Friction stir welding tool assembly

Abstract

The present disclosure relates to a friction stir welding (FSW) tool assembly including a retention mechanism that mechanically engages both the tool insert and the tool holder to prevent separation of the two. The retention mechanism includes an annular locking collar disposed about the tool insert and / or the tool holder and matingly coupled to the tool insert and / or the tool holder.

Description

[Technical field]

[0001] The present disclosure relates to a friction stir welding (FSW) tool assembly including a tool insert and a tool holder. Specifically, the present disclosure relates to an FSW tool assembly for friction stir welding high temperature ferrous alloys and other high temperature alloys. More specifically, the present disclosure relates to an FSW tool assembly in which the tool insert is made of polycrystalline cubic boron nitride (PCBN) or tungsten-rhenium (W-Re). [Background technology]

[0002] FSW is a technique in which a rotating tool is brought into forceful contact with two adjacent workpieces to be joined, and the rotation of the tool creates friction and viscous heating of the workpieces. Extensive deformation occurs along the plastic zone as they intermix. Upon cooling of the plastic zone, the workpieces are joined along the weld joint. Since the workpieces remain in a solid phase, the process is technically a forging process rather than a welding process, but it is nevertheless conventionally referred to as welding or friction stir welding, and such convention will be followed herein.

[0003] For FSW of low temperature metals, the entire tool / tool ​​holder may be a single piece made of formed tool steel, in which case the single piece is often called a "probe." When the tool is for welding or joining high temperature alloys such as steel, the tool is made up of two or more pieces, with an end element in direct contact with the material being joined, often called a "puck" or "tool insert," and the remainder of the tool is the "tool holder" that holds the puck securely and fits into the FSW machine, so that together the tool puck and tool holder make up the "tool" or "tool assembly." The tool puck is typically shaped to form a shoulder and stir pin, and often has a reverse spiral cut in the surface so that during rotation, the cut draws the metal towards the pin and pushes it down into the hole formed by the pin.

[0004] Generally, an FSW operation involves a number of steps, such as: a) a penetration or insertion step (also called the plunge step) from the point when the tool contacts the workpiece to the point when the pin is fully embedded up to its shoulder in the heated and softened workpiece; b) tool traverse, when the tool moves laterally in a straight line between the workpieces to be joined; and c) A removal step where the tool is lifted or traversed away from the workpiece.

[0005] Tool traverse, which is primarily the step of forming the weld, is usually performed under constant conditions; typically, these conditions are rotation speed, plunge conditions, traverse speed, and the like.

[0006] PCBN-based tools can withstand the harsh FSW environment where temperatures reach over 1100°C. Tool packs made of PCBN are relatively cost-effective and durable. However, one drawback of the PCBN pack manufacturing process is the need for bulk PCBN pieces from which the packs are made. The monolithic PCBN blocks need to be large, 50 mm in diameter and 50 mm high, with the aim of making packs with 12 mm pin heights that can be welded and formed to 12 mm plate thicknesses. Monolithic PCBN blocks (and thus PCBN packs) larger than this are not currently feasible due to limitations of the high pressure, high temperature (HPHT) presses used during the PCBN sintering process. Presses larger than this can compromise material homogeneity. In short, the size of PCBN packs that can be practically achieved at present is limited to those that can be welded and fabricated to plates up to 12 mm thick.

[0007] There is a strong need to develop PCBN tools and associated tool holders capable of welding and fabricating steel plate materials with thicknesses greater than 12 mm.

[0008] A significant challenge faced with large PCBN tools is retaining the tool in the tool holder, especially during the entry and traversing phases. In some cases separation occurs and is believed to be caused by a mismatch in thermal conductivity between the PCBN tool insert and the tool holder, which is typically made of steel. Due to the extreme conditions of the FSW process, traditional methods and means, such as screws, are ineffective. This problem reduces the performance of the PCBN tool insert and limits the weld length that could otherwise potentially be obtained. Summary of the Invention [Problem to be solved by the invention]

[0009] There is a need for an FSW tool assembly that welds high temperature alloys that retain the tool insert within the tool holder during extended use. [Means for solving the problem]

[0010] According to the present invention there is provided a friction stir welding (FSW) tool assembly having a longitudinal axis of rotation about which it rotates during use, the tool assembly including a tool insert and a tool holder which coaxially retains the tool insert, the tool assembly further including a retention mechanism which mechanically engages both the tool insert and the tool holder to prevent relative separation, the retention mechanism including an annular locking collar disposed about the tool insert and / or the tool holder and which couples in mating engagement with the tool insert and / or the tool holder.

[0011] Preferred and / or optional features of the invention are set out in the dependent claims.

[0012] The present invention will now be particularly described, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a perspective view of a first embodiment of a tool assembly in an assembled state. [Diagram 2] FIG. 2 is a side view of the tool assembly of FIG. 1. [Diagram 3] FIG. 2 is a plan view of the tool assembly of FIG. 1. [Figure 4] FIG. 4 is a cross-sectional view of the tool assembly of FIG. 3 taken along line S-S. [Diagram 5] FIG. 2 is a perspective view of the tool holder of FIG. 1; [Figure 6] FIG. 6 is a perspective view of the tool holder of FIG. 5 with a locking collar, the tool insert being omitted for clarity of the drawing. [Figure 7] FIG. 7 is a perspective view of a portion of the locking collar of FIG. 6. [Figure 8] FIG. 7 is a plan view of the tool holder and locking collar portion of FIG. 6. [Figure 9]9 is a cross-sectional view of the tool holder of FIG. 8 taken along line Z1-Z1. [Figure 10] FIG. 2 is a perspective view of the tool insert of FIG. 1; [Figure 11] FIG. 11 is a bottom perspective view of the tool insert of FIG. 10. [Figure 12] FIG. 11 is a side view of the tool insert of FIG. [Figure 13] FIG. 11 is a plan view of the tool insert of FIG. [Figure 14] FIG. 14 is a cross-sectional view of the tool insert of FIG. 13 taken along line W1-W1. [Figure 15] FIG. 13 is a perspective view of a second embodiment of a tool assembly, also in an assembled state. [Figure 16] FIG. 16 is a side view of the tool assembly of FIG. [Figure 17] FIG. 16 is a plan view of the tool assembly of FIG. [Figure 18] 18 is a cross-sectional view of the tool assembly of FIG. 17 taken along line ZZ. [Figure 19] 18 is a cross-sectional view of the tool assembly of FIG. 17 taken along line YY. [Figure 20] FIG. 16 is a perspective view of the tool holder of FIG. 15. [Figure 21] FIG. 16 is a plan view of the tool holder of FIG. [Figure 22] 22 is a cross-sectional view of the tool holder taken along line T-T in FIG. 21 . [Diagram 23] FIG. 16 is a perspective view of the tool insert of FIG. 15. [Figure 24] FIG. 24 is a side view of the tool insert of FIG. 23. [Diagram 25] FIG. 24 is a plan view of the tool insert of FIG. 23. [Figure 26] 26 is a cross-sectional view of the tool insert of FIG. 25 taken along line VV. [Figure 27] FIG. 13 is a perspective view of a tool insert according to another embodiment. [Figure 28] FIG. 28 is a bottom perspective view of the tool insert of FIG. 27. [Figure 29] FIG. 28 is a plan view of the tool insert of FIG. 27. [Diagram 30]30 is a cross-sectional view of the tool insert of FIG. 29 taken along line Y1-Y1. [Diagram 31] FIG. 2 is a cross-sectional view of a tool assembly according to an embodiment of the present invention, particularly showing a braze layer between a tool insert and a tool holder. [Diagram 32] FIG. 34 is an image of a prior art design example obtained from finite element analysis, showing the maximum principal stresses occurring within the tool insert and tool assembly, for comparison purposes with FIG. [Diagram 33] FIG. 33 is an image of an example braze design resulting from finite element analysis, showing the maximum principal stresses occurring within the tool insert and tool assembly, for comparison purposes with FIG. 32. [Diagram 34] FIG. 13 is a cross-sectional view of a tool assembly according to another embodiment of the present invention, particularly illustrating a cooling system located within and adjacent the area of ​​the blaze. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Throughout the embodiments, similar parts are denoted by the same reference numerals and will not be described further for the sake of brevity.

[0015] 1-4, one embodiment of a tool assembly of the present invention is shown generally at 10. The tool assembly includes a polycrystalline cubic boron nitride (PCBN) tool insert 12 and a tool holder 14 that holds the PCBN tool insert 12. The tool holder 10 has a longitudinal axis of rotation (not shown) about which it rotates during use in a friction stir welding process. Note that this axis of rotation is not an axis of rotational symmetry due to the asymmetric thread pattern machined into the tool insert 12. The tool insert 12 and tool holder 14 are coaxially aligned about the axis of rotation.

[0016] The tool assembly 10 further includes a retention mechanism that mechanically locks the tool insert 10 and tool holder 12 together, thereby preventing separation during FSW. This positive locking is separate and superior to passive shrink fitting techniques known in the art. The term "mechanically engaged" is specifically intended to exclude configurations that utilize frictional engagement and frictional engagement to prevent relative separation. This positive locking is also separate and distinct from a threaded screw cap structure that may be attached about the tool holder. In this embodiment, the retention mechanism includes a locking collar 16, which is described in more detail below.

[0017] Tool Insert

[0018] 10-14, the tool insert 12 has a stir pin 18, a shoulder portion 20 and a body portion 22, all of which are in axial alignment with one another, with the shoulder portion 20 being essentially the interface between the stir pin 18 and the body portion 22. The stir pin 18, shoulder portion 20 and body portion 22 are all integrally formed with one another, such that the tool insert 12 is one piece. The tool insert 12 is machined from a single PCBN block after the block is sintered in a HPHT press.

[0019] The agitating pin 18 has a conical profile that tapers outwardly from a rounded apex 24 to a shoulder portion 20. The agitating pin 18 has an inscribed helical feature 26 that extends downwardly and upwardly from the apex 24 to the shoulder portion 20. The helix 26 has a planar path that is axially oriented and a working surface that is radially oriented.

[0020] The shoulder portion 20 is disk-shaped and has a larger diameter than the circular bottom of the agitator pin 18. The shoulder portion 20 extends axially downward to merge with the body portion 22.

[0021] Body portion 22 is generally cylindrical.

[0022] Advantageously, a circumferentially extending locking groove 28 is provided in the upper region of the body portion 22 near the shoulder portion 20 for mechanically mating with the locking collar 16 as part of the retention mechanism. The locking groove 28 extends all around along the entire circumference of the body portion 22. However, this does not have to be the case and alternatively the locking groove 28 may extend only partially around the circumference of the body portion 22 and the locking collar 16 is configured accordingly.

[0023] In an alternative embodiment, the circumferentially extending groove 28 on the tool insert 12 is replaced by a circumferentially extending flange (not shown). The flange may extend partially around the tool insert 12 or may extend completely around the tool insert 12. In such an embodiment, the flange cooperates with one or more circumferentially extending grooves (not shown) on the locking collar 16.

[0024] As shown in Figure 11, two segmental slots 30 are cut into the lower end of the body portion 22. The segmental slots 30 are diametrically opposite one another. The segmental slots 30 cooperate with two segmental steps 32 (see Figure 5) to form part of an anti-rotation mechanism when the tool insert 12 is in place and supported by the tool holder 14. The anti-rotation mechanism prevents relative rotational movement between the tool insert 12 and the tool holder 14 about the axis of rotation. Alternative embodiments of the anti-rotation mechanism are described in detail below.

[0025] In use, rotation of the tool assembly 10 is such that the helix 26 drives the workpiece material flow from the edge of the shoulder portion 20 to the center and then down the length of the stir pin 18. This causes the workpiece material to circulate within the stir zone and fill in the voids created by the stir pin 18 as the tool insert 12 traverses in a known manner.

[0026] Tool holder

[0027] 4, 5, 6 and 9, the tool holder 14 has a retaining member 34 for receiving a tool insert and an elongated stem member 36 joined at one end to the retaining member 34.

[0028] The stem 36 is solid and cylindrical. The purpose of the stem 36 is to facilitate connection of the tool assembly 10 to an FSW machine.

[0029] The retaining member 34 is cylindrical on the outside and has an internal recessed cup 38 which receives the tool insert 12. The recessed cup 38 is centered about the axis of rotation. The recessed cup 38 has a lower bottom surface 40, an upper opening 42 through which the tool insert 12 is inserted, and a sidewall 44 connecting the bottom surface 40 to the opening 42.

[0030] In this embodiment, the sidewall 44 is generally cylindrical and has a constant circular cross-section about its length and is intended for use with a tool insert that is at least partially cylindrical.

[0031] In an alternative embodiment, side wall 44 is generally frusto-conical in shape, with the side wall having a circular cross section whose diameter increases moving away from bottom surface 40. This profile of recessed cup 38 is intended for use with a tool insert that is at least partially conical in shape.

[0032] The recessed cup 38 is sized and shaped to receive only a portion of the body portion 22 so that, when coupled, the tool insert 12 protrudes from the tool holder 14 with the shoulder portion 20 exposed.

[0033] Regardless of whether the inner profile of the recessed cup 38 is conical or cylindrical, two segmental steps 32 are incorporated into the side wall 44. The side wall 44 is therefore stepped when viewed in longitudinal section as shown in FIG. 22. The segmental steps 32 form part of the anti-rotation mechanism described above. When the tool insert 12 is in position within the recessed cup 38, the segmental steps 32 abut against the segmental slots 30 of the tool insert 12, thereby preventing rotation of the tool insert 12 relative to the tool holder 14. It is important to avoid rotation, as this is one way in which the tool insert can become loose and come off the tool holder 14.

[0034] Retention mechanism

[0035] As mentioned above, the retention mechanism includes the locking collar 16 (FIG. 7) and the circumferentially extending groove 28 in the tool insert 12. Optionally, the retention mechanism further includes a high temperature seal disposed beneath the locking collar 16.

[0036] As shown in Figures 1 and 6, the locking collar 16 has two arcuate collar portions 16a, 16b, although more collar portions may alternatively be used. Preferably, the arcuate collar portions 16a, 16b are of equal length. Essentially, the arcuate collar portions 16a, 16b are adapted to join tightly end-to-end to form a single ring. Providing the locking collar 16 with the arcuate collar portions 16a, 16b allows for a tight fit around the tool insert 12 and / or tool holder 14, but without compressive forces.

[0037] The locking collar 16 is annular, more specifically ring-like, with an L-shaped cross-section. When the tool insert 12 is in situ supported by the tool holder 14, the locking collar 16 extends around the opening 42 of the tool holder against its rim. The locking collar 16 is also provided against an outer surface 46 of the retaining member 34. The locking collar 16 extends into the circumferentially extending groove 28 of the tool insert 12 in a mating engagement relationship. The arcuate collar portions 16a, 16b, when securely coupled together, hold the tool insert 12 securely in place within the tool holder 14, thereby preventing the tool insert 12 from being removed from the tool holder 14.

[0038] 15-26, an alternative embodiment of a tool assembly is generally indicated at 100. The tool assembly 100 includes an alternative embodiment of a tool insert 112 and an alternative embodiment of a tool holder 114. In this embodiment, the retention mechanism includes a locking pin 48 that mates with a locking hole 50 in the tool insert 112 and / or the tool holder 114. In a preferred embodiment, the retention mechanism includes two or more locking pins 48. The two locking pins 48 are diametrically opposed from one another. Preferably, the locking pins 48 are made from mild steel to minimize stress. In one embodiment, the locking hole 50 includes a radially extending through hole 52 through the tool holder 114 and a radially extending blind hole 54 in the tool insert 112 that is aligned with the through hole 52 of the tool holder 114.

[0039] 27-30 show another implementation of an anti-rotation feature in another embodiment of a tool insert generally designated 212. The anti-rotation member includes a square shaped boss on the underside of the tool holder and a correspondingly shaped recess 56 in the tool insert 112. As another example, a square boss may be provided on the tool insert and a square recess may be provided in the bottom surface 40 of the tool holder 114.

[0040] Tool Holder Material

[0041] Another aspect of the retention mechanism that complements the mechanical solutions discussed above is the tool holder material. The retention member 34 and stem member 36 are preferably integrally formed with one another so that the tool holder 14 is a single piece. However, these members may also be made as two separate components that include or consist of two separate materials and are then joined together.

[0042] The tool holder 12 is made of a high temperature, high strength alloy. For example, the tool holder 12 may be made of any one or more of the following materials: NIMONIC® 80A, Inconel alloy (a grade of nickel-chromium based superalloy), W-Ni (tungsten-nickel) alloy, TZM (molybdenum-titanium-zirconium), high entropy alloy. Generally, these alloys are characterized by good strength even at high temperatures.

[0043] Tests performed on tool holders 14 comprised of high entropy alloys NIMONIC® 80A and Al4Nb4HEA have resulted in excellent retention of the tool insert 12 within the tool holder 14. Without being bound by theory, it is believed that as the temperature increases during the initial stages of FSW, the alloy softens, allowing the tool insert 12 to recess the tool holder 14 to a depth of 10-50 microns. Once the plunge stage is complete, precipitation hardening then occurs due to the thermal cycling action, thereby hardening the alloy and surprisingly gripping the tool insert 12 in place.

[0044] For some materials, instead of precipitation hardening, alternative or additional hardening mechanisms, such as strain hardening and / or phase changes, are triggered. These are intentionally initiated during the FSW process at elevated temperatures and while the tool holder is under load. The effect of the hardening mechanisms is exploited to hold the tool insert in the tool holder.

[0045] Brazing and Materials

[0046] In another embodiment, the tool assembly 300 further includes a brazing layer 302 located between the tool insert 12 and the tool holder 14, see FIG. 31. The brazing layer 302 chemically bonds to the tool insert 12 and the tool holder 14, forming a strong joint therebetween. The brazing material 302 provides enough strength to prevent the tool from collapsing during plunging. The heat generated due to friction then deforms the tool holder 14, and the tool insert 12 sinks into the tool holder 14 due to the hardening mechanism described above.

[0047] Preferably, the braze layer 302 is made of a palladium-based alloy, such as a suitably selected Pallabraze™ filler metal from Johnson Matthey™. Such alloys exhibit good oxidation resistance and good strength at high temperatures. When properly selected, palladium-based alloys have melting temperatures in excess of 950° C. and high shear strength at high temperatures.

[0048] Alternative brazing materials suitable for this application include Active Brazing Alloy (ABA®) from Johnson Matthey™, Ticusil® and NiCrInMn alloys from Morgan Advanced Materials™.

[0049] During assembly, the brazing is performed at high temperature and high vacuum, with pressures >10 -5 It's a bar.

[0050] The inventors have unexpectedly found that brazing is a viable technique for joining steel plates thicker than 12 mm. The traditional limiting factor for joining thick plates is the length of the stir pin 18 and the resulting overall size of the PCBN tool insert 12. With prior art designs for tool inserts, manufacturing large PCBN blocks (also called "cylinders") to accommodate tool inserts with high pin thicknesses is a tremendous challenge due to limitations on the HPHT press die bore length as well as uneven pressure distribution caused by tall HPHT capsules. Increasing the height of the stir pin 18 without using long cylinders for pressurization offers significant manufacturing advantages.

[0051] When a tool insert is attached to a tool holder using filler metal, the overall height of the tool insert can be significantly reduced since the large surface area required to shrink fit the tool insert in place is no longer required. Advantageously, this also means that the commonly used threaded screw cap that is provided around the tool holder can be omitted, thereby providing cost benefits.

[0052] With the shorter tool insert 12, the peak stress in the tool insert that would normally result in failure is also significantly lower compared to the existing design, see Figure 32. Finite element analysis modeling shows that even though the average stress is higher in the brazed design, the peak stress for the brazed design is approximately 50% lower than the existing design, see Figure 33.

[0053] It is contemplated that the brazing may not be used to bond the tool insert and tool holder, but instead high temperature glues and other similar adhesives may be used. Similarly, mechanical bonding is also possible.

[0054] Cooling System

[0055] As shown in Figure 34, the tool assembly 300 may include a cooling system 304. The cooling system 304 protects the braze joint. Optionally, the cooling system 304 includes a network of conduits that carry a coolant, for example water. Optionally, the cooling system 304 may consist of a single conduit, for example arranged in a serpentine pattern. Preferably, the cooling system 304 is adapted to maintain the temperature of the braze region at a temperature below 150°C.

[0056] Ideally, the conduits are located in or near the bottom surface 40 of the tool holder 14. The cooling system 304 should also extend all the way to the sidewall 44 of the recessed cup 38. Alternatively, the cooling system 304 may be located in or behind the sidewall 44 rather than the bottom surface 40, although this may be less practical.

[0057] In this manner, the cooling system 304 can carry away heat generated during the FSW, which is generated at the stir pin 18 and shoulder portion 20, and which is conducted through the body portion 22 of the tool insert 12. By reducing the temperature of the braze region between the tool insert 12 and the tool holder 14, the joint is shielded from high temperatures, minimizing the adverse effects on braze strength that would otherwise occur. This facilitates retention of the tool insert 12 within the tool holder 14.

[0058] While the invention has been particularly shown and described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes in form and details can be made therein without departing from the scope of the invention as set forth in the appended claims.

[0059] For example, just one set of segment slots and steps for the anti-rotation feature could be used in place of the two sets described above, as well as three or more sets of segment slots and steps could be provided instead.

[0060] The mechanical retention mechanism may be used in conjunction with any one or more of the following elements: brazing layer, specified tool holder material (i.e., high temperature high strength alloy), and / or cooling system. However, any one of these elements provides its own benefits. Thus, these elements may be embodied individually or in combination with any one or more of the other elements in the list.

Claims

1. 1. A friction stir welding (FSW) tool assembly having a longitudinal axis of rotation about which it rotates during use, the tool assembly including a tool insert and a tool holder coaxially holding the tool insert, the tool assembly further including a retention mechanism mechanically engaging both the tool insert and the tool holder to prevent relative separation, the retention mechanism including an annular locking collar disposed about the tool insert and the tool holder and matingly engaging with the tool insert and the tool holder, the tool insert having a circumferentially extending groove and a locking collar mechanically engaging the groove.

2. The tool assembly of claim 1 , wherein the tool insert is comprised of polycrystalline cubic boron nitride (PCBN).

3. The tool assembly of claim 1 or 2, wherein the tool insert is comprised of tungsten rhenium.

4. A tool assembly according to any preceding claim, wherein the locking collar comprises two or more arcuate collar portions.

5. 5. A tool assembly as claimed in claim 4, wherein said arcuate collar portions are adapted to join together in an end-to-end relationship to form a single locking collar.

6. A tool assembly as claimed in claim 4 or 5, wherein said arcuate collar portions are equal in length dimension to one another.

7. The tool assembly of claim 1 , wherein the groove extends partially around the tool insert.

8. The tool assembly of claim 1 , wherein the groove extends completely around the tool assembly.

9. A tool assembly as claimed in any preceding claim, wherein the tool insert has a circumferentially extending flange.

10. The tool assembly of claim 9 , wherein the flange extends partially around the tool insert.

11. The tool assembly of claim 9 , wherein the groove extends completely around the tool assembly.

12. A tool assembly as claimed in any preceding claim, wherein the retention mechanism includes a locking pin which mates with a locking hole provided in the tool insert and / or the tool holder.

13. The tool assembly of claim 12 , wherein the retention mechanism includes two or more locking pins.

14. The tool assembly of claim 13 , wherein the locking pins are diametrically opposed.

15. 15. A tool assembly as claimed in any one of claims 1 to 14, wherein the tool insert has a shoulder with first and second ends, a stirring pin extending from the first end of the shoulder, and a body portion extending from the second end of the shoulder, the stirring pin, the shoulder and the body portion being integrally formed.

16. 16. A tool assembly as claimed in any one of claims 1 to 15, wherein the tool holder has a recessed cup, the tool insert being at least partially disposed within the recessed cup, the recessed cup having a bottom and an opening for receiving the tool insert.

17. The tool assembly of claim 16 , wherein the recessed cup is cylindrical, the recessed cup having a constant circular cross-section, and the tool insert is at least partially cylindrical.

18. 17. The tool assembly of claim 16, wherein the recessed cup is configured to receive only a portion of the tool insert such that the body portion protrudes from the tool holder.

19. A tool assembly as claimed in any preceding claim, further comprising an anti-rotation member preventing relative movement of the tool insert and tool holder about the axis of rotation.

20. 20. A tool assembly according to claim 19 when dependent on claim 16, wherein the anti-rotation member comprises a single segmental step at the bottom of the recessed cup.

21. 20. A tool assembly according to claim 19 when dependent on claim 16, wherein the anti-rotation member has two segmented steps at the bottom of the recessed cup.

22. 20. The tool assembly of claim 19, wherein the anti-rotation member comprises a square shaped boss and a correspondingly shaped recess on the tool holder and the tool insert, respectively, or a square shaped boss and a correspondingly shaped recess on the tool insert and the tool holder, respectively.

23. A tool assembly according to any preceding claim, further comprising a cooling system provided at an interface between the tool insert and the tool holder.

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