Method and apparatus for welding together a first object and a second object

Abstract

A method and an apparatus for welding together a first object and a second object. The method comprises applying a layer of carbon nanotubes onto a surface of the first object and bringing the first object and the second object into contact, such that the layer of carbon nanotubes on the surface of the first object is in contact with a surface of the second object. The method further comprises applying a voltage to the layer of carbon nanotubes, such that an electrical current flows through the layer of carbon nanotubes, wherein material of the first object adjacent to the layer of carbon nanotubes and material of the second object adjacent to the layer of carbon nanotubes is heated and melted by the electrical current and thereby welded together. Further, an apparatus for welding together a first object and a second object is presented.

Claims

1. A method for welding together a first object and a second object, comprising: applying a layer of carbon nanotubes onto a surface of the first object; bringing the first object and the second object into contact, such that the layer of carbon nanotubes on the surface of the first object is in contact with a surface of the second object; applying a voltage to the layer of carbon nanotubes, such that an electrical current is caused to flow through the layer of carbon nanotubes, wherein material of the first object adjacent to the layer of carbon nanotubes and material of the second object adjacent to the layer of carbon nanotubes is heated and melted by the electrical current and thereby welded together.

2. The method according to claim 1, further comprising: before the step of bringing the first object and the second object into contact, applying a further layer of carbon nanotubes onto the surface of the second object, wherein in the step of applying the voltage, the electrical current also is caused to flow through the further layer of carbon nanotubes.

3. The method according to claim 1, wherein the material of the first object and the material of the second object is heated by remote Joule heating.

4. The method according to claim 1, wherein at least one of the first object and the second object comprises carbon fiber-reinforced plastic.

5. The method according to claim 4, wherein at least the one of the first object and the second object comprises carbon fiber-reinforced thermoplastic.

6. The method according to claim 1, wherein the layer of carbon nanotubes is applied by using a solvent comprising a plurality of carbon nanotubes.

7. The method according to claim 1, wherein the carbon nanotubes in the layer of carbon nanotubes are arranged in a grid-like structure.

8. The method according to claim 1, further comprising: during the step of applying the voltage, measuring a temperature of at least one of the material of the first object or of the material of the second object; and controlling the applied voltage based on the measured temperature.

9. The method according to claim 8, wherein a thermal camera is used for measuring the temperature.

10. An apparatus for welding together a first object and a second object, comprising: at least two contact units configured to apply a voltage to a layer of carbon nanotubes, which layer is arranged at a contact surface between a first object and a second object; a temperature measuring device configured to measure a temperature of at least one of material of the first object adjacent to the layer of carbon nanotubes or material of the second object adjacent to the layer of carbon nanotubes; and a control unit configured to apply a voltage to the layer of carbon nanotubes via the contact units, and to control the applied voltage based on the measured temperature.

11. The apparatus of claim 10, wherein the temperature measuring device is a thermal camera.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Preferred embodiments of the invention are now described in greater detail with reference to the appended schematic drawings, wherein

[0022] FIG. 1 shows the principle of remote Joule heating, whereas, exemplarily, one single carbon nanotube is embedded in surrounding material and a current is flowing through the carbon nanotube;

[0023] FIG. 2 shows a step of applying a layer of carbon nanotubes onto a surface of a first object;

[0024] FIG. 3 shows a step of bringing the first object and a second object into contact; and

[0025] FIG. 4 shows an apparatus for welding together the first object and the second object, during a step of applying a voltage to the layer of carbon nanotubes, such that an electrical current flows through the layer of carbon nanotubes and such that the first object and the second object are welded together.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Although the following disclosure describes welding of two objects together, wherein each of these objects comprises at least one layer of thermoplastic CFRP, it should be appreciated by those skilled in the art that the invention is not limited to this material. Any kind of suitable materials may be welded together by the method described herein, as long as these materials are suitable for being welded by heat. Further, only one of the two objects that are welded together may comprise thermoplastic CFRP, whereas the other object may be made of another suitable material. Further, although the present disclosure describes a welding process with reference to the physical phenomenon called remote Joule heating, other physical principles, such as direct (or classical) Joule heating, may be used for generating heat at a contact surface between the two objects.

[0027] FIG. 1 schematically shows the principle of remote Joule heating by a carbon nanotube 2. The phenomenon of remote Joule heating was discovered by Kamal H. Baloch et al. at the University of Maryland in 2012. It has been discovered that if a carbon nanotube 2 is placed under electric current I and is inserted in a surrounding material 4, the electric current I in the carbon nanotube 2 can couple to the vibrational modes of the surrounding material 4, heating it remotely. More precisely, atoms 6 of the surrounding material 4 start to vibrate or oscillate, as indicated by arrows in FIG. 1. Therefore, by applying a voltage, which leads to an electrical current I through the carbon nanotube 2, material 4 surrounding the carbon nanotube 2 can be remotely heated. The phenomenon of remote Joule heating significantly differs from the typically expected principle of (direct) Joule heating, where it is assumed that electrons collide with the atoms of a conductor, generating heat locally and only in regions of non-zero current density. Although the present disclosure focuses on the phenomenon of remote Joule heating, the surrounding material 4 may also be heated by the current I in the carbon nanotube 2 in case the carbon nanotube 2 should exhibit direct (or classical) Joule heating. In this case, the heat is transferred from the carbon nanotube 2 to the surrounding material 4.

[0028] A voltage source 8 is used to apply a particular voltage U, which leads to a predetermined current I in the carbon nanotube 2. For this, the current I in the carbon nanotube 2 may be monitored by a current measurement device (not shown) and the voltage U of the voltage source 8 may be controlled accordingly.

[0029] FIG. 2 shows a step of applying a layer of carbon nanotubes 2 onto a surface 10 of a first object 12. In the described embodiment, the first object 12 comprises thermoplastic CFRP. For the sake of simplicity, the first object 12 is shown as a plate-like object having one large top surface 10. In the shown example, the surface 10 of the first object 12 shall be welded to a corresponding surface of a second object.

[0030] In the first step shown in FIG. 2, a layer of carbon nanotubes 2 is applied on the surface 10 of the first object 12. As shown in FIG. 2, a carbon nanotube grid is applied on the surface 10 of the first object 12, by pouring a solvent 14 containing long carbon nanotubes 2 onto the surface 10 under controlled conditions. For this step, a dispensing device 16 may be used, which is configured to apply a homogeneous layer of carbon nanotubes 2 onto the surface 10 of the first object 12.

[0031] As shown in FIG. 2, the entire surface 10 of the first object 12, which shall later represent a contact surface with regard to the second object, is covered with carbon nanotubes 2 in a grid-like structure. It is to be noted that the grid-like structure shown in FIG. 2 is only a schematic representation and that the layer of carbon nanotubes 2 may be much denser and the carbon nanotubes may be much smaller than shown in FIG. 2. Further, the individual carbon nanotubes 2 do not need to have a particular orientation. It is rather desirable that the layer of carbon nanotubes 2 covers the entire surface 10 to be welded. Further, the individual carbon nanotubes 2 overlap each other, as shown in the magnified representation in FIG. 2. By these overlapping carbon nanotubes 2, an electrical connection is established from one end of the surface 10 to another end of the surface 10 (in the representation of FIG. 2, for example, from left to right).

[0032] Further, the same process step as shown in FIG. 2 may be used for depositing a layer of carbon nanotubes 2 onto a surface of the second object that shall be welded together with the first object 12. However, this step is optional and also a second object may be used, which has no layer of carbon nanotubes 2 deposited on it.

[0033] FIG. 3 shows a step of bringing the first object 12 and the second object 18 into contact. As shown in the left part of FIG. 3, the first object 12 comprises a layer of carbon nanotubes 2 on a surface 10 thereof. The layer of carbon nanotubes 2 has been applied, for example, by using the method step described with reference to FIG. 2.

[0034] Further, also the second object 18 has a surface, on which a layer of carbon nanotubes 2 has been applied. However, the layer of carbon nanotubes 2 on the second object 18 is optional. In the described example, both the first object 12 and the second object 18 are made of thermoplastic CFRP. As shown in FIG. 3, the first object 12 and the second object 18 are brought into contact, such that the layer of carbon nanotubes 2 on the surface 10 of the first object 12 is in contact with the surface of the second object 18, which shall be welded to the surface 10 of the first object 12. After bringing the first object 12 and the second object 18 into contact, a contact surface 20 is formed between the first object 12 and the second object 18. At this contact surface 20, the layer of carbon nanotubes 2 of the first object 12 is present. In case also a layer of carbon nanotubes 2 has been applied onto the second object 18, the two layers of carbon nanotubes 2 conjoin with each other and form a conjoined layer of carbon nanotubes 2 at the contact surface 20. Pressure may be applied during bringing the two objects 12 and 18 into contact, wherein this pressure may be maintained during the next step of applying a voltage.

[0035] FIG. 4 shows a schematic representation of a step of applying a voltage to the layer of carbon nanotubes 2, such that an electrical current flows through the layer of carbon nanotubes 2. For carrying out this step of applying the voltage, an apparatus 21 for welding together the first object 12 and the second object 18 is used. FIG. 4 shows the first object 12 and the second object 18 stacked together, as it is the result of the step shown in FIG. 3. The layer of carbon nanotubes 2 in the contact layer 20 is electrically contacted on two opposite sides of the contact layer 20 by respective contact units 22 of the apparatus 21. The layer of carbon nanotubes 2 has been applied between the first object 12 and the second object 18, such it can be contacted by the contact unit 22. For example, the layer of carbon nanotubes 2 may overlap over the edge of the contact surface 20 and the first object 12 and/or the second object 18. In that case, the layer of carbon nanotubes 2 can be contacted from outside. In case one of the surfaces of the first object 12 or the second object 18 is larger than the surface of the other object, the layer of carbon nanotubes 2 can extend over this larger surface in order to be connectable by the connecting unit 22 when the two objects 12 and 18 have been brought into contact. Further, the connecting unit 22 may be deposited between the first object 12 and the second object 18 before the step of bringing the two objects together, such that the connecting unit 22 contacts the layer of carbon nanotubes 2 inside the combined objects 12 and 18.

[0036] A voltage is applied to the layer of carbon nanotubes 2 by a control unit 24 of the apparatus 21. The control unit 24 comprises a voltage source 8. The voltage may be controlled by the control unit 24 such that a constant, predefined current I flows through the layer of carbon nanotubes 2. A temperature measuring device 26 for measuring a temperature T of the material of the first object 12 and/or of the material of the second object 18 may be provided. In the example shown in FIG. 4, this temperature measuring device 26 of the apparatus 21 is a thermal camera 26 configured to output an electrical signal representative of a two-dimensional thermal image. The thermal image may indicate a temperature distribution within the contact surface 20. Thus, it is possible to monitor the temperature within the two combined objects 12 and 18. A temperature rise is caused by the current flowing through the layer of carbon nanotubes 2.

[0037] According to the principle of remote Joule heating (see above) the current flowing through the layer of carbon nanotubes 2 causes the material surrounding the carbon nanotubes 2 to be heated. This heating is observed by the thermal camera 26 in the form of temperature values. The electrical signal output by the thermal camera 26 is input into the control device 24 of the apparatus 21 via a respective input interface (not shown). This makes it possible for the control unit 24 to control the applied voltage U and/or the flowing current I based on a measured temperature T. For example, a feedback loop may be used in the control unit 24. For example, the control unit 24 may carried out control such that it is ensured that the temperature T at the contact surface 20 is within a predetermined temperature range. The predetermined temperature range may be set such that the temperature is high enough to melt the material of the first object 12 and the second object 18 at the contact surface 20, but not too high in order to not burn the surrounding material.

[0038] For carrying out the control of the control unit 24, a processor (for example, a CPU) may be used with a respective programming by software and/or by hardware.

[0039] As shown in FIG. 4, the layer of carbon nanotubes 2 may be contacted by using one large contact unit 22 over an entire length of the layer of carbon nanotubes 2. Alternatively, the layer of carbon nanotubes 2 may be contacted by using a contact unit 22 that is configured to apply different voltage values U to different positions of the layer of carbon nanotubes 2. Thus, certain regions of the layer of carbon nanotubes 2 may be individually supplied with a predefined current value I in order to individually control a temperature T in this region.

[0040] As described above, the contact surface 20 is heated up by the effect of remote Joule heating, which causes material adjacent to the layer of carbon nanotubes 2 to melt. Material of the first object 12 and of the second object 18 melts and conjoins with each other, which welds the first object 12 and the second object 18 together. After a step of cooling, the material is hardened again and the first object 12 and the second object 18 are welded together.

[0041] The above-described technique provides a method and an apparatus for welding together a first object and a second object without requiring an external heating source or an external vibration source, and without connecting any magnetic circuits or complex electric circuits. Thus, the presented technique is cheap, easy to use and convenient, compared to welding techniques of the prior art.

[0042] Although the above description is given with reference to the appended FIGS. 1 to 4, it should be appreciated that the present disclosure is not limited to these specific embodiments. For example, a different material may be used for the first object and/or the second object. Further, the first object and the second object (and, in particular, their surfaces) are not limited to the shape shown in the figures. Further, a plurality of layers of carbon nanotubes may be formed between the first object and the second object. This conjoined layer of carbon nanotubes may be contacted in any desired way suitable for letting a current flow through the layer of carbon nanotubes.

[0043] While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms comprise or comprising do not exclude other elements or steps, the terms a or one do not exclude a plural number, and the term or means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.