Do we have to make a gunna for the waw letter?

Do we have to make a  gunna for the waw letter?  On what letters do we have to make gunna?
Do we have to make gunna only when tashjid (little waw) is present?

The only two letters that have a ghunnah (nasalization) in them are the noon and meem; this is an intrinsic characteristic of these letters, and the ghunnah never leaves them.  When a saakinah or tanween meet a or a  between two words, there is an incomplete merging of the saakinah or tanween into the wow.   The ghunnah (nasalization) is what remains of the saakinah.  So in this merging, the merges into the or , so that we do not hear the as far as the letter, but we hear the ghunnah (nasalization) of the .  
Since this merging is incomplete, most copies of the Qur'an do not have a shaddah on the or  when this idghaam (merging) happens, there are a few copies printed that put a shaddah, but the more accepting way is without the shaddah. 

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