Metal Bonded Diamond Wheel Research Articles

Modelling and optimisation of electro-discharge diamond face grinding of cemented carbide-cobalt composite

Electro-discharge diamond grinding is a hybrid process of electrodischarge machining (EDM) and diamond grinding which is obtained by replacing the tool electrode of conventional EDM by a metal bonded diamond wheel. When face of the wheel is used for machining then the process is termed as electro-discharge diamond face grinding (EDDFG). In this study, modelling and optimisation of EDDFG of cemented carbide–cobalt composite has been done using a hybrid methodology comprising of Taguchi methodology (TM) and response surface methodology (RSM) with material removal rate (MRR), wheel wear rate (WWR) and average surface roughness (ASR) as the objective functions. The approach first uses the TM for finding the optimum level of input machining parameters such as wheel speed, current, pulse on-time and duty factor. The optimum input parameter values are further used as the central values in the RSM to develop second-order response model for MRR, WWR and ASR after conducting experiments using central composite rotatable design matrix. The simultaneous optimisation of weighted response has been obtained using MINITAB software. The results show considerable improvement in three quality characteristics when the hybrid approach is used, as compared with the results of only a TM approach.

E23 SiCセラミックスの超音波援用内面研削におけるメタルボンドダイヤモンド砥石の加工特性(OS7 研削・砥粒加工(1))

E23 SiCセラミックスの超音波援用内面研削におけるメタルボンドダイヤモンド砥石の加工特性(OS7 研削・砥粒加工(1))

Applying Wire Electrical Discharge Dressing (Wedd) to Improve Grinding Performance of Metal Bounded Diamond Wheels

In order to improve grinding performance of metal-bonded diamond wheels, a proper conditioning method has to be used. In this work, wire electrical discharge dressing (WEDD) is evaluated. With a self-designed WEDD-device the dressing process can be carried out inside a grinding machine, reducing non-productive time. Moreover, the in-process WED-dressing was assessed, showing potential for future applications. Dressing experiments indicated that high erosion material removal rates can be achieved and, in comparison to conventionally conditioned wheels, a better grinding wheel topography is generated. Finally, a model to calculate the axial dressing feed rate in WED-sharpening is proposed.

Laminated manufacturing and milling electrical discharge dressing of metal-bonded diamond grinding wheels

Metal-bonded diamond wheels are widely used in high-precision grinding of hard and brittle materials; unfortunately, they are difficult to true and dress. This paper addresses this problem in that it proposes a variation on the electrical discharge dressing technique. The advantages of the proposed method are discussed and an electrode compensation model is formulated. The topography and surface profile of the diamond wheel are analysed as a function of various dressing parameters. The performance of the wheel after dressing is evaluated using experimentally measured grinding forces and surface roughness values. It is shown that the proposed method is a viable technique for the truing and dressing of diamond grinding wheels.

In-Process Truing for ELID (Electrolytic In-Process Dressing) Grinding by Pulsewidth Control

Electrolytic in-process dressing (ELID) grinding is a well established technology for achieving highest quality surface finish on hard and brittle materials such as optical glass, ceramics, and silicon compounds. In conventional ELID grinding, constant voltage is applied on the metal-bonded diamond wheels to ensure constant protrusion of super fine cutting grits throughout the grinding cycle. However, this method is not suitable to achieve grinding wheel truing which is very important to maintain the stability of the grinding. In this study, a novel approach of wheel truing has been developed by controlling the dressing voltage duty ratio for ELID grinding. An inductive sensor is used to measure the wheel profile based on the gap between the sensor head and wheel edge, and this is used as the feedback signal to control the duty ratio of the power supply. Detailed mathematical design of the control algorithm has been presented and simulation results have been substantiated by experimental findings. The experimental finding shows that the wheel work piece contact gradually improves from 40° to ~ 360° as the grinding progresses when this new controlled dressing technique is implemented.

Grinding damage of BK7 using copper-resin bond coarse-grained diamond wheel

Coarse-grained wheels can realize high efficient grinding of optical glass. However, the serious surface and subsurface damage will be inevitably introduced by the coarse-grained wheels. In this paper, the grinding damage of a copper-resin bond coarse-grained diamond wheel with grain size of 150μm was investigated on optical glass BK7. The wheel was first properly trued with a metal bond diamond wheel, then pre-dressing for the wheel and grinding experiments are carried out on a precision grinder assisted with electrolytic in process dressing (ELID) method. The surface roughness (Ra) of ground surface was measured using an atomic force microscope (AFM) and the surface topography were imaged by a white light interferometer (WLI) and the AFM. The subsurface damage level of ground surface was evaluated by means of both MRF spot method and taper polishing-etching method, in term of the biggest depth of subsurface damage, distribution of micro defects beneath the ground surface, the cluster depth of subsurface damage, relationship between subsurface damage (SSD) and PV surface roughness (SR), propagating distance and pattern of cracks beneath the ground surface. Experimental results indicate that a well conditioned copper-resin bond coarse-grained diamond wheel on a precision grinder can generate good surface quality of Ra less than 50nm and good subsurface integrity with SSD depth less than 3.5e for optical glass BK7.

Grinding Performance of Porous Diamond Wheels on Different Materials

In this paper, metal-bonded diamond wheels of different sized abrasive grain with different porosity were fabricated. Grinding experiments with these wheels on three kinds of materials were carried out under different grinding conditions. Experimental results revealed that wheel with high porosity (38%) had smaller grinding forces and specific energy than the one with a medium porosity (24%) on grinding G603. However, on grinding harder materials like Red granite or ceramics of Al2O3, the wheel with 38% porosity had bigger grinding forces and specific energy than the wheel with 24% porosity. Both wheels exhibited good self-sharpening capability during the grinding process of G603 and Red granite, but on grinding ceramics of Al2O3 the wheel with 38% porosity displayed in dull state during the grinding process . With the same porosity, the grinding forces of the wheel with a grain size of 230/270 US mesh were lower than the one with a grain size of W10 when grinding Red granite and ceramics of Al2O3. However revising results were obtained on grinding G603.

A System Development Approach for Electrolytic In-Process Dressing (ELID) Grinding

This study aims to present the development and performance evaluation of an ultra-precision ELID grinding machine. The machine is a 3-axis machine, including three conventional linear axes (X,Y, andZ). On top, another rotational axis has been included to assist aspheric/spherical lens grinding. In order to introduce intelligence to the machine, several on-machine measuring systems have been developed and incorporated. In ELID grinding, pulsed DC voltage is applied to the metal-bonded diamond wheels to ensure the constant protrusion of sharp cutting grit throughout the grinding cycle. The peak dressing voltage is kept constant irrespective of the wheel sharpness in conventional ELID grinding, which may lead to over dressing of the grinding wheel. The grinding force ratio, also known asKvalue, is an indicator of grit sharpness. In this study, a new approach to wheel dressing is proposed: the peak dressing voltage is varied according to the change in theKvalue during grinding. In conventional ELID grinding, the duty ratio of the dressing power supply is kept constant throughout the grinding cycle. However, this method does not achieve grinding wheel truing, which is very important to maintaining the stability of the grinding. This research work proposes a novel approach to wheel truing by controlling the dressing voltage duty ratio for ELID grinding.

Study on Precision Machining of Glass Lens Mold with Minute Structures (2nd Report)

In recent years, the demand of optical devices with complicated and highly accurate shape such as Fresnel lens and f-q lens is growing up in terms of miniaturization and improvement of information equipments. Moreover, the demand of glass lenses increases for the purpose of improving its heat resistance and optical performances. The study proposes a machining process for non-axisymmetric aspheric cemented tungsten carbide mold with minute structures, aiming at high precision machining. In the proposed process, the non-axisymmetric aspheric surfaces except for minute structures are at first machined by the spiral form grinding tool path with a spherical resinoid bonded diamond wheel. The machined surface center is corresponding to the center of the rotation axis of ultraprecision machine tool. Afterwards, the surfaces are ground for compensation, based on allover shape measurement interpolated by cubic spline. Then, minute structures are created on non-axisymmetric aspheric surfaces by the grinding with a disk type metal bonded diamond wheel. As a result, it is found that the proposed machining method has the potential of producing a high precision non-axisymmetric aspheric glass lens mold with minute structures effectively.

On-machine wire electrical discharge dressing (WEDD) of metal-bonded grinding wheels

Metal-bonded diamond wheels, due to its strong grain retention and thermal conductivity properties, are generally used for grinding difficult-to-cut materials, such as high-performance ceramics. On the other hand, the poor dressability of this type of bond limits its application. This study aims to evaluate the use of a wire electrical discharge machining (EDM) principle for truing and dressing metal-bonded grinding wheels. Through the EDM process, the electrically conductive grinding bond is eroded, so that grain protrusion can be generated. For evaluating this dressing process, a wire electrical discharge dressing unit was designed, manufactured, and integrated into a universal cylindrical grinding machine. The dressing process is carried out using the grinding oil also as dielectric fluid. High material removal rates were achieved. Cylindrical plunge grinding tests on silicon nitride workpieces indicated that in comparison to conventionally dressed wheels, smaller cutting forces and wheel wear are achieved by using EDM-dressed grinding wheels.

Research on Wheel Wear in HIPSN Bearing Ring High Speed Grinding

This paper reports on the wheel wear in high speed grinding silicon nitride used metal bond diamond wheels. The investigation focuses on the relation among grinding force, grinding ratio and wheel wear. Experiments have been performed to investigate the factor of wheel wear such as grinding ratio and grinding force. The results of these investigations are presented in this paper. With the application of this technology, a low cost production and high efficiency of ceramic bearing ring grinding can be realized.

Analysis of Factors Effecting Profile Accuracy of Metal-Bonded Ball-Headed Diamond Wheel in Electrical Discharge Dressing Process

Metal-bonded ball-headed diamond wheel with small diameter has been widely used in the ultra-precision grinding of optical parts, especially in the parts with complex surface. In-position precise dressing technique of ball-headed diamond wheel is the key technology to improve grinding precision. The effect of mechanical errors on the profile accuracy of wheel dressing were theoretically analyzed firstly. Afterwards a ball-headed diamond wheel dressing equipment based on electrical discharge principle has been designed and built. Orthogonal experiments have been carried out on the dressing equipment, and the dressing quality of wheels under different dressing electrical parameters were analyzed in terms of wheel profile accuracy and wheel surface micro-topography. The influence of dressing electrical parameters on the dressing quality were investigated and the best electrical parameter combination was obtained. Experimental result showed that the wheel profile accuracy can reach upward 0.8μm after dressing, and the protrusion heights of diamond grain were uniformity and the protrusion effect was better than without dressing.

Efficient dressing of the wheel in ELID grinding by controllable voltage with force feed back

Electrolytic in-process dressing (ELID) grinding is a new method for achieving ultraprecision surface on hard and brittle materials. In ELID grinding, pulsed direct current voltage is applied on the metal-bonded diamond wheels to ensure constant protrusion of sharp cutting grits throughout the grinding cycle. The peak dressing voltage is kept constant irrespective of the wheel sharpness in conventional ELID grinding, which may lead to overdressing of the grinding wheel. Grinding force ratio (which is also known as K value) is an indicator for the grit sharpness. In this paper, a new approach of wheel dressing has been proposed where the peak dressing voltage is varied according to the change in the K value during grinding. A Kistler three-component dynamometer has been used to monitor the grinding force ratio in real time for this purpose. The methodology to implement the new “dressing-on-demand” concept has been discussed thoroughly in this paper. The experimental comparison with the conventional ELID grinding has also been carried out to prove the advantages of the proposed system.

Laser-Assisted Truing for Metal-Bonded Diamond Wheel

Truing and dressing are time-consuming processes in precise finishing with super-abrasive wheels because of the hard super-abrasive grains which cause extensive wear of truer. In this paper, laser-assisted truing method for super-abrasive wheels is introduced. Feasibility of the proposed method is confirmed by fundamental experiments conducted with metal-bonded diamond wheel and pulsed Nd:YAG laser. On the surface of wheel irradiated with laser beam, it is found that the abrasive grains are degraded and the machinability of surface layer is remarkably improved.

Study on Precision Finishing of PCD by Constant-Pressure Grinding and UV-Polishing

Polycrystalline diamond (PCD) has been widely used for various cutting tools and die components making use of its hardness and wear resistance properties. The polishing method of a single crystal diamond substrate and SiC using ultraviolet irradiation was newly developed to obtain mirror-finished surfaces. Due to the long polishing time in this method, a better pre-machined surface is required to shorten the total processing time. In this work, the constant-pressure grinding was performed using a cup type metal-bonded diamond wheel and a constant pressure device. After the good constant-pressure grinding, the PCD was finished by the polishing under the ultraviolet irradiation, and the microroughness was reached to be 0.71 nmRa.

Development of Polishingless Ultra-Smoothness Grinding Method (5th Report)

The ultra-smoothness grinding method based on the new concept, which can finish to almost the same smoothness formed by polishing method, in the previous research, is developed as the countermeasure answering the recently strong requirement about high efficiency production of high quality components. The surface roughness of various kinds of materials formed by the method using the #140 diamond wheel is ascertained to attain below about 50nm(Rz). Furthermore, in the 2nd to 4th reports, the influence of grinding parameters such as wheel speed, normal feed to grinding direction and parallel step feed on the surface roughness is investigated. In the report, the possibility of ultra-high depth of cut of grinding of brittle materials such as fine ceramics and glass is examined. In even the ultra-high depth of cut of 1000 μm, the surface roughness of silicon carbide ceramic and Al2O3-TiC ceramic formed by the ultra-smoothness grinding method using #140 metal bonded diamond wheel is found to attain below 60nm (Rz) and 80nm (Rz) in three dimensional measurement of 256μm square, respectively. And also the surface roughness of a glass becomes below 50nm (Rz) in the range of depth of cut below 30μm.

Study on Precision Finishing of PCD by Constant-Pressure Grinding and UV-Polishing

Polycrystalline diamond (PCD) has been widely used for various cutting tools and die components making use of its hardness and wear resistance properties. The polishing method of a single crystal diamond substrate and SiC using ultraviolet irradiation was newly developed to obtain mirror-finished surfaces. Due to the long polishing time in this method, a better pre-machined surface is required to shorten the total processing time. In this work, the constant-pressure grinding was performed using a cup type metal-bonded diamond wheel and a constant pressure device. After the good constant-pressure grinding, the PCD was finished by the polishing under the ultraviolet irradiation, and the microroughness was reached to be 0.71 nmRa.

S1302-2-2 小径内面の超音波援用研削におけるメタルボンドダイヤモンド砥石の加工特性(超精密加工(2))

S1302-2-2 小径内面の超音波援用研削におけるメタルボンドダイヤモンド砥石の加工特性(超精密加工(2))

Experimental Trial of Fullerene Wheel Fabrication

The purpose of this study is to fabricate a wheel using fullerenes with nano-scaled particles, and to investigate the polishing performance of fullerene wheel. A super smooth surface was formed on a silicon wafer by polishing the wafer with metal-bonded diamond wheels using a diamond abrasive grit of 0-0.125 μm and fullerenes with a diameter of 0.7 nm. We used two kinds of metal-bonded diamond wheels for pre-polishing and a metal-bonded fullerene wheel for the finishing process. Though the surface roughness after polishing with the fullerene wheel was almost equal to that obtained by polishing with the metal-bonded diamond wheel using diamond abrasive grit of 0-0.125 μm, the chemical-mechanical polishing process was clarified by AFM (atomic force microscope) observation when we used a metal-bonded fullerene wheel with 5wt% KOH (potassium hydroxide) solution. The greater number of smoothed portions on the surface of the silicon wafer indicated that the fullerenes provided the same polishing ability as that of the abrasive grit.

Study on Precision Machining of Glass Lens Mold with Minute Structures

In optical devices, the demand of glass lenses with complicated shapes like Fresnel shape is recently growing up for the purpose of improving its heat resistance and optical performances. The study suggests a new machining process for cemented tungsten carbide mold with Fresnel shape, aiming at high precision machining. In the proposed process, the curved surfaces except for sharp edges are at first machined by the conventional grinding method with a disk type metal bonded diamond wheel. Then, sharp edges are created on curved surfaces by fly cutting method with knife edged single crystal diamond tool. Fly cutting method is expected to reduce tool wear due to the intermittent machining process. From fundamental V-microgrooving experiments of WC by fly cutting and shaping, it is clarified that the damage of cutting tool by fly cutting is reduced, compared to shaping. Therefore, complex machining of Fresnel shape by proposed machining method allows sharp edges to create to WC mold. As a result, it is found that the proposed machining method has the potential of producing a high precision glass lens mold with Fresnel shape effectively.