Negative Rake Angle Research Articles

Effect of Chip Morphology during Grinding Bearing Steel Using Single Layer Brazed and Galvanic Bonded Cubic Boron Nitride (cBN) Wheel

Chip formation in grinding involves high specific energy compared to other machining processes due to high negative rake angle of grains, adverse grinding process parameters and physical–mechanical properties of the workpiece material. This causes excessive friction between chip-grit and chip-bond interfaces as there are no free flow of chip between grits and work surface. It generates high heat, which can have harmful effects on workpiece surface in case of dry grinding. But single layer brazed type (BT) or galvanic bonded (GB) cBN wheel could be the solution for the above mentioned problem, as the protrusion and gap of the grits may be monitored during manufacturing. Unlike conventional grinding, the single layer counterpart produces favorable chips during grinding bearing steel in ductile mode with lesser grinding forces and specific energy. This investigation also shows that the chips of larger volume cannot be accommodated in the intergrit spaces, which are very small in the GB wheel due to dense grit distribution and shorter grit protrusion, whereas, even with such a large chip load, the BT wheel works effectively for wider and uniform spacing and larger protrusion of the grits.

On chip formation in cutting metallic materials using tools with a large negative rake

It has been noted that the chip formation mechanism in metal cutting with edge tools with a large negative rake angle γ is not fully understood. Methods for assessment of some chip formation characteristics are put forward and examples are given of how they are implemented during the comparison between calculated and experimental values for the case of cutting lead workpieces using tools with a rake angle γ ranging from zero to −60°.

Energy Cost Modeling for High Speed Hard Turning

This study presented an empirical study to model the cost of the energy for high speed hard turning. A set of experimental machining data to cut hard AISI 4340 steel was obtained with a different range of cutting speed, feed rate and depth of cut with negative rake angle. Regression models were developed by using Box-Behnken Design (BBD) as one of Respond Surface Methodology (RSM) collections. Neural network technique was deployed using MATLAB to predict the energy as a part of the artificial intelligent methods. The data collected was statistically analyzed using Analysis of Variance (ANOVA) technique. Second order energy prediction models were developed by using (RSM) then the measured data were used to train the neural network models. A comparison of neural network models with regression models is also carried out. Predictive Box-Behnken models are found to be capable of better predictions for energy within the range of the design boundary

Effect of Machining Parameters on Deformation Field in Machining by Finite Element Method

Formation of chip is a typical severe plastic deformation progress in machining which is only single deformation stage. The large strain, low temperature and deformation force are the major premises to create significant microstructure refinement in metals and alloys. A finite element method was developed to characterize the distribution of strain, temperature and cutting force. Effects of rake angle, cutting velocity and friction on effective strain, cutting force imposed in the chip are researched and the conditions which lead to the large stain deformation in machining are highlighted. The results of simulation have shown that chip materials with ultrafine grained and high hardness can be produced with negative tool rake angle at some lower cutting velocity.

Tool Life in High Speed Turning with Negative Rake Angle

The present work studies some aspects of turning process applied on mild steel using cermets tools at high speed cutting (1000mm/min) by using negative rake angle (0 to-12). The influence of increasing the cutting speed and negative rake angle on flank tool wear, cutting forces, feeding forces and tool temperature were analyzed. The research studies and concentrates on the tool life estimation and the effect of the negative rake angle and higher cutting speed on tool life. It was found that the maximum tool life is obtained in (-6) rake angle for the cutting parameters.

Flank Wear Modeling in High Speed Hard Turning by Using Artificial Neural Network and Regression Analysis

Predicting and modeling flank wear length in high speed hard turning by using ceramic cutting tools with negative rake angle was conducted using two different techniques. Regression model is developed by using design of expert 7.1.6 and neural network technique model was built by using matlab2009b. A set of experimental data for high speed hard turning of hardened AISI 4340 steel was obtained with different cutting speeds, feed rate and negative rake angle. Flank wear length was measured to train the neural network models and to develop mathematical model by using regression analysis. Predictive neural network models are found to be capable of better predictions tool flank wear within the range that they had been trained.

Modeling of grain refinement in aluminum and copper subjected to cutting

Plane-strain orthogonal cutting has recently been exploited as a means to refine the microstructure of metallic materials from tens of micrometers or greater to a few hundred nanometers. While experimental work has produced a significant body of knowledge with regard to microstructure and properties of machined materials, only a handful of studies can be found in the literature to discuss the microstructural evolution mechanism and to predict grain refinement during cutting. In this paper, dislocation density-based material models are developed to model grain size refinement and grain misorientation during cutting of Al 6061 T6 and OFHC Cu under various cutting conditions. It is shown that the developed CEL finite element model embedded with the dislocation material models captures the essential features of the deformation field and grain refinement mechanism during cutting. The model predicts the grains in the machined chips are refined from an initial size of 50–100μm to about 100–200nm for Al 6061 T6 and OFHC Cu at a low cutting speed of about 0.02m/s with negative rake angle tools. It is shown that a small applied strain, high cutting speed or high cutting temperature will all contribute to a coarser elongated grain structure during cutting.

Design of micro square endmills for hard milling applications

In experiments of machining hardened tool steels (such as AISI H11, H13, and D2, up to 56 HRC) by commercial Ø 0.5 mm square endmills, it is observed that the tested micro endmills showed severe wear at an early stage of the process due to chipping off around cutting edge corners, resulting in unsatisfactory tool life and product appearance (burr formation). Detailed examination of current tool geometry shows that it is mainly inherited from that of macro endmills, making the cutting edge corners the weakest part on the tool. As the micromilling process is characterized by small values of machining parameters, the cutting edge corners of the micro endmill are the most loaded part of the cutting edges. New design rules are studied for improving the stiffness and strength of micro endmills used in micro hard milling applications. Analytical modelling and finite element method analysis are used to aid the design of tool geometry. By using a larger neck angle, optimizing tool core geometry, and choosing a negative rake angle, tool stiffness and cutting edge strength are improved. The new endmill designs, both two-flute and four-flute, are tested in experiments on hardened tool steels and showed considerable lower tool wear and increased tool life. Furthermore, the geometrical accuracy and appearance of the workpiece (burr formation) has been improved drastically.

Finite Element Simulation of Quick – Stop Experiments for Better Understanding of Chip Formation in Grinding

Several authors have previously simulated chip formation and their behaviour at the orthogonal cutting process. In contrast the chip formation for grinding was less investigated. This paper introduces a quick-stop device which allows easy investigation of the chip formation for the grinding process. For this process a workpiece forced by compressed air is shot against a single grain diamond with a large negative rake angle. Cutting forces were measured with a piezo electric sensor and discussed for a cutting speed range from 10m/s up to 30m/s. In Abaqus/Explicit a lagrangian formulation based finite element model was built to describe the chip formation for the grinding process. Chip formation, stress and heat distribution in the workpiece material can be calculated by this simulation model. The material behaviour was described with the Johnson Cook law. The simulation results show a good correlation compared to the quick stop experiments. All in all this simulation leads to a better understanding of the chip formation during grinding.

A Lagrangian FEM Model to Produce Saw-Toothed Macro-Chip and to Study the Depth of Cut Influence on its Formation in Orthogonal Cutting of Ti6Al4V

The foundations of micro-milling are similar to macro-milling but the phenomena it involves are not a simple scaling-down of macro-cutting. The importance of the minimum chip thickness is one of the significant differences between the two processes. The lagrangian FEM model presented in this paper aims to study the depth of cut influence on chip formation of Ti6Al4V in orthogonal cutting. It is firstly used to compare the modelled saw-toothed macro-chip morphology and cutting forces to experimental cutting results from literature. Then a minimum chip thickness prediction is performed by decreasing the depth of cut. Finally this study is the opportunity to highlight the specific features of micro-cutting reported in literature, such as the effective negative rake angle of the tool or the size effect. The model presented brings therefore a numerical contribution to the comprehension of these phenomena.

3D laser investigation on micron-scale grain protrusion topography of truncated diamond grinding wheel for precision grinding performance

A grain tip (GT) truncation is proposed to truncate grain protrusion tips of #270 diamond grinding wheel in plunge grinding of hard and brittle material. In this study, a 3D laser microscopy was employed to measure the wheel working surface and parameterize its 3D grain protrusion topography. The objective is to investigate how micron-scale grain protrusion parameters influence grinding performance such as grinding force and surface roughness. First, the GT truncation was performed after dressing of diamond grinding wheel in grinding experiment of quartz glass; then its 3D grain protrusion topography was constructed by smoothing 3D measured noise, matching measured point cloud, transferring protrusion frame and extracting 3D diamond grains; finally, the grain protrusion parameters such as grain protrusion number, grain protrusion height, grain protrusion volume, grain rake angle, grain clearance angle, etc. were investigated in connection with ground surface and grinding force. It is shown that GT truncation averagely decreases grain protrusion number, grain protrusion height, grain protrusion volume, grain rake angle and grain clearance angle by about 44%, 74%, 75%, 24% and 70% on whole wheel surface, respectively. However, it greatly increases active grain number by about 32 times and active grain volume by about 181 times in actual grinding with the depth of cut in 1 μm, thus leading to a decrease (about 80%) in surface roughness and an increase (about 40 times) in grinding force. It is also found that truncated diamond grain tips are mostly shaped with nanometer-scale tip wedges along grain cutting direction, leading to about 75% very large negative grain rake angles and about 75% large grain clearance angles, thus contributing to ductile-mode grinding. It is confirmed that the active grain number and active grain volume for the actual depth of cut may be regarded as main grain protrusion parameters to evaluate and predict the precision grinding performance of a coarser diamond grinding wheel.

THE DETERMINATION OF SURFACE ROUGHNESS VIA FUZZY APPROACH IN TURNING

In this study, it has been aimed to predict adequate surface roughness values at turning operation that has important place in industry. The machining process in universal lathe is carried out on AISI 1040 steel in dry cutting condition using various approaching/entering angles, and rake angles, at depth of cut of 0,5 mm. Then surface roughness values were measured by using MAHR M1 perthometer. By using the data obtained from these experiments, Fuzzy Rule Based (FRB) approach was developed. The inputs of the developed FRB modelling were determined as tool nose radius (r), approach angle (κ), negative rake angle (γ) whereas output of system was surface roughness (Ra). This modelling was implemented by using MATLAB software. It has been seen that proposed model was applied successfully regarding to the comparison made between results of experiments and proposed FRB modelling.

Deformation Characteristics of Ultra-Fine Grained Al6061 Chip in Machining by Finite Element Method

Ultra-fine grained chips with higher hardness and strength than bulk can be produced by severe plastic deformation during orthogonal metal cutting. A finite element method was developed to characterize the distribution of stress, strain, strain rate and temperature in the deformation area at different rake angles and cutting velocities. The coefficient of friction in the tool-chip interface is approximately obtained according model of mean coefficient of friction which is based on experiments in any machining conditions. The formation mechanics of ultra-fine grained chip is discussed and effect of rake angle on microstructure of chips is highlighted. The results of experiment and modeling have shown that chip materials with ultra-fine grained and high hardness can be produced with more negative tool rake angle at some lower cutting velocity.

Study on Mechanism of Tap Breakage in Low Frequency Torsional Vibration Tapping

Early breakage of tap often occurs when tapping on difficult-to-cut materials with the method of low frequency torsional vibration tapping, which decreases the technological effect and restricts its application. The effect of impact load on tap breakage in vibration tapping was analyzed, and the stress state in tap teeth was simulated by FEM, on this basis, it is concluded that too large tensile stress in tap teeth is the main cause of early breakage of tap. To reduce the tensile stress and enhance the shock resistance of tap teeth, the tap should be ground to minor negative rake angle. Experiments showed that the failure mode of grinded taps changed to wear, and thereby the service life of tap was prolonged significantly.

Cutting force model of orbital single-point micromachining tool

This paper presents an analytical, ductile cutting force model of a novel micromachining tool that is based on micro-orbital motion of a single-point tool tip. The single-point tool tip used in this study is a single crystal diamond stylus that consists of a cone section of 50° and a spherical tip with radius less than 1 μm. The tool is actuated by a piezo tube that generates a high frequency micro-orbital motion of a single-point tool tip in a circular trajectory. Unlike conventional micromilling, where the cutting occurs at the edges of the tool flutes, a single-point tool may utilize any point on the circumference surface of the tool tip. Also, due to its extreme negative rake angle at small depths of cut, the technique can machine brittle materials such as silicon in the ductile regime. Experiments were performed on an aluminum alloy (AL2024) to obtain the specific cutting force and the coefficient of friction in order to calculate the cutting forces in all 3 axes and to verify the model.

Molecular dynamics investigations on polishing of a silicon wafer with a diamond abrasive

During the final stages of polishing silicon wafers, much of the interactions between silicon and diamond abrasive takes place at the silicon asperities. These interactions, leading to material removal, were investigated in a MD simulation of polishing of a silicon wafer with a diamond abrasive under dry conditions. Simulations were conducted with silicon asperities of different geometries, different abrasive configurations, and polishing speeds. Under the conditions of polishing, the silicon atoms from the asperities were found to bond chemically to the surface of the diamond abrasive. Continued transverse motion of the diamond abrasive (relative to the silicon asperity) leads to tensile pulling, necking, and ultimate separation of the silicon asperity material instead of conventional material removal in polishing (chip formation) involving cutting/ploughing, which takes place in the absence of chemical bonding between the abrasive and the asperity material. This phenomenon has not been reported previously in the literature. The thrust and cutting forces initially increase due to the increase in the number of asperity atoms affected finally reaching a maximum. This is followed by a decrease of these forces due to tensile pulling and formation of individual strings followed by ultimate separation or breakage of the final string. The ratio of thrust force (F z ) to the cutting force (F x ), i.e. |(F z /F x )| was found to increase continuously to a maximum of ∼0.8 followed by continuous decrease to ∼0.25. This is in contrast to a more or less constant value of ∼2 in the case of tools with rounded radii or tools with large negative rake angles, where material is removed in the form of chips ahead of the tool. Three regions of the asperity have been identified that are useful in the development of a phenomenological model for polishing that enables computation of material removal rates: (1) the region directly in front of the abrasive for which the probability of the removal of an asperity atom is close to unity, (2) the distant region where this probability is nearly zero, and (3) an intermediate region from which the probability of removal is close to half.

Statistical analysis of surface roughness and cutting forces using response surface methodology in hard turning of AISI 52100 bearing steel with CBN tool

The present work concerns an experimental study of hard turning with CBN tool of AISI 52100 bearing steel, hardened at 64 HRC. The main objectives are firstly focused on delimiting the hard turning domain and investigating tool wear and forces behaviour evolution versus variations of workpiece hardness and cutting speed. Secondly, the relationship between cutting parameters (cutting speed, feed rate and depth of cut) and machining output variables (surface roughness, cutting forces) through the response surface methodology (RSM) are analysed and modeled. The combined effects of the cutting parameters on machining output variables are investigated while employing the analysis of variance (ANOVA). The quadratic model of RSM associated with response optimization technique and composite desirability was used to find optimum values of machining parameters with respect to objectives (surface roughness and cutting force values). Results show how much surface roughness is mainly influenced by feed rate and cutting speed. Also, it is underlined that the thrust force is the highest of cutting force components, and it is highly sensitive to workpiece hardness, negative rake angle and tool wear evolution. Finally, the depth of cut exhibits maximum influence on cutting forces as compared to the feed rate and cutting speed.

Geometrical analysis of thread milling—part 1: evaluation of tool angles

Thread milling is a method which is increasingly used for machining thread. For this operation, a helical interpolation is required. Furthermore, the thread mill is a tool whose geometry is rather complex. Its envelope profile is linked to the thread profile, and a single tooth of the thread mill is composed of three continuous cutting edges. The present study proposes a geometrical model and an analytical formulation to define the rake face and the cutting edge. Furthermore, the calculations of cutting planes and cutting angles are explained. The analysis shows specific aspects of thread mills, in particular the fact that the flute angle may lead to a negative rake angle. This study is a contribution to cutting geometry aspect and constitutes a step for cutting force model in thread milling.

Effect of Machining Parameters on Microstructure and Hardness of Ultra-Fine Grained Material Created by Large Strain Machining

Effect of plane strain machining parameters such as rake angle and cutting velocity on the formation of ultra-fine structure in several materials has been studied. The microstructure and hardness of chips generated by machining were characterized by optical microscopy, scan electron microscopy and hardness tester respectively. The experimental results indicated that chip materials with ultra-fine grained and high hardness can be produced with more negative tool rake angle at some lower cutting velocity. The rake angle has more important effect on the formation of ultra-fine grain chips than cutting velocity. The rake angle for getting chips of obvious refined and significant hardened is different for different materials respectively. While the temperature of shear plane and tool-chip interface are increased with the increasing cutting velocity which alleviates the increase of hardness produced by decreasing rake angle.

Effect of Helical Drill Points on Delamination in Drilling Carbon Fiber Reinforced Plastics (CFRP)

A study of helical drill points for drilling carbon fiber reinforced plastics (CFRP) is presented. A helical drill point has an “S” contour with a radiused crown chisel that reduces the thrust force and make the drills self-centering. The S-shape chisel edge has a lower negative rake angle than a conventional chisel edge, and therefore may cut rather than extrude material. Experiments of drilling CFRP with helical drill points and conventional drill points were conducted. The results indicate that the helical drill points can reduce delamination significantly as compared to the conventional drill points under same cutting condition. Otherwise, delamination size decreases with increasing the cutting speed and increases with increasing the feed