Theoretical and experimental study on laser rotary grooving for 40Cr bar low-stress shearing

A laser rotary grooving method on metal bar for low-stress shearing was developed to improve the precision of billets. A mathematical model was established through theoretical analysis on the laser rotary grooving process of 40Cr bars, and then L₂₅(5⁶) orthogonal tests were conducted to study the influence of factors including the laser parameters such as peak power (P_k), pulse width (τ) and pulse frequency (f), and the processing parameters such as processing speed (n), defocusing amount (s) and repeat turns (N). The influence order and optimum range of these factors were obtained by means of ANOVA analysis, and further shearing experiment was carried out on 40Cr bars. The results indicate that the influence order of the factors is N>s>P_k>f>τ>n, and the F values of N and s are 11.925 and 5.268 respectively, both of which have remarkable effects. The optimum ranges of these influencing factors are: P_k≥9.6 kW, τ≥0.3 ms, 3≤N≤10, 10 r/min≤n≤25 r/min, and s=0 mm. The sum of squares of errors (ε) between theoretical depth and real depth is 0.112 mm² which proves that the calculation formula of theoretical groove depth h is accurate. Compared with the 40Cr billets processed by traditional shearing, the sheared surface inclination is 0.3°, and the weight tolerance is only 0.35%, resulting in an accuracy improvement of more than 13 times and 8 times, respectively.