Why does my son bang his head and should I be concerned. Sometimes he hurts himself when doing it. Wat do I do to get him to stop?

Positive ignoring. Head banging is just an amplification of early infant fussing.It peaks in preverbal years .I've never heard or seen a head banger with a real head injury. This likely caught on when he noticed it grabbed your attention.If you ignore it(don't lock eyes), watching him out of peripheral vision, for safety, it should fade over time.Teaching some sign language may help with the frustration.
Head banging. How old is your son? Head banging is considered normal until certain age but usually it does not lead to self injury. Divert his attention to something else, every time you find him doing so. If he tries to gain attention through head banging, do not provide him with attention-- as he will continue as long as he gets rewarded by your attention.