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、微型设备和要求焊接区表面光滑的产品。该方法具有以下几个特点：(1)在焊接过程中，将对红外辐射束透明的固体散热器与照射的塑料接触，以冷却表面；(2)在焊接过程中，不使用色素或染料来增强辐射吸收；(3)保持表面的热损伤；(4)避免塑料分解产生有害气体。对聚烯烃和全氟烷氧基树脂等天然透明塑料，采用CO2激光器(简称半导体激光器)作为固体散热片的辐射源，对其表面无损伤焊接工艺的可行性进行了研究。通过目标模型中的传热数值分析，证实了固定散热片冷却对塑料表面降温是有效的，但相对消耗的热量较大。在这种方法中，证明了它不能在厚物品的深处被很好地加热。然后对“脉冲照射”方法进行了试验：首先，在一定的激光照射下，在塑料表面设置热沉；然后，释放热沉，激光直接照射塑料(重复多次)。因此，防止表面热损伤是首要问题，适当利用散热器冷却，在短时间内以直接照射补充热量，以获得平衡的温度分布。实验证实了这一效果。

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.