Following the design of experiment approach in this experimental stage, a fractional factorial design 25í1 was adopted. It is a resolution V design (with a defining relation of I = ABCDE and design generator E = ABCD), so no main effect or two-factor interaction is aliased with other main effects or two-factor interactions. However, each main effect is aliased with a four-factor interaction, and each two-factor interaction is aliased with a three-factor interaction [8]. The adopted control factors are the following: laser power (A), cutting speed vc (B), feed per tooth fz (C), defocus distance (D) and milling mode (E). The defocus is the distance between laser lens and workpiece surface. Laser spot size is directly dependent on defocus distance. Excluding the control factors, each test was performed under the same experimental conditions.
Fig