So, I'm trying to make a metal stab for one of our robots who has big blade like arms. I tried stabbing a soda can with a butcher knife, but I'm not loving the result. Pitched down it just sounds like a crumple more than anything.I don't have the time or the means to bring my metal stake to a junkyard, I feel like that would be a good start. Any pointers for some more home remedies?
I have done this sort of thing before. I have use good, resonant kitchen knives or a long blade/sword. Slide them against another blade for the ring sound for stab in and out. Maybe try to mount sheet metal or two pieces of metal close together and slide the blade in between them. Then use metal cutting scissors and cut the metal for the metal "crunch" sound or collapse a soup can.
@oinkaudio has some great suggestions. Another great sound layer would be hitting empty paint cans with a baseball bat. I did a session of that recently and the sound of metal buckling with the impact was pretty cool - better, as you can imagine, pitched down a bit. Just need to make sure they're sitting on blanekts or similar so the can doesn't bounce upwards after being struck. I've also gotten some nice metal buckling sounds by striking car hoods and other kinds of sheet metal.
This may sound weird but when you cut metal it has sort of a low rusty sound which you may be able to achieve by crumpling plastic or cellophane and then lowering the sound a few octaves. You can also try punching or rolling your fist in some corn start if this is the classic sort of iron giant robot.
I have also found that the arcing of electricity onto a metallic surface from a bare wire makes a nice metal impact noise. (think the sound of darth sidious' lightning, the low tones not the high pitched ones).
If you need a cleaner thunk you can try hitting a shovel against a rock.
Also the crack of a bullwhip is always a good sound for over-the-top punching and impact noises which, layered with a track of a spatula slid against a metal rod, makes a good piercing sword sound combined with metal slicing.
(By the way, I'm assuming the robot is slicing up another robot not an organic person. that sound is very different and involves the use of several vegetables and fruit)