BibTeX does not have the right entry for preprints. This is a hack for producing the correct reference:
@booklet{EasyChair:720,
author = {Chunping Fang and Jingze Zhao and Li Ling and Wenping Wang and Min Wan},
title = {Electromagnetic peening - a novel sheet metal forming method},
howpublished = {EasyChair Preprint 720},
year = {EasyChair, 2019}}
