooves or a spiral. The depth of the shoulder grooves/spiral; varies along the radial distance between the central stirring pin and the peripheral edge of the shoulder surface; and may be greater or smaller towards the centre of the tool insert. An integrally formed FSW stirring pin 14, shoulder 16 and body 18 may be machined from a single block of polycrystalline cubic boron nitride. The pin 14 may have an inscribed scroll (24, fig 2). The shoulder 16 may be generally planar and extend at an obtuse angle. The spiral or groove may be a recess with an arcuate lateral cross section; and may have a depth which changes gradually or incrementally. The shoulder may have an arithmetic spiral, nautilus spiral, or have a logarithmic profile in plan view.

Description

FRICTION STIR WELDING TOOL INSERT

FIELD OF THE INVENTION

This disclosure relates to a friction stir welding (FSW) tool insert. In particular, it relates to a FSW tool insert for friction stir welding high temperature ferrous alloys and other high temperature alloys. More particularly, it relates to a FSW tool assembly in which the tool insert comprises polycrystalline cubic boron nitride (PCBN).

BACKGROUND

FSW is a technique whereby a rotating tool is brought into forcible contact with two adjacent workpieces to be joined and the rotation of the tool creates frictional and viscous heating of the workpieces Extensive deformation as mixing occurs along a plastic zone Upon cooling of the plastic zone, the workpieces are joined along a welding joint. Since the workpiece remains in the solid phase, this process is technically a forging process rather than a welding process, none the less by convention, it is referred to as welding or friction stir welding and that convention is followed here.

In the case of FSW in low temperature metals, the whole tool/tool holder can be a single piece of shaped tool steel, in which case it is often referred to as a 'probe'. In the case here where the tool is for welding higher temperature alloys such as steel, the tool is often in two or more parts, with an end element that is in direct contact with the material being welded, often referred to as a 'puck' or tool insert', and the remainder of the tool being the 'tool holder' which holds the puck securely and which fits into the FSW machine, so that the tool puck and tool holder together make up the 'tool' or 'tool assembly'. The tool puck is typically shaped to form a shoulder and a stirring pin, often with a reverse spiral cut into the surface so that during rotation it pulls metal towards the pin and pushes this down into the hole being formed by the pin.

In general, FSW operations comprise a number of steps, for example: a) an insertion step (also known as the plunge step), from the point when the tool comes into contact with the workpieces to the point where the pin is fully embedded up to the shoulder in the heated and softened workpieces, b) a tool traverse, when the tool moves laterally along the line in between the workp eces to be joined, and c) an extraction step, when the tool is lifted or traversed out of the workpieces.

The tool traverse, which is the stage primarily forming the weld, is usually performed under constant conditions, typically these conditions are rotational speed, conditions of the plunge, speed of traverse etc. F SW tool inserts must be capable of withstanding high axial forces required as part of the F SW process. There are many tool insert geometries available. However, they do not automatically transfer to materials such as PCBN without issue. It has been demonstrated that PCBN based tool inserts are capable of withstanding the harsh FSW operating environment, where temperatures reach in excess of 1000°C. Also, tool pucks made from PCBN are relatively cost effective and highly durable. Unfortunately, the inventors have found that PCBN tool inserts wear at different rates across the shoulder. This reduces tool life and introduces inconsistency, thereby rendering such tools obsolete for welding steel or superalloys.

It is therefore an aim of the invention to provide a PCBN based tool insert that addresses the above-mentioned problem.

SUMMARY OF THE INVENTION

In accordance with the invention, there is provided a friction stir welding tool insert comprising polycrystalline cubic boron nitride and having, a longitudinal axis of rotation about which it rotates during use, the tool insert further comprising a stirring pin and a coaxial shoulder region, wherein the shoulder region comprises a shoulder surface for engaging with the workpiece during use, the shoulder surface comprising a spiral or concentric grooves with a depth, D, wherein the depth, D, varies with the radial distance between the stirring pin and a peripheral edge of the shoulder surface.

Optional and/or preferable features of the invention are provided in claims 2 to 13

BRIEF DESCIPTION OF THE DRAWINGS

The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a tool insert in accordance with the invention; Figure 2 is a side view of the tool insert of Figure 1; Figure 3 is a plan view of the tool insert of Figure 1; Figure 4 is cross-sectional view through the line Z-Z from Figure 3; and Figure 5 is an enlarged view of the encircled detail from Figure 3 The Figures are not drawn to scale.

Throughout the description, similar parts have been assigned the same reference numerals, and a detailed description is omitted for brevity.

DETAILED DESC TIPTON

Referring to the Figures, a tool insert in accordance with the invention is indicated generally at 10. The tool insert 10 has a longitudinal axis of rotation 12 about which it rotates during use in the friction stir welding process. Note that this axis of rotation is not an axis of rotational symmetry due to an asymmetric thread pattern machined into the tool insert 10.

The tool insert 10 comprises a stirring pin 14, a shoulder region 16 and a body portion 18, all in axial alignment with each other, with the shoulder region 16 being axially intermediate the stirring pin 14 and the body portion 18. The stirring pin 14, shoulder region 16 and body portion 18 are all integrally formed with each other such that the tool insert 10 is one-piece. The tool insert 10 is machined out of a single PCBN block after the block has been sintered in a HPHT press. The shoulder region 16 extends axially and merges into the body portion 18, which is adapted to couple with a tool holder that is connectable with a FSW machine.

The stirring pin 14 has a conical profile, tapering outwardly from rounded apex 20 towards circular base 22 The stirring pin 14 comprises an inscribed spiral 24 running from the apex 20 downwards towards the shoulder region 16. The spiral 24 has an arcuate working surface 26. Notably, there is no (vertical) overhang on the spiral 24 to facilitate laser shaping from the direction of the apex 20.

The shoulder region 16 comprises a shoulder surface 28 that extends from the stirring pin base 22. The shoulder surface 28 extends generally perpendicularly to the longitudinal axis of rotation 12. The shoulder surface 28 comprises a spiral 30 (also known as 'scroll') for engaging 10 with the workpiece during F SW.

The spiral 30 is essential to the invention. The benefit of the spiral 30 is that it balances the wear of the shoulder region 16 across the shoulder surface 28. In other words, the wear experienced by the tool insert 10 during FSW is more evenly distributed across the shoulder region 16 thanks to the special configuration of spiral 30 The spiral 30 has a depth, D, that varies radially outwards from the core of the tool insert 10 towards a peripheral edge 32 of the shoulder region 16. In this embodiment, the shoulder surface 28 is planar, and it extends at an obtuse angle with respect to the longitudinal axis of rotation 12. Preferably, this angle is between 92 and 100 degrees from the vertical. In such an embodiment, the depth, D is measured perpendicularly to the shoulder surface 28. The depth, D, gradually decreases with the distance away from the stirring pin 14. This configuration is beneficial because the greatest amount of wear is experienced closest the stirring pin 14; the lowest amount of wear is radially further out. At a maximum, the location of which is indicated generally at X which is proximate the stirring pin 14, the depth is around 0.5 mm. At a minimum, the location of which is indicated generally at Y which is remote from the stirring pin 14, the depth is around 0.2 mm. The depth changes gradually between the locations of the maximum and minimum depths.

In another embodiment (not shown), the depth, D, gradually increases with the distance away from the stirring pin 14. During initial trials, the inventors have found that with this configuration, the tool produces longer lengths of good quality weld since the tool life is enhanced. At a maximum depth, the location of which would be generally at Yin Figure 5 and remote from the stirring pin 14, the depth is around 0.5 mm. At a minimum, the location of which is indicated generally at X which is proximate to the stirring pin 14, the depth is around 0.2 mm As shown in Figure 3, the spiral 30 is an arithmetic type of spiral, although other types are envisaged within the scope of the invention. For example, the spiral may have a logarithmic profile in plan view.

In another embodiment, the shoulder surface is generally planar, and it extends perpendicularly to the longitudinal axis of rotation 12. In such an embodiment, the depth, D, of the spiral 30 is measured in a plane that is parallel with the longitudinal axis of rotation 12.

In another embodiment (not shown), grooves provided as concentric rings are used in place of the spiral 30. In such an embodiment, the depth changes incrementally from ring to ring, from the maximum point to the minimum point While this invention has been particularly shown and described with reference to embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as defined by the appended claims.

Claims

CLAIMS1 A friction stir welding tool insert comprising polycrystalline cubic boron nitride and having a longitudinal axis of rotation about which it rotates during use, the tool insert further comprising a stirring pin and a coaxial shoulder region, wherein the shoulder region comprises a shoulder surface for engaging with the workpiece during use, the shoulder surface comprising a spiral or concentric grooves with a depth, D, wherein the depth, D, varies with the radial distance between the stirring pin and a peripheral edge of the shoulder surface.
2. The tool insert as claimed in claim I, wherein the shoulder surface is generally planar.
3. The tool insert as claimed in claim 2, wherein the shoulder surface extends radially perpendicularly to the longitudinal axis of rotation.
4. The tool insert as claimed in claim 2, wherein the shoulder surface extends radially at an obtuse angle with respect to the longitudinal axis of rotation.
5. The tool insert as claimed in any preceding claim, wherein the depth, D, decreases towards the peripheral edge of the shoulder surface.
6. The tool insert as claimed in any of claims I to 4, wherein the depth, D, increases towards the peripheral edge of the shoulder surface.
7. The tool insert as claimed in any preceding claim, wherein the depth, D, varies between 0.2 and 0.5 mm.
8. The tool insert as claimed in any preceding claim, wherein the spiral or groove is a recess with an arcuate lateral cross-section.
9. The tool insert as claimed in any preceding claim, wherein the depth, D, changes gradually.
10. The tool insert as claimed in any preceding claim, wherein the spiral is an arithmetic spiral as viewed from above.
11. The tool insert as claimed in any of claims 1 to 10, wherein the spiral is a nautilus spiral as viewed from above
12. The tool insert as claimed in any of claims Ito 8, comprising a plurality of concentric annular grooves
13. The tool insert as claimed in claim 12, wherein the depth changes incrementally with adjacent grooves.