Abstract:
A method of producing a welded assembly from a first metal part and a second metal part includes bringing the first metal part and the second metal part into contact with one another at a joint region while providing a flash ring separator adjacent the joint region configured to intercept and separate flash. After heating the joint region, the first and second metal parts are forced together to join the first metal part to the second metal part, extruding metal flash from the joint region. The extruded flash impinges on the flash ring separator, forming a flash ring having at least one indentation. During subsequent machining of the welded assembly to remove the flash ring, the flash ring may fragment at the indentation, so that it does not cause damage by becoming hung around the assembly.

Description:
TECHNICAL FIELD 
     This patent disclosure relates generally to the friction-welding of metal components and, more particularly to a system for reducing potential for damage caused by flash rings during turning of welded parts. 
     BACKGROUND 
     In the fabrication of metal components, it is often necessary to join two previously produced pieces together. This may be the case, for example, where one part is formed by milling while the other is formed by forging. It also occurs when the two parts have different finishes, such as one that is nitride or bead-blasted and one that is chromed. Whatever the case, when a permanent joint between metal parts is needed, welding is often employed. In general, a welded joint tends to be stronger and more resilient that joints made by mechanical fasteners such as screws, bolts, or rivets. 
     Although many welding techniques have been developed and used throughout the years, friction welding fulfills a unique role. Friction welding is solid-state welding process that induces plasticity in the metals being joined via heat generated by mechanical friction between the pieces. In general, friction welding is accomplished by interfacing a spinning component to a stationary one to generate heat at the interface, and then forcing the pieces together when plasticity occurs in the parts. This fuses the materials. Although friction welding may be viewed as a form of forging by some, the term “welding” herein is used to denote a process by which two metals are permanently joined in a process wherein material at the joint is at sufficient temperature and pressure to produce metal flash at the joint. 
     As will be appreciated, friction welding provides numerous benefits. Total joining times as low as a few seconds make friction welding a time-efficient technique. Moreover, the use of friction rather than direct heat means that very little of the metal volume beyond the weld interface is affected, and the fact that little or no full melting occurs means that grain growth and other melt-related issues can be largely avoided. Yet another advantage of friction welding is that it can be used to weld materials of very different types, where a wide difference in melting points precludes the use of traditional welding techniques. Examples of welds where friction welding is required include the welding of aluminum to high-strength steel, steel to copper, aluminum alloy to high-nickel-alloy materials and others. 
     During friction welding, some amount of plastic metal is forced out of the joint during the final forcing phase to create “flash,” which is later removed. While the production of flash may beneficially remove surface impurities from the joint volume itself, the hardened flash can also cause problems in the final welded product. During spin welding where the stationary part is generally cylindrical, the flash forms a flash ring at or just slightly displaced from the level of the joint. Once the weld itself is complete, the welded item is turned as a whole, e.g., in a lathe, and a cutting tool is progressively applied to slowly remove the spinning flash. 
     Unfortunately, the flash ring sometimes breaks from the part during turning, but remains as a ragged ring of metal hung on the spinning part. When this happens, the flash ring can quickly scour the surface of the spinning part and destroy any precision finish that may have existed there. This is especially troublesome and costly when the part is chromed or otherwise finely finished, and in some cases may result in the need to scrap the entire welded assembly. Thus, while friction welding has many benefits, the occurrence of loose flash rings in this manner has the potential to significantly counteract the efficiency and economy of materials that might otherwise be enjoyed via friction welding. 
     It will be appreciated that this background description has been created by the inventors to aid the reader, and is not to be taken as a reference to prior art nor as an indication that any of the indicated problems were themselves appreciated in the art. 
     SUMMARY 
     In an embodiment, a method is provided for producing a single welded assembly from a first metal part and a second metal part. The method includes bringing the first metal part and the second metal part into contact with one another at a joint region and providing a flash ring separator adjacent the joint region configured to intercept and separate flash impinging upon it. The metal in the joint region is heated to a temperature such that the metal becomes plastic, at which point the first and second metal parts are forced together at the joint region to join the first metal part to the second metal part. In this process, metal flash is extruded from the joint region to impinge on the flash ring separator, forming a flash ring having at least one indentation therein formed by the flash ring separator. 
     In another embodiment, a method is provided for welding a first metal part to a second metal part, including heating the joint region between the parts to a point of plasticity and forcing the first metal part and the second metal part together at the joint region, thus joining the first metal part to the second metal part and extruding an annulus of metal flash from the joint region. While extruding the annulus of metal flash from the joint region, the flash is impeded in at least one location to form at least one indentation in the annulus of metal flash. 
     In yet another embodiment, a flash ring separator is provided. The flash ring separator has a body formed of a heat-resistant material. The body includes a top portion having an extending edge for contacting and separating extruding metal flash during welding as well as a bottom portion configured to mate with and attach to a rod clamp for holding a rod during welding of the rod. 
     Further and alternative aspects and features of the disclosed principles will be appreciated from the following detailed description and the accompanying drawings, of which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a friction weld setup prior to spinning and forcing within which an embodiment of the disclosed principles may be implemented; 
         FIG. 2  is cross-sectional view of a typical friction weld between a non-rotating rod and a spun eye showing a typical flash pattern; 
         FIG. 3  is a perspective view of a stationary clamp including a mounted flash ring separator for preventing flash rings in accordance with an embodiment; 
         FIG. 4A  is a side view of a flash ring separator such as that shown in  FIG. 3 , taken along axis A, in accordance with an embodiment; 
         FIG. 4B  is a side view of a flash ring separator such as that shown in  FIG. 3 , taken along axis B, in accordance with an embodiment; 
         FIG. 5  is a perspective view of a friction welded rod and rod end showing the weld flash produced by the welding process as well as the scoring produced by the flash ring separator; 
         FIG. 6  is a perspective view of an alternative flash ring separator for creating frangible flash rings in accordance with an embodiment; and 
         FIGS. 7A-7D  are side views of a pair of alternatively configured flash ring separators in accordance with alternative embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure relates to welding of metal components, and specifically to friction spin welding (herein referred to as friction welding). As noted above, friction welding often creates a flash ring made up of hardened metal extruded from the joint, and the flash ring often needs to be removed in order to create a finished part. However, the traditional use of a lathe to turn down the flash ring can result in the flash ring breaking loose while still remaining hung about the spinning part. When this happens, the loose flash ring may scour the part, ruining its finish and potentially ruining the entire part. 
     The described system, in general terms, reduces the occurrence of this problem by providing a mechanism that forms the flash in a frangible manner. This allows for the continued use of friction welding and the continued use of a lathe to turn down the flash, but without allowing a flash ring that could break loose as an annular unit and remain suspended around the spinning part. 
       FIG. 1  is a simplified cross-sectional view of exemplary friction weld components used to create a finished hydraulic rod, i.e., a cylindrical rod  10  and a rod end  11  with a straight bearing  12  and a cylindrical shank  13  of generally the same diameter as the cylindrical rod  10 . In the illustrated configuration, the rod end  11  is being spun about an axis A while the cylindrical rod  10  is held stationary adjacent the spinning rod end  11 . As the cylindrical shank  13  of the rod end  11  spins about the axis A against the end of the cylindrical rod  10 , the interface region becomes heated due to friction. 
     As shown in  FIG. 2 , once the metal at the joint region  14  is heated sufficiently to become plastic, the spinning of the rod end  11  about the axis A is stopped and the cylindrical rod  10  is forced into the rod end  11  laterally along axis A. The forcing process essentially forges the pieces together, but in the process, a flash ring  15  around the joint is created. In general, the flash ring  15  curls away from the spun part, in this case the rod end  11 , and toward the forced part, which in this case is the cylindrical rod  10 . 
     Although in theory it is possible to leave the flash ring  15  in place without affecting the joint, it is often a practical necessity that the flash ring  15  be removed to allow installation and/or use of the welded assembly. However, as can be seen in  FIG. 2 , the flash ring  15  often contains an annular hollow  16  due to the manner in which the extruded flash curls during the welding process. If the welded assembly is turned on a lathe to remove the flash ring  15 , there is a possibility, as often happens, that the lower annular portion  17  of the flash ring  15  will break loose from the joint as an annular unit when the cutting tool reaches the annular hollow  16 . As discussed above, the loose flash ring or portion thereof hanging suspended from the spinning assembly often causes severe damage. 
     To prevent such damage, a flash ring separator is provided for use in scoring the flash ring  15  during the weld. In this way, during subsequent turning on a lathe, the flash ring  15  will fragment at one or more points on its circumference rather form a singular annular piece suspended from, and potentially damaging, the spinning part. An exemplary flash ring separator  20  is shown in  FIG. 3 . 
     In particular,  FIG. 3  is a perspective view of a rod clamp comprising a first rod clamp half  19  and a mating second rod clamp half  21  used together to clamp the cylindrical rod  10  stationary while the rod end  11  is spun, and then to force the cylindrical rod  10  into the rod end  11  once a point of plasticity is reached. In an embodiment, each rod clamp half  19 ,  21  has an attached rod contact portion, not visible in this view, which actually contacts the rod. The rod contact portions may include or be constructed of a fiber or other non-marring heat-resistant material, not shown, to avoid scratching or deforming the part being held. 
     The flash ring separator  20  is shown affixed to the first rod clamp half  19 , and a matching separator  22  may optionally be fixed in a diametrically opposed position (or other position if desired) on the second rod clamp half  21 . Alternatively, a single flash ring separator  20  may be used. Although the top edge  23  of the flash ring separator  20  is pointed upward along the rod axis rather than inward toward the joint, it will be appreciated that when flash forms as illustrated in  FIG. 2 , it initially emerges perpendicular to the rod axis, but then curls downward along the rod. Thus, in the illustrated orientation on the rod clamp half  19 , the flash ring separator  20  serves to impinge the flash from beneath as it curls away from the spun part (now stationary), scoring the flash as it forms and preventing an unbroken ring from forming. 
     The flash ring separator  20  may be formed as an integral part of the first rod clamp half  19 . However, in view of the heat-induced wear to which the flash ring separator  20  may be subjected, the flash ring separator  20  is included as a separate removable component in the illustrated embodiment. In this embodiment, a means of attachment of the flash ring separator  20  to the first rod clamp half  19  is provided. In the illustrated embodiment, a set screw may be inserted into a suitable threaded opening  24  in the first rod clamp half  19  to secure a base portion, not shown in this figure, of the flash ring separator  20 . In the event that two separators are used, a similar arrangement may be used to retain the second flash ring separator  22 . The base and other features and configurations of the illustrated flash ring separator  20  according to an embodiment of the described principles will be discussed in greater detail with respect to  FIG. 4 . 
     In particular,  FIGS. 4A and 4B  are two different enlarged views of the flash ring separator  20 . Although  FIGS. 4A and 4B  are described with reference to flash ring separator  20  and first rod clamp half  19 , it will be appreciated that the second flash ring separator  22  may have generally the same features.  FIG. 4A  is a side view of the flash ring separator  20  taken along axis A of  FIG. 3 , while  FIG. 4B  is a side view of the flash ring separator  20  taken along axis B of  FIG. 3 . The illustrated flash ring separator  20  includes a base portion  25  for insertion into the first rod clamp half  19 , with the base portion  25  having an indented flat  26  for engaging a set screw (not shown) such as may be threaded into the threaded opening  24  in the first rod clamp half  19  to secure the base portion  25 . 
     The flash ring separator  20  includes a flat underside  27  for resting against the adjacent surface of the first rod clamp half  19  when the flash ring separator  20  is mounted. In this way, the flash ring separator  20  is held in place against the first rod clamp half  19  during use of the clamp, e.g., during friction welding. 
     The flash ring separator  20  further includes a generally wedge-shaped upper portion  28  leading to a curved ramp portion  29 . It is this upper portion  28  upon which the hot flash material first impinges. Although the upper portion  28  may be more or less sharp, i.e., come to a more acute or less acute edge, the flash ring separator  20  works by separation of flow and not by cutting. Moreover, the inventors have found that broader edges, as opposed to sharper edges, are better able to resist heat damage. Thus, separators having an upper portion  28  that is either rounded or faceted from a plurality of flats as in the illustrated structure may perform better than devices that come to a cutting edge, e.g., a single linear edge of 45 degrees or less. 
     As such, a flash ring separator  20  having a relatively blunt upper portion  28  has been found to be most effective. Although the illustrated upper portion  28  is made of multiple flats, it will be appreciated that the exact form of the upper portion  28  is not important, and a rounded or pointed upper portion  28  may instead be used. Other non-limiting examples of alternative flash ring separator shapes will be discussed later after a discussion of how the illustrated flash ring separator  20  operates in principle. 
     The manner in which the flash ring separator  20  operates during welding may be better appreciated from the perspective view of a welded rod as shown in  FIG. 5 . In particular,  FIG. 5  shows a perspective view of a welded rod assembly  30  after friction welding but prior to finishing to remove the flash ring  31 . The welded rod assembly  30  includes a rod end  32  and a rod  33  joined at a weld joint  34 . The weld joint  34  is surrounded by flash ring  31  formed when the weld joint  34  was made in the manner discussed above. 
     As can be seen, the flash ring  31  includes an impression or indentation  35  made during impingement of the hot flash on a flash ring separator such as that shown in  FIGS. 3 ,  4 A and  4 B. The flash ring  31  may also include a second impression or indentation, not visible in this view, if a second additional flash ring separator is used. As noted, the illustrated welded rod assembly  30  is shown after the weld is made but prior to finishing and removal of the flash ring  31 . 
     In order to finish the welded rod assembly  30 , the welded rod assembly  30  may be turned on a lathe and a cutting tool introduced against the flash ring  31 . As the cutting of the flash ring  31  proceeds, it will reach a point when the remaining portion of the flash ring  31  fragments at the indentation  35  and falls away from the welded rod assembly  30  without damaging the assembly. The point when the flash ring  31  fragments may be when the cutting tool reaches the internal cavity ( FIG. 2 ) of the flash ring  31 . After removal of the flash ring  31 , the weld joint  34  may be further smoothed and finished if needed or desired. 
     Having discussed the form and function of the flash ring separator  20  according to an embodiment, and the resulting flash structure, a number of structural and compositional options and alternatives will be discussed. The joint and extruded flash may reach substantially elevated temperatures (e.g., 1300° F.) during the welding process. Thus, a flash ring separator generally benefits from high heat tolerance. 
     One material option having suitable if marginal heat resistance characteristics is H13 tool steel. This material is resistant though not impervious to the hot weld during the bonding process. However, this material works best with a large surface area in contact with the hot flash; the larger the surface area the more the heat is spread out in order to resist melting. While H13 is capable of a high Rockwell hardness (e.g., around 47 RC for use as a flash ring separator), a flash ring separator should also have high “heat” hardness to avoid deformation during impingement by the hot flash. For example, while Titanium is resistant to temperatures up to 3000° F., it has very low heat hardness, and thus, though usable, is subject to rapid deformation. 
     In order to improve reusability and wear characteristics without increasing the surface area of the flash ring separator blade or upper portion beyond practical limits, other materials with greater heat hardness may be employed. While H13 may need to be replaced frequently, other materials such as INCONEL HX may provide greater wear resistance. This material holds heat hardness up to 2000° F. The composition of INCONEL HX is: Cr—20.5-23.0; Fe—17.0-20.0; Mo—8.0-10.0; Co—0.5-2.5; W—0.2-1.0; C—0.05-0.15; Si—1.0 (max); Mn—1.0 (max); P—0.04 (max); S—0.03 (max); remainder Ni. 
     A flash ring separator as shown in  FIGS. 4A-4B  composed of INCONEL HX was tested on 12 welds and showed little to no wear. As such, INCONEL HX is a further alternative to H13. Another alternative is H26 tool steel, which also has high heat hardness. H26 is a medium carbon, 18% tungsten hot work tool steel that retains good working hardness at welding temperatures. Its composition is C—57; W—18.00; Cr—4.00; and V—1.00. 
     Overall, although all the materials discussed above are functional in the described role for parting the flash, not all were equal in terms of longevity. In particular, among the listed options, INCONEL HX provided the best hot wear characteristics. Nonetheless, it will be appreciated that many materials could be used to form the described flash separators. 
     In addition to the material from which the flash ring separator is made, the shape of the separator also affects the operational and wear characteristics of the device. In particular, the extent to which the flash ring separator extends from the face of the rod clamp can also affect performance. Since the curved ramp portion  29  of the flash ring separator  20  ( FIGS. 4A-4B ) operates to form the flash while the wedge-shaped upper portion  28  of the flash ring separator  20  operates to groove the flash as it forms, it is desirable, though not strictly required, to engage the flash with both the curved ramp portion  29  and the wedge-shaped upper portion  28  during the welding process. Thus, although flash ring separators of one inch or greater in projection from the clamp face may be used, a projection of 0.5″ has been found to work well, providing good contact of the flash ring to both the curved ramp portion  29  and the wedge-shaped upper portion  28  or “edge.” 
     In addition to the length of the flash ring separator from the clamp face, the shape of the flash ring separator also has an effect on operation. One variable in the configuration of the flash ring separator is the direction in which the blade of the device faces. As noted above, the device shown in  FIGS. 3 ,  4 A and  4 B have edges that face upward away from the rod clamp face and along the rod axis toward the weld joint. This configuration accommodates the tendency of the flash to curl down along the rod. 
     However, the flash may be intercepted radially closer to the weld joint and/or may, in some applications, be extruded directly away from the joint without curling. Thus, a non-limiting possible alternative flash ring separator  36  is shown in  FIG. 6 . The illustrated alternative flash ring separator  36  includes a top portion  37  and base portion  38 . Unlike the previously discussed configurations, the edge  39  of the top portion  37  of the alternative flash ring separator  36  faces radially along the rod clamp face (not shown) to which the base portion  38  is mounted. In this way, the alternative flash ring separator  36  engages the extruded flash as it exits the joint radially in direction C. 
     Other non-limiting example configurations for the flash ring separator are shown in  FIGS. 7A-7D . In particular,  FIG. 7A  is a side view of an alternative ovoid flash ring separator  40  having a roughly ovoid top portion  41  for intercepting the extruded flash radially from the weld joint. The alternative ovoid flash ring separator  40  also includes a bottom portion  42  similar to the foregoing embodiments for mounting the flash ring separator  40  to the rod clamp face, e.g., via a set screw. As such, the bottom portion  42  as illustrated includes a flat  43  for engaging a set screw.  FIG. 7B  shows the same flash ring separator  40  from the side again, but rotated axially by 90°. 
       FIG. 7C  is a side view of an alternative blunt flash ring separator  44  having a top portion  45  for intercepting the extruded flash axially from the weld joint. The top portion  45  in this embodiment is of the same general shape as that shown in  FIGS. 3 ,  4 A and  4 B, but is shorter, e.g., having an extent away from the rod clamp face of about 50% relative to the device shown in  FIGS. 3 ,  4 A and  4 B. The alternative blunt flash ring separator  44  also includes a bottom portion  46  similar to the foregoing embodiments for mounting the flash ring separator  44  to the rod clamp face, e.g., via a set screw. As such, the bottom portion  46  as illustrated includes a flat  47  for engaging a set screw.  FIG. 7D  shows the same flash ring separator  44  as in  FIG. 7C , but wherein the flash ring separator  44  is rotated axially by 90°. 
     Although several alternative shapes have been shown for the flash ring separator device herein, it will be appreciated that the illustrated shapes are only examples, and that other suitable shapes, sizes, numbers and/or arrangements of flash ring separators may be used to notch the flash ring in one or more places to create a frangible flash ring. Moreover, a flash ring separator used in a given installation need not match all other flash ring separators used in the same installation. Further, although the flash ring separator is illustrated as being a separable component so that it may be replaced if needed, it is also contemplated that one or more flash ring separators will be formed unitarily with the rod clamp in an embodiment. 
     INDUSTRIAL APPLICABILITY 
     The described principles are applicable to the welding of metallic parts wherein the welding operation creates a generally annular ring of unwanted flash material, an annular portion of which may become loosely detached but remain hung about the part in question. Within this context, the described devices and principles create a frangible flash ring, such that during machining of the ring, it will fragment and fall away rather simply detach as an annular unit and remain hung about the welded assembly. 
     By reducing the ability of flash rings to damage welded assemblies, the described flash ring separator reduces scrap substantially, resulting in cost savings. The flash ring separator also raises throughput not only through the reduction of scrap but also by speeding the removal of the flash ring by eliminating the need for slow and careful handling. It also eliminates the need for operator intervention in many cases, e.g., to cut a detached flash ring so that it drops away from the assembly. By making the flash ring frangible, the flash ring separator also increases tooling life by reducing the amount of machining required to remove the ring. 
     It will be appreciated that the foregoing description provides useful examples of the disclosed system and technique. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to the disclosure or examples thereof are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the scope of the disclosure more generally. All language of distinction and disparagement with respect to certain features is intended to indicate a lack of preference for the features of interest, but not to exclude such from the scope of the disclosure entirely unless otherwise specifically indicated.