Patent Application
20080048005
The present teachings will become more fully understood from the detailed description and the accompanying drawings, wherein:
The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the present teachings, their application, or uses.
Referring to
In accordance with the method of the present teachings, the device 10, in addition to being rotated at high RPM, has its orientation changed relative to the substrates 12 and 14. In this regard, the device 10 is tilted and moved relative to the substrates 12 and 14 through a plurality of points that is essentially a conical shape 22.
As shown in
To eliminate, or at least substantially diminish, the thinning of the substrate 12, the device 10 is again engaged to the substrates 12 and 14. The device 10, however, is now tilted and moved relative to the substrates 12 and 14 through a plurality of points that forms an inverse conical shape 26. By tilting and sweeping the device 10 in this manner, plasticized material of the substrates 12 and 14 generated by the frictional forces between the rotating device 10 and the substrates 12 and 14 is forced or pushed to positions inside of the conical shape 26. In other words, the annular protrusion of plasticized material that was initially pushed outside of the conical shape 22 shown in
It should be understood that, in addition to eliminating the thinning section of the substrate 12 where the device 10 initially engaged the substrate 12, the movement of the device 10 through the plurality of points that is conical in shape also results in a more robust joining of the substrates 12 and 14 because, as shown in
Moreover, it should be understood that thinning of the substrate 12 is also avoided by the cone stir method of the present teachings because the shoulder 16 of the device 10 is not required to sink into the upper substrate 12 before pin 18 withdrawal. More particularly, according to prior art friction stir spot welding methods, a friction stir spot welding device is engaged to the substrates orthogonally. To fully engage the lower substrate and sufficiently join the upper and lower substrates together, the shoulder of the device was required to sufficiently penetrate (or sink into) the upper substrate. This penetration of the shoulder into the upper substrate causes unnecessary thinning of the upper substrate, which as stated above, results in a poor joint between the substrates. The present teachings eliminate, or at least substantially diminish, this thinning by not requiring penetration of the shoulder 16 of the device 10 into the substrate 12 just before pin 18 withdrawal. Further, as described above, the tilting and sweeping of the device 10 through the cone 22 and inverse cone 26 increases the amount of plasticized material between the substrates 12 and 14, as well as returns it to generally its original position. In this manner, a more robust joint is achieved between the substrates 12 and 14.
Furthermore, by properly manipulating the process parameters such as the size of the conical-shaped surfaces 22 and 26 that the friction spot welding device 10 is swept through, a cone angle, RPM, an amount of time the device 10 is engaged with the substrates 12 and 14 etc., a mechanical structure can be generated between the first and second substrates 12 and 14. More specifically, now referring to
The collar-shaped interlock 28 results in a mechanical inter-lock between the substrates 12 and 14. That is, as stated above, the collar-shaped interlock 28 between the substrates 12 and 14 substantially “hooks” the substrates 12 and 14 mechanically together with a surprising amount of strength. More particularly, referring to Table 1 below, it can be seen that the joint strength achieved by sweeping the device 10 through a conical shape 22 and 26 according to the friction stir spot welding process according to the present teachings results in a maximum load strength that is approximately twice as strong as those found in prior art friction stir spot welding methods (i.e., where the device 10 merely engages the substrates 12 and 14 orthogonally).
The generation of the collar-shaped interlock 28 is particularly advantageous when joining substrates 12 and 14 that are formed of dissimilar materials. That is, as stated above, friction stir spot welding methods are generally advantageous when joining substrates 12 and 14 that are formed of the same material. In this regard, preferable substrates include materials such as steel, aluminum, magnesium, etc. Orthogonally engaging the substrates 12 and 14 with the device 10, however, is not particularly advantageous when joining substrates 12 and 14 formed of metallurgically mismatched materials. For example, it is particularly difficult to join an aluminum substrate to a magnesium substrate. Notwithstanding, by tilting and sweeping the device 10 through a plurality of positions that are essentially conical-shaped, substrates 12 and 14 formed of dissimilar materials can be joined together more easily with a strong joint, regardless of the bonding nature between the materials. Accordingly, an aluminum substrate can be joined to a magnesium substrate.
The present teachings should not be limited to merely joining aluminum substrates to magnesium substrates. On the contrary, the present teachings are applicable to joining any combination of substrates selected from materials such as, without limitation, steel, stainless steel, aluminum (Al), magnesium (Mg), tungsten (W), titanium (Ti), cobalt (Co), silver (Ag), copper (Cu), brass, bronze, Fe-Austenite, nickel (Ni), platinum (Pt), platinum iridium (Pt—Ir), chromium (Cr), iridium (Ir), Fe-Martensite, molybdenum (Mo), niobium (No), tantalum (Ta), and other difficult-to-weld alloys such as Inconel, Monel, and nickel-based (Ni) superalloys. In addition, although only a pair of substrates 12 and 14 are shown in
The substrates 12 and 14 can be joined in an unheated state. The substrates 12 and 14, however, may also be pre-heated or heated simultaneously when being engaged by the device 10. In this regard, heating of the substrates 12 and 14 further enables easier plastic deformation and, hence, the formation of the interlock 28 at the interface 30 between the substrates 12 and 14. This is a result of an improved ductility of the substrates 12 and 14 when the substrates 12 and 14 are heated, and is also a result of the substrates 12 and 14 being plastically deformed during the welding process.
In addition to the friction stir spot welding method, and as an alternative to heating the substrates 12 and 14, the present teachings also provide a linear stitch friction stir welding method that utilizes a dual pin concept. That is, referring to
Contrary to the leading device 32, the trailing device 34 penetrates the pair of substrates 12 and 14 at the interface 30 between the substrates to create the desired bonding structure. That is, the trailing device 34 should penetrate the substrate interface 30 to form the desired mechanical locking structure (
By controlling the flow of the material of the substrates 12 and 14 with the leading and trailing devices 32 and 34, the substrates 12 and 14 can have an interlocking joint structure that runs along the direction of the weld. This structure, as shown in
In addition, formation of the interlocks 28 can be optimized by controlling the inter-device distance, RPM, rotating direction of each device, pin geometries, and thread orientation. That is, the present teachings enable synchronized material motion/flow between the two devices 32 and 34 to generate certain patterns that would not be possible with a single device. For example, although the leading and trailing devices 32 and 34 are shown to be rotating in the same direction (here a clockwise direction), it should be understood that the devices 32 and 34 may be rotated in a counter-clockwise direction. Or the leading and trailing devices 32 and 34 may be rotated in opposite directions. That is, at least one of the leading and trailing devices 32 and 34 may be rotated in a clockwise direction and the other of the leading and trailing devices 32 and 34 may be rotated in a counter-clockwise direction. Accordingly, the flow of plasticized material 35 of the substrates 12 and 14 can be tailored according to a specific application.
Moreover, although the leading and trailing devices 32 and 34 are shown in line with one another, the present teachings should not be limited thereto. That is, the trailing device 34 can be offset from the leading device 32 such that the trailing device 34 travels along an axis that runs parallel to an axis that is concentric with a center of the leading device in the weld direction on which the leading device 32 travels. Further, although preferable, the trailing device 34 does not have to travel behind the leading device 32. In this regard, the trailing device 34 may travel side-by-side with the leading device 32 without departing from the spirit and scope of the present teachings.
Also, more than two devices may be used. Referring to
In another variation, referring to
In another embodiment of the present teachings, a single friction stir welding device 42 having a pin 44 with a non-axisymmetric cut as illustrated in
The non-axisymmetric pin 42 may also be used in both the spot welding and linear stitch welding methods described above. The non-axisymmetric cuts 46 and 48 primarily bring two benefits. First, the cuts 46 and 48 greatly reduce a clogging problem by providing more outlets for the thread grooves 52 and enable a self-cleaning action to these grooves 52 due to larger friction force on the pin surface. Secondly, the non-axisymmetric cuts 46 and 48 provide a larger sideways pushing action, which is desired for generating a locking structure in both the cone stir scenario and the stitch welding scenario, addressed above. Additionally, it has been determined that a partial-cut 46 of the pin provides good performance in the cone stir application and a full cut 46 of the pin provides good performance in the linear stitch welding applications, although the present teachings should not be limited to these scenarios.
For spot welding, the non-axisymmetric cuts 46 and 48 are employed to generate a force for pushing material sideways at the bottom part of the weld when the pin 42 rotates. The sideways movement of the material is constrained by the pin shoulder 16 and the lateral non-deformed material (i.e., non-plasticized) so that the material changes deformation direction and moves upward as shown by the arrows in
Another pin design that may be used in conjunction with the present teachings is an opposed thread pin 54. This pin 54 is particularly advantageous when joining a plurality of sheets together. The pin 54, as shown in
It should be understood that the motion of the material during the friction stir welding processes described above is important to providing a solid inter-lock between the substrates 12 and 14 to be joined. Accordingly, the present teachings provide for a spot welding method where the device 10 is tilted and moved through a plurality of points that make a conical shape 22 and 26; a linear stitch welding method where a plurality of pins 32 and 34 are used to manipulate the flow of the plasticized material 35; a non-axisymmetric pin 42 that assists in pushing material in predetermined directions; and a dual-threaded pin 54 with opposing threads 56 and 58. Yet another way to manipulate the flow of material in predetermined directions is to use an anvil 68 with a protruding annular ring 70.
Referring to
Lastly, the present teachings provide a friction stir-based welding method that can create a patch-like joined area by sweeping a friction stir welding device 10 through a single or multiple spiral pattern 74 and 76 that enables formation of the interlocks 28 that are hook-shaped (i.e., the interlocks 28 shown in
It should be understood that the device 10 may have an orthogonal orientation to the substrates 12 and 14 when following the spiral patterns 74 and 76. Notwithstanding, the device 10 may be tilted in any direction to assist in following the spiral patterns 74 and 76 or to sufficiently commingle the materials of the substrates 12 and 14 to form the interlocks 28. Further, although this embodiment has been described using the schematic friction stir welding device 10 shown in
Further, although the above method describes sweeping the device 10 through a first spiral pattern 74 and then a second spiral pattern 76 to form the interlocks 28, the present teachings should not be limited thereto. That is, the interlocks 28 may be formed simply by using the single spiral pattern 74 where the device 10 is engaged to the substrates 12 and 14 at the origin and swept along the spiral pattern 74 away from the origin. Moreover, the interlocks 28 may be formed simply by using the single spiral pattern 76. In this regard, the device 10 is engaged to the substrates 12 and 14 at a point away from the origin and then swept through the spiral pattern 76 to return to the origin.
Another pattern that is contemplated is that the device 10 is engaged to the substrates 12 and 14 at a point away from the origin, swept through a circular pattern about the origin, and then spirally swept from the circular pattern towards the origin. Regardless of the pattern chosen, it should be understood that substrates 12 and 14 are sufficiently plasticized in manner that the mechanical interlocking structure 28 is formed between the substrates 12 and 14 to provide a robust joint.
The description of the present teachings is merely exemplary in nature and, thus, variations that do not depart from the gist of the present teachings are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the present teachings.
