Ductile Grinding Research Articles

Process induced sub-surface damage in mechanically ground silicon wafers

Micro-Raman spectroscopy, scanning electron microcopy, atomic force microscopy and preferential etching were used to characterize the sub-surface damage induced by the rough and fine grinding steps used to make ultra-thin silicon wafers. The roughly and ultra-finely ground silicon wafers were examined on both the machined (1 0 0) planes and the cross-sectional (1 1 0) planes. They reveal similar multi-layer damage structures, consisting of amorphous, plastically deformed and elastically stressed layers. However, the thickness of each layer in the roughly ground sample is much higher than its counterpart layers in the ultra-finely ground sample. The residual stress after rough and ultra-fine grinding is in the range of several hundreds MPa and 30 MPa, respectively. In each case, the top amorphous layer is believed to be the result of sequential phase transformations (Si-I to Si-II to amorphous Si). These phase transformations correspond to a ductile grinding mechanism, which is dominating in ultra-fine grinding. On the other hand, in rough grinding, a mixed mechanism of ductile and brittle grinding causes multi-layer damage and sub-surface cracks.

An experimental study of flat fixed abrasive grinding of silicon wafers using resin-bonded diamond pellets

The purpose of this paper is to investigate the effect of the diamond grain size, the wheel rotation speed, the table rotation speed, and the applied pressure in the vertical flat grinding on the surface roughness of silicon wafers using Taguchi orthogonal array design. Besides, the pits and resistivity on the wafers were studied as well. The experiment results showed that the diamond grain size and the wheel rotation speed of the vertical flat grinding for the roughness of wafers obtained are the relatively larger significant contribution. When the smaller diamond grit size, the faster wheel rotation speed, the faster table rotation speed, and the smaller applied pressure in the flat grinding are employed, the traces produced by the grains are denser and the chip thickness and the depth of cut were smaller, which cause the silicon wafer to produce the higher degree of the ductile grinding. This will lead the wafer surface to produce the smaller amount and size of the pits, thereby generating the lower surface roughness. In addition, the center site of the wafer obtained is the smaller amount and size of the pits than the outer of the wafer, which produces the better surface roughness and the lower resistivity.

ELID Assisted Precision Conditioning of Coarse-Grained Diamond Grinding Wheel

In order to realize ductile machining of optical glasses using mono-layer nickel electroplated coarse-grained diamond grinding wheel, a novel conditioning technique features using a copper bonded diamond grinding wheels of 15m grain size dressed by ELID (electrolytic inprocess dressing) to condition the 46m grain sized diamond wheel has been developed. During the conditioning process, a force transducer was used to monitor the conditioning force, a coaxial optical distance measurement system was used to in-situ monitor the modified wheel surface status. White-light interferometry (WLI), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the conditioned wheel surface status as well as the ground optical glass surface topography correspondingly. The experimental result indicates that a minimized wheel radial run-out error of less than 2μm as well as the top-flattened diamond grains of constant wheel peripheral envelop profile were generated on a 5-axis ultra-precision machine tool. The grinding experiment proved that the well conditioned 46μm coarse-grained diamond wheel can be used in realizing the ductile grinding of optical glass BK7, which indicates that the newly developed conditioning technique is feasible and applicable to introduce the coarse-grained diamond wheels into precision machining of brittle and hard-to-machine materials.

3D Fractal Analysis of Ultra Precision Grinding Influencing on the Surface Topography of Brittle Material

3Dfractal dimension and 2D profile fractal dimension distribution of the surfaces made by brittle or ductile grinding are calculated. From the calculated results of 3D fractal dimension, it can be found that the microtopograhpy of ductile ground surface is more exquisite than brittle ground surface and 3D fractal dimension Ds has inverse relation with the roughness parameter Rq. Through the analysis of 2D profile fractal dimension distribution in different ground surfaces, it is revealed that the topography of ground surface is changed with grinding parameters such as ground surfaces may have weakly or strongly anisotropic even isotropic features when different grinding parameters are adopted. Using fractal method to analyze the topography of ground surface is helpful to understand the generating mechanism of surface topography.

Thermal Study in Diamond Grinding of Zirconia

In the present study, zirconia ceramic was ground with a resin-bonded diamond wheel on a precision surface grinding machine. Grinding temperatures generated at the wheel-workpiece contact zone were measured using a sandwiched foil thermocouple, and the net consumed grinding powers were also measured. The energy partition to the diamond abrasives was estimated using measured grinding temperatures and powers. Based on the energy partition values obtained from the analyzed results, the diamond tip temperature was calculated and found to be over 1000°C if the circular grain contact of radius was less than a critical value for ductile field grinding of zirconia ceramic.

Surface and Sub-Surface Integrity of Ultra- Machined BK7 Using Fine and Coarse Grained Diamond Wheels

This paper aims to evaluate the surface and sub-surface integrity of optical glasses which were correspondingly machined by coarse and fine-grained diamond grinding wheels on Tetraform ‘C’ and Nanotech 500FG. The experimental results show that coarse-grained diamond grinding wheels are capable of ductile grinding of optical glasses with high surface and sub-surface integrity. The surface roughness values are all in nanometer scale and the sub-surface damages are around several micros in depth, which is comparative to those machined by fine-grained diamond wheels.

Effects of Actively Cooled Coolant for Grinding Ductile Materials

An active cooling approach for coolant during ductile material grinding is proposed and examined. The aim is to enhance surface quality and to enhance productivity. The problem associated with the cryogenic cooling approach and the one with the chilled air approach are addressed. An active cooling prototype was developed utilizing a compact heat pump design, which is easy to use, movable, and can be easily fitted into different type of machine designs with relatively low costs. The system is based on the use of forced convection of the heat generated during the machining process. Experimental and computational studies of the effects of actively cooled coolant for grinding ductile materials are carried out. The experimental results show that the use of actively cooled coolant is able to improve surface quality by up to 29.95% on average in terms of surface roughness Ra. Computational testing results show that the heat can be taken away more effectively by using the proposed approach. The results of optical and SEM examinations also confirmed that the proposed approach is advantageous.

Modeling of High Efficiency Removal in the Grinding of Aluminal/ZrO<sub>2</sub> Nanocomposites with the Aid of Two-Dimensional Ultrasonic Vibration

Based on the single abrasive particle motion locus of elliptical spiral in two-dimensional ultrasonic vibration grinding (WTDUVG), the theoretical model representing the material removal rate are deduced and verified, and the reason of high efficiency material removal by applying two-dimensional ultrasonic vibration is analyzed. Finally, experimental researches on material removal rate of ceramics were carried out using coarse grit diamond wheel both with and without workpiece two-dimensional ultrasonic vibration assistance grinding. Experimental results indicated that (1) Material removal rate (MRR) in vibration grinding process is about 1.5 times as large as that of in conventional grinding, the experimental results are in good agreement with the calculated ones. (2)The material removal rate increases along with increases of the grinding depth and workpiece velocity both in with and without vibration grinding. (3)The vibration grinding surface had no spur and build-up edge and its surface roughness was smaller than CG significantly. Surface quality of WTDUVG is superior to that of conventional grinding, it is easy for ultrasonic vibration grinding that material removal mechanism is ductile regime grinding.

Study on Surface Quality of Nano ZrO<sub>2</sub> Ceramics in Grinding by the Aid of Ultrasonic Vibration

Nano ceramics possesses excellent mechanical property and physical characteristics in contrast to conventional engineering ceramics, so it has tremendous application prospect. Adopting ultrasonic composite processing we describe the influences of grinding speed, grinding depth, wheel granularity and no-spark grinding times on the surface roughness of nano ZrO2 ceramics. By means of SEM and AFM the surface character and critical ductile grinding depth of nano ZrO2 ceramics in the condition of conventional and ultrasonic grinding are also discussed. At last, the residual stress of surface and crystalline phase transformation under the condition of conventional grinding and ultrasonic vibration grinding were analyzed by X-ray diffraction. The research indicated that ultrasonic vibration grinding could obtain nano finished surface with high efficiency. The residual stress of nano ZrO2 ceramics surface is determined much by different grinding styles.

The Study on Ductile Removal Mechanisms of Ultrasonic Vibration Grinding Nano-ZrO<sub>2</sub> Ceramics

On the basis of analyzing the brittleness, ductileity, and the removal mechanisms of the^nano-ZrO2 Ceramics, the critical ductile grinding depth formula of the nano-ceramics was established. Due to superductileity of the nano-ZrO2 ceramics, it couldn’t apply the formula of the common engineering ceramic material according to experimental results. The value of material coefficient ζ has relations with not only the material characteristics but also the processing methods and the processing parameters. It was proved that ζ has great effects on the accuracy of theoretical calculation. Experimental results showed that the critical ductility grinding depth of the nano-ZrO2 ceramics is up to 12 µm in common grinding methods, while in ultrasonic grinding is up to 20µm. The grinding chips with and without ultrasonic vibration assistance were discussed.

Study on Critical Ductile Grinding Depth of Nano ZrO<sub>2</sub> Ceramics by the Aid of Ultrasonic Vibration

The crack extension course and ductile removal mechanism of nano ZrO2 ceramics were analyzed in this paper. On the basis of contrast tests with or without ultrasonic vibration, the influences of critical ductile grinding depth on grinding forces and surface quality were studied by dynamometer, SEM and AFM in different grinding condition. The reason for the increase of the critical grinding depth was discussed based on the analysis of grinding force and ultrasonic vibration course. At last, the formation mechanism of surface topography observed by AFM in ductile domain was analyzed. The research indicated that ultrasonic machining could obtain nano finished surface with high efficient.

A Fundamental Modeling Approach for Nano-Grinding of Silicon Wafers

The advantages of ductile regime grinding of silicon wafer such as smooth surface roughness (Ra < 10 nm) and minimum subsurface damage layer (< 10μm) have great impact on the production process of wafer. With ductile regime grinding, the subsequent processes such as etching and rough polishing processes can be minimized. To achieve ductile regime grinding, a fundamental concept is the application of grain depth of cut being less than the critical cut depth, dc, of the silicon wafer. However, dc is dependent on material properties, cutting conditions, and crystallographic orientation [1].The objective of this paper is to derive, and to investigate by experiment, the dc value for silicon wafer grinding. Following these key steps, the effects of dc on various major grinding parameters are studied.

ULTRA-PRECISION GRINDING OF BK7 OPTICAL GLASS USING COARSE-GRAINED ELECTROPLATED DIAMOND WHEEL

A novel conditioning technique is developed to precisely and effectively condition the 151μm grain-sized nickel electroplated monolayer coarse- grained diamond grinding wheel in aiming to realize ductile grinding of brittle materials. During the conditioning process, a copper bonded diamond grinding wheel (91μm grain size) dressed by ELID (electrolytic in-process dressing) is applied as a conditioner, a force transducer was used to monitor the conditioning force, and a coaxial optical distance measurement system are used to in-situ monitor the modified wheel surface status. Ultimately the coarse-grained diamond wheel is conditioned to achieve an ideal state in terms of less than 2μm run-out error, top-flattened diamond grains and constant wheel envelop profile. Then the well- conditioned 151μm wheel is applied to conduct taper grinding and contour grinding tests, the ground surface and sub-surface integrity are measured by WLI (white light interferometer), AFM (atomic force microscope) and SEM (scanning electrical microscope) respectively. The experimental results indicate that the well-conditioned 151μm grain-sized diamond wheel is able to realize ductile grinding of BK7 with nano-scale surface roughness, as well as the almost damage free sub-surface integrity. The results also show the promising prospect of the conditioning technique and coarse-grained diamond wheels to be applied in machining the hard-machine-materials and the other brittle materials such as ceramic and silicon carbide, etc.

Study on the Surface and Subsurface Integrity of Ground Monocrystalline Silicon Wafers

Wafer rotation grinding, as an important processing technology, is widely used in manufacturing and back thinning of the silicon wafer. However, the surface/subsurface integrity of the ground wafer, which has important influences on the surface quality and the output of the wafer in subsequent process, is becoming an attention-catching problem. This study is aimed at experimental investigation of the surface/subsurface integrity in wafer rotation grinding. The surface roughness, the subsurface crack configurations, the subsurface damage depth (SSD) and the phase transformations are evaluated by corresponding methods. The results show that the integrity of the ground wafer has a close relationship with the grit size of the grinding wheel. The surface roughness and the SSD increase with increasing of the grit size. The subsurface crack configurations of (100) silicon wafers are complicated. The material removal mechanism is different under different grinding conditions. Ductile grinding is accompanied by the phase transformations of diamond structure silicon (Si-I). The amorphous silicon (α-Si), the Si-XII phase (r8-rhombohedral structure) and the Si-III phase (bc8-body-centered cubic structure) exist on the near surface region of the wafer ground by #600 and #2000 grinding wheels.

Study on Ultrasonic Vibration Grinding Character of Nano ZrO<sub>2</sub> Ceramics

Nano ceramics possessed ascendant mechanical property and physical characteristics contrast with engineering ceramics, so it has extensive application prospect in various industries. On the basis of applying the indentation fracture mechanics to analyze the removal mechanics of ceramic material, this paper analyzed the critical ductile grinding depth of the nano ZrO2 ceramics. Adopting ultrasonic composite processing we describe the influence of different processing parameters and grain size of diamond wheel on the grinding forces and surface roughness. Based on the grinding forces and surface roughness the grinding process with and without vibration is analyzed. By means of SEM and AFM the surface character and critical ductile grinding depth of nano ZrO2 ceramics are also discussed. The paper supplied the theoretical and experimental basis for the grinding of the large-sized ultraprecision plate structure of nano ZrO2 ceramics (nm).

On the design and implementation of an instrumented grinding testbed

PurposeThe need for an instrumented grinding system that addresses the requirements of ductile regime machining of brittle materials is implemented. The static and dynamic stiffness of the structural loop of the grinding system meets or exceeds those of previous researchers. An instrumented spindle is introduced which features capacitance gages embedded in the stator of an air bearing spindle.Design/methodology/approachThe instrumented spindle is demonstrated to provide valuable force feedback for fine grinding and is capable of resolving intra‐revolution force components. Tests are performed to demonstrate the use of the instrumented spindle for ductile grinding of brittle materials with superabrasive wheels.FindingsThe results of the test show that the instrumented spindle is capable of determining intra‐revolution force components for square alumina‐titanium carbide wafers.Originality/valueOutlines some important work developing and building instrumented spindles to aid the precision grinding industry.

High-Precision Low-Damage Grinding of Polycrystalline SiC

Spherical grinding was conducted with a ductile regime mode using a CNC grinding machine and a metal-bond diamond tool with a grit size of 25 mum. The ductile grinding process generated silicon carbide spherical surfaces with surface roughness of <10 nm Ra, evaluated by an optical profiler and an atomic force microscope. Using a scanning electron microscope, the ground silicon carbide exhibited little visible grinding-induced cracks except for some residual porosity associated with the fabrication process of the polycrystal. The x-ray diffraction tests indicated that no phase transformation in silicon carbide occurred during the grinding process.

The ductile grinding of glass using diamond fibres oriented radially in a grinding wheel

Diamond-coated fibres, produced by a hot filament chemical vapour deposition technique and having a high facet density, have been prepared for use as abrasives. Two grinding wheels containing such fibres have been fabricated with the fibres placed in a radial orientation. One wheel contained a single fibre, the other contained multiple fibres. The single diamond fibre wheel was used first to evaluate the potential for ductile grinding of BK7 glass. A ductile-brittle transition was found, occurring at a depth of cut of ∼1 μm over a range of feed rates (5–50 μm/s). The multiple diamond fibre wheel was then used to grind an area, using parameters identified by the single fibre tests. Microstructural analysis revealed that material removal was predominantly in the ductile mode.

Influence of the Grinding Wheel in the Ductile Grinding of Brittle Materials: Development and Verification of Kinematic Based Model

Empirical evidence has shown that grinding wheel characteristics significantly affect performance in the grinding of brittle materials. In this research a grit depth of cut model was developed based on a kinematic simulation of the grinding process. The model describes the relationships between grinding wheel parameters (grit size, concentration, binder modulus) and chip thickness and area. It was corroborated by the measurement of number of cutting grits in tests using a fly wheel with small abrasive area. Based on this grit depth of cut model, the “critical depth of cut” model for the grinding of brittle materials was modified to include wheel parameter effects. The new critical depth of cut model was tested using “crossfeed” experiments. Although the theoretical and experimental results show less agreement than for the grit depth of cut model, the model equations provide guidelines for choosing wheel specifications.

Partial-Ductile Grinding and Reduced Polishing for Ophthalmic Glass Molds

Plastic lenses are manufactured by the classical replication technique where two glass molds are assembled in a jacket and liquid plastic is injected into it. The glass molds are fabricated conventionally by fracture mode grinding, followed by lapping, and Finally polishing. This paper presents an alternative fabrication process using partial-ductile grinding, followed by a short polishing in an industrial polishing machine. The partial-ductile surfaces were generated on a laboratory ultra-precision machine using Fine grit resinoid-bond diamond wheel and they were compared to the glass molds prepared by industry. The results showed that (i) as much as 100% ductile streaks (fully ductile grinding) can be obtained in the ultra-precision ground surface and (ii) a net saving of 55 seconds polishing time if only 60% of ductile streaks on the glass mold surface was used prior to polishing.