Evaluation of Chip Formation Mechanisms in the Turning of Sintered ZnO Electro-Ceramics

Abstract

The sintered zinc oxide (ZnO) electro-ceramics are a brittle class of hard-to-cut materials such that shaping them with the post-finishing operations necessitates careful handling and precision machining. The conventional machining approach using the grinding and lapping processes represents limited productivity, an inability to produce the required geometries and frequent uncontrolled chipping of the edges of the final products. This study thus investigates the turning performance of dense sintered ZnO varistors and chip formations to obtain the parametric range (cutting mechanism) which causes the chipping or the trans-granular/sudden failure in these brittle materials. With the analysis of the cutting tool vibration in relation to the machining parameters (f and VC), the vibration-induced chipping correlations are made and interlinked with the occurrence of grain pull-out during the turning operation. The results show that the reflected vibratory motion of the tools is directly correlated with the chip formation mechanisms in the turning of ZnO ceramics and thus provide robust measurements for quality assurance in final products.

Effects of Dopants and Processing Parameters on the Properties of ZnO-V2O5-Based Varistors Prepared by Powder Metallurgy: A Review

“…Mn doping reduced the mean ZnO grain size in all the ternary systems compared to undoped MOVs from ZnO-V2O5 systems, but the densification of the Mn3O4or MnO2-doped MOVs was almost equal, with a relative density (RD) of 94.6-96% of theoretical density (TD). These densities comply with the accepted values for commercial MOVs, with RD greater than 95% of TD, where TD is around 5.6-5.7 g/cm 3 [111].…”

“…Additionally, the selected VFO and dopants [ 7 , 103 , 104 , 105 , 106 , 107 ] also play a crucial role. Furthermore, the techniques used for preparing MOV powder mixtures [ 108 , 109 ], as well as the consolidation (pressing of MOV powders) and densification techniques (sintering of MOV compacts) ( Figure 3 ), including post-annealing and post-processing techniques of MOVs [ 13 , 76 , 77 , 94 , 110 , 111 ], have a significant impact on the properties of MOVs.…”

“…The liquid phase can enhance GB mobility, but the formed intragrain pores can decrease the sintered density of MOVs [ 118 ]. Lower-density MOVs (RD < 95% of TD) can yield defects such as spherical holes, indicating inadequately joined grains, leading to a decrease in the mechanical strength of MOVs [ 111 ].…”

Comparative Characterization of Different Cutting Strategies for the Sintered ZnO Electroceramics

“…However, at feed rate v = 160 mm/min, the resultant slice roughness at the edges was trimmed down to 65 µm. This implies unsuitability of AWJ cutting at higher feed rates, as the edge regions and taper did not adhere to the principal electrical impulse testing requirements [30]. Further on, the comparison of surface roughness was also made by investigating the topographical color scans.…”

Advances in understanding of damage formation during laser-assisted milling of ZnO-based varistor ceramics

“…Before extensive study, preliminary experiments on turning of ZnO ceramics with PCD tools were performed and tool life, comparable to metal cutting was achieved. It was also concluded that the main factor reducing ZnO ceramics machinability is excessive machining-induced damage like grain pull-out and edge chipping [31]. A study using a conventional milling strategy, based on the turning parameters, yielding the best results, showed that surface microstructure can have a noteworthy impact on the machining characteristics of this material and substantially better surface roughness was achieved by abrasive waterjet machining [32].…”