Porosity Analysis in Metal Additive Manufacturing by Micro-CT
Porosity Analysis in Metal Additive Manufacturing by Micro-CT
复制标题
DOI：
10.1115/imece2018-87897
复制
发表时间：
2018-11
期刊：
影响因子：
--
通讯作者：
Subin Shrestha;T. Starr;K. Chou
中科院分区：
文献类型：
--
作者：
Subin Shrestha;T. Starr;K. Chou
本研究旨在分析激光粉末床熔融增材制造（AM）工艺中选择性激光熔化（SLM）过程中产生的气孔。多孔性是SLM零件中最容易出现的缺陷之一。它损害了零件的性能，然而，对SLM工艺本身的参数非常敏感。为了了解不同工艺条件下的孔隙度水平，需要使用计算机断层扫描（CT）技术对SLM孔隙结构进行详细分析。在SLM系统中，采用Ti-6Al-4V粉末，在60 μm的层厚下，通过不同的激光功率和扫描速度来改变能量密度，形成单径迹。采用micro-CT （μ-CT）扫描仪对未进行后期处理的SLM试样进行了内部特征测量，并分析了不同能量密度形成的单道内孔隙率。SLM的孔隙形成机制不同，本研究首先关注的是高能量密度引起的锁孔现象导致的孔隙形成。μ-CT扫描在6 μm分辨率下能够清晰地显示SLM样品中的孔隙。从CT扫描和分析结果可以看出，增加能量密度会增加孔隙体积。例如，在195 W、200 mm/s条件下，扫描长度为12 mm时，孔隙数为93个，总孔隙体积为0.014 mm3。另一方面，当能量密度小于0.24 J/mm时，很少或没有观察到气孔，这可能是因为熔化过程从钥匙孔模式转变为传导模式。
This study aims at analyzing process-induced pores in selective laser melting (SLM), a laser powder-bed fusion additive manufacturing (AM) process. Porosity is one of the most problematic defects in SLM parts; it impairs the part performance, and yet, is sharply sensitive to the parameters of the SLM process itself. Detailed analysis of SLM pore formations using a computed tomography (CT) technique is desired in order to understand the porosity level under different process conditions. In this study, an SLM system was used to fabricate samples, using Ti-6Al-4V powder, with single tracks formed, at 60 μm layer thickness, with different laser powers and scanning speeds to vary the energy density. A micro-CT (μ-CT) scanner was used to measure the internal features of the SLM specimens without any post-build treatments and to analyze the porosity inside single tracks formed with different energy densities. There are different mechanisms of pore formation in SLM, in particular, this study first focuses on the pore formation due to the keyhole phenomenon, caused by a high energy density. μ-CT scanning at a 6 μm resolution is able to clearly reveal the pores in the SLM samples. From the CT scan and analysis results, it is observed that increasing the energy density increases the volume of pores. For example, with 195 W and 200 mm/s, the number of pores is 93 and the total pore volume is 0.014 mm3 for a scanning length of 12 mm. On the other hand, if the energy density is less than 0.24 J/mm, few or no pores were observed, because possibly the melting process changes from the keyhole mode to the conduction mode.