GH3536合金选择性激光熔化微小缺陷超声检测

Ultrasonic Testing of Tiny Defects in GH3536 Alloy by Selective Laser Melting

针对GH3536合金选择性激光熔化(Selective laser melting,SLM)工艺中,孔隙和裂纹等微小缺陷与完好区域的声阻抗差异小,超声检测缺陷回波不明显问题,提出基于变分模态分解结合小波分析的信号处理方法。首先对回波信号进行变分模态分解,分析不同分量与原始信号的相关性进行降噪重构,然后选择db7小波函数对信号进行3层分解,以极大极小规则进行硬阈值平滑处理,提取信号突变点来判别缺陷回波。仿真和实际测试结果表明:该方法比单一的经验模态分解及小波重构效果明显,能够检出加工层厚为0.15 mm的人工缺陷,为高温合金SLM成型工件超声检测回波信号微小缺陷识别提供了新方法。

Aiming at the problems of selective laser melting(SLM)processing of GH3536 alloy,the difference in acoustic impedance between the unfused small defect and the intact area is small,and the ultrasonic echo defect defect is not obvious,this paper presents a signal processing method based on variational modal decomposition.Ultrasonic testing is performed on different micro-sized defect specimens,and the db7 wavelet function is used to decompose the signal into three layers.Then,the minimum and minimum(Minimaxi)rules are used as thresholds to perform hard threshold noise reduction and reconstruct the signal to extract defect echoes in the signal mutation points to identify defects.Results show that the method has obvious noise reduction effect,can detect the smallest detectable defect size of 0.15 mm and significantly improves the sensitivity of defect detection.