1941
Today , the optimization of process parameters , for a given metal powder , is generally attained through an empirical trial and error approach .
 optimization, process parameters, metal powder, empirical, error
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:
 optimization, process parameters, metal powder, empirical, error