Ultrasonic welding and welding horn having indenter

A method of joining includes disposing a second workpiece adjacent to a first workpiece. The method further includes identifying a determined hardness parameter of at least one of the first and second workpieces at a welding position. The determined hardness parameter is determined by at least one of estimation, calculation, and measurement. The method includes selecting a weld schedule based on the determined hardness parameter and welding the first and second workpieces together using the selected weld schedule. A welding horn includes a shank and a tip having an end face, the tip being disposed at an end of the shank and configured to contact a workpiece and to transmit energy to the workpiece. Knurls are disposed on the end face, each knurl having a distal end. A curved indenter extends from the end face beyond the distal ends of the knurls.

FIELD

The present disclosure generally relates to welding and more specifically to techniques for ultrasonic welding, as well as to a welding horn, which are particularly useful for joining polymeric composite components.

INTRODUCTION

Ultrasonic welding may be used to join polymeric and/or metal components. In ultrasonic welding, the plastic or metal components are clamped between a welding horn and an anvil. To weld using ultrasonic energy, high-frequency vibrations are applied to the components to be joined by a high frequency vibration of the horn. The horn, or sonotrode, is a tool that creates ultrasonic vibrations that are applied to a workpiece or material such as for welding, machining, or mixing. In the case of ultrasonic welding, component joining occurs as the result of applied mechanical force and heat generated at the interface between the components by the mechanical vibration.

Delivering consistent weld quality using ultrasonic welding requires overcoming a number of challenges. Process variables including clamp load, vibration amplitude, and weld time must be set precisely and must take into consideration variations in stack height and material. With the welding of plastic, clamp forces must be kept low enough to avoid distortion of the components, while stiffer materials require higher clamp loads. If the clamp forces are too low or if misalignment occurs, insufficient weld formation may result.

Additional complications are present when attempting to join polymeric composite materials, and weld joints of these materials may become discrepant. Accordingly, polymeric composite materials are typically joined mechanically, such as by staking or riveting, or through adhesives, to avoid the issue with weld joints breaking apart, but these methods may add time and expense.

SUMMARY

The inventors hereof have discovered that a main reason for weld failure in welded polymeric composite materials is that the material itself varies in hardness or local material properties across a single workpiece. Accordingly, applying the same weld schedule to all of the welding locations in the workpiece stack-up is highly likely to create both good welds and welds that become discrepant, due to the use of a weld schedule that is only tuned for the hardness or local material properties of a portion of the workpiece. Accordingly, a method is provided herein that includes varying the weld schedule based on the hardness, or on a hardness parameter, at each of the individual weld locations. The hardness or hardness parameter may be determined at each of the individual weld locations, for example, through correlation of a depth of displacement of an indenter or through correlation of power applied through an initial force. A welding horn that includes an indenter is also provided.

In one form, which may be combined with or separate from the other forms or examples provided herein, the present disclosure provides a method of joining. The method includes providing a first workpiece and disposing a second workpiece adjacent to the first workpiece. The method includes identifying a determined hardness parameter of the second and/or of the first workpiece at a welding position, where the determined hardness parameter is determined by estimation, calculation, and/or measurement. The method also includes selecting a weld schedule based on the determined hardness parameter to identify a selected weld schedule and welding the first and second workpieces together using the selected weld schedule.

In another form, which may be combined with or separate from the other forms or examples provided herein, a welding horn for ultrasonic welding a plurality of workpieces together is provided. The welding horn includes a shank and a tip having an end face. The tip is disposed at an end of the shank and configured to contact a first workpiece and to transmit energy to the first workpiece. A plurality of knurls is disposed on the end face, each knurl having a distal end. A curved indenter extends from the end face beyond the distal ends of the knurls.

Additional details may optionally be provided, including but not limited to the following: wherein the first and second workpieces are each formed of a polymeric composite material; wherein the polymeric composite material comprises a thermoplastic polymer matrix and a plurality of reinforcing chopped fibers disposed within the thermoplastic polymer matrix; wherein the polymeric composite material is a carbon-reinforced nylon having a plurality of chopped carbon fibers disposed within the nylon; the plurality of chopped carbon fibers having an average fiber length no greater than 50 millimeters and an average diameter no greater than one micrometer; wherein the step of welding includes ultrasonically welding the first and second workpieces together; wherein the step of identifying the determined hardness parameter includes pressing an indenter into a surface of the first workpiece with a predetermined force and determining a depth of a displacement of the indenter after pressing the indenter into the surface of the first workpiece; providing the indenter on a face of a welding horn; the step of welding including applying the selected weld schedule through a tool set comprising the welding horn and a mating anvil; providing the welding horn having a plurality of knurls disposed on the face of the welding horn; the face being curved and defining a tip radius of curvature; the indenter defining an indenter radius of curvature; the tip radius of curvature being greater than the indenter radius of curvature; the shank defining an end shank radius at the end of the shank; the tip radius of curvature being at least four times the end shank radius; the shank defining an end shank diameter at the end of the shank; the indenter radius of curvature being less than the end shank diameter; the end shank diameter being no greater than four times the indenter radius of curvature; the indenter extending no more than 2.0 mm beyond the distal ends of the knurls in a direction normal to the end face; the plurality of knurls defining a knurl pitch between adjacent knurls; each knurl being defined by a knurl angle extending from a knurl base to an outwardly extending knurl edge; the knurl angle being in range of 40 to 60 degrees; and a ratio of the knurl pitch to the end shank diameter being at least 0.045 and no greater than 0.065.

The selected weld schedule may include one or more of the following: a predetermined horn amplitude, a predetermining total welding time, an initial horn trigger force, a total distance of displacement of the welding horn into the first workpiece, a total amount of energy applied to the first workpiece through the welding horn, a velocity of moving the welding horn into the first workpiece, a maximum amount of force applied to the first workpiece by the welding horn, and an amount of melted material of the first workpiece after an initial application of energy from the welding horn prior to moving the welding horn into the first workpiece.

Further additional optional details may be provided, including but not limited to the following: wherein the step of identifying the determined hardness parameter includes pressing a tool into a surface of one of the first and second workpieces with a predetermined force and a predetermined amplitude and determining a power applied through the tool upon pressing the tool into the surface with the predetermined force and the predetermined amplitude; wherein the tool is a welding horn of a tool set comprising the welding horn and a mating anvil; and wherein the step of ultrasonically welding includes applying the selected weld schedule through the tool set.

In addition, the method may include identifying a plurality of additional determined hardness parameters of at least one of the first and second workpieces at a plurality of additional welding positions, selecting a weld schedule for each of the plurality of additional welding positions based on the plurality of additional determined hardness parameters to identify a plurality of additional selected weld schedules, each additional selected weld schedule correlating with an additional welding position of the plurality of additional welding positions, and welding the first and second workpieces together at each of the additional welding positions using the plurality of additional selected weld schedules.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and is not intended to limit the application and uses.

Referring now toFIGS. 1-2, a welding horn, or sonotrode, for use in vibrational or ultrasonic welding, such as conventional ultrasonic welding or ultrasonic torsional welding, to weld a plurality of workpieces together, is illustrated and generally designated at10. The welding horn10includes a shank12and a tip14disposed at an end16of the shank12. The tip14has an end face18, which may be slightly curved to define a relatively large radius of curvature R1. The tip14is configured to contact a workpiece and to transmit energy to the workpiece to perform a welding operation, which will be described in further detail below.

Referring toFIGS. 1-3, a number of knurls20may be disposed on the end face18. The knurls20may be disposed adjacent to one another and uniformly distributed on the end face18except where interrupted by an indenter22. In the illustrated example, each knurl20is shaped as a diamond pyramid, or four-sided pyramid, having a base24and sloping sides26that end in a distal end28of the knurl20. Thus, each distal end28is a pointed tip of the knurl20, and the distal ends28are separated by grooves30between the knurls20. Though the knurls20are illustrated as being arranged in a pattern of straight lines, side by side, the knurls20could alternatively be illustrated in other patterns, such as a staggered or annular pattern, by way of example. Further, although the knurls20are illustrated as four-sided pyramids, they could be other shapes, such as three-sided pyramids, conical, or another shape.

Except with respect to the indenter22being disposed amongst the knurls20on the end face18, the knurls20are separated from one another by a uniform knurl pitch d. The knurl pitch d may be defined as the distance from the pointed distal end28(or the center) of one knurl20to the pointed distal end28(or center) of an adjacent knurl20. Each knurl also defines a knurl angle θ. The knurl angle θ may be defined as the angle between each side26of a knurl20and the base24of the knurl20, or as the angle between a side26of the knurl20and a tangent plane P that extends tangentially across the face18where the base24meets the side26of the knurl20. The knurl pitch d and the knurl angle θ determine the size of each knurl20, including the height h. The height h may be defined as the distance from the base24to a distal end28of a knurl20along a line normal to the base24or to a plane that extends tangentially along the base24of the knurl20at a point directly under the distal end28, so that such plane runs perpendicular to a central axis X of the welding horn10.

A variety of knurl pitches d, knurl angles θ, and tip radii R1may be desirable, depending on the application. For example only, the knurl pitch d may be provided in the range of 0.75 to 1.25 millimeters, the knurl angle θ may be provided in the range of 30 to 60 degrees, or 40 to 60 degrees, and the tip radius R1may be provided in the range of 32 to 41 millimeters.

The indenter22is curved and extends from the end face18of the tip14beyond the distal ends28of the knurls20. The indenter22may be located centrally on the face18, symmetric about the central axis X of the welding horn10, but it could also be located on another part of the face18, or the indenter may be provided on a separate tool. In some examples, the indenter22may be shaped as a portion of a sphere and may define a radius of curvature R2. The tip radius of curvature R1is greater than the indenter radius of curvature R2, as can be seen inFIG. 1. The shank12defines an end shank radius R3and an end shank diameter E at the end32of the shank12that connects to the tip14. The tip radius of curvature R1is preferably at least four times the end shank radius R3. The indenter radius of curvature R2is less than the end shank diameter E. In some examples, the end shank diameter E is no greater than four times the indenter radius of curvature R2. In one preferred example, the relationship between the end shank diameter E and the indenter radius of curvature R2may be defined as follows:
0.78*E≥R2≥0.29*E(1)
In some examples, the indenter radius of curvature R2may be approximately half of the shank radius R3, or the indenter radius of curvature R2may be in the range of ¼ to ¾ of the shank radius R3. In a preferred example for use with the workpiece materials described herein, the indenter22extends no more than 2.0 mm beyond the distal ends28of the knurls20in a direction normal to the end face18or to a plane tangential to the end face18at the central axis X of the horn10. In some examples, a ratio of the knurl pitch d to the end shank diameter E is at least 0.045 and no greater than 0.065.

Referring now toFIG. 4, a method of joining is illustrated in a block diagram and generally designated at100. Referring toFIG. 5A, and with continued reference toFIG. 4, the method100includes a step102of providing a first workpiece36and a step104of disposing a second workpiece38adjacent to the first workpiece36so that the first and second workpieces36,38form a workpiece stack-up40. A welding assembly42includes the welding horn10disposed on an outer side44of the first workpiece36and a corresponding anvil46disposed on an outer side48of the second workpiece38.

The first and second workpieces36,38may each be formed of the same or different polymeric composite materials. For example, the polymeric composite material may comprise a thermoplastic polymer matrix and a plurality of reinforcing chopped fibers disposed within the thermoplastic polymer matrix. In one form, the polymeric composite material is a carbon-reinforced nylon, such as nylon 6, having a plurality of chopped carbon fibers disposed within the nylon. The plurality of chopped carbon fibers may be short fibers and may have an average fiber length no greater than 50 millimeters and an average diameter no greater than one micrometer.

As shown inFIG. 5A, the welding horn10is initially pressed against the outer side44of the first workpiece36with an initial force, preferably without applying energy or heat, to press the indenter22into the first workpiece36. Pressing the indenter22against the outer side44of the first workpiece36creates an indented portion50in the outer side44of the first workpiece36, as can be seen inFIG. 5Bafter the welding horn10has been moved away from and out of contact with the first workpiece36.

The method100includes a step106of identifying a determined hardness parameter of at least one of the first and second workpieces at a welding position60. As used herein, the hardness parameter is indicative of local hardness or other local material properties at a given location. The determined hardness parameter may be determined by estimation, calculation, and/or measurement. In the illustrated example, the determined hardness parameter of the first workpiece36includes the depth F of the indented portion50. The depth F varies based on the hardness of the first workpiece36at the welding location. For workpieces formed of a composite thermoplastic fiber material, hardness may vary along the outer side44of the workpiece36because fibers are disposed in random different ways throughout a thermoplastic matrix of the material. Upon application of a predetermined force by the horn10to press the indenter22into the first workpiece, the depth F of the indented portion50may be correlated to a set of predetermined hardness values or ranges, such as in a look-up table or a calibrated program. Thus, the depth F may be the determined hardness parameter, which may be used to determine a hardness at the welding location60, or the depth F may be input into a program and used directly to select a welding schedule, which will be described in further detail below.

Instead of using the welding horn10, the indented portion50may alternatively be formed by a separate indenter tool to determine a displacement at each welding location, without falling beyond the spirit and scope of the present disclosure.

In still another example, the step106of identifying the determined hardness parameter may include pressing a tool, such as horn10or a horn having no indenter, into the outer surface44with a predetermined force and a predetermined amplitude. A power applied through the tool upon pressing the tool into the surface44with the predetermined force and the predetermined amplitude may be determined and identified as the determined hardness parameter. The amount of applied power when a predetermined force and amplitude are applied will vary based on the local hardness of the material. That applied power may be correlated to a predetermined set of hardness values, if desired, to ultimately select a schedule, or the applied power itself may be used to select the welding schedule without the intermediate step of correlating the power to a hardness value.

The method100then includes a step108of selecting a weld schedule based on the determined hardness parameter. Weld schedules may have various parameters. For example, a weld schedules may include one or more of the following parameters: a predetermined initial horn amplitude; a predetermining total welding time; an initial horn trigger force; a total distance of displacement of the welding horn into the workpiece; a total amount of energy applied to the workpiece through the welding horn; a velocity of moving the welding horn into the workpiece; a maximum amount of force applied to the workpiece by the welding horn; an amount of melted material of the workpiece after an initial application of energy from the welding horn prior to moving the welding horn into the workpiece; and/or any other desired parameter. Thus, a welding controller (not shown) may be calibrated to select a predetermined weld schedule based on the determined hardness parameter, and the parameters of the weld schedule may differ depending on the selected weld schedule, which is selected based on the determined hardness parameter. Thus, for a first welding location on the workpiece36having a first determined hardness parameter, a first weld schedule may be selected, and for a second welding location on the same workpiece36having a second determined hardness parameter, where the second determined hardness parameter is different from the first determined hardness parameter, a second weld schedule may be selected. In that case, because of the different hardness parameters, the first and second schedules may be different from one another, having different weld schedule parameter values.

Referring toFIG. 4B, the step108of selecting the weld schedule is illustrated in additional detail. The determined hardness parameter is provided via step106, and then the step108may include a substep108A whereby the method100includes determining a range in which the determined hardness parameter lies. In the illustrated example, if there are three predetermined hardness parameter ranges that may be chosen, the step108A determines whether the determined hardness parameter107is in a first range, a second range, or a third range. If the determined hardness parameter is in the first range, the method100proceeds to substep108B to select a first predetermined weld schedule; if the determined hardness parameter is in the second range, the method100proceeds to substep108C to select a second predetermined weld schedule; and if the determined hardness parameter is in the third range, the method100proceeds to substep108D to select a third predetermined weld schedule. Although three ranges and weld schedules are described here, any number of desired ranges and corresponding weld schedules may be used, without falling beyond the spirit and scope of the present disclosure.

The selected weld schedule, selected in step108, is then provided to a step110. In step110, the method100then includes welding the first and second workpieces36,38together using the selected weld schedule. Referring toFIG. 5C, the welding step110may include first applying an initial weld amplitude via the horn10using an initial trigger force. Thus, in step5C, an initial energy is applied to the outer side44of the first workpiece36through horn10. This causes some of the first workpiece36to melt or soften at the interface52between the horn10and the outer side44, and an initial melt54starts to form at a faying interface56between the first and second workpieces36,38. After the initial welding amplitude and trigger force are applied, the welding horn10may then be moved away from the outer side44of the first workpiece36, if desired.

Referring now toFIG. 5D, the welding horn10is then moved back into contact with the first workpiece36(if moved away) and the rest of the weld schedule is applied to complete the forming of the weld nugget54at the faying interface56. The welding step110includes applying the selected weld schedule, for example, through the tool set that includes the welding horn10and the mating anvil46to weld the workpieces36,38together and form a welded assembly. Although two workpieces36,38are illustrated in the stack-up40, additional workpieces may be included, if desired.

The welding assembly42may be an ultrasonic type configured to perform the welding step110using ultrasonic welding. The workpiece stack-up40is clamped between the horn10and the anvil46. The horn10may be electrically connected to a converter/booster (not shown), which converts an electrical signal into a mechanical vibration and produces the amplitude of the welding horn10. The horn10applies the vibration to the components36,38. The vibration frequency is generally in the range of 20-40 kilohertz. The motion of the vibration at the horn face18is transferred to the two components36,38. The vibration moves through the first workpiece36and creates friction and visco-elastic deformation at the faying interface56between the first and second workpieces36,38. As a result, heat is created at the faying interface56that melts the material, which is then cooled to form a weld joint fusing the components36,38together.

Referring now toFIG. 6, a portion of the first workpiece36is illustrated. The method100described above is performed at the welding position60on the first workpiece36. The determined hardness parameter at the first welding position60is a first determined hardness parameter, and the selected weld schedule is a first selected weld schedule. However, many parts that need to be joined are large and may need many weld joints to adequately join them together. Thus, the method100may further include identifying a plurality of additional determined hardness parameters of at least one of the first and second workpieces (in this case, of the first workpiece36) at a plurality of additional welding positions62,64,66,68. At each additional welding position62,64,66,68, a weld schedule may be selected based on the determined hardness parameters at each of the welding positions62,64,66,68. The first and second workpieces36,38are then welded together at each of the additional welding positions62,64,66,68using the plurality of additional selected weld schedules.

The hardness parameter at each of the welding positions62,64,66,68may be determined in any suitable way, such as those described above. For example, an indenter, such as the indenter22, may be used to form an indented portion70,72,74,76at each of the welding positions62,64,66,68, respectively. The depth of each indented portion70,72,74,76, which correlates to a predetermined hardness parameter, may then become the basis on which a weld schedule is selected for each welding position62,64,66,68.

In some examples, the steps of the method are performed by a controller, and the hardness itself may never be separately identified, such that the controller advances to selecting the weld schedule after it has the depth measurement, calculation, or estimation, because the intermediate step of determining the hardness value and then selecting the weld schedule may need not be shown to a user. Thus, the determined hardness parameter may be any determined value that correlates to hardness, such as depth of the indented portion or applied power based on a predetermined amplitude and force. Thus, the controller would then use the depth or other identifying information (e.g., applied power) as the determined hardness parameter as the basis on which it selects a predetermined weld schedule based on a calibration or program in the controller. Any number of interim calculations or estimations may be performed to arrive at the selected weld schedule based on the determined hardness parameter. Furthermore, multiple determined hardness parameters may be used together to select the weld schedule; for example, the weld schedule may be selected based on both the applied power and the depth of the indented portion. It should be understood that, due to variances in the composite thermoplastic materials, the determined hardness parameters at each of welding positions60,62,64,66,68are likely to vary from one another.

Weld quality overall is improved by the method disclosed herein because the appropriate weld schedule based on local material hardness is applied, based on the determined hardness parameter that is calculated, estimated, or measured at the local welding location, and the weld schedule may be adjusted for each weld being made so that every weld has the most effective weld schedule for the hardness of the local area upon which the welding operation is performed. Therefore, a weld schedule that will result in a well-fused joint is selected based on the determined hardness parameter, which correlates to the hardness of the material at the local welding location.

The method100described herein may be performed by a controller or a set of controllers, by way of example. The controller(s) may be part of, or include, an Application Specific Integrated Circuit (ASIC); an electronic circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor (shared, dedicated, or group) that executes code; other suitable components that provide the described functionality; or a combination of some or all of the above, such as in a system-on-chip. The controller(s) may include memory (shared, dedicated, or group) that stores code executed by the processor. The term code, as used above, may include software, firmware, and/or microcode, and may refer to programs, routines, functions, classes, and/or objects. The term shared, as used above, means that some or all code from multiple modules may be executed using a single (shared) processor. In addition, some or all code from multiple modules may be stored by a single (shared) memory. The term group, as used above, means that some or all code from a single module may be executed using a group of processors. In addition, some or all code from a single module may be stored using a group of memories.

The description is merely exemplary in nature and variations are intended to be within the scope of this disclosure. The examples shown herein can be combined in various ways, without falling beyond the spirit and scope of the present disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the present disclosure.