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In this paper, the modified slip/fracture activation model has been used in order to understand the mechanism of ductile-brittle transition on the R-plane of sapphire during ultra-precision machining by reflecting direction of resultant force. Anisotropic characteristics of crack morphology and ductility of machining depending on cutting direction were explained in detail with modified fracture cleavage and plastic deformation parameters. Through the analysis, it was concluded that crack morphologies were mainly determined by the interaction of multiple fracture systems activated while, critical depth of cut was determined by the dominant plastic deformation parameter. In addition to this, by using proportionality relationship between magnitude of resultant force and depth of cut in the ductile region, an empirical model for critical depth of cut was developed.
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Experimental Study of Forces Induced in Mechanical Excavation of Rock
This paper presents preliminary results of an experimental campaign aimed at mapping the dependence of the cutting force on the depth of cut in scratch tests performed with a sharp cutter. Tests conducted in Berea sandstone and Indiana limestone confirm that the scaling of the force with the depth of cut depends on the cutting regime. They also show a dependence of the nature of the frequency distribution of the cutting force on the modes of failure.
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- Award ID(s):
- 1742823
- PAR ID:
- 10188014
- Date Published:
- Journal Name:
- Geo-Congress 2020: Modeling, Geomaterials, and Site Characterization
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The Japan Society for Precision Engineering (Ed.)Machining is in general conducted in multiple paths and thus residual stress and subsurface damage formed by previous cut may influence subsequent cutting. Ceramics materials are extremely brittle and prone to cracks. Ultra-precision machining with very small depth of cut enables ductile mode cutting. There have been various reports that critical depth of cut (CDC) for single crystal sapphire exists, where the ductile to brittle transition occurs. However, the CDC of subsequent cutting changes due to the influence of residual stress and subsurface damage by previous cut. This study investigates the indirect effect of residual stress and subsurface damage on the critical depth of cut of the second cut by analyzing the plastic deformation mechanisms activated during 2-step machining on A-plane of sapphire. It was found that the [1#100] machining orientation was most suitable since the critical depth of cut remained fairly constant due to dominant rhombohedral twinning activation during subsequent machining operations.more » « less
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Abstract In recent years, semiconductors, electronics, optics, and various other industries have seen a significant surge in the use of sapphire materials, driven by their exceptional mechanical and chemical properties. The machining of sapphire surfaces plays a crucial role in all these applications. However, due to sapphires’ exceptionally high hardness (Mohs hardness of 9, Vickers hardness of 2300) and brittleness, machining them often presents challenges such as microcracking and chipping of the workpiece, as well as significant tool wear, making sapphires difficult to cut. To enhance the machining efficiency and machined surface integrity, ultrasonic vibration-assisted (UV-A) machining of sapphire has already been studied, showing improved performance with lower cutting force, better surface finish, and extended tool life. Scribing tests using a single-diamond tool not only are an effective method to understand the material removal mechanism and deformation characteristics during such UV-A machining processes but also can be used as a potential process for separating IC chips from wafers. This paper presents a comprehensive study of the UV-A scribing process, aiming to develop an understanding of sapphire’s material removal mechanism under varying ultrasonic power levels and cutting tool geometries. In this experimental investigation, the effect of five different levels of ultrasonic power and three different cutting tool tip angles at various feeding depths on the scribe-induced features of the sapphire surface has been presented with a quantitative and qualitative comparison. The findings indicate that at feeding depths less than 6 μm, UV-A scribing with 40–80% ultrasonic power can reduce cutting force up to 50% and thus improve scribe quality. However, between feeding depths of 6 to 10 μm, this advantage of using ultrasonic vibration gradually diminishes. Additionally, UV-A scribing with a smaller tool tip angle (60°) was found to lower cutting force by 65% and improve scribe quality, effectively inhibiting residual stress formation and microcrack propagation. Furthermore, UV-A scribing also facilitated higher critical feeding depths at around 10 μm, compared to 6 μm in conventional scribing.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1061/9780784482841.012
