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

doi:10.3901/JME.2022.10.012

Abstract

Abstract: 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%.

Key words: high-temperature detection, EMAT, orthogonal test, pulse compression, optimization design

CLC Number:

TB552

CHEN Weiwei, SHI Wenze, LU Chao, CHENG Jinjie, CHEN Yao, CHEN Guo. Optimal Design of Spiral Coil EMAT for Online and Rapid Detection of High-temperature Forgings[J]. Journal of Mechanical Engineering, 2022, 58(10): 12-23.

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