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The main question we sought to answer was if traditional foundry sand or “ non-standard ” sand could be used within a 3D printing system ? We report herein that the although the increase in surface roughness may be tolerable , the use of foundry sand within a 3D printer produces molds with less than optimal results , mainly due to the absence of compaction .
 foundry, sand, be, 3D printing, surface roughness, be, foundry, 3D printer, molds, compaction
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:
 foundry, sand, be, 3D printing, surface roughness, be, foundry, 3D printer, molds, compaction