I briefly remember watching a movie when i was little that has monsters in it. The scene i remember has monsters that captured people and there was a slide type thing that they pushed people down that chopped the people up and killed them. It was either late 80’s possible 90.
Mindwarp (1992)?
http://www.imdb.com/title/tt0100152/?ref_=fn_al_tt_1
there are few monsters (judge etc), but sliding thing and chopping exist in the movie,
Nothing But Trouble, http://www.imdb.com/title/tt0102558/ , perhaps?
Sounds like Phantasm… Takes place in a mortuary, little robed monsters are present, grabbing people and “processing” them somehow – I don’t think they chop them up, but you could get that impression
Now that I think about it… There’s a scene exactly like this in Frankenstein’s Army, but that is a newer film (2013), though it does have an older movie feel to it thanks to the great visual effects and almost complete lack of CGI