Patent Application
20210146471
The invention relates to manufacturing, and more specifically methods of joining and welding parts.
Manufacturing encompasses a wide variety of techniques to fabricate and join parts. Welding is one family of techniques used to join parts, involving the application of heat to melt or otherwise plasticize and join parts, which are often referred to as workpieces. Fusion-based welding techniques rely on a heat source to bond workpieces by melting an interface of the workpieces or in some cases by melting a filler material. Solid-state welding techniques rely on a non-consumable tool to stir and plasticize workpiece materials to thereby bond workpieces.
In one solid-state welding technique known as friction stir welding (FSW), frictional heat is generated by moving a rotating non-consumable tool along an interface between workpieces to thereby plasticize and join the workpieces. A related technique referred to as friction stir spot welding (FSSW) employs a non-consumable tool to join workpieces arranged in a lap joint configuration through a combination of frictional heat and pressure. The non-consumable tool is plunged into the workpieces to a certain depth, and after a period, the tool is retracted from the workpiece, leaving a joint that bonds the workpieces. In FSSW, no lateral motion occurs; rather, the non-consumable tool is vertically displaced. This process forms a keyhole in the joint, however, which has adverse effects on the mechanical performance of the joint.
Other manufacturing methods employ fasteners such as rivets to form joints. A typical implementation of riveting involves inserting the tail of a rivet into an aperture and deforming the tail by applying force at the opposing head of the rivet. Deformation of the tail causes the tail to expand within the aperture, thereby creating a rivet joint. For example, a hammer or riveting machine can be used to deform the tail. Other methods employ fasteners in the form of bolts. A bolt restrains unthreaded parts between the head of the bolt and a nut threaded at an opposing end via a thread on the external surface of the bolt. Rivets and bolts add weight to the device or system in which they are implemented, however. When implemented in a vehicle, rivets and bolts decrease the fuel efficiency of the vehicle by virtue of such added weight. Further, rivets and bolts can be prone to corrosion, potentially prompting the use of coatings configured to prevent corrosion.
Thus, in view of the above, challenges exist in joining parts using current welding and joining techniques.
To address the above issues, according to one aspect of the present disclosure, a method of joining workpieces is provided. In this aspect, the method comprises positioning a workpiece assembly relative to a spindle of an additive friction stir deposition (AFSD) machine, the workpiece assembly comprising a first workpiece and a second workpiece, and clamping the first workpiece to the second workpiece. The method further comprises depositing, via at least rotation of the spindle, feedstock material from the AFSD machine into an aperture extending through one or both of the first workpiece and the second workpiece, the feedstock material deposited into the aperture forming a weld nugget that joins the first workpiece to the second workpiece.
Another aspect of the present disclosure relates to an apparatus. In this aspect, the apparatus comprises a clamp configured to restrain a first workpiece against a second workpiece. The apparatus further comprises an additive friction stir deposition (AFSD) machine comprising a spindle, the AFSD machine configured to deposit, via at least rotation of the spindle, feedstock material into an aperture extending through one or both of the first workpiece and the second workpiece, the feedstock material deposited into the aperture forming a weld nugget that joins the first workpiece to the second workpiece.
Another aspect of the present disclosure relates to another apparatus. In this aspect, the apparatus comprises a clamp configured to restrain a first workpiece against a second workpiece to form a workpiece assembly, the clamp comprising a machine-side element contacting the first workpiece and an opposite-side element contacting the second workpiece. The apparatus further comprises an additive friction stir deposition (AFSD) machine comprising a spindle, the AFSD machine configured to deposit, via at least rotation of the spindle, feedstock material into a preformed aperture extending through one or both of the first workpiece and the second workpiece of the workpiece assembly, the feedstock material deposited into the aperture forming a lap joint between the first workpiece and the second workpiece.
The features, functions, and advantages that have been discussed can be achieved independently in various embodiments or can be combined in yet other embodiments, further details of which can be seen with reference to the following description and drawings.
In view of the considerations discussed above, methods and apparatuses are provided that relate to joining workpieces via additive friction stir deposition (AFSD). AFSD employs a non-consumable tool to deposit material onto a substrate or previously formed layer. In this process, a consumable feedstock material is plasticized by heat generated from frictional stirring between a rotating spindle of an AFSD machine holding the feedstock material and the substrate/layer. Workpieces are joined via spot welds formed by depositing plasticized feedstock material from the AFSD machine into an aperture extending through one or more of the workpieces. The plasticized feedstock material deposited into the aperture forms a weld nugget in the aperture that joins the workpieces. Further, a clamp restrains the workpieces together and confines deposition to substantially within the workpieces, thereby maintaining stable positioning of the workpieces and controlling the flow of deposited feedstock. The disclosed approaches enable joint formation and workpiece bonding without the presence of keyholes that adversely affect mechanical joint performance.
To deposit feedstock material into aperture 104, a feedstock bar 112 is pushed through a spindle 114 placed in contact with first workpiece 108A. Frictional heating generated by a combination of downward force imparted to feedstock bar 112 (for example, by a vertical actuator), and rotation of spindle 114 against first workpiece 108A, plasticizes feedstock bar 112, thereby creating softened feedstock material. Then, the softened feedstock material is deposited into aperture 104 to form a weld nugget in aperture 104 that bonds first and second workpieces 108A and 108B together. Feedstock bar 112 can assume any suitable form, including solid and powder forms.
Apparatus 100 includes a clamp 118 configured to restrain first workpiece 108A against second workpiece 108B. Clamp 118 comprises a machine-side element 119 configured to contact and apply pressure to first workpiece 108A. In one exemplary implementation, machine-side element 119 may include a cylinder 120 at least partially surrounding spindle 114, where cylinder 120 is configured to contact and apply pressure to first workpiece 108A. In other implementations, machine-side element 119 may include other component(s) with any suitable geometry to contact and apply pressure to first workpiece 108A. For example, in another implementation, machine-side element 119 may include a rectangular component having a cylindrical hole configured to at least partially surrounds spindle 114 and apply pressure to first workpiece 108A. In yet another implementation, a separate device that does not surround spindle 114 may be used to contact and apply pressure to first workpiece 108A.
Clamp 118 comprises an opposite-side element 121 configured to contact and apply pressure to second workpiece 108B. In one exemplary implementation, opposite-side element 121 may be a backing surface that restrains workpiece assembly 106. For example, opposite-side element 121 may be a static backing surface fixed to a surrounding environment. In another exemplary implementation, opposite-side element 121 may include an anvil 122 configured to contact and apply pressure to second workpiece 108B. Opposite-side element 121 may be removable or non-removable relative to workpiece assembly 106. For example, in an implementation of joining a skin to a bulkhead, the opposite-side element 121 may be the bulkhead. In this implementation, the opposite-side element 121 would become a part of the structure after the joining process and will not be removed afterward. In another exemplary implementation, opposite-side element 121 may be removable relative to workpiece assembly 106, either by moving opposite-side element 121 away from workpiece assembly 106 or by moving workpiece assembly 106 away from opposite-side element 121.
Machine-side element 119 and opposite-side element 121 work together to apply force in substantially opposite directions to thereby restrain first and second workpieces 108A and 108B against each other. In this way, desired positioning of workpiece assembly 106 relative to AFSD machine 102, and particularly substantial axial alignment between aperture 104 and spindle 114, is maintained as spindle 114 is stirred against first workpiece 108A. Accordingly, rotation and distortion of workpiece assembly 106 due to shearing forces that might otherwise be imparted by rotation of spindle 114 can be averted.
Clamp 118 is configured to confine deposition of feedstock material from spindle 114 to substantially within workpiece assembly 106. To this end, machine-side element 119 can be placed in contact with spindle 114 and/or first workpiece 108A during feedstock deposition, such that deposited feedstock material is confined to substantially within an upper surface 124 of first workpiece 108A without protruding outside of upper surface 124. Contact between machine-side element 119 and spindle 114 can take any suitable form. For example, machine-side element 119 can be in direct contact with spindle 114, or in indirect contact with intermediate component(s) between machine-side element 119 and spindle 114, such as a lubricant and/or bearing(s). Where machine-side element 119 is in direct contact with spindle 114, one or both of the facing contact surfaces of machine-side element 119 and spindle 114 can be configured with material and/or geometric properties that minimize frictional losses due to relative motion. Where machine-side element 119 is in indirect contact with spindle 114 and is variably positioned relative to spindle 114, machine-side element 119 can be specifically positioned during deposition to confine deposited feedstock material to substantially within aperture 104 of workpiece assembly 106.
As alluded to above, aperture 104 can extend through both first and second workpieces 108A and 108B or extend through first workpiece 108A only. In particular, aperture 104 may extend from upper surface 124 of first workpiece 108A to a lower surface 126 of second workpiece 108B. In such examples, opposite-side element 121 confines deposition of feedstock material to substantially within workpiece assembly 106 by abutting second workpiece 108B and blocking the spread of deposited feedstock beyond aperture 104 out of lower surface 126.
Any suitable mechanism can be used to position machine-side element 119 and opposite-side element 121. As examples,
Prior to initiating feedstock deposition, machine-side element 119 is placed into contact with first workpiece 202A, and opposite-side element 121 is placed into contact with second workpiece 202B. For example, machine-side element 119 can be placed into contact with first workpiece 202A via upper connection arms 128, and opposite-side element 121 can be placed into contact with second workpiece 202B via lower connection arm 130. Together, machine-side element 119 and opposite-side element 121 restrain first workpiece 202A and second workpiece 202B to maintain stable positioning of workpiece 204 and substantial axial alignment of spindle 114 with aperture 200 during later rotation of spindle 114 against first workpiece 202A, as described above. At this stage, spindle 114, which holds a feedstock bar 208 therein, is spaced away from workpiece assembly 204 and aperture 200.
Following the stage depicted in
Following the stage depicted in
As shown in
In one exemplary implementation, the diameter or width of aperture 200 may be greater than the diameter or width of feedstock bar 208, enabling feedstock bar 208 to make contact with second workpiece 202B when inserted into aperture 200. However, in other implementations, the diameter or width of aperture 200 may be less than the diameter or width of feedstock bar 208, enabling feedstock bar 208 to make contact with first workpiece 202A, with plasticized feedstock derived from feedstock bar 208 making contact with second workpiece 202B, rather than feedstock bar 208 itself achieving such contact.
As plasticized feedstock material from feedstock bar 208 is deposited into aperture 200, a mechanical and metallurgical bond is formed among the deposited feedstock material, first workpiece 202A, and second workpiece 202B. These bonded components include the deposited feedstock material with any portions of workpiece assembly 204 that are plasticized as spindle 114 and feedstock bar 208 are rotated, as described above. The bonded components form a weld nugget 210 that joins first workpiece 202A with second workpiece 202B, as shown in
After depositing a desired portion of feedstock material, feedstock deposition and formation of weld nugget 210 is ceased. For example, feedback deposition could be ceased by disabling downward actuation of feedstock bar 208 and/or rotation of spindle 114. Then, machine-side element 119 and opposite-side element 121 are removed from contact with workpiece assembly 204 after a predetermined cooling period. As described above, the predetermined cooling period can be selected such that weld nugget 210 achieves a desired degree of cooling and/or hardening, providing a desired degree of bonding between first and second workpieces 204A and 204B without undesired flow of weld nugget 210. After removing machine-side element 119 and opposite-side element 121 from contact with workpiece assembly 204, workpiece assembly 204 is exposed, and can be removed for further processing.
At the stage depicted in
Following the stage depicted in
At 402, a workpiece assembly is positioned relative to a spindle of an AFSD machine (for example, spindle 114 of AFSD machine 102). The workpiece assembly comprises a first workpiece (for example, first workpiece 202A) and a second workpiece (for example, second workpiece 202B).
At 404, a first workpiece is clamped to the second workpiece. Clamping the first workpiece to the second workpiece may include, at 406, contacting the first workpiece with a machine-side element (for example, machine-side element 119). Contacting the first workpiece with a machine-side element may include, at 408, contacting the first workpiece with a cylinder (for example, cylinder 120) at least partially surrounding the spindle. Clamping the first workpiece to the second workpiece may include, at 410, contacting the second workpiece with an opposite-side element (for example, opposite-side element 121). Contacting the second workpiece with an opposite-side element may include, at 412, contacting the second workpiece with an anvil (for example, anvil 122).
At 414, feedstock material is deposited, via at least rotation of the spindle, from the AFSD machine into an aperture (for example, aperture 200 or aperture 300) extending through one or both of the first workpiece and the second workpiece. The feedstock material deposited into the aperture forms a weld nugget (for example, weld nugget 210) that joins the first workpiece to the second workpiece.
At 416, deposition of the feedstock material is confined to substantially within the first workpiece and the second workpiece. Where the aperture extends through the first workpiece and not the second workpiece, feedstock deposition could be confined by placing the machine-side element in contact with the first workpiece during deposition. Where the aperture extends through both the first and second workpieces, feedstock deposition could be confined by placing the machine-side element in contact with the first workpiece during deposition, and by backing the second workpiece with the opposite-side element during deposition.
Method 400 may include alternative or additional steps not illustrated in
The approaches described herein provide spot welding and the formation of lap joints without the presence of keyholes using consumable materials from an AFSD machine. As such, degraded static and fatigue joint performance associated with keyholes is averted. Further, the disclosed approaches may provide a desirable alternative where other techniques, such as resistance welding, riveting, and fastening, are employed. In some examples, deposited feedstock material that forms joints as described herein may have a density less than or equal to the density of the workpieces the deposited feedstock joins. In such examples, the disclosed approaches may provide joints with savings in weight, for example in contrast to other welding techniques that use a filler material having a higher density than the workpieces that are joined using the filler material. Significant weight savings may be achieved in aerospace applications where hundreds or thousands of joints are typical, and where the use of higher density materials penalizes fuel economy.
The disclosed approaches may be applied to any suitable type of workpiece material, including but not limited to titanium, aluminum, and magnesium alloys, as examples. The solid-state nature of the disclosed techniques may be desirable in applications where materials susceptible to hot cracking are used, such as 7000 series aluminum (e.g., 7050, 7075), and/or where materials not amenable to welding via fusion-based techniques are used, such as magnesium alloys.
The present disclosure includes all novel and non-obvious combinations and subcombinations of the various features and techniques disclosed herein. The various features and techniques disclosed herein are not necessarily required of all examples of the present disclosure. Furthermore, the various features and techniques disclosed herein may define patentable subject matter apart from the disclosed examples and may find utility in other implementations not expressly disclosed herein.
