Method and apparatus for infrared welding of polymer composites

Abstract

A system (1) and method for infrared welding of two carbon fiber reinforced thermoplastic workpieces is disclosed, which enables better quality and strength workpieces to be obtained. The system (1) removes the heating means and engages the contact between the two workpieces more quickly.

Description

Technical Field

[0001] The present invention relates to a manufacturing process for welding of polymer composite materials. More specifically, the present invention provides a solution for welding polymers by infrared welding. Background Art

[0002] Infrared welding is a technique that is well used to bond plastic materials together. It involves placing two workpieces in a holder (such as in a forging die) and, after illuminating appropriate portions of the workpieces with infrared light, applying a force between the two workpieces to bond them together.

[0003] Figure 1 This technique is shown. The system 1 comprises a lower tool 2 and an upper tool 4, which is movable vertically (direction z). A heating assembly 6 comprising a series of infrared lamps 6' is movable laterally (along x), together with a screen 8 preventing radiation from the lamps 6' from reaching the entire workpieces 10 and 12 to be joined together.

[0004] Figure 1 The four main steps of infrared welding are shown: in step (a), the lamp is switched on and starts radiating; in step (b), the parts 10.1, 12.1 of the workpieces 10, 12 start to melt or disintegrate (and thus increase in width); in step (c), the heating lamp and shield are retracted, and in step (d), the tools 2, 4 are moved towards each other to apply welding pressure.

[0005] In the known art, the retraction of the heating device and the subsequent application of welding pressure takes about 3 to 5 seconds. This corresponds to the incompressible time required to operate the pneumatic or hydraulic actuator to retract the heating device, the time for the sensor to detect the complete retraction of the heating device and the PLC to confirm the retraction of the heating device, and the time for the upper tool to start its vertical descent.

[0006] However, this known technology is not suitable for welding operations of materials with high thermal conductivity. For example, carbon fiber reinforced thermoplastics (CFRTP) have a thermal conductivity that is 5 to 10 times higher than that of some other polymers (4-7 W.m in the fiber direction). -1 .K -1 , 0.5-1W.m in the horizontal direction -1 .K -1 ). Temperature variations across the workpiece can significantly affect the structure of the final product (porosity, crystallization rate). Due to its high thermal conductivity, a CFRTP material heated at 350°C loses 30 to 80°C per second. This means that in order to ensure that the temperature of the CFRTP is appropriate at the moment the two workpieces come into contact (i.e. 3 to 5 seconds after heating stops), the CFRTP should theoretically be overheated above 450°C.

[0007] However, excessive heat is not suitable for CFRTP materials because the materials will degrade and possibly cross-link, preventing them from being subsequently weldable.

[0008] Therefore, there is a need to provide a welding system and method for welding CFRTP by infrared radiation. Summary of the invention

[0009] The present invention aims to provide a system and a method which overcome the above-mentioned drawbacks and finally enable to properly bond two CFRTP workpieces by infrared radiation, with a high quality bond.

[0010] The present invention relates to a system for infrared welding a first workpiece made of carbon fiber reinforced thermoplastic polymer CFRTP to a second workpiece made of CFRTP, the system comprising: an upper tool for holding the first workpiece, wherein the upper tool is movable in a vertical direction; a lower tool for holding the second workpiece; a heating assembly, the heating assembly comprising an infrared heating device and configured to move in a lateral direction between an operating position and a rest position, in which the heating device is capable of simultaneously heating corresponding portions of the first workpiece and the second workpiece; and a mechanism configured to synchronously move the upper tool and the heating assembly, the mechanism comprising: a mechanical connection connecting the upper tool to the heating assembly; and an actuator acting directly on one of the upper tool or the heating assembly, while the other of the upper tool or the heating assembly is moved via the mechanical connection.

[0011] With such a system, the time between the end of heating and the moment when the two workpieces come into contact with one another is substantially reduced to approximately 1.5 seconds, thus being half to three times faster than with known systems.

[0012] According to an advantageous embodiment, the system further comprises springs to support the lower tool in a vertically movable manner on a vertically fixed support. These springs are able to control the maximum pressure exerted between the two workpieces.

[0013] According to an advantageous embodiment, the system comprises a stop for interrupting the downward movement of the upper tool.The stop enables the geometry of the final product to be controlled.

[0014] According to an advantageous embodiment, the system comprises a damper for damping the movement of the heating assembly.

[0015] According to an advantageous embodiment, the mechanical connection is a rod which forms a pivot connection with the upper tool and a pivot connection with the heating assembly.Alternative connections are also foreseen, such as a chain and pulley assembly, a scissor bar with rollers engaged in a track, etc.

[0016] The present invention also relates to a method for infrared welding a first workpiece made of carbon fiber reinforced thermoplastic polymer (CFRTP) to a second workpiece made of CFRTP, the method being performed using a system according to the above-mentioned embodiment, the method comprising: heating corresponding portions of the first workpiece and the second workpiece using an infrared heating assembly; synchronizing the lateral movement of the heating assembly and the downward movement of the upper tool.

[0017] According to an advantageous embodiment, the system further comprises a spring for supporting the lower tool in a vertically movable manner, so that the welding pressure between the two workpieces generated by the downward movement of the upper tool is limited by the spring.

[0018] According to an advantageous embodiment, the system comprises a stopper and when the upper tool contacts the stopper during its downward movement, the movement of the heating assembly and the upper tool is stopped simultaneously.

[0019] According to an advantageous embodiment, the system comprises a damper, and the movement of the heating assembly and the upper tool is damped by the damper.

[0020] Benefits of the Invention

[0021] Several aspects of the invention ensure, to varying degrees, that high quality (aerospace quality standards) carbon fiber reinforced products can be obtained by infrared welding. The system and method of the invention also allow strong products of various thicknesses (even more than 12 mm thick) to be obtained.

[0022] The system is able to reduce the time interval between the end of the heating step and the start of applying welding pressure to about 1.5 seconds. This makes the process faster, but more importantly, this duration significantly improves the quality of the final product, as there is no need to overheat the CFRTP material and a better quality weld joint is ensured.

[0023] The system is also reliable and cost effective, and is simpler to control since it only requires commanding one actuator.

[0024] Further benefits may be readily appreciated with respect to the discussion of the following figures. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A method according to the prior art is shown;

[0026] Figure 2 A system of the present invention is shown. DETAILED DESCRIPTION

[0027] The following examples and drawings are given for illustrative purposes only. The present invention is not limited by these examples, but only by the appended claims. The various parts of the system can have various attributes or be embodied in various ways. Unless otherwise explicitly mentioned, each variation of each part of the system can be combined with each variation of any other part of the system.

[0028] The drawings are schematic and not drawn to scale. Some elements of the system are not shown, such as, for example: elements for assembling the various components together (flanges, screws, etc.), elements for properly ensuring the sealing of the various compartments (seals, etc.), or elements for controlling the system (wires, sensors, actuators, valves, safety devices, etc.).

[0029] The above background technology discusses Figure 1 .

[0030] Figure 2 The system of the invention is shown in two extreme positions of the system.

[0031] In the heating step (a), the infrared light 6' of the heating assembly 6 is positioned in an operating position between the two tools 2, 4 holding the workpieces 10, 12. The heating assembly 6 can thus be substantially similar to Figure 1 Known heating components.

[0032] The connecting rod 14 movably connects the upper tool 4 to the heating assembly 6. The rod 14 is pivotally engaged with the upper tool 4 at a first pivot joint 14.1 and is pivotally engaged with the heating assembly 6 at a second pivot joint 14.2.

[0033] An actuator may be provided, as indicated by arrow A, to move the upper tool 4 downwards. Alternatively, the actuator moves the heating assembly 6 laterally as indicated by arrow B. In both cases, due to the connecting rod 14, the actuator moves both the upper tool and the heating assembly simultaneously.

[0034] Once the workpieces 10, 12 are heated to their melting or pyrolysis point, the actuator is operated to simultaneously move the lamp laterally apart and the upper tool 4 downwardly so that the workpieces 10, 12 contact each other.

[0035] Figure 2 The bottom part of shows the system 1 in the final position.

[0036] The lower tool 2 is supported on a fixed platform 17 by springs 16. The springs 16 are selected to have a predetermined stiffness so that the pressure exerted by the upper tool 4 on the interface between the two workpieces 10, 12 does not exceed a predetermined amount.

[0037] A stop 18 is foreseen to stop the vertical movement of the upper tool 4 so that the path of the upper tool and therefore the final geometry of the weld joint can be controlled.

[0038] Furthermore, the damper 20 may be arranged to slow the movement of the heating assembly 6 (and upper tool) before or after the workpieces 10, 12 contact each other. The heating assembly may include fragile elements (lamps) and dampening the movement may avoid any failure due to sudden stops.

[0039] The present application is particularly directed to welded joints of two workpieces that are at least partially flat near the welded joint. For example, Figure 2 A stiffener 10 is shown to be welded to the skin. However, the invention is not limited to this particular example and may be applied to welds of various types or geometries.

[0040] Furthermore, those skilled in the art will appreciate from the teachings of this application that the present invention can be practiced with alternative heating devices (other than infrared) and with materials other than carbon reinforced thermoplastics.

Claims

1. A system (1) for infrared welding a first workpiece (10) made of carbon fiber reinforced thermoplastic polymer (CFRTP) to a second workpiece (12) made of CFRTP, the system comprising: an upper tool (4) for holding the first workpiece (10), wherein the upper tool (4) is movable in a vertical direction (z); a lower tool (2) for holding the second workpiece (12); a heating assembly (6) comprising infrared heating means and being configured to move in a transverse direction (x) between an operating position and a rest position, in which the heating means is capable of simultaneously heating respective portions (10.1, 12.1) of the first and second workpieces (10, 12); and A mechanism configured to synchronously move the upper tool (4) and the heating assembly, the mechanism comprising: a mechanical connection (14) connecting the upper tool (4) to the heating assembly (6); and An actuator (A, B) acts directly on one of the upper tool (4) or the heating assembly (6), while the other of the upper tool (4) or the heating assembly (6) is moved via the mechanical connection (14).

2. The system (1) according to claim 1, characterized in that The system (1) also comprises springs (16) for supporting the lower tool (2) in a vertically movable manner on a vertically fixed support (17).

3. The system (1) according to claim 1 or 2, characterized in that The system (1) comprises a stop (18) for interrupting the downward movement of the upper tool (4).

4. The system (1) according to any one of claims 1 to 3, characterized in that The system (1) comprises a damper (20) for damping the movement of the heating assembly (6).

5. The system (1) according to any one of claims 1 to 4, characterized in that The mechanical connection (14) is a rod that forms a pivot connection (14.1) with the upper tool (4) and a pivot connection (14.2) with the heating assembly (6).

6. A method for infrared welding a first workpiece (10) made of carbon fiber reinforced thermoplastic polymer CFRTP to a second workpiece (12) made of CFRTP, the method being performed using a system (1) according to any one of claims 1 to 5, the method comprising: - heating (a) corresponding portions (10.1, 12.1) of the first workpiece (10) and the second workpiece (12) using the infrared heating assembly (6); -Synchronously perform the following operations (c): - moving the heating element (6) laterally; and - Moving the upper tool (4) downwards.

7. The method according to claim 6, characterized in that The system (1) further comprises a spring (16) for supporting the lower tool (2) in a vertically movable manner, so that the welding pressure between the two workpieces (10, 12) generated by the downward movement of the upper tool (4) is limited by the spring (16).

8. The method according to claim 6 or 7, characterized in that: The system (1) comprises a stopper (18), and when the upper tool (4) contacts the stopper (18) during its downward movement, the movement of the heating assembly (6) and the upper tool (4) is stopped simultaneously.

9. The method according to any one of claims 6 to 8, characterized in that The system comprises a damper (20), and the movement of the heating assembly (6) and the upper tool (4) is damped by the damper (20).

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