Free Surface Of Chip Research Articles

On understanding the cutting mechanism of SiCp/Al composites during ultrasonic elliptical vibration-assisted machining

SiCp/Al composites play a significant role in achieving equipment lightweight, but its mechanical properties weaken the machinability. Ultrasonic elliptical vibration-assisted machining (UEVM) is a potential way to improve the machinability of difficult-to-cut materials, provides an efficient and precise solution for SiCp/Al composites in industrial manufacturing. However, the removal mechanism of SiCp/Al composites during UEVM and the effective guidance for practical machining are rarely investigated. In this paper, the cutting mechanism of SiCp/Al during UEVM is analyzed through theoretical analysis, finite element (FE) simulation and systematic experiments. Specifically, a multi-phase 2D microscopic FE simulation model is implemented and verified through systematically scratching tests. The research results indicate that particle stress distribution is influenced by variable tool-particle relative position during UEVM, promoting particle fracture and forming high-density zone of broken particles. Segmented chips with shorter length and greater curvature are the main form during UEVM, and dense layered structure appears on free surface of chips. Surface defects include cavities, crushing particles and scratches, while subsurface damage is dominated by pits and crack invasion. In addition, removal rate affects the surface formation, especially under very low scratching speed. Higher scratching speed weakens the ability of particle crushing under vibration effect, which is not helpful for improving surface integrity. Therefore, a reasonable cutting speed of 200 mm/min should be set during UEVM. This paper brings in a deeply understanding on cutting mechanisms of SiCp/Al composites, provides a theoretical guidance for the design and optimization of the vibration assisted processing of metal matrix composite.

Influence of Material Microstructure on Machining Characteristics of OFHC Copper C102 in Orthogonal Micro-Turning

Micro-cutting is different from conventional cutting in its mechanics. The workpiece material is not considered to be homogeneous in the micro-cutting process. As a result, it is critical to comprehend how microstructure affects surface integrity, cutting forces, and chip formation. In this paper, we experimented with micro-turning on oxygen-free high-conductivity (OFHC) copper with different microstructures after annealing. Feed rate parameters were smaller than, larger than, and equal to the grain size, respectively. Experimental results show that when the feed rates are equivalent to the grain size, the surface roughness of the machined surface is low and the width of the flake structure on the free surface of chips is minimal, and the explanations for these occurrences are connected to dislocation slip.

Fragmented chip formation mechanism in high-speed cutting from the perspective of stress wave effect

In this study, fragmented chip formation mechanism in high speed cutting (HSC) process is explored by using continuum-based discrete element method (DEM) based on the stress wave theory. The continuum-based DEM model established with Godunov frame is suitable for capturing multiple cracks propagation under high-speed impact. The chip forming mechanism based on stress wave theory is quantitatively analysed by DEM simulations against experimental data, which shows that the unloading wave reflected by the free surface of chips under high-speed conditions has a fundamental influence on chip formation.

Machining of Inconel 718 Using Coated WC Tool: Effects of Cutting Speed on Chip Morphology and Mechanisms of Tool Wear

Inconel 718 is a nickel-based superalloy extensively used in aerospace industries for its excellent physical, mechanical and chemical properties. Poor thermal conductivity, high toughness and strong work hardening tendency of this alloy adversely affect its machinability. Inconel 718 is therefore treated as ‘difficult to cut’ or ‘hard to cut’. Conventional machining of Inconel 718 faces various challenges like high cutting forces, evolution of huge cutting temperature and rapid tool wear. As a consequence, surface integrity of the machined part becomes disappointing. Excessive tool wear incurs additional cost of tool replacement. To overcome machining difficulties of this alloy, application of coated tool insert is recommended. To this end, the present work attempts to investigate machining performance of Inconel 718 using coated carbide (cemented carbide) tool with chemical vapour deposition multi-layer coating TiN/TiCN/Al2O3/TiN (TN4000) under dry cutting environment. Turning experiments are conducted with varied cutting speeds: 50, 75, 100 and 125 m/min at constant feed rate 0.1 mm/rev and constant depth of cut 0.4 mm. Chip morphology including features of chip cross section, free surface of chip and chip reduction coefficient as affected by cutting speed is studied herein. Abrasion, adhesion, chipping off, coating delamination, built-up edge formation, diffusion, etc. are identified as potential wear mechanisms. In addition to flank wear and crater wear, occurrence of notch wear is also distinctly identified. Surface roughness of the finished work part is found better in case of coated tool than uncoated one. Coated tool corresponds to lesser cutting force magnitude, lower cutting temperature and higher value of chip reduction coefficient than the case of traditional uncoated tool.

Study on dynamic chip formation mechanisms of Ti2AlNb intermetallic alloy

Ti2AlNb alloy is a relatively newly developed high-temperature-resistant structural material due to its excellent mechanical properties, which is also regarded as one of the most difficult-to-cut materials. The aim of this study is to characterize the chip formation during the machining of Ti2AlNb intermetallic alloy due to its critical role in studying optimization of machining process variables. A geometry model of chip formation was established to analyze the influence of strain rate hardening effect and thermal softening effect on the flow stress in the shear zone. A series of orthogonal cutting tests and quick-stop cutting tests were conducted with varying cutting speeds and cutting depths to validate the evolutions of flow stress inside the shear band. Results associated with cutting forces, cutting temperature, chip morphology, and microhardness are discussed and compared with those of most commonly used Ti6Al4V alloy. It is shown that the cutting forces and cutting temperature of Ti2AlNb alloy are higher than those of Ti6Al4V alloy by 35.3 and 20%, respectively. The chip morphologies of Ti2AlNb alloy show very different characteristics with different cutting conditions (i.e., some very small sawtooth on the free surface of chips under low cutting speed, then transform into irregular serrated chips with increasing cutting speed, and to serrated chip with adiabatic shear band under high cutting speed), which correlate well with the evolutions of microhardness distribution. The chip morphologies and chip formation characteristics are dependent largely on the dynamic flow stress, which is sensitive to the competition of the thermal softening effect with strain rate hardening effect.

Chip Formation in High-Speed Milling of Titanium Alloy with PCD Tools

This paper presents a detailed analysis of chip morphology through an experimental study of high-speed milling of Ti-6Al-4V alloy with PCD tools. Milling tests were conducted for cutting speed range from 125 m/min to 2000 m/min with water-soluble cutting fluid. The collected chips were firstly examined with a digital cameras and the free surface of the chips was analyzed by a scanning electron microscope (SEM). Geographical parameters of chip morphologies were described in saw-tooth/lamella frequency on the free surface and chip width. Experimental results show that the variation of chips in high-speed end milling of Ti-6Al-4V alloy is as follows, long and straight-shaped → spiral-shaped → curly-shaped → irregular-shaped. The free surface of chips exhibits saw-tooth lamella structures. The lamella becomes clearer and more obvious at higher cutting speeds. Within the same measurement distance, there is a sharp decrease in the lamella number within same measuring range. This should be attributed to the enhancement of the thermal mechanical coupled field applied to the chip formation processes.

Analytical study on the relationship between chip geometry and equivalent strain distribution on the free surface of chips in metal cutting

Abstract Chip breakage is one of the most important indicators for process stability in metal cutting. It ensures efficient chip removal in automated systems and prevents mechanical damage to the machined workpiece surface. It is well known that chip breakage initially occurs after the plastic strain on the chip surface, which is not contacting the tool (chip free surface), exceeds a critical value. However, the theoretical understanding on how the plastic strain on the chip free surface is affected by the tool/process parameters remains limited. In a first step this problem can be approached by assessing the relationship between the plastic strain on the chip free surface and the chip geometry. Both are direct and interdependent outcomes of the complex interactions between the cutting conditions, tool geometry and thermo-mechanical material properties. However, the impact of the tool/process parameters on the chip geometry is much easier experimentally assessable than the plastic strain, which is hardly measurable at all. Thus, the scientific understanding of the relationship between chip strain and chip geometry lays the foundation for understanding the influence of the tool/process parameters on the strain in the chip free surface and chip breakage. This paper proposes an analytic model of the equivalent plastic strain fields on the free surface of chips in metal cutting. The local strain tensors are derived as a function of the feed, depth of cut, cutting edge angle, tool nose radius, chip up-curl radius, side-curl radius and side flow angle. It is shown how each of these parameters influences the equivalent strain fields. The validation of the model includes longitudinal turning experiments on steel AISI 1045 and validated FEM-machining simulations.

アルミニウム単結晶の超精密二次元切削機構

The cutting mechanism in ultraprecision-machining of aluminum single crystals having various orientations using a trial ultraprecision machine was investigated. The (111) plane cutting requires the lowest cutting force and provides the best finished surface roughness among those for (001), (110) and (111) planes. The cutting in the direction of [011] on (111) plane gives the best finished surface roughness .The cutting forces and shear angles were affected by the crystal orientation when the depth of cut was 3 and 4μm. The crystal orientation dependency was not observed at a cutting depth of 1 and 2μm. This is reasonably explained by an affected layer, and this characteristic phenomena is shown in the micro cutting. The cutting force varies when shear strain is less than 3 according to the result on the relation between shear stress and shear strain. The finished surface roughness is affected by the cutting direction, suggesting that the control of the workpiece orientation is effective for improving the working accuracy. Width of lamella on the free surface of chips is affected by the cutting direction and depth of cut.

一方向凝固させたAg-Cu共晶合金の切削変形領域の観察

This paper describes the cutting mechanism of directionally solidified Ag-Cu eutectic alloy. The eutectic alloy has two prefered orientations, i.e. (113)[1\bar10] and (111)[1\bar10]. {113} and {111} planes are parallel with the side plane of the workpiece and a 〈110〉 axis is parallel with the direction of solidification. The experiment is conducted under orthogonal cutting. The inside of chip and the shear zone which are considered approximataly to be the plane-strain condition are observed by optical microscope and SEM, and also the relation between the texture and the cutting mechanism is investigated.The main results obtained are as follows.(1) In applying the tool rake angle of 40 deg., the cutting process is stable and a continuous ribon-like chip is formed. However, the shear angle shows the periodic change slightly. Consequently the streamline makes chevron-type markings and the free surface of chip is uneven.(2) In applying the tool rake angle of 30 deg., chevrons of streamlines become acute. In this case the cutting mechanism transforms from the shear plane to the shear zone model. Reducing the tool rake angle to 20 or 10 deg., shear deformation becomes discontinuous and the cutting mechanism tends to become the shear type model.(3) In cutting the workpiece having the texture with the rake angle of 40 deg., the cutting process is stable, and there is good agreement between the observed shear angle and the estimated one based on the assumption that shear deformation occurs in the slip system {111}〈110〉.

銅粗大結晶の切削機構

This paper describes the crystal-lographical cutting mechanism of large crystals of copper following the preceding work on Fe-3.5%Si. The experiment was conducted under the two dimensional cutting. The large crystals (about 4∼25 mm) were produced by slow solidification in vacuum furnace. The orientation of the crystals were determined by the Laue X-ray back reflection method.The main results obtained are as follows:(1) The {111}〈110〉 slip system is the only one in copper and is classified into the positive and the negative slip system. The ratio of the activated negative slip system to the positive one is 0.1∼0.3 for almost all grains and can be forecast from both the crystal orientation and the cutting direction.(2) In this experiment the specific cutting resistance varied from 41 kg/mm2 up to 93 kg/mm2 depending upon the crystal orientation. This variation is based on both the area of the shearing plane and the work-hardening.(3) In applying the critical cutting angle of annealed polycrystal copper, the thrust force becomes positive for a large shear angle.(4) The cut surface becomes good under a small cutting force.(5) Lamella spacing on the free surface of chip is affected by the situation of chip flow, i.e., it becomes coarser with the increased restriction of chip flow. The direction of lamella is perpendicular to that of chip flow.