As greencheapsk8 said, a forge is needed for making spear heads.
I don't have made one yet, but I've made a javelin head, and I did it wrongly, because I heated and hammered a flat bar of iron.
For a spear head, I'd use a bigger ingot, and proceed as follows:
Heat one end, then hammer it to flatten and stretch it.
Heat the other end, to lenghten it and stretch its sides, thus making the point and the blades still mantaining a central rib.
Heat the first end, to bend it and make its sides touch each other.
Put a steel round ingot inside, then heat the cylinder until you can weld its sides toghether, and with the rib of the blade (this is optional, you can just hammer these parts until they are flattened, and if you fix the spear heads with rivets to its pole, this will prevent the cylinder to split).
Heat the whole thing and then temper it.
Once tempered, when the iron is cold, hammer the cylinder to make it aligned with the spear head, and then polish and sharpen it.
The whole work may last from a couple of hour, to a maximum of even a couple of days, depending on the forge, on your experience and on the dimension of the object.
It's a funny thing to make, but I suggest you to buy one, if you don't want to get involved in blacksmithing
I'm going to make a spear head too, but only after I've done a war hammer and a short sword, the first for fantasy purpose, and the second for my archaeological experimentations.
Greetings,
Mauro.