The present invention relates to plastic welding, and more particularly to laser welding of plastic parts.
Laser welding is commonly used to join plastic or resinous parts, such as thermoplastic parts, at a welding zone. An example of such use of lasers can be found in U.S. Pat. No. 4,636,609, which is expressly incorporated herein by reference.
As is well known, lasers provide a semi-focused beam of electromagnetic radiation at a specified frequency (i.e., coherent monochromatic radiation). There are a number of types of lasers available; however, infrared lasers or non-coherent sources provide a relatively economical source of radiative energy for use in heating a welding zone. One particular example of infrared welding is known as through-transmission infrared (TTIr) welding. TTIr welding employs an infrared laser capable of producing infrared radiation that is directed by lenses, diffractive optics, fiber optics, waveguides, lightpipes, or lightguides through a first plastic part and into a second plastic part. This first plastic part is often referred to as the transmissive piece, since it generally permits the laser beam from the laser to pass therethrough. However, the second plastic part is often referred to as absorptive piece, since this piece (and/or an absorbtive additive at the weld interface) generally absorbs the radiative energy of the laser beam to produce heat in the welding zone. This heat in the welding zone causes the transmissive piece and the absorptive piece to be melted and, with intimate contact, welded together.
With reference to
Oftentimes, the plastic parts are a relatively low absorber of the infrared light, particularly in cases where the second plastic part is made of the same material as the first plastic part and both plastic parts have a color having high transmissivity to infrared laser light, such as being clear or relatively clear. The infrared absorber additive used at the weld interface may also be a relatively low absorber of the infrared light. Further, in some cases, the infrared absorber additive cannot be used.
With low absorbers, either too low a laser energy is delivered to the weld interface to make a weld, or relatively high laser energies need to be used to translate into enough energy at the weld interface to make a weld.
In accordance with an aspect of the present disclosure, two high transmissivity plastic parts are laser welded together using infrared laser welding. One or both of the plastic parts has a modified surface that increases the absorbtivity to infrared laser light of the plastic part having the modified surface at the modified surface. The two plastic parts are then laser welded by directing a beam of infrared laser light to the plastic parts which are oriented so that the beam of infrared laser light passes through one the plastic parts, impinges the modified surface or surfaces at a weld interface where the plastic parts abut each other, and then passes through the other plastic part. The modified surface or surfaces increase the absorbtivity of infrared laser light of the plastic part or parts at the weld interface to melt the plastic parts at the weld interface so as to weld them together.
In an aspect, the surface of each part to be modified is modified by roughening. In an aspect, roughening is mechanical roughening. In an aspect, the surface of each part to be modified is modified by etching. In an aspect, etching is laser etching. In an aspect, etching is chemical etching. In an aspect, the surface of each part to be modified is modified by laser burning that discolors that surface. In an aspect, the surface the surface of each part to be modified is modified by laser etching to roughen that surface and that also burns that surface to discolor it.
In an aspect, each part having a modified surface is formed to have the modified surface. In an aspect, each part having a modified surface is molded to have roughened surface that is the modified surface.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
With reference to
When parts 200, 202 are welded, they are positioned in an infrared laser welding system, such as infrared laser welding system 100 of
The modified surface (or surfaces) 204, 206 can be provided in any manner that sufficiently alters the characteristics of the surface of the plastic part to increase the absorbtivity of infrared laser light to melt the plastic parts 200, 202 at the weld interface 208 so as to weld them together. In an aspect, the surface (or surfaces) 204, 206 is modified after the respective part 200, 202 has been formed to provide the modified surface. In an aspect, the surface (or surfaces) 204, 206 is modified by roughening. In an aspect, the surface (or surfaces) 204, 206 is roughened by etching, such as laser etching or chemical etching. In an aspect, the surface (or surfaces) 204, 206 is modified by laser burning the surface (or surfaces) 204, 206 to discolor it. In an aspect, the surface (or surfaces) 204, 206 is also modified by laser etching. In an aspect, the surface (or surfaces) 204, 206 is roughened by mechanical roughening, such as grinding, sanding, or other mechanical abrasion.
In an aspect, the modified surface (or surfaces) 204, 206 is provided by forming the plastic part (or parts) 200, 204 having the modified surface so that surface (or surfaces) 204, 206 has the different characteristics. For example, if the part is formed by molding, the part is molded so that the modified surface (or surfaces) 204, 206 is a roughened surface. That is, the modified surface (or surfaces) 204, 206 is rougher than a surface (such as surface 210 of part 202 in
When parts 200, 202 are welded in an infrared laser welding system, such as infrared laser welding system 100 of
When laser etching and/or burning is used to modify the surface (or surfaces) 204, 206 of parts 200, 202, the same infrared welder that is used to weld the parts 200, 202 can also be used to etch and/or burn the surface (or surfaces) 204, 206.
The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.
This application claims the benefit of U.S. Provisional Application No. 61/433,308, filed on Jan. 17, 2011. The entire disclosure of the above application is incorporated herein by reference.
Number | Date | Country | |
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61433308 | Jan 2011 | US |