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This research compared twenty-one AM service providers worldwide and found that the main cost drivers for this scenario are total volume of the order , packing density in the build envelope and the number of parts ordered .
 concept or principle: research; manufacturing process: AM; concept or principle: volume; machanical property: density; process parameter: build envelope
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: 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:
 concept or principle: research; manufacturing process: AM; concept or principle: volume; machanical property: density; process parameter: build envelope