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Since the mechanical properties of an FFF part are most greatly affected by the bead orientation and printed density , or solidity ratio , techniques to precisely control these variables are required .
 mechanical properties, FFF, bead, density
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: manufacturing standard, machanical property, manufacturing process, material, engineering feature, process parameter, machine or equipment, application, process characterization, enabling technology, biomedical, concept or principle 
Text: {0} 
Answer:
 mechanical properties, FFF, bead, density