Create webform field on node create
I am not sure about your use case. 

But the following module does exactly that. 

Webform Default Fields


  With this module you can easily create much of nodes with same webform
  fields. It can be applicable in case of job vacancies with reply form,
  kind of quality feedback control or whatever your mind suggests you.
  
  Because you can create more than one webform-enabled content types,
  you respectively can attach different default fields for each of them.