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Title:
SYSTEM AND METHOD FOR THERMOPLASTIC WELDING USING AN INDUCED THERMAL GRADIENT
Document Type and Number:
WIPO Patent Application WO/2021/080843
Kind Code:
A1
Abstract:
A system and method for thermoplastic composite welding comprising a cooling means and a heat source. The cooling means cools a heat-side laminate so as to create a thermal gradient in the heat-side laminate. The heat source heats the heat- side laminate after the cooling step is initiated but before the thermal gradient dissipates so that a first side of the heat-side laminate closer to the heat source does not deform as faying surfaces of the heat-side laminate and another laminate farther away from the heat source are welded together.

Inventors:
WADSWORTH MARK ANTHONY (US)
Application Number:
PCT/US2020/055737
Publication Date:
April 29, 2021
Filing Date:
October 15, 2020
Export Citation:
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Assignee:
SPIRIT AEROSYS INC (US)
International Classes:
B29C65/02; B29C43/36; B29C65/00; B29C65/22; H05B6/36
Foreign References:
US2617752A1952-11-11
US4978825A1990-12-18
US3982991A1976-09-28
US20170129163A12017-05-11
EP2801472A12014-11-12
Attorney, Agent or Firm:
LUEBBERING, Thomas B. (US)
Download PDF:
Claims:
CLAIMS:

1. A system for thermoplastic composite welding a heat-side laminate having opposing first and second sides and an opposing laminate having opposing first and second sides together, the system comprising: a cooling means configured to cool the heat-side laminate so as to create a thermal gradient in the heat-side laminate; and a welding shoe configured to heat the heat-side laminate after the heat-side laminate is cooled but before the thermal gradient dissipates so that the first side of the heat-side laminate does not deform as the second side of the heat-side laminate and the first side of the opposing laminate are welded together.

2. The system of claim 1 , wherein the cooling means includes a piccolo tube and a heat sink, the piccolo tube being configured to disperse cooled fluid to the heat sink.

3. The system of claim 1 , wherein the welding shoe comprises an induction coil configured to heat the heat-side laminate via a magnetic field.

4. The system of claim 1, wherein the welding shoe further comprises an elastomeric pressure pad configured to press the heat-side laminate and the opposing laminate together.

5. The system of claim 1, wherein the cooling means is an elastomeric thermal capacitor, the welding shoe comprising the elastomeric thermal capacitor.

6. A method of thermoplastic composite welding, the method comprising the steps of: placing a heat-side laminate having opposing first and second sides adjacent to an opposing laminate having first and second sides; cooling the heat-side laminate so as to create a thermal gradient in the heat-side laminate; and heating the heat-side laminate after the cooling step is initiated but before the thermal gradient dissipates so that the first side of the heat-side laminate does not deform as the second side of the heat-side laminate and the first side of the opposing laminate are welded together.

7. The method of claim 6, wherein the step of cooling the heat-side laminate includes at least one of immersing the first side of the heat-side laminate in a cold fluid, spraying the first side of the heat-side laminate with a cold fluid, positioning a cooled heat sink near the first side of the heat-side laminate, and subjecting the first side of the heat-side laminate to a convective cooling jet.

8. The method of claim 6, further comprising the step of applying pressure to at least one of the heat-side laminate and the opposing laminate.

9. The method of claim 8, wherein the pressure is applied via an elastomeric pressure pad.

10. The method of claim 9, wherein the step of heating the heat-side laminate is performed via a welding shoe having the elastomeric pressure pad.

11. The method of claim 8, wherein the pressure is applied via a pressure application means, the method further comprising the steps of cooling the pressure application means and cooling the heat-side laminate via the cooled pressure application means before heating the heat-side laminate.

12. The method of claim 11, wherein the step of cooling the pressure application means is performed before the step of applying pressure.

13. The method of claim 7, wherein the heat sink includes magnetic flux controller material, the heating step including induction welding the second side of the heat-side laminate and the first side of the opposing laminate together, wherein the induction welding includes controlling magnetic fields via the magnetic flux controller material.

14. The method of claim 6, wherein the induction welding includes exposing at least the heat-side laminate to high-frequency alternating magnetic fields to induce eddy current heating near the second side of the heat-side laminate and the first side of the opposing laminate.

15. The method of claim 6, wherein the step of cooling the heat-side laminate includes the step of passing cooled fluid through a piccolo tube so as to cool a heat sink adjacent to the heat-side laminate.

16. A method of thermoplastic composite welding, the method comprising the steps of: placing a heat-side laminate having opposing first and second sides adjacent to an opposing laminate having opposing first and second sides; cooling a thermal capacitor; cooling the heat-side laminate via the cooled thermal capacitor so as to create a thermal gradient in the heat-side laminate; and heating the heat-side laminate via a welding shoe after the step of cooling the heat-side laminate is initiated but before the thermal gradient dissipates so that the first side of the heat-side laminate does not deform as the second side of the heat-side laminate and the first side of the opposing laminate are welded together.

17. The method of claim 16, wherein the welding shoe comprises the thermal capacitor, the step of cooling the heat-side laminate including drawing heat from the heat-side laminate to the thermal capacitor.

18. The method of claim 16, wherein the step of cooling the thermal capacitor includes submersing at least a portion of the welding shoe in a cooled fluid.

19. The method of claim 16, wherein the welding shoe repeatedly alternates between cooling the heat-side laminate and heating the heat-side laminate.

20. A method of thermoplastic composite welding, the method comprising the steps of: placing a heat-side laminate having opposing first and second sides adjacent to an opposing laminate having first and second sides; cooling the heat-side laminate via a cold fluid so as to create a thermal gradient in the heat-side laminate; applying pressure to the heat-side laminate via an elastomeric pressure pad; and heating the heat-side laminate via high-frequency alternating magnetic fields to induce eddy currents near the second side of the heat-side laminate and the first side of the opposing laminate after the cooling step is initiated but before the thermal gradient dissipates so that the first side of the heat-side laminate does not deform as the second side of the heat-side laminate and the first side of the opposing laminate are welded together.

Description:
SYSTEM AND METHOD FOR THERMOPLASTIC WELDING USING AN INDUCED

THERMAL GRADIENT

BACKGROUND

[0001] Thermoplastic composite laminates are often welded together at adjacent faying surfaces via a heat source positioned near a non-faying surface of one of the laminates. The heat source typically has an inverse heat intensity to distance profile, which results in undesired melting or deformation of the non-faying surface.

[0002] Heat sinks made of electrically insulative and thermally conductive materials can be positioned between the heat source and the laminates during welding to prevent melting near the heat source, but such materials are rare, expensive, and/or difficult to process. Furthermore, heat sinks increase the heat required and/or slow the welding procedure. Cold fluids have been used to draw heat from the laminates during welding, but this technique is often ineffective because vacuum bags, pressure feet, and other devices used to apply pressure during welding reduce the effective heat transfer coefficient of cold fluids below an acceptable value, thus resulting in a thermal gradient in the laminate near the heat source insufficient to prevent melting or deformation of the laminate’s non-faying surface.

SUMMARY

[0003] Embodiments of the present invention solve the above-mentioned problems and other problems and provide a distinct advance in the art of thermoplastic composite welding. More particularly, embodiments of the invention provide a system and method of welding thermoplastic composite laminates together in which a desired pre-welding thermal gradient is established in the laminates.

[0004] A first embodiment of the invention is a thermoplastic composite welding system for welding a heat-side laminate and an opposing laminate together. The thermoplastic composite welding system broadly comprises a piccolo tube, a heat sink, and a welding shoe.

[0005] The piccolo tube includes a number of openings for dispersing cooled fluid to the heat sink (and hence to the heat-side laminate). Alternatively, other cooling means such as cold fluid immersion, a cold fluid convective jet, or a cold fluid spray may be used.

[0006] The heat sink draws heat from the heat-side laminate to cool the heat-side laminate and may be formed of copper, aluminum, or any other suitable thermally conductive material. The heat sink may also include flux controller material (magnetic composite) for aiding in controlling magnetic fields during heating. The heat sink and piccolo tube may be combined into a single device or may be separate components. [0007] The welding shoe includes an induction coil and an elastomeric pressure pad for welding the laminates together. The welding shoe may also include a frame or other structural members.

[0008] The induction coil includes left and right arms and a magnetic induction region. The left and right arms extend to an electrical power source for passing electrical current through the magnetic induction region. The magnetic induction region is positioned near a bottom end of the welding shoe for generating a magnetic field in the laminates.

[0009] The elastomeric pressure pad is positioned near a bottom of the welding shoe below the magnetic induction region of the induction coil. The elastomeric pressure pad promotes contact between the laminates. Specifically, the elastomeric pressure pad promotes compliance to textured or contoured surfaces.

[0010] A second embodiment of the invention is a method of thermoplastic welding two laminates together via the above-described welding system. First, the piccolo tube and the heat sink cool a heat-side laminate in a precooling stage so as to create a thermal gradient therein. For example, a cold fluid may be passed through the piccolo tube and dispersed to the heat sink adjacent to the heat-side laminate. The heat sink in turn draws heat from the heat-side laminate. Alternatively, the first side of the heat-side laminate may be immersed in a cold fluid, introduced to a convective cooling jet, or sprayed with a cold fluid. As such, a first side of the heat-side laminate may be super cooled or near super cooled whereas the second side of the heat-side laminate is relatively warmer.

[0011] Pressure is then applied to the heat-side laminate and/or an opposing laminate during a heating stage via the elastomeric pressure pad of the welding shoe. This provides compliance to textures or contours of the second side of the heat-side laminate and a first side of the opposing laminate.

[0012] The heat-side laminate is then heated in a heating stage via the welding shoe so as to weld the second side of the heat-side laminate and the first side of the opposing laminate (i.e. , the faying surfaces) together. Magnetic induction, microwave, radiation, or any other suitable heating mechanism may be used. A temperature of the first side of the heat-side laminate stays below a glass temperature during welding due to the thermal gradient induced during the precooling stage.

[0013] The above-described system and method and other embodiments effectively weld two laminates together without melting, deforming, or degrading other portions of the laminates. In particular, a surface of one of the laminates near the heat source is cooled before welding so that its temperature remains below a glass temperature during welding.

[0014] A third embodiment of the invention is another method of thermoplastic composite welding two laminates together. First, an elastomeric pressure pad of a welding shoe is cooled. For example, the elastomeric pressure pad may be introduced to dry ice, liquid nitrogen, a refrigeration cycle, or the like.

[0015] The heat-side laminate is then cooled via the elastomeric pressure pad in a precooling stage so as to create a thermal gradient therein. As such, a first side of the heat-side laminate may be super cooled or near super cooled whereas the second side of the heat-side laminate is relatively warmer. Pressure is also applied to the heat-side laminate and/or opposing laminate via the elastomeric pressure pad.

[0016] The heat-side laminate is then heated in a heating stage via the welding system so as to weld the second side of the heat-side laminate and a first side of the opposing laminate together. A temperature of the first side of the heat-side laminate stays below a glass temperature during welding due to the thermal gradient induced during the precooling stage.

[0017] A fourth embodiment of the invention is yet another method of thermoplastic composite welding two laminates together. First, an elastomeric thermal capacitor of a welding shoe is cooled. For example, the elastomeric thermal capacitor may by introduced to dry ice, liquid nitrogen, a refrigeration cycle, or the like. [0018] The heat-side laminate is then cooled in a precooling stage so as to create a thermal gradient therein. As such, a first side of the heat-side laminate may be super cooled or near super cooled whereas the second side of the heat-side laminate is relatively warmer.

[0019] The heat-side laminate is then heated in a heating stage via the welding system so as to weld the second side of the heat-side laminate and the first side of the opposing laminate together. A temperature of the first side of the heat-side laminate stays below a glass temperature during welding due to the thermal gradient induced during the precooling stage.

[0020] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0021] Other aspects and advantages of the present invention will be apparent from the following detailed description of the embodiments and the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0022] Embodiments of the present invention are described in detail below with reference to the attached drawing figures, wherein:

[0023] FIG. 1 is a front elevation view of a piccolo tube and a heat sink of a welding system constructed in accordance with an embodiment of the invention;

[0024] FIG. 2 is a front elevation view of a welding shoe of the welding system constructed in accordance with an embodiment of the invention;

[0025] FIG. 3 is a side elevation view of the welding shoe of FIG. 2;

[0026] FIG. 4 is a schematic view of a thermal gradient progression in accordance with an embodiment of the invention;

[0027] FIG. 5 is a thermal and pressure profile graph in accordance with an embodiment of the invention; [0028] FIG. 6 is a flow diagram depicting certain steps of a method of thermoplastic composite welding in accordance with an embodiment of the invention; [0029] FIG. 7 is a flow diagram depicting certain steps of a method of thermoplastic composite welding in accordance with another embodiment of the invention;

[0030] FIG. 8 is a side elevation view of a welding shoe constructed in accordance with another embodiment of the invention;

[0031] FIG. 9 is a front elevation view of the welding shoe of FIG. 8; and [0032] FIG. 10 is a flow diagram depicting certain steps of a method of thermoplastic composite welding in accordance with another embodiment of the invention.

[0033] The drawing figures do not limit the present invention to the specific embodiments disclosed and described herein. The drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] The following detailed description of the invention references the accompanying drawings that illustrate specific embodiments in which the invention can be practiced. The embodiments are intended to describe aspects of the invention in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments can be utilized and changes can be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense. The scope of the present invention is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled.

[0035] Turning to FIGS. 1-3, a thermoplastic composite welding system 10 constructed in accordance with various aspects of the invention for welding a heat-side laminate 100 and an opposing laminate 102 together is illustrated. The thermoplastic composite welding system 10 broadly comprises a piccolo tube 12, a heat sink 14, and a welding shoe 16. [0036] The piccolo tube 12 includes a number of openings for dispersing cooled fluid to the heat sink 14 (and hence to the heat-side laminate 100). Other cooling means may be used as described below.

[0037] The heat sink 14 draws heat from the heat-side laminate 100 to cool the heat-side laminate 100 and may be formed of copper, aluminum, or any other suitable thermally conductive material. The heat sink 14 may also include flux controller material (magnetic composite) for aiding in controlling magnetic fields during heating. The heat sink 14 and piccolo tube 12 may be combined into a single device or may be separate components.

[0038] The welding shoe 16 includes an induction coil 18 and an elastomeric pressure pad 20. The welding shoe 16 may also include a frame or other structural members.

[0039] The induction coil 18 includes left and right arms and a magnetic induction region. The left and right arms extend to an electrical power source for passing electrical current through the magnetic induction region. The magnetic induction region is positioned near a bottom end of the welding shoe 16 for generating a magnetic field in the laminates 100, 102.

[0040] The elastomeric pressure pad 20 is positioned near a bottom of the welding shoe 16 below the magnetic induction region of the induction coil 18. The elastomeric pressure pad 20 promotes contact between the laminates 100, 102. Specifically, the elastomeric pressure pad 20 promotes compliance to textured or contoured surfaces.

[0041] Turning to FIG. 6, and with reference to FIGS. 1-5, a method of thermoplastic composite welding will now be described in detail. First, the heat-side laminate 100 may be placed adjacent to the opposing laminate 102 such that their faying surfaces (e.g., the second side 106 of the heat-side laminate 100 and the first side 108 of the opposing laminate) contact each other, as shown in block 200.

[0042] The heat-side laminate 100 may then be cooled in a precooling stage so as to create a thermal gradient therein, as shown in block 202. For example, a cold fluid may be passed through the piccolo tube 12 and dispersed to the heat sink 14. The heat sink 14 may then draw heat from the heat-side laminate 100 so as to cool the heat- side laminate 100. Alternatively, the first side 104 of the heat-side laminate may be immersed in a cold fluid, introduced to a convective cooling jet, or sprayed with a cold fluid. As such, the first side 102 of the heat-side laminate 100 may be super cooled (to Tsc) from ambient temperature (Tamb) or near super cooled whereas the second side 104 and the first and second sides 106, 108 of the opposing laminate 102 may be relatively warmer.

[0043] Pressure may then be applied to the heat-side laminate 100 and/or the opposing laminate during a heating stage to a compaction pressure Pcompaction via the elastomeric pressure pad 20, as shown in block 204. This provides compliance to textures or contours of the second side of the heat-side laminate 100 and the first side 102 of the opposing laminate 104.

[0044] The heat-side laminate 100 may then be heated in a heating stage via the welding shoe 16 so as to weld the second side 104 of the heat-side laminate and the first side 106 of the opposing laminate 102 (i.e., the faying surfaces) together, as shown in block 206. Specifically, an electrical current may be passed through the induction coil 18 to generate a high-frequency alternating magnetic field. The high-frequency alternating magnetic field thereby induces eddy current heating in the heat-side laminate 100. The high-frequency alternating magnetic field may be controlled via flux controller material in the heat sink 14.

[0045] In the heating stage, a temperature of the second side 106 of the heat- side laminate 100 and the first side 108 of the opposing laminate 102 at least temporarily surpasses a molten temperature T m such that matrix resin at those sides is molten. Meanwhile, a temperature of the first side 104 of the heat-side laminate 100, which is closer to the heat source, peaks below a glass temperature T g due to the earlier-induced thermal gradient.

[0046] The induction coil 18 may be turned off during the heating stage to effect a desired maximum temperature of the faying surfaces. The faying surfaces and the first side 104 of the heat-side laminate 100 may then being to cool to Tamb. Meanwhile, the elastomeric pressure pad 20 may apply pressure or be in contact with the heat-side laminate 100 during the entire heating stage and into a cooling stage. [0047] The elastomeric pressure pad 20 may then be withdrawn in the cooling stage so as to reduce pressure on the laminates 100, 102 to zero. In particular, pressure may be reduced or eliminated when the temperature at the faying surfaces decreases below T g. The laminates 100, 102 continue to cool to Tamb in the cooling stage.

[0048] The above-described system and method provide several advantages. For example, the induced thermal gradient in the laminates 100, 102 provides a thermal sink before welding such that portions of the heat-side laminate 100 do not melt during welding and such that only regions of the laminates 100, 102 near the faying surfaces reach molten temperature (T m ). Heat transfer occurs in advance of welding, thus rendering a heat transfer rate (of the laminates 100, 102 in this case) less important. A variability of heat transfer rate between the laminates 100, 102 and any heat sink or other component positioned near the first side 104 of the heat-side laminate 100 can be overcome by varying a cooling time to achieve a desired surface temperature and thermal gradient. The first side 104 of the heat-side laminate 100 also does not undergo deformation or distortion because the first side 104 stays under glass temperature.

[0049] Turning to FIG. 7, another method of thermoplastic composite welding will now be described in detail. First, the heat-side laminate 100 may be placed adjacent to the opposing laminate 102 such that their faying surfaces (e.g., the second side 106 of the heat-side laminate 100 and the first side 108 of the opposing laminate) contact each other, as shown in block 300.

[0050] The elastomeric pressure pad 20 may then be cooled, as shown in block 302. For example, the elastomeric pressure pad 20 may be introduced to a heat sink such as dry ice, liquid nitrogen, a refrigeration cycle, or the like. This reduces the temperature of the elastomeric pressure pad 20.

[0051] The heat-side laminate 100 may then be cooled in a precooling stage so as to create a thermal gradient therein, as shown in block 304. Specifically, the elastomeric pressure pad 20 may be positioned adjacent to the first side 104 of the heat-side laminate 100 so as to cool the heat-side laminate 100. The first side 102 of the heat-side laminate 100 may be super cooled (to T sc ) from ambient temperature (Tamb) or near super cooled whereas the second side 104 and the first and second sides 106, 108 of the opposing laminate 102 may be relatively warmer. Pressure may also be applied to the heat-side laminate 100 and/or opposing laminate 102 via the elastomeric pressure pad 20.

[0052] The heat-side laminate 100 may then be heated in a heating stage via the welding shoe 16 so as to weld the second side 104 of the heat-side laminate and the first side 106 of the opposing laminate 102 together, as shown in block 306. Specifically, an electrical current may be passed through the induction coil 18 to generate a high-frequency alternating magnetic field. The high-frequency alternating magnetic field thereby induces eddy current heating in the heat-side laminate 100. The high-frequency alternating magnetic field may be controlled via flux controller material in the elastomeric pressure pad 20.

[0053] In the heating stage, a temperature of the second side 106 of the heat- side laminate 100 and the first side 108 of the opposing laminate 102 at least temporarily surpasses a molten temperature T m such that matrix resin at those sides is molten. Meanwhile, a temperature of the first side 104 of the heat-side laminate 100 peaks below a glass temperature T g due to the earlier-induced thermal gradient.

[0054] The elastomeric pressure pad 20 may then be withdrawn in the cooling stage so as to reduce pressure on the laminates 100, 102 to zero. In particular, pressure may be reduced or eliminated when the temperature at the faying surfaces decreases below T g. The laminates 100, 102 continue to cool to Tamb in the cooling stage.

[0055] Turning to FIGS. 8 and 9, the thermoplastic composite welding shoe 16 may alternatively or additionally include an elastomeric thermal capacitor 22. The elastomeric thermal capacitor 22 is positioned near a bottom end of the welding shoe 16 below the magnetic induction region of the induction coil 18. The elastomeric thermal capacitor 22 is configured to be cooled via a heat sink 24 for drawing heat from the heat-side laminate 100.

[0056] Turning to FIG. 10, and with reference to FIGS. 8 and 9, another method of thermoplastic composite welding will now be described in detail. First, the heat-side laminate 100 may be placed adjacent to the opposing laminate 102 such that their faying surfaces (e.g., the second side 106 of the heat-side laminate 100 and the first side 108 of the opposing laminate) contact each other, as shown in block 400.

[0057] The elastomeric thermal capacitor 22 may then be cooled, as shown in block 402. For example, the elastomeric thermal capacitor 22 may by introduced to a heat sink 24 such as dry ice, liquid nitrogen, a refrigeration cycle, or the like. This reduces the temperature of the elastomeric thermal capacitor 22.

[0058] The heat-side laminate 100 may then be cooled in a precooling stage so as to create a thermal gradient therein, as shown in block 404. Specifically, the elastomeric thermal capacitor 22 may be positioned adjacent to the first side 104 of the heat-side laminate 100 so as to cool the heat-side laminate 100. The first side 102 of the heat-side laminate 100 may be super cooled (to T sc ) from ambient temperature (Tamb) or near super cooled whereas the second side 104 and the first and second sides 106, 108 of the opposing laminate 102 may be relatively warmer.

[0059] The heat-side laminate 100 may then be heated in a heating stage via the welding shoe 16 so as to weld the second side 104 of the heat-side laminate and the first side 106 of the opposing laminate 102 together, as shown in block 406. Specifically, an electrical current may be passed through the induction coil 18 to generate a high-frequency alternating magnetic field. The high-frequency alternating magnetic field thereby induces eddy current heating in the heat-side laminate 100. The high-frequency alternating magnetic field may be controlled via flux controller material in the elastomeric thermal capacitor 22.

[0060] In the heating stage, a temperature of the second side 106 of the heat- side laminate 100 and the first side 108 of the opposing laminate 102 at least temporarily surpasses a molten temperature T m such that matrix resin at those sides is molten. Meanwhile, a temperature of the first side 104 of the heat-side laminate 100 peaks below a glass temperature T g due to the earlier-induced thermal gradient.

[0061] The elastomeric thermal capacitor 22 may then be withdrawn in the cooling stage. The laminates 100, 102 continue to cool to Tamb in the cooling stage. [0062] Having thus described various embodiments of the invention, what is claimed as new and desired to be protected by Letters Patent includes the following: