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There has been significant research on the humping phenomenon in the downhand welding , but it is doubtful whether the existing theories of humping formation can be applied in the positional deposition during WAAM process .
 concept or principle: research; manufacturing process: welding; material: be; concept or principle: deposition; manufacturing process: WAAM; concept or principle: process
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: welding; material: be; concept or principle: deposition; manufacturing process: WAAM; concept or principle: process