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• Introducing a new severe plastic deformation method. • Imposing high amounts of strains per pass. • Developing well homogenized strain on the cross section of the processed ...materials.
A new method of severe plastic deformation, cyclic expansion-extrusion (CEE), is introduced; CEE is considered as a substitute for the well-known, cyclic extrusion-compression (CEC), by implementing its advantage which is processing samples for the desired number of passes with no need to remove them from the die until the whole number of passes are accomplished. In addition, no external back-pressure system is needed which is the main advantage of this process compared to CEC. This modified process was performed experimentally on aluminum alloy 1050 and was also investigated by finite element analysis. Results reveal that, performing CEE makes it possible to impose large strain values per pass while maintaining a homogeneous hardness distribution in the sample's cross section as well.
Experimental and computational methods of studying the stress state in the plastic region are characterized by various methods and accuracy of measurements, methods of mathematical processing of ...experimental information, and interpretation of results. The experimentally determined kinematics as a starting point is the most widely used method to study the stress-strain state in the plastic region. When studying the process of plastic deformation of porous blanks, the model of a rigid-plastic isotropic-strengthening porous body with a loading surface that has the shape of an ellipsoid with semi-axes. It depends on the amount of porosity and the ratio of the associated flow law as a mechanical model of the material. In the axisymmetric extrusion of porous blanks, the viscoplasticity method was used to determine the field of flow velocities based on the results of experimental studies. R-functions were applied to approximate experimentally obtained values. The problem of finding approximations was formulated in a variational statement. Cubic splines of one argument were used to interpolate functions. As a result, an approach was proposed, which consists of a particular sequence of calculating the derivatives of the coordinates of the nodes in time in combination with the R-functions approach. All the calculations were performed in Euler variables, eliminating the need to switch from Lagrangian variables and simplifying the solution. Additionally, this method allowed for working with an irregular and non-rectangular grid in areas with any shape of boundaries. This approach is more effective from the point of view of the approximation’s accuracy and the speed of calculations. Finally, the equation for calculating the porosity in the volume of the deformable workpiece based on the information about the distortion of the dividing grid elements was obtained. For stationary axisymmetric processes, a technique was developed that allowed for replacing the calculation of the accumulated deformation of the base material along the deformation trajectory by integration over the region. A technique was developed for determining the stress-strain state at unstable and stable stages of axisymmetric plastic deformation of porous blanks. The calculation results were compared based on the proposed experimental and calculation techniques and the finite element method.
Today, vegetable oil is much desired for its application as a lubricant in metal forming processes, because it is a renewable resource and has high biodegradability compared to mineral oil. According ...to the Organization for Economic Cooperation and Development for the European Union 301C (OECD) testing method, the biodegradability levels of vegetable oils are better compared to petroleum-based lubricants. Palm oil is used more often than other vegetable oils. Therefore, palm oil has the potential to fulfill the demand for vegetable-based lubricants. The purpose of this paper is to evaluate the viability of palm oil when used as a lubricant in cold work such as the forward plane strain extrusion process. The performances of palm oil were compared with additive-free paraffinic mineral oil. Experimental work with a plane strain extrusion apparatus with a symmetrical workpiece was carried out at room temperature. The material of the workpiece is annealed pure aluminum A1100. The visioplasticity method was used to calculate the velocities and effective strain in the deformation zone of the workpiece. The results obtained from the experimental work showed that palm oil has satisfactory lubrication performances, as compared to paraffinic mineral oil, and has advantages in reducing the extrusion load.
► Performances of palm oil were compared with paraffinic mineral oil as cold extrusion lubricant. ► Experimental works were done using plane strain extrusion apparatus, at room temperature. ► Billet is aluminum and the analytical results were calculated using the visioplasticity method. ► Results conclude that palm oil has advantages in reducing load. ► Palm oil shows satisfactory lubrication performances, as compared to paraffinic mineral oil.
Vortex extrusion (VE) is a single pass severe plastic deformation (SPD) technique which can impose high strain values with almost uniform distribution within cross section of the processed material. ...This technique needs no additional facilities for installation on any conventional extrusion equipment. In this study the deformation behavior of material during VE is investigated and the results are compared with those of conventional extrusion (CE). These investigations include finite element analysis, visioplasticity, and microstructural characterization of the processed samples. The results indicate that the VE process can accumulate a higher strain value by applying an additional torsional deformation. The role of this additional deformation mode on the microstructural evolution of the VE sample is discussed and compared with the results obtained on the CE samples.
The article presents the results of measuring the amount of deformation during the formation and propagation of Lüders bands through the deformation zone. The amount of deformation was determined by ...applying the visioplasticity method with digital image correlation, and analyzing the captured images using the MatchID software package. Results show that during the formation of Lüders bands, the deformation of 0,004 mm/mm was achieved. Furthermore, it was determined that during the propagation of Lüders bands through deformation zone, the sample was deformed in the amount of 0,05 mm/mm.
Determination and distribution of stresses in the deformation zone can be obtained by advanced plasticity theory, especially by experimental-analytical method such as visioplasticity. The ...visioplasticity method is very useful in providing a detailed analysis of the distribution of stresses, strains or strain rates in deformed material. In this paper shear stress distribution in cold formed aluminum alloy is analyzed by using visioplasticity method. The specimens were cold forward extruded trough a conical die. Further, the influence of the coefficient of friction on shear stress distribution in deformed zone of the material is investigated. The results are presented in form of diagrams.
Surface texturing is among the cheapest solutions for die modification if compared to tool change and hot works. In extrusion die design, the addition of micro-pits has increasingly been used to ...balance the metal flow. Such balance is particularly important for multiple cavity dies or sections with varying thicknesses in order to maintain a uniform velocity profile across the face of the die. In this research, surface texturing (called as micro-pits) was embedded on taper die sliding contact surface to explore its effectiveness on finish product of cold extrusion process. Palm oil based lubricants were tested for cold extrusion processes and mineral oils were used for comparison purpose. It was found that taper die with micro-pits (PA) performed a lessened extrusion load than taper die without micro-pits (NA), so as enhanced the performance of other tests parameter. In addition, viscosity of lubricant seems to be very important in ensuring that no material and tribological failures occur during the metal forming process.
The evolution of microstructure and the mechanical properties of equal channel angular pressing (ECAP) processed materials depend on the plastic deformation behavior during ECAP, which is governed ...mainly by the die geometry, the constitutive behavior of the material itself and the processing conditions. In this study, we describe some of our results of continuum modelling and microstructural modelling of ECAP in order to illustrate the capabilities of the models. In particular, results of modelling ECAP using analytical and finite element methods in combination with visioplasticity experiments are presented for various geometric and processing conditions. The non-homogeneous deformation is accounted for in terms of the strain hardening properties of the material. Finally, modelling the evolution of microstructural features of misorientation angle using a dislocation cell model during ECAP is presented.
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