A computer-implemented method for 3D printing planning, comprising: - providing: ∘ a set of spare parts to be manufactured in one or more factories comprising 3D printers and other manufacturing machines; ∘ 3D printing constraints, the 3D printing constraints including: ▪ one or more constraints each representing a 3D printing constraint and/or a mechanical constraint for a spare part; and ▪ one or more 3D printing capacity constraints for the one or more factories; and ∘ a reference set of one or more spare parts each classified either as compatible with the 3D printing constraints or as non-compatible with the 3D printing constraints; - determining an optimal subset of the set of spare parts to be 3D printed, the determining including optimizing one or more objective manufacturing functions under the 3D printing constraints and based on the reference set, the optimization comprising learning a Multiple Criteria Decision Aiding sorting model configured to take as input an input set of spare parts and to output an optimal subset of spare parts, the learning being based on the set of spare parts, on the 3D printing constraints, on the one or more objective manufacturing functions, and on the reference set, the one or more manufacturing functions corresponding to lead time and/or carbon footprint; - establishing a 3D printing plan for the one or more factories based on the determined optimal subset; and - 3D printing the optimal subset in the one or more factories based on the established 3D printing plan and manufacturing the other spare parts which are not in the optimal subset by one or more other manufacturing processes than 3D printing. - providing: ∘ a set of spare parts to be manufactured in one or more factories comprising 3D printers and other manufacturing machines; ∘ 3D printing constraints, the 3D printing constraints including: ▪ one or more constraints each representing a 3D printing constraint and/or a mechanical constraint for a spare part; and ▪ one or more 3D printing capacity constraints for the one or more factories; and ∘ a reference set of one or more spare parts each classified either as compatible with the 3D printing constraints or as non-compatible with the 3D printing constraints; ∘ a set of spare parts to be manufactured in one or more factories comprising 3D printers and other manufacturing machines; ∘ 3D printing constraints, the 3D printing constraints including: ▪ one or more constraints each representing a 3D printing constraint and/or a mechanical constraint for a spare part; and ▪ one or more 3D printing capacity constraints for the one or more factories; and ▪ one or more constraints each representing a 3D printing constraint and/or a mechanical constraint for a spare part; and ▪ one or more 3D printing capacity constraints for the one or more factories; and ∘ a reference set of one or more spare parts each classified either as compatible with the 3D printing constraints or as non-compatible with the 3D printing constraints; - determining an optimal subset of the set of spare parts to be 3D printed, the determining including optimizing one or more objective manufacturing functions under the 3D printing constraints and based on the reference set, the optimization comprising learning a Multiple Criteria Decision Aiding sorting model configured to take as input an input set of spare parts and to output an optimal subset of spare parts, the learning being based on the set of spare parts, on the 3D printing constraints, on the one or more objective manufacturing functions, and on the reference set, the one or more manufacturing functions corresponding to lead time and/or carbon footprint; - establishing a 3D printing plan for the one or more factories based on the determined optimal subset; and - 3D printing the optimal subset in the one or more factories based on the established 3D printing plan and manufacturing the other spare parts which are not in the optimal subset by one or more other manufacturing processes than 3D printing.