Workpiece Surface Finish Research Articles

Grinding wheel redress life estimation using force and surface texture analysis

Grinding characterized by low material removal rate and high surface finish is an abrasive machining process. Geometrically undefined grits of grinding wheel influences part surface finish. Cutting edges worn out during grinding are retained by timely dressing. Operators on shop floor decides on the dressing interval based on end of wheel life such as burns, chatter marks and deterioration in the workpiece surface finish. Incorrect dressing of grinding wheel increases unnecessary machining time and wheel wastage. The present work defines the usefulness of grinding force signal and ground surface texture analysis in the estimation of grinding wheel redress time. Grinding experiments were performed in surface grinding machine with white Alumina wheel on D2 tool steel specimen. During the experiments, the force signals were acquired from 9257B Kistler dynamometer, for each grinding pass with 16 KHz sampling frequency. Ground workpiece surface images were captured using multi-sensor Coordinate Measuring Machine (CMM). Experiments were continued till the grinding wheel reaches its end of life. Grinding force signal features prominent to the assessment of grinding wheel deterioration in time, frequency and time-frequency domains were extracted based on prognostic metric evaluation. Hough transform based image texture features were also extracted. The test results depict that a good correlation exists between grinding force signals and ground surface images in measuring the wear deterioration level and thus the ground surface features can be considered as an explicit criterion in the redress life estimation of the grinding wheel.

Formation of the Workpiece Shape and Surface Finish During Electrical Discharge Machining

Electrical discharge machining is a promising non-traditional machining process, which is quite well investigated in relation to the formation of the plasma channel and the formation of single erosional craters. However, the influence of geometrical and energetic heterogeneities of electrodes on the formation of the workpiece shape and surface finish is insufficiently investigated.In this work the analysis of the influence of geometric and energetic heterogeneities of the surfaces of the electrodes on the discharge and its location, the shape and size of the erosion craters is performed.Theoretical studies based on multidischarge numerical simulation of electrical discharge machining, which includes a cyclical execution of the following steps: 1) modeling of thermal processes for a single discharge; 2) modeling of the workpiece material removal and crater formation during the pause; 3) determining of the location of the subsequent discharge, are carried out.For the simulation of thermal processes the equation of transient heat conduction in a medium with variable physical-chemical properties was used. Thus the workpiece material removal was replaced by an anisotropic material with low heat capacity, which allowed to eliminate the necessity of changing the computational domain when this material was removed.The experimental investigation on the distribution of discharges over the workpiece surface at the initial stage of EDM was performed. The emergence of the phenomenon of “nesting” craters in the zones of maximum energy disposition (bulges, zones of differential surface and temperature) was shown. The process of how these zones are distributed over the entire workpiece surface was shown.

Development of magnetorheological fluid-based process for finishing of ferromagnetic cylindrical workpiece

ABSTRACTA magnetorheological fluid-based process is developed for the internal surface finishing of ferromagnetic cylindrical workpiece. The existing finishing processes based on magnetorheological fluid are not equipped to finish the internal ferromagnetic cylindrical surface significantly as it obtained higher magnetic flux density than the MR polishing fluid. At present, magnetorheological fluid-based finishing tools are designed to ensure the maximum magnetic flux density always present on the outer finishing tool core surface as compared to internal surface of ferromagnetic cylindrical workpiece surface. To validate this present principal idea, the magnetostatic finite element analysis has been performed on the newly designed finishing tools. The preliminary experiments have also been conducted to evaluate the finishing performance with the two newly designed finishing tools. The percentage reduction in surface roughness (Ra) values with I-shaped tool core is found as 65–78% after 150 min of finishing, whereas, with rectangular shaped tool core is found as 78–81% after 90 min of finishing. The results clearly revealed that the present finishing tool with rectangular shaped core is more suitable for uniform significant finishing of ferromagnetic cylindrical internal workpiece than the I-shaped core. The developed process can be useful in finishing of cylindrical mold and dies, hydraulic cylinder, barrel for injection molding, etc.

Application of the wavelet packet transform to vibration signals for surface roughness monitoring in CNC turning operations

Abstract The wavelet packet transform method decomposes a time signal into several independent time-frequency signals called packets. This enables the temporary location of transient events occurring during the monitoring of the cutting processes, which is advantageous in monitoring condition and fault diagnosis. This paper proposes the monitoring of surface roughness using a single low cost sensor that is easily implemented in numerical control machine tools in order to make on-line decisions on workpiece surface finish quality. Packet feature extraction in vibration signals was applied to correlate the sensor signals to measured surface roughness. For the successful application of the WPT method, mother wavelets, packet decomposition level, and appropriate packet selection methods should be considered, but are poorly understood aspects in the literature. In this novel contribution, forty mother wavelets, optimal decomposition level, and packet reduction methods were analysed, as well as identifying the effective frequency range providing the best packet feature extraction for monitoring surface finish. The results show that mother wavelet biorthogonal 4.4 in decomposition level L3 with the fusion of the orthogonal vibration components (ax + ay + az) were the best option in the vibration signal and surface roughness correlation. The best packets were found in the medium-high frequency DDA (6250–9375 Hz) and high frequency ADA (9375–12500 Hz) ranges, and the feed acceleration component ay was the primary source of information. The packet reduction methods forfeited packets with relevant features to the signal, leading to poor results for the prediction of surface roughness. WPT is a robust vibration signal processing method for the monitoring of surface roughness using a single sensor without other information sources, satisfactory results were obtained in comparison to other processing methods with a low computational cost.

Comparison of evolutionary techniques for the optimization of machining fixture layout under dynamic conditions

Modern manufacturing industries are striving to improve the machining accuracy and productivity to reduce the rejection rate and unit cost of the machined parts. The properly designed fixture layout enables the designer to minimize the vibration so that the requisite machining accuracy can be achieved. During machining, especially in end milling, the intermittent engagement of multitooth cutter induces vibration on the workpiece. When the excitation frequency of multitooth cutter coincides with any one of the natural frequencies of the fixtured workpiece, it leads to the condition of resonance. The vibration increases under these circumstances, which degrades the machining accuracy and surface finish of the machined workpiece. Hence, the issues related to the design of fixture layout are to be addressed by recognizing the dynamic behavior of the fixture–workpiece system. In this research paper, finite element method is utilized to simulate the end milling operation and to determine the natural frequency of the workpiece. The main focus is to maximize the difference between natural frequency of the fixtured workpiece and excitation frequency of the cutter to minimize the vibration on the workpiece. Two different evolutionary techniques genetic algorithm and particle swarm optimization are employed to maximize the difference between these frequencies by optimizing the machining fixture layout. The performance of genetic algorithm and particle swarm optimization on the fixture layout optimization is compared. The comparison of results concludes that particle swarm optimization is the most appropriate approach than the genetic algorithm in achieving the better results.

Modeling and simulation of surface roughness in magnetorheological fluid based honing process

A newly magnetorheological fluid based honing process is developed for internal surface finishing of ferromagnetic cylindrical workpiece as existing magnetorheological fluid based finishing processes are not found suitable to finish the ferromagnetic internal surfaces. The performance of the present developed finishing process in terms of reduce wear and improve the functional application of cylindrical components, mainly depends on the normal force acting on abrasive particles due to magnetic behavior of carbonyl iron particles in magnetorheological polishing fluid. Also, it depends on shear force acting on surface by abrasive particles due to translational and rotational motion of tool as similar to the honing operation. For the newly developed finishing process, the modeling of surface roughness with the effect of induced magnetic field and magnetic normal force for different finishing cycles have been proposed. To validate the model and understand the wear mechanism during finishing, the experiments have been performed on the internal surface of cylindrical ferromagnetic workpiece with the three different sets of finishing cycles. The surface roughness of cylindrical workpiece has experimentally measured with Mitutoyo SJ-400 surftest. Also, to understand wear mechanism during finishing, the scanning electron microscopy has been performed. The theoretical calculated values of surface roughness with number of finishing cycles are validated with experimentally obtained surface roughness values for the same number of finishing cycles and conditions. Both were found in close agreement within 5.88%. Thus, the present developed finishing process is found suitable to reduce wear on internal surface of cylindrical components which leads to saving in service, energy consumption, maintenance costs, and improves its functional applications as compared to traditional finishing techniques.

Utilization of sulphurized palm oil as cutting fluid base oil for broaching process

Broaching is one of the most severe metal cutting operation that requires the use of cutting fluids formulated with extreme pressure (EP) additives to minimize metal-to-metal contact and improve tool life. Enhancement of EP performances of the cutting fluids can be achieved by addition of sulphur containing compounds that will allow the formation of metal sulfide film that has low shear strength and good antiweld properties and acts as protection layer from wear and seizure. Most of the cutting fluids are mineral oil based. However, as regards to health and environmental issues, reseach on vegetable oil based cutting fluid have been increased recently. This paper reports a study on the sulphurization of palm oil derivatives and its usage as broaching oil. Sulphurization of the palm oil derivative was conducted via non-catalytic sulphurization using elemental sulphur at various composition and under heating of 150-160°C for 3 hr. Broaching oil was made by blending the sulphurized palm oil and additive packages. The performance parameters of the broaching oil that has been observed including load carrying capacity, wear scar diameter, corrosion protection, oxidative stability, and surface finish of workpiece. From this research, it was found that sulphurized FAME based broaching oil has excellent EP properties. The optimum formulation was obtained on composition of sulphurized FAME-mineral oil with 6% wt of sulphur. The result from the test showed that kinematic viscosity of sulphurized palm oil was about 25.3 cSt (at 40 °C), load carrying capacity was 400 kgf, and wear scar diameter was 0.407 mm. In addition, it can be concluded that the class of corrosion protection of modified palm oil was 1.b (slight tarnish category), oxidative stability at 160 °C was obtained for 0.11 hr, and the surface roughness of workpiece was about 0.0418-0.0579 μm. These performances are comparable to commercial broaching oil. By this result, it indicates that sulphurized palm oil is applicable for industrial cutting fluids formulation.

The application of computational fluid dynamics to vibratory finishing processes

Vibratory finishing processes are finding increased application in the finishing of high value metallic components. Despite the growth of these processes, few models exist to predict workpiece material removal variations and surface finish uniformity. This paper explores the potential of modelling the media as a continuum and utilizing commercial computational fluid dynamic (CFD) packages to predict local velocity and pressure fields around stationary workpieces. Predicted 2D velocity fields are compared to those measured via Particle Image Velocimetry. Initial insights are provided on how local media fields and the system’s driving frequency combine to affect the resulting workpiece topography.

Molecular Dynamics Model of Nano-metric Peripheral Grinding

Ultra high precision grinding can render sub-micrometric surface finish of workpieces in an effective way. Accordingly, grinding in the nano-level can be used to produce surface finish of nanometric level or removal of several atomic layers of the substrate. As direct measurements in this scale are either expensive or impossible to be conducted, appropriate simulation models need to be created in order to study the underlying mechanisms of nanometric machining processes. Molecular Dynamics (MD) method is a widely accepted simulation method for this purpose, as it enables direct observation of the process at atomistic level. In this study, an MD simulation of nanometric peripheral grinding with two single crystal diamond grains is conducted with a view to determine cutting forces and temperatures as well as surface integrity and subsurface damage in the workpiece. Using this model, favourable cutting conditions for this process will be able to be determined.

Optimization of Cutting Parameters to Minimize the Surface Roughness in the End Milling Process Using the Taguchi Method

This paper presents a study of the Taguchi design application to optimize surface quality in a CNC end milling operation. The present study includes feed per tooth, cutting speed and radial depth of cut as control factors. An orthogonal array of L9 was used and the ANOVA analyses were carried out to identify the significant factors affecting the surface roughness. The optimal cutting combination was determined by seeking the best surface roughness (response) and signal-to-noise ratio. The study was carried-out by machining a hardened steel block (steel 1.2738) with tungsten carbide coated tools. The results led to the minimum of arithmetic mean surface roughness of 1.662 µm, being the radial depth of cut the most influent parameter, with 64% of contribution for the workpiece surface finishing.

The Machining of Hard Mold Steel by Ultrasonic Assisted End Milling

This study describes the use of ultrasonic-assisted end milling to improve the quality of the machined surface of hard Stavax (modified AISI 420) mold steel and to reduce the amount of work involved in the final polishing process. The effects of input voltage, the stretch length and cutter holding force on the amplitude of the ultrasonic vibration used were measured. The effect of ultrasonic frequency (25 and 50 kHz) and amplitude (0, 2.20 and 3.68 μm) as well as the effect of the rake angle (6° and −6°) and the cutter helix angle (25°, 35° and 45°) on tool wear and quality of the workpiece surface finish were also investigated. It was found that the ultrasonic amplitude increased with cutter stretch length and input voltage, as expected. The amplitude remained constant when the cutter holding force exceeded 15 N. The experimental results showed that the ultrasonic amplitude had an optimum value with respect to surface finish. However, large amplitude ultrasonics did not necessarily improve quality. Furthermore, the cutters used for ultrasonic-assisted milling show less wear than those used for normal milling. It was also found that a positive rake angle and cutters with a large helix angle gave a better surface finish.

COMPARISON OF EXPERIMENTALLY MEASURED AND SIMULATED WORKPIECE AND GRINDING WHEEL TOPOGRAPHY USING A NEW DRESSING MODEL

This paper presents a new empirical model of the dressing process in grinding which is then incorporated into a 3D metal removal computer simulator to numerically predict the ground surface of a workpiece as well as the dressed surface of the grinding wheel. The proposed model superimposes a ductile cutting dressing model with a grain fracture model to numerically generate the resulting grinding wheel topography and workpiece surface. Grinding experiments were carried out using “fine”, “medium” and “coarse” dressing conditions to validate both the predicted wheel topography as well as the workpiece surface finish. For the grinding conditions used in this research, it was observed that the proposed dressing model is able to accurately predict the resulting workpiece surface finish for all dressing conditions tested. Furthermore, similar trends were observed between the predicted and experimentally-measured grinding wheel topographies when plotting the cutting edge density, average cutting edge width and average cutting edge spacing as a function of depth for all dressing conditions tested.

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.

GAP CONTROL OF ELECTRICAL DISCHARGE GRINDING WITH HIGH BANDWIDTH DUAL STAGE ACTUATORS

Electrical discharge grinding process has four types of discharge states and abnormal states, such as arcs and short circuits have great impact on the machining efficiency and the surface finish of workpieces, for example, polycrystalline diamond cutting tools. The aim of this study had been to develop a new servo system with high bandwidth dual stage actuators, which can quickly change the gap width to eliminate these harmful discharge states. The structure of the dual stage system is that a piezoelectric actuator stands on a linear actuator and both move along one axis. The piezoelectric actuator, which has high bandwidth but short travel distance, was used for the gap width control and the linear actuator, which is relatively slow but has long travel distance, tunes the feed rate of the workpiece to match the erosion rate. The gap information obtained from the electrical discharge waveform was used as a feedback signal. The linear actuator system adjusted its velocity based on the average piezoelectric displacement value. Hence, an electrical discharge machine was developed with a one-axis dual stage system. The results from simulations and experiments showed that the new system provided a high bandwidth response, as well as enhanced the machining rate and stability.

Experimental Investigation of Microcutting Mechanisms in Oxide Ceramic CM332 Grinding

The paper contains an experimental study of microcutting intended to help the optimization of the grinding process of the oxide ceramic CM332 (99.5% Al2O3) grinding. The need for investigating the mechanisms occurring between the abrasive material and the ceramic is imposed by the fact that grinding is the dominant technology used to achieve the required quality of the workpiece surface finish. The microcutting process was performed with a single diamond cone-shaped grain of tip radius of 0.2 mm at varying depths of cut. The investigations were carried out to determine the normal and tangential cutting forces, the critical penetration depth and the specific grinding energy as a function of the grain penetration speed and depth. The critical grain penetration depth separating ductile flow from brittle fracture falls within the 4–6 μm range. The values of the critical penetration depth are also consistent with the results of changes in the cutting forces and the specific grinding energy. The chip formation mechanism is associated with the presence of median/radial and lateral cracks, ductile flow, chipping along the groove, and crushing beneath the diamond grain, all this affecting the quality of the ceramic's machined surface.

Quick On-Machine Measurement of Ground Surface Finish Available for Mass Production Cylindrical Grinding Processes

In mass production cylindrical grinding operations, the ground surface finish has never been measured in each grinding cycles because existing surface roughness testers take a relatively long time to measure surface finishes, and the introduction of a surface roughness tester in each grinding cycle would affect mass production processes. Therefore, the surface finish of all parts manufactured in a production lot is generally evaluated based on the measured results of only few parts by sampling checks. We have proposed a unique quick technique for measuring surface roughness. It uses electromotive force based on the slight frictional heat to evaluate the surface finish of cylindrical workpieces rotating on cylindrical grinding machines, and it can do this in a split second just after each grinding cycle, so it does not hamper mass production grinding processes. The proposed quick measurement system can capture the variations in surface finish in a set of repeated cylindrical grinding cycles without dressing. The possibility of accurate judging dressing time by using the quick measurement system in mass production grinding processes is shown experimentally.

The effect of aCN/TiAlN coating on tool wear, cutting force, surface finish and chip morphology in face milling of Ti6Al4V superalloy

As a widely used material in aerospace and medical industry, Ti6Al4V titanium alloy is regarded as difficult-to-machine. In this study, aCN/TiAlN coating was deposited on carbide cutting tools as an attempt to increase the machinability of this alloy. Wear behavior and cutting performance of the aCN/TiAlN coated carbide tools in face milling of Ti6Al4V were investigated under dry conditions. The effect of coating on cutting forces, chip formation and surface integrity of the workpiece with regard to surface finish was investigated. Mechanical and tribological properties of coated samples were characterized by nanoindentation, scratch test, 3D-profilometer, confocal microscope and pin-on-disc test. SEM was employed in combination with EDS for structural and compositional characterization of worn samples. According to the results, abrasive wear and adhesive wear are dominant tool failures on the coated tools. Higher wear resistance and ~15% longer lifetime were obtained with aCN/TiAlN coated carbide tools in milling of Ti6Al4V. The coating proved to be effective on chip formation and workpiece surface finish. Due to its superior properties in terms of adhesion, wear resistance, surface finish and chip formation, aCN/TiAlN coating is a good candidate for use in face milling of Ti6Al4V alloy.

Investigation on the effect of copper tool’s grain refinement on surface finish in EDM processing

Abstract. Electrical discharge machining is a modern machining method. With the ever-increasing industrial developments, much research is conducted to improve the output parameters of this process. Meanwhile, previous studies have considered changing the structure and properties of the machining tool materials through different methods as an approach to improve such parameters. The extrusion process or the equal channel angular pressing is a new and efficient method for the production of fine-grained high-strength materials with desirable mechanical and physical properties which can also be used as a new method to improve machining conditions. This study investigated the effect of extruding the electrical discharge machining tool through this method on the output parameter of workpiece surface finish. The machining tool was made of pure copper, and the extrusion process was performed in four and eight stages. Grain size was determined using EBSD. Tool conditions, spark current, and pulse on-time were considered as variable parameters, each of which was changed in three levels. Test results showed that extruding the copper tools reduced the workpiece surface finish quality by 14.1%.

Effect of cutting edge preparation on tool performance in hard-turning of DF-3 tool steel with ceramic tools

This study presents an experimental investigation on turning hardened DF-3 tool steel (∼58HRC) with PVD-TiN coated mixed ceramic. We focused on the effect of chamfer and honed edge geometry on tool wear, tool life, cutting forces and surface finish of the machined workpiece. The effects of the process parameters on performance characteristics were investigated using ANOVA. It was found that longer tool life was recorded with chamfered edge geometry at various cutting conditions. The typical damage observed as flank and crater wear for ceramic tools and abrasive wear was found as the main mechanism.The optimal cutting speed was 155 m/min, with which a tolerable tool life and volume of material removal was obtained for both edges geometry. Finer machined surface was left by chamfered tool with feeds and speeds in the range of 0.125–0.05 mm/rev and 155–210 m/min, respectively; also, cutting forces decrease with increased cutting speed. The obtained consequence of cutting forces shows that tool wear has a considerable effect on cutting forces and greater forces values recorded with honed tools.

Influence of Cutting Speed and Offset Distance over Cutting Tool Vibration in Multi-Tool Turning Process

Multi-tool turning process employs more than one cutting tool for machining the work piece simultaneously. In the conventional turning process, effect of machining parameters over cutting forces, vibration, work piece surface finish and dimensional tolerances have been discussed in detail, however no attempt has been made in the multi-tool turning process. Cutting tool vibration is very important as it reveals the condition of cutting tool as well as work piece quality. In this study, a second cutting tool is introduced at the rear side of the lathe with some distance from conventional front cutting tool to machine the work piece simultaneously. Accelerometers are used to measure the vibration signals in the tangential direction of cutting. Obtained time domain vibration signals are converted to frequency domain signals by Fast Fourier Transform to reveal its power spectral density. In this work cutting speed and distance between front and rear cutting tool are varied to understand the cutting tool vibration. With increase in cutting speed and increase in distance between front and rear cutting tool, vibration reduces.