Anisotropy Effect on Cutting Monocrystal Sapphire by Micro-Laser Assisted Machining Technique

2016 ◽  
Author(s):  
Hossein Mohammadi ◽  
John A. Patten
Keyword(s):  
Laser Heating ◽  
Removal Rate ◽  
Single Point ◽  
Brittle Materials ◽  
Single Crystal Silicon ◽  
Shear Stresses ◽  
Crystal Silicon ◽  
Anisotropy Effect ◽  
Fracture Damage ◽  
Scratch Tests

Machining of hard and brittle materials such as ceramics and semiconductors has been a challenge for many years. They have many applications in optics, MEMS and electronic industries due to their many desirable properties, such as being light weight, strong, and hard. Achieving good surface finish, avoiding surface and subsurface damage and at the same time achieving a high material removal rate are extremely challenging for these materials. Materials such as single crystal silicon and sapphire have a crystal orientation or anisotropy effect which makes their machining even more difficult. Because of this characteristic, their behavior is directional and they have different fracture toughness for each direction. In past works in our research group, it has been demonstrated that machining of brittle materials in ductile regime is possible due to the high pressure phase transformation (HPPT) occurring in the material caused by the high compressive and shear stresses induced by a single point diamond tool tip. In the current study scratch tests were performed on the monocrystal sapphire in four different perpendicular directions and to further augment the process, traditional cutting is coupled with a laser to heat and soften the material to either enhance the ductility, resulting in a deeper cut, or reducing brittleness leading to decreased fracture damage. Results of scratch tests, with and without laser heating, for different cutting loads have been compared. The effect of laser heating was studied by analyzing the image of cuts and verifying the depth of cuts which were made using varying laser power during the process. Microscopic images and three-dimensional profiles of the cuts taken by using a white light interferometer were investigated.

scholarly journals Effect of Thermal Softening on Anisotropy and Ductile Mode Cutting of Sapphire Using Micro-Laser Assisted Machining

2017 ◽  
Vol 5 (1) ◽  
Author(s):  
Hossein Mohammadi ◽  
John A. Patten
Keyword(s):  
Removal Rate ◽  
Brittle Materials ◽  
Single Crystal Silicon ◽  
Thermal Softening ◽  
Depth Of Cut ◽  
Crystal Silicon ◽  
Ductile Mode ◽  
Hard And Brittle Materials ◽  
Fracture Damage ◽  
Diamond Cutting Tool

Ceramics and semiconductors have many applications in optics, micro-electro-mechanical systems, and electronic industries due to their desirable properties. In most of these applications, these materials should have a smooth surface without any surface and subsurface damages. Avoiding these damages yet achieving high material removal rate in the machining of them is very challenging as they are extremely hard and brittle. Materials such as single crystal silicon and sapphire have a crystal orientation or anisotropy effect. Because of this characteristic, their mechanical properties vary significantly by orientation that makes their machining even more difficult. In previous works, it has been shown that it is possible to machine brittle materials in ductile mode. In the present study, scratch tests were accomplished on the monocrystal sapphire in four different perpendicular directions. A laser is transmitted to a diamond cutting tool to heat and soften the material to either enhance the ductility, resulting in a deeper cut, or reducing brittleness leading to decreased fracture damage. Results such as depth of cut and also nature of cut (ductile or brittle) for different directions, laser powers, and cutting loads are compared. Also, influence of thermal softening on ductile response and its correlation to the anisotropy properties of sapphire is investigated. The effect of thermal softening on cuts is studied by analyzing the image of cuts and verifying the depth of cuts which were made by using varying thrust load and laser power. Macroscopic plastic deformation (chips and surface) occurring under high contract pressures and high temperatures is presented.

Scratch Tests on Granite Using Micro-Laser Assisted Machining Technique

2015 ◽  
Author(s):  
Hossein Mohammadi ◽  
John A. Patten
Keyword(s):  
Laser Heating ◽  
Laser Power ◽  
Single Point ◽  
Brittle Materials ◽  
Past Research ◽  
Depth Of Cut ◽  
Shear Stresses ◽  
Granite Sample ◽  
Laser Assisted Machining ◽  
Scratch Tests

In this study, micro-laser assisted machining (μ-LAM) technique is used to perform scratch test on a granite sample. Rocks are generally considered as brittle materials with poor machinability and severe fracture can be resulted when trying to cut them due to their low fracture toughness. Due to increasing demand for these materials in industry with many applications, finding a fast and cost effective process with higher product quality seems essential. In past research in our research group, it has been demonstrated that machining of brittle materials such as semiconductors and ceramics in ductile regime is possible due to the high pressure phase transformation (HPPT) occurring in the material caused by the high compressive and shear stresses induced by a single point diamond tool tip. Scratch tests were performed on the granite sample and to further augment the process, traditional cutting is coupled with the laser to soften the material and get the higher depth of cut. In this research, results of scratch tests done on granite, with and without laser heating have been compared. The effect of laser heating was studied by verifying the depths of cuts for scratch tests with varying the laser power during the process. Microscopic images and three-dimensional profiles of cuts taken by using a white light interferometer were investigated. Results show that using laser can increase depth of cut and with 15 W laser power it is increased — for different regions of granite sample — from 25% to 95%.

scholarly journals Novel Abrasive-Impregnated Pads and Diamond Plates for the Grinding and Lapping of Single-Crystal Silicon Carbide Wafers

2021 ◽  
Vol 11 (4) ◽  
pp. 1783
Author(s):  
Ming-Yi Tsai ◽  
Kun-Ying Li ◽  
Sun-Yu Ji
Keyword(s):  
Silicon Carbide ◽  
Wear Rate ◽  
Single Crystal ◽  
Traditional Method ◽  
Removal Rate ◽  
Chemical Mechanical Planarization ◽  
Single Crystal Silicon ◽  
Crystal Silicon ◽  
Diamond Grit ◽  
Ceramic Binder

In this study, special ceramic grinding plates impregnated with diamond grit and other abrasives, as well as self-made lapping plates, were used to prepare the surface of single-crystal silicon carbide (SiC) wafers. This novel approach enhanced the process and reduced the final chemical mechanical planarization (CMP) polishing time. Two different grinding plates with pads impregnated with mixed abrasives were prepared: one with self-modified diamond + SiC and a ceramic binder and one with self-modified diamond + SiO2 + Al2O3 + SiC and a ceramic binder. The surface properties and removal rate of the SiC substrate were investigated and a comparison with the traditional method was conducted. The experimental results showed that the material removal rate (MRR) was higher for the SiC substrate with the mixed abrasive lapping plate than for the traditional method. The grinding wear rate could be reduced by 31.6%. The surface roughness of the samples polished using the diamond-impregnated lapping plate was markedly better than that of the samples polished using the copper plate. However, while the surface finish was better and the grinding efficiency was high, the wear rate of the mixed abrasive-impregnated polishing plates was high. This was a clear indication that this novel method was effective and could be used for SiC grinding and lapping.

Examining pressure-induced phase transformations in silicon by spherical indentation and Raman spectroscopy: A statistical study

2004 ◽  
Vol 19 (10) ◽  
pp. 3099-3108 ◽  
Author(s):  
Tom Juliano ◽  
Vladislav Domnich ◽  
Yury Gogotsi
Keyword(s):  
Raman Spectroscopy ◽  
Phase Transformations ◽  
Statistical Study ◽  
Single Crystal Silicon ◽  
Maximum Load ◽  
Spherical Indentation ◽  
Shear Stresses ◽  
Crystal Silicon ◽  
Stability Range ◽  
Unloading Rate

Unloading rate and maximum load have been previously shown to affect the response of silicon to sharp indentation, but no such study exists for spherical indentation. In this work, a statistical analysis of over 1900 indentations made with a 13.5-μm radius spherical indenter on a single-crystal silicon wafer over a range of loads (25–700 mN) and loading/unloading rates (1–30 mN/s) is presented. The location of “pop-in” and “pop-out” events, most likely due to pressure-induced phase transformations, is noted, as well as pressures at which they occur. Multiple occurrences of pop-in and pop-out events are reported. Raman micro-spectroscopy shows a higher intensity of metastable silicon phases at some depth under the surface of the residual impression, where the highest shear stresses are present. A stability range for Si-II is demonstrated and compared with previous results for Berkovich indentation.

Failure of micron scale Single Crystal Silicon bars due to torsion developed by MEMS micro instruments

1998 ◽  
Vol 518 ◽  
Author(s):  
Taher Saif ◽  
N. C. MacDonald
Keyword(s):  
Single Crystal ◽  
Single Crystal Silicon ◽  
Theory Of Elasticity ◽  
Shear Stresses ◽  
Electrostatic Actuator ◽  
Crystal Silicon ◽  
Cross Sectional ◽  
Lever Arm ◽  
Spring Constants

AbstractWe present an experimental study on a single crystal silicon (SCS) bar subjected to pure torsion using MEMS micro instruments. The bar is in the form of a pillar, anchored at one end to the silicon substrate. It is attached to a lever arm at the other end. The pillar has a minimum cross sectional area at its mid height. The cross section coincides with the (100) plane of SCS. Torsion is generated by applying two equal forces on the lever arm on either side of the pillar. Two micro instruments apply the forces. Each consists of an electrostatic actuator and a component that calibrates it. The actuator generates high force (≈ 200 µN at 50 V) and is capable of developing large displacements (≈ 10 μm). Calibration involves determination of the force generated by the actuator at an applied voltage, as well as the linear and higher order spring constants of its springs. Each microinstrument is thus calibrated independently.With the application of forces by the two micro instruments, a torque is generated which twists the pillar. The angle of twist at different applied voltages are recorded using an angular scale. The corresponding torques are determined from the calibration parameters of the actuators. Torque is applied until the pillar fractures. Two such sample pillars, samples 1 and 2, are tested. There cross sectional areas are 1 and 2.25 µm2. We find that both the pillars behave linearly until failure. The stresses prior to fracture are evaluated based on anisotropic theory of elasticity. Samples 1 and 2 fail at shear stresses of 5.6 and 2.6 GPa respectively. The fracture surfaces seem to coincide with the (111) plane of SCS.

An Experimental Study on Single Point Diamond Turning of an Unpolished Silicon Wafer via Micro-Laser Assisted Machining

2014 ◽  
Vol 1017 ◽  
pp. 175-180 ◽  
Author(s):  
Hossein Mohammadi ◽  
H. Bogac Poyraz ◽  
Deepak Ravindra ◽  
John A. Patten
Keyword(s):  
Single Point ◽  
High Hardness ◽  
Industrial Applications ◽  
Diamond Turning ◽  
Shear Stresses ◽  
Workpiece Material ◽  
Crystal Silicon ◽  
Laser Assisted Machining ◽  
Diamond Cutting Tool ◽  
Si Wafer

Single Pointe Diamond Turning (SPDT) of silicon can be an extremely abrasive process due to the hardness of this material. In this research SPDT is coupled with the micro-laser assisted machining (μ-LAM) technique to machine an unpolished single crystal silicon (Si) wafer. Si is increasingly being used for industrial applications as it is hard, strong, inert, light weight and has great optical and electrical properties. Manufacturing this material without causing surface and subsurface damage is extremely challenging due to its high hardness, brittle characteristics and poor machinability. However, ductile regime machining of Si is possible due to the high pressure phase transformation (HPPT) occurring in the material caused by the high compressive and shear stresses induced by the single point diamond tool tip. The μ-LAM system is used to preferentially heat and thermally soften the workpiece material in contact with a diamond cutting tool. Different outputs such as surface roughness (Ra, Rz) and depth of cuts (DoC) for different set of experiments with and without laser were analyzed. Results show that an unpolished surface of a Si wafer can be machined in two passes to get a very good surface finish.

Development of a Combined Diamond Impregnated Lapping Plate

2017 ◽  
Vol 739 ◽  
pp. 157-163
Author(s):  
Guan Fu Lin ◽  
Ming Yi Tsai ◽  
Chiu Yuan Chen
Keyword(s):  
Surface Roughness ◽  
Material Removal Rate ◽  
Material Removal ◽  
Removal Rate ◽  
Single Crystal Silicon ◽  
High Quality ◽  
Crystal Silicon ◽  
Temperature Heating ◽  
Oxidized Diamond ◽  
High Temperature Heating

This paper presents a combined diamond-impregnated lapping plate for single crystal silicon carbide (SiC) to improve the material removal rate due to SiC having very low material removal rate. Three different dimaond shapes were prepared: (1) "sharp," a sharp-edged diamod; (2) "blocky," a high quality crystalline diamond; (3) "oxidized diamond". The diamonds were manufactured by using high temperature heating method in a furnace to induce diamond oxidation resulting in improvement of Ra and sharpness of the diamonds. Three combined diamond-impregnated lapping plates were fabricated using the above mentioned diamond shapes with diamond size of 6μm. The surface roughness and removal rate of the SiC lapping with these plate were investigated. Experimental results showed that the average material removal rate (MRR) of oxidized diamond is higher than that of the other diamond shapes. The MRR of oxidized diamond for C-face and Si-face SiC are 4.72μm/hr and 6.26μm/hr, respectively. It is found that the surface roughness (Ra) of oxidized diamond for C-face and Si-face are 7.547nm and 8.06nm, respectively. This indicates that the combined diamond-impregnated lapping plate can be effectively used for SiC machining.

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