Chip Pocket Research Articles

A hybrid process technology of SiC die separation

ABSTRACT Silicon carbide (SiC) is ideal for making powerful, high-frequency chips for 5 G and electric vehicles due to its wide band gap and resistance to high voltage. However, its powerful chemical bond strength and extreme hardness make it difficult for die separation in the post-wafer process. A hybrid process technology is proposed, where die scribing is performed on SiC wafer using a femtosecond pulsed laser-assisted ablation. The extremely short energy pulses forced the ablation of traces of SiC at extreme speed, breaking chemical bonds and thereby reducing strength and hardness for easy high-speed cutting along the scribed lanes with a polycrystalline diamond wheel. The experiment showed that the average stage current dropped from 0.90 A to 0.45 A and kerf chipping ratio from 11.7 to 4.1 during die separation, proving that the process removed materials along the separation lanes using a wheel tool at low grinding force, creating separation lanes of outstanding straightness and minimal kerf chippings and SiC dies of high integrity. Furthermore, thanks to the on-line rotational machining and dressing of the wheel tool, the blunt diamond abrasive cutting edge could be redressed to expose chip pockets of appropriate depth and protruding grinding edges with a favorable negative rake angle. The established grinding regime utilizing a pressure-grinding force in cutting and material removal reduced cracking at the SiC surface. In this paper, the laser energy density, scanning speed, number of ablations, focus position, as well as the speed, feed-rate and grinding depth of the wheel tool are also discussed in detail.

Identification of Tool Life Stages and Redressing Criterion for Polycrystalline Diamond Micro-Grinding Tools Using a Machine Learning Approach

Abstract Interactions of wear debris at the tool-workpiece interface in micro-grinding are quite random which leads to considerable variability in the working life of similar tools. It is not possible to capture the effect of wear debris entrapment on process signals using the available physics-based model, which makes it difficult to identify the tool life stages. The present study highlights the wear pattern and life stages of a polycrystalline diamond tool (PCD) during micro-grinding of BK7 glass. Based on the time and frequency domain cutting force features and tool surface morphology, life of a typical PCD tool could be divided into three stages viz., abrasion stage (0–23% of total tool life), loading stage (23–77% of total tool life), and chipping stage (77–100% of total tool life). A machine learning model utilizing support vector machine (SVM) could predict the life stages of a tool with a prediction accuracy of around 80.5%, and the wear pattern of a new tool coming into service becomes more deterministic on using more datasets for model training. A new modified textured PCD tool, which provided better tool-work interaction and improved debris disposal, shows little variation in cutting force features across many similar design tools which enabled identifying the life stages with higher confidence. Prognosis of tool redressing criterion enabled timely redressing of the tool which led to refined tool surface condition, such as increased number of available chip pockets, greater protrusion height of the abrasives, and lowered roughness of the machined surface.

Reconditioning of diamond dicing blades via electrolytic dressing

In this study, the process of “co-axial rotational electrolytic dressing reclaiming” is proposed to explore the possibility of reclaiming an electroformed diamond dicing blade by dressing, and thinning. The dicing blade was rotated slowly in an electrolysis tank controlled by a negative plate design and electrolysis conditions. The nickel atoms on the dicing blade surface were gradually and evenly dissolved and the grinding debris in the chip pockets were able to escape effortlessly, thus exposing fresh diamond grains. Whether dressing or thinning, the time required was only about 300 seconds, and the dicing blade was restored to an equivalent grinding force. After dressing, grinding current was reduced from 0.82 A to 0.21 A, increasing grinding length by at least 5.5 meters, while die edge chipping was very little. It was also experimentally proven that thinning reduces the width of the grinding lane from 66 μm to 45 μm and extended the length of grinding up to an additional 4.5 meters. The experiments showed that dressing and thinning with high-accuracy and -concentricity could be rapidly realized even for a very thin dicing blade, since there was no mechanical or thermal stress. This proves that ‘co-axial rotational electrolytic dressing reclaiming’ facilitates rapid reclaiming of an electroformed diamond dicing blade without deformation. It prolongs service life and produces narrower lanes between dies. • Use of the reclaimed wheel tool gives a grinding length increased by at least 5.5 meters. • The dressed dicing blade has a slight increase in grinding resistance. • The thinned dicing blade contained fewer abrasive grains, resulting in slightly die chipping. • The grinding resistance behavioral model of the dressed dicing blade is described by exponential growth. • The grinding resistance behavioral model of the thinned dicing blade is described by logarithmic growth.

Stability Analysis and Structure Optimization of Unequal-Pitch End Mills.

The damping performance of unequal tooth milling cutters is controlled by the pitch parameters. How to improve the vibration damping and dynamic balance of milling cutters needs to be further studied. This paper analyzes the pitch angle through the stability of the lobe diagram and the spectral characteristics, and unequal-pitch end mills with asymmetric structure were determined to have better cutting stability. Due to the principle error of the asymmetrical tool, dynamic balance accuracy is poor. The dynamic balance of the tool is analyzed, and the centroid model of the tool is established. In order to improve the dynamic balance accuracy of tools, the parameters of the groove shape are analyzed and optimized, and balance accuracy is improved. Through modal and milling-force analysis, the relative vibration displacement and cutting force of the optimized tool were reduced by 17% and 10%, respectively, which determined that such tools have better dynamic performance. Here, unequal tooth end mills could reduce vibration and had higher accuracy in dynamic balance by adjusting the parameters of the pitch angles and chip pockets, so that the tool could have higher cutting stability.

Modelling and analysis of micro-grinding surface generation of hard brittle material machined by micro abrasive tools with helical chip pocket

The abrasive particles on the surface of micro abrasive tool are very small and tightly distributed, which is prone to appear debris blockage and accelerate tool wear, so the service life and performance of existing micro abrasive tools have become one of the key factors restricting the engineering application of micro-grinding technology. Compared to ordinary cylindrical micro abrasive tools, the micro abrasive tool with micro helical chip pocket (MAT-HCP) presents excellent performance in facilitating debris discharge and improving wear resistance, but the existence of helical chip pocket will significantly affect grains distribution, grinding contact area and surface generated mechanism in the micro-grinding process. In this work, the micro-grinding surface topography model of hard brittle materials obtained with MAT-HCP is built by considering grain size and distribution, dynamic impact, helical chip pocket structures, transient chip thickness and hard brittle material removal mechanism. The micro- grinding experiments are carried out to analyze surface morphology characteristics and surface generated mechanism of sapphire material machined by MAT-HCP. The contrast of simulated and experimental results showed that the average predicted error of contour supported ductility domain ratio and surface roughness respectively can be confined to be 10 % and 5%, which indicates that this surface topography predicted model can succeed in capturing the micro-grinding surface characteristics of sapphire material fabricated by MAT-HCP. Moreover, experimental results disclosed that the increase of pitch length will make MAT-HCP harder to realize the plastic region machining for sapphire, and this novel micro abrasive tool is potential to obtain better surface quality at high feed velocity compared with ordinary micro abrasive tools. The research results are of great significance for extending the service life of micro abrasive tools and promoting engineering application of micro-grinding technology.

Improvement of Removal Rate of Tape Lapping by Applying Fluid with Ultrasonic Excited Cavitation

Lapping with a lapping tape refers to a finishing process in which a new tape is continuously supplied to its processing area and pressed down with a pressure roller during its relative motions. In response to the growing demand for lapping high-hardness materials with high efficiency, lapping tapes with superabrasive grains formed in a textured structure with a bond have been recently utilized. In this study, we supply a working fluid that has passed through the slit between ultrasonically oscillating blades to processing points. Variations of sound pressure generate cavitation in the working fluid. Impulse waves due to the collapse of cavitation bubbles inhibit chips from getting adhered to the chip pockets of the lapping tape. We have lapped hardened SUJ2 with plural lapping tapes of different characteristics. In lapping with a lapping tape using diamond abrasive grains, we have improved the time constant for the changes in surface roughness in relation to the lapping time from 18.9 s to 7.6 s by superimposing ultrasonic oscillations; consequently, the lapping speed improved. We have compared the effects of ultrasonic oscillations for three types of lapping tapes and discovered that fewer abrasive grains and lower chip adhesion firmness due to the abrasive grains formed in a textured structure increased the effects of ultrasonic oscillations.

Development of fixed abrasive grain tool with continuous spiral chip pocket

Development of fixed abrasive grain tool with continuous spiral chip pocket

Effects of swarf discharge of continuous chip pocket in spiral tool

Effects of swarf discharge of continuous chip pocket in spiral tool

Effects of Grinding Fluid Excited by Ultrasonic Vibration

Ultrasonic excited fluid has been researched for machining of hard-to-grind materials. Ultrasonic vibration is applied to grinding fluid by an ultrasonic oscillating comb-shape effecter with integrated nozzle. Grinding fluid discharges from a nozzle placed between the comb’s feet and passes through the vacant space between comb teeth. By this setup, flowing grinding fluid can be continuously excited by ultrasonic vibration. Based on the principle of an ultrasonic washing machine, impulsive force caused by cavitation bubble will reduce the adhesion of chips on the cutting face of grain and chip pockets. Some effects of ultrasonic excited grinding fluid have been recorded such as reducing grinding heat in the case of grinding for Titanium alloy and decreasing in grinding force, improving surface roughness in the case of grinding for Aluminum and stainless alloy. However, the reason of better grinding performance is still unknown. Therefore, experiments conducted with different type of grinding fluids with and without ultrasonic vibration are needed. Pure Titanium, which considered a hard-to-cut material, is chosen as work material. Grinding forces and grinding heat during grinding will be measured and evaluated to clarify the mechanism of ultrasonic excited grinding fluid.

A017 Thermal Dressing of Metal Bonded Diamond Wheel by Nd:YAG Laser : Optimization of air-jet irradiation angle

In this study, a pulsed Nd:YAG laser beam is used as a non-contact thermal dressing tool for a metal bonded diamond wheel. In order to efficiently remove the bond material, it is necessary to direct air on the spot irradiated by the laser so as to blow away the molten binder. The new integrated laser-air head makes it possible to make an appropriate chip pocket depth with less residual re-solidification layer of bond material. The grinding experiments of the hot-pressed SiC reveals that the laser-dressed wheel has somewhat better grinding performance than the conventional rotary dressed wheel.

Research on the Topography Feature of the Diamond Grinding Wheel under Elliptical Ultrasonic Assisted Dressing with Diamond Stylus

In this paper, topography feature of the diamond grinding wheel under the diamond stylus elliptical ultrasonic vibration assisted dressing was studied experimentally. The results indicate that: the increase in dressing power of elliptical ultrasonic vibration will result in the increase in amplitude, and that can increase abrasive protrusion height of the dressing grinding wheel, and also increase the depth of chip pocket. With the increase of feed rate, surface peak and valley values of elliptical ultrasonic vibration dressing grinding wheel increase, that is the average protrusion height of abrasive grain increases. With the increase of dressing depth, surface peak and valley values of elliptical ultrasonic vibration dressing grinding wheel increases, while the number of static effective abrasive grain reduces. In comparison with the ordinary dressing grinding wheel, elliptical ultrasonic assisted dressing in the same parameters can bring about more static effective abrasive grain , more uniform abrasive distribution, a higher abrasive protrusion height and more chip space.

Development of Wheel Surface Forming Technique for Ultra-smoothness Vertical Surface Grinding Method (2nd Report)

In the ultra-smoothness vertical grinding method developed previously, the wheel surface conditions are found to influence largely on ground workpiece surface. Thus the building of wheel surface forming technique is important. In the 1st report, from the point of view, the change of ground workpiece surface and wheel surface with grinding process of silicon carbide ceramic by using #140 resin bonded diamond wheel is examined and discussed. In the report following the 1st report, first of all, the change of macroscopic wheel shape in addition to surface conditions such as cutting edge wear, depth of chip pocket and so on with grinding time is examined. It is cleared that the wheel wear begins to occur at wheel outside edge and proceeds to wheel inside. Wheel life is ascertained to occur due to the contact of workpiece with bond, which is caused from the radial wheel wear. On the basis of the results, trued wheel shape for low rate of radial wheel wear is discussed. The sharp edge in the wheel outside shape is found to be effective for long wheel life in grinding of silicon carbide ceramic.

3416 PCDディスクによる小径CBNホイールのツルーイング(S48 砥粒加工,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

In grinding operation, there are two important preparations, truing which forms wheel geometry and conditioning which generates chip pockets around abrasive grains on wheel surface. Truing has very strong influence on the performance of grinding wheel in terms of determining sharpness of grain cutting edges. In this study, truing of CBN wheel by PCD which has excellent wear resistance is attempted and correlations between truing force, grinding force and surface roughness are examined. Very sharp ridge end of PCD disk effectively reduces truing force and eliminate flexure of the quill of small diameter CBN wheels. Also, accuracy of sharpness control of grain cutting edges is improved compared to conventional truing tools.

Development of Automatic Evaluation System for Working Surface of Super Abrasive Wheel (1st Report)

The performance of super abrasive wheels is influenced largely by the wheel working surface conditions such as the distribution and shape of cutting edges, the loading formation status, the depth of chip pocket and so on, which change with truing and dressing conditions, and grinding process in addition to the wheel specification. The research deals with the automatic image processing system for working surface of CBN wheel. The system is newly developed by adding two following matters to the system developed in our previous researches. The software programs of image processing for the dressed cutting edge and loading are newly built in addition to the software programs developed previously for the trued and ground cutting edge. And also the computer control equipment for deciding automatically the microscope observation position parallel to wheel spindle direction is manufactured additionally. Using the new system, the behavior of wheel surface in dressing process and grinding process is examined and, as the results, the availability of system is ascertained.

Shape and Uniformity of Pores Contained in Vitrified Bonded CBN Wheels

The main purpose of this study is to evaluate quantitatively a shape and a uniformity of the pores contained in vitrified bonded cBN wheels. The distributions in the pore size and the distance between adjacent pores are measured and moreover the cross-sectional profile of pores is evaluated using a fractal analysis. The variations in the pore size and the distance between adjacent pores in cBN wheel-U made by newly developed “coating manufacturing method” are smaller than those in cBN wheel-C made by “conventional manufacturing method”, respectively. Fractal dimension calculated for a cross-sectional profile of the pores distributed in cBN wheel-U is larger than that in cBN wheel-C. Such difference in fractal dimension between wheel-U and wheel-C is mainly due to a quality in coating of vitrified bond on the cBN grain. By making the wheel structure uniform, the wheel wear due to shedding and grazing occurred locally on the wheel surface decreases, because an action referred to as “opening phenomenon of chip pocket” occurs uniformly over the wheel working surface.

A New Diamond Wheel Containing Boron Doped Diamond Abrasives Enabling Electrically Conductive Cutting Edge and High Thermal Stability

Electrically conductive cutting edges diamond grinding wheels (EC-cutting edges D wheels) have properties such as, 1) convenient precise forming by EDM, 2) realization of high cutting edge density, 3) sufficiently large chip pockets along with fine cutting edges on large diamond grits, 4) contact sensing of the cutting edges with workpiece due to electrical conductivity, 5) expected application to the grinding of various types of steels due to high thermal resistance. Until now, the grinding ability of the sharp edges generated on the electrically conductive CVD diamond thick film wheel by electrodischarge trueing (ED trueing) was confirmed by grinding experiments using a small diameter lapping wheel and a small diameter disk wheel. In this research work, metal bonded diamond wheels containing boron doped electrically conductive diamond (EC diamond) grits, which possess high oxidation temperature, were trial manufactured. From the results of grinding test for an optical glass (BK7), it was found that the wear and grinding force for the EC diamond grits wheel were significantly low compared to a conventional diamond grits wheel. Furthermore, from the results of the investigation on ED trueing performance, a high trueing efficiency along with the possibility of cutting edge tip formation was confirmed.

Development of a Chip-breaking Tool for Tapping (1st Report)

In tapping, chips jamming in the tap's flute or twining around the tap cause tool breakage very frequently. It has been an obstacle to automation of tapping. In order to resolve this problem, a chip-breaking tool has been developed, which forms grooves axially on the inner wall of hole before tapping. In this paper described are design of the tool and its effectiveness. The tool was composed of a cylindrical body and three V-groove cutting edges. The diameter of body was equal to that of tap drills. The major diameter of V-groove cutting edges was slightly larger than that of taps. Each V-groove cutting edge had a chip pocket designed after observing the chip formation in similar V-groove cutting. To investigate the effectiveness of the tool, tapping experiments for M3 and M6 threads were performed with and without using the tool. The work material was structural steel SS400 and the taps used were the conventional spiral fluted taps made of high speed steel. By using a machining center the tapping operations were automatically repeated till when the tap was broken without any human assistance for removing the chips jamming in the tap's flute or twining around the tap. To shorten the experimental time, the cutting velocity for tapping was set at 30m/min which was much higher than conventional, and besides, the thread was long as two and a half times of diameter. It has been ascertained by experiments that by using the newly developed tool, the tool life of tap lasts much longer and the tapping torque becomes smaller and stable, and moreover, the surface roughness becomes smoother.

415 熱可塑性フィルムを用いたラッピングテープの研磨特性

Polishing by using lapping tape can get fine surface very efficiently and keep working environment clean. So the lapping tapes are used in many fields, including the field of electronics. But the lapping tapes with a polyester film backing are poorly flexible and their chip pockets on their plane of action are small. So the new lapping tape which has better polishing functions has been wanted. Then this study develops the new one with rough pattern on its plane of action by polishing. The new one is much more efficient than usual one. We study the characteristics of polishing experimentally.

Electrophoretic Truing and Dressing for Spherical Resin-Bonded Diamond Wheels with Fine Grains.

Precision truing and dressing techniques using an electrophoretic phenomenon was developed for spherical resin-bonded diamond wheels with fine grains. Truing was carried out by bringing the wheel into contact with the anode, and dressing was carried out by bringing the wheel into contact With a gelled fiim on the anode. Both truing and dressing were conducted by moving the wheel around the cylindrical anode that was attached to an A. C. induction motor. In addition, the revolution speed of the anode was varied periodically to change the direction of the resultant velocity by means of which the wheel surface was scratched. It was connrmed through the truing test that the wheel surface was scratched multidirectionally so that alapped-like wheel surface without any unidirectional groove could be obtained. Also, it was confirmed by the dressing test that the gelled film on the anode behaved like a soft polisher, so that a sufficient chip pocket could be achieved without any residual damage on the bond surface.

ニッケル‐銅‐すず合金系結合橋の強じん化について 有気孔メタルボンドダイヤモンドホイールの開発

It has been aimed to develop porous metal bonded diamond wheel with an ideal bond bridge like a vitrified bond, the pore rates of about 50 vol% and the bending strength of 10 to 50 MPa, because a lot of merits, such as low grinding temperature and a few grinding force, many chip pockets and easy dressing and truing, may be obtained. The following conclusions are obtained by some treatments. (1) The phosphorus diffuses into bond bridge with oxygen by heating after the phosphorating treatment. (2) The shear strength of bond bridge and the elastic modulus of bending test pieces increased by the heat treatment under high pressure by the diffusion of phosphorus and the subzero treatment by a martensite transformation of metal. (3) The original targets of development of porous metal bonded diamond wheel are accomplished with such treatments.