Proposal of ‘accelerative cutting’ for suppression of regenerative chatter

A novel speed variation method, namely ‘accelerative cutting’, is proposed for suppression of regenerative chatter in short-duration plunge cutting, e.g. finishing of sealing, seating, and bearing surfaces. Although the cutting time is short in these processes, the large cutting width often causes chatter. Compared to conventional speed variation methods where moments exist when present and previous cutting speeds do not change and cause the growth of chatter, a unidirectional acceleration is applied resulting in sufficient speed difference throughout the cutting. Since accelerative cutting cannot be realized by conventional NC functions, it is verified through analyses and specially designed cutting experiments.     

Microstructure and properties of cutting magnesium-brass containing no lead

1 INTRODUCTIONLead-brass has excellent cutting ability , me-chanical and physical properties and is one of themost widely used copper alloys . The occupationratio of brass tube to all kinds of tubes reaches90 % in developed countries . The cutting lead-brass is a dual-phase brass and fine lead particlesdistribute dispersivelyin grains and on grain boun-ries . Theleadin wasted brass can easily beleachedand dissolvedinto soil .If the wasted lead-brass isburned in air ,the lead will become p…     

Effects of tool flank wear on orthogonal cutting process of aluminum alloy

The tool flank begins to wear out as soon as cutting process proceeds. Cutting parameters such as cutting forces and cutting temperature will vary with increasing degree of flank wear. In order to reveal the relationship between them, the theoretical situations of cutting process were analyzed considering the tool flank wear effect. The variation rules of cutting force, residual stress and temperature distributions along with the tool flank wear were analyzed comparing with the sharp tool tip. Through FEM simulation method, affections of the tool flank wear value VB on cutting forces, residual stress and temperature distributions were analyzed. A special result in this simulation is that the thrust force is more sensitive to tool flank wear, which can be used as a recognition method of tool condition monitoring. The FEM simulation analysis result agrees well with the experimental measuring data in public literatures and some experiments made also by the authors.     

Prospects of application of resistance‐arc cutting and treatment of metals in industry

Technological innovation of guide apparatus component restoration using the method of arc spraying by the 12Kh13+08G2S pseudoalloy is given. A submersible pump component restoration and hardening installation are designed and implemented, it includes a component surface vapour blasting unit, electroarc metallizator EM-12 and partially automated feed system for component transfer and pivoting at processing. Bench test results of the remanufactured parts showed that their wear resistance is more than twice as high.     

On-line measurement of electrical variables of the transducer during ultrasonic welding and cutting

A measurement system for high power electrical variables with ultrasonic frequency was established. It can measure the effective values of the voltage and the current, the active power, the phase difference of voltage and current, the frequency of the transducer during ultrasonic welding and cutting. In sampling circuits of the system, the measured current is sensed by using a no-capacitance and no-inductance precision resistor and is treated with a difference amplifier, the measured voltage is processed by using a proportional amplifier. For achieving good amplitude-frequency characteristics and rapid measurement of high frequency signals, the resistors, capacitors and amplifiers used in the system are rationally selected. Calibrating experiments show that relative errors are less than 1% for voltage and current effective values and less than 2.5% for active power, and absolute errors are ±1 Hz for frequency and ±1.7°for phase difference of voltage and current in the range of 17～23 kHz.     

Deposition of diamond/β-SiC nanocomposite films onto a cutting tool material

The motivation behind depositing nanocrystalline diamond/β-SiC composite thin films onto a cutting tool material is not only to obtain films having a whole range of combined properties of the components but also to enhance their fracture toughness without compromising on the hardness aspect. Nanocrystalline diamond composites are expected to behave differently owing to the large volume of grain boundaries. With smooth surface morphology and improved adhesion, diamond/β-SiC nanocomposite film system may not only serve as a separate film system but may also serve as an interlayer for the further deposition of adherent diamond top layers with regard to cutting tool applications. In this paper we report the deposition of nanocrystalline diamond/β-SiC composite thin films onto WC-6 wt.% Co substrates by employing microwave plasma chemical vapor deposition (MWCVD) technique using gas mixtures of H₂ and CH₄ and tetramethylsilane [TMS, Si(CH₃)₄]. Scanning electron microscopy (SEM), glancing angle X-ray diffraction (GIXRD), energy-dispersive X-ray (EDX), micro Raman scattering and Fourier transform infrared (FTIR) spectroscopic analyses have been carried out to characterize the microstructure and composition of the deposited films. The microstructure of the composite films constitutes a phase mixture of nanometer sized diamond and β-SiC grains. By adjusting TMS gas flow during deposition, β-SiC content in the nanocomposite films can be controlled. This aspect was utilized to successfully realize diamond/β-SiC nanocomposite gradient films with diamond top layers on the hard metal substrates in a single process step.     

Microstructure and cutting performance of Ti（C, N）-based cermets heat-treated in nitrogen

Ti（C, N）-based cermets were treated using hot isostatic pressing （HIP） at 1423 K in nitrogen. The microstructures compared with the as-sintered cermets were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray analysis, and electron microprobe analysis. It was found that high nitrogen activity in the surface zone resulted in the formation of gradient structure. Approximately 20-1am-deep, nitrogen-rich and titanium-rich hard surface zone was introduced by the heat treatment. The nitrogen activity was the driving force that caused the transportation of the atoms through the binder, titanium towards the surface, and tungsten and molybdenum inwards. In the surface zone, the particle size became fine, the inner rim disappeared, and the volume fraction of the outer rim and the binder phase considerably reduced. Small grains of TiN, WC, Mo2C, and nitrogen-rich carbonitlide phases formed in the surface zone during the heat treatment, improving the tlibological property of the heat-treated cermet.     

Realization of non HF air plasma cutting power source based on a complexisolated inverter

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Can higher cutting speeds and temperatures improve the microstructural surface integrity of advanced Ni-base superalloys?

Future Ni-base superalloys are designed to deliver outstanding mechanical behaviour at high temperatures, which may translate in significant machining challenges. In this work, a paradigm is presented by which is proven how machining of these materials could benefit from increased cutting speeds and temperatures provided that they are able to promote shear localisation and thermal softening in the chip deformation zones, whilst retaining high-temperature strength within the machined surface. In this way, thermal control of chip formation leads to both lower cutting forces and energies, as well as enhanced surface integrity with lower levels of microstructural reconfiguration.     

单晶锗纳米切削过程分子动力学仿真与实验研究

为深入理解单晶锗纳米切削特性,提高纳米锗器件光学表面质量,采用三维分子动力学(MD)模拟方法研究了单点金刚石压头与单晶锗表面的接触和滑动过程。研究了压头在滑动切削过程中的材料变形、切削力、切屑堆积、表面形貌尺寸。仿真结果表明,随着垂直载荷的增加,切削力、表面形貌尺寸、切屑堆积在接触过程中逐渐增加,且与切削速度无明显关联。切削过程中切削力波动的根本原因是由于单晶锗晶格破坏引起位错的产生和能量波动。为了验证仿真结果的正确性,使用纳米划痕仪对单晶锗进行了纳米切削实验。实验结果与仿真结果一致,验证了MD模型的正确性和有效性。     

Marble cutting with single point cutting tool and diamond segments

An investigation has been undertaken into the frame sawing with diamond blades. The kinematic behaviour of the frame sawing process is discussed. Under different cutting conditions, cutting and indenting-cutting tests are carried out by single point cutting tools and single diamond segments. The results indicate that the depth of cut per diamond grit increases as the blades move forward. Only a few grits per segment can remove the material in the cutting process. When the direction of the stroke changes, the cutting forces do not decrease to zero because of the residual plastic deformation beneath the diamond grits. The plastic deformation and fracture chipping of material are the dominant removal processes, which can be explained by the fracture theory of brittle material indentation.     

An experimental method for studies of intermittent cutting at small cutting depths

Most devices for metal cutting experiments are designed to simulate continuous cutting at relatively large cutting depths. However, there is also a need for techniques to study the more complex situations prevailing in other important cutting operations like milling, sawing, hobbing, shaper cutting and grinding. These operations are characterized as being intermittent and having a relatively small and varying cutting depth per edge. In order to supply an experimental set-up for basic studies of chip formation and cutting forces under these conditions a new method for single stroke, single edge metal cutting has been developed.

The experiments are performed in a modified Charpy pendulum which offers force measurement and accurate selection of cutting speed and feed in the ranges typical of many intermittent cutting operations. The equipment is also provided with an excellent quick-stop mechanism to aid in chip formation studies.

The test method is described in detail and examples of metallographical and scanning electron microscopical studies of quick-stopped samples as well as registrations of specific thrust and cutting forces are presented.     

Three-dimensional cutting force analysis based on the lower boundary of the shear zone. Part 1: Single edge oblique cutting

Traditional models of cutting based on Merchant's shear plane idealization are incapable of predicting any of the cutting force components without a priori knowledge of chip-tool friction. However, Rubenstein's work on orthogonal cutting has shown that this limitation can be avoided by utilizing the stress distributions on the lower boundary of the shear zone. The present work aims to extend this approach to oblique cutting with. single and two edged tools. This paper focuses on single edge oblique cutting whereas Part 2 analyses two edge cutting. It is assumed that the progressive deformation of the work material into chip material occurs within the effective plane. The resulting stress distributions on the lower boundary are integrated to yield expressions for estimating cutting forces from given tool and chip geometries. This provides a mechanism for predicting the power and lateral components of the cutting force in single edge oblique cutting. The predictions are verified against new and previously published experimental data.     

Modelling and experimental investigation on nanometric cutting of monocrystalline silicon

A new model to understand the behaviour of how materials are removed from workpiece in nano cutting is proposed. This model postulates that the mechanism of nanometric scale material removal is based on extrusion, which is different from the shearing mechanism in conventional cutting. It also explains why brittle materials are removed in ductile mode. Analytical results from molecular dynamics and nano indentation show good agreement with the proposed modelling. Experiments are conducted to verify the new model for nanometric cutting of monocrystalline silicon. The theoretical modelling and experimental verification present a good understanding of nano-scale material removal and provide an approach to fundamentally control the machining performance.     

A chip formation based analytic force model for oblique cutting

An oblique cutting force model has been developed using an analytic orthogonal force model. The force model uses a thermo-visco-plastic material constitutive law to represent the shear stress during deformation of the material. The strains and strain rates used for defining the shear stress were obtained from chip formation and morphology derived from orthogonal cutting tests and has been extended to oblique cutting. A time domain simulation using the in-cut chip geometry to define the chip load area has been developed. The oblique force model was used to predict the cutting forces during ball milling of hardened AISI D2 tool steel. The predicted forces were verified experimentally and showed good correlation.     

The material removal mechanism in mechanical lapping of diamond cutting tools

In order to reveal the surface layer removal nature and explain the anisotropy of material removal rate in mechanical lapping single crystal diamond cutting tools, a brittle-ductile transition lapping mechanism is proposed. And then, the dynamic critical depths of cut for brittle-ductile transition in different directions on different planes can be calculated. The lapped surface layer of diamond cutting tool will be removed in plastic mode as long as the embedding depth of diamond grit into the lapped surface is less than the corresponding critical depth of cut. Lapping experiments on the named (110) plane and (100) plane are carried out and the lapped surfaces are measured with atomic force microscope (AFM). The results show that all the lapped surfaces of diamond cutting tools consist of plastic grooves in nanometric scale and the maximal groove depths have prominent anisotropy in different orientations and on different planes, which are consistent with the critical depths of cut well. Therefore, the material removal rate anisotropy of lapped surface layer can be analyzed by comparing the critical depths of cut on different crystallographic planes and in different orientations of the identical plane quantitatively.     

Investigations of yield stress,fracture toughness,and energy distribution in high speed orthogonal cutting

This paper presents a novel prediction method of the yield stress and fracture toughness for ductile metal materials through the metal cutting process based on Williams' Model [38]. The fracture toughness of the separation between the segments in serrated chips in high speed machining is then deduced. In addition, an energy conservation equation for high speed machining process, which considers the energy of new created workpiece surfaces, is established. The fracture energy of serrated chips is taken into the developed energy conservation equation. Five groups of experiments are carried out under the cutting speeds of 100, 200, 400, 800 and 1500 m/min. The cutting forces are measured using three-dimensional dynamometer and the relevant geometrical parameters of chips are measured with the aid of optical microscope. The experiment results show that the yield stress of machined ductile metal material presents an obviously increasing trend with the cutting speed increasing from 100 to 800 m/min while it decreases when the cutting speed increases to 1500 m/min further. Meanwhile, the fracture toughness between the chip and bulk material displays a slightly increasing tendency. In high speed machining, the fracture toughness of the separation between the segments in serrated chips also presents increasing trend with the increasing cutting speed, whose value is much greater than that between the chip and bulk material. In the end, the distribution of energy spent in cutting process is analyzed which mainly includes such four portions as plastic deformation, friction on the tool–chip interface, new generated surface and chip fracture. The results show that the proportion of plastic deformation is the largest one while it decreases with the cutting speed increasing. However, the proportions of energy spent on new created surface and chip fracture increase due to the increasing of both the chip's fracture area and the fracture toughness.     

Experimental and numerical investigations of single abrasive-grain cutting

The present work will provide an in-depth analysis of the abrasive-grain cutting process using a combination of experimental observations and finite element simulations. The workpiece material was AISI 4340. The cutting tool was spherical in shape with a 0.508 mm radius and was fabricated from diamond. The experiments were conducted at cutting speeds of 5−30 m/s in 5 m/s increments and depths of cut from 0.3 to 7.5 μm. The analysis provided a comprehensive understanding of the abrasive-grain cutting process related to the friction between the cutting tool and the workpiece, the material mechanics of the workpiece, and the cutting mechanics of the operation. It was found that the normal forces increased as cutting speed increased due to strain-rate hardening of the workpiece and that the tangential forces decreased as cutting speed was increased due to a reduction in tool-workpiece friction and due to a change in cutting mechanics. The scratch profiles showed that the cutting mechanics changed as cutting speed was increased due to a reduction in material pile-up height. The approximate uncut chip thicknesses for the transitions from elastic, elastoplastic, and fully plastic cutting were identified and were found to increase as cutting speed was increased.     

A study of the tool-chip interface contact problem under low cutting velocity with an elastic cutting tool

To understand the effects of elastic deformation of the tool and the crater phenomenon generated by the cutting force and high pressure during metal cutting processing on the cutting process, an iterative mathematical model for calculating the tool-chip contact is developed in this paper under the assumption of elastic cutting tools. In this model, the finite-element method is used to simulate the cutting of mild steel by a cutting tool of three different materials. The results obtained in the simulation are found to match experimental data reported by related studies. The simulation results also indicate that tools with a smaller stiffness produce greater elastic deformation. Further, decrease of the rake angle due to elastic deformation of the tool can result in greater difficulty in internal deformation of the material and an increase in cutting force. The micro-crater phenomenon on the tool face generated by high pressure at the tool-chip interface is the preliminary symptom of crater wear on the tool face. Therefore, under some machining conditions, such as in precision machining or in automation processing where tool compensation is required, the phenomenon of elastic deformation of the tool must be considered carefully to ensure product precision.