synergism vs welding

synergism

noun
  • synergy 

  • The theological doctrine that salvation is brought about by a combination of human will and divine grace 

welding

noun
  • binding together inseparably; uniting closely or intimately. 

  • joining two materials (especially two metals) together by applying heat, pressure and filler, either separately or in any combination, or 

How often have the words synergism and welding occurred in a corpus of books? (source: Google Ngram Viewer )