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The industrial relevance of this research is outlined with respect to four current challenges in AM , including the length of time to determine optimal process parameters for a new machine , ability to organize relevant knowledge , quantification of machine variability , and transfer of knowledge to new operators .
 industrial, research, AM, optimal process, machine, machine
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:
 industrial, research, AM, optimal process, machine, machine