Lacerate their exoskeleton? Do you have a source for that? According to Wikipedia, the honeydew is excreted from the aphids' anus and happens even when the ants aren't involved https://en.wikipedia.org/wiki/Aphid#Ant_mutualism

Edit: I'm not trying to be the guy who yells "SoUrCe!?" whenever presented new information, I'd just like to correct my misunderstanding if I'm wrong but don't want to incorporate misinformation XD