Towards Efficient Modelling Of Macro And Micro Tool Deformations In Sheet Metal Forming

During forming, the deep drawing press and tools undergo large loads, and even though they are extremely sturdy\ud structures, deformations occur. This causes changes in the geometry of the tool surface and the gap width between the tools.\ud The deep drawing process can be very sensitive to these deformations. Tool and press deformations can be split into two\ud categories. The deflection of the press bed-plate or slide and global deformation in the deep drawing tools are referred to as\ud macro press deformation. Micro-deformation occurs directly at the surfaces of the forming tools and is one or two orders\ud lower in magnitude.\ud The goal is to include tool deformation in a FE forming simulation. This is not principally problematic, however, the FE\ud meshes become very large, causing an extremely large increase in numerical effort. In this paper, various methods are\ud discussed to include tool elasticity phenomena with acceptable cost. For macro deformation, modal methods or ’deformable\ud rigid bodies’ provide interesting possibilities. Static condensation is also a well known method to reduce the number of DOFs,\ud however the increasing bandwidth of the stiffness matrix limits this method severely, and decreased calculation times are not\ud expected. At the moment, modeling Micro-deformation remains unfeasible. Theoretically, it can be taken into account, but\ud the results may not be reliable due to the limited size of the tool meshes and due to approximations in the contact algorithms

Extracting material data for superplastic forming simulations

In subatomic particle physics, unstable particles can be studied with a so-called vertex detector placed inside a particle accelerator. A detecting unit close to the accelerator bunch of charged particles must be separated from the accelerator vacuum. A thin sheet with a complex 3D shape prevents the detector vacuum from polluting the accelerator vacuum. Hence, this sheet should be completely leak tight with respect to gases. To produce such a complex thin sheet, superplastic forming can be very attractive if a small number of products is needed. This is a forming process in which a sheet of superplastic material is pressed into a one-sided die by means of gas pressure.\ud In order to develop a material model which can be used in superplastic forming simulations, uniaxial and biaxial experiments are necessary. The uniaxial, tensile, experiments provide information about the one-dimensional material data, such as the stress as a function of equivalent plastic strain and strain rate. These data are extracted from the experiments by using inverse modeling, i.e. simulation of the tensile experiment. To fit these curves into a general material model, three parts in the uniaxial mechanical behavior are considered: initial flow stress, strain hardening and strain softening caused by void growth. Since failure in superplastic materials is preceded by the nucleation and growth of cavities inside the material, the void volume fractions of the tested specimens were also observed.\ud A very important factor in this research is the study of the permeability of the formed sheet with respect to gas. If internal voids start to coalesce, through-thickness channels will start to form, thereby providing a gas leak path. To study the twodimensional behavior, including the gas leakage, bulge experiments were performed. Within these experiments, circular sheets were pressed into a cylindrically shaped die. From these experiments it followed that the plastic straining is dependent on an applied backpressure during the forming stage. This backpressure can postpone cavity nucleation and growth

Sensitivity improvement of a laser interferometer limited by inelastic back-scattering, employing dual readout

Inelastic back-scattering of stray light is a long-standing and fundamental problem in high-sensitivity interferometric measurements and a potential limitation for advanced gravitational-wave detectors. The emerging parasitic interferences cannot be distinguished from a scientific signal via conventional single readout. In this work, we propose the subtraction of inelastic back-scatter signals by employing dual homodyne detection on the output light, and demonstrate it for a table-top Michelson interferometer. The additional readout contains solely parasitic signals and is used to model the scatter source. Subtraction of the scatter signal reduces the noise spectral density and thus improves the measurement sensitivity. Our scheme is qualitatively different from the previously demonstrated vetoing of scatter signals and opens a new path for improving the sensitivity of future gravitational-wave detectors and other back-scatter limited devices

A constitutive model for the superplastic material ALNOVI-1 including leak risk information

For some applications, it is important that a formed sheet of material is completely gas tight, therefore it is beneficial to be able to predict whether a formed sheet will be leak tight for gases or not. Superplastic materials show the ability to attain very high plastic strains before failure. These strains can only be reached within a small range of tempera-ture and strain rate. In thecase of the alu-minium alloy ALNOVI-1 by Furukawa Sky Aluminium, the optimum superplastic be-haviour is found at 520 °C and at strain rates roughly between 10-4 to 10-2 s-1. Under these conditions, the mechanical behaviour of the material is highly strain rate depend-ent. This article describes a proposal for the constitutive model of ALNOVI-1, as can be incorporated into an FE code (like a user-defined material UMAT in ABAQUS), in which the leak risk can be implemented, as function of the cavity volume fraction. This will be done in a phenomenological way, using the results of uniaxial tensile and biaxial bulge experiments

Compensation of deep drawing tools for springback and tool-deformation

Manual tool reworking is one of the most time-consuming stages in the\ud preparation of a deep drawing process. Finite Elements (FE) analyses are now widely\ud applied to test the feasibility of the forming process, and with the increasing accuracy of the\ud results, even the springback of a blank can be predicted. In this paper, the results of an FE\ud analysis are used to carry out tool compensation for both springback and tool/press\ud deformations. Especially when high-strength steels are used, or when large body panels are\ud produced, tool compensation in the digital domain helps to reduce work and save time in the\ud press workshop. A successful compensation depends on accurate and efficient FE-prediction,\ud as well as a flexible and process-oriented compensation algorithm. This paper is divided in\ud two sections. The first section deals with efficient modeling of tool/press deformations, but\ud does not discuss compensation. The second section is focused on springback, but here the\ud focus is on the compensation algorithm instead of the springback phenomenon itself