Prediction of Forces and Damage at Forming Sheet on Multipoint Die MANEA Marius Costin 1, a *, TIMOFTE Damian 2,b and VELICU Stefan 3,c

Transcription

1 Applied Mechanics and Materials Vol. 656 (2014) pp Submitted: Online available since 2014/Oct/27 at Revised: (2014) Trans Tech Publications, Switzerland Accepted: doi: / Prediction of Forces and Damage at Forming Sheet on Multipoint Die MANEA Marius Costin 1, a *, TIMOFTE Damian 2,b and VELICU Stefan 3,c 1 Faculty of Engineering and Management of Technological Systems, Polytechnic University of Bucharest, Romania, a marius_manea86@yahoo.com, b damiantimofte@yahoo.com, c velstefan@hotmail.com Keywords: deformation, multi-point, punches, sheet metal, finite element simulation, Deform 2D. Abstract. This paper presents aspects of a simulation based on multi-point die optimization sheet metal deformation using for types of materials: titanium grade 1, aluminium 2024, carbon steel 1010 and Due to processing methods of the sheet metal appeared, multi-point deformation is a very interesting process industry. For the finite element simulation of sheets metal using multipoint die was chosen Deform 3D software. Simulations were performed for four types of materials used in the construction industry. With the development of computer software, specialized programs appeared on the market forming process simulation, for determining the stresses and strains of the deformed material, the distribution of temperature field, how the material is flowing, the final form of the product, etc. Modeling and numerical simulation of deformation processes can be viewed at any time of their deployment, which allows rethinking solutions for problems arising in the process. Also by this method of finite element simulation can be optimized in the design engineering processes and tools. Introduction Sheet metal processing was considered to be a very difficult deformation process due to the emergence of springback. With the passing of the years were developed different methods of processing, one of them is deformation using multi-point die. The method of processing multi-point die is based on deformation of sheet metal using sets of punches (pins). Should consider the following parameters on the deformation of multi-point die: radius, size, stroke of punches, complexity parts made. Fig. 1: Multi-point die Deformation of sheet metal it involves bending to reach the desired surface. Using punches can theoretically obtain any form surfaces and different radius. When force is applied on a material that is constrained tend to thin, event to break resulting states of stress and strain. To observe the states of stress and strain appeared at multi-point forming will do more simulations using Deform-2D software module Forming. This software uses the classical method of finite element simulation to describe the plastic deformation of the material under different actions. They are made in software both sheet metal and punches. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, (ID: , Pennsylvania State University, University Park, USA-10/03/15,11:10:53)

2 216 Monitoring, Controlling and Architecture of Cyber Physical Systems At simulation may appear different deformations of the mesh network, where the network automatically remodeling [1]. To prevent the return of springback behavior must be known laws of mechanics of material: modulus of elasticity, plasticity module, yield strength, breaking limit, resistance. Springback is determined by the material properties and the geometry of the tool used in this case punches. The test used to determine the behavior of the material is tensile testing. Conventional curve is the laboratory curve is different from the actual curve, because it takes into account the request made on the basis of elastic stress and strain values and not the values obtained on test pieces [2] [ 3]. Fig. 2: a) The conventional and actual curve; b) shear stress-strain curve Where: τ r - tensile strength τ c - yield strength τ e - elastic limit τ p - limit of proportionality The method used in this case as principal stage: data colecting about deformations of sheet metals using a software for finite element numerical simulation Deform 3D data acquisition interpretation of data data validation Interpretation data and Post-Processing To analyze the behavior of these materials to cold plastic deformation using Deform 2D software have the following steps:

3 Applied Mechanics and Materials Vol Fig. 3: Steps necessary for the analysis In Deform-2D simulated 4 types of material: 2 types of steel (AISI 1010, AISI 1137); grade 1 titanium and aluminum 2024 used in the construction industry. We used a sheet size 50x1mm and 3 punch with radius of 10 mm. The mold consists of two parts: the upper part containing a punch for fixing the sheet and the other two who carry out that movement speed of 250 mm / sec, and the bottom containing the same punches but they were not in a move. Temperature is constant of 20 0 C and coefficient of friction is 0.2.

4 218 Monitoring, Controlling and Architecture of Cyber Physical Systems Fig. 4: The attachment of punches on sheet metal In the area where the sheet touches punch, tensions arise which may lead to material deformation, thinning even breaking it. Force deformation of a uniform bar determined by other researchers through various research and experiments are given by the relations: ℇ = ΔL/L, F = σ A (1) where σ is tensile stress, ℇ a constant factor, E is the modulus of elasticity and describes the response to linear stress, L - length, F - force and A represents the cross-sectional area. The relationship may also be expressed as: σ = E ℇ being Hooke's law (2) which says that the size of the deformation is directly proportional to the deforming force. In the case of torsion force, Hooke's law between tangential stress τ and specific deformation angle γ has the form: τ = G γ law (3) where the constant G is called the shear modulus or modulus of rigidity The most treated equations for describe the stress and strain curves are the Hollomon-Ludwik's equations expressed as: σ = K ε n equation Hollomon (4) σ = σ 0 + K ε n equation Ludwik (5) where σ is the stress, σ 0 is the yield stress, K is the strength index, ε is the plastic strain and n is the strain hardening exponen Table 1. Chemical compozition of the materials[4] Grade 1 titanium Al 2024 AISI 1010 AISI 1137 Titanium 99.1 Aluminum 93.5 Iron Iron ~98 Iron 0.20 Copper 4.4 Magnesium Magnesium Oxigen 0.18 Magnesium 1.5 Sulfur Carbon Carbon Manganese 0.6 Phosphorous Sulfur Nitrogen Carbon Phosphorous 0.04 (max) Hydrogen Using software Deform-2D to simulate prediction of deformation forces, respecting the parameters established above. The materials were taken from the library database software. In the figures below can see punches that do not show forces deformation punch up, punch down three, punch down one and certainly the workpiece. Moreover is observed forces increases in the area maximum bending, then they start to drop. For the load prediction on AISI 1010 the graphic was zoom out and move to fit in the table. At first tensions emerged on both sides of inside and outside contact surface. After propagation and joining tensions on the contact surfaces they tend to spread to the edges and then force increase. Also this time side of the sheet from edge has small angle increase.

5 Applied Mechanics and Materials Vol Fig. 5: Prediction deformation forces in the Y direction for four types of material Using the post-processor in Deform 2D extracted data on the state of stresses and strains occurring in the 4 types of material studied. Fig. 6: State of stresses and strains occurring in time of simulation for titanium grade 1 and AL 2024

6 220 Monitoring, Controlling and Architecture of Cyber Physical Systems Fig. 7: State of stresses and strains occurring in time of simulation for AISI 1010 and AISI 1137 Differences between stress of the two sides of the material can be explained by the fact that the material is tensile stretching the outside surface of the workpiece. Residual stress distribution in this case shows a variation on sheet thickness. [5] The terms of damage describe the progressive loss of material due to the emergence of integral cracks, necking or other defects. D f = (6) where σ* is the tensile maximum principal stress, σ is the effective stress and is the effective strain increment.[6] Shown in the figure 8 and 9 if the damage percentage is ten or below the material can be subject to minimal risk of breaking. Fig. 8: Histograms with damage of Titanium Grade 1 and AL2024

7 Applied Mechanics and Materials Vol Conclusions Fig. 9: Histograms with damage for AISI 1010 and AISI 1137 Table 2. Proprieties mechanical of materials [4] [7] Proprieties Titanium Al 2024 AISI 1010 AISI 1137 Grade 1 Tensile strength [Mpa] Yield strength [Mpa] Elongation [%] Area reduction [%] Hardness Elastic modulus [Gpa] Deform 2D software was developed at first for simulations of plastic deformation processes hot and cold being able to draw some conclusions for the parameters obtained by simulation. Simulations were performed in order to determine the influences of deformation forces on the sheet metal. It can be seen increasing stress and strains in the sheet metal, when the punch start. Simulations were performed on four types of material to see the difference between tension and deformation occurred. The program can provide all kinds of information on the state of steress and strain, Y-axis displacement, damage of materials, surface analysis deformed. Mention that they were not taken into account the problems encountered in the deformation and temperature of the ends punches. By performing these simulations can deduct damages deformation of materials in order to optimize growth obtained parts quality. Acknowledgement The results presented in this article were obtained with the support of the Ministry of Labour, Family and Social Protection through the European Social Fund Operational Programme Human Resources Development , Contract no. POSDRU/107/1.5/S/ References [1] LICENSE DEFORM 2D. beneficiary: POLITEHNICA University of Bucharest. National Center for Technological Systems Performances Research OPTIMUM. [2] VALERIA SUCIU, M. V. S. Stiinta si Ingineria Materialelor Studiul Materialelor. Editura Fair Partners, ISSN [3] VIOREL PAUNOIU, E. G. S. A. D. SpringBack analysis in reconfigurable multipoint forming of thick plates. The annals of "Dunarea De Jos" University of Galati Fascicle V, Technologies in machine building, ISSN

8 222 Monitoring, Controlling and Architecture of Cyber Physical Systems [4] Information on [5]. Brabie Gh, S. C., C. B, A. C, C. C. Deformarea plastica la rece a tablelor metalice, Fenomene de instabilitate a formei si dimensiunilor pieselor, Editura Junimea, Iasi 2005, ISBN [6] Deform 3D V60 Manual pp [7] CROITORU, D.-A. C. S. S.-M. Prediction of Cutting Forces at 2D Titanium Machining. 24th DAAAM International Symposium on Intelligent Manufacturing and Automation, 2013, v. 69, p , 2013.

9 Monitoring, Controlling and Architecture of Cyber Physical Systems / Prediction of Forces and Damage at Forming Sheet on Multipoint Die /