Mechanical Properties Of Workpiece Research Articles

On the Influence of Binder Material in PCBN Cutting Tools for Turning Operations of Inconel 718

Inconel 718 is a highly valued material in the aerospace and nuclear industries due to the fact of its exceptional properties. However, the processing of this material is quite difficult, especially through machining processes. Machining this material results in rapid tool wear, even when low material removal rates are considered. In this study, instrumented turning experiments were employed to evaluate the machinability of Inconel 718 alloy using PCBN tools while assessing the usage of two distinct binder phases, TiN and TiC, for those cutting tools. It was found that the tool life was highly sensitive to the cutting speeds but also affected by the workpiece mechanical properties. At lower cutting speeds, notch wear significantly impacted the tool integrity, whereas at higher cutting speeds, flank wear was the primary failure mode of the tool. The flank wear of the tools with TiN-based binder outperformed TiC by almost 30%, presenting a more consistent behavior when machining.

Acoustic emission monitoring of immersion quenching bath attributes

This paper describes the use of acoustic emission (AE) testing for monitoring immersion quenching bath attributes. Immersion quenching is a heat treatment process used to change the mechanical properties of metallic workpieces. The quenching bath cooling attributes degrade with prolonged use, thus affecting the workpiece mechanical properties. A non-destructive monitoring method of the quenching bath is required. An AE measurement system is proposed for this purpose. Steel specimens are quenched in tap water, deionized water, 5 % NaCl-water solution and 5 % detergent-water solution. AE is measured with four piezoelectric sensors. The influence of quenching bath attributes on specimen cooling is described together with the measured AE signals. AE signal peak amplitude diagrams are evaluated. A reference AE peak amplitude signal is presented with the measurements. The quenching bath attribute assessment method is established by monitoring the amount of outlying AE signals in regard to the reference AE signal. The results confirm that AE monitoring provides a decent way of assessing quenching bath attributes and thus also the quenched specimen mechanical properties.

Temperature monitoring of milling processes using a directional-spectral thermal radiation heat transfer formulation and thermography

Temperature is an important property to be monitored during cutting operations, such as in the milling of metals, because it affects the workpiece mechanical properties, the machining tool performance, and the process efficiency. For this reason, authors have used thermography to monitor thermal and spatial gradients, and to estimate temperature. The problem is that IR cameras native applications are mostly based on the diffuse-gray approximation, with emissivity set as a constant value. The diffuse-gray approach is a reasonable choice for opaque surfaces with emissivity approximately constant in respect to the wavelength, which is not the case in most of the time for metals under cutting operation. In this work we propose a more suitable methodology that uses radiative heat transfer directional-spectral relations to estimate cutting process temperatures during face milling of metals, using the full electrical response of commercial infrared cameras as an input. AISI H13 steel was used as the workpiece material. In the first part of the experiments, emissivity was estimated for eight different temperatures from 50 °C to 250 °C, using both directional-spectral and diffuse-gray approaches. Temperature was measured using a thermocouple type T, calibrated using a PT-100 reference from 50 °C to 250 °C. In the second part, we used the emissivity obtained in the first part to estimate the temperature for twelve different cutting conditions, again using both directional-spectral and diffuse-gray approaches. We compared the results of both methods, also with the direct application of emissivity provided in infrared cameras manuals. The temperature deviation between the different approaches were up to 41%, which demonstrates that the temperature estimation procedure affects the results substantially.

Experimental approach for a grinding burn in-process inspection system based on Eddy Current

During grinding some detrimental microestructural changes can appear in the workpiece if the temperature reaches the tempering point in the contact zone. This “thermal damage”, commonly known as grinding burn, has negative consequences in the workpiece mechanical properties and its avoidance and detection is crucial to optimize grinding operations. Magnetic methods (Barkhausen noise, Eddy Current) are nowadays applied post process to detect burns automatically and without the subjectivity of the inspector (Acid Etching Method). However, the potential use of these magnetic methods during in-process inspection is a matter that has not been studied in detail yet.The objective of this paper is to evaluate the Eddy Current technology for the grinding burn inspection in combination with other process out-puts. Experimental tests have been performed in the machine at different conditions considering different inspection strategies. The results show the benefits of the present approach and serve as a starting point for the development of a future in-process inspection system.

Study of the measurement and mathematical modelling of temperature in turning by means equivalent thermal conductivity

The temperature measurement in the workpiece/tool interface is one of the main difficulties in the machining process. The lower temperatures are required because the workpiece or the tool are affected by the heat generated in the tool/chip interface. The cutting temperature affects the workpiece mechanical properties and consequently the cutting forces. The work is focused on the temperature prediction in turning by a modified equation. The analysis of variance (ANOVA) was used to evaluate the influence of cutting speed, feed and tools coating in the temperature. These factors presented a significant influence. The lowest temperature was obtained using multilayer coated tool. For this, an equation was developed considering the cutting speed, feed and equivalent thermal conductivity (Keq). The predicted results show that the use of Keq of the materials involved allows the decrease of errors within the experimental and prediction values. The formulated model allowed to obtain a simplified equation.

Numerical and experimental analysis of turbulent flow and heat transfer of minimum quantity lubrication in a turning process using discrete phase model

Utilizing coolant strategies is vital in the manufacturing industry to reduce the tool wear and heat dissipation through the workpiece and cutting insert consequently maintaining workpiece mechanical properties and enhancing tool life. This becomes more significant when machining difficult to cut materials, such as Austempered Ductile Iron (ADI), where the amount of heat generated significantly affects the insert life and the mechanical properties of the workpiece. To the best of the authors knowledge there is a gap in the open literature on machining of ADI. An environmental friendly coolant strategy known as minimum quantity lubrication (MQL) uses small amounts of oil such as rapeseed or castor. A computational fluid dynamics (CFD) model was developed in this investigation using ANSYS Fluent to model the temperature profile and the oil droplet behavior in the cutting zone. The tool temperatures employed in the CFD model were generated by a numerical frictional model. The CFD model compared multiple coolant strategies (MQL, Dry, Flood, Aerosol Water) at different flow rates and inlet pressures to predict the thermal effects on the tool and to select optimum process parameters. Experimental tests, conducted using a CNC Lathe on Grade 2 (ADI), validated the numerical model's results for both dry, flood coolant and MQL with a 1.25%, 1.33% and 6.56% relative error respectively. The experimental results indicated that the measured flank wear of the cutting insert was 1.260 mm, 0.341 mm and 0.302 mm for the dry, flood and MQL coolants respectively.

Prediction about ground hardening layers distribution on grinding chatter by contact stiffness

The grinding hardening is an integrated manufacturing technology which combines the surface hardening theory and the grinding technology. However, the grinding chatter accompanies with the whole grinding hardening process. It is the existence of the grinding chatter that makes the transformation unsteady. To this end, the paper presents a three-hybrid model to investigate the relationship between the grinding chatter and the grinding hardening layers distribution. The dynamic grinding force with the analytic and numerical method is calculated firstly. Then the finite difference method (FDM) is used to obtain the dynamic temperature distribution accordingly. Thirdly, the cellular automata (CA) method is applied to calculate the transformed microstructure distribution under different chatter strengths. The study shows that the thickness of the grinding hardening layers goes up with the increase of the grinding chatter. However, the quality of the grinding hardening layers reduces with the increase of the chatter strength. In addition, the martensite content varies with different hardening layers since each layer has its own unique temperature distribution. Moreover, metallurgical experiments are conducted to validate the proposed model. The model is anticipated to be meaningful for the improvements of workpiece's mechanical properties by controlling the chatter strength in the industry manufacturing.

Effects of processing parameters on underfill defects in deep penetration laser welding of thick plates

Underfill defect in welding affects not only the surface integrity but also the mechanical properties of workpiece. In this paper, the effects of the process parameters on underfill defects were investigated, and the deep penetration welding by a 10-kW fiber laser on 12-mm-thick stainless steel plates was used as the case study. The correlation of the processing parameters with the formation and elimination of underfill defects was analyzed and discussed. It was found that during the autogenous laser welding of thick plates, the direction of laser beam relative to gravity has a significant effect on the formation of underfill defects, and the preferable direction was an inclination angle of 60° with respect to the gravity. A negative defocus tended to obtain a full penetration weld with underfill and undercut defects. The higher the welding speed was, the lower the underfill depth was on the top surface. This phenomenon was observed on the full penetration welds at a defocus of − 10 mm. With a negative defocus, it became feasible to optimize the combination of the focal position and the welding speed to achieve a satisfactory appearance of welds. In addition, a bottom-shielding ambience helped the full penetration in the laser welding process positively.

Application of Micro Structured, Boron Doped CVD-diamond as μEDM Tool Electrodes

High precision cavities are used for micro injection and micro embossing tools in the field of tool making and are mainly used for small batch or mass production of micro parts. In order to fabricate a large quantity of parts, wear resistant tool materials are required. In possession of a high hardness and a high Young's Modulus, such materials are often hard or even impossible to machine by conventional fabrication processes. Being independent of the work piece's mechanical properties, Micro-Electrical Discharge Machining (μEDM) is predestined for this case.μEDM is based on the modification of state of the art process technologies and universal machine tools applied for electrical discharge machining operations [1,2]. Besides the adjustment of the electrical parameters, the μEDM-process is also determined by the tool electrode's material which has a big influence on the material removal rate VW, the electrode's wear behavior, as well as the process results concerning surface quality and dimensional accuracy [3]. Experimental investigations aim at decreasing the wear of tool electrodes using novel electrode materials. To assure an efficient process, short production times and low tool wear ϑ are demanded. Therefore, electrodes with excellent electrical and thermal conductivity along with a high mechanical strength have to be used.Boron doped CVD-diamond is fulfilling these criteria. Microstructures within thin CVD-diamond foils are realized by direct structuring utilizing laser ablation and by indirect structuring using micro-structured copper substrates in the CVD-process, which transfer the micro-structure onto the growing diamond layer. Experiments were conducted in order to identify suitable EDM-parameters for different workpiece materials, namely steel 90MnCrV8, silicon carbide SiSiC and tungsten carbide K40F, which lead to lower tool wear ϑ and high accuracy.

Eccentric rotary swaging variants

Rotary swaging is an incremental cold forming process that changes beneath the geometry also the microstructure and mechanical properties of workpiece. Especially a new process design with Eccentric Flat Shaped Dies (EFSD) influences both the kind and amount of stress and plastic strain and consequently the material structure and hence the material and workpiece properties. Eccentric rotary swaging typically provides a helical material flow. According to the process parameters the microstructure features a typical eddy pattern with a spiral shaped grain orientation. The forming process can be carried out in one or more process steps. In a multi-stage process, it is possible to change the feed direction and, hence, the material flow helix direction. This approach can be used as a possibility to improve the homogeneity of the workpiece and material properties. In addition, for this aims an intermediate heat treatment in multi-stage forming operations could be realised. Following the goal of optimising the final properties, the question arises how these mechanical and thermal treatments affect the material microstructure and the forming properties of the workpiece and how they interact. Experiments were conducted with austenitic stainless steel rods of grade AISI304. The effects of the varied feed direction, feed velocity and heat treatment between the forming operations are discussed.

Material microstructure affected machining: a review

The machining induced material microstructure evolution path is determined from the temperature and mechanical loading history. Inversely, the machining forces and machined part surface integrity are dependent on the material microstructure attributes. Most of the previous research work with a microstructure consideration in machining stays largely on the experimental observation stage. A comprehensive thermal-mechanical-microstructure coupled machining process modeling framework is still missing. This paper reviews the recent research work on the material microstructure evolution in the context of machining components. The material microstructure property change on the workpiece material in the machining process are analyzed. The effects of material microstructure evolution on workpiece mechanical properties and surface integrity are investigated. It is concluded that a physical based material microstructure affected machining model is needed for the machining process optimization.

Machinability of Hastelloy C-276 using Hot-pressed sintered Ti(C7N3)-based cermet cutting tools

C-276 nickel-based alloy is a difficult-to-cut material. In high-speed machining of Hastelloy C-276, notching is a prominent failure mode due to high mechanical properties of work piece, which results in the short tool life and low productivity. In this paper, a newly developed Ti(C7N3)-based cermet insert manufactured by a hot-pressing method is used to machine the C-276 nickel-based alloy, and its cutting performances are studied. Based on orthogonal experiment method, the influence of cutting parameters on tool life, material removal rates and surface roughness are investigated. Experimental research results indicate that the optimal cutting condition is a cutting speed of 50 m/min, depth of cut of 0.4 mm and feed rate of 0.15 mm/r if the tool life and material removal rates are considered comprehensively. In this case, the tool life is 32 min and material removal rates are 3000 mm3/min, which is appropriate to the rough machining. If the tool life and surface roughness are considered, the better cutting condition is a cutting speed of 75 m/min, depth of cut of 0.6 mm and feed rate of 0.1 mm/r. In this case, the surface roughness is 0.59μm. Notch wear, flank wear, chipping at the tool nose, built-up edge(BUE) and micro-cracks are found when Ti(C7N3)-based cermet insert turned Hastelloy C-276. Oxidation, adhesive, abrasive and diffusion are the wear mechanisms, which can be investigated by the observations of scanning electron microscope and energy-dispersive spectroscopy. This research will help to guide studies on the evaluation of machining parameters to further advance the productivity of nickel based alloy Hastelloy C-276 machining.

Experimental Study of Geometrical Parameters of Abrasive Grains in Modeling their Cutting Edges with the Surface of Rotation

In machining with grinding, it is necessary to know values of geometrical parameters of cutting edges of abrasive grains. In this paper for modeling of cutting edges of abrasive grains with rotation surfaces based on generatrix as a power function and for division cutting edges on both plowing and forming a chip, values of basic parametersBP,NPwere obtained experimentally. The influence of abrasive grain size, sieve-shaking procedure, mechanical properties of workpiece and type of abrasive material on these parameters was determined. The restrictions of this model were designated. It is established that traditional parameters such as corner radiusrand apex angle 2θ can be used in case of microcutting with small grain penetration depth.

Numerical Simulation of Workpiece Thermal Field in Drilling CFRP/Aluminum Alloy

Machining is a process implying extremely high coupled thermo-mechanical stresses. The workpiece mechanical properties decrease with the temperature generated during the process and that temperature has a direct influence on wear intensity undergone by the tool. In the case of a drilling operation, the temperature generated by the cutting process can lead to metal burr formation and/or composite matrix degradation by burning. When these two materials are used in the form of a sandwich-type stacking, the temperature attained in the metallic part can cause new defects such as: i) a difference between the diameters measured in each material and ii) organic matrix damages due to heat diffusion from the metal towards the CFRP layer. Temperature reached at the tool/workpiece interface is difficult to measure during drilling operation, due to its enclosed configuration; numerical simulation is therefore a good alternative to access to this information. The purpose of this study is to develop and carry out numerical simulations in order to estimate the workpiece thermal field generated during drilling. The simulations are validated by comparing simulated and measured temperatures at 4 mm from the holes wall. This method is applied to evaluate thermal field generated during drilling (with chip removing cycles) of CFRP/Aluminum alloy stacks. The influence of the drilling kinematics on the workpiece thermal field is also investigated.

Analytical prediction and experimental verification of surface roughness during the burnishing process

Burnishing is a superficial plastic deformation process used as a surface smoothing and surface enhancement finishing treatment after some machining processes to generate a compact and wear-resistant surface for longer and efficient component life.In this study, the smoothing mechanism of burnishing is established, in which the geometries of burnishing tool and workpiece, the microscopic topography of the machined surface and the mechanical properties of workpiece are taken into consideration. The elasto-plastic deformation law of the cross-section of a stripy asperity is established by the solutions to the Boussinesq–Flamant problem and then by the slip-line field theory. The expressions describing the relation between surface roughness and burnishing force are derived using the Winkler foundation assumption where the shear between adjacent cross-sections is ignored.The expressions reveal that the decrease of surface roughness is proportional to burnishing force to the 2/3 power in roller burnishing and to the 1/2 power in ball burnishing. The proportional constants are only determined by the yield stress of workpiece with geometrical parameters held constant, and have nothing to do with the elastic constants such as Young's modulus and Poisson's ratio used in Hertz theory. The lowest surface roughness and the optimum burnishing force can be obtained. The lowest surface roughness is proportional to the initial surface roughness, and burnishing can decrease the surface roughness of workpiece up to about 75% to 87.5% which depends only on the semi-angle of asperity. The above adopted assumptions, the conclusions worked out and the predicted results are verificated by the experiments and related literatures.

The influence of die geometry and workpiece mechanical properties in T-Shape friction test

In this study, T-Shape friction test was redesigned to make it more suitable for application to microforming processes. Workpiece with aspect ratio (length/diameter) of 5 was proposed in order to ease workpiece handling. The die geometry was also modified from the original test to improve friction sensitivity especially within the range of friction factors commonly observed in metal forming. Geometric deviation of the die was simulated using Deform-2D to establish the acceptable tolerance for the fabrication. The effect of variation in workpiece mechanical properties on the test behavior was also investigated through Deform-2D simulation. Based on simulations on a 1mm diameter copper workpiece, a tolerance of 0.01mm (1% of workpiece diameter) was found to be the most suitable for the die fabrication. In addition, it was shown that variations in workpiece mechanical properties of up to 10% do not significantly influence the friction test results. Ultimately, T-Shape test experiment was conducted using copper workpieces to examine how the test complied with the friction behavior observed in the experiment.

Wear characteristics of nano TiAlN-coated carbide tools in ultra-high speed machining of AerMet100

In this paper cutting experiments of AerMet100 (52 HRC) using nano TiAlN-coated carbide tools with cutting speed from 250m/min to 7000m/min are carried out. The cutting tool wear characteristics under ultra-high cutting speeds are examined and the corresponding mechanisms are analyzed. The focus is put on the tool wear characteristics and mechanisms at cutting speed above 500m/min. The influences of cutting temperature and workpiece dynamic mechanical properties on tool wear are discussed. The results show that the tool wear mechanism is highly influenced by cutting temperature and workpiece mechanical properties. At cutting speed of 500m/min the dominate wear mechanism is micro chipping and fracture due to the cutting force vibration and cold welding of contacting materials between cutting tool and workpiece. At higher cutting speed from 1000m/min to 7000m/min the predominant tool wear mechanisms are abrasion, adhesion, and fracture due oxidation, and thermal softening, and grooving by hard grains. The roughness of tool flank at this cutting stage decreases with the increase of cutting speed due to the high thermal softening. The increase of workpiece material brittleness with the increase of cutting speed lowers the elastic rebound of machined surface and reduces the tool wear rate.

Test Research on the Surface Residual Stress of Dimensional Ultrasonic Vibration Grinding for Al<sub>2</sub>O<sub>3</sub>/ZrO<sub>2(n)</sub>

Based on the research for the structure of the ceramic nanocomposites’ intragranular for Al2O3/ZrO2(n)，we did the test by the workpiece two-dimensional vibration grinding(WTDUVG), and focus on analyzing the characteristic and the effect element of the two-dimensional ultrasonic vibration grinding ceramic surface residual stress by the XRD diffraction. The result show that ceramic dimensional ultrasonic vibration grinding surface tensile stress is less than the same conventional grinding (CG) surface under tensile stress; two-dimensional ultrasonic vibration grinding surface residual compressive stress than conventional ground surface residual stress under the same grinding. Material removal mechanism of the grinding nature of the surface residual stress, when the material removaled by ductile deformation, grinding surface equal residual stress; when the material removaled by brittle- ductile mixed mode, the grinding surface tensile stress reduced, because the fracture of the ground surface, tensile stress released. As a results, the grit size of grinding wheel, Grinding depth and workpiece mechanical properties are the main technology factors affected the nature and size of the residual stress of ground surface.

The effect of peel ply layer on hole integrity when drilling carbon fibre-reinforced plastic

Fibre/matrix delamination is a common problem when cutting carbon fibre-reinforced plastic (CFRP) that can have a detrimental effect on workpiece mechanical properties and hence compromise the in-service performance of the composite part. The present paper details experimental results when drilling small holes (1.5 mm diameter) through backed and un-backed CFRP laminates using tungsten carbide twist drills to determine the effect of peel ply layers (∼100 µm thick nylon sheet attached on both sides of 3 mm thick laminates) on hole entry and exit delamination. Considerable reduction in damage relating to fuzzing, spalling, edge chipping, and delamination was observed when drilling the nylon-backed CFRP material, with scanning electron micrographs showing significantly inferior hole quality for the corresponding un-backed workpieces, particularly at hole exit.

被加工材性質がスピニング成形性に及ぼす影響に関する解析的検討(G04-2 先進加工技術とその評価,G04 機械材料・材料加工)

被加工材性質がスピニング成形性に及ぼす影響に関する解析的検討(G04-2 先進加工技術とその評価,G04 機械材料・材料加工)