In LS-DYNA, there are only two occasions that you can trim the mesh, i.e. before and after forming analysis.
If you try to trim the mesh after forming, then two files will be generated: one ‘dynain’ and one ‘nikin’ files. The file ‘dynain’ contains the information just before trimming, and ‘nikin’ file contains the information after trimming. As long as LS-NIKE is no longer supported, it is suggested that this kind of trimming be not used.
If you want to trim the mesh after forming, it is easily to generate a ‘dynain’ file after forming simulation. And then do another run with zero termination time, and trim this ‘dynain’ file. With this method, you can get another ‘dynain’ file containing all the information for the trimmed mesh.