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In this paper , a universal and simplified model has been proposed to predict the energy density suitable for SLM of a variety of metallic materials including Ti and Ti alloys , Al alloy , Ni-based superalloy and steel , on the basis of the relationship between energy absorption and consumption during SLM .
 concept or principle: model; process parameter: energy density; manufacturing process: SLM; material: metallic materials; material: Ti; material: Ti alloys; material: Al alloy; material: steel; process characterization: energy absorption; manufacturing process: SLM
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: model, energy density, SLM, metallic materials, Ti, Ti alloys, Al alloy, steel, energy absorption, SLM 
Answer:
 concept or principle: model; process parameter: energy density; manufacturing process: SLM; material: metallic materials; material: Ti; material: Ti alloys; material: Al alloy; material: steel; process characterization: energy absorption; manufacturing process: SLM