Electrolytic In-process Dressing Grinding Research Articles

A grinding force model considering the arc-track feeding unit device in ELID grinding of the non-standard ultra-precision bearings

Bearings play an important role in the national defense industry. The demands for the ultra-precision non-standard bearings are increasing year by year. Correspondingly, the requirements for the surface roughness of bearing raceways are getting higher and higher. The surface roughness Ra value of the bearing groove raceway has been significantly improved by the ELID (Electrolytic In-Process Dressing) grinding assisted by the arc-track feeding unit. In this research, a grinding force model for the ELID groove grinding assisted by the arc-track feeding unit is established. The modelling of the swing speeds, swing angles and duty ratios of the arc-track feeding unit are carried out as the basis for the predicting of the tangential and the normal forces. For the first time, the equivalent elastic modules are used to characterize the variation of the ELID oxide layer in the new model. Validated by the linear-groove ELID grinding with varying swing speeds, swing angles and duty ratios of the arc-track feeding unit, the predicting results of the force capture well the fluctuation of different force components due to the changing of the variables. The new grinding force model involving the arc-track feeding device is able to give accurate predictions to the tangential and normal forces. The maximum error between the predicting tangential forces and the experimental tangential force is 5 %; the maximum error between the predicting normal forces and the experimental normal forces is 6.2 %. It provides an insight into the material removal mechanism and the grinding force characteristics in the ELID grinding assisted by the arc-track feeding unit for further improving the forming accuracy of this new method.

Understanding of highly-oriented 3C-SiC ductile-brittle transition mechanism in ELID ultra-precision grinding

Highly-oriented 3C-SiC possesses good out-of-plane orientation uniformity, and has more potential to obtain uniform surface quality during ultra-precision machining, compared with randomly-oriented SiC (such as RB-SiC and S-SiC, et al.). Through ultra-precision machining of highly-oriented 3C-SiC under electrolytic in-process dressing (ELID), the oxide film formed on the grinding wheel enhances the contact stiffness between the grinding wheel and the workpiece during the process. Further, compressive residual stress of 0.29 MPa on highly-oriented 3C-SiC surface conducive to the removal of material ductile was generated. It enabled ELID to perform better material ductile removal ability than conventional grinding (CG) does. On the other hand, numerous stacking faults (SFs) in highly-oriented 3C-SiC promoted the migration of dislocations in the material and generated more dislocations in the material under the shear stress of ELID grinding wheel. In addition, the accumulated dislocations at the grain boundary continued to slip to the next grain rather than resulting in dislocation pile-up and material crack due to the consistency of grain orientation. This phenomenon has the materials been ductile removal rather than brittle fracture. All above findings would provide a beneficial reference for the control of grinding process and the analysis of material removal mechanism of highly-oriented materials.

Investigations on a hybrid chemo-magnetorheological finishing process for freeform surface quality enhancement

Surface roughness improvement of the freeform surfaces is essential for the enhanced functionality of the components, including implants, turbine blades, microchannels, etc. The exclusion of human involvement during the finishing of freeform surfaces prevents hazardous exposure to particulate and provides uniform surface quality. Different surface finishing techniques, including vibratory finishing, Abrasive Flow Finishing (AFF), Electron Beam (EB) Irradiation, Electrolytic in-process Dressing (ELID) grinding, etc., have been developed to automate the finishing operation. However, some limitations are associated with the preexisting techniques, e.g., the process controllability of AFF and vibratory finishing, recast layer formation during EB irradiation, and low productivity of ELID grinding. Hence, a novel method for surface improvement, namely, Hybrid Chemo-Magnetorheological Finishing (HC-MRF), is proposed in the present study to reduce the surface roughness (Ra) (~up to a few nanometer) without affecting the surface topography of the workpiece. HC-MRF simultaneously utilizes the synergic action between Magnetorheological Finishing (MRF) and chemical etching to reduce surface finishing time and escalate process efficiency. Herein, the carrier medium of the Magnetorheological (MR) fluid is replaced by a reagent to facilitate the chemical etching process, and its synchronized action with mechanical abrasion reduces surface irregularities. Furthermore, the design of the developed apparatus to enable the HC-MRF process, where permanent magnets are used to produce the desired external magnetic field, is also discoursed. A case study on the surface roughness enhancement through the HC-MRF on the WC-Co (tungsten carbide in a cobalt-rich matrix) is investigated using Response Surface Methodology (RSM). Herein, Murakami's reagent is used as the carrier medium in the MR fluid, and a reduction in surface roughness (Ra) from an initial value of 312.87 nm to a final value of 34.50 nm is noticed. Moreover, the inclusion of Murakami's reagent enhances the process efficiency. The change in surface roughness with and without Murakami's reagent in the MR fluid is 88.97 % and 43.12 %, respectively, for a constant finishing time.

ELID Mirror Surface Grinding for Concave Molds by Conductive Elastic Wheel Containing Carbon Black

Elastic grinding wheels have previously been adopted for the development of the mirror surface finishing method for concave spheres. In this study, new conductive elastic grinding wheels, to which electrolytic in-process dressing (ELID) can be applied, are developed; the aim of the study is to address the challenge of maintaining a constant removal rate for rubber bond wheels. When ELID grinding is performed using a non-diene (isobutane isoprene rubber, IIR)-based wheel, a larger removal amount is achieved, and a higher-quality surface is also achieved compared to a diene (acrylonitrile-butadiene rubber, NBR)-based wheel. In addition, to investigate the effect of grinding wheel bond hardness on the removal amount and ground shape accuracy, grinding wheels with various levels of hardness are prepared by controlling the amount of carbon black contained in them, and grinding experiments are conducted. Thus, a larger removal amount is achieved using a harder grinding wheel, but the roughness of the ground surfaces deteriorates. Therefore, in practice, it is necessary to select an appropriate grinding wheel that can achieve both productivity and surface quality. Finally, to obtain a high-quality mirror finish on a concave spherical surface, ELID grinding is performed on the workpieces as is done for spherical lens molds. Thus, high-quality mirror surfaces with roughness Ra < 10 nm were generated. When the work pieces are ground using a grinding wheel of the same radius, excessive removal occurs at the edge of the concave spherical profile, decreasing the form accuracy. Numerical simulation demonstrates that chamfering of the grinding wheel is effective for improving the shape accuracy. The results of this study are expected to contribute to automation and cost reduction in the mirror-finishing process for concave molds.

Experimental study on the characteristic and function of oxide film formed on grinding wheel in ELID precision grinding

PurposeThe purpose of this study is to investigate the characteristic and function of oxide film formed on grinding wheel in electrolytic in-process dressing (ELID) precision grinding and improve the quality of ELID grinding.Design/methodology/approachDynamic film forming experiments were carried out with a simulation device close to the actual processing conditions. Then, the ELID grinding experiments of bearing rings were performed using grinding wheels with good film forming effect. The experiment was designed by quadratic regression general rotation combination method. The influence of grinding depth, electrolytic voltage, duty cycle and grinding wheel linear speed on grinding effect is analyzed.FindingsA mathematical model for the formation rate of oxide film was established. The experiments show that the composition of grinding wheel and grinding fluid, as well as the electrical parameters, influence the film forming effect. Thus, the oxide film plays an important role in ELID grinding.Originality/valueThis study provides a reference for the design and selection of grinding wheel and grinding fluid and the setting of process parameters in ELID grinding.

Effects of O2 Fine Bubbles on ELID Grinding Using Conductive Rubber Bond Grinding Wheel

This study proposes a new grinding system using grinding fluid containing oxygenic fine bubbles (O2FBs) to realize high-performance electrolytic in-process dressing (ELID) using a conductive rubber bond grinding wheel. It was found that grinding fluid containing O2FBs dramatically increases the dissolved oxygen in the grinding fluid. In addition, the O2FBs in the fluid are drawn to the conductive rubber bond grinding wheel, which is the positive pole, during ELID. These effects are thought to enhance the dressing performance of the conductive rubber bond grinding wheel. Grinding of pure titanium using the proposed grinding system was found to realize mirror surface finishing while increasing the amount of removed workpiece material, compared to when ELID was not applied and to when ELID grinding was conducted using a normal grinding fluid. Effects of ELID grinding on surface modification were also observed, confirming that the proposed grinding system is able to form a thick oxidized film on pure titanium.

Microscopic characterization and modeling of oxide layer for electrolytic in-process dressing (ELID) grinding with focus on voltage, electrode-wheel gap, and coolant flow

Electrolytic in-process dressing (ELID) is a grinding technique used to generate high-quality surfaces on hard and brittle material. Oxide layer formed on grinding wheel during ELID grinding heavily influences the surface roughness of the workpiece. To study the microscopic structure of the oxide layer and model the thickness of it, we conducted a previously reported study on metallic-bonded prism samples with major adjustments and implementations. The parameter studied are voltage, electrode-grinding wheel gap, and coolant flow rate. Scanning electron microscopy (SEM) images of cross-section of the oxidation sites were captured and compared and oxide layer thickness was accurately measured. All three parameters are found to significantly affect the formation of the oxide layer.

Research on ELID Grinding Mechanism and Process Parameter Optimization of Aluminum-Based Diamond Composites for Electronic Packaging

Abstract Aiming at the problem of poor processing performance and difficult processing in the process of aluminum-based diamond composites for electronic packaging, this paper uses electrolytic in-process dressing (ELID) grinding technology to grind the aluminum-based diamond composites. The quadratic orthogonal rotation combination method was used to investigate the influence law and degree of grinding depth, grinding wheel linear velocity, duty cycle and electrolysis current on surface roughness. The ELID grinding optimization process parameters of aluminum-based diamond composites obtained by LINGO software are: grinding depth 9.3μm, grinding wheel linear speed 36m/s, duty cycle 63.7%, electrolysis current 11.5A. The surface of the aluminum-based diamond composite with a surface roughness of 125 nm was machined by this optimized process parameter combination.

Research on Generation and Polishing Mechanisms of Nano Grain α-Fe2O3 in Precision Electrolytic in process dressing (ELID) Grinding

Electrolytic in process dressing (ELID) grinding holds tremendous promise for ultra-precision grinding on hard and brittle materials. Besides oxide films on the grinding wheels it is important to study the content generation and transformation of α- Fe2O3 inside the oxide film and its effect on polishing process. In this study, X-ray diffractometer (XRD) measurement, SEM, TEM was performed in ELID grinding with different grinding wheels in order to investigate the content and transformation procedure of α- Fe2O3. Results shown, transformation of α- Fe2O3 is bound up with grinding temperature, the grain size of α- Fe2O3 5-10nm, the α- Fe2O3 in oxide film formed membrane structure.

Wear life characterization of the grinding wheel for electrolytic in-process dressing (ELID) grinding of ball bearing raceways: a new perspective based on a moving normal distribution curve of the grit state variation

Many advantages make electrolytic in-process dressing (ELID) grinding desirable for cutting hard and brittle material with high surface requirements. The self-electrolytic in-process dressing property in ELID grinding is also largely responsible for the shorter wear life and lower forming accuracy of the grinding wheel. In ELID grinding, except for traditional mechanical wear, the electrolytic oxidation wear also adds more uncertainties to the wear velocity of the grinding wheel. To date, few investigations focused on the grinding wheel wear life characterization in ELID cut-in grinding of ball bearing raceway. In this study, the wear life characterization of the grinding wheel during ELID grinding was quantitatively simulated by a moving normal distribution curve of the grit state variation. As all types of cutting grits wear out, so did the normal distribution curve, showing movement towards the grinding wheel center. With the normal distribution curve moving towards the grinding wheel center, a local acceleration and local deceleration in moving velocities occurred. It is the diversity of the moving speed of the normal distribution curve that provides a quantitative description to understand the wear life characterization of the ELID grinding wheel. Some experimental results can easily explain this new proposed perspective. This new perspective can also be extended to predict the forming accuracy and surface topography of the bearing raceway during ELID grinding.

Mechanical Behavior of Iron-bonded Grinding Wheel after ELID (Electrolytic In-process Dressing) Electrolysis Procedure by Nanoindentation

We have evaluated the effect of oxide films on polishing behavior during ELID grinding process. The evaluation procedure used nano-indenter to analysis quantitatively the oxide film’s mechanical properties on iron-bonded grinding wheel after ELID electrolysis. As a result, the oxide film’s mechanical properties increased with the indent depth increasing. The plots of indent load and displacement for oxide films showed slight variations with time. The content of iron group elements in grinding wheel also has higher impact on oxide film’ s properties.

A comparative study on state of oxide layer in ELID grinding with tool-cathode and workpiece-cathode

As a relatively new grinding technology, ELID (electrolytic in-process dressing) is widely used in some businesses. The oxide layer plays an important role in ELID grinding performance. The purpose of this work is to investigate the state of the oxide layer on ELID grinding wheel surfaces based on workpiece-cathode and tool-cathode. The thickness and surface topography of the oxide layer were measured from ELID grinding experiments based on workpiece-cathode and tool-cathode in different controlled dressing current. The normal grinding force was also compared in ELID grinding with workpiece-cathode and tool-cathode. According to the results, there are some caves on the surface of the oxide layer in ELID grinding with workpiece-cathode. With increasing controlled dressing current, the surface of the oxide layer becomes discontinuous in ELID grinding with workpiece-cathode. And the surface of the oxide layer becomes smoother with increasing controlled dressing current in ELID grinding with tool-cathode. Meanwhile, it was found that the oxide layer in ELID grinding with workpiece-cathode is thicker than that in ELID grinding with tool-cathode. Moreover, the normal grinding force in ELID grinding with workpiece-cathode is smaller than that in ELID grinding with tool-cathode. The results are helpful to improve the ELID grinding performance and apply ELID grinding technology with workpiece-cathode to abroad industrial applications.

Surface quality prediction model of nano-composite ceramics in ultrasonic vibration-assisted ELID mirror grinding

Ultrasonic vibration-assisted Electrolytic in-process dressing (ELID) grinding is a highly efficient and highly precise machining method. The surface quality prediction model in ultrasonic vibration-assisted ELID mirror grinding was studied. First, the interaction between grits and workpiece surface was analyzed according to kinematic mechanics, and the surface roughness model was developed. The variations in surface roughness under different parameters was subsequently calculated and analyzed by MATLAB. Results indicate that compared with the ordinary ELID grinding, ultrasonic vibration-assisted ELID grinding is superior, because it has more stable and better surface quality and has an improved range of ductile machining.

Study of α-Fe2O3 formation and its measurement in oxide films of wheel surface during ELID grinding process

This paper presents the study of forming mechanism of [Formula: see text]-Fe2O3 in oxide films on electrolytic in-process dressing (ELID) grinding wheel surface. To investigate the component content and the microtopography of oxide films, XRD, XPS, IR spectrum analysis, SEM, and TEM measurements are performed on ELID grinding wheels. In XRD test results, the characteristic absorption band of [Formula: see text]-Fe2O3 is found in the oxide film. XPS tests show that there is full of ferrous iron and oxygen element in the oxide film. Also, the characteristic spectral line of XPS is identical to the standard spectrum of [Formula: see text]-Fe2O3. Several vibration peaks (471, 1029, 1384, 1630, 3430) are observed by IR spectrum analysis. It can be easily seen by contrast with the standard photographs that the vibration peak of 1029 is of Fe-O vibration band in IR spectrum of [Formula: see text]-Fe2O3 powder. Therefore, these measurement results confirm the existence of [Formula: see text]-Fe2O3 in the oxide films, and explain the polishing effect of oxide films during ELID grinding. The fresh oxide film is porous and moisture rich. However, the oxide film after squeezing to dry is investigated by SEM imaging to present tortoiseshell cracks. Geometrically, [Formula: see text]-Fe2O3 appears to be nearly spherical with particle size around 5–50 nm. This indicates fine polishing improvement by oxide films, and is identified as the mechanism responsible for excellent surface quality by ELID grinding.

ELID Fine Grinding of SiC Bearing Rollers

Electrolytic in-process dressing (ELID) grinding is drawing more and more attention by the researchers for its smart method of in-process dressing of the grinding wheel. Many researches place emphasis on study of in-processing dressing and oxide layer. In this study, the effects of three grinding factors, including wheel speed, load applied on workpiece and eccentricity of three parts in one holder, on surface roughness (Ra) and material removal rate (MRR) were investigated in a single-side ELID grinding experiment. Each factor has three levels. The experimental results show that each factor has different influence: 1. Applied load is the main factor which significantly affects the Ra and MRR; 2. the speed of grinding wheel doesn’t show much influence; 3. eccentricity has a great influence on roughness but not on material removal rate.

ELID grinding characteristics of SiCp/Al composites

In this study, electrolytic in-process dressing (ELID) grinding experiments were conducted on SiCp/Al composites, and the effects of grinding depth and feed speed of work table on grinding force, surface roughness, and surface morphology were investigated. The experimental results showed that the fluctuation range of grinding force and grinding force ratio Cf under ELID condition were smaller than that of the same grinding parameters under wet grinding condition. Additionally, ELID grinding is effective in providing the uniformly grit protrusion and chip storage space. SiC particles were removed in ductile mode, and the brittle fracture of SiC particles were reduced substantially. The high integrity surface of the SiCp/Al composites could be obtained under ELID condition.

ELID Fine Grinding of Sapphire Rollers with Emphasis on Roughness and Material Removal Rate

The demand for sapphire (α-Al2O3) has significantly increased due to its reliable properties. Sapphire is known for its high hardness and high brittleness. Sapphire has excellent properties such as optic, mechanical and physical properties, which can be maintained even if machined in high temperatures. Due to these properties, sapphire has been used in many different applications such as aerospace, optics, and electronics as well as other industries. Machining of Sapphire is challenging due to its high hardness and brittleness. Fine grinding can be preferable over conventional grinding when machining ceramics because of the ability to provide a flat surface. However, the manufacturing cost for such materials is very high because of high tool wear and longtime machining. In addition, most of the grinding process is followed by a lapping process. Elimination of lapping process can be accomplished using many techniques, one of which is the use of electrolytic in process dressing (ELID). Therefore, the use of fine ELID grinding will reduce the machining time which in turn reduces the manufacturing cost. Part of the solution also investigates the influence of different variables on the workpiece surface finish. This paper presents the influence of four parameters with three level each: different pressures, different eccentricities, different spindle speeds, and different wheel speed ratios. A full factorial design, for both roughness (Ra) and material removal rate (MRR) conducted to present mathematical models which predict future results. The kinematics of the process will be investigated based on the effect of different eccentricity. The mesh size of the diamond grinding wheel used in this experiment is #400.

MLCC 적층용 진공척의 자기연마와 ELID연삭을 이용한 미세버 제거 기술

This study has focused on the deburring technology of a vacuum plate for MLCC lamination using electrolytic in-process dressing (ELID) grinding, and the magnetic-assisted polishing (MAP) process. The surface of the vacuum plate has many micro-holes for vacuum suction. They are easily blocked by the burrs created in the surface-flattening process, such as the conventional grinding process. In this study, the MAP process, the ELID grinding process, and an ultrasonic vibration table are examined to remove the micro-burrs that lead to the blockage of the holes. In the results of the experiments, the MAP process and ELID grinding technology showed significant improvements of surface roughness and deburring performance.

Experimental study on internal cylindrical grinding of bearing steel with electrolytic in-process dressing grinding

Precision cylindrical surfaces have attracted considerable attention and interest, due to the continual pursuit of perfect quality and high-performance products. Especially in bearing industry, high-performance bearing often requires specific cylindrical surface properties such as high hardness, wear resistance, high strength, and toughness, because it is normally used in poor working environment. Besides, it is usually finished to a mirror-like surface for higher chemical stability. Most of enterprises adopt bearing steel to manufacture bearing components. However, the bearing steel is known to be difficult to finish a mirror-like surface in conventional grinding, owing to its high hardness. Electrolytic in-process dressing (ELID) grinding has been proven as an effective grinding process especially for hard and brittle materials. In this paper, ELID grinding technique was used to obtain a better surface and accuracy on bearing steel. A series of experiments were done to study a law of craft parameters’ influence on the internal cylindrical surface quality with ELID grinding. The experimental results show that ELID grinding method can realize a stable grinding process to produce internal cylindrical grinding surface of bearing steel. The optimization of process parameters with respect to ground surface roughness is analyzed by design of experiments.

高度な流体膜維持機能を有する人工股関節摺動部コンポーネントの開発

We have developed an ELID (ELectrolytic In-process Dressing) grinding technique that creates mirror-like surfaces on Ti-13Zr-13Nb alloys. To create a smooth surface, a metal-bonded grinding wheel was used for rough grinding and then a rubber-bonded wheel was used for final grinding. The optimum conditions for rough processing were a rotational speed of 400 rpm, a cut depth of 0.5 μm, a 40 mm/s feed rate of the work, and pitch interval for feeding in the y-direction of 1 mm. For final grinding, the optimum spark-out scanning time was 20 min. This new ELID processing technology decreased surface roughness to 30 nm (Ra).