I will assume, since you are using AE, that you already have the Molecular Assembly chamber attached to your all-in-one storage complex, however you made it. first, encode a blank pattern with 3 refined iron, 3 copper, and 3 tin as your crafting recipe, and force your output to be a mixed metal ingot. Put the encoded pattern in your chamber. Go to your rolling machine, and make sure the internal pattern is the one used for mixed metal ingots. Make an ME Interface, place it above your rolling machine, place an import bus attached to the side of your rolling machine, attach both to your AE network, power the rolling machine, and there you go. Done. Go to your access terminal, and you should be able to see the mixed metal ingot as craftable. In short, the interface takes the crafting recipe (iron, copper, tin), sends it into the rolling machine, where it crafts the mixed metal ingot, and then pulls it out with the input bus. If I didn't explain it well, tell me, and I'll make a video later.