A Study on CO2 Laser Butt Welding of Plastics by Heat Transfer Control Using a Heat Sink

2006 Fiscal Year Final Research Report Summary

• Project/Area Number: 17560175
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Thermal engineering
• Research Institution: The University of Electro-Communications
• Principal Investigator: KUROSAKI Yasuo The University of Electro-Communications, Cooperative Research Center, Visiting professor, 共同研究センター, 客員教授 (70016442)
• Co-Investigator(Kenkyū-buntansha): SATO Kimitoshi Hiroshima Institute of Technology, Faculty of Engineering, Lecturer, 工学部, 講師 (80313419)
• Project Period (FY): 2005 – 2006
• Keywords: CO2 laser / radiation / thermal conduction / heat sink / plastics / butt welding

Research Abstract

This report introduces a novel concept of CO2 laser welding of thermoplastics which is applicable to manufacturing medical appliances, micro-scale devices and the products requiring the smooth surface of welded region.
The procedure has a few features: (1) to place a solid heat sink transparent to a infrared radiation beam in contact with an irradiated plastic to cool the surface during welding process, (2) to use no pigmentation or dye for radiation absorption enhancement, (3) to sustain thermal damage on the surface, and (4) to avoid the emission of harmful gas due to decomposition of plastics. The feasibility of the welding procedure for natural transparent plastics such as polyolefin and perfluoroalkoxy resins without any surface damage was examined using a CO2 laser (expediently diode laser) as a radiation source with a solid heat sink.
By the numerical analysis of heat transfer in the objective model, it was confirmed that the cooling by fixed heat sink is effective for temperature reduction on the surface of the plastics, but it relatively takes much heat from there. In this method, it was proven that it could not be well heated deep within the thick articles. Then we tested the "pulse-irradiation": firstly, heat sink was set on the surface of the plastic during a certain irradiation of laser, secondly, heat sink was released and laser irradiate the plastic directly (This way was repeated several times). As the result, to prevent the thermal injury of the surface was the priority problem, the cooling by heat sink is moderately utilized and heat is supplemented with the direct irradiation in the short time for balanced temperature profile. This effect was confirmed by the experiment.