Purpose -The purpose of this paper is to investigate the influence of the oxidation on the cracks of DZ125L nickel-based superalloy thin-walled parts in laser metal direct forming (LMDF). Design/methodology/approach -Thin-walled cylinders were fabricated in protective atmosphere with different oxygen contents in order to reveal the influence of oxidation on the morphology of cracks. The influence of oxidation on the cracks was investigated in detail by measuring the wall thicknesses of cylinders, the residual stress in the top surface of the cylinders and the composition of the cracks. Finally, the validity of the results was verified by fabricating a thin-walled turbine blade in protective atmosphere. Findings -The experimental results showed that wall thickness fluctuation of cylinders, unequal residual stress distribution of cylinders and the oxides in the crack were all the critical factors which led to crack of DZ125L thin-walled parts. Thin-walled turbine blades with no cracks can be fabricated when the oxygen content was about less than 150 ppm in protective atmosphere.Research limitations/implications -The appropriate oxygen content in protective atmosphere is helpful for fabricating thin-walled parts of nickelbased superalloy like DZ125L, and the results can show what will happen at different oxygen levels. Moreover, the results show that the cracks can be eliminated as the oxygen content reduce to less than 150 ppm rather less than 10 ppm or even less, which can reduce the cost of protective gas as forming thin-walled parts of nickel-based superalloy such as DZ125L. Practical implications -The appropriate oxygen content in protective atmosphere is helpful for fabricating thin-walled parts of nickel-based superalloy like DZ125L. However, when heavy solid parts of some other material other than DZ125L were fabricated, the oxygen content of less than 150 ppm may be not suitable. Originality/value -The influence of oxidation on the cracks of DZ125L thin-walled parts in LMDF was investigated in detail, and a DZ125L thin-walled turbine blade with no cracks was fabricated by adjusting the oxygen content in protective atmosphere.

In the wire arc additive manufacturing (WAAM) process, the geometry of single welding beads has significant effects on the stability process and the final quality and shape of manufactured parts. In this paper, the geometry of single welding beads of 308L stainless steel was predicted as functions of process parameters (i.e. welding current I, voltage U, and travel speed v) by using the response surface methodology (RSM). A set of experimental runs was carried out by using the Box-Behnken design method. The adequacy of the developed models was assessed by using an analysis of variance (ANOVA). The results indicate that the RSM allows the predictive models of bead width (BW) and bead height (BH) to be developed with a high accuracy: R2-values of BW and BH are 99.01% and 99.61%, respectively. The errors between the predicted and experimental values for the confirmatory experiments are also lower than 5% that again confirms the adequacy of the developed models. These developed models can efficiently be used to predict the desirable geometry of welding beads for the adaptive slicing principle in WAAM.

To discuss the effect of temperature field distribution on the curvature change and layer thickness of thin-wall parts, the numerical simulation and experimental was studied. The numerical results showed that the molten pool temperature of the thin-wall increases with the layer number, and the molten pool temperature of thin-wall cylinders were increases when decrease curvature radius; the rules of laser power changing with the layer number and curvature in the processing of the thin-wall blade can be obtained when keeping molten pool temperature stable. According to the numerical results, the thin-wall blades were fabricated by experiments. The experimental results showed that the excessive build-up occurred and unevenness thickness layer at small radius corner with constant laser power because of the increase of energy density at corners, with varied laser power is more uniform than the constant laser power, which is in agreement with the numerical simulation.

The effect of machining parameters on the surface roughness in dry-turning Ti6Al4V alloy using an experimental design method was investigated. A mathematical equation based on the response surface methodology was established to fully understand the influence of machining parameters (cutting speed, feed rate, and depth of cut) on the surface roughness. A set of experiments based on a three-level statistical full factorial design of the experimental method was performed to collect the mean of surface roughness data. The model of R2=0.9656 shows a good correlation between the experimental results and predicted values. The analysis results from the model revealed that the feed rate is the dominant factor affecting surface roughness, followed by cutting speed, and depth of cut. The surface roughness was minimized when the feed rate and depth of cut are set to the lowest, and the cutting speed was set to the highest level. Verification of the experimental results indicated that the surface roughness of 0.832 µm at cutting speed of 200 m/min, feed rate of 0.1 mm/rev, and depth of cut of 0.1 mm were achieved under the optimal conditions