Bulk Material Removal Research Articles

Design and optimization of unit production cost for AWJ process on machining hybrid natural fibre composite material

It is very difficult to handle composite material using cutting edge process. The surface defects, fibre – matrix delamination, fibre pullouts and bulk material removal are some of the common effects while machining composite material. To reduce such machining effects, an advanced machining processes are suggested for difficult to cut composite materials. In this research, a hybrid natural fibre composite material is developed inhouse to study the performance of machinability through abrasive water jet cutting process. The natural composite material is developed with two filler materials such as palm and coconut shell powder. During machining the water jet pressure, nozzle traverse speed and standoff distance are varied to predict the optimal process condition. Further the unit production cost for two different combination of material is optimized using a natural evolutionary based genetic algorithm. It was found that the unit production cost for 10 wt% filler reinforce natural fibre composite yields maximum production cost compared to 7.5 wt% filler material reinforcement for nearby machining process parameters. The variation in production cost is due to the influence of mechanical cum metallurgical quality, distribution and densification of filler material reinforced. The level of experiments is also validated using regression analysis.

Anomalous enhancement of focused ion beam etching by single raster propagating toward ion beam at glancing incidence

Focused ion beam (FIB) sample preparation for electron microscopy often requires large volumes of materials to be removed. Prior efforts to increase the rate of bulk material removal were mainly focused on increasing the primary ion beam current. Enhanced yield of etching at glancing ion beam incidence is known but has not found widespread use in practical applications. In this study, etching at glancing ion beam incidence was explored for its advantages in increasing the rate of bulk material removal. Anomalous enhancement of material removal at glancing angles of ion beam incidence was observed with single-raster etching in along-the-slope direction with toward-FIB direction of raster propagation. Material removal was inhibited in an away-from-FIB direction of raster propagation. The effects of glancing angles and ion doses on depth of cut and volume of removed materials were also recorded. We demonstrated that the combination of single-raster FIB etching at glancing incidence in along-the-slope direction with toward-FIB raster propagation and a “staircase” type of etching strategy holds promise for reducing the processing time for bulk material removal in FIB sample preparation applications.

Mode transition from adsorption removal to bombardment removal induced by nanoparticle-surface collisions in fluid jet polishing

The effects of impacting particles from a jet of liquid on the removal of a surface material (on the impacted workpiece) were investigated. Experimental observations show that the cross section of the material removed changed from ‘W’-shaped to ‘U’-shaped as the size of abrasive particles was increased. Comparisons between removed material profiles and particle collision distributions indicate that the particle-surface collisions are the main reason for the material removal. The deduced number of atoms removed by a single collision implies that a transition occurs in the removal mode. For nanoscale particles, the polished surface is likely to be removed in an atom-by-atom manner, possibly due to the chemisorption of the impacting particles on the impacted surface. Contrarily, for the case of microscale particles, bulk material removal produced by particle bombardment is more likely to occur. The present mechanism of material removal for particle-surface collisions is further corroborated experimentally.

Theoretical Study of Path Adaptability Based on Surface Form Error Distribution in Fluid Jet Polishing

In the technology of computer-controlled optical surfacing (CCOS), the convergence of surface form error has a close relationship with the distribution of surface form error, the calculation of dwell time, tool influence function (TIF) and path planning. The distribution of surface form error directly reflects the difference in bulk material removal depth across a to-be-polished surface in subsequent corrective polishing. In this paper, the effect of path spacing and bulk material removal depth on the residual error have been deeply investigated based on basic simulation experiments excluding the interference factors in the actual polishing process. With the relationship among the critical evaluation parameters of the residual error (root-mean-square (RMS) and peak-to-valley (PV)), the path spacing and bulk material removal depth are mathematically characterized by the proposed RMS and PV maps, respectively. Moreover, a variable pitch path self-planning strategy based on the distribution of surface form error is proposed to optimize the residual error distribution. In the proposed strategy, the influence of different bulk material removal depths caused by the distribution of surface form error on residual error is compensated by fine adjustment of the path spacing according to the obtained path spacing optimization models. The simulated experimental results demonstrate that the residual error optimization strategy proposed in this paper can significantly optimize the overall residual error distribution without compromising the convergence speed. The optimized residual error distribution obtained in sub-regions of the polished surface is more uniform than that without optimization and is almost unaffected by the distribution of parent surface form error.

Multiphysics Modeling of Surface Finishing Performance in Pulsed-Waveform Electrochemical Machining

Electrochemical machining (ECM) is a manufacturing technology that allows metal to be precisely removed by electrochemical oxidation and dissolution into an electrolyte solution. ECM is suited for machining parts fabricated from “difficult to cut” materials and/or parts with complicated and intricate geometries. In ECM, the workpiece is the anode and the tool is the cathode in an electrochemical cell; by relative movement of the shaped tool into the workpiece, the mirror image of the tool is “copied” or machined into the workpiece. One notable difficulty with ECM is an inability to predict a priori the tool and process parameters required in order to satisfy the final specifications of the fabricated part [[1]]. Accordingly, there is potential value in development of a physical phenomenon-based design platform to predict optimal ECM tool shape. Such a capability is anticipated to dramatically shorten the process/tooling development cycle. A further goal of ECM is to simultaneously achieve a target surface finish on the machined part. It is thus of interest to develop the capability also to predict the distribution of local surface finish resulting from ECM processing. Modeling of the changes in local surface finish intrinsically operates on a different length scale from that of bulk material removal (μm, versus mm or cm), and thus is most easily treated separately. The physicochemical phenomena involved in the evolution of surface finish during ECM processing are strongly coupled, and include the electric field itself (primary current distribution), surface polarization and electrochemical kinetics (secondary current distribution), and fluid flow and mass transfer (tertiary current distribution). Of particular interest is modeling of pulsed-waveform ECM, for which significant practical advantages have been demonstrated [[2],[3],[4]]. While an extensive body of literature exists analyzing pulsed electrodeposition [[5],[6]], comparatively little work has been published to date on pulsed ECM [[7],[8]]. This talk will discuss recent modeling work seeking to develop a solid foundation for a predictive understanding of the surface finishing aspects of ECM processes. The work described herein encompasses time-dependent modeling of concentration profiles and other relevant physical quantities under the application of pulse(-reverse) current ECM waveforms, starting from simulations assuming a locally flat surface and working toward quantitative descriptions of the transient and steady-periodic behavior on structured substrates. Prior work (see, e.g., Ref. 3) has demonstrated the value in differential pulsed-ECM processing of surfaces with features of size comparable to or larger than the hydrodynamic boundary layer thickness (“macroprofiles”) versus surfaces with features much smaller than the boundary layer thickness (“microprofiles”). Figure 1 (left) plots a schematic of the pulsating concentration profiles at the end of the pulse on-time in forward-only pulsed ECM, assuming 100% current efficiency. Here, the pulse period (ton + toff) and the peak applied current density (jpeak) are assumed constant, with the curves corresponding to different values of ton. The saturation concentration of the dissolved metal is Cs, and the bulk metal concentration Cb equals zero. The quantity τ is the “transition time,” which is the value for ton for which the metal concentration at the surface rises exactly to Cs at the end of the forward pulse. As can be seen, for ton < τ, metal dissolution is not mass transfer limited, but for any ton > τ the rate of dissolution is constrained by the diffusion of the dissolved material, approaching the DC mass transfer rate for sufficiently high ton. Figure 1 (right) illustrates that preliminary simulations performed with COMSOL Multiphysics® exhibit behavior consistent with this qualitative concept.

Fundamental investigation on influence of external heat on chip formation during thermal assisted machining

Various heat sources have been investigated by numerous researchers to reveal machinability benefits of thermally assisted machining (TAM) process. Fewer engineering materials have been tested. In the same vein, those researches continue to demonstrate effective performance of TAM in terms of bulk material removal rate, improved surface finish, prolong tool life and reduction of cutting forces among others. Experimental investigation on the strain-hardenability and flow stress of material removed with respect to increase in temperature in TAM has not been given attention in previous studies. This study investigated the pattern of chip morphology and segmentation giving close attention to influence of external heat source responsible for strain – hardenability of the material removed during TAM and dry machining at room temperature. Full immersion down cut milling was used throughout the machining conditions. Machining was conducted on AISI 316L using uncoated tungsten carbide end mill insert at varying cutting speeds (V) of 50, 79, and 100 m/min, and feed rates (f) of 0.15, 0.25, and 0.4 mm/tooth while the depth of cut was maintained at 0.2mm throughout the machining trials. The analyses of chip formation, segmentations and stain hardenability were carried out by using LMU light microscope, field emission microscopy and micro indentation. The study observed that build up edge is formed when a stagnation zone develops in front of tool tip which give rise to poor thermal gradient for conduction heat to be transferred within the bulk material during dry machining. This promotes varying strain – hardening of the material removed with evident high chips hardness and thickness, whereas TAM circumvents such impairment by softening the shear zone through local preheat.

A novel method to recover DD fusion proton CR-39 data corrupted by fast ablator ions at OMEGA and the National Ignition Facility.

CR-39 detectors are used routinely in inertial confinement fusion (ICF) experiments as a part of nuclear diagnostics. CR-39 is filtered to stop fast ablator ions which have been accelerated from an ICF implosion due to electric fields caused by laser-plasma interactions. In some experiments, the filtering is insufficient to block these ions and the fusion-product signal tracks are lost in the large background of accelerated ion tracks. A technique for recovering signal in these scenarios has been developed, tested, and implemented successfully. The technique involves removing material from the surface of the CR-39 to a depth beyond the endpoint of the ablator ion tracks. The technique preserves signal magnitude (yield) as well as structure in radiograph images. The technique is effective when signal particle range is at least 10 μm deeper than the necessary bulk material removal.

Study on blasting erosion arc machining of Ti–6Al–4V alloy

Blasting erosion arc machining (BEAM) was applied to improve the machining efficiency of Ti–6Al–4V alloy. 5-factor, 2-level fractional factorial experiment was firstly employed to find out the main factors for MRR (material removal rate). According to the results of fractional factorial experiment, 3-factor, 2-level full factorial experiment was conducted to find out the relationship between machining performance and the main factors (peak current, pulse duration, and pulse interval) under the negative electrode machining. Results revealed that when peak current was 500 A and pulse duration was 8 ms, MRR could achieve 16,800 mm3/min, which means the specific energy efficiency was 33.6 mm3/(A · min). Then, MRR was optimized base on MATLAB optimization toolbox and could reach 20,100 mm3/min when adopting the optimized parameters (peak current 600 A, pulse duration 8.8 ms, and pulse interval 3.0 ms). Although TWR (tool wear ratio) can be effected by the machining parameters, it appeared to be stable (around 3 ± 1 %). Besides, the polarity effect was also studied, and flow field simulations were employed to illustrate the influence of feeding direction on the surface roughness. In addition, the machined surface was analyzed by utilizing SEM, EDS, XRD, etc. Results of the surface analysis disclosed that the oxygen content in the negative electrode machined surface was obviously higher than that in the positive electrode machined surface. Since the positive electrode machined surface was much smoother, it can be used to improve the surface quality while the negative electrode machining is suitable for the bulk material removal with high energy. Finally, a Ti–6Al–4V turbine blade sample was machined to demonstrate the feasibility of high efficiency BEAM in difficult-to-cut material processing.

Experimental investigations and development of cutting force model for self-propelled rotary face milling cutter in machining of titanium alloy

In self-propelled rotary tool machining, a circular cutting tool insert is used that continuously rotates about its axis during machining, as the tool is fed into the workpiece. The continuous rotation of the insert allows the insert to cool between engagements and improves tool life. In order to make use of this methodology for rough machining and bulk material removal in machining of aerospace materials, a self-propelled rotary face milling cutter is developed at Defence Research and Development Laboratory, Hyderabad. This cutter was developed to study the influence of inclination angle on the cutting forces generated during machining, and hence the cutter is provided with the provision to have the inclination angle of the insert for 20°, 30°, 40° and 50°. This article discusses the performance of the developed self-propelled rotary face milling cutter in face milling of titanium alloy at different inclination angles. The cutting forces developed in FX, FY and FZ directions are evaluated at different cutting speed, feed, depth of cut and inclination angles. The cutting forces obtained in self-propelled rotary face milling cutter is compared with that of conventional face milling cutter and the results are presented and discussed. Finally, regression models for prediction of cutting forces are developed.

Correlation-based smoothing model for optical polishing

A generalized model is developed to quantitatively describe the smoothing effects from different polishing tools used for optical surfaces. The smoothing effect naturally corrects mid-to-high spatial frequency errors that have features small compared to the size of the polishing lap. The original parametric smoothing model provided a convenient way to compare smoothing efficiency of different polishing tools for the case of sinusoidal surface irregularity, providing the ratio of surface improvement via smoothing to the bulk material removal. A new correlation-based smoothing model expands the capability to quantify smoothing using general surface data with complex irregularity. For this case, we define smoothing as a band-limited correlated component of the change in the surface and original surface. Various concepts and methods, such as correlation screening, have been developed and verified to manipulate the data for the calculation of smoothing factor. Data from two actual polishing runs from the Giant Magellan Telescope off-axis segment and the Large Synoptic Survey Telescope monolithic primary-tertiary mirror were processed, and a quantitative evaluation for the smoothing efficiency of a large pitch lap and a conformal lap with polishing pads is provided.

Experimental and finite element analysis of temperature and energy partition to the workpiece while grinding with a flexible robot

Grinding processes performed with flexible robotic tool holders are very unlike conventional types of grinding because of low stiffness of the robot's structure. A special flexible robotic grinding process is used for in situ maintenance of large hydroelectric equipment for bulk material removal over large areas rather than as a finishing step, as is the case for most conventional grindings. Due to the low structural stiffness of tool holder, cutting is interrupted at each revolution of wheel during the grinding process. In this study, an investigation is carried out to determine the temperatures and energy partition to the workpiece for the above-mentioned flexible robotic grinding process by a three-dimensional finite element thermal model. Experiments were undertaken using embedded thermocouples to obtain the subsurface temperature at several points in the workpiece during the process. Then, energy partition to the workpiece was evaluated using a temperature-matching method between the experimental and numerical results. This ratio is used for predicting the temperature field at the wheel–workpiece interface with a relevant heat source function. Kinematics of cut and the flexible robot's dynamic behavior are considered in applying the heat input to the model. The energy partition to the workpiece in this specific flexible grinding process is found to be lower than for analogous conventional precision grinding processes. Two models, one from the literature and one from the power model of the process, are modified and proposed for determining the energy partition. The results showed that the energy partition ratio decreases by increasing the process power. Also, this ratio slightly decreases at higher feed speeds. In addition, lower temperatures were seen at higher powers due to the lower intensity of heat input over a larger contact area. Experimental observations show close agreement between simulated contact temperatures and measured results.

Influence of flushing on performance of EDM with bunched electrode

The existing applications of electrical discharge machining (EDM) for bulk material removal are restricted by their comparatively low material removal rates. The bunched-electrode EDM proposed in this study, using the powerful multi-hole inner flushing, is an effective way of being released from this restriction. This paper investigates the mechanism by which flushing (flushing modes and flushing parameters) influences machining performance indices, i.e., material removal rate and tool wear rate, using experiments and simulations. Based on an investigation conducted, compared with traditional solid electrode with mono-hole inner flushing, a bunched electrode with multi-hole inner flushing endures higher peak current and results in larger material removal rate and higher relative tool wear ratio because of a more effective flushing process. By properly choosing inlet velocity and electrode effective-area ratio, a higher material removal rate is achieved and relative tool wear ratio is kept at a lower level.

Examination of the material removal mechanisms during the lapping process of advanced ceramic rolling elements

Two types of HIPed Si 3N 4 bearing ball blanks with different surface hardness and fracture toughness were lapped under various loads, speeds, and lubricants using a novel eccentric lapping machine. The lapped surfaces were examined by optical microscope and SEM. The experimental results show that the material removal rate for type 1 ball blanks were 3–4-fold of type 2 in most cases. Different lapping fluids affected the material removal rate at lower lapping loads, but they had much less influence on the material removal rate at higher lapping loads. The SEM micrographs reveal that the grain pullout prevailed on the lapped surface of type 1 ball blanks, and the surface of type 2 featured bulk material removal by microcracking. Under extreme high lapping load, surface cracks and damages were found, and SEM with EDX disclosed steel from the lapping plate had transferred to the ceramic ball surface. The preliminary conclusion is that the material removal mechanism during the lapping process of silicon nitride balls using this eccentric lapping machine is mainly mechanical abrasive wear. Lawn and Wilshaw's indentation model on brittle materials is used to explain the difference in material removal rate for the two types of ball blanks.