Abstract:
Thermoplastic welding apparatus and related methods are disclosed. An example method includes providing a smart susceptor between composite parts that are to be joined via thermoplastic welding. The example method includes positioning the composite parts and the smart susceptor on a tooling surface within a cavity of a tooling apparatus and applying a seal to the composite parts and the tooling surface to form a vacuum chamber between the composite parts and the tooling surface at a welding joint of the composite parts; producing a magnetic field at the welding joint. The example method includes providing a vacuum in the vacuum chamber during a welding operation.

Description:
CROSS-RELATED APPLICATION 
       [0001]    This patent arises from a divisional of U.S. patent application Ser. No. 13/109,061, filed on May 17, 2011, entitled “Thermoplastic Welding Apparatus and Related Methods.” In addition, this application is related to U.S. patent application Ser. No. 13/109,051, (now U.S. Pat. No. 8,980,029) filed concurrently with U.S. patent application Ser. No. 13/109,061 on May 17, 2011. Both U.S. patent application Ser. No. 13/109,061 and U.S. patent application Ser. No. 13/109,051 are incorporated by reference herein in their entireties. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    This invention was made with Government support under contract number DE-FG36-08GO18135 awarded by the United States Department of Energy. The government has certain rights in this invention. 
     
    
     TECHNICAL FIELD 
       [0003]    The disclosure generally relates to thermoplastic welding techniques. More particularly, the disclosure relates to a thermoplastic welding apparatus and method in which an induced magnetic field is oriented parallel to the plane of the composite parts being welded and concentrates uniform heating at the joint between the composite parts, preventing or minimizing heating of the parts. 
       BACKGROUND 
       [0004]    Fiber-reinforced organic resin matrix composites have a high strength-to-weight ratio, a high stiffness-to-weight radio and desirable fatigue characteristics that make them increasingly popular in aerospace applications. Therefore, composite materials are increasingly being used in the fabrication of structural components for aircraft. 
         [0005]    A variety of techniques are used to join composite structures in aerospace and other applications. These fastening techniques include mechanical fastening, adhesive bonding and thermoplastic welding. Thermoplastic welding has numerous advantages over the other fastening techniques including the ability to join thermoplastic composite components at high speeds and with minimum touch labor and little, if any, pretreatments. The welding interlayer (which includes a susceptor and surrounding thermoplastic resin either coating or sandwiching the susceptor) also can simultaneously take the place of shims which are required in mechanical fastening. Therefore, composite welding promises to be an affordable fastening technique. 
         [0006]    In the thermoplastic welding of thermoplastic and thermoset composite parts, the susceptor between the composite parts is heated and, in turn, heats and melts the resin of the parts. The melted resin functions as a hot melt adhesive at the welding interlayer between the parts. Upon subsequent cooling, the resin solidifies and secures the composite parts to each other. 
         [0007]    In thermoplastic welding, it is desirable to heat the welding interlayer between the composite parts as uniformly as possible. Thermal uniformity and repeatability, as well as the amount of time necessary to develop acceptable tooling and parameters to meet these acceptable thermal uniformity conditions, has been a primary impediment to utilizing induction welding of thermoplastic composites. Extensive experimentation in developing the parameters has been used in applications in which induction parameters and tooling with heat sinks have been used. Often, however, the thermoplastic welding process is not selected due to these thermal uniformity issues. 
         [0008]    Therefore, a thermoplastic welding apparatus and method in which an induced magnetic field is oriented parallel to the plane of the composite parts being welded and concentrates uniform heating at the joint between the composite parts, preventing or minimizing heating of the parts, is needed. 
       SUMMARY 
       [0009]    An example method includes providing a smart susceptor between composite parts that are to be joined via thermoplastic welding; positioning the composite parts and the smart susceptor on a tooling surface within a cavity of a tooling apparatus; applying a seal to the composite parts and the tooling surface to form a vacuum chamber between the composite parts and the tooling surface at a welding joint of the composite parts; producing a magnetic field at the welding joint; and providing a vacuum in the vacuum chamber during a welding operation. 
         [0010]    Another example method includes positioning a smart susceptor between a first composite part and second composite part; positioning the first composite part, the second composite part and the smart susceptor in a cavity formed between opposing first and second tools of a thermoplastic welding apparatus such that the first composite part engages a first tooling surface of the first tool; applying a tape to a perimeter of the first composite part and the second composite part and only to a portion of the first tooling surface of the first tool about perimeter edges of the first composite part and the second composite part to form a gas seal over a welding joint defined by the smart susceptor and the first and second composite parts positioned on the first tool within the cavity; applying a welding pressure to cause the smart susceptor to compress between the first composite part and the second composite part; and generating a first magnetic flux field adjacent the smart susceptor via a first inductor provided in the first tool adjacent the tooling surface. 
         [0011]    Another example method includes positioning a smart susceptor between opposing surfaces of at least two component parts; positioning the parts and the smart susceptor in a cavity of a welding tool such that the parts engage a tooling surface of the welding tool; sealing a perimeter of the parts and a portion of the tooling surface adjacent the perimeter of the parts to provide a sealed portion in communication with the tooling surface and a non-sealed portion in communication with the cavity; applying a pressure differential to a weld joint of the parts to compress the smart susceptor between the at least two parts during a welding operation; and generating a magnetic flux field oriented generally parallel to a plane of the smart susceptor during the welding operation. 
     
    
     
       BRIEF DESCRIPTION OF THE ILLUSTRATIONS 
         [0012]      FIG. 1  is a cross-sectional view of an illustrative embodiment of the thermoplastic welding apparatus in exemplary application of the apparatus. 
           [0013]      FIG. 2  is a cross-sectional view of a portion of an illustrative embodiment of the thermoplastic welding apparatus of  FIG. 1 , more particularly illustrating parallel orientation of a magnetic flux field with a smart susceptor between adjacent composite parts in thermoplastic welding of the parts to each other. 
           [0014]      FIG. 3  is an enlarged sectional view of the composite parts and the smart susceptor illustrated in  FIG. 2 . 
           [0015]      FIG. 4  is a cross-sectional view of an illustrative embodiment of the thermoplastic welding apparatus in alternative application of the apparatus. 
           [0016]      FIG. 5  is an enlarged sectional view of the composite parts and the smart susceptor illustrated in  FIG. 4 . 
           [0017]      FIG. 6  is a flow diagram of an illustrative embodiment of a thermoplastic welding method. 
           [0018]      FIG. 7  is a flow diagram of an aircraft production and service methodology. 
           [0019]      FIG. 8  is a block diagram of an aircraft. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    The following detailed description is merely exemplary in nature and is not intended to limit the described embodiments or the application and uses of the described embodiments. As used herein, the word “exemplary” or “illustrative” means “serving as an example, instance, or illustration.” Any implementation described herein as “exemplary” or “illustrative” is not necessarily to be construed as preferred or advantageous over other implementations. All of the implementations described below are exemplary implementations provided to enable persons skilled in the art to practice the disclosure and are not intended to limit the scope of the claims. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. 
         [0021]    Referring initially to  FIGS. 1-3 , an illustrative embodiment of the thermoplastic welding apparatus is generally indicated by reference numeral  100 . The thermoplastic welding apparatus  100  may include a thermoplastic welding tool  101 . In some embodiments, the thermoplastic welding tool  101  may be a castable ceramic tool. Reinforcing rods  105 , which may be fiberglass, may extend through the thermoplastic welding tool  101 . 
         [0022]    The thermoplastic welding tool  101  may include a tooling space  106  having at least one tooling surface  103 . Magnetic induction coils  102  may extend through the thermoplastic welding tool  101 . The magnetic induction coils  102  may be disposed on both sides of the tooling space  106  and may generally surround or envelope the tooling surface  103 . 
         [0023]    A non electrically-conductive material  104  ( FIG. 2 ) may be disposed generally beneath or adjacent to the tooling surface  103 . In some embodiments, the non electrically-conductive material  104  may be an elastomeric material. A ferrite material such as ferrite powder  108 , for example and without limitation, may be embedded in the thermoplastic welding tool  101  on at least one side and preferably, on respective sides of the non electrically-conductive material  104 . The ferrite powder  108  may be distributed in a plane which is generally parallel to the plane of the smart susceptor  116  and the planes of the first composite part  112  and the second composite part  113 , respectively. 
         [0024]    In application of the thermoplastic welding apparatus  100 , a first composite part  112  is placed on the tooling surface  103  in the tooling space  106  of the thermoplastic welding tool  101 . A smart susceptor  116  is placed on the first composite part  112 . The smart susceptor  116  may be an electrically-conductive, magnetic metal with high thermal conductivity such as molypermalloy, for example and without limitation. A second composite part  113  is placed on the smart susceptor  116 . In some applications, tape  118  may be applied to the edges of the second composite part  113  to form a gas seal over the welding joint defined by the first composite part  112 , the smart susceptor  116  and the second composite part  113 . A vacuum is pulled on the tooling surface  103  and internal gas pressure  120  applies welding pressure against the second composite part  113 , compressing the smart susceptor  116  between the first composite part  112  and the second composite part  113 . 
         [0025]    The magnetic induction coils  102  generate a magnetic flux field  122  which generally envelopes the first composite part  112  and the second composite part  113 , as shown in  FIG. 1 . In some applications, the magnetic flux field  122  may be an 80 kHz field with  10  amps excitation energy. Due to the high magnetic permeability of the smart susceptor  116 , the magnetic flux lines  123  of the magnetic flux field  122  stream into the smart susceptor  116 . The ferrite powder  108  focuses the magnetic flux field  122  and eliminates leakage of the magnetic flux field  122  into the first composite part  112  and the second composite part  113 . Accordingly, the magnetic flux lines  123  of the magnetic flux field  122  follow the magnetic path of least resistance through the embedded ferrite powder  108  and the smart susceptor  116 , as shown in  FIG. 3 . Consequently, the magnetic flux field  122  sustains a thermal reaction in the smart susceptor  116 , heating the smart susceptor  116  to its Curie temperature point. The smart susceptor  116  heats and melts the resin at the welding interface between the first composite part  112  and the second composite part  113 . Because the magnetic flux lines  123  of the magnetic flux field  122  encompass the entire part and are oriented parallel to the plane of the smart susceptor  116 , minimal heating of the first composite part  112  and the second composite part  113  occurs and heating is focused, concentrated or localized to the welding interface between the first composite part  112  and the second composite part  113 . The magnetic induction coils  102  are then turned off and the first composite part  112  and the second composite part  113  allowed to cool. The melted resin at the welding interface solidifies, forming an adhesive bond between the first composite part  112  and the second composite part  113 . The composite structure which includes the first composite part  112  and the second composite part  113  may then be removed from the thermoplastic welding tool  101 . 
         [0026]    It will be appreciated by those skilled in the art that a 0.006″ thick molypermalloy smart susceptor  116  is capable of being heated from room temperature to about 670 degrees F. in about 3 minutes when exposed to a 80 kHz magnetic flux field  122  with an equilibrium temperature in the 670-680 degree F. temperature range. A graphite/epoxy composite part  112 ,  113  does not heat noticeably when exposed to the same magnetic flux field  122 . This characteristic enables thin, intrinsically-controlled susceptor materials to be used for thermoplastic composite welding to facilitate even or precise heating and repeatable processing. 
         [0027]    Referring next to  FIGS. 4 and 5 , a cross-sectional view of an illustrative embodiment of the thermoplastic welding apparatus  100   a  in alternative application of the apparatus is shown. In application of the thermoplastic welding apparatus  100   a,  multiple smart susceptors  138  may be placed between a first composite part  134  and a second composite part  135  at selected intervals in the thermoplastic welding tool  101  depending on the desired locations of the welding interfaces between the parts. A non electrically-conductive material such as an elastomeric material  132 , for example and without limitation, may extend adjacent to the first composite part  134  and the second composite part  135 , respectively. A ferrite material  130  may be provided in the thermoplastic welding tool  101  generally on respective sides of the elastomeric material  132 . The ferrite material  130  may be oriented in a plane which is generally parallel to the plane of the smart susceptor  108  and the planes of the first composite part  134  and the second composite part  135 , respectively. Accordingly, upon energizing of the magnetic induction coils  102 , the magnetic flux field  122  ( FIG. 5 ) follows the path of least magnetic resistance through the ferrite material  130  and the smart susceptor  138 . The smart susceptor  138  uniformly and selectively heats the welding interface between the first composite part  134  and the second composite part  135  without heating the first composite part  134  and the second composite part  135 . Upon cooling, the melted resin at the welding interface solidifies and secures the parts to each other, after which the composite structure including the first composite part  134  an the second composite part  135  is removed from the thermoplastic welding tool  101 . 
         [0028]    Referring next to  FIG. 6 , a flow diagram  600  of an illustrative embodiment of a thermoplastic welding method is shown. In block  602 , molded composite parts may be trimmed to net shape. In block  604 , a smart susceptor may be placed between the composite parts which are to be joined via thermoplastic welding. In block  606 , the composite parts and the susceptor may be placed in a thermoplastic welding tool. In block  608 , magnetic induction coils of the tool may be arranged so that a magnetic flux field produced by the induction coils in the tool encompasses the entire part and is oriented parallel to the plane of the smart susceptor and parallel to the planes of the composite parts being joined. In block  610 , tape may be placed around the joint edges of the composite parts and a vacuum may be pulled at the joint. In block  612 , tooling force may be applied against the composite parts to supply welding pressure. In some embodiments, the tooling force may be a pressurized gas. In block  614 , the induction coil may be energized. In block  616 , polymeric material at the welding interface between the composite parts may melt to form the weld. In block  618 , power to the coil may be terminated to cool and solidify the joint and the composite structure may be removed from the tool. 
         [0029]    Referring next to  FIGS. 7 and 8 , embodiments of the disclosure may be used in the context of an aircraft manufacturing and service method  78  as shown in  FIG. 7  and an aircraft  94  as shown in  FIG. 8 . During pre-production, exemplary method  78  may include specification and design  80  of the aircraft  94  and material procurement  82 . During production, component and subassembly manufacturing  84  and system integration  86  of the aircraft  94  takes place. Thereafter, the aircraft  94  may go through certification and delivery  88  in order to be placed in service  90 . While in service by a customer, the aircraft  94  may be scheduled for routine maintenance and service  92  (which may also include modification, reconfiguration, refurbishment, and so on). 
         [0030]    Each of the processes of method  78  may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of vendors, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on. 
         [0031]    As shown in  FIG. 8 , the aircraft  94  produced by exemplary method  78  may include an airframe  98  with a plurality of systems  96  and an interior  100 . Examples of high-level systems  96  include one or more of a propulsion system  102 , an electrical system  104 , a hydraulic system  106 , and an environmental system  108 . Any number of other systems may be included. Although an aerospace example is shown, the principles of the invention may be applied to other industries, such as the automotive industry. 
         [0032]    The apparatus embodied herein may be employed during any one or more of the stages of the production and service method  78 . For example, components or subassemblies corresponding to production process  84  may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft  94  is in service. Also one or more apparatus embodiments may be utilized during the production stages  84  and  86 , for example, by substantially expediting assembly of or reducing the cost of an aircraft  94 . Similarly, one or more apparatus embodiments may be utilized while the aircraft  94  is in service, for example and without limitation, to maintenance and service  92 . 
         [0033]    Although the embodiments of this disclosure have been described with respect to certain exemplary embodiments, it is to be understood that the specific embodiments are for purposes of illustration and not limitation, as other variations will occur to those of skill in the art.