Effects Of Machining Conditions Research Articles

Prediction of machining deformation induced by turning residual stress in thin circular parts using ritz method

Workpiece deformation induced by surface residual stress during turning is a serious concern in the manufacturing of thin-walled parts. Prediction of machining deformations caused by residual stress is essential to explain deformation mechanism and design machining strategies. Although many studies have been focused on calculating those deformations using the finite element method (FEM), it is time-consuming and redundant. Based on energy equations considering residual stress fields developed by the three-dimensional elastic theory and the principle of minimum potential energy, a new analytic model was established to predict machining deformation of the thin circular parts. In this model, the modified Rayleigh-Ritz method and pseudo inverse method were used to solve energy equations under various machining conditions to obtain machining deformation. Corresponding experiments and existing methods were considered to validate the accuracy and efficiency of the proposed model. Based on the quantitative results of the proposed model, the effects of machining conditions on machining deformation were discussed comprehensively, which provides guidance for machining strategies. • The energy equations of the thin circular plates considering residual stress distributions in all directions is developed. • The improved Rayleigh–Ritz method associated with the pseudo inverse method are used to solve the machining deformation . • The influence factors of machining deformation induced by residual stresses are comprehensively analyzed.

Wear Mechanism of Multilayer Coated Carbide Cutting Tool in the Milling Process of AISI 4340 under Cryogenic Environment.

Cryogenic technique is the use of a cryogenic medium as a coolant in machining operations. Commonly used cryogens are liquid nitrogen (LN2) and carbon dioxide (CO2) because of their low cost and non-harmful environmental impact. In this study, the effects of machining conditions and parameters on the wear mechanism were analysed in the milling process of AISI 4340 steel (32 HRC) under cryogenic conditions using a multilayer coated carbide cutting tool (TiAlN/AlCrN). A field emission scanning electron microscope with energy-dispersive X-ray analysis was used to examine the wear mechanisms comprehensively. At low machining parameters, abrasion and adhesion were the major wear mechanisms which occurred on the rake face. Machining at high machining parameters caused the removal of the coating material on the rake face due to the high temperature and cutting force generated during the cutting process. In addition, it was found that continuously adhered material on the rake face would lead to crater wear. Furthermore, the phenomenon of oxidation was also observed when machining at high cutting speed, which resulted in diffusion wear and increase in the crater wear. Based on the relationship between the cutting force and cutting temperature, it can be concluded that these machining outputs are significant in affecting the progression of tool wear rate, and tool wear mechanism in the machining of AISI 4340 alloy steel.

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.

Effects of machining conditions on the specific cutting energy of carbon fibre reinforced polymer composites

This article presents an approach to evaluate the effects of different machining conditions on the specific cutting energy of carbon fibre reinforced polymer composites (CFRP). Although research works in the machinability of CFRP composites have been very substantial, the present literature rarely discussed the topic of energy consumption and the specific cutting energy. A series of turning experiments were carried out on two different CFRP composites in order to determine the power and specific energy constants and eventually evaluate their effects due to the changes in machining conditions. A good agreement between the power and material removal rate using a simple linear relationship. Further analyses revealed that a power law function is best to describe the effect of feed rate on the changes in the specific cutting energy. At lower feed rate, the specific cutting energy increases exponentially due to the nature of finishing operation, whereas at higher feed rate, the changes in specific cutting energy is minimal due to the nature of roughing operation.

MD Simulations of Nanomachining Monocrystalline Silicon

Molecular dynamics (MD) simulations of nanomachining of monocrystalline silicon were performed with the aid of Tersoff potential. The effects of machining conditions on the nature of heat distribution and corresponding phase transformation during nanomachining were investigated. It is clearly demonstrated that heat distribution shows a roughly concentric shape around the shear zone. A steep temperature gradient is observed in diamond tool and the highest temperature lies in chip. Stress distribution presents dual annular shapes, the highest compressive stress and tensile stress lay in shear zone and machined surface, respectively. Phase transformation mainly occurred in chips, shear zone and machined surface. Additionally, atoms in the machined surface are transformed from diamond cubic structure (Si-I) to β-tin structure (Si-II) and bct5-Si.

Fine Metallic Particle Emission when Milling Aluminium Alloys and Aluminium Metal Matrix Composites

Machining activities generate aerosols that can be harmful, degrade the environment or slow down theproduction. The main objective of this study was to evaluate the effects of machining conditions (cutting parameters and workpieces materials) on metallic particle emission during milling to help determining the machining conditions leading to ecological and occupational safe machining practices. The workpieces materials tested were aluminium alloys (6061-T0, T4 and T6 and A319) and aluminiummetal matrix composites (MMC) containing hard particles (SiC) for wear resistance and nickel-coated graphite particles for improved friction and machinability. It is found that the reinforcement within the aluminium MMCs reduces the fine particle emission as compared to unreinforced aluminium alloys. In general, the quantity of the particle emitted depends on the machining parameters settings. Among the aluminium alloys, the particle emission appeared to be dependent on material’s ductility.

Performance of nanocomposite ceramics by wire electrical discharge machining

A new process of machining the TiN/Si3N4 nanocomposite ceramics using wire electrical discharge machining is proposed in this paper. The process is able to effectively machine a large surface area on the TiN/Si3N4 nanocomposite ceramics with good surface quality and low cost. The effects of machining conditions on the material removal rate, and surface roughness have been investigated. The surface microstructures machined by the new process are examined with a scanning electron microscope (SEM). The results show that the TiN/Si3N4 nanocomposite ceramics is removed by melting, evaporation and thermal spall. The experimental results indicate that the cutting speed (material removal rate), the surface roughness and the width of the slit of cutting test material significantly depend on experiment parameters. An appropriate servo voltage, a short pulse-on time, and a short pulse-off time, which are normally associated with a high cutting speed, have little effect on the surface roughness. During experiments, parameters such as open circuit voltage, pulse duration and dielectric fluid pressure were changed to explore their effect on the surface roughness.

Prediction of machining induced microstructure in Ti–6Al–4V alloy using 3-D FE-based simulations: Effects of tool micro-geometry, coating and cutting conditions

Machining process affects surface integrity of Ti–6Al–4V titanium alloyed end-products. During thermal-mechanical loading and subsequent processing that take place in machining, grain size is altered at the subsurface through dynamic recrystallization and subsequent recovery. This can cause softening or hardening of the machined surfaces affecting surface integrity depending on the resultant grain sizes and phase fractions. Prediction of machining induced surface integrity specifically microstructure and grain size can be achieved by using Finite Element-based process simulations and calculated temperature, strain, stress and strain rate fields. This study presents experimental and numerical investigations in machining induced subsurface microstructure, microhardness and grain size in Ti–6Al–4V titanium alloy. Machining surfaces are investigated by measuring subsurface microhardness and grain size and phase fractions in each cutting conditions through scanning electron microscopy and image processing. 3-D FE machining simulations are conducted at the same cutting conditions and tool geometry to predict dynamic recrystallization (DRx) and resultant grain size by utilizing the Johnson–Mehl–Avrami–Kolmogorov model for Ti–6Al–4V alloy. The study also presents investigations and discussions about the effects of machining conditions (tool geometry, coating, and cutting conditions) on the microhardness and grain size in machining Ti–6Al–4V. Numerical modeling results are compared with experimental results and distinct effects of tool edge radius, coating, and cutting conditions on machining induced subsurface microstructure specifically on the changes in grain size due to dynamic recrystallization and recovery have been reported.

Effects of machining conditions on specific surface of PM<sub>2.5</sub> emitted during metal cutting

Indoor air quality has become an important matter for health and safety. Most manufacturing processes generate aerosols. In the metal cutting industry, dry machining processes are accompanied by dust emission (fogs, fine chips and metallic dust in both micrometers and nanometers scales) that has impacts on workers’ health. This research work aimed to understand and reduce the harmful impacts of the machining process on the occupational safety. In this study, an experimental investigation was carried out on fine and ultrafine metallic dust emission during slot milling of 2024-T351, 6061-T6 and 7075-T6 aluminum alloy in dry conditions. It was confirmed that the cutting conditions influence significantly the specific surface area of ultrafine particles. It was also found that the cutting speed is a determinant factor for specific surface area of ultrafine particles and control during the slot milling process.

A new thermal model for bone drilling with applications to orthopaedic surgery

This paper presents a new thermal model for bone drilling with applications to orthopaedic surgery. The new model combines a unique heat-balance equation for the system of the drill bit and the chip stream, an ordinary heat diffusion equation for the bone, and heat generation at the drill tip, arising from the cutting process and friction. Modeling of the drill bit-chip stream system assumes an axial temperature distribution and a lumped heat capacity effect in the transverse cross-section. The new model is solved numerically using a tailor-made finite-difference scheme for the drill bit-chip stream system, coupled with a classic finite-difference method for the bone. The theoretical investigation addresses the significance of heat transfer between the drill bit and the bone, heat convection from the drill bit to the surroundings, and the effect of the initial temperature of the drill bit on the developing thermal field. Using the new model, a parametric study on the effects of machining conditions and drill-bit geometries on the resulting temperature field in the bone and the drill bit is presented. Results of this study indicate that: (1) the maximum temperature in the bone decreases with increased chip flow; (2) the transient temperature distribution is strongly influenced by the initial temperature; (3) the continued cooling (irrigation) of the drill bit reduces the maximum temperature even when the tip is distant from the cooled portion of the drill bit; and (4) the maximum temperature increases with increasing spindle speed, increasing feed rate, decreasing drill-bit diameter, increasing point angle, and decreasing helix angle. The model is expected to be useful in determination of optimum drilling conditions and drill-bit geometries.

Machining performance of silicon carbide ceramic in end electric discharge milling

A new process of machining silicon carbide (SiC) ceramic using end electrical discharge milling is proposed in this paper. The process is able to effectively machine a large surface area on SiC ceramic with good surface quality and low cost. The effects of machining conditions on the material removal rate, electrode wear ratio, and surface roughness have been investigated. The surface microstructures machined by the new process are examined with a scanning electron microscope (SEM), an energy dispersive spectrometer (EDS), and an X-ray diffraction (XRD). The results show that the SiC ceramic is removed by melting, evaporation and thermal spalling, the material from the tool electrode can transfer to the workpiece, and a combination reaction takes place during end electric discharge milling of the SiC ceramic.

Machining Performance and Surface Integrity of SiC Ceramic Machined Using Electrical Discharge Milling and the Mechanical Grinding Compound Process

A new combined process that integrates electrical discharge milling and mechanical grinding is presented. The process is able effectively to machine a large surface area on SiC ceramic with a good surface quality and low cost. The effects of machining conditions on the material removal rate, relative electrode wear ratio, and surface roughness were investigated. The surface microstructures machined by the new process were observed by a scanning electron microscope (SEM), an X-ray diffraction, and an energy dispersive spectrometer. The SEM micrographs show that the surfaces machined at rough machining mode and semi-finish machining mode are characterized by an uneven fusing structure, globules of debris, shallow craters, and micropores; the surface machined at finish machining mode is smooth, and covered by fewer little craters and pockmarks.

チタン電極を用いた炭素粉混入放電加工による表面改質

Recently, it was reported that a hard TiC layer could be made on the machined surface by EDM using a titanium electrode in kerosene and this technique was applicable to cutting tool such as throwaway tip or endmill. However, the layer is relatively thin and the surface roughness is not so small. Then, it is difficult to apply this method to a metal mold which needs glossy surface. In this study, a new method to form TiC layer by EDM for smaller surface roughness and thick layer is proposed, and the effects of machining conditions on characteristics of the layer are experimentally investigated. Furthermore, the wear resistance of EDMed surface was evaluated.Experimental analysis made it clear that a thick and smooth TiC layer could be generated on the machined surface by EDM using a titanium electrode in carbon powder mixed fluid. It was also pointed out that the hardness of modified surface became higher with increases of discharge duration or carbon powder concentration in the kerosene type machining fluid, and that the wear resistance of the layer was much larger than that of base material.

The effects of machining conditions on the flank wear of TiN-coated high speed steel tool inserts

The effects of machining conditions on the flank wear of TiN-coated high speed steel tool inserts

The effects of machining conditions on the flank wear of tin-coated high speed steel tool inserts

This paper explores the effects different machining conditions can have on the flank wear characteristics of TiN-coated high speed steel (HSS) tool inserts during dry turning. It is found that the extent of reduction in the measured wear rates depends strongly on the conditions of machining. Three major dominant wear mechanisms for TiN-coated HSS inserts have been identified; they are micro-abrasion, micro-abrasion and attrition, and edge chipping. The transition from one dominant mechanism to another is found to be more sensitive to cutting speed than to feed rate. Wear maps showing how wear rates and wear mechanisms vary with machining conditions have been constructed. They are useful in explaining some of the wear behaviour reported for TiN-coated HSS tools, and they provide an insight into how these coated tools may be better used to increase productivity.

Wire Electrical Discharge Machining of TiB<sub>2</sub> Composite

Wire electrical discharge machining of pressureless sintered TiB2 containing Cr and C as the sintering aids was investigated. The effects of machining conditions on the surface roughness and bending strength were discussed. The surface roughness increased with increase in the cutting speed. The bending strength remained with increase in the cutting speed to 5-40mm2/min. The bending strength of 320MPa was very close to the values for sintered body prepared by cut and polished with a diamond disc and powder.

オーステナイトステンレス鋼の研削性に及ぼす加工の影響

The effects of machining conditions on the grindability of austenite stainless steel were investigated by measuring the grinding forces, wheel wear and the effective cutting edge spaces under various grinding conditions.The grinding forces for austenite stainless steel increased rapidly at the initial stage of grinding process, it is observed that many chips of work material adhered to the peripheral surface of wheel and many abrasive grains failed off actively from the wheel surface.It is found that the effective improvement of grindavility for austenite stainless steel was obtained by using of high gradewheel and grinding fluid.

Electro-Discharge Machining of Ceramics (Part 2)

Electroconductive sialon-titanium nitride ceramic composite was machined with the electro-discharge machining method. Surface damage caused during machining in machined members was evaluated with the three point bend test. The machined and fracture surface were observed with a scanning electron microscope (SEM). The effects of machining conditions on the surface damage were discussed. Heat treatment of machined members was carried out in air for recovering their strength. Effects of the pulse duration and duty factor on the strength of machined members were noticiable. The flexural strength of machined member increased with decreases in pulse current and duty factor. Annealing in air had a good effect on the strength of a machined member. The highest strength of machined member attained after annealing was 856MPa, which was about the average flexural strength of the original body.