FIELD OF THE INVENTION
This invention is directed generally to laser welding of thermoplastic materials, and, more particularly, to a system for laser welding thermoplastic components.
BACKGROUND OF THE INVENTION
Laser welding of thermoplastics typically utilizes diode or Nd:YAG lasers in the near-infrared spectrum, and is accomplished using the through-transmission technique. High intensity infrared laser light passes through a part that is relatively transmissive to light of that wavelength, such as a natural (without added color or filler) polymer, and is absorbed (converted to heat) by material of the second part in the assembly, such as a polymer loaded with carbon black. Various color combinations can be welded, but one must always be relatively transmissive and the other relatively absorbtive at the specific wavelength of laser light used.
Due to the relatively high cost of laser equipment, laser welding has generally only been used where the benefits of clean and precise joints without external heat, vibration, or particulate are requirements of the end use. Since most of the laser welding applications have come from the displacement of other joining technologies, few laser welded assemblies have been designed specifically for laser welding from the initial part concept.
The problem with using assemblies that are not designed specifically for laser welding is that the parts may not be suitable for laser welding. In traditional welding, the assemblies comprise two components, such as the components 12 and 14 shown in . As can be seen the first component 12 includes a substantially planar flange 16 that fits into a groove 18 of the second component. To weld the two components 12, 14 together, the two components are clamped together with the flange 16 projecting into the groove 18, creating a welding surface interface 20. The clamping force is directed perpendicular to the welding surface interface 20. In the embodiment shown in , collapse welding is used, which results in flash or excess material 21 to fill in the rest of the groove 18. However, due to the flow of molten material, the clamping force on the assembly has an influence on the finished part strength and appearance. Too little clamping force will result in weak welds or “skips” in the weld, while too much will result in excessive flash (excess material) or excessive molecular orientation and shear thinning in the joint, leading to reduction in the weld strength.
In contained welding, as illustrated in , flash is eliminated. An assembly designed for traditional welding but converted to contained welding includes two components 22 and 24. As can be seen, the first component 22 includes a substantially planar flange 26 that fits into a groove 28 of the second component 24, creating a welding surface interface 30. Similar to collapse welding, the two components are clamped together, with the direction of the clamping force being perpendicular to the welding surface interface 30. If too little clamping force is used, it can result in weak welds or “skips” in the weld, but one of the advantages of contained welding is that the upper limit of the clamping force is relatively high.
SUMMARY OF THE INVENTION
According to one embodiment of the present invention, a welding system is provided that includes a pair of thermoplastic components forming a weld interface extending at an acute angle to the direction of application of a clamping force. A clamping mechanism applies a clamping force to the two components to urge the components together at said weld interface, and laser light is directed onto the weld interface to weld the two components together.
In one embodiment of the invention, the interface between the thermoplastic components includes engaging surfaces on the components to prevent sliding movement of the components relative to each other along the weld interface in response to the application of the clamping force. The engaging surfaces are preferably in the shape of registered projections and grooves formed by opposed surfaces of the thermoplastic components. The laser light is preferably directed onto the weld interface in a direction substantially perpendicular to the weld interface, from an exterior surface of at least one of the thermoplastic components that is substantially transparent to the laser light.
The above summary is not intended to represent each embodiment or every aspect of the present invention. The detailed description and accompanying drawings will describe and illustrate certain exemplary embodiments of the present invention.
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