Initial Temperature Of Workpiece Research Articles

Investigation of the Temperature Field during Radial-Shear Rolling of Technical Copper

Radial-shear rolling is one of the most promising methods of metal forming, allowing to develop a level of strain in the rolled bar sufficient to obtain an ultrafine-grained structure. At the same time, it has already been theoretically and experimentally confirmed that after metal processing by this method, a gradient distribution of grain size is observed in the cross section of the rod, which is a consequence of the laminar-turbulent flow of metal in the deformation zone. This work, carried out within the framework of grant №AP14869128, funded by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan, is devoted to the study of the temperature field during radial-shear rolling of M1 technical copper at an initial workpiece temperature of 20°C. To study the temperature distribution over the bar cross section, finite element modeling of radial-shear rolling of M1 technical copper was performed in the Deform program. A rod with a diameter of 30 mm and a length of 150 mm was set as the initial workpiece. It was decided to conduct three passes of radial-shear rolling with compression of 3 mm per pass. In addition to studying the temperature fields on the workpiece, the temperature distribution on the rolls was also considered. Analysis of the simulation results showed that the temperature distribution over the cross-section of the rod has a gradient character.

Effect of temperature on milling stability of thin-walled parts

Milling, as a common machining method, is widely used in rough machining and final finishing of various materials. In this paper, according to the milling temperature produced in the milling process, the formula of heat distribution coefficient for workpiece milling is established. By means of Deform-3D finite element software to carry out orthogonal cutting simulation of workpiece, the influence of different machining parameters on milling heat distribution coefficient is studied, the optimal machining parameters are determined, and the milling temperature experiment is carried out to verify the simulation temperature. The experimental results show that the simulation temperature is very close to the experimental workpiece temperature, and the error is very small, which verifies the accuracy of the method. At the same time, the influence of different initial temperature of workpiece on the milling force and stability is also studied. The results show that proper heating of the workpiece can effectively improve the milling stability of the thin-walled parts.

A Review of the Boiling Curve with Reference to Steel Quenching

This review presents an analysis and discussion about heat transfer phenomena during quenching solid steel from high temperatures. It is shown a description of the boiling curve and the most used methods to characterize heat transfer when using liquid quenchants. The present work points out and criticizes important aspects that are frequently poorly attended in the technical literature about determination and use of the boiling curve and/or the respective heat transfer coefficient for modeling solid phase transformations in metals. Points to review include: effect of initial workpiece temperature on the boiling curve, fluid velocity specification to correlate with heat flux, and the importance of coupling between heat conduction in the workpiece and convection boiling to determine the wall heat flux. Finally, research opportunities in this field are suggested to improve current knowledge and extend quenching modeling accuracy to complex workpieces.

Characterization of material strain and thermal softening effects in the cutting process

Accurate descriptions of workpiece behaviors are indispensable for achieving reliable simulations of the cutting process. However, the material plastic constitutive models obtained through conventional material tests do not apply in the ranges of strain and strain rate encountered in the realistic machining processes. To address this issue, in this study, we attempt to develop a methodology to understand and identify the plastic deformation behaviors based on high-speed filming and induction preheating during the cutting tests. Different levels of strain, strain rate, and temperature are realized by varying the rake angle, cutting velocity, and initial workpiece temperature, respectively. The plastic deformation and temperature rise in the primary shear zone are characterized by the fine-scale digital image correlation technique and heat convection–conduction equation, respectively, thus rendering the machining test into a high-dynamic-material testing method. The material exhibits strain softening in the primary shear zone and a reduced thermal softening effect under rapid heating conditions. These initial findings can deepen the understanding of material behaviors during the cutting process and can be further developed for implementation in numerical machining models.

Influences of key process parameters on orbital forging of thin-walled smartphone shell frame of aluminum alloy

Smartphone shell frame is a thin-walled component, which is quite difficult to be fabricated by integral die forging process because of narrow die cavity and high forging load. In this paper, an orbital forging process is proposed to forge the thin-walled smartphone shell frame. Firstly, a FE model on orbital forging of thin-walled smartphone shell frame is developed under Deform-3D platform. By using this model, the influences of initial temperature of workpiece T, tilt angle of swing die γ and feed moment per rotation λ on temperature distribution, equivalent strain distribution and forging load are comprehensively discussed. The results show that final temperature of workpiece compared with initial temperature of workpiece T can be improved with decreasing initial temperature of workpiece T, increasing tilt angle of swing die γ and increasing feed moment per rotation λ. Equivalent strain is positively correlated with tilt angle of swing die γ, negatively correlated with feed moment per rotation λ and almost unaffected by initial temperature of workpiece T. Moreover, forging load can be obviously reduced by increasing initial temperature of workpiece T, increasing tilt angle of swing die γ and decreasing feed moment per rotation λ.

Dimensional inequalities in chip segments of titanium alloys

A change in segment shape and geometry provides vital information about the strain in the chip segments, plastic deformation and correspondingly a pattern of energy consumption during a machining. These machinability parameters are related with segment dimensions using dimensional inequalities. Dimensional inequalities capture geometrical features of chip segments such as segment width, length of free chip surface, length of uncut segment, shear angle, included angle and their correlation with each other. To validate these inequalities, chip freezing experiments and numerical simulations were performed by changing the initial temperature of work piece from room, to LN2 pre-cooled, to elevated temperature of 260 °C. Measurements of chip segment dimensions both, experimentally and numerically validate the proposed inequalities.

Numerical analysis of die wear characteristics in hot forging of titanium alloy turbine blade

This paper provides a simple and effective numerical modeling procedure to determine the thermal effects of initial workpiece temperature (Tw) and preheated die temperature (Td) on the die wear behavior in turbine blade forging. In particular, a local 3D finite element (FE) approach embedded with the modified Archard wear model is developed for the numerical modeling and subsequently validated by comparing the simulated average contact pressure to the analytical one, as well as the experiment from literature. Then, the wear evolution and distribution of blade forging dies are characterized numerically. Further, the thermal effects of both initial workpiece and preheated die temperatures on the die wear characteristics are assessed, and the strategies for decreasing the die wear volume are consequently suggested. The results show that the die wear depth distribution is uneven and the wear volume is more influenced by the preheated die temperature in hot forging process of the blade.

Effects of Process Parameters on Deformation and Temperature Uniformity of Forged Ti-6Al-4V Turbine Blade

This work is motivated by the frequent occurrence of macro- and microdefects within forged Ti-6Al-4V turbine blades due to the severely nonuniform strain and temperature distributions. To overcome the problem of nonuniformity during the blade forging operation, firstly, a 2D coupled thermo-mechanical finite element approach using the strain-compensated Arrhenius-type constitutive model is employed to simulate the real movements and processing conditions, and its reliability is verified experimentally. Secondly, two evaluation indexes, standard deviation of equivalent plastic strain and standard deviation of temperature, are proposed to evaluate the uniformity characteristics within the forged blade, and the effects of four process parameters including the forging velocity, friction factor, initial workpiece temperature and dwell time on the uniformity of strain and temperature distributions are carefully studied. Finally, the numerically optimized combination of process parameters is validated by the application in a practical process. The parametric study reveals that a reasonable combination of process parameters considering the flow resistance, flow localization and the effects of deformation and friction heating is crucial for the titanium alloy blade forging with uniformity. This work can provide a significant guidance for the design and optimization of blade forging processes.

Analysis on Shear Deformation for High Manganese Austenite Steel during Hot Asymmetrical Rolling Process Using Finite Element Method

Based on the rigid-plastic finite element method (FEM), the shear stress field of deformation region for high manganese austenite steel during hot asymmetrical rolling process was analyzed. The influences of rolling parameters, such as the velocity ratio of upper to lower rolls, the initial temperature of workpiece and the reduction rate, on the shear deformation of three nodes in the upper, center and lower layers were discussed. As the rolling parameters change, distinct shear deformation appears in the upper and lower layers, but the shear deformation in the center layer appears only when the velocity ratio is more than 1.00, and the absolute value of the shear stress in this layer is changed with rolling parameters. A mathematical model which reflected the change of the maximal absolute shear stress for the center layer was established, by which the maximal absolute shear stress for the center layer can be easily calculated and the appropriate rolling technology can be designed.

Effects of forming parameters on coupled thermomechanical behaviours in combined ring rolling

Combined ring rolling (CRR) is a new method for manufacturing rings which feature thick walls, deep grooves and small bores. Compared with general ring rolling, two driven rolls with fixed axes are added to control the circumferential metal flow and form the deep groove. Rolling force and energy, strain distribution uniformity, and temperature distribution uniformity are very important to the process design and forming quality of rings, which are sensitive to rolling parameters, such as motions of the driving roll, temperature and friction. In this paper, the reasonable ranges of feed parameters were determined based on stable rolling conditions. A reliable 3D coupled thermomechanical finite element model was then established using the dynamic explicit code ABAQUS/Explicit and the effects of rolling parameters investigated, including rotational velocity of driving roll n, the feed velocity of the driving roll v, initial temperature of workpiece and friction among the rolls and the ring. The research results are significant for process design and forming optimisation of CRR production.

SPH/FE modeling of cutting force and chip formation during thermally assisted machining of Ti6Al4V alloy

SPH method was employed in this study to develop machining models to study the thermally assisted machining of Ti6Al4V process. Both 2D and 3D models were developed for investigations of chip formation and cutting force, respectively. Two sets of machining parameters under four different target initial workpiece temperatures were simulated. Corresponding thermally assisted machining experiments were conducted for the validation of the models. The influence of the initial workpiece temperature on the chip formation and cutting force was studied. The chip formation mechanism and its relationship with the cyclic cutting force were also discussed.

3D numerical investigation of thermally assisted high efficiency ductile machining of nanocrystalline hydroxyapatite

This study investigates the effects of four different variables (initial workpiece temperature, side rake angle, edge radius/feed rate, and nose radius/depth of cut) on ductile regime machining of a bioceramic material known as nanohydroxyapatite (nano-HAP) using 3D numerical simulation. AdvantEdge FEM Version 5.9 is used to conduct turning simulations of the nano-HAP workpiece. Tecplot 360 is used to analyze the results of the simulations. Because the workpiece is thin, the entire workpiece is set to a uniform initial temperature to simulate laser preheating of the material. Initial workpiece temperature, rake angle (side rake angle), edge radius, and nose radius are varied, and the effects of these operating conditions on critical feed are investigated. It is found that critical feed increases as initial workpiece temperature increases, and also as negativity of rake angle increases. For the edge radius, it is concluded that an initial increase causes an increase in critical feed – however, at some value of edge radius, critical feed shows no further increase; for the nose radius, critical feed appears to show no significant dependence.

FEA Modelling of Cutting Force and Chip Formation in Thermally Assisted Machining of Ti6Al4V Alloy

The improvement of machinability during thermally assisted turning of Ti-6Al-4V alloy was investigated by finite element modelling. A 2D thermally assisted turning model was developed and validated by comparing the simulation results with experimental results. Detailed analyses were carried out on the simulations in terms of the influence of the initial work-piece temperature on cutting forces and chip formation in the TAM process. The predicted cutting forces showed a very good correlation to the experimental results, and both the simulation and experiments have proved that the initial work-piece temperature plays an important role in determining the cutting force, with increasing initial temperature reducing the cutting force.

Effects of micro-milling conditions on the cutting forces and process stability

Determining stable cutting conditions for corresponding cutting tools with specific geometries is essential for achieving precision micro-milling with high surface quality. Therefore, this paper investigates the influence of the tool rake angle, tool wear and workpiece preheating on the cutting forces and process stability. An advanced micro-milling cutting force model considering the tool wear is proposed. The micro-milling cutting forces are predicted and compared with experimentally obtained results for two cutting conditions and four edge radii measured at different stages of the tool wear. It is found that the cutting forces increase by increasing the edge radius. It is also observed that the cutting forces are higher at a rake angle of 0° compared with a rake angle of 8°. The increase of the cutting forces is mainly associated with the change of the friction conditions between the tool and workpiece contact. Stability lobes are obtained for different edge radii, rake angles of 0° and 8°, initial workpiece temperature and different measured static run-outs. The predicted stability lobes are compared with the micro-milling force signals transformed into the frequency domain. It is observed that the predicted stability limits result in good correlation with the experimentally obtained chatter free conditions. Also, the stability limits are higher at smaller edge radii, higher preheating workpiece temperature and positive rake angles.

Study of surface temperature on laser cutting and welding power absorption

This paper studied the absorption of CO 2 laser beam in AISI 4340 steel under conditions of laser welding. The influence of the power density, the type of shielding gas, the shielding gas flow rate and the initial temperature of workpiece on absorption of laser beam were considered. The temperature were measured at various monitoring locations and the measured values of dimensionless temperature profiles are plotted as a function of time. The absorptivity was determined from good matching between the measured temperature profiles and the corresponding predicted values. In summary, shielding gas will decrease the absorption of laser beam in welding, especially the using of He gas obtained the lowest absorptivity. The absorption of laser beam increases with increasing initial temperature of workpiece.