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This research investigates a two-stage facility model to optimize the locations and capacities for new metal AM hubs which require two sequential post-processing services : heat treatment and machining .
 concept or principle: research investigates; concept or principle: model; manufacturing process: metal AM; concept or principle: post-processing; manufacturing process: heat treatment; manufacturing process: machining
Given options, please tell me the categories of all the listed entity words.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} 
 Entities: research investigates, model, metal AM, post-processing, heat treatment, machining 
Answer:
 concept or principle: research investigates; concept or principle: model; manufacturing process: metal AM; concept or principle: post-processing; manufacturing process: heat treatment; manufacturing process: machining