高温锻件在线快速检测螺旋线圈EMAT优化设计

Optimal Design of Spiral Coil EMAT for Online and Rapid Detection of High-temperature Forgings

在高温铸造/锻造过程中进行缺陷的检测、控制和修复以及厚度测量,并据此调整加工工艺参数,及时剔除缺陷/尺寸超标件,避免进入下一步工序,对提高产品合格率、实现环保制造,具有重要的工程应用价值。针对电磁超声换能器(Electromagnetic ultrasonic transducer,EMAT)在大提离、强环境电磁干扰、高温等严苛条件下对表面粗糙形貌、晶粒粗大的铸锻件进行快速检测时的信噪比和空间分辨率差这一难题,建立基于chirp信号激励的螺旋线圈EMAT检测过程的有限元模型,采用正交试验表,分析EMAT设计参数、chirp信号带宽、脉宽等因素对脉冲压缩后的回波主瓣峰值和主瓣宽度的影响,分别获取主瓣峰值主瓣宽度最佳参数组合,并通过试验加以验证。设计耐高温EMAT探头,比较单一正弦脉冲激励信号和chirp脉冲压缩在650℃以上高温锻件检测的信噪比和主瓣宽度。结果表明,采用chirp脉冲压缩技术,高温EMAT检测的信噪比(Signal-to-noise ratio,SNR)、空间分辨率和检测效率更高。在720℃高温锻件、提离为3 mm且无同步平均条件下,与单一正弦脉冲激励相比,采用脉冲压缩技术,SNR提高了至少5.4 dB,主瓣宽度减小了58.8%。

To detect,control,and repair the defects or to measure the thickness of castings and forgings in the process of casting and forging with high temperatures is of practical engineering value.Manufacturing process parameters can be adjusted based on the inspection result,and the product with defects and dimensions down to relevant standards can be abandoned,and the product can be prevented to the next manufacturing process step.In this way,the product qualified rate can be enhanced,and environment protection manufacturing is realized.To improve the signal-to-noise ratio(SNR)and range resolution of the electromagnetic ultrasonic transducer(EMAT)for the quick inspection of these castings and forgings with rough surface and coarse grains under the harsh conditions of large lift-off distance,strong electromagnetic noise and high temperature,a finite element model for the testing process of a spiral coil EMAT with a chirp wave transmitting pulse was built.With the orthogonal test table,the influences of EMAT design parameters,bandwidth and pulse width of the chirp signal on both the peak and pulse width of the main lobe of the echoes after pulse compression were analyzed.Optimal parameter combinations for the peak and pulse width of the main lobe were obtained,and they were verified by experiments.A high-temperature resistant EMAT probe was designed,and the SNR and main lobe width between the excitation of tone-burst signal and chirp pulse compression with the object of high-temperature testing of forgings at temperatures exceed 650℃were compared.Results show that the SNR,range resolution and detection efficiency of high-temperature EMAT testing can be enhanced by pulse compression technology with chirp signal.Besides,at the testing conditions of the forging with a temperature of 720℃,a lift-off of 3mm,and no synchronous averaging,compared with the excitation of a tone-burst pulse,after pulse compression,the SNR is improved by at least 5.4 dB,and the pulse width can be reduced by 58.8%.