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In this study , the effect of shielding gas flow velocity on porosity and melt pool geometry in laser powder bed fusion additive manufacturing is studied .
 gas, porosity, melt pool, geometry, laser powder bed fusion additive manufacturing
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:
 gas, porosity, melt pool, geometry, laser powder bed fusion additive manufacturing