【作者】 龚飞；

【导师】 王春明；

【作者基本信息】 华中科技大学 ， 材料工程， 2011， 硕士

【摘要】 随着塑料制品业的不断发展和产品轻量化的发展要求,以汽车制造业为代表的众多行业对塑料产品特别是复杂塑料零部件的需求日益扩大。塑料焊接以其经济、简单、快捷、可靠等特点,既可以在工艺上实现一次性整体或复杂结构的紧密连接,又十分适合于大批量生产,已成为热塑性塑料件连接的首选加工方法。激光透射焊接作为一种新兴的焊接技术,以其独特的技术优势和特点弥补了常规塑料连接手段的不足,正成为人们研究的热点。本文首先从塑料的光学性能出发,介绍了塑料对近红外线激光的反射、吸收、散射和透射作用,然后深入分析了塑料的热力学性能,包括三种不同的力学状态、熔体的流体特点等。基于激光透射焊接的原理和过程,采取搭接接头形式进行焊接,同时焊接关键技术和难点也被考虑。其次,设计并确定了激光透射焊接的实验方案,具体包括激光器和焊接材料的选择,焊接方法和实验过程的设计等。为了研究焊接工艺因素对焊接质量的影响,采用剪切强度测试和金相实验作为焊后测试手段。相对于大功率光纤激光塑料焊接的实验结果,能量分布相对均匀的半导体激光器更适合于塑料焊接。利用波长为808nm的半导体激光器,讨论了激光功率、焊接速度、夹紧力和吸收剂等工艺因素对PP激光透射焊接质量的影响,得出:在激光光斑大小一定的情况下,焊接线能量(激光功率与焊接速度的比值)存在一个最佳范围以获得良好的塑料焊缝成形,同时金相显微观察表明,两种PP材料在界面处发生交联并形成了新的化学键;拥有良好焊缝成形的接头一般表现出较高的剪切拉伸强度,而当焊缝中存在分解、烧蚀和气孔等缺陷时,缺陷周围易出现应力集中,接头强度将大大降低;保持一定的夹紧力是实现塑料激光焊接的前提,而在无夹紧力或夹紧力较小的情况下,焊缝易出现未焊合、漏焊和焊缝不均匀等缺陷;利用Clearweld吸收剂可以实现两种透光PP之间的焊接,但接头强度普遍偏低。更多还原

【Abstract】 With the continuous development of plastic products industry and development requirements of product lightweight, many industries represented by automobile manufacturing industry are on the growing demand for plastic products, especially complex plastic parts. Because of its economic, simple, fast, reliable, both achieving the tight junction of whole or complex structures in process and very suitable for mass production of plastic parts, plastic welding has become the preferred processing methods of connecting thermoplastic parts. Laser transmission welding, as a new kind of welding technologies, make up the shortage of conventional plastic connection means with its unique technical advantages and features, and is becoming a hot research.Firstly this paper introduced reflection, absorption, scattering and transmission effects starting from the optical properties of plastic. The thermodynamic properties of plastics were analysed in depth, including three different mechanical states, flow characteristics of the melt. Based on the principle and process of laser transmission welding, the lap joint form was taken and the key technology and difficulty of welding were also considered. Secondly, experimental scheme was determined, including choosing laser equipment and welding materials, designing welding method and experiment process. Shear strength test and metallographic microscopy after welding were made to study the effects of welding process factors on the welding quality.Compared with the results of high-power fiber laser welding plastic, diode laser with relatively uniform energy distribution was more suitable for plastic welding. Using 808nm diode laser, the effects of welding process factors such as laser power, welding speed, clamping force and absorbent on the PP laser transmission welding quality were discussed. Under a certain laser spot size, an optimal scope of the welding energy (laser power and welding speed ratio)existed to obtain good plastic weld formation. Metallographic microstructure observation showed that the two kinds of PP material crosslinked at the interface and new chemical bond was formed. Good weld joints generally showed a higher shear tensile strength, while the strength of weld joints would be greatly reduced as a result of stress concentrations when decomposition, erosion and cavity appeared in the weld. Maintaining a certain clamping force was a prerequisite to achieve plastic laser welding. No clamping force or relatively small clamping force was liable to occur unbinding, lack of weld or uneven weld. Clearweld absorbent could be used to weld two pieces of transparent PP, but the strength of all joints generally was not very high.更多还原