Experimental Analysis on the Influence and Optimization of μ-RUM Parameters in Machining Alumina Bioceramic

Abstract

Fabrication of precise micro-features in bioceramic materials is still a challenging task. This is because of the inherent properties of bioceramics, such as low fracture toughness, high hardness, and brittleness. This paper places an emphasis on investigating the multi-objective optimization of fabrication of microchannels in alumina (Al2O3) bioceramics by using rotary ultrasonic machining (RUM). The influence of five major input parameters, namely vibration frequency, vibration amplitude, spindle speed, depth of cut, and feed rate on the surface quality, edge chipping, and dimensional accuracy of the milled microchannels was analyzed. Surface morphology and microstructure of the machined microchannels were also evaluated and analyzed. Unlike in previous studies, the effect of vibration frequency on the surface morphology and roughness is discussed in detail. A set of designed experiments based on central composite design (CCD) method was carried out. Main effect plots and surface plots were analyzed to detect the significance of RUM input parameters on the outputs. Later, a multi-objective genetic algorithm (MOGA) was employed to determine the optimal parametric conditions for minimizing the surface roughness, edge chipping, and dimensional errors of the machined microchannels. The optimized values of the surface roughness (Ra and Rt), side edge chipping (SEC), bed edge chipping (BEC), depth error (DE), and width error (WE) achieved through the multi-objective optimization were 0.27 μm, 2.7 μm, 8.7 μm, 8 μm, 5%, and 5.2%, respectively.

Rotary Ultrasonic Machining of Alumina Ceramic: An Experimental Investigation of Tool Path and Tool Overlapping

“…It can be observed from Figure 9 that the surface morphology of the machined pockets changes with varying the percentage of the tool overlapping. The SEM images indicate that, in agreement with observations documented in [1,17] whereas in RUM of ceramics, two material removal modes exist: brittle fracture and ductile fracture. Brittle fracture is observed as tear-outs forming on the pockets surfaces machined at a low percentage of overlapping (0%-10%) as shown in Figure 9a,b.…”

“…The tool paths of the remaining strategies (Spiral and Mix-1) can be observed by following the direction of the arrow in schematic diagrams in Figure 4. The range of the machining conditions (see Table 4) was selected based on trial experiments and guidance taken from previous studies reported in the machining of alumina materials by using RUM [14,15,17]. Based on the results of the overlapping test, the experiments of the tool strategies test were carried out by fixing the tool overlapping at 20%, which results in the best surface roughness and morphology as will be explained in the results and discussion section.…”

“…The tool paths of the remaining strategies (Spiral and Mix-1) can be observed by following the direction of the arrow in schematic diagrams in Figure 4. The range of the machining conditions (see Table 4) was selected based on trial experiments and guidance taken from previous studies reported in the machining of alumina materials by using RUM [14,15,17]. In order to measure the dimensions of the fabricated pockets, optical microscopic images of the milled pockets were captured by using mikroskop technik rathenow from ASKANIA company-Germany (see Figure 5a).…”

“…Recently, RUM was applied for milling microchannels and drilling microholes in Al2O3 materials. For example, Abdo et al [17,18] used RUM to fabricate microchannels on Al 2 O 3 . The authors investigated the significance of RUM input parameters on the surface roughness, edge chipping, and dimensional accuracy of the fabricated microchannels.…”

“…Furthermore, the effect of tool overlapping and tool path strategies on the surface quality and dimensional accuracy of the machined parts have never been investigated in all studies conducted for the RUM of Al 2 O 3 ceramic. Moreover, the effect of the tool overlap and tool path were not considered in the studies documented on the fabrication of the microchannels through RUM [17,18]. This is because, in those investigations, the selected sizes (widths) of the fabricated channels were equal to the diameter of the used RUM tools.…”