Orthogonal cutting of Wire and Arc Additive Manufactured parts

Abstract

Wire and Arc Additive Manufacturing (WAAM) is increasingly being used to produce complex and nontraditional geometries that other technologies are not able to create. Finishing operations, as machining, are often required to accomplish the components functionality. However, recent studies suggest that several machining issues arise due to the lack of geometrical tolerances and complex shapes of the manufactured parts, like chattering effects, appropriate work holding selection and component alignment. This work aimed to evaluate if the established scienti c knowledge for machining homogeneous and isotropic materials remains valid for machining WAAM parts.Two different variants of WAAM were analysed, namely, conventional MIG/MAG and hot forging (HF-WAAM).The cutting operations were carried out varying the undeformed chip thickness (UCT) and the cutting speed, using a tool rake angle of 25°. A systematic comparison was conducted between the existing theoretical principles and the obtained practical results of the orthogonal cutting process, where material properties (hardness, grain size, yield strength) and important machining outcomes (cutting forces, speci c cutting energy, friction, shear stress, chip formation and surface roughness) are addressed. Additionally, high-speed camera records were used to evaluate the generated shear angle and chip formation process during the experimental tests.The machinability indicators shown that, through the appropriate cutting parameters, machining forces and energy consumption can be reduced up to 12%, when machining the mechanical improved HF-WAAM material, without compromising the surface quality requirements.

Machining Strategy Determination for Single- and Multi-Material Wire and Arc Additive Manufactured Thin-Walled Parts

“…Several methods exist for examining force data [3,13,19,20]. The forces Fx (axial) and Fy (radial), both of which are considered to be active, are frequently evaluated, whereas Fz, a passive force, is rarely included in evaluations [3].…”

“…The forces Fx (axial) and Fy (radial), both of which are considered to be active, are frequently evaluated, whereas Fz, a passive force, is rarely included in evaluations [3]. Fx and Fy cause the deflection of the workpiece and the tool and are thus considered in many studies [13,23,24]. Moreover, the Fz force is considerably lower than Fx and Fy in thin-wall machining [23].…”

“…Therefore, the machined volume varies due to the high surface irregularity, even in a single machining pass. It is known that a high volume increases the resultant force [13]. The force data for each pass were thus divided into three regions, as shown in Figure 9.…”

“…The specific cutting energy U, expressed in Equation ( 2), was calculated using the resultant force and machined volume values (Equation ( 3)). A few studies have related surface defects to surface roughness due to the fact of machining using a specific cutting energy [13,23,24,26]. In Equation ( 3), F x is the axial force, F y is the radial force, V c is the cutting speed, and MRR is the material removal rate.…”

“…According to the general machining methodology, high hardness causes high cutting forces [5,8]. However, no specific influence of hardness on the machinability of low-carbon steels produced with WAAM has been found [13]. Nevertheless, the stiffness of parts decreases due to the changes in cooling rates, causing unwanted conditions, such as chatter during machining [1].…”