Variable Feed Rate Research Articles

Effects of machining conditions on the hole wall delamination in both conventional and ultrasonic-assisted CFRP drilling

The need of carbon fiber–reinforced plastics (CFRP) has been driven by the increasingly wide applications in many industrials including sports, transportation, and energy. However, until now, the poor machinability of CFRP can be still considered the key problem and the most urgent machining-induced issue can be the delamination damage in the drilling process. Although many efforts have been paid to investigate this topic, most of them investigated the delamination at either the hole entrance and the exit. Very few of these studies focused on the internal delamination defects on the hole wall, although these internal defects can be as important as the entrance and exit defects. To fill this gap, this paper investigated the condition effects (feed rate, spindle speed, ultrasonic vibration of drills, and the workpiece support strategy) on the delamination in CFRP drilling, with the special focus on the internal delamination damage on the inside hole walls. Based on both the experimental and theoretical analysis, the effectiveness of the back supports and the variable feed rates was investigated as well. Considering few published studies reported the delamination on the hole wall, the key findings in this paper are expected to be meaningful to deepen the understanding of CFRP drilling and helpful to provide some industrial guidance.

An evaluation of fluid distribution at the implant site during implant placement by using a computational fluid dynamics model

Statement of problemHeat reduction during implant site preparation is critical. However, studies that assess fluid distribution at the implant site by using saline irrigation as the cooling method during osteotomies are lacking. PurposeThe purpose of this study was to evaluate the effect of various parameters on fluid distribution at the implant site by using a computational fluid dynamics numerical model and thus predict the cooling effect at the drill site. Material and methodsThe computational fluid dynamics code Flow-3D was adopted to simulate implant site preparation. A 10-mm-deep implant site was prepared by using a 2.2-mm pilot drill, with 4 °C saline sprayed onto the drill from an external injection hole. Different drilling procedures were performed with irrigation volumes of 20, 40, 60, and 80 mL/min at various drill speeds (600, 800, 1000, 1200 rpm) and feed rates (0.5, 1.0, 1.5, 2.0 mm/s), and the fluid distribution under various circumstances was respectively investigated and compared. Data were analyzed by using 1-way ANOVA or the Friedman test according to the normality of the data distribution (P>.05). ResultsBelow the irrigation volume of 60 mL/min, the saline inside the implant site increased with the irrigation volume (P<.001), but further increase in irrigation volume to 80 mL/min had no significant influence on the fluid distribution (P>.05). The obtained fluid had an inverse relationship with the drill speed under the irrigation volumes 20 and 40 mL/min (P<.001), and deeper areas received less cooling under 20 mL/min (P<.001). However, no significant differences were observed under 60 and 80 mL/min (P>.05). In addition, the variation of feed rate had no significant effect on the mean fluid fraction for all the tested groups (P>.05). ConclusionsThe fluid distribution at the implant site could be affected by the irrigation volume and drill speed but was not correlated with the feed rate.

ENERGY-BASED CHARACTERIZATION OF PRECISION HARD MACHINING USING PARTIALLY WORN CBN CUTTING TOOLS

This paper highlights the performance of precision hard turning with CBN cutting tools from energy point- of-view with additional tool wear effect. For this purpose several wear tests were performed during which the tool nose wear VBC and the corresponding changes of component forces Fc, Ff and Fp were continuously measured. Based on the measured forces and geometrical characteristic of the uncut layer, specific cutting and ploughing energy were determined for several combinations of cutting parameters. Consequently, changes of energy consumption resulting from tool wear evolution for variable feed rate, depth of cut and tool nose radius were presented.

Model Predictive Control for Real-Time Point-to-Point Trajectory Generation

The problem of planning a trajectory for robots starting in an initial state and reaching a final state in a desired interval of time is tackled. We propose an approach based on model predictive control to solve the problem of point-to-point trajectory generation for a given final time. We discuss various choices of models, objective functions, and constraints for generating trajectories to transfer the state of the robot, while respecting physical limitations on the motion as well as fulfilling computational real-time requirements. Extensive simulation results illustrate the use of the approach, and experiments on an industrial robot in a challenging ball-catching task show the effectiveness of the approach also in demanding scenarios with real-time constraints on the computation. Note to Practitioners —This paper was motivated by the problem of generating movements to transfer a robot from its current state to a new position and velocity at a certain time, when the target state and the final time may require correction at a high rate. For example, for picking small objects from a conveyor belt with a variable feed rate, an off-line planning would fail, since the motion has to be adjusted as soon as the speed is changed. Under the assumption that the desired pickup position and velocity and arrival time can be predicted, the approach in this paper is applicable. The movements can be optimized, for example, for energy efficiency or for reduction of vibrations in the robot. We discuss how to mathematically express the desired performance criteria and other requirements on the motion, such as not violating a maximum joint speed. Quick reactions to sensor inputs are computationally demanding. Thus, we limit ourselves to a class of motion-generation problems that lends itself to numerical optimization. Additionally, we save computation power by gradually refining the motion.

Increased thermal inertia of ball screws by using phase change materials

A major issue by implementing ball screw drives in machine tools is the occurrence of transient thermal fluctuations in normal operation leading to unsteady thermal distortions, especially at highly variable feed rates. One way to overcome this issue and thereby improve the thermoelastic machine performance is through thermal management solutions. The objective of this work is the reduction of temperature fluctuations by increasing the thermal inertia of ball screws. For this aim, a latent heat storage unit was designed based on phase change materials. In addition, a thermal resistance network was developed for evaluation of the ball screw behaviour. Functional validation of the developed system was carried out on a ball screw test rig.

Experimental analysis of ductile-brittle transitions for parallel and intersecting micro-slot grinding in BK-7 glass

In real scenario, along with parallel micro-slots/channel, intersecting micro-slots are also needed in optical industry or microfluidics sector. This paper, therefore, investigates the material removal mechanism and analyzes the damage occurrence for parallel as well as intersecting micro-slot grinding. Micro-slot grinding of BK7 glass is performed using a modified polycrystalline diamond micro-tool at wide range of feed rate keeping tool rotational speed and depth of cut constant. During single/parallel micro-slot grinding, two critical steps of undeformed chip thickness for transition from ductile to ductile-brittle regime and for transition from ductile-brittle to brittle regime are instituted to be 15.72 nm and 29.80 nm, respectively, based on edge crack length and surface topography analysis. Damage and chipping at the intersection of micro-slots intersecting at different intersection angles of 90, 60 and 45° are observed and it is found that chipping quantity is higher at the intersecting locations due to possible crack growth and crack superimposition. As the intersecting angle reduces from 90° to 60 and further to 45°, damage at the corners having less load bearing areas are found to be significantly enhanced due to multiplied chances of crack superimposition. Finally, critical chip thickness values to fabricate parallel and intersecting micro-slots in BK7 glass are determined. As critical chip thickness value reduces at the intersection, adoption of variable feed rate during intersecting micro-slot fabrication is also suggested and validated with confirmation experiments.

Experimental investigation on novel drilling strategy of CFRP laminates using variable feed rate

This study focused on the influences of drilling parameters on hole quality and thrust force in drilling of carbon fiber-reinforced polymer (CFRP) composite laminates via variable feed rate. Drilling experiments were carried out by using three different cutting speeds, feed rates and the qualities of tungsten carbide drill. Scanning electron microscopy and coordinate measurement machine were used for hole surface damage and diameter analyses, and also a portable instrument and 3D optical profilometer were utilized for surface roughness measurement. It was identified that thrust force (Fz), delamination factor (Fd) and average surface roughness (Ra) values attained in drilling processes by variable feed rate are lower than those of constant feed rate with average of 14%, 3% and 18%, respectively. Besides, the hole diameter (D) values obtained with variable feed rate in hole exit were higher than those of constant feed rate. Moreover, the higher Fz values were obtained with diamond-coated and TiAlN-coated drills than those of uncoated drill with 55% and 77%, respectively. The interactive influences of drilling parameters on machinability factors were evaluated via analysis of variance, and then, the most significant parameter was specified as the feed rate for Fd, just as the drill quality for Fz, Ra and D. According to the experimental and statistical results, we suggested that the novel drilling strategy is a significant alternative for the step hole and conventional drilling of CFRP laminates.

Impacts of seasonal variation and operating parameters on double-stage trommel performance

The high-level objective of this research was to quantify and assess impact of uncertainties of trommel screening with respect to feed-rate variation, clogging of screen apertures, and seasonal variation in waste characteristics, including particle size distribution (PSD) and composition using full-scale trials. A two-stage trommel screen which is operated at a municipal solid waste processing facility located in a cold region (Edmonton, Canada) was evaluated. The waste processed was co-mingled refuse with the recyclable material removed. The variation of size separation mass balance and recovery with respect to total and overs loading feed rate, season and operation time were monitored. The characteristics of the feedstock and separated waste streams were determined by sieve and compositional analyses. Separation and recovery results verified that the performance of the first stage where <5 cm of organic-rich waste was screened out, varied seasonally. Further, a strong linear correlation was obtained between recovery results and corresponding overs loading rate that varied between seasons. This correlation also varied within operation cycle during the winter trials due to clogging of screens. An equation is proposed to quantify clogging formation according to operation uptime and feed rate. Waste characterization results indicated the waste generated in the winter, spring, and summer had three distinct PSDs, especially the compostable fraction, contributing to the seasonality in trommel performance. In contrast, the PSD of the combustible fraction remained consistent in all seasons. This research successfully quantified the impact of uncertainties of full trommel operations in different seasons and during the operation cycle.

Trajectory generation in 5-axis milling of freeform surfaces using circular arc approximation and its influence in surface roughness

Current methods used to generate toolpath in 5-axis machining, multiply the program lines when the precision is sought, producing a deficient approach to the points and a highly variable feed rates. These factors cause geometric imprecision and poor surface finishes. In this work, a new method for approximating trajectories through circular arcs between selected points has been developed. It has been checked through the machining of an elliptical toroid surface and its results have been compared with those produced by other CAM strategy. The part produced by the new method shows a considerable improvement in the surface roughness.

Effect of cryogenic coolant on turning performance: a comparative study

In the recent years, environmental regulations became stringent in terms of disposal of chemically contaminated conventional coolants. Cryogenic cooling is an alternative technique to the conventional cooling technique with conventional coolants. In this work, new findings were reported in turning of 17-4 precipitation hardenable stainless steel (PH SS) at varying feed rate conditions under cryogenic cooling and the results were compared with the minimum quantity lubrication (MQL), conventional wet and dry cutting conditions, respectively. Turning performance considered in this work includes cutting temperature, surface roughness and tool wear. From the findings, it was noticed that a maximum of 24%, 26% and 69% reduction in surface roughness was observed in cryogenic machining when compared to MQL, wet and dry environments, respectively. Also, the maximum flank wear reduction found in cryogenic machining was 42%, 48% and 53%, respectively, over the MQL, wet and dry environments. Overall, it was concluded that cryogenic machining is a feasible method for improving the turning performance characteristics in machining of 17-4 PH SS.

Dynamic Indicators of a Corn Ear Threshing Process Influenced by the Threshing-Separation Unit Load

Corn ear feed rate variations in the threshing-separation unit of a combine harvester have a significant impact on the dynamic indicators of the threshing process. In this study, we conducted experiments using a stationary tangential threshing device and measured the forces acting on the rear part of the concave as well as the torque of the rotating cylinder during a threshing process. The ThreshLab software was developed for this purpose. We found that increasing the corn ear feed rate made the threshing process more even, due to decreasing the fluctuation of forces acting on the rear part of the concave and torque of the rotating cylinder. The corn ear threshing process may be more stable if the threshing cylinder is fitted with filler plates (FP-II). A comparison of the results obtained for variations in the forces acting on the rear part of the concave with those obtained for variations in the total torque of resistance and the speed of the threshing cylinder revealed a linear correlation between these parameters at varied feed rates.&#x0D; DOI: http://dx.doi.org/10.5755/j01.mech.24.4.20721

An investigation into the effect of surface integrity on the fatigue failure of AISI 4340 steel in different drilling strategies

Abstract DTH bits often fail because of fatigue fracture at the machined holes location. In order to understand the failure mechanism and improve the fatigue life of drill bits, the effects of drilling parameters and surface integrity on fatigue life of the AISI 4340 holed samples have been investigated. Three hole making strategies, including drilling with and without pre-drill and helical milling were utilized and compared. Results showed that the fatigue life increased by raising the cutting speed and decreasing the feed rate. The only exception was the two-fold variations of fatigue life versus feed rate when using pre-drill. Besides, the higher fatigue life was achieved in drilling with pre-drill, helical milling and conventional drilling, respectively. In fact, using pre-drill resulted in a better surface integrity compared to conventional drilling and higher work hardening relative to helical milling. Also, images of fractured surfaces represented radiation of discontinuous fatigue cracks from an initiation site near the hole middle plane.

Optimization and characterization of friction surfaced coatings of ferrous alloys

Abstract In the present work, the scientists were successful in obtaining a friction surfaced coating of mild steel over mild steel, mild steel over stainless steel (AISI 304) and stainless steel over stainless steel using a low-cost conventional milling machine. A 22 factorial method with three replications was used to design the experiments. The influence of variation in rotational speed (1400 rpm and 1000 rpm) and table feed rate (4.17 mm/s and 2.67 mm/s) on coating width, thickness and interface temperature of the coating and substrate was investigated. Multi-response optimization was performed and the developed model was validated by confirmatory experiments. The results showed that, with an increase in rotational speed and table feed rate, width and thickness of the coating decreases, while temperature increases. An infrared (IR) camera provided thermographs that elaborated the distinct stages of heat dissipation during the process of coating formation. The bond integrity and strength of the coating was analyzed by bend tests and Vickers micro hardness test. The results revealed that a higher hardness value was obtained at the interface of the coating as compared to coating and interface.

Fabrication and Characterization of a Thin, Double‐sided Air Breathing Micro Fuel Cell

AbstractAn air‐breathing micro fuel cell (μFC) with laterally fed porous anode electrode is realized and reported. The performance of this microdevice with embedded flow channels and electrodes is characterized in ambient conditions. To realize this device, we used negative epoxy‐based photoresist (SU‐8) as a stamp to transfer a microchannel pattern into a Nafion 1110 membrane by micro hot embossing. A Nafion 212 layer served to seal the device as a blanket top layer. The fabrication process of microchannels and μFC assembly is evaluated with optical and scanning electron microscopy (SEM) step by step. Variations of hydrogen feed rate on performance are investigated. The cell is composed of two individual fuel cells with a shared anode. The characteristics of the cell are further studied by performance and electrochemical impedance spectroscopy (EIS) measurements of the separate constituent cells and compared with data for the complete cell. The maximum power density per superficial (footprint) area is 68.4 mW cm−2 for the shared anode stack. In the present μFC architecture, the external packaging is Nafion polymer, which results in a thin and light energy source with simplicity of manufacturing. The device performance offers a high volumetric and gravimetric energy density for portable applications.

What drives interaction strengths in complex food webs? A test with feeding rates of a generalist stream predator.

Describing the mechanisms that drive variation in species interaction strengths is central to understanding, predicting, and managing community dynamics. Multiple factors have been linked to trophic interaction strength variation, including species densities, species traits, and abiotic factors. Yet most empirical tests of the relative roles of multiple mechanisms that drive variation have been limited to simplified experiments that may diverge from the dynamics of natural food webs. Here, we used a field-based observational approach to quantify the roles of prey density, predator density, predator-prey body-mass ratios, prey identity, and abiotic factors in driving variation in feeding rates of reticulate sculpin (Cottus perplexus). We combined data on over 6,000 predator-prey observations with prey identification time functions to estimate 289 prey-specific feeding rates at nine stream sites in Oregon. Feeding rates on 57 prey types showed an approximately log-normal distribution, with few strong and many weak interactions. Model selection indicated that prey density, followed by prey identity, were the two most important predictors of prey-specific sculpin feeding rates. Feeding rates showed a positive relationship with prey taxon densities that was inconsistent with predator saturation predicted by current functional response models. Feeding rates also exhibited four orders-of-magnitude in variation across prey taxonomic orders, with the lowest feeding rates observed on prey with significant anti-predator defenses. Body-mass ratios were the third most important predictor variable, showing a hump-shaped relationship with the highest feeding rates at intermediate ratios. Sculpin density was negatively correlated with feeding rates, consistent with the presence of intraspecific predator interference. Our results highlight how multiple co-occurring drivers shape trophic interactions in nature and underscore ways in which simplified experiments or reliance on scaling laws alone may lead to biased inferences about the structure and dynamics of species-rich food webs.

Feedrate modulation for accurate traversal of trimmed planar offset paths

In milling planar shapes with cylindrical tools, CNC machines must employ tool paths offset from the desired part shape by the tool radius. To prevent gouging the part geometry and to ensure continuous paths, the offset path construction invokes trimming and filling operations at tangent discontinuities of the part shape, and smooth concave regions where the tool radius exceeds the part radius of curvature. A constant feedrate of the tool center along the offset path can result in large chip load variations. Conversely, a variable feedrate that (approximately) achieves a constant chip load can cause large acceleration/deceleration rates at the tool center. Moreover, feedrate reduction is required in the vicinity of the trimmed offset path tangent discontinuities, to ensure accurate execution and to minimize vibrations. A feedrate modulation methodology for trimmed offset paths is proposed, incorporating user-specified parameters to balance the competing demands of minimizing path contour error, chip load variations, and the overall traversal time. The feedrate modulation scheme is compatible with simple real-time interpolator algorithms, and its practical performance is demonstrated by real-time data obtained from several experiments performed on a CNC mill with an open-architecture software controller.

Effect of hybrid wire EDM conditions on generation of residual stresses in machining of HCHCr D2 tool steel under ultrasonic vibration

This experimental examination exhibit a novel Hybrid Wire electrical discharge machining (H-WEDM) process of ultrasonic vibration combined with traditional Wire-EDM. The metal cutting for form tool and extrusion die with WEDM is liked to give better surface morphology. The effect of residual stresses has been dissected for H-WEDMed machined surface alongside the surface roughness and erosion rate to enhance surface integrity and longer service life of High Carbon High Chromium D2 tool steel. The process parameters chose for this investigation are type of vibration continuous/discontinues, amplitude of vibration, workpiece dimension, duty cycle, peek current and wire feed rate with objective to optimize the residual stresses and erosion rate. Portable X-ray Residual Stress Analyzer, a non-destructive X-ray analyzer is used to measure the residual stress efficiently by detecting the full Debye ring data from a single incident X-ray angle and Non goniometer stage influence on the measurements. An endeavor was made to compare the residual stresses for continuous/discontinues vibration and without vibration. The impacts of amplitude of vibration, peak current, duty cycle and wire feed rate variations on erosion rate was study using Taguchi method. From experimental study, it was observed that discontinuous vibration enhances the erosion rate and diminishes the resultant stresses. High Peak current and duty cycle altogether deteriorate the surface texture, which creates high tensile residual stresses because of debris and micro cracks. The optimum value of residual stresses 86.53 MPa and material erosion rate 6.45 mm/min was achieved using H-WEDM.

Investigating tool wear mechanisms in machining of Ti-6Al-4V in flood coolant, dry and MQL conditions

The objective of this study is to identify and explain tool wear mechanisms that dominate during machining of titanium alloy Ti-6Al-4V in dry, flood coolant, and minimum quantity lubrication (MQL) conditions. A series of experiments were conducted using end milling of Ti-6Al-4V by varying feed rate and depth of cut, while the cutting speed was kept constant at comparatively higher cutting speed. Both uncoated and titanium aluminum nitride (TiAlN)-coated carbide tools were used for machining Ti-6Al-4V at the same settings of parameters. It was observed that abrasion was the most dominant tool wear mechanism for all dry, flood coolant and MQL machining conditions. Edge chipping and tool nose wear were the next dominating tool wear mechanisms in conventional flood coolant machining, which may be associated with the thermal fatigue caused by the periodic cooling of tool tip from the high temperature generated during machining. On the other hand, adhesion was the second most dominant tool wear mechanism in the dry machining. Both the edge chipping and adhesion of chips to the cutting tools were reduced significantly in MQL machining. The delamination of coating film was observed when TiAlN-coated carbide tools were used for machining Ti-6Al-4V. The delamination was more significant in wet and MQL machining compared to dry machining, indicating the effectiveness of coated tools in dry machining condition compared to wet and MQL machining conditions. Among three conditions, MQL provided the least occurrences of tool wear, indicating suitability of MQL in productive machining of titanium alloys.

Experimental Study of Deflection and Surface Roughness in Thin Wall Machining of Aluminum Alloy

Thin walled structures and other monolithic components are used in aerospace as well as automobile industries. They have structural homogeneity and excellent strength to weight ratio. Ribs, stingers, spars and bulk heads are few other monolithic components. These monolithic components are also used as structural parts. More workpiece material is removed in end milling, which is possible athigh speeds. In thin wall machining, thickness of wall is reduced graduallyduring cutting, which makes ita very complicated process. At high speed, deflection of the machinedthin wall work piece is expected due to end mill forces, machining error and reduced machining accuracy. In this current study, the thin wall aluminium workpiece is fabricated using high end milling speeds and deflections as well as surface roughness of thin walls are investigated.The work piece is machined on conventional milling machine. Experiments are carried out to study the deflection and surface roughness of the thin walls of the work piece at varying feed rate, speed and depth of cut. Deflections and surface roughness of thin walls are measured by optical microscope and non-contacting surface profilometer. The effects of process parameters on the deflection and surface roughness of thin walls are analysed by ANOVA regression technique.

Improvement of boring quality of CFRP and evaluation of tool wear by inclined planetary milling

In recent years, CFRP is widely used as an alternative structural material to improve fuel consumption with high strength and light weight comparing to conventional aluminum alloy.CFRP is also expected to be the structural material for next generation automobiles - especially electric vehicles - in order improve fuel and/or electric power efficiency. However, CFRP is categorized as one of the difficult-to-cut material and burrs and delamination could occur with conventional drilling and cutting ways due to their severe cutting tool wear. For above mentioned reasons, in order to improve the machinability of CFRP drilling situations, the authors have proposed the inclined planetary milling process as a novel high quality boring technique for CFRP.According to our past experiments, the effectiveness for reduction of burrs and delamination of CFRP boring by the inclined planetary milling has been demonstrated. However, demands for higher speed and wear resistance of cutting tools are rising in the industrial field. The objective of the study is to achieve shorter processing time of CFRP boring and reduction of tool wear with maintaining high bore quality. The authors have carried a set of experiments for evaluating the relationship between feed rate variations and bore quality transition. The workpiece materials were unidirectional and fabric CFRP stack plates and the cutting tool shape was corner radius end-mill. From the experimental results, it was confirmed that the feed rate per one cutting edge strongly affected the generation of cross-sectional profile of the bore. This was also theoretically confirmed by our developed kinematic cutting model of the inclined planetary milling theoretically.In the article, the optimal cutting conditions of the inclined planetary milling for CFRP boring and factorial effect of feed rate to the bore quality are reported.