Energy action model of spark assisted chemical engraving (SACE) for improving surface quality of micro cavities in ZrO₂ ceramics

Abstract

ZrO2 ceramic has a wide range of applications, such as in the thermal barrier coating (TBC) of turbine blades, micro actuators, and gas sensors. However, this material is challenging to machine due to its high hardness and brittleness. Although spark assisted chemical engraving (SACE) can be used to machine ZrO2 ceramics, the traditional SACE models for glass are difficult to apply to ZrO2 ceramics since the melting point of ZrO2 is much higher than that of glass. A theoretical basis for applying the SACE process to ZrO2 ceramics is still lacking, which makes applying the SACE process to machine micro cavities with high surface quality in ZrO2 ceramics very challenging. This paper proposes an energy action model based on the processing voltage, pulse width and machining gap by analyzing the energy transfer process of SACE. The energy model expresses difference in the spark energy between physical removal and chemical removal. Through machining experiments, the contact effect of the SACE process on ZrO2 ceramics was found, and the reasons why the SACE process is sensitive to the machining gap were clarified. Furthermore, physical and chemical removal process models with or without the discharge constraint onto the end of the tool electrode were established. Using the above theoretical models, a circular ring microcavity without micro cracks on the surface was achieved in a ZrO2 ceramic workpiece by using the SACE process with the regulating energy effect trending to the chemical removal. Additionally, considering the contact effect and the process models applied in the SACE scanning process of ZrO2 ceramics, a tool electrode with a spring structure was employed to solve the bending problem of the micro tool electrode. As a result, a square micro-cavity with high surface quality was machined successfully.

Reducing Tool-Tip Wear in Micro ECDM Scanning Process with Feedback Control of Flexible Contact Force

“…In this way, the contact force can be maintained at an expected constant value during a scanning process of micro ECDM. The bending of tool electrode can be avoided even if the contact force has an instantaneous change on uneven machining surface owing to the flexible force [7].…”

“…On the one hand, this demands a suitable micro machining gap maintained between the workpiece surface and the tool electrode along the feeding direction. On the other hand, the material removal efficiency is lowered if the tool electrode does not contact the workpiece surface because of the contact effect [7]. A novel spindle with servo feedback control of flexible force in real time was designed in previous research to keep a stable micro contact force between the tool electrode and the workpiece surface [8].…”

Micro ECDM process comparison using different tool feed methods of constant gravity and spring-force

“…On the one hand, under a lower material removal rate, the faster feed velocity could break the tool electrode; on the other hand, the lower feed velocity would decrease the machining efficiency obviously. Recent research indicates that a spring contact force can improve the scanning process of ECDM [9]. The tool electrode with a spring structure can reduce the tool stiffness and exert a smaller contact force onto the workpiece under the same compression, therefore the scanning process is stabilized and the bending problem is avoided.…”