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

Jaka Dugar,Awais Ikram,Franci Pušavec

doi:10.3390/pr9081422

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.

Highlights

The sintered zinc oxide (ZnO) electro-ceramics are a class of functional materials that are highly brittle due to low fracture toughness, so finishing them with the post-finishing operations necessitates careful handling and precision machining [1]
The investigation of the vibration signals during the turning operation was performed with the accelerometer, to corelate the surface topography with the chipping frequency and the optimal machining characteristics of ZnO varistors
The vibrational feedback obtained from 0.2 mm/rev signifying the higher cutting force in play is quite evident in Figure 5; the requirement for the cutting force was lower for the higher feed velocities in the time domain to complete the respective turning operation on a sintered ZnO ceramic

Summary

Introduction

The sintered ZnO electro-ceramics are a class of functional materials that are highly brittle due to low fracture toughness, so finishing them with the post-finishing operations necessitates careful handling and precision machining [1]. Multi-sensor accelerometer units are proficient in supporting the milling and machining processes by rendering real-time vibrational feedback of the cutting forces and tooling characteristics [16]. The accelerometer sensor in parallel with turning supports data acquisition related to the range of vibration-induced chip formations and simultaneously, the measurement of the cutting forces was corelated for different functional materials. The stud mounted Triaxial DeltaTron® Accelerometer Type 4525-B-001 was attached to the turning machine to record the vibrations in relation to the increase in the material feed rate during the machining operations. The surface integrity analysis was based on the surface roughness of the machined ceramics and the vibrational amplitude was based on the edge chipping while the feed rate was varied. TheTheelescutrrfoance mroiucgrhonsecsospmyeaimsuaregminegntswuansdepredriffoferrmenetdfeebdyvaeloJcEitOieLs w7e6r0e0mFefaiseulrdedemissio scanonninthgeetolepct(mroanrkmedicrreods)caonpdebaotttoamn (amccaerkleerdabtilnuge) vsiodletsagoef tohef m20ackhVineind cseercaomnicdsa, royn electro modrreoanutdgohoomnbelstyassimneleetachsteuedrseu5mrmefnamtcselwoanangsdcportnoofispildoeesgrirenadpthahleoicxna-galxtvhiseiedywi-raexocitfsiotahnp.epArcoerxeriapmmeattiitecilosyn, 1wo0fhμtemhreeasapusarrfttahcteoe in focu backosbctaatintetrheedmeelaenctvraolnueds.etector at a working distance of 15 mm was utilized to obtain th phase coTnhteraesltecintrfoonrmmiactrioosnco. pAynimEDagXinSgpwoainstppehrfaosrme aednablyysaisJEwOaLs 7p6e0r0fForfimeleddemwiistshioann Oxfor Incas2ca0nmninmg2edleectterocntomr iucrtoilsiczoinpeg a2t0ankVaccoeflearcactienlgervaotiltnagevooflt2a0gkeVainndseacopnrdoabrey delieacmtroenter of ap proximately 1 μm

Results and Discussion

Accelerometer Turning Signals Feedback

The Three-Dimensional Roughness Measurements of the Machined Surfaces

Conclusions