[Retracted] An Improved Ant Colony Optimization Approach for Optimization of Process Planning

Table 6

Precedence constraints for Part 2.

Features	Operation	Precedence constraints description	Hard or soft
F1	Milling (OP1)	F1 (OP1) is the datum and supporting face for the part; hence it is machined prior to all features and operations.	Hard
F2	Milling (OP2)	F2 (OP1) is prior to F10 (OP12, OP13, and OP14) and F11 (OP15, OP16) for the material removal interactions.	Hard
F5	Milling (OP5)	F5(OP5) is prior to F4 (OP4) and F7(OP7) for the datum interactions	Hard
F6	Milling (OP6)	F6 (OP6) is prior to F10 (OP12, OP13, and OP14) for the datum interaction.	Hard
F7	Milling (OP7)	F7 (OP7) is prior to F8 (OP8, OP9, and OP10) for the datum interactions.	Hard
F8	Drilling (OP8)	OP8 is prior to OP9 and OP10; OP9 is prior to OP10 for the fixed order of machining operations.	Hard
	Reaming (𝑂𝑃9)
	Boring (OP10)
F9	Milling (OP11)	F9 (OP11) is prior to F10 (OP12, OP13, and OP14) for the datum interaction	Hard
F10	Drilling (OP12)	OP12 is prior to OP13 and OP14; OP13 is prior to OP14 for the fixed order of machining operations. F10 (OP12, OP13, and OP14) is prior to F11 (OP15, OP16), and OP12 of F10 is prior to F14 (OP19, OP20) for the datum interaction.	Hard
	Reaming (OP13)
	Boring (OP14)
F11	Drilling (OP15)	OP15 is prior to OP16 for the fixed order of operations.	Hard
	Tapping (OP16)
F13	Milling (OP18)	F13 (OP18) is prior to F4 (OP4) and F12 (OP17) for the material removal interaction.	Soft
F14	Reaming (OP19)	OP19 is prior to OP20 for the fixed order of machining operations.	Hard
	Boring (OP20)