José Divo Bressan

A computational approach to blanking processes

Abstract The present work presents a general framework for numerical simulation of blanking processes using finite elements. Blanking consists of a metal forming operation characterised by complete material separation. Experimental observations show that the shear process occurs in three stages: contact engaging, penetration/plastic deformation and rupture. In the first and second stages, large plastic deformation takes place, being primarily affected by punch displacement and clearance between punch and die. In the third stage, catastrophic failure occurs, leading to a complete material separation. A numerical approach to the problem requires a comprehensive finite element modelling due to the diversity of physical phenomena involved, such as large plastic deformation, material failure and coupled heat transfer. Furthermore, use of error estimation and re-meshing procedures is highly recommended due to element distortion, caused by lager deformation. This work discusses some of the issues involved in blanking modelling and analyses the influence of the clearance in stress distribution prior to material separation.

Sensitivity analysis of the ECAE process via 2 k experiments design

In this work the theoretical solutions based upon the upper-bound theorem recently proposed by Perez and Luri [Mech. Mater. 40 (2008) 617] for the equal channel angular extrusion process (ECAE) are analyzed by performing a 25 central composite factorial analysis. The uniaxial mechanical properties of commercial pure aluminium are considered by assuming isotropic nonlinear work-hardening combined to von Mises and Drucker isotropic yield criteria to predict the ECAE load and the effective plastic strain. From the proposed 25 factorial analysis, the main parameters affecting the ECAE pressure may be ranked as: (1) Friction factor, (2) die channels intersection angle, (3) outer and (4) inner die corners fillet radii and lastly, (5) plunger velocity. Alternatively, the effective plastic strain is mainly controlled by the die channels intersection angle and, in a less extent, by the outer and inner die corners fillet radii.

The influence of material defects on the forming ability of sheet metal

Abstract A relevant aspect of sheet forming is the analysis of the influence of material imperfections on the forming ability. These imperfections can be defined as local variations in thickness and in plastic properties which can affect the plastic flow and therefore, influence the neck formation phenomena. From the microstructural point of view this could be due to the variations in grain size and orientation, inclusions and second-phase contents, porosity, as well as residual cold work, originating from the melting, solidification and rolling processes. As a consequence of these imperfections within the material, the thickness, strain hardening, strain-rate sensitivity and strength coefficients and initial prestrain may exhibit local variations and thereby the initiation of the neck and the limit strains can be influenced. Using the concept of a strain gradient at the neck, the limiting strains are investigated with respect to the material parameters mentioned above. The role of these defects on the development of the local neck and the forming-limit diagram (FLD) are discussed.

Prediction of strain rate sensitivity variations in the deformation of superplastic materials

Abstract The maximum strain rate sensitivity coefficient is obtained theoretically from the material parameters that describes the constitutive equation of superplastic materials. This m-value correspond to a specific strain rate and are investigated as a function of those parameters. The variation of the strain rate sensitivity m with strain rate is also shown. The new constitutive equation for superplasticity is used.

Abrasive Wear Resistance of Tool Steels Evaluated by the Pin‐on‐Disc Testing

Present work examines tool steels abrasion wear resistance and the abrasion mechanisms which are one main contributor to failure of tooling in metal forming industry. Tooling used in cutting and metal forming processes without lubrication fails due to this type of wear. In the workshop and engineering practice, it is common to relate wear resistance as function of material hardness only. However, there are others parameters which influences wear such as: fracture toughness, type of crystalline structure and the occurrence of hard precipitate in the metallic matrix and also its nature. In the present investigation, the wear mechanisms acting in tool steels were analyzed and, by normalized tests, wear resistance performance of nine different types of tool steels were evaluated by pin‐on‐disc testing. Conventional tool steels commonly used in tooling such as AISI H13 and AISI A2 were compared in relation to tool steels fabricated by sintering process such as Crucible CPM 3V, CPM 9V and M4 steels. Friction an...

Extrusion Process by Finite Volume Method Using OpenFoam Software

The computational codes are very important tools to solve engineering problems. In the analysis of metal forming process, such as extrusion, this is not different because the computational codes allow analyzing the process with reduced cost. Traditionally, the Finite Element Method is used to solve solid mechanic problems, however, the Finite Volume Method (FVM) have been gaining force in this field of applications. This paper presents the velocity field and friction coefficient variation results, obtained by numerical simulation using the OpenFoam Software and the FVM to solve an aluminum direct cold extrusion process.

Experimental Waviness Evolution of Interstitial Free - IF Steel Sheet under Biaxial Stretching

The purpose of present study is to present experimental results and a mathematical model for the evolution of surface waviness parameters with plastic strain of Interstitial Free - IF steel sheet under uniaxial and biaxial stretching tests. Roughness and waviness are very important quality parameters to be evaluated in sheet metal forming. Various waviness profile parameters such as the arithmetic average waviness Wa, the total height peak-valley waviness Wt, maximum peak height Pp and maximum valley depth Pv were measured during uniaxial and biaxial tests. Tensile test specimens at 0º, 45º and 90º to the direction of rolling and Nakazima type specimens of IF steel were fabricated. After preparing the test specimens, incremental simple tensile and Nakazima biaxial tests with flat punch were performed to characterize the negative and positive quadrant of the Map of Principal Surface Limit Strains, MPLS, of IF steel sheet. Measurements of waviness parameters of the specimen surface at incremental plastic strain stages were performed at the same surface site. Also, during the uniaxial and biaxial tests, the following plastic strains were calculated from printed circular mesh at each incremental step: ε1 longitudinal major strain and ε2 transverse minor strain. From these data, curves of waviness parameters versus equivalent strain were plotted to obtain a phenomenological equation of 4th or 3rd degree polynomial type. Furthermore, the growth rates of Wa and Wt parameters with the equivalent plastic strain were assessed. From the growth rate curves, it was possible to verify how the sheet thickness imperfections evolves during straining, being possible to predict the influence of plastic strain on the waviness values of IF steel sheets. From the analysis of Wa and Wt growth rates during straining, it was possible to proposed a criteria for the onset of local necking or limit strains in the MPLS. The waviness parameters Wt is the best for characterizing the onset of local necking in sheet metal forming.

Evolution of Roughness on Straining of Interstitial Free – IF Steel Sheet

This study aims to assess the evolution of surface roughness and waviness parameters with plastic strain in Interstitial Free – IF steel sheet. For the achievement of this study, it was considered various roughness and waviness profile parameters such as: arithmetic average roughness (Ra), maximum distance peak-valley (Rt), average waviness (Wa) and waviness of the total height peak-valley (Wt). Tensile test specimens of IF steel at 0º, 45º and 90º to the direction of rolling were fabricated. After preparing the sheet proof specimens, it was performed simple tensile tests and measurements of roughness and waviness of the specimen surface at various strain stages resulting in a large quantity of data. During the tensile test, it has been measured the following plastic strain to indicate the incremental step: (e1) longitudinal strain and (e2) transverse strain. From these data, it was possible to obtain points needed to plot the curves of roughness and waviness parameters versus strain and to determine the material behavior using equations of the equivalent strain. From the curves drawn it was possible to see how the material roughness and waviness behaves during the straining in the uniaxial tensile state, with the possibility to predict the influence of plastic strain on roughness and waviness parameters and the onset of local necking of IF steel sheet. The waviness parameters Wt is the best for characterizing the onset of local necking.

Experimental kinetic friction coefficient (μk) determination in the interface polycarbonate blade and flat rubber-belt when interacting with ore, lubricant and pressure

It is well known that even the most advanced Finite Element Analysis (FEA) version is not able to predict friction coefficients among materials. This paper presents an alternative and experimental method based on Design of Experiments (DOE) to determine the friction coefficient between polycarbonate blades against rubber belt. Those experiments correlate ore, lubricant and pressure to determine the friction coefficients in the interface between these materials with polycarbonate and rubber belt. The experiments results are of extreme importance for polycarbonate application on belt conveyor scraper and other applications involving polymeric surfaces under friction.

Plastic Behavior and Fracture of Aluminum and Copper in Torsion Tests

Present work investigates the plastic behavior, work hardening and the beginning of plastic instabilities, of cylindrical specimens deformed by high speed cold plastic torsion tests and at low speed tensile test. The tests were carried out in a laboratory torsion test equipment and an universal tensile test machine. The tensile tests were performed at room temperature in an universal testing machine at low strain rate of 0.034/s. Experimental torsion tests were carried out at constant angular speed that imposed a constant shear strain rate to the specimen. In the tests, the rotation speed were set to 62 rpm and 200 rpm which imposed high strain rates of about 2/s and 6.5/s respectively. The torsion tests performed at room temperature on annealed commercial pure copper and aluminum. Two types of torsion specimen for aluminum were used: solid and tubular. The solid aluminum specimen curves presented various points of maximum torque. The tubular copper specimens showed two points of maximum. Shear bands or s...