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Detection of ductile to brittle transition in microindentation and microscratching of single crystal silicon using acoustic emission
Abstract
Machining of brittle materials entails two modes of material removal: pure plastic deformation and brittle fracture. The mode of material removal is generally identified by surface quality observations in a scanning electron microscope (SEM) or an atomic force microscope (AFM) after machining. Hence, there is a need for the development of in-process monitoring technology in order to detect whether the mode of material removal is ductile or brittle, and thereby predict surface quality. In the present paper, acoustic emission (AE) is proposed as a means of monitoring the ductile to brittle transition. Microindentation and microscratching tests of single crystal silicon were conducted using an ultrafine-motion table with very small motion error. The obtained AE signals were correlated with crack initiation and the ductile to brittle transition. The critical force fc defined as the force at which AE was induced during the microindentation and microscratching tests was measured to be 40 ∼ 50 mN. AFM observations revealed the critical depth of cut dc to be 0.20 μm in the microscratching test.
... The burst-type AE signals are usually accompanied by low strength reflection waves which, along with the background signals, can be ignored via appropriate sensor lockout time and voltage thresholding [23]. Furthermore, the output AE signals can be exploited to characterize different fracture types: Koshimizu et al. (2001) examined ductile to brittle fracture transitions in silicon workpieces with AE sensors and noticed higher AE activity at brittle fracture than at ductile ones. Therefore, the AE sensors are capable of examining not only the structural condition but also different fracture types in sheet metals. ...
... Furthermore, the cumulative AE signals at 700 • C levelling off at a lower value than at 600 • C indicate that the AE signals depend not only on the amount of cracking events but also on the temperature at which cracks are initiated. At 700 • C, it is likely that the AlSi coating undergoes ductile-dominated coating fracture, which releases relatively low intensity AE signals than the brittle fracture at 600 • C. According to the literature, different fracture types cause variation in AE signal intensity [43]. ...
In this article, the fracture behavior of AlSi coating at elevated temperatures is investigated. During the heating stage, Fe−Al intermetallics and voids are formed, both of which define the fracture behavior of the AlSi coating layer. After heating, the effects of deformation temperature, strain level and strain rate on the fracture of AlSi coating is investigated, during deformation of the coated press hardening steel. For this purpose, tensile experiments are conducted at elevated temperatures. The experiments include heating the coated steel at 920 °C for 6 minutes, uniaxial tensile deformation at isothermal conditions (400−800°C) and then quenching to room temperature. Acoustic emission (AE) sensors are incorporated to detect coating fracture at each stage. After quenching, the distribution of coating cracks and its micro-structure are examined via optical and scanning electron microscopy techniques, respectively. The results show that there is a strong correlation between AlSi coating fracture and the deformation temperature, macroscopic strain level and the output AE signals. According to the acoustic and optical measurements, the uniaxial tensile experiments at 400−700 °C show coating fracture: at 400 and 500 °C coating fracture is severe with spallation, while at 600 and 700 °C mode-I coating cracks are generated. However, at 800 °C no coating cracks are observed until 30% macroscopic strain. In conclusion, the experimental results demonstrate that the AlSi coating fracture is strongly dependent on the temperature and strain but not on the strain rate. Furthermore, the agreement between AE signals and optical images confirms that the AE sensors can be reliably used for in-situ detection of AlSi coating fracture during tensile experiments.
... Researchers have defined ductile to brittle transition based methods such as: visual observation of cracks on the scratch path [7,8], force measurement [8], Acoustic Emission (AE) measurement [9] during scratching of silicon, etc. M. Yoshino, et al. [6] had performed scratching study on silicon at low cutting speed of 265.9x10 -6 m/s in vacuum inside a Scanning Electron Microscope (SEM) and the dc was determined as 600 nm, below which no cracks were observed on the scratch path. Hao Wu, et al. [7] conducted scratching experiments on silicon at speeds of 1 mm/min (0.00002 m/s) with two different indenter shapes namely, truncated conical tip (60° included angle) and conical tip (120° included angle), and the dc was reported as 318 nm and 52 nm respectively, based on visual interpretation of scratch path under SEM. ...
... Arkadeep Kumar, et al. [8] had defined ductile to brittle transition using normal and tangential forces during scratching under dry and wet conditions. Koshimizu, et al. [9] had performed scratching and indentation of silicon to define ductile to brittle transition using acoustic emission signals. The transition region of the scratch (region where cracks start to form before catastrophic brittle fracture starts to occur) is usually ignored and not analysed in the above works. ...
During machining of single-crystal silicon, material removal involves two modes ductile shear-based removal and brittle fracture-based removal. Ductile shear-based chip removal occurs when fracture is suppressed due to local stress conditions along with reduced chances of defect involvement and is desirable for achieving better surface integrity of the machined silicon wafer. In this work, we use charged particle emissions to identify mode of material removal (ductile or brittle) during scratching of a silicon wafer. Scratching tests were performed using a pin-on-disc tribometer setup with a conical diamond tip indenter, in which the wafer was held at an inclined position to achieve a varying-depth tapered scratch. The varying-depth scratch test was performed in such a manner that both ductile-to-brittle and brittle-to-ductile modes occur in a single scratch test. The charged particles emitted during the material deformation were collected using a Faraday plate mounted in the vicinity of the indenter and the intensity of the charged particles were measured using a sensitive femto/picoammeter. The scratch depth was measured using a 3D surface profiler and the mode of fracture was identified by examining crack density per unit length in a scanning electron microscope. These results were then correlated with the emission intensity signals. From the experimental results, a positive current intensity was observed for ductile mode of scratching and highly varying current intensity signal is observed during brittle mode of scratching. The results obtained were consistent over time and exhibited good repeatability. The present work indicates suitability of employing charge emission signals to detect mode of material removal during scratching of silicon. This work can be field-tested by conducting diamond turning experiments of silicon in real-time machining environment further testing the scope of use of charged particle emission to monitor real-time machining process.
... Furthermore, a quantitative comparison between experimental results and FE simulation prediction data in diamond grooving is still lacking. Moreover, while the BTD transition can be experimentally identified from various aspects such as groove profile [24][25][26][27], cutting force [25,33], and acoustic emission signal [34,35], the BTD transition in previous FE simulations is solely distinguished from the evolution of chip profile. Therefore, other theoretical aspects are also expected for providing robust evidence of the BTD transition in FE simulations. ...
... Consequently, material removal within the shielding zone is dominated by dislocation flow [6,8,25]. In addition to dislocation activity-governed plastic flow, phase transformation and amorphization occurred under highly compressive pressure also play an important role in the BTD transition of silicon [34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49]. Yan et al. [50] reported a combined effect of both phase transformation and dislocation motion on the ductile mode cutting of silicon. ...
Brittle-to-ductile transition plays a crucial role in ultra-precision machining of hard brittle materials. In the present work, we investigate the brittle-to-ductile transition in diamond grooving of monocrystalline silicon by finite element modeling and simulation based on Drucker-Prager constitutive model. The brittle-to-ductile transition behavior is distinguished by analyzing evolutions of chip profile and cutting force. Corresponding diamond grooving experiment using the same machining configuration with the finite element simulation is also carried out to derive the critical depth of cut for the brittle-to-ductile transition. The comparison of experimental value of the critical depth of cut and predicted one by the finite element simulation demonstrates the high accuracy of as-established finite element model. Subsequent finite element simulations are performed to investigate the influence of rake angle of cutting tool on both diamond grooving and conventional diamond cutting with a constant depth of cut, which demonstrates a prominent dependence of brittle-to-ductile transition of silicon on the rake angle ranging from -60o to 0o. And a critical rake angle for the most pronounced ductile machinability of silicon is found.
... These low intensity, high frequency (100 kHz-1 MHz) elastic waves propagate in all directions through the structure to a detector on the surface of the workpiece. In previous research, AE has been shown to be sensitive to a variety of characteristics in precision manufacturing processes including nano-order applications [12][13][19][20]]. Fig. 2 shows the parameter definitions of digitized AE signals. ...
... In addition, the friction and shearing energies dissipated in the primary, secondary and tertiary zones (Fig. 14) during cutting are already known as major sources of AE signal generations [29]. With the depth near or over d c value (brittle regime), not just AE energy levels, but more sophisticated analysis such as detailed spectral analysis should be performed to investigate various signal characteristics during the deformation and/or fracture processes [19][20]30]. For the AE RMS signals (Fig. 15), the average values show a sharp increase at the regime 2 (cutting mode) compared with regime 1 (ploughing mode), which indicates greater rubbing action due to the initiation of chip formation and debris. ...
The goal of this research is to investigate/monitor the machining characteristics and mode transitions during AFM nanoscratching of a brittle material such as Si (100) using acoustic emission (AE). By utilizing a specially designed AFM/nano stage setup, nano experiments were performed for various AFM tip engaging depths. With the aid of AFM and FE-SEM images, not only the typical features of each mode, such as pile-ups, chip formations, and crack propagations, but major mode changes including elastic/plastic and ductile brittle/transitions are observed and analyzed. To estimate mode transition depths, such as the yielding depth, the cutting initiating depth and the crack starting depth, theoretical models are employed and compared with the experimental results. Regarding in-process AE monitoring, various AE parameters such as AE RMS, AE count rate and AE frequency contents are generated from the monitoring signals and utilized to detect the mode states and transitions. Our results, which shows reasonably close theoretical estimations and appropriate sensitivity in AE monitoring, indicate that the proposed scheme can be used to characterize machining states and to differentiate various mode transitions from plastic deformation to the brittle crack generations during nano-scale machining.
... The mechanism of removing single crystalline and amorphous silicon at scratching at the nanolevel at ultralow load was studied in [30,31]. In [32,33] the registration of acoustic emission was proposed as a means of determining a ductile brittle transition in scratching silicon [32], silicon carbide and quartz [33]. A method of the direct infrared optical registration of phase transitions in scratching is described in [34]. ...
... The mechanism of removing single crystalline and amorphous silicon at scratching at the nanolevel at ultralow load was studied in [30,31]. In [32,33] the registration of acoustic emission was proposed as a means of determining a ductile brittle transition in scratching silicon [32], silicon carbide and quartz [33]. A method of the direct infrared optical registration of phase transitions in scratching is described in [34]. ...
Theoretical and experimental studies of the ductile mode of cutting brittle materials (semiconductors, ceramics, and glass) have been considered. The ductile mode of cutting has been based on the implementation of high-pressure-induced phase transformations in a material machined that followed by a cutting of a transformed amorphous layer, which makes it possible to avoid cracking. Publications on studies of phase transitions in brittle materials in the course of the indentation, scratching, friction, and cutting have been reviewed. It has been shown that the cutting depth, cutting edge radius of a tool, chip thickness, tool cutting edge inclination, and crystallographic orientation of a material machined and diamond tool as well as a type of lubricoolant are the decisive factors in implementing the ductile mode of cutting
... the layer-type and particle-type chips are associated with DRM and BRM, respectively [18]. Acoustic emission is another effective technology for the in-process monitoring of material removal mode [19,20]. ...
The brittle-ductile transition (BDT) widely exists in the manufacturing with extremely small deformation scale, thermally assisted machining, and high-speed machining. This paper reviews the BDT in extreme manufacturing. The factors affecting the BDT in extreme manufacturing are analyzed, including the deformation scale and deformation temperature induced brittle-to-ductile transition, and the reverse transition induced by grain size and strain rate. A discussion is arranged to explore the mechanisms of BDT and how to improve the machinability based on the BDT. It is proposed that the mutual transition between brittleness and ductility results from the competition between the occurrence of plastic deformation and the
propagation of cracks. The brittleness or ductility of machined material should benefit a specific manufacturing process, which can be regulated by the deformation scale, deformation temperature and
machining speed
... Besides sapphire, AE technology has also been widely applied for the plastic and brittle damage characterization of other ceramics, including alumina [8,9], silicon carbide [10,11], single crystal silicon [12] and ceramic matrix composites [13]. Considerable achievements on characterization methods were obtained by these researches. ...
In this paper, the study on damage evolution of sapphire induced in scratching process using acoustic emission (AE) technology was carried out. Single-grit scratches with ramp scratch depth were conducted on C-plane of sapphire with AE signal monitoring. Groove microstructure after scratching shows that the damage evolution process is mainly determined by the interactions among cracks, specimen surface and groove boundary. To evaluate the damage evolution, the AE waveform indexes, i.e. fractal and frequency characteristics, were fully analyzed and correlated with groove microstructure of specimen after tests. It is found that the fractal dimension (FD) can identify the three basic damage modes as well as various damage behaviors during scratching process. In addition, the model of damage evolution is further proposed. The frequency characteristics of AE signals are distinctive to various damage behaviors during their evolution, especially to the occurrences of the critical damages and removal modes. Furthermore, the characteristic frequency band (CFB) of AE signals was extracted. It is found that FD of the reconstructed AE signals in CFB (86.8–161.4 KHz herein) can highlight damage details and features during initial damage stage of sapphire in scratch test effectively.
... These high-frequency (100 kHz to 1 MHz) waves propagate in all directions through the inside structure to a (piezo) transducer on the surface of the workpiece. Previous research has shown that AE is sensitive to a variety of characteristics in precision manufacturing processes, such as AFM nano machining, micro indentation/ scratching, and ultraprecision metal cutting [20][21][22]. The generation of AE signals is most influenced by the attributes of the materials being processed, and relevant information can be extracted from AE signals using various signal processing techniques, including time series and spectral analyses. ...
In this study, a novel setup for a nanoscale finishing process -magnetic abrasive finishing (MAF) -was investigated together with in-process monitoring using acoustic emissions (AE). A specially fabricated direction control piece with a neodymium magnet was attached to an MAF setup to perform surface finishing of thin-film (IZO) coated Pyrex glass workpieces within a selective area. For the selective finishing experiments, design of experiment (DOE) was applied to optimize the surface roughness of the workpieces. In addition, an acoustic emission (AE) sensor, which can effectively monitor surface roughness and process states during ultraprecision machining/polishing of nanoscale workpieces, was adopted to detect the depth of the polished surface during MAF. The experimental results show that the proposed MAF setup produces uniform surfaces with nano-level surface roughness in a confined (target) area. Moreover, AE monitoring appears to have strong correlations with process states and sufficient sensitivity to detect the critical thickness (the end point of the coating layer). The processed AE signals were utilized as input parameters for an artificial neural network (ANN) to determine whether the polishing was reached to the coating-substrate (Pyrex) boundary. With the proposed polishing and monitoring scheme, controlled nano-finishing of a thin film coated material are feasible in a selective area within specific thickness/layer.
... On the other hand, to investigate fractures of not only on surface but also inside the material, the acoustic emission (AE) wave is employed as scientific tool [16][17][18], where the AE is an elastic wave including the mechanical vibration, acoustic wave, and ultrasonic wave that rises with the mechanical events such as the elastic deformation, the creation and evolution of the crack, friction, wear of materials, and indentation of the material. Because the destruction process of the material can be monitored, the AE sensing is already in commercial use, and is used as a non-destructive analysis and maintenance method of the operating mechanical system. ...
The fracture of the atomic-scale contact should be investigated for understanding the mechanism of the mechanical processing. Using a combination of the scanning probe microscope (SPM) with possible high space resolution and the acoustic emission (AE) with high sensitivity for fracture is one of the possible way of investigating the fracture mechanism. When using the SPM, the AE signal might be detected with receiving the AE wave by the piezoelectric tube scanner of the SPM receiving the AE wave, where by the piezoelectric effect the electric signal due to the AE wave is superimposed on the scan signal. Based on that, in this study, a novel method to detect AE signal from the scan signal is proposed. With this method, without changing the SPM body, the AE could be detected, and a two-dimensional AE source location could be possible by using four divided electrodes of the piezoelectric tube scanner. By a simple experiment using the AE wave simulator, the AE signal seems to be detected by the piezoelectric scanner of the SPM. Also, one of the typical data from the experiment suggests the AE source location might be possible. In the experiment of the indentation using atomic force microscope (AFM), which is one of the SPM, the AE signal is observed reproducibly.
... These low-intensity, high-frequency (100 kHz-1 MHz) elastic waves propagate in all directions through the structure to a detector on the surface of the workpiece. In previous research, AE has been shown to be sensitive to a variety of characteristics in precision manufacturing processes including nano-order applications [15,[27][28][29]. Figure 3(a) shows examples of applicable sensors including AE according to the material removal length scale and signal source mechanism. Figure 3(b) shows the parameter definitions of digitized AE signals. ...
This study aims to determine the machining characteristics during nano-scratching of silicon wafers using AFM and to monitor the machining states using acoustic emission (AE). Along with a specially designed AFM experimental setup, simplified geometric models are employed to estimate the friction coefficient and the minimum chip formation depth for nano-machining. In the nano-experiments, with the increase of the engaging depth of an AFM tip, two modes of plastic deformation—ploughing mode and cutting mode—are observed. With the aid of AFM and FE-SEM images, typical features of each mode, such as pile-up and chip formations, are illustrated and analyzed. Moreover, it is shown that pile-up formation is closely related to the deformation characteristics at the corresponding scratching depth, and the ratio of pile-ups to the groove depth can be used as an index to indicate the mode transition. As far as in-process monitoring is concerned, during the ploughing mode, related AE RMS values are relatively low. By contrast, the RMS values during the cutting mode are significantly higher than those during the ploughing mode, with apparent chip formation. In addition, AE count rates show appropriate sensitivity to detect the mode transition. Our results indicate that the proposed scheme can be used to characterize nano-scale machining and to monitor the mode transition.
This paper aims to improve the machining efficiency of silicon carbide (SiC), reduce residual surface stress, inhibit surface cracks, and reduce surface damage. Single-point diamond scratch experiments were performed on SiC samples after hydrogen ions implantation to study the macro-scale machining performance. The improvement mechanism by which ion implantation reduces surface cracks and machining defects in 4H–SiC samples under different loading forces was comparatively studied. Scale-like cracks and brittle fracture fragments in the scratched area of the ion-implanted samples were reduced significantly. Acoustic emission sensors were used to detect the acoustic signal of brittle fracture. The lower intensity of the acoustic emission signal in the ion-implanted sample indicates that less brittle fracture was generated during scratching. Variation of the contour line in the scratch area with loading force was measured using laser scanning confocal microscopy. The depths of the smooth contours in the scratched area of the samples without and with ion implantation were 96 nm and 360 nm, respectively. The scratch area was scanned by a Raman spectrometer to quantitatively study the effect of ion implantation on micro-level defects. Formulas illustrating the relationship between residual stresses and Raman shift displacement were derived by integrating Raman shift and a secular equation. The results show a reduction in defects at microscale, an enhancement of machinability, and a reduction in residual stresses on the surface of the ion-implanted sample. Ion implantation assisted machining technology can effectively improve the machining quality and efficiency of SiC wafers.
For hard-brittle materials, crack initiation and growth is an important factor to determine the surface quality of components during machining process. In this paper, the crack growth stage of sapphire was investigated based on acoustic emission (AE) signals through single-grit scratch experiments. The AE waveform indexes, i.e. fractal and frequency characteristics, were fully analyzed and correlated with groove microstructure of specimen after tests. The research shows that the specimen undergo four stages of crack growth successively as scratch depth increasing. It is found that the fractal dimension (FD) and frequency characteristics of AE signals are distinctive to various damage behaviors and be used to evaluate crack growth stage induced in machining process effectively. Especially, the FD distribution is sensitive to the occurrences of the critical damages and removal modes resulting from crack growth in scratch procedure. This paper can shed light on the control of surface integrity and subsurface damage of hard-brittle materials in ultra-precision manufacturing.
The goal of this research is to investigate and monitor machining mode transitions during nanoscale scratching of IZO-coated Pyrex glasses using atomic force microscope (AFM). Among the AFM nanomachining mode features, which include elastic/plastic deformations and crack generation, pile-up (by ploughing) is a key surface phenomenon that can represent plastic deformation characteristics, such as a sign of chip making. Moreover, because the pile-up formation mechanism of coated materials is reported to be distinct from that of bulk materials, the examination of pile-up in coated materials is challenging, along with brittle transition (crack initiation). In this research, the pile-up formation and crack initiation, that occur during nanoscratching, were examined and analyzed near the coating-substrate (glass) boundary. In addition, acoustic emission (AE), a sensing scheme with nanoscale sensitivity, was introduced to detect significant machining state variations and mode transitions. Experimental and analysis results indicate that the proposed scheme is viable for characterizing/monitoring the nanoscale machining of coated materials.
AFM (atomic force microscope) scratching is a simple yet versatile material removing technique for nanofabrication. It has evolved from a purely mechanical process to one in which the tip can be loaded by additional energy sources, such as thermal, electric, or chemical. In this chapter, scratching techniques using tips with both single and dual sources are reviewed with an emphasis on associated material removing behavior. Recent developments in scratching systems equipped with automated stages or platforms using both single tip and multiple tips are assessed. The characteristics of various approaches for scratching different types of materials, including polymers, metals, and semiconductors, are presented and evaluated. The effects of the major scratching parameters on the final nanostructures are reviewed with the goal of providing quantitative information for guiding the scratching process. Advances in several techniques using dual sources for AFM scratching are then studied with a focus on their versatility and potential for different applications. Finally, following a section on the applications of AFM scratching for fabricating a fairly wide range of nanoscale devices and systems, concluding remarks are presented to recommend subjects for future technological improvement and research emphasis, as well as to provide the author’s perspective on future challenges in the field of AFM scratching.
We investigate a surface finishing scheme fitted for AFM scratched nanopatterns on a coated surface using magnetic abrasive finishing (MAF). First, nanoscale patterning was carried out on IZO-coated Pyrex glass, with a specially-designed AFM machining setup. After AFM machining, nonuniform surface features such as pile-ups are generated, and the final shapes are often more complicated for coated materials. For this reason, MAF was implemented for the nanoscale removal of pile-up/debris of coated materials and design of experiment (DOE) was utilized to obtain optimal process conditions for the finishing process.
The process was monitored using acoustic emission (AE) for coating-substrate (glass) boundary detection, as well for monitoring the polishing status/depth. Experimental results indicate the viability of the proposed scheme as a nanoscale selective finishing technique for various material setups.
The configuration of automated polishing systems requires the implementation of monitoring schemes to estimate surface roughness. In this study, a precision polishing process - magnetic abrasive finishing (MAF) - was investigated together with an in-process monitoring set-up. A specially designed magnetic quill was connected to a CNC machining center to polish the surface of Stavax (S136) die steel workpieces. During finishing experiments, both acoustic emission (AE) signals and force signals were sampled and analyzed. The finishing results show that MAF has nanoscale finishing capability (up to 8nm in surface roughness), and the sensor signals have strong correlations with parameters such as the gap between the tool and workpiece, feed rate, and abrasive size. In addition, the signals were utilized as input parameters of artificial neural networks (ANNs) to predict generated surface roughness. To increase accuracy and resolve ambiguities in decision making/prediction from the vast amount of data generated, sensor data fusion (AE+force)-based ANN and sensor information-based ANN were constructed. Among the three types of networks, the ANN constructed using sensor fusion produced the most stable outcomes. The results of this analysis demonstrate that the proposed sensor (fusion) scheme is appropriate for monitoring and prediction of nanoscale precision finishing processes.
This study aims to obtain machining characteristics during AFM (Atomic force Microscope) machining of silicon wafers and to monitor the machining states using acoustic emission. As in micro scale machining, two distinct regimes of deformation, i. e. ploughing regime and cutting regime were observed. First, the transition between the two regimes are investigated by analyzing the "pile-up" during machining. As far as in process monitoring is concerned, in the ploughing repime, no chips have been formed and related AE RMS values are relatively low, In the mean time, in the cutting regime, the RMS values are significantly higher than the ploughing regime, with apparent chip formation. From the results, we found out that the proposed scheme can be used for the monitoring of nanomachining, especially for the characterization of nanocutting mode transition.
Grinding process is affected by many factors, such as the selection of grinding wheel, the dressing condition, and of course the grinding condition. In addition, performance of the grinding wheel changes considerably during the grinding process. It becomes, therefore, important to monitor the dressing as well as the grinding process so that the grinding result required is satisfied. In this study, the acoustic emission (AE) signal is applied to monitor these processes. Dressing process is monitored to generate a grinding wheel surface of constant quality. Grinding process is monitored to define the tool life of the grinding wheel. It is also confirmed that the contact of grinding wheel and workpiece is successfully detected with AE signal, which means that the method is effective as a gap-eliminator.
Because of recent advances in precision engineering that allow controlled grinding infeed rates as small as several nanometers per grinding wheel revolution, it is possible to grind brittle materials so that the predominant material-removal mechanism is plastic-flow and not fracture. This process is known as ductile-regime grinding. When brittle materials are ground through a process of plastic deformation, surface finishes similar to those achieved in polishing or lapping are produced. Unlike polishing or lapping, however, grinding is a deterministic process, permitting finely controlled contour accuracy and complex shapes. In this paper, the development of a research apparatus capable of ductile-regime grinding is described. Furthermore, an analytical and experimental investigation of the infeed rates necessary for ductile-regime grinding of brittle materials is presented. Finally, a model is proposed, relating the grinding infeed rate necessary for ductile material-removal with the properties of the brittle workpiece material.
When the stress field due to an applied load on a brittle material like glass is localized in spatial extent, there will be a transition from plastic flow to fracture at a critical load. Previous studies of the crack-initiation thresholds have relied primarily upon static indentation tests to simulate the localized loading conditions. Critical loads for crack initiation were detected using either acoustic emission or in situ optical microscopy with transparent materials. In a recent study, Tanikella and Scattergood developed a controlled loading system with an acoustic emission sensor that demonstrated a one-to-one correspondence between crack initiation and acoustic signal thresholds during static Vickers indentation of soda-lime glass. The purpose of the work reported here was to examine the fracture threshold response for a borosilicate glass during controlled microcutting (scratching) with a Vickers indentor and to compare the results to static Vickers indentation. The microcutting behavior is important because it plays a fundamental role in determining the subsurface fracture damage produced in manufacturing processes such as polishing and grinding.
A new machining model has been developed for single point diamond turning of brittle materials. Experiments using the interrupted cutting method allow model parameters to be determined that provide a quantitative method for determining the machinability of a material with respect to the rake angle, tool nose radius and machining environment. The model uses two parameters, the critical depth of cut and the subsurface damage depth, to characterize the ductile-regime material removal process. Also included in the model is a parameter used to set a process limit defined as the maximum feed rate. Machining experiments have verified the model, and allow for determination of optimum machining conditions.
The grinding process is affected by many factors. These include the selection of grinding wheel, the dressing condition and of course the grinding condition. In addition, the performance of the grinding wheel changes considerably during the grinding process. Therefore, it becomes important to monitor the dressing as well as the grinding process, so that the required result is achieved. In this study the acoustic emission (AE) signal is used to monitor these processes. The dressing process is monitored to produce a grinding wheel surface of constant quality. The tool life of the grinding wheel can be defined by monitoring the change of the amplitude and the frequency characteristic of the AE signal. Contact between the grinding wheel and the workpiece can be successfully detected with the AE signal, which means that this method is effective as a gapeliminator.
Damage-free processes of grinding of brittle materials have been widely used in industry for producing electronic and optical components with high surface integrity. It has been found that the transition threshold from ductile flow to brittle fracture during the process of material removal plays a central role in the quality control of a machined surface. However, the precise microscopic mechanism which governs the formation of dislocation structure and micro-cracking when machining a brittle material such as alumina, remains unclear. The mechanism of formation and structure of the plastic or damage zones in alumina of two different grain sizes (1 and 25 m) subjected to single-point scratching with sharp and blunt indenters were studied in this paper. Using transmission electron microscopy, characteristic features of the plastic/damage zone in terms of loading conditions and microstructure of the materials were carefully investigated. It was found that the grain size and the geometry of the indenter had a great effect on the dislocation structure of the plastic zone and that the subsurface damage could be very severe, even though the machined surfaces appeared damage-free. These results indicate that the ductile flow to brittle fracture transition in machining brittle ceramics is more complicated than previously thought and that a reliable criterion has yet to be established to predict a real damage-free grinding process.
AbstractThe applications of hard and brittle materials, typically represented by advanced ceramics, for a number of high-performance components have recently generated high interest. To meet this increasing demand, high efficiency machining technologies are needed. In this keynote paper, the characteristic features of hard and brittle materials are outlined. Considering these features, a fundamental principle for grinding those materials is discussed, followed by practical examples of advanced ceramic grinding. Remarks for attaining high-efficiency grinding of hard and brittle materials are presented.
Acoustic emission (AE) spectra were recorded during microgrinding of brittle materials. It was found that the specific AE energy (i.e., the measured AE energy divided by the material removal rate) was lower for fracture-dominated grinding than for plastic flow-dominated grinding. Two subsequent experiments were performed to measure AE energy while holding the material-removal rate constant. By controlling either the critical depth of cut (for ductile-brittle transition) of the workpiece material, or the actual depth of cut of the grinding machine, the sensitivity of AE energy to grinding regime was investigated for grinding with a constant material-removal rate. Contrary to conventional thinking about the relative contributions of plastic flow and fracture in generation of AE activity, it was found that the AE energy was larger in ductile-regime grinding than in brittle-regime grinding, for identical material removal rates. As a result of the experiments described in this paper, it can be concluded that AE energy measured during microgrinding is sensitive to changes in the mechanism of material removal. For a given volume of material removed, there is more AE energy in a plastic flow-dominated process than in a fracture-dominated process. The relationship found between AE energy and material removal regime could lead to an in-process sensing strategy for controlling grinding ductility.
This article addresses the problem of monitoring the material removal regime (ductile versus brittle) that occurs during the grinding of brittle materials. Often a ductile grinding regime is desired, but currently there is no way to measure the grinding ductility “in process.” A model is developed to describe the dependence of the specific grinding energy on the material removal regime. It is found that the specific grinding energy will remain relatively constant for ductile-regime grinding but will decrease in a power-law relationship with an increasing material removal rate for brittle-regime grinding. Experimental confirmation of the proposed model is presented. The potential for using measurements of specific grinding energy to control the grinding ductility is established, and the benefits of such a closed-loop feedback system in ductile-regime grinding are explained.
The widespread utilization of high strength ceramic materials has been limited by the high cost of machining these materials by grinding. A technological basis for cost-effective ceramic machining requires a fundamental understanding of the prevailing grinding mechanisms. The present paper is intended to provide an overview of what happens during grinding as abrasive grains cut through ceramic workpiece materials. Most past research on grinding mechanisms for ceramics has followed either the “indentation fracture mechanics” approach or the “machining” approach. The indentation fracture mechanics approach likens abrasive workpiece interactions to idealized small-scale indentations. The machining approach typically involves measurement of cutting forces together with microscopic observations of grinding debris and surfaces produced. Both approaches provide important insights into the grinding mechanisms for ceramic materials.
Ultra-Micro indentation Hardness Tester
- T Sata
- K Takamoto
- H Yoshikawa
T. Sata, K. Takamoto and H. Yoshikawa: Ultra-Micro indentation Hardness Tester, Bull. the Japan Soc. of Prec. Engg., Vol. 3, No.1 (1969) 13–15.
Tool Shape Effects on Diamond cutting Process and Finished Surface Quality
- J Yan
- H Suzuki
- T Kuriyagawa
- K Syoji
J. Yan, H. Suzuki, T. Kuriyagawa and K. Syoji: ''Tool Shape Effects on Diamond cutting Process and Finished Surface Quality,'' Proc. of Intl. Conf. on MM21, (1997) 83–88.