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Weld seam morphology and bond strength of infrared and vibration welded SLS parts of polyamide 12 as a function of the layer build-up direction and the welding process
Additive Manufacturing ( IF 11.0 ) Pub Date : 2020-07-15 , DOI: 10.1016/j.addma.2020.101451
Michael Wolf , Jannik Werner , Dietmar Drummer

Selective laser sintering (SLS) offers the possibility of manufacturing complex parts without tools and thus enables the cost-effective production of individualized products. In contrast to this advantage, the producible component dimension is restricted due to the dimensions of the building chamber of commercial SLS systems. Furthermore, a great amount of cost-intensive powder is necessary for the production of large SLS parts. In order to overcome these limitations, reliable joining processes, which enable high mechanical bond properties in SLS assemblies, are indispensable. Especially welding processes are suitable in this case. However, there is only limited knowledge available about the welding of SLS parts. In particular, the influence of the characteristics of the SLS process on the resulting bond quality has not been analyzed so far. Within this paper, the influence of the SLS layer build-up direction on the resulting weld seam morphology and bond strength as a function of the welding process is investigated. Infrared and vibration welding, which differ in the method of energy input into the joining zone, are used.

The investigations carried out show that high weld seam strengths can be achieved in SLS assemblies for both welding processes. The resulting bond strength is thereby largely independent of the SLS build-up direction. Vibration welded SLS parts exhibit high bond strengths in the range of the base material strength. SLS joints produced via infrared welding have lower bond strengths, which is expected to be caused by an already beginning recrystallization in the generated melt layer during the changeover phase. Furthermore, the investigations show that the weld seam morphology for SLS parts deviates from the characteristic structure of polymeric weld seams, as welded SLS samples do not show the typical separated multi-layer structure. The weld seam shows a very fine spherulitic, partly optically amorphous structure. This is probably the case because of additives contained in the SLS powder (e.g. pyrogenic silicon dioxide), which have an accelerating effect on crystallization. Deformed spherulites in the transition area to the base material are only visible for vibration welded SLS specimens. Due to larger occurring spherulites within the SLS samples compared to injection molded parts, their deformation takes place over a much wider area. The analysis of the weld seam morphology further substantiates the assumption that recrystallization already begins during the changeover phase in the infrared welding process. A highly oriented area with growing spherulites can be detected in the area of the joining plane. In summary, however, it can be noted that both welding processes are well suited for joining SLS parts.



中文翻译:

聚酰胺12的红外焊接和振动焊接的SLS零件的焊缝形态和结合强度与镀层方向和焊接工艺的关系

选择性激光烧结(SLS)提供了无需工具即可制造复杂零件的可能性,因此可以经济高效地生产个性化产品。相对于此优点,由于商用SLS系统构建室的尺寸,可生产的部件尺寸受到限制。此外,生产大型SLS零件需要大量成本密集型粉末。为了克服这些限制,可靠的连接过程必不可少,该过程可实现SLS组件中的高机械粘合性能。在这种情况下,焊接工艺尤其适用。但是,关于SLS零件的焊接知识很少。特别是,到目前为止,尚未分析SLS工艺特性对所得粘合质量的影响。在本文中,研究了SLS层堆积方向对所得焊缝形态和结合强度随焊接过程的影响。使用的红外焊和振动焊的能量输入接合区的方法不同。

进行的研究表明,在两种焊接工艺中,SLS组件均可实现较高的焊缝强度。因此,所得的粘合强度在很大程度上与SLS的堆积方向无关。振动焊接的SLS零件在基材强度范围内表现出较高的粘结强度。通过红外焊接生产的SLS接头具有较低的粘结强度,这可能是由于在转换阶段在生成的熔体层中已经开始重结晶而引起的。此外,研究表明,SLS零件的焊缝形态不同于聚合物焊缝的特征结构,因为焊接的SLS样品未显示出典型的分离多层结构。焊缝显示出非常细的球状,部分光学非晶态的结构。可能是这种情况,因为SLS粉末中包含的添加剂(例如热解二氧化硅)对结晶具有促进作用。仅在振动焊接的SLS样品中可见到基体材料过渡区域的变形球晶。由于与注射成型零件相比,SLS样品中存在更大的球晶,它们的变形发生在更大的区域。对焊缝形态的分析进一步证实了这样的假设,即在红外焊接过程的转换阶段中已经开始了重结晶。在连接平面的区域中可以检测到球状生长的高度定向区域。总之,可以注意到,两种焊接工艺都非常适合于连接SLS零件。热解二氧化硅),对结晶具有促进作用。仅在振动焊接的SLS样品中可见到基体材料过渡区域的变形球晶。由于与注射成型零件相比,SLS样品中存在更大的球晶,它们的变形发生在更大的区域。对焊缝形态的分析进一步证实了这样的假设,即在红外焊接过程的转换阶段中已经开始了重结晶。在接合平面的区域中可以检测到球状生长的高度定向区域。总之,可以注意到,两种焊接工艺都非常适合于连接SLS零件。热解二氧化硅),对结晶具有促进作用。仅在振动焊接的SLS样品中可见到基体材料过渡区域的变形球晶。由于与注射成型零件相比,SLS样品中存在更大的球晶,它们的变形发生在更大的区域。对焊缝形态的分析进一步证实了这样的假设,即在红外焊接过程的转换阶段中已经开始了重结晶。在接合平面的区域中可以检测到球状生长的高度定向区域。总之,可以注意到,两种焊接工艺都非常适合于连接SLS零件。仅在振动焊接的SLS样品上可见到基体材料过渡区域的变形球晶。由于与注射成型零件相比,SLS样品中存在更大的球晶,它们的变形发生在更大的区域。对焊缝形态的分析进一步证实了这样的假设,即在红外焊接过程的转换阶段中已经开始了重结晶。在连接平面的区域中可以检测到球状生长的高度定向区域。总之,可以注意到,两种焊接工艺都非常适合于连接SLS零件。仅在振动焊接的SLS样品上可见到基体材料过渡区域的变形球晶。由于与注射成型零件相比,SLS样品中存在更大的球晶,它们的变形发生在更大的区域。对焊缝形态的分析进一步证实了这样的假设,即在红外焊接过程的转换阶段中已经开始了重结晶。在接合平面的区域中可以检测到球状生长的高度定向区域。总之,可以注意到,两种焊接工艺都非常适合于连接SLS零件。对焊缝形态的分析进一步证实了这样的假设,即在红外焊接过程的转换阶段中已经开始了重结晶。在接合平面的区域中可以检测到球状生长的高度定向区域。总之,可以注意到,两种焊接工艺都非常适合于连接SLS零件。对焊缝形态的分析进一步证实了这样的假设,即在红外焊接过程的转换阶段中已经开始了重结晶。在连接平面的区域中可以检测到球状生长的高度定向区域。总之,可以注意到,两种焊接工艺都非常适合于连接SLS零件。

更新日期:2020-07-15
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