Patent Publication Number: US-11648737-B2

Title: Sonotrode

Description:
PRIORITY CLAIM 
     This disclosure is a divisional of U.S. patent application Ser. No. 17/132,960 filed on Dec. 23, 2020, which is a continuation of PCT Application No. PCT/US2019/039214 filed on Jun. 26, 2019, which claims priority to U.S. Provisional Application Ser. No. 62/690,071 filed on Jun. 26, 2018, U.S. Provisional Application Nos. 62/702,411, 62/702,401 and 62/702,429 all filed on Jul. 24, 2018, all of which are incorporated by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to a sonotrode or “horn” for use in ultrasonic welding applications, for example. 
     BACKGROUND 
     In a typical ultrasonic welding application, a fixture supports a workpiece to be welded, which may comprise multiple plastic components. An ultrasonic welder typically includes a converter having a piezoelectric stack that selectively vibrates in response to power from a generator. A booster may be used at a working end of the converter to modify the amplitude of the vibrational frequency supplied by the converter. A horn is mounted to the booster opposite the converter and is used to impart vibration to the workpiece. 
     During a welding operation, the horn is advanced by a pneumatic cylinder to engage the workpiece. The pneumatic cylinder maintains a desired force on the workpiece via the horn. A controller energizes the generator for a time sufficient to weld the components to one another. The horn is retracted once the weld is complete. 
     Typical horn materials include steel, aluminum and titanium. The horns are constructed from extruded bar stock that is cut to length to provide blanks, which are then CNC lathe machined, for example, to a desired profile that corresponds to a desired design frequency. A computer software suite is often used to design a horn profile that will meet the desired design frequency, which may be between 15 kHz and 40 kHz, but the initial iteration of the machined horn is often not at the desired frequency. 
     One common plastic welding horn profile includes a narrow cylindrical shaft connected to a cylindrical base by an annular fillet. The base includes a threaded hole that is used to secure the horn to the booster, if one is used, or to the converter. A terminal end of the shaft is polished and includes a shape chosen for the type of welding operation. All external surfaces of the horn are machined by a cutting operation. 
     The converter, booster and horn are tuned for the overall effectiveness and efficiency in ultrasonic welding. The sonotrode has multiple modes that each have a resonant frequency. For ultrasonic welding, the sonotrode is designed to resonate at a longitudinal mode, which induces a particular displacement at the sonotrode tip used to generate heat and weld the workpiece. Typical machined horns are not repeatable part-to-part such that each horn must be checked to determine if it is at the desired resonant frequency at the longitudinal mode, otherwise a “near neighbor”, such as a twisting or a bending mode, may reach resonance. This results in the horn failing to achieve a sufficient displacement in the longitudinal direction, which can compromise the weld or damage the sonotrode over time. Accordingly, it is common to tune each individual horn after machining to ensure resonance at the desired longitudinal mode. Each horn is excited post-machining to determine its vibrational characteristics. The horn&#39;s profile is then further machined to increase or decrease its vibrational frequency to match the desired design frequency for the given welding application. 
     SUMMARY 
     In one exemplary embodiment, a sonotrode includes multiple layers of a material melted to one another to form a structure. The structure provides a base that has an attachment feature that is configured to operatively secure to an ultrasonic converter. The structure includes a shaft that extends from the base to a terminal end that provides a working surface that is configured to selectively engage a workpiece. The structure has at least one shaft that includes a first shaft that extends from the base to a first terminal end that provides a first working surface that is configured to selectively engage a workpiece. The first shaft is integrally formed with the base from the multiple layers to provide an unbroken, monolithic construction. 
     In a further embodiment of the above, the structure includes an outer surface that is provided by a substantially unmachined surface. 
     In a further embodiment of any of the above, the unmachined surface is at least 50% of an area of the outer surface. 
     In a further embodiment of any of the above, the shaft and base are interconnected by an integral fillet, and the fillet is provided by the unmachined surface. 
     In a further embodiment of any of the above, the base and the first shaft is constructed of the same material. 
     In a further embodiment of any of the above, an internal cavity is substantially enclosed by the multiple layers and is arranged interiorly of an exterior surface of the structure. 
     In a further embodiment of any of the above, a cooling passage is provided within the structure and formed in situ within the multiple layers. 
     In a further embodiment of any of the above, the cooling passage includes multiple passageways that intersect one another at non-perpendicular junctions. 
     In a further embodiment of any of the above, the cooling passage is curved and provides an extrados and an intrados at one of the non-perpendicular junctions. 
     In a further embodiment of any of the above, the structure has a density that varies across at least portions of the multiple layers by greater than 0.1%. 
     In a further embodiment of any of the above, the attachment feature is one of a stud and a threaded hole. The attachment feature has an unmachined external surface that is formed by the multiple layers. 
     In a further embodiment of any of the above, the structure extends in a longitudinal direction from the base to the working surface. The attachment feature is provided at a mounting face of the base. The mounting face has a first central point. The working surface has a second central point. The first and second central points are offset relative to one another with respect to the longitudinal direction. 
     In a further embodiment of any of the above, the structure includes an outer surface, and the structure has a fluid attachment that is provided at the outer surface by the multiple layers. The fluid attachment is in fluid communication with an internal fluid passage. 
     In a further embodiment of any of the above, the fluid attachment is a barb that is configured to connect to a fluid line. 
     In a further embodiment of any of the above, the cooling passage includes a venturi that has first and second tapered portions joined at a throat. 
     In a further embodiment of any of the above, the venturi impinges upon a protrusion at a junction between outlet portions of the cooling passage. The outlet portions are provided in the neck near the terminal end. 
     In a further embodiment of any of the above, the cooling passage includes an annular passage that is fluidly connected to multiple secondary passages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure can be further understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
         FIG.  1    schematically illustrates a common ultrasonic welder. 
         FIG.  2    depicts an example machine used to manufacture the disclosed sonotrode. 
         FIG.  3 A  is an isometric view of one example sonotrode. 
         FIG.  3 B  is an isometric view of an end of the sonotrode shown in  FIG.  3 A . 
         FIG.  4    is a schematic view of multiple sonotrodes printed on a plate. 
         FIG.  5 A  schematically illustrates raw, laser sintered layers of the sonotrode. 
         FIG.  5 B  depicts the sintered layers shown in  FIG.  5 A  after media-blasting. 
         FIG.  6    is a flow chart illustrating an example method of manufacturing the disclosed sonotrode. 
         FIG.  7    is a schematic view of an ultrasonic welding machine using at least one disclosed sonotrode to weld a workpiece. 
         FIG.  8    depicts one example mother-daughter sonotrode. 
         FIG.  9    illustrates a terminal end with a waffle pattern suitable for staking operations. 
         FIG.  10    is a cross-sectional view through a sonotrode, illustrating multiple types of cavities and different length shafts. 
         FIG.  11    is a cross-section through one example sonotrode illustrating a fluid flow feature. 
         FIG.  11 A  is a partial cross-sectional view of an end of a prior art sonotrode. 
         FIG.  12 A  is a partial perspective view of a base of the sonotrode shown in  FIG.  11   . 
         FIG.  12 B  is a partial perspective view of an end of the sonotrode shown in  FIG.  11   . 
         FIG.  12 C  is an enlarged cross-sectional view of another example sonotrode end. 
         FIG.  13    is an isometric view of another example sonotrode illustrating a corkscrew cooling passage. 
         FIG.  14 A  is a partial cross-sectional view of one example cooling passage restriction. 
         FIG.  14 B  is a partial cross-sectional view of another example cooling passage restriction. 
         FIG.  15    is a perspective view illustrating a sonotrode end with porosity extending to the external surface to provide a cooling passage outlet. 
         FIG.  16    is a partial perspective view illustrating an annular cooling passage. 
         FIGS.  17 A and  17 B  depict example attachment features for a sonotrode. 
         FIG.  18    illustrates a denser region containing a nodal point to provide strengthening. 
         FIG.  19    shows an integrated fluid attachment. 
         FIG.  20    illustrates circumferentially spaced holes formed during the laser sintering process and configured to receive a tool for installation of the sonotrode. 
         FIG.  21    depicts a unitary booster and sonotrode that are produced together in the same laser sintering process. 
         FIG.  22    illustrates a sonotrode with a terminal end offset from the base. 
         FIG.  23    shows an internal cavity that has a larger diameter than the mounting face to provide a “drum effect” when excited by the generator. 
     
    
    
     The embodiments, examples and alternatives of the preceding paragraphs, the claims, or the following description and drawings, including any of their various aspects or respective individual features, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible. In many instances, like numerals (e.g., 34, 134, 234, etc.) are used to indicate like features. 
     DETAILED DESCRIPTION 
     An example ultrasonic welder  10  is shown in  FIG.  1   . The welder  10  is typically used to join multiple components of a workpiece  14  that is supported in a fixture  12 . In one example, the workpiece  14  includes plastic automotive components. It should be understood that the ultrasonic welder  10  can be used in other applications, such as packaging and food processing, for example. The disclosed sonotrode can be used with other materials. 
     A sonotrode  20  selectively engages the workpiece  14  to impart a vibration on the workpiece  14  sufficient to generate heat and melt the components to one another. To this end, the sonotrode  20  is operatively secured to an ultrasonic converter  16 , which includes piezoelectric or other elements that vibrate (e.g., at up to 50 kHz) in response to a signal from a generator  22  commanded by a controller  24 . The sonotrode  20  may be designed to be used at other frequencies, if desired. A booster  18  may be mounted between the converter  16  and the sonotrode  20  to tune the frequency provided by the converter  16  to the sonotrode  20 . The sonotrode  20  has a shaft  34  that extends from a base  32  to a terminal end  38 . A fillet  36  provides a transition between the base  32  and the shaft  34 . 
     During operation, a cylinder  26 , which may be pneumatic, advances the sonotrode  20  to engage the surface  40  of the workpiece  14  with the terminal end  38  and maintain a contact pressure. Cylinder movement may be regulated by a valve  30  that selectively controls the flow of compress air from an air source  28  to the cylinder  26  in response to a command from the controller  24 . The welder  10  can be configured in a different manner than described. 
     The sonotrode  20  is manufactured using a three dimensional printing process, such as direct metal laser sintering (DMLS). One example DMLS machine is an EOS  290 . An example DMLS machine  50  is schematically shown in  FIG.  2   . Multiple layers  54  of a material  66  are deposited onto a plate  52  in an enclosed environment  56  filled with a shielding gas  58 . As each layer  54  is laid down by a depositing element  62  onto the prior layer, a scraper or roller 68 levels the deposited layer to a desired layer thickness, for example, 20-60 μm. The scraper  68  does not provide any significant compacting, that is, the material  66  does not “stick” to itself, and is primarily used to level the layer. 
     A hopper  64  supplies the material  66  to the depositing element  62 . The material  66  is at least one of titanium (e.g., Ti 6-4), aluminum and steel, including stainless steel. In one example, the material consists of only one of titanium, aluminum and steel. The material  66  comprises spherically shaped particles of varying sizes, which enables close packing of the particles resulting in maximum density. 
     The DMLS machine  50  is provided three dimensional CAD data  72  relating to a structure  70  to be manufactured, i.e., the sonotrode  20 . The CAD data is parsed into cross-sections that correspond to the layers  54 . A computer guided laser  60  sinters the layers  54  together to provide the structure  70  layer-by-layer. In one example, the laser  60  may move at speeds up to 7 m/s. Control parameters  74 , such as laser speed and/or intensity, may be varied to achieve desired characteristics of the structure  70 , such as density. In one example, the density of the structure  70  is 99.95% of a similarly sized component of the same chemical makeup. In the example, substantially uniform density is maintained in the sonotrode  20  from the base  32  to the terminal end  38 . 
     Multiple parts, i.e., sonotrodes  20 , are manufactured on a common plate  52 , as shown in  FIG.  4   . Since the parts are laser welded to the plate  52  during one example printing process, the parts must be removed from the plate, such as by wire electrodischarge machining (EDM). 
     An example sonotrode  20  produced by a DMLS machine  50  is shown in  FIGS.  3 A- 3 B . The sonotrode  20  is constructed on the plate  52  from the base  32  to the terminal end  38  along a longitudinal direction  80 , although other build orientations may be used. The base  32 , the fillet  36  and the shaft  34  respectively extend in the longitudinal direction  80  first, second and third lengths  82 ,  84 ,  86 . The base  32  includes a generally planar mounting face  88  that has an attachment feature  90 , such as a threaded hole. The attachment feature  90  is used to secure the sonotrode  20  to the converter  16  or the booster  18 , for example. 
     The terminal end  38  provides a working surface  92  that is configured to engage the workpiece  14  during ultrasonic welding. In the example, the working surface  92  is provided by a machined surface  98 , which includes geometry adapted for the particular application. One example is a dimple  94 , or raised area, that extends from a concavity  96 , or recessed area. Such a geometry is suitable for upsetting a plastic component during welding under the pressure of the cylinder  26 . The disclosed sonotrode can be used with other materials. 
     The sonotrode  20  has an outer surface  100  that is significantly rougher than the machined surface  98 . In one example, the machined surface  98  has an average surface roughness of less than 30 Ra, for example, less than 10 Ra. As shown in  FIGS.  5 A- 5 B , the outer surface  100  has an unmachined surface  104 . The laser sintering process may result in scale  102  or undesired remnants at the periphery of the outer surface  100 ; the outer periphery circumscribes the longitudinal direction of the shaft  34 . Media blasting, such as by using glass beads or other material, can remove this scale  102  providing a smoother media-blasted surface  106 . In this disclosure, “machining” does not include media blasting; rather, “machining” is interpreted as cutting with a cutting tool carried by a cutting fixture, such as by a CNC mill or lathe or a grinding machine. Even so, the average surface roughness of the unmachined surface is greater than 150 Ra, for example, 150-450 Ra. In one example, the unmachined surface has an average surface roughness of 325 Ra+/−10% and the machined surface has an average surface roughness of 3.2 Ra+/−50%. 
     A sonotrode manufacturing method  110  is shown in  FIG.  6   . The method  110  includes the step of laser sintering layers  54  to form the sonotrode  20  according to CAD data  72 , as indicated in block  112 . The sonotrodes  20  are removed from the plate  52 , for example, by wire EDM. The sonotrode  20  may then media blasted to remove undesired remnants, as indicated at block  114 , or this step may be omitted. The working surface  92  is machined (block  116 ) while the majority of the outer surface  100  is left unmachined (block  118 ) to produce a finished sonotrode having desired tuning characteristics for the welder  10  (block  120 ). 
     It is possible that the working surface  92  need not be machined and step  116  omitted if, for example, the layers at the tip are deposited and sintered at a finer resolution, i.e., using thinner layers. That is, some layers may be, for example, 60 μm, and the layers at the tip may be 20-30 μm or less. The finer resolution will result in a smoother surface finish at the working surface  92  providing a suitable Ra for plastic welding. 
     Unlike prior methods of manufacturing sonotrodes, a substantial area of the outer surface  100  of the sonotrode  20  is provided by an unmachined surface  104 . In one example, at least 50% is unmachined, and in another example, at least 75% is unmachined. In still another example sonotrode, at least 90% of the outer surface  100  is unmachined, for example, 95% or more, but less than 100%, for example. The outer surface of the base  32 , shaft  34  and fillet  36  is left unmachined, in one embodiment. Machining of the mounting face  88  may also be omitted (i.e., left as an unmachined surface) with precise laser sintering of the layers  54 , although a machining process may be used if desired to smooth the surface after cutting the sonotrodes from the plate  52 . 
     According to the disclosed manufacturing method, the sonotrode is laser sintered with the desired tuning characteristics such that the typical machining is not needed. The desired tuning characteristics correspond to transmitting a desired frequency to the workpiece  14  via the working surface  92 . The homogeneous properties of the powdered material within a batch and batch-to-batch is quite uniform and the DMLS process is very precise such that harmonics of the end sonotrode are highly repeatable. Sonotrodes of the same part number produced on a common plate and/or plate-to-plate are within 0.75% (e.g., for approximately a 20 kHz converter) of the longitudinal mode resonant frequency of one another and of the desired design frequency for the longitudinal mode so that the individual sonotrodes need not be tuned after manufacturing. In another example, the sonotrodes are repeatable within 0.50% (e.g., for approximately a 35 kHz converter) of one another and the desired frequency, and in another example the sonotrodes are repeatable within 0.25% (e.g., for approximately a 40 kHz converter) of one another and the desired frequency. That is, the sonotrode frequency need not be checked and then machined for being out of frequency, as is commonplace with current sonotrode manufacturing practices in order to avoid resonating at undesired near neighbor modes. Said another way, no more that one machining operation is used at the terminal end to provide the initial surface finish to the working surface, nor is machining needed on unmachined surfaces at other locations on the sonotrode; additional machining of the sonotrode is not required to bring the sonotrode within the desired frequency. 
     As shown in  FIG.  7   , a typical workpiece  14 ′ may include multiple weld points that are welded simultaneously during the manufacturing operation. The workpiece  14 ′ is held in a fixture, and the sonotrodes  20 ,  20 ′ are respectively operatively mounted to converters  16 ,  16 ′. The sonotrodes are advanced and excited to weld the components to one another, as described in connection with  FIG.  1   . The performance and/or efficiency of the sonotrodes  20 ,  20 ′ may be improved by incorporating one or more internal cavities  122 ,  122 ′, which may be used for cooling, lightening or other performance enhancing effects. In one example, the sonotrodes may be lightened such that smaller converters may be used, which may significantly lower the overall cost of the welding system. 
     As shown in  FIG.  7   , some sonotrodes  20 ′ have multiple points, referred to as “mother-daughter”, such that a single sonotrode may be used to weld multiple weld points. That is, the base  232  includes multiple shafts  234  that each provide a terminal end  238  for welding. More than one attachment feature  290  may be provided on the base  232  depending upon its size. Thus, a first shaft extends from the base to a first terminal end providing a first working surface configured to selectively engage a workpiece, and a second shaft extends from the base to a second terminal end providing a second working surface configured to selectively engage the workpiece. The first and second working surfaces are spaced apart and discrete from one another. 
     As shown in  FIG.  9   , the working surface has multiple raised features providing an increased surface area as compared to a planar working surface bounded by a correspondingly sized and shaped periphery. For example, the working surface of the terminal end  238  may include a waffle or PIP pattern  60 , which may be entirely or substantially (e.g., greater than 50%) 3D-printed rather than machined, if desired. 
     A typical multi-point sonotrode is constructed from shafts that are discrete and separate from the base. The shafts and base are separately manufactured, and then the shafts are secured to the base, for example, by a stud. One common type of multi-point sonotrode manufactures the base from a light weight material, such as aluminum, and the shafts of a more durable material, such as steel or titanium. By way of contrast, the disclosed multi-point sonotrode forms the first and second shafts integrally with the base to provide an unbroken, monolithic construction. 
     In one example, the base  232  and the shafts  234  are constructed of the same material, such as titanium or steel, which are relatively heavy compared to aluminum. The heavy base  232  may be lightened by incorporating one or more substantially enclosed internal cavities  262  or substantially open cavities  264 , for example, as shown in  FIG.  10   , that are provided within the structure and formed in situ within the multiple layers  54  ( FIG.  2   ). The cavity  264  is surrounded substantially entirely by the multiple layers  54  and arranged interiorly of an exterior surface of the structure (e.g., outer surface  100 ;  FIGS.  5 A- 5 B ). The substantially enclosed internal cavity (e.g., at least 75%, and in another example, at least 90%) may include at least a small hole sufficient to permit the unsintered powder to escape the cavity subsequent to printing. A fully, 100% enclosed cavity would otherwise retain all of the loose powder. In one example, the base  232  includes at least one opening that extends laterally from one side through to another side (e.g., substantially open cavity  264 ) in a direction that is at an angle to the longitudinal direction of the shafts  234 . 
     Various portions of the sonotrode may be manufactured to vary the characteristics of the portions. With continuing reference to  FIG.  10   , at least two of the shafts extend in a longitudinal direction and have lengths that are different than one another. In another example, the base  232  has a first density and at least one of the shafts  234  has a second density that is different than the first density. The density of the shafts may also be varied among one another such that the density of one shaft is greater than the density of another shaft. The greater density may be achieved through porosity differences and/or by varying the thickness of the sintered layers, for example. 
     The disclosed mother-daughter are provided by a single piece, without separate discrete shafts as is typical in prior art arrangements. There is no complicated set up procedure as the multiple shafts are provided as an integrated inseparable structure with the base. Moreover, a potential failure mode at the prior threaded connection between the mother-daughters is eliminated. 
     The base can be made lighter than the shafts by incorporating one or more cavities or forming the base in a less dense manner than the shafts during the laser sintering process. The cavities may be internal, external or a combination thereof. This ensures that the base is not too heavy to excite to achieve the desired frequency and amplitude, which enables a smaller, less costly generator. 
     Internal cavities may also be used to provide cooling passages that are not possible based upon known sonotrode manufacturing techniques. Referring to  FIG.  11   , a cooling passage  350  is fluidly connected to the air source  28  ( FIG.  1   ) at one or more inlets  352 . A portion of the cooling passage  350  is curved from the inlet  352  to a junction  354  where the cooling passage  350  extends longitudinally within the shaft  334  to one or more outlets  370  at an end of the shaft  334 . 
     The cooling passage  350  includes an intrados  356  and an extrados  358 , which extend to the junction  354  in the example. Where multiple portions of the cooling passage  350  extend from multiple inlets  352 , a peak  360  may be formed. This smooth transition of intersecting passageways reduces restrictions and associated losses within the cooling passage  350 , providing more efficient use and delivery of the cooling fluid. 
     The cooling passage  350  may include a venturi  362  provided by first and second tapered portions  364 ,  366  joined at a throat  368 . The venturi  362  increases velocity and reduces pressure downstream from the throat  368 , which may be beneficial for cooling the terminal end  338 . A diffuser provided by a single taper may also be used, if desired. 
     The portion of the cooling passage  350  extending to the outlet  370  may be at a non-perpendicular angle with respect to the longitudinally extending portion within the shaft  334 . A protrusion  372  may be provided where multiple outlet portions are joined to one another. Thus, fluid exiting the venturi  362  may impinge upon the protrusion  372 , which provides increased cooling surface and, thus, increased cooling of the terminal end  338 . The cooling may further be enhanced by providing one or more roughened or dimpled surfaces  376  to enable heat to dissipate more quickly near the terminal end, as shown in  FIG.  12 C . These configurations provide smoother fluid flow and reduced losses as compared with intersecting, straight passages as is found in drilled cooling passages of prior art horns ( FIG.  11 A ). Such configurations may, at best, may have a dimple  374  provided as an artifact of drilling the cooling passage  350 , which is not repeatable and has minimal effect. Moreover, conventional drilled features may lead to stress risers that result in failure of the sonotrode from repeated cycling. 
     Other fluid flow- and cooling-enhancing features may be incorporated into the sonotrode, as shown in  FIGS.  13 - 16   . These features, which are much more elaborate than possible with conventional drilling operations, are formed in situ during the laser sintering process of the multiple layers of material.  FIG.  13    illustrates a spiral or corkscrew cooling passage  378  which provides increased length and surface area in addition to providing a swirling motion of fluid exiting the outlet  370 . 
       FIGS.  14 A and  14 B  illustrate restrictions that may create a Joule-Thompson effect. In the example shown in  FIG.  14 A , a porous plug or blockage  380  is provided in the cooling passage  350 , separating the passage into first and second passageways  350 A,  350 B. In the example shown in  FIG.  14 B , the restriction is provided by a valve or orifice  382  that throttles the fluid flow. As a result of the restriction, the temperature downstream of the restriction is reduced. 
       FIG.  15    illustrates an arrangement in which an end of the shaft  334  near the terminal end  338  incorporates external porosity  384  intentionally created during the 3D laser sintering that extends radially inward to fluidly connect to the cooling passage  350 . The porosity is like a “fish filter” and provides diffuse, distributed flow at the outlet of the cooling passage  350 . The porosity  384  may extend about the entire circumference of the shaft  334  or just portions of its circumference. 
     Another cooling configuration is shown in  FIG.  16   . An annular passage  386  is arranged in the base  332 , the annular passage  386  received fluid from the inlet  352  and is fluidly connected to multiple secondary passages  388  that deliver cooling fluid to fillet  336 , which expels the fluid through the outlet  372  and down the exterior of the shaft  334 . The secondary passages may be angled or otherwise shaped to generate a vortex of cooling fluid down the shaft  334 . 
     The above-described cooling features can provide improved cooling of the sonotrode, which increases duty cycle, improves weld quality thereby eliminating the need for external vortex coolers that are sometimes used on high duty cycle applications. 
     Referring to  FIGS.  17 A and  17 B , the attachment feature  490  arranged at the mounting face  432  is provided by an unmachined external surface formed by the multiple layers. That is, the attachment features  490  are not machined by a cutting tool, but rather formed during the DMLS process. In the examples, the attachment feature  490  is one of a stud ( FIG.  17 A ) and a threaded hole ( FIG.  17 B ). 
     As described, the density within the sonotrode may be varied. In one example, it may be desirable to vary the density across at least portions of the multiple layers by greater than 0.1%, for example. The ultrasonic converter  16  ( FIG.  1   ) is configured to induce a vibratory frequency in the structure that produces a wave form having at least one nodal point, as schematically illustrated in  FIG.  18   . The nodal points in the shaft  434  experience greater stresses. In one example, the wave form is configured to flow in a direction that runs primarily through the multiple layers, although other layer orientations may be employed. The structure has a greater density in a region  494  of the structure with the nodal point than in adjacent regions  492 , which provides increased strength at the nodal point. 
     Increased strength may also be provided at the tip of the sonotrode. In one example, it is desirable to have a greater density and/or less porosity or voids at the terminal end and the working surface as compared to adjacent structure in the shaft. For example, a first portion of the structure extending from the working surface to 10% of the length has a first density, and the adjacent structure has a second density that is less than the first density. 
     Referring to  FIG.  19   , the sonotrode, for example, the base  432 , has a fluid attachment  496  provided at the outer surface by the multiple layers, i.e., integral with the sonotrode and without machining. The fluid attachment  496 , which may be near the fillet  436 , is in fluid communication with an internal fluid passage  450 . In the example, the fluid attachment  496  is a barb configured to connect to a fluid line to the air source  28  ( FIG.  1   ). 
     The base  432  may include circumferentially spaced holes  498  each provided by an unmachined external surface formed by the multiple layers, i.e., integral with the sonotrode and without machining, as shown in  FIG.  20   . An installation tool cooperates with the holes  498  to torque the sonotrode relative to the converter  16  ( FIG.  1   ). 
     Referring to  FIG.  21   , the attachment feature is not provided by a stud or threaded hole, but is instead an integral transition to a booster  418  configured to attenuate a frequency from the ultrasonic converter  16  ( FIG.  1   ). In the example, the booster  418 , the base  432  and the shaft  434  provide a monolithic, unitary structure. 
     As shown in  FIG.  22   , the sonotrode extends in a longitudinal direction from the base  432  to the working surface of the terminal end  438 . The longitudinal direction is perpendicular to at least one of the mounting face and the working surface. The mounting face has a first central point  499 , and the working surface has a second central point  400 , such that the first and second central points  499 ,  400  are offset relative to one another with respect to the longitudinal direction. In this manner, the working surface may be positioned in difficult to reach work areas that would not be feasible using traditional sonotrode manufacturing methods. 
       FIG.  23    depicts an internal cavity  402  that has a larger diameter D than the diameter d of the mounting face to provide a “drum effect” when excited by the generator. 
     It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom. Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present invention. 
     Although the different examples have specific components shown in the illustrations, embodiments of this invention are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples. 
     Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For that reason, the following claims should be studied to determine their true scope and content.