Patent Publication Number: US-2017355149-A1

Title: Inspection and repair of adhesive-bonded joint using ultrasonic pulses

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 62/347,371 filed on Jun. 8, 2016, the disclosure of which is hereby incorporated by reference. 
    
    
     INTRODUCTION 
     The disclosure relates generally to inspection and repair of adhesive-bonded joints using ultrasonic pulses. In many industries, adhesive bonding is employed for bonding many different types of materials. For example, adhesive bonding is used to bond polymeric composites, which are lightweight, conformable and durable. The adhesive employed may have missing portions over time. A method of inspection to determine the state of an adhesive-bonded joint is desirable, including subsequent repair of a discrepant joint. 
     SUMMARY 
     A method of inspection and repair of a joint in an assembly. The joint is formed by a first work piece and a second work piece. An adhesive placed between the first and second work pieces to define the joint. The assembly includes an ultrasonic welding device including an ultrasonic horn configured to deliver ultrasonic energy to the joint. A controller is operatively connected to the ultrasonic welding device. The controller includes a processor and tangible, non-transitory memory on which is recorded instructions for executing a method of inspecting and repairing the adhesive-bonded joint. The controller is programmed to deliver a first ultrasonic pulse (P 1 ) to the joint, via the ultrasonic welding device, and determine an adhesive coverage (AC) based at least partially on the first ultrasonic pulse (P 1 ). 
     The first work piece and the second work piece may be composed of identical materials. The first work piece and the second work piece may be composed of dissimilar materials. At least one sensor may be operatively connected to the controller and configured to measure a depth of displacement of the ultrasonic horn in the joint. Determining an adhesive coverage (AC) includes determining if the adhesive is cured. If the adhesive is not cured, the controller is programmed to obtain a depth of displacement of the ultrasonic horn in the joint after delivery of the first ultrasonic pulse (P 1 ), via the at least one sensor. If the adhesive is not cured, the controller is programmed to obtain the adhesive coverage (AC) for the joint based at least partially on the depth of displacement and a first look-up table. If the adhesive is cured, determining an adhesive coverage (AC) includes obtaining an energy delivered to the joint by the first ultrasonic pulse (P 1 ) and obtaining the adhesive coverage (AC) based at least partially on the energy delivered by the joint and a second look-up table. 
     The controller may be further programmed to determine if the adhesive coverage (AC) is at or below a predefined threshold coverage (TC). If the adhesive coverage (AC) is at or below the threshold coverage (TC), the controller is programmed to determine the energy of a second ultrasonic pulse (P 2 ) based at least in part on the adhesive coverage (AC) and a third look-up table. 
     If the adhesive coverage (AC) is at or below the threshold coverage (TC), the controller is programmed to deliver the second ultrasonic pulse (P 2 ), via the ultrasonic welding device, to the joint under a compressive force to form a weld at the joint, thereby repairing the joint. The predefined threshold coverage (TC) may be selected such that a joint strength (S U,TC ) of an un-repaired bonded joint at the threshold coverage is less than or equal to a joint strength (S R,TC ) of a repaired welded joint at the threshold coverage [S U,TC ≦S R,TC ]. The predefined threshold coverage may be 50%. 
     The above features and advantages and other features and advantages of the present disclosure are readily apparent from the following detailed description of the best modes for carrying out the disclosure when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic fragmentary view of a joint assembly having a controller, a first work piece, a second work piece and an adhesive bonding the first and second work pieces, showing application of a first ultrasonic pulse; 
         FIG. 2  is a schematic top view of the adhesive of  FIG. 1 ; 
         FIG. 3  is a schematic fragmentary view of the joint assembly of  FIG. 1 , showing application of a second ultrasonic pulse; 
         FIG. 4  is a flowchart of a method stored on and executable by the controller of  FIG. 1 ; and 
         FIG. 5  is an example graph showing joint strength (in pounds), for the given joint configuration, on the vertical axis and percentage adhesive coverage on the horizontal axis. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings, wherein like reference numbers refer to like components,  FIG. 1  is a schematic illustration of an assembly  10  which may take many different forms and include multiple and/or alternate components. Referring to  FIG. 1 , the assembly  10  includes a first work piece  12  and a second work piece  14 . The first work piece  12  and the second work piece  14  may be composed of identical materials. The first work piece  12  and the second work piece  14  may be composed of dissimilar materials. The first work piece  12  may be composed of carbon fiber nylon composite and the second work piece  14  may be composed of nylon. In one example, the first work piece  12  and the second work piece  14  are both composed of thermoplastics. In another example, the first work piece  12  is composed of a thermoplastic and the second work piece  14  is composed of a metal. In another example, the first work piece  12  and the second work piece  14  are both composed of metals. A spacer  16 , such as an energy director for example, may be positioned between the first work piece  12  and the second work piece  14  to create a gap  17 . As shown in  FIG. 1 , an adhesive  18  is positioned between the first work piece  12  and the second work piece  14 , to bond the first and second work pieces  12 ,  14  and define an adhesive-bonded portion  20 , referred to herein as “joint  20 ”. 
       FIG. 2  is a schematic top view of the adhesive  18 . At the time of application, the adhesive  18  is spread over a “total area,” shown in  FIG. 2  as “TA.” While the total area TA is a rectangle in the example shown, it may be of whatever shape or size as needed. For a variety of reasons, portions of the adhesive  18  may wear off over time, shown in  FIG. 2  as missing portion  22 . The size, shape and location of the missing portion  22  in the total area TA may be selected based on the application at hand. The remaining portion of the total area TA that continues to have the adhesive  18  is labeled as adhesive coverage (AC) (shown lightly shaded). 
     Referring to  FIG. 1 , the assembly  10  includes an ultrasonic welding device  24 . The ultrasonic welding device  24  is configured to apply ultrasonic acoustic vibrations to the joint  20 . The ultrasonic welding device  24  may include an ultrasonic horn  26 , a transducer  28  and an amplifier  30 . A power source  32  may be operatively connected to the ultrasonic welding device  24 . The ultrasonic welding device  24  may include other electronic or acoustic components suitable for the ultrasonic welding device  24 . 
     Referring to  FIG. 1 , the transducer  28  may be configured to transform an output voltage of the power source  32  into a mechanical vibration or amplitude. This vibration may be sent through the amplifier  30 , which can increase or decrease the mechanical vibration that is coming from the transducer  28 . The ultrasonic horn  26  is configured to efficiently transfer the acoustic energy from the transducer  28  (via the amplifier  30 ) into the joint  20 . 
     Referring to  FIG. 1 , the ultrasonic welding device  24  is configured to deliver a first ultrasonic pulse P 1  to the joint  20 . The ultrasonic horn  26  is brought into contact with the first work piece  12  and the ultrasonic welding device  24  is energized for a predetermined period of time. The first ultrasonic pulse P 1  causes localized melting of the first and second work pieces  12 ,  14 , and decomposing (or degrading) of adhesive  18 , due to heat generated at the faying interfaces. Depending on the state of the adhesive  18 , the heat generated by the ultrasonic vibration may cause the ultrasonic horn  26  to be displaced or “sink” into the joint  20 . The assembly  10  may include a depth sensor  34  operatively connected to the controller  40  and configured to measure the depth of displacement (labeled “D” in  FIG. 1 ) of the ultrasonic horn  26  in the joint  20 . 
       FIG. 3  is a schematic fragmentary view of the application of a second ultrasonic pulse P 2  to the joint  20 . The ultrasonic horn  26  is brought into contact with the first work piece  12 . Subsequently, the ultrasonic welding device  24  is energized for a predetermined period of time to cause the transfer of ultrasonic energy to the joint  20  and resulting in localized melting. For a brief dwell period, the first and second work pieces  12 ,  14  are retained under a compressive force F between the ultrasonic horn  26  and a fixed anvil  36 , thereby allowing the softened localized material to become rigid and form a weld  38 . 
     Referring to  FIG. 1 , a controller  40  is operatively connected to the ultrasonic welding device  24 . The controller  40  includes a processor  42  and tangible, non-transitory memory  44  on which is recorded instructions for executing a method  100 , described below with reference to  FIG. 4 , of inspecting and repairing the (adhesive-bonded) joint  20 . The method  100  may include repairing discrepant joints based on the inspection results. A discrepant joint is defined as a joint  20  differing undesirably from a target configuration or coverage or not meeting target mechanical properties such as strength or fatigue life. 
     The controller  40  of  FIG. 1  may include other driver circuits (not shown) and other components for controlling the ultrasonic welding device  24 . The ultrasonic horn  26  may be formed with a shape, cross-section and length suitable to the application at hand. The length of the ultrasonic horn  26  is selected such that there is mechanical resonance at the desired ultrasonic frequency of operation. The specific frequency of ultrasound produced by the transducer  28  may vary based on the application. The frequency of ultrasound vibration may range from 15 to 300 kHz. 
     Referring now to  FIG. 4 , a flowchart of the method  100  stored on and executable by the controller  40  of  FIG. 1  is shown. The start and end of method  100  are shown by “S” and “E,” respectively. Method  100  need not be applied in the specific order recited herein and it is to be understood that some steps may be eliminated. The execution of the method  100  improves the functioning of the assembly  10  in many ways. 
     Method  100  may begin with block  102 . In block  102 , the controller  40  is programmed to deliver a first ultrasonic pulse (P 1 ) to the joint  20 , via the ultrasonic welding device  24 . As shown in  FIG. 2A , the first ultrasonic pulse (P 1 ) causes localized melting of the first and second work pieces  12 ,  14 , and decomposing (or degrading) of adhesive  18 , due to the absorption of ultrasonic vibration energy. The first ultrasonic pulse (P 1 ) is configured such that no weld is formed at the joint  20 , for example, by being of insufficient intensity. 
     In block  104 , the controller  40  is programmed to determine an adhesive coverage (AC) of the joint  20  based at least partially on the first ultrasonic pulse (P 1 ). Block  104  includes sub-blocks  106 ,  108 ,  110 ,  112  and  114 , described below. In sub-block  106 , the controller  40  is programmed to determine if the adhesive  18  is cured. Curing is defined as a process, such as a chemical reaction or physical action, which results in a tougher or stronger adhesive bond. An adhesive bond may be cured via a baking step where the adhesive  18  is subject to an elevated temperature for a predetermined amount of time. The controller  40  may determine if the adhesive  18  is cured or not by a method available to those skilled in the art. For example, a user can determine this from visual inspection or knowledge of the history of the joint  20 , and convey the information to the controller  40  via a user interface  52  (see  FIG. 1 ). Also, a physical test available to those skilled in the art may be used determine the state of the adhesive  18 , including but not limited to, a joint strength or displacement depth D of the ultrasonic horn  26 . 
     If the adhesive  18  is not cured, the method  100  proceeds from sub-block  106  to sub-block  108 , where the controller  40  is programmed to obtain the depth of displacement D of the ultrasonic horn  26  in the joint  20  after delivery of the first ultrasonic pulse (P 1 ). The measurement of the depth of displacement D may be made via the depth sensor  34 . As mentioned above the measurement of displacement depth (D in  FIG. 1 ) of the ultrasonic horn  26  may also be used to identify the state of the adhesive  18  in sub-block  106 . For a given energy of the ultrasonic pulse, the depth displacement D of an adhesive  18  that is cured would be smaller than an adhesive  18  that is not cured. 
     The method  100  then proceeds to sub-block  110 , where the controller  40  is programmed to obtain the adhesive coverage (AC) for the joint  20  based at least partially on the depth of displacement D (from block  108 ) and a first look-up table. The values of the first look-up table (and second and third look-up tables described below) may be obtained via calibration or in a test cell or laboratory. The first, second and third look-up tables may be a type of data repository or storage medium. Interpolation may be employed to determine values in between the data points in the respective look-up tables. A non-limiting example of a first look-up table is shown below in Table 1: 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Depth of Displacement 
                   
               
               
                   
                 (mm) 
                 Adhesive Coverage (AC) (%) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 0.14 
                 0 
               
               
                   
                 0.20 
                 42 
               
               
                   
                 0.26 
                 85 
               
               
                   
                 0.33 
                 95 
               
               
                   
                 0.42 
                 100 
               
               
                   
                   
               
            
           
         
       
     
     If the adhesive  18  is cured, the method  100  proceeds from sub-block  106  to sub-block  112 , the controller  40  is programmed to obtain an energy delivered (ED) to the joint  20  by the first ultrasonic pulse (P 1 ). The energy delivered (ED) to the joint  20  may be obtained based at least partially on the power delivered to the joint  20 , e.g., via integration of power delivered over time. The power source  32  may be rated by the peak power it can deliver, which may vary from a few hundred watts to several kilowatts. Based on a constant power output, a 0.5-second pulse from a 1.5-kW ultrasonic welding device would deliver 750 joules of energy. The assembly  10  may include a voltage sensor  48  and a current sensor  50  to assess the voltage and current, respectively, delivered to the ultrasonic welding device  24 . The assembly  10  may include other sensors or employ other methods or models available to those skilled in the art to obtain the energy delivered (ED) to the joint  20  by the first ultrasonic pulse (P 1 ). 
     The method  100  proceeds to sub-block  114 , where the controller  40  is programmed to obtain the adhesive coverage (AC) based at least partially on the energy delivered (ED) to the joint  20  and a second look-up table. The values of the second look-up table may be obtained via calibration or in a test cell or laboratory. An example of a second look-up table is shown below in Table 2: 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Energy Delivered 
                 Adhesive coverage (AC) % 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 ED1 
                 0 
               
               
                   
                 ED2 
                 25 
               
               
                   
                 ED3 
                 50 
               
               
                   
                 ED4 
                 75 
               
               
                   
                 ED5 
                 100 
               
               
                   
                   
               
            
           
         
       
     
     In block  116 , the controller  40  is programmed to determine if the adhesive coverage (AC) is at or below a predefined threshold coverage (TC). The predefined threshold coverage (TC) may be selected for the application at hand. The predefined threshold coverage (TC) may be selected such that a joint strength (S U,TC ) of an un-repaired bonded joint at the threshold coverage is less than or equal to a joint strength (S R,TC ) of a repaired welded joint at the threshold coverage [S U,TC ≦S R,TC ],  FIG. 5  is an example graph showing joint strength “JS” (in pounds) on the vertical axis and percentage adhesive coverage on the horizontal axis.  FIG. 5  is shown for illustrative purposes and is intended as a non-limiting example. Referring to  FIG. 5 , the joint strengths of an un-repaired bonded joint at 25%, 50%, 75% and 100% adhesive coverage are about  1100 ,  1700 ,  1900  and  2200  pounds, respectively. Referring to  FIG. 5 , the joint strengths of a repaired welded (previously bonded and then repaired via ultrasonic pulse welding) joint at 25%, 50%, 75% and 100% adhesive coverage are about  1700 ,  1700 ,  1800  and  1700  pounds, respectively. In this example, the predefined threshold coverage (TC) may be set to 50%. 
     If the adhesive coverage (AC) is above the threshold coverage (TC), the method is ended. If the adhesive coverage (AC) is at or below the threshold coverage (TC), the method proceeds to block  118 , where the controller  40  is programmed to determine the energy of a second ultrasonic pulse (P 2 ) based at least in part on the adhesive coverage (AC) and a third look-up table. The energy of the second ultrasonic pulse (P 2 ) is required to be of sufficient intensity to form a weld  38  at the joint  20 . An example of a third look-up table is shown below in Table 3: 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                   
                 Energy of Second Pulse 
               
               
                   
                 Adhesive coverage (AC) % 
                 (P2) (Joules) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 0 
                 E1 
               
               
                   
                 25 
                 E2 
               
               
                   
                 50 
                 E3 
               
               
                   
                 75 
                 E4 
               
               
                   
                   
               
            
           
         
       
     
     In block  118 , the controller  40  is programmed to deliver the second ultrasonic pulse (P 2 ), via the ultrasonic welding device  24 , to the joint  20  under a compressive force F. The application of the second ultrasonic pulse (P 2 ) fuses the locations at the faying interfaces between the first and second work pieces  12 ,  14  and the adhesive  18  to form a weld  38 , thereby repairing the joint  20  to a desired joint strength. 
     The controller  40  of  FIG. 1  may include a driver circuit (not shown) for controlling the ultrasonic welding device  24 . Referring to  FIGS. 1-2 , the controller  40  may include a respective computer-readable medium (also referred to as a processor-readable medium), including a non-transitory (e.g., tangible) medium that participates in providing data (e.g., instructions) that may be read by a computer (e.g., by a processor of a computer). Such a medium may take many forms, including, but not limited to, non-volatile media and volatile media. Non-volatile media may include, for example, optical or magnetic disks and other persistent memory. Volatile media may include, for example, dynamic random access memory (DRAM), which may constitute a main memory. Such instructions may be transmitted by one or more transmission media, including coaxial cables, copper wire and fiber optics, including the wires that comprise a system bus coupled to a processor of a computer. Some forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, other magnetic medium, a CD-ROM, DVD, other optical medium, punch cards, paper tape, other physical medium with patterns of holes, a RAM, a PROM, an EPROM, a FLASH-EEPROM, other memory chip or cartridge, or other medium from which a computer can read. 
     Look-up tables, databases, data repositories or other data stores described herein may include various kinds of mechanisms for storing, accessing, and retrieving various kinds of data, including a hierarchical database, a set of files in a file system, an application database in a proprietary format, a relational database management system (RDBMS), etc. Each such data store may be included within a computing device employing a computer operating system such as one of those mentioned above, and may be accessed via a network in one or more of a variety of manners. A file system may be accessible from a computer operating system, and may include files stored in various formats. An RDBMS may employ the Structured Query Language (SQL) in addition to a language for creating, storing, editing, and executing stored procedures, such as the PL/SQL language mentioned above. 
     The detailed description and the drawings or figures are supportive and descriptive of the disclosure, but the scope of the disclosure is defined solely by the claims. While some of the best modes and other embodiments for carrying out the claimed disclosure have been described in detail, various alternative designs and embodiments exist for practicing the disclosure defined in the appended claims. Furthermore, the embodiments shown in the drawings or the characteristics of various embodiments mentioned in the present description are not necessarily to be understood as embodiments independent of each other. Rather, it is possible that each of the characteristics described in one of the examples of an embodiment can be combined with one or more desired characteristics from other embodiments, resulting in other embodiments not described in words or by reference to the drawings. Accordingly, such other embodiments fall within the framework of the scope of the appended claims.