During Act 2
, after picking up the Curious Device and using it to slow time in order to drop through the fan, you'll be in a circular incinerator room with a lava hole in the center.
You will then be ambushed by about 12 robots. Press
to push these robots into the smelter in the center, using the Curious Device to slow time if you get swarmed.
After you push 7 into the smelter the achievement will unlock.