Friction stir welding tool assembly

Abstract

The present disclosure relates to a friction stir welding (FSW) tool assembly comprising a bonding layer that bonds together a tool insert and a tool holder, wherein the bonding layer is a braze layer having a melting temperature of at least 900 °C.

Description

Technical Field

[0001] This disclosure relates to a friction stir welding (FSW) tool assembly, including a tool insert and a tool holder. More specifically, this disclosure relates to an FSW tool assembly for friction stir welding of high-temperature ferroalloys and other high-temperature alloys. More specifically, this disclosure relates to an FSW tool assembly wherein the tool insert comprises polycrystalline cubic boron nitride (PCBN) or tungsten-rhenium (W-Re). Background Technology

[0002] Friction stir welding (FSW) is a technique in which a rotating tool is forced into contact with two adjacent workpieces to be joined. The rotation of the tool generates frictional and viscous heating of the workpieces. Extensive deformation occurs as the workpieces mix along the plastic zone. As the plastic zone cools, the workpieces are joined along the weld joint. Because the workpieces remain in the solid phase, this process is technically a forging process rather than a welding process, but by convention it is referred to as welding or friction stir welding, and this article follows that convention.

[0003] In the case of low-temperature metal welding (FSW), the entire tool / tool ​​holder can be a single piece of formed tool steel, in which case it is often referred to as the "probe". When the tool is used to weld high-temperature alloys (such as steel), the tool typically consists of two or more parts, where the end element, which is in direct contact with the material being welded, is often called the "disc" or "tool insert," while the remaining part of the tool is called the "tool holder." The tool holder securely holds the disc and assembles it into the FSW machine, so that the tool disc and tool holder together constitute the "tool" or "tool assembly". The tool disc is typically shaped to form a shoulder and a stirring pin, and a counter-spiral is usually cut into the surface of the stirring pin, so that during rotation, the counter-spiral pulls the metal toward the stirring pin and pushes the metal downward into the hole formed by the stirring pin.

[0004] Generally, FSW operations involve many steps, such as:

[0005] a) The insertion step (also known as the piercing step) is from the moment the tool contacts the workpiece until the pin is fully embedded in the shoulder of the heated and softened workpiece.

[0006] b) The tool moves laterally, during which it moves laterally along the line between the workpieces to be connected, and

[0007] c) Extraction step, in which the tool is lifted or moved laterally from the workpiece.

[0008] Lateral movement of the tool is the main stage for weld formation, and it is usually carried out under constant conditions; typically, these conditions include rotational speed, penetration conditions, and lateral movement speed.

[0009] PCBN-based tools can withstand the harsh working environment of the FSW (Freestanding Swing), where temperatures exceed 1100°C. PCBN-based tool discs are relatively inexpensive and very durable. However, a limitation of PCBN disc manufacturing is the need for a large PCBN block from which the disc is made. This single PCBN block requires a diameter and height of up to 50mm to produce a disc with a 12mm pin height, capable of soldering boards up to 12mm thick. Larger PCBN blocks (and therefore PCBN discs) are currently not feasible due to the limitations of the high-pressure, high-temperature (HPHT) presses used in the PCBN sintering process. Larger presses could compromise material uniformity. In short, the size of PCBN discs currently achievable in practice is limited to those capable of soldering boards 12mm thick or less.

[0010] There is indeed an incentive to develop PCBN tools and matching tool holders that can solder iron plates with a thickness of more than 12mm.

[0011] The main challenge with large PCBN tools is retaining the tool within the tool holder, especially during the insertion and lateral movement phases. Occasionally, separation occurs, believed to be caused by a thermal conductivity mismatch between the PCBN tool insert and the typical steel tool holder. Traditional methods (such as screws) are ineffective due to the extreme conditions of FSW processing. This problem hinders the performance of the PCBN tool insert and limits the solder length that could otherwise be achieved.

[0012] There is a need for an FSW tool assembly for welding high-temperature alloys that retains the tool insert within a tool holder during prolonged use. Summary of the Invention

[0013] According to the present invention, a friction stir welding (FSW) tool assembly having a longitudinal axis of rotation is provided, the tool assembly rotating about the longitudinal axis of rotation during use, the tool assembly including a tool insert and a tool holder coaxially holding the tool insert, the tool holder including a recessed cup-shaped portion in which the tool insert is at least partially received, the tool assembly further including a bonding layer that joins the tool insert and the tool holder together, wherein the bonding layer is a brazing layer disposed in the recessed cup-shaped portion having a melting temperature of at least 900°C.

[0014] Preferred and / or optional features of the invention are provided in the dependent claims. Attached Figure Description

[0015] The invention will now be described more specifically by way of example only, with reference to the accompanying drawings, in which:

[0016] Figure 1 This is a perspective view of a first embodiment of a tool assembly in an assembled state;

[0017] Figure 2 yes Figure 1 The side view of the tool component;

[0018] Figure 3 yes Figure 1 A plan view of the tool components;

[0019] Figure 4 yes Figure 3 A cross-sectional view of the tool components along line SS;

[0020] Figure 5 yes Figure 1 A perspective view of the tool holder;

[0021] Figure 6 It has a locking ring. Figure 5 The perspective view of the tool holder, with the tool insert omitted for clarity;

[0022] Figure 7 yes Figure 6 A perspective view of a portion of the locking ring;

[0023] Figure 8 yes Figure 6 A plan view of the tool holder and locking ring section;

[0024] Figure 9 yes Figure 8 A cross-sectional view of the tool holder along line Z1-Z1;

[0025] Figure 10 yes Figure 1 A perspective view of the tool insert;

[0026] Figure 11 yes Figure 10 A bottom perspective view of the tool insert;

[0027] Figure 12 yes Figure 10 Side view of the tool insert;

[0028] Figure 13 yes Figure 10 A plan view of the tool insert;

[0029] Figure 14 yes Figure 13 The tool insert is shown in a cross section view along line W1-W1;

[0030] Figure 15 This is a perspective view of a second embodiment of a tool assembly, also in an assembled state;

[0031] Figure 16 yes Figure 15 The side view of the tool component;

[0032] Figure 17 yes Figure 15 A plan view of the tool components;

[0033] Figure 18 yes Figure 17 The tool component is a cross-sectional view along line ZZ;

[0034] Figure 19 yes Figure 17 The tool component is a cross-sectional view along line YY;

[0035] Figure 20 yes Figure 15 A perspective view of the tool holder;

[0036] Figure 21 yes Figure 15 A plan view of the tool holder;

[0037] Figure 22 yes Figure 21 The tool holder is shown in a cross section view along line TT;

[0038] Figure 23 yes Figure 15 A perspective view of the tool insert;

[0039] Figure 24 yes Figure 23 Side view of the tool insert;

[0040] Figure 25 yes Figure 23 A plan view of the tool insert;

[0041] Figure 26 yes Figure 25 The tool insert is shown in a cross section view along line VV;

[0042] Figure 27 This is a perspective view of the tool insert in another embodiment;

[0043] Figure 28 yes Figure 27 A bottom perspective view of the tool insert;

[0044] Figure 29 yes Figure 27 A plan view of the tool insert;

[0045] Figure 30 yes Figure 29 The tool insert is shown in a cross section view along line Y1-Y1;

[0046] Figure 31 This is a cross-sectional view of the tool assembly in an embodiment of the present invention, particularly showing the brazing layer between the tool insert and the tool holder;

[0047] Figure 32 The image was obtained from finite element analysis of existing technology designs, in order to... Figure 33 The purpose of the comparison is to show the maximum principal stress generated within the tool insert and tool assembly;

[0048] Figure 33 These images are taken from the finite element analysis of the brazing design, in order to be consistent with... Figure 32 The purpose of the comparison is to show the maximum principal stress generated within the tool insert and tool assembly; and

[0049] Figure 34 This is a cross-sectional view of a tool assembly according to another embodiment of the invention, particularly showing the cooling system of the adjacent brazing area.

[0050] In all embodiments, similar components are denoted by the same reference numerals, and further descriptions are omitted for brevity. Detailed Implementation

[0051] First refer to Figures 1 to 4 An embodiment of the tool assembly according to the invention is generally designated as 10. The tool assembly includes a polycrystalline cubic boron nitride (PCBN) tool insert 12 and a tool holder 14 for retaining the PCBN tool insert 12. The tool assembly 10 has a longitudinal axis of rotation (not shown) about which the tool assembly rotates during the friction stir welding process. Note that this axis of rotation is not rotationally symmetric due to the asymmetric thread pattern machined into the tool insert 12. The tool insert 12 and the tool holder 14 are coaxially aligned about the axis of rotation.

[0052] The tool assembly 10 also includes a retaining mechanism to mechanically lock the tool insert 10 and the tool retainer 12 together, thereby preventing separation during the FSW process. This active locking action differs from and is significantly superior to passive shrink-fit assembly methods known in the prior art. It also differs from threaded nut devices sometimes mounted around the tool retainer. In this embodiment, the retaining mechanism includes a locking ring 16, which will be described in detail below.

[0053] Tool inserts

[0054] Go to Figures 10 to 14The tool insert 12 includes a stirring pin 18, a shoulder 20, and a body portion 22, all axially aligned with each other. The shoulder 20 essentially forms the boundary between the stirring pin 18 and the body portion 22. The stirring pin 18, shoulder 20, and body portion 22 are integrated together, making the tool insert 12 a single unit. The tool insert 12 is manufactured after a single PCBN block is sintered in an HPHT press.

[0055] The agitator pin 18 has a conical profile, tapering outwards from a rounded top 24 toward a shoulder 20. The agitator pin 18 includes an inscribed helical feature 26 extending downwards from the top 24 toward the shoulder 20 and into the shoulder. The helix 26 has a planar path that is axially oriented while the working surface is radially oriented.

[0056] The shoulder 20 is disc-shaped and has a larger diameter than the circular base of the agitator pin 18. The shoulder 20 extends axially downward to engage with the main body 22.

[0057] The main body 22 is roughly cylindrical.

[0058] Advantageously, a circumferentially extending locking groove 28 is provided in the upper region of the body portion 22, near the shoulder 20, to mechanically engage with the locking ring 16 as part of the retention mechanism. The locking groove 28 extends around the entire circumference of the body portion 22. However, this is not mandatory, and alternatively, the locking groove 28 may extend only partially around the circumference of the body portion 22, with the locking ring 16 configured accordingly.

[0059] 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 it may extend around the entire tool insert 12. In such an embodiment, the flange mates with one or more circumferentially extending grooves (not shown) on the locking ring 16.

[0060] like Figure 11 As shown, two petal-shaped grooves 30 cut into the lower end of the main body portion 22. The petal-shaped grooves 30 are radially opposite each other. When the tool insert 12 is in place and supported by the tool holder 14, the petal-shaped grooves 30, forming part of the anti-rotation mechanism, and the two petal-shaped steps 32 within the tool holder 14 (see...) Figure 5 The anti-rotation mechanism prevents relative rotational movement between the tool insert 12 and the tool holder 14 about the axis of rotation. An alternative example of the anti-rotation mechanism will be described in more detail later.

[0061] In use, the rotation of the tool assembly 10 causes the helix 26 to drive the workpiece material from the edge of the shoulder 20 toward the center, and then downward along the length of the agitator pin 18. This forces the workpiece material to circulate within the agitation zone and fills the gaps formed by the agitator pin 18 as the tool insert 12 moves laterally in a known manner.

[0062] Tool Holder

[0063] refer to Figure 4 , Figure 5 , Figure 6 and Figure 9 The tool holder 14 includes a retaining member 34 for receiving a tool insert, and an elongated main member 36 connected to the retaining member 34 at one end.

[0064] The main component 36 is a solid cylinder. The purpose of the main component 36 is to facilitate the connection of the tool assembly 10 to the FSW machine.

[0065] The retaining member 34 is cylindrical on the outside and includes a recessed cup-shaped portion 38 on the inside to receive the tool insert 12. The recessed cup-shaped portion 38 is centrally located about the axis of rotation. The recessed cup-shaped portion 38 includes a lower base surface 40, an upper opening 42 (through which the tool insert 12 is inserted), and a sidewall 44 connecting the base surface 40 to the opening 42.

[0066] In this embodiment, the sidewall 44 is generally cylindrical and has a constant circular cross-section along its length, intended for use with a tool insert that is at least partially cylindrical.

[0067] In an alternative embodiment, the sidewall 44 is generally truncated conical and has a circular cross-section whose diameter increases with distance from the base surface 40. This profile of the recessed cup-shaped portion 38 is intended for use with tool inserts that are at least partially conical.

[0068] The size and shape of the recessed cup-shaped portion 38 accommodate only a portion of the main body portion 22, such that when together, the tool insert 12 protrudes from the tool holder 14 with the shoulder 20 exposed.

[0069] Regardless of whether the internal contour of the recessed cup-shaped portion 38 is conical or cylindrical, two petal-shaped steps 32 are constructed into the sidewall 44. Therefore, as... Figure 22As shown, the longitudinal section of the sidewall 44 is stepped. The petal-shaped steps 32 form part of the anti-rotation mechanism described above. When the tool insert 12 is positioned within the recessed cup-shaped portion 38, the petal-shaped steps 32 abut against the petal-shaped grooves 30 of the tool insert 12, preventing the tool insert 12 from rotating relative to the tool holder 14. It is important to avoid rotation, as this is one way the tool insert 12 could gradually loosen and detach from the tool holder 14.

[0070] Reservation of institutions

[0071] As described above, the retention mechanism includes a locking ring 16 ( Figure 7 The retaining mechanism also includes a circumferentially extending groove 28 on the tool insert 12. Optionally, the retaining mechanism also includes a high-temperature seal located below the locking ring 16.

[0072] like Figure 1 and Figure 6 As shown, the locking ring 16 includes two arcuate ring portions 16a and 16b, although more arcuate ring portions may be used. Preferably, the arcuate ring portions 16a and 16b are of equal length. Essentially, the arcuate ring portions 16a and 16b are adapted to be securely joined end-to-end to form a single ring. Assigning the locking ring 16 with arcuate ring portions 16a and 16b allows for a tight but not compressive fit around the tool insert 12 and / or tool holder 14.

[0073] The locking ring 16 is an annular ring with an L-shaped cross-section. When the tool insert 12 is supported in place by the tool holder 14, the locking ring 16 extends around the edge of the opening 42 of the tool holder. The locking ring 16 is also mounted against the outer surface 46 of the retaining member 34. The locking ring 16 extends into the circumferentially extending groove 28 on the tool insert 12 in a mating engagement manner. When securely connected, the arcuate ring portions 16a and 16b hold the tool insert 12 securely in place within the tool holder 14, preventing the tool insert 12 from disengaging from the tool holder 14.

[0074] refer to Figures 15 to 26Alternative embodiments of the tool assembly are generally designated 100. Tool assembly 100 includes another embodiment of a tool insert 112 and another embodiment of a tool retainer 114. In this embodiment, the retaining mechanism includes a locking pin 48 that engages with a locking hole 50 in the tool insert 112 and / or the tool retainer 114. In a preferred embodiment, the retaining mechanism includes two or more locking pins 48. The two locking pins 48 are radially opposite each other. Preferably, the locking pins 48 are made of mild steel to minimize stress. In one embodiment, the locking hole 50 includes a radially extending through hole 52 and a radially extending blind hole 54, the through hole being arranged through the tool retainer 114 and the blind hole being arranged in the tool insert 112, the blind hole being aligned with the through hole 52 of the tool retainer 114.

[0075] Figures 27 to 30 An alternative example of an anti-rotation mechanism in another embodiment of the tool insert, indicated by 212, is shown. The anti-rotation member includes a square boss on the underside of the tool holder and a correspondingly shaped recess 56 on the tool insert 112. As another example, the square boss may be located on the tool insert, while the square recess may be located on the base surface 40 of the tool holder 114.

[0076] Tool holder material

[0077] As a complement to the mechanical solution described above, another aspect of the retaining mechanism is the tool retainer material. The retaining member 34 and the main member 36 are preferably integrated together, making the tool retainer 14 a single component. However, they can be manufactured as two separate components, comprising or composed of two different materials, and then joined together.

[0078] The tool holder 12 comprises a high-temperature, high-strength alloy. For example, the tool holder 12 may comprise any one or more of the following materials: 80A, Inconel alloys (a type of nickel-chromium-based superalloy), W-Ni (tungsten-nickel) alloys, TZM (molybdenum-titanium-zirconium) alloys, and high-entropy alloys. Generally, these alloys are characterized by good strength at high temperatures.

[0079] Use inclusion The results of tests conducted on the tool holder 14, made of 80A and Al4Nb4 HEA high-entropy alloy, show that the tool insert 12 is well retained within the tool holder 14. Without being bound by theory, it can be assumed that during the initial stage of FSW, the alloy softens as the temperature increases, allowing the tool insert 12 to press the tool holder 14 into a depth of 10 to 50 micrometers. Once the insertion stage is complete, precipitation hardening occurs due to thermal cycling, causing the alloy to harden and surprisingly clamp the tool insert 12 into place.

[0080] In some materials, instead of precipitation hardening, alternative or additional hardening mechanisms are triggered, such as strain hardening and / or phase transformation. These occur intentionally during FSW treatment, at high temperatures, and when the tool holder is under load. The effects of the hardening mechanisms are utilized to retain the tool insert within the tool holder.

[0081] Brazing and materials

[0082] 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 Figure 31 The brazing layer 302 is chemically bonded to the tool insert 12 and the tool holder 14, thereby forming a strong connection between them. The brazing 302 provides sufficient strength to the tool so that it will not fall out during insertion. Subsequently, the heat generated by friction deforms the tool holder 14, and the tool insert 12 is embedded in the tool holder 14 via the aforementioned hardening mechanism.

[0083] Preferably, the brazing layer 302 comprises a palladium-based alloy, for example from Johnson Matthey. TM Appropriate selection of Pallabraze TM Solder. This alloy exhibits good oxidation resistance and strength at high temperatures. With proper selection, palladium-based alloys have melting temperatures above 950°C and high shear strength at high temperatures.

[0084] Alternative brazing materials suitable for this application include: Johnson Matthey TM Active BrazingAlloys Morgan Advanced Materials TM of And NiCrInMn alloy.

[0085] During assembly, brazing is performed under high temperature and high vacuum conditions, with pressures exceeding 10. -5 bar.

[0086] The inventors unexpectedly discovered that brazing is a feasible technique for welding steel plates thicker than 12 mm. To date, the limiting factor for welding thicker plates has been the length of the agitator pin 18, and therefore the overall size of the PCBN tool insert 12. In existing tool insert designs, manufacturing a large PCBN block (also called a "cylinder") to accommodate a tool insert with a large pin height is extremely challenging due to limitations on the HPHT press die orifice length and the uneven pressure distribution caused by the taller HPHT container. Increasing the height of the agitator pin 18, without relying on pressing a longer cylinder, offers significant advantages in manufacturing.

[0087] By using filler metal to attach the tool insert to the tool retainer, the overall height of the tool insert can be significantly reduced because the large surface area required for retracting and assembling the tool insert into place is no longer needed. Advantageously, this also means that the threaded nut typically used for mounting around the tool retainer can be omitted, resulting in cost savings.

[0088] Compared with existing designs ( Figure 32 Compared to the previous design, using a shorter tool insert 12 significantly reduced the peak stress in the tool insert, which typically leads to failure. Finite element analysis models show that although the average stress in the brazing design is higher, the peak stress in the brazing design is approximately 50% lower than in existing designs (see...). Figure 33 ).

[0089] It is conceivable that, instead of brazing, high-temperature adhesives and other similar bonding agents could be used to join the tool insert and tool holder. Similarly, mechanical bonding is also feasible.

[0090] Cooling system

[0091] like Figure 34 As shown, the tool assembly 300 may include a cooling system 304. This cooling system 304 protects the brazed joint. Optionally, the cooling system 304 includes a network of conduits for delivering a coolant (e.g., water). Optionally, the cooling system 304 may include, for example, individual conduits arranged in a serpentine pattern. Preferably, the cooling system 304 is adapted to maintain the temperature in the brazing region below 150°C.

[0092] Ideally, the conduit is arranged in or near the base surface 40 of the tool holder 14. The coverage of the cooling system 304 may also extend upward to the sidewall 44 of the recessed cup-shaped portion 38. Alternatively, the cooling system 304 may be arranged in or behind the sidewall 44, rather than on the base surface 40, although this arrangement is less efficient.

[0093] In this way, the cooling system 304 is able to remove the heat generated during FSW, which is produced at the stir pin 18 and shoulder 20 and has been conducted through the body portion 22 of the tool insert 12. By lowering the temperature in the brazing area between the tool insert 12 and the tool holder 14, the joint is protected from higher temperatures, thereby minimizing the detrimental effects on brazing strength. This helps to retain the tool insert 12 within the tool holder 14.

[0094] Although the invention has been specifically shown and described with reference to embodiments, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of the invention as defined by the appended claims.

[0095] For example, for an anti-rotation mechanism, it is conceivable to use only one set of petal-shaped grooves and steps, instead of the two sets mentioned above. Similarly, it is possible to provide three or more sets of petal-shaped grooves and steps instead.

[0096] Mechanical retaining mechanisms can be used in conjunction with any one or more of the following components: brazing layers, specific tool retainer materials (i.e., high-temperature, high-strength alloys), and / or cooling systems. However, each of these components has its own advantages. Therefore, they can be implemented individually or in combination with any one or more other components listed.

Claims

1. A friction stir welding (FSW) tool assembly having a longitudinal axis of rotation about which the tool assembly rotates during use, the tool assembly including a tool insert and a tool retainer, the tool retainer including a retaining member for coaxially retaining the tool insert and an elongated main member connected at one end thereto to the retaining member, wherein the retaining member is externally cylindrical, the main member is cylindrical, and wherein the diameter of the retaining member is larger than the diameter of the main member, the tool insert comprising polycrystalline cubic boron nitride (PCBN), the retaining member of the tool retainer including a recessed cup-shaped portion, the tool insert at least partially Receiving in the recessed cup-shaped portion, the tool assembly further includes a bonding layer that bonds the tool insert and the tool holder together, wherein the bonding layer is a brazed layer disposed in the recessed cup-shaped portion with a melting temperature of at least 900°C, wherein the recessed cup-shaped portion includes a base surface, an opening for inserting the tool insert, and a sidewall connecting the base surface to the opening, wherein the longitudinal section of the sidewall is stepped, wherein the stepped sidewall includes at least two petal-shaped steps, and wherein the tool insert includes at least two corresponding petal-shaped grooves, and wherein when the tool insert is positioned in the recessed cup-shaped portion, the at least two petal-shaped steps abut against the at least two corresponding petal-shaped grooves.

2. The tool assembly according to claim 1, characterized in that, The bonding layer is disposed on the surface of the base.

3. The tool component according to claim 1, characterized in that, The bonding layer is disposed on the sidewall.

4. The tool assembly according to claim 1, characterized in that, The brazing layer is in the form of a disc.

5. The tool assembly according to claim 1, characterized in that, The brazing layer is in the form of a ring.

6. The tool assembly according to claim 1, characterized in that, The brazing layer comprises a palladium-based alloy.

7. The tool assembly of claim 1 further includes a cooling system.

8. The tool assembly according to claim 7, characterized in that, The cooling system is positioned adjacent to or close to the base surface of the tool holder.

9. The tool assembly according to claim 7, characterized in that, The cooling system is located adjacent to or close to the side wall of the tool holder.

10. The tool assembly according to claim 7, characterized in that, The cooling system includes a network of ducts.

11. The tool assembly according to claim 7, characterized in that, The cooling system includes a single conduit arranged in a serpentine pattern.

12. The tool assembly according to claim 1, characterized in that, The tool insert includes W-Re.

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