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

本文介绍了一种热塑性塑料的CO2激光焊接新概念，适用于制造医疗器械、微型器件和要求焊接区域表面光滑的产品。该工艺具有以下特点：（1）在焊接过程中，将对红外辐射束透明的固体散热器与被照射的塑料接触以冷却表面，（2）不使用色素或染料来增强辐射吸收，（3）承受表面的热损伤，（4）避免因塑料分解而排放有害气体。采用CO2激光器对聚烯烃和全氟烷氧基树脂等天然透明塑料进行无表面损伤焊接通过对目标模型中的传热进行数值分析，证实了固定热沉冷却对降低塑料表面温度是有效的，但相对来说，它会从那里带走很多热量。在这种方法中，它被证明，它不能很好地加热厚制品的深处。然后进行了“脉冲辐照”实验：在一定的激光辐照时间内，先在塑料表面放置热沉，然后释放热沉，激光直接辐照塑料（重复多次）。因此，为了防止表面的热损伤是优先考虑的问题，适度利用散热器的冷却，并在短时间内通过直接照射补充热量，以平衡温度分布。这一效应得到了实验的证实。

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.