Positive Rake Angle Research Articles

A comprehensive guide to milling techniques for smoothing the surfaces of 3D-printed thermoplastic parts

PurposeThis study aims to thoroughly examine the milling process applied to fused filament fabrication (FFF) parts. The primary objective is to identify the key variables in creating smooth surfaces on FFF specimens and establish trends about specific parameters.Design/methodology/approachIn this study, PLA and ABS samples fabricated by FFF are subjected to side milling in several experiments. Achievable surface quality is studied in relation to material properties, milling parameters, tooling and macrostructure. The surface finish is quantified using profile measurements of the processed surfaces. The study classifies the created chips into categories that can be used as criteria for the anticipated quality. Spectral analysis is used to examine the various surface formation modes. Thermal monitoring is used to track chip formation and surface temperature changes during the milling process.FindingsThis study reveals that effective heat dissipation through proper chip formation is vital for maintaining high surface quality. Recommended methodology demands using a tool with a substantial flute volume, using high positive rake and clearance angles and optimizing the feed-per-tooth and cutting speed. Disregarding these guidelines may cause the surface temperature to surpass the material’s glass transition, resulting in inferior quality characterized by viscous folding. For FFF thermoplastics, optimal milling can bring the average surface roughness down to the micron level.Originality/valueThis research contributes to the field by providing valuable guidance for achieving superior results in milling FFF parts. This study includes a concise summary of the theoretically relevant insights, presents verification of the key factors by qualitative analysis and offers optimal milling parameters for 3D-printed thermoplastics based on systematic experiments.

Investigation of Single Grain Grinding of Titanium Alloy Using Diamond Abrasive Grain with Positive Rake Angle

Traditional grinding, which is predominantly performed with a negative rake angle (NRA), can be transformed into grinding with a positive rake angle (PRA) by employing femtosecond pulsed laser technology to modify the apex angle of the grains to be less than 90°. This innovative approach aims to reduce grinding forces and grinding temperatures while improving the surface quality of typical hard-to-machine materials. To assess the performance of PRA single grain grinding and to investigate the underlying mechanisms, the finite element simulation software ABAQUS 6.14 was employed to model the grinding of Ti6Al4V titanium alloy with a single diamond abrasive grain. The dependence of grinding force and temperature in single grain grinding with a PRA or an NRA under different grinding parameters was studied and compared. PRA and NRA single diamond grain grinding experiments on Ti6Al4V alloy were carried out, with grinding forces measured using a dynamometer and compared with the simulation results. The grinding surface morphology and surface roughness were observed and measured, and a comparison was made between PRA and NRA grinding. The results indicated that in single diamond grain grinding, transforming to a PRA significantly enhances grinding performance, as evidenced by reduced grinding forces, lower temperatures, improved surface morphology, and decreased surface roughness. These findings suggest that PRA single diamond grain grinding offers substantial benefits for the precision machining of hard-to-machine materials, marking a step forward in optimizing surface finishes.

Molecular dynamics simulation of the effect of tool parameters on nano-cutting of polycrystalline γ-TiAl alloys

As one of the most promising lightweight high-temperature structural materials in the future, the surface quality of γ-TiAl alloys has a great influence on the performance of the workpieces, and the tool parameters are an important factor affecting the machining results. In this study, molecular dynamics simulations of the nano-cutting process of polycrystalline γ-TiAl alloys with different tool parameters were carried out. The results show that increasing the tool rake angle and decreasing the tool edge radius within a certain range helps to reduce the average cutting force, cutting force fluctuation, cutting temperature, and stabilize the cutting process, while the change of the tool clearance angle has less influence on the cutting process. In contrast, negative rake angle cutting is more likely to produce grain rotation and grain boundary steps in the processed substrate and increase the processed surface roughness than positive rake angle cutting; increasing the tool rake angle within a certain range will weaken the elastic recovery effect of the substrate. During cutting at a positive rake angle, whether a portion of the substrate is prone to slip toward the surface of the substrate, thereby reducing the surface quality, depends on the relative state of grain orientation and force applied in the substrate.

Performance Evaluation of Strengthened Scrapped Mating Rings of Face Seals Used as Single Point Turning Tool

The scrapped mating ring of face seals has been studied and recycled into single point turning tools (SPTTs) and performed comparably with standard turning tools. Three sets of tools, namely, standard tungsten tool, strengthened and unstrengthened scrapped ring, have been studied and performed satisfactorily as SPTTs. Standard tungsten tool, strengthened and unstrengthened scrapped mating ring of face seal respectively. The tools were configured with a nose radius 2mm, positive rake angles of 3o, 5o and 8o and used to perform turning operations on mild carbon steel (CS1030) with surface roughness measured. The results showed that the strengthened tools generated the best surface finish for mild carbon steel among all three tools under consideration. The statistical analysis showed that surface finish, the model, cutting speed and feed rate are significant with their P-values < 0.0001 but the depth of cut, rake angle and tool have no significant impact on surface finish at 95% confidence level. This research will provide the machine tools shop with more durable SPTT and enhance reliability, quality, minimize downtimes and accidents in machining processes.

Investigations on chip breakability in lead-free brass alloy CW511L using different chip breaking geometries

Brass is an alloy of copper and zinc, commonly alloyed with lead. Due to legal restrictions, the lead-content is decreasing nowadays. This leads to higher cutting forces and worse chip breakability. To face these challenges, adapted tool geometries were investigated. To decrease cutting forces, positive rake angles can be utilized. On the other hand, this will lead to worse chip breakability in single phase lead-free brass alloys. Therefore, chip breaking geometries are necessary. This paper investigates and compares different forms of chip breaking geometries to improve chip breakability when using highly positive rake angles in lead free brass alloy CW511L.

Study of a Methodology for Calculating Contact Stresses during Blade Processing of Structural Steel

The article presents data about the distribution of contact stresses on the rake surface of the cutter when turning steel (Fe-0.4 C-1Cr), which were obtained by the split cutter method. The article also provides graphs of the effect of the uncut chip thickness a and the rake angle γ on the main parameters of the plots of shear τ and normal σ contact stresses. For this case, The initial data were obtained by longitudinal turning of a steel workpiece with the measurement of the technological components of the cutting force by a three-component Kistler dynamometer, followed by the calculation of the physical components of the cutting force. The rake angle varied widely, from +35 to −10°, and the uncut chip thickness a varied from 0.05 to 0.37 mm. A decrease in the rake angle from +35 to −10° leads to a significant increase in the maximum normal contact stress at the cutting edge σmax: from 400 to 1400 MPa with the uncut chip thickness a = 0.37 mm. In the area of small uncut chip thickness, a (less than 0.1 mm), the paradoxical increase in the magnitude of the greatest normal contact stress with a large positive rake angle (more than +15°) is explained by the indentation (pressing) of the being machined material under the rounded cutting edge of the cutter in the chip formation zone, and their paradoxical decrease with a negative rake angle is due to the presence of a sag (deflection) of the transient surface. According to the magnitude of the reference points obtained on the basis of experimental data, it is possible to plot the contact stresses epures on the rake surface of the cutting tools when machining steel.

Fabrication of PCD face grinding wheel with positive rake angle by femtosecond laser and its performance evaluation in cemented carbide grinding

Super-hard abrasive grinding is considered to be the main approach to realize precision and ultra-precision machining of difficult-to-machine materials such as cemented carbide, engineering ceramics, titanium alloys and superalloy materials encountered. However, heavy grinding force, high grinding temperature and poor surface integrity are prone to be encountered in conventional negative rake angle grinding of difficult-to-machine materials. In response to these problems, a novel concept of positive rake angle grinding is first proposed and an abrasive grain regularly arranged binder-less polycrystalline diamond face grinding wheel with positive rake angle has been designed and fabricated by femtosecond laser ablation. To evaluate the grinding performance of the face grinding wheel with positive rake angle, grinding experiments of YG8 cemented carbide are conducted and compared with the traditional electroplated diamond grinding tool with equivalent abrasive grain dimension and distribution. The results show that compared with the conventional negative rake angle grinding, the normal and tangential forces in positive rake angle face grinding are reduced by 30.3 % ∼ 36.4 % and 21.1 % ∼ 29.3 %, respectively, and the ratio of normal to tangential force is reduced by 12.6 % ∼ 20.3 %. The surface roughness and average depth of subsurface metamorphic layer are also significantly smaller. The laser fabricated polycrystalline diamond face grinding wheel also has better wear resistance in the grinding of cemented carbide. Therefore, it can be concluded that better ground surface quality is obtained by the novel grinding wheel with positive rake angle. The innovative grinding method can fill the research gap on the grinding mechanism of positive rake angle grinding and further enrich the grinding theory of difficult-to-machine materials.

Machinability of High Mn Steel Using Tool Life Criteria

High Mn steel alloys have shown to provide both high strength and ductility. However, current literature offers limited guidance on the machinability of these steel alloys. Therefore, this work provides turning recommendations for high Mn steel that is based on tool life data. Several indexable carbide inserts with various rake angles were used to machine cast billets of high Mn steel. Turning characteristics from various feed rates, cutting speeds, and depths of cut were analyzed. Through a design of experiments, it was determined that the feed rate was the most significant factor affecting tool life and that a tool with a negative rake angle had a longer tool life than one with a positive rake angle. The effect of coolant on tool life was seen to be dependent on the tool material. Optimal cutting conditions, which provided a long tool life while maintaining a decent material removal rate, were found for a cutting speed of 150 ft/min, a feed rate of 0.008 in/rev, and a depth of cut of 0.080 inches. In addition, microhardness analysis was used to determine the thickness of the work-hardened layer on machined surfaces. Microhardness was seen to increase between 0.028 and 0.040 inches from the machined surfaces for each cutting condition, explaining the difficulty experienced in machining high Mn steel alloys. The availability of these recommendations for machining high Mn steel encourages the application of this material in a more efficient and productive manner.

Chip Formation and Orthogonal Cutting Optimisation of Unidirectional Carbon Fibre Composites.

This study presents a thorough experimental investigation utilising the design of experiments and analysis of variance (ANOVA) to examine the impact of machining process parameters on chip formation mechanisms, machining forces, workpiece surface integrity, and damage resulting from the orthogonal cutting of unidirectional CFRP. The study identified the mechanisms behind chip formation and found it to significantly impact the workpiece orientation of fibre and the tool's cutting angle, resulting in increased fibre bounceback at larger fibre orientation angles and when using smaller rake angle tools. Increasing the depth of cut and fibre orientation angle results in an increased damage depth, while using higher rake angles reduces it. An analytical model based on response surface analysis for predicting machining forces, damage, surface roughness, and bounceback was also developed. The ANOVA results indicate that fibre orientation is the most significant factor in machining CFRP, while cutting speed is insignificant. Increasing fibre orientation angle and depth leads to deeper damage, while larger tool rake angles reduce damage. Machining workpieces with 0° fibre orientation angle results in the least subsurface damage, and surface roughness is unaffected by the tool rake angle for fibre orientations between 0° to 90° but worsens for angles greater than 90°. Optimisation of cutting parameters was subsequently carried out to improve machined workpiece surface quality and reduce forces. The experimental results showed that negative rake angle and cutting at moderately low speeds (366 mm/min) are the optimal conditions for machining laminates with a fibre angle of θ = 45°. On the other hand, for composite materials with fibre angles of θ = 90° and θ = 135°, it is recommended to use a high positive rake angle and cutting speeds.

Estimation of temperature in the cutting area during orthogonal turning of grade 2 titanium

The authors introduce an experimental-analytical method for determining the average temperature values in the PSZ (primary shear zone) and the SSZ (secondary shear zone) during orthogonal turning of grade 2 titanium with a use of an uncoated carbide tool with a positive rake angle and a flat rake face. The presented method is based on an algorithm in which the values of shear stress in the PSZ and the SSZ are calculated by means of the Johnson–Cook constitutive equation and Oxley’s model of cutting mechanics. Average temperature values in the PSZ and the SSZ are determined by iteratively finding the minimum difference between the calculated stress values. As its inputs, the algorithm uses the values of the feed and the tangential cutting force components, the value of chip flow velocity on the rake face, and the constants of the Johnson–Cook constitutive equation. The model was validated with a use of empirical data collected during the experiments. The test rig consisted of a KNUTH Masterturn 400 precision lathe equipped with a dynamometer, a high-speed camera, and a thermal imaging camera.

Modeling Grinding Processes—Mesh or Mesh-Free Methods, 2D or 3D Approach?

The objectives of this study are mainly two: (1) to validate whether a single grain scratch process can be modeled in two dimensions under the assumption of plane strain, and (2) to select the best discretization approach to model a single grain scratch process. This paper first focuses on the simulation of the orthogonal cutting process (aluminum alloy A2024 T351) using two mesh-based discretization approaches, the pure Lagrangian method (LAG) and the arbitrary Lagrangian–Eulerian method (ALE), and two particle-based approaches, the particle finite element method (PFEM) and smooth particle hydrodynamics (SPH), for both positive and negative rake angles. Benchmarking of the orthogonal cutting models at a rake angle of γ=20∘ is performed with the results of the process forces (cutting and passive forces) of a turning experiment from the literature. It is shown that all models are able to predict the cutting forces, but not the passive force. The orthogonal cutting model is further extended to simulate the cutting mechanism with negative rake tool geometries typically found in grinding and single grit scratching processes. The effects of the negative rake angles on the discretization approaches are studied. The calculated process forces are also compared to the measurements of the single grit scratch process performed at our laboratory. The 2D orthogonal cutting models significantly overestimate the process forces. One of the reasons why the orthogonal 2D cutting model is inadequate is that it cannot describe the complex mechanisms of material removal such as rubbing, plowing, and cutting. To account for these phenomena in LAG, ALE, and SPH discretization approaches, a 3D scratch model is developed. When comparing the process forces of the 3D model with the experimental measurements, all three discretization approaches show good agreement. However, it can be seen that the ALE model most closely matches the process forces with the experimental results. Finally, the ALE 3D scratch model was subjected to sensitivity analysis by changing the cutting speed, the depth of cut and the tool geometry. The results clearly show that the ALE method not only predicts the process forces and form the trends observed in the scratching experiments, but also predicts the scratch topography satisfactorily. Hence, we conclude that a 3D model is necessary to describe a scratch process and that the ALE method is the best discretization method.

Machinability and Chip Morphology Study of Inconel 740H and Haynes 282 for Advanced-Ultra Supercritical Applications

Abstract: High speed machining of Nickel based alloys has gained a lot of research interest since the last decade owing to their applications in areas like power generation, aerospace, marine propulsion, and nuclear reactors. For the realization of an advanced ultra-supercritical (A-USC) thermal plant, operating at service temperatures of about 700 to 760oC and pressures of around 24 MPa, the use of Nickel-based super alloys is indispensable. Some these parts used for the application may be required to be machined before use, although the machinability of these materials is relatively poor. Chip morphological studies are performed for better understanding of cutting force and surface finish of the alloys. In this work, authors have tried to study the effect of machining parameters like cutting speed, feed rate, rake angle, and nose radius on chip morphology like peak height, valley height, tooth height, tooth pitch, and segmentation frequency. The results of chip morphology studies indicate the need for saw tooth chips for better machining. Accordingly, Inconel 740H is found to have better machinability than Haynes 282 for the used range of machining parameters. Moreover, higher cutting speeds, lower feed rates, and positive rake angles are found to yield optimum conditions for an improved machinability

Effects of tool geometry on tungsten removal behavior during nano-cutting

Although the researches in effects of tool geometry on the removal behavior of many metals have been studied, the deformation and removal mechanisms of tungsten have changed greatly due to the higher brittleness of tungsten compared with other metals and the research on the removal behavior of tungsten involved changing of tool geometry during nano-cutting has not been reported, which limits the development of high precision manufacturing of tungsten components. Herein, molecular dynamics (MD) simulation model of nano-cutting tungsten was established, and the material removal behavior induced by changing of tool geometry was comprehensively studied. The results showed that a larger positive rake angle or larger clearance angle or smaller edge radius of the tool was beneficial to reduce the surface roughness, elastic recovery, thickness of subsurface damage layer, cutting force, cutting temperature, friction coefficient, and maximum stress while the surface presented less residual compressive stress or even tensile stress. In the plastic deformation dominated by phase transition and dislocation slip, the region of 1/2<111> dislocation line presented compressive stress state whereas the region of <100> dislocation line presented tensile stress state during nano-cutting tungsten. Meanwhile, there was no phase transition from BCC structure to other crystal structures, but rather from ordered structure to disordered structure (amorphous structure). The correlation between amorphous phase transition and dislocation slip was affected by the tool geometry owing to the fact that the temperature and stress were different under different tool geometries. The research findings provide a comprehensive theoretical basis for the micro removal behavior of tungsten and technical reference for the design of tools in nano-cutting.

Understanding the structure and cutting mechanism of shaver blades: A case study on articular cartilage.

Mechanical shaver blades have been used in minimally invasive knee arthroscopy surgery for nearly 50 years, however, the tooth structure and cutting mechanism of shaver blades were less reported. This paper designed several shaver blades (triangular tooth/TT, circular tooth/CT and convex arc tooth/CAT), defined the cutting edges and angles of the original shaver (OS) and proposed a newly designed shaver (NDS) with a positive secondary rake angle to optimize cutting performance. The cutting process and theoretical model of the OS and NDS were analysed from 2D and 3D perspectives. A comparative experimental analysis of cutting performance, including cutting force, surface roughness, and groove geometries, was carried out to verify the influence of tooth structures and secondary rake angle. The results showed that the tooth of the OS has three different cutting edges, among which the secondary cutting edge sited at the tube section contributes to the puncturing process, and the primary cutting edge located on the outer wall of the tube participates in the oblique cutting process and finally removes the soft tissue. The cutting process of the secondary cutting edge of NDS has been changed from puncturing to oblique cutting, therefore, only the oblique cutting exists throughout the shaving process. This makes the shape and quantity of the chips of OS and NDS different, which has been verified by experiment. The cutting performance of CT was superior to that of TT and CAT, highlighting the importance of tooth roots in the cutting process. Positive secondary rake angle significantly improved the cutting performance of CAT, but not that of TT with a small profile angle (30°) and CT, which means both the puncturing and oblique cutting play important roles. Not all the positive secondary rake angle was helpful to the cutting process and 30° and 45° were suggested.

Novel crescent drill design and mechanistic force modeling for thrust force reduction in bone drilling

Bone drilling tends to cause mechanical damages and thermal necrosis in the vicinity of the drilled hole, which can deteriorate the surgery quality and patients’ recovery. Understanding the cutting forces generation mechanism is crucial in controlling thrust force and bone temperature for optimum tool design. In this study, a novel crescent drill bit featuring an improved positive rake angle distribution was designed to reduce the thrust force and temperature elevation. On this basis, a mechanistic model for predicting thrust force and torque was proposed for drill bits with different geometries (twist drill and crescent drill). The proposed model was established in the polar coordinate system to precisely calculate the curvilinear integral of the crescent cutting edges. Drilling experiments were carried out using two types of drill bit under different cutting conditions and results showed that our proposed model agrees well with the experimental data. The experimental results also demonstrated that our tool design can significantly reduce the thrust force and reduce the bone temperature below the thermal threshold without coolant, providing a clinical option for coolant free drilling.

Development and implementation of crater and flank tool wear model for hard turning simulations

This paper concerns the tool wear in hard turning of AISI 52100 hardened steel by means of PCBN tools. The purposes of this work are the development of a tool wear model and its implementation in a FEM-based procedure for predicting crater and flank wear progression during machining operations for studying the influence of tool wear on the process in terms of tool geometry modifications and stress variation on the tool. The developed tool wear model, able to update the geometry of the worn tool as a function of the wear rate, has been implemented in the utilized Deform 2D FEM software. This new analytical model differs from the already proposed methods of existing research, since it concerns both crater and flank wear evaluation. The validation of the model has been achieved by the comparison between experimental and simulated wear parameters. For doing this, an extended experimental campaign has been accomplished. The comparison results have shown good agreement. Once validated, the FEM strategy has been utilized for examining the influence of tool wear on the effective rake angle and the related tool stresses, individuating the excessive positive rake angle value as the final tool breakage mechanism.

Investigation of the Influence of Tool Rake Angles on Machining of Inconel 718

It is essential for superalloys (e.g., Inconel 718) to obtain an anticipated surface integrity after machining, especially for safety critical areas (e.g., aerospace). As one of the main characteristics for cutting tools, the rake angle has been recognized as a key factor that can significantly influence the machining process. Although there are large research interests and outcomes in the machining of nickel-based superalloys, most of them focus on the surface integrity and macroscale temperature observation, whereas the temperature distribution in the tool rake face is not clear. Thus, it is necessary to investigate the basic role of rake angles and the tool–workpiece interaction mechanism to determine the machining condition variations and surface integrity. In the present study, both experimental and numerical methods are employed to explore the cutting force, thermal distribution, and shear angles during the process and the metallurgy characteristics of the subsurface after machining, as well as the mechanical properties. The research has emphasized the importance of rake angles on both the cutting process and machined surface integrity, and has revealed the microscale temperature distribution in the tool rake face, which is believed to have a close relationship with the tool crater wear. In addition, it is clearly presented that the surface generated with positive rake angle tools generates the minimum subsurface deformation and less strain hardening on the workpiece.

Effects of tool rake angle and workpiece surface roughness on nanocutting of cu investigated using Multiscale simulation

ABSTRACT The effects of tool rake angle and workpiece surface roughness on the cutting mechanism and mechanics of Cu are studied using quasi-continuum simulations. These effects are investigated in terms of atomic trajectories, stress distribution, cutting force, resistance factor, and cutting ratio. The simulation results show that negative rake angles lead to a larger cutting force, lower resistance coefficient, and higher cutting ratio than those obtained with positive rake angles. For tools with an initial rake angle of 2° to 8°, the rake angle becomes negative during the cutting process due to the strong adhesion interaction between the tool rake face and chips. The resistance coefficient decreases with increasing tool rake angle for rake angles in the range of 2° to 8°. Tools with negative rake angles of −2° to −8° have similar cutting ratios. The cutting ratio decreases and cutting force increases with increasing surface roughness of the workpiece.

Finite element analysis of orthogonal cutting of cellular metals: influence of cutting conditions on chip formation and surface damage

Cellular metals are highly porous materials with very distinctive properties. Although it is possible to manufacture near-net-shape parts of these materials with some manufacturing processes, additional machining operations are usually required. However, as conventional machining causes surface damage and poor precision, finishing operations are often performed using alternative, cost-intensive methods. In the present work, a mesoscopic finite element model was used to analyze the influence of cutting conditions and tool geometry in the orthogonal cutting process of cellular metals. The study considered the variability of the mesostructure, as the behavior of multiple cell arrangements under cutting conditions was evaluated. The influence of cutting speed, depth of cut, and tool rake angle on chip formation and surface damage was explored. Chip formation at higher cutting speed was different, as chip fragmentation was visible. Tools with a positive rake angle and a higher cutting speed led to a decrease in subsurface damage. Nevertheless, surface quality is markedly dependent on the stochastic nature of the mesostructure, as material separation is defined by the response of the cell array. Hence, a set of cutting parameters for optimal surface quality could not be identified.

The finite element modelling of machining of NST 37-2 steel

NST 37-2 has vast applications in building construction and in machine components production in Nigeria, but the effects of induced residual stress in the material, optimum cutting parameters, efficient process planning, chip formation process and surface roughness of the machined products are some of the challenges faced in the industry. In this study, the finite element simulation of orthogonal cutting of NST 37-2 steel was carried out, and the effect of geometry on chip morphology, residual stress distribution, strain energy was investigated to address informed predictability on the material. Different rake angles of -15°, 0°, 15°, and 30° were adopted for the tool geometry. In each case, the chip formed was continuous due to the plastic nature of the material. At negative and 0 rake angles, there were narrow bands of heavily strained chip, and as the rake angle increased, the chip tended to narrow due to low adhesion in the tool-work-piece region and decreasing work for chip folding. Uniform deformation was also observed with positive rake angle simulations. Residual stress was found to increase with negative rake angle. However, with positive rake angle, residual stress led to an increase in tensile strength due to the shearing action of the cutting tool in the cutting direction on the material layers below the cut plane. Cutting and thrust forces were observed to decrease with increasing rake angles. Adiabatic shear bands with high temperatures and thermoplastic shear instability were observed in machining with negative rake angles. High temperatures were generated in the shear zone due to large amount of work done by deformation of work material in machining with negative rake tools. The shear zone temperatures were much less in machining with positive rake tools. Temperatures on the rake face reduced with increasing rake angles, but not as significantly as the temperatures in the primary shear zone.