Character melee attack collision

im trying to make my character punch a monster,
and when he hit him, the monster should receive the attack and back off.
I tried activating the collision on both of the character.
and enabled the collision on each bone in the physics asset , but they overlap every time i try an attack.
i followed the example tutorial, physichs animation, within ue4 library, but probably i miss something.
i used the two node Set All Bodies Simulate Physics and Set All Bodies Below Physics Blend Weight nodes on the characther, i should activate them only when the player attack so the bone start simulate physics and after a delay disable them with a volor of blend weight 0?.
So im kinda lost.
if there are any tutorial that can be useful
please link here.
thank for any help!