87
Based on geometric modelling and experimentation , this paper presents an efficient technique for producing the thin-walled metallic structures , including objects with undercut features .
 concept or principle: geometric modelling; machine or equipment: metallic structures; engineering feature: undercut
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: geometric modelling; machine or equipment: metallic structures; engineering feature: undercut