Cold forging has high potential as a sustainable production technology. With net-shape production, only the material needed for the produced part is used. By not heating up the workpiece, energy ...consumption is also low. However, this leads to high forming forces and consequently critical stresses in the tools. An accurate prediction of tool life is therefore necessary; both to find measures for its increase and to plan tool changes with minimal machine downtime. Currently there is little data about the fatigue properties of cold forging tool materials. Existing tests to determine this data strongly simplify the tools’ stress state to a uniaxial load. Therefore, a new fatigue test is presented in this paper, which incorporates the actual load conditions of cyclically swelling inner pressures. For this purpose, a high-strength elastomer is used as pressure medium. Its low compressibility and high elasticity allow for cyclic testing with pressures up to at least 2000 MPa. This load causes wear on the elastomer, as it is pressed into the gap between the punch used to apply the load and the fatigue specimen. Therefore, the gap between punch and fatigue specimen should be as low as possible to ensure stable test conditions. Within the scope of the research, fatigue failure already occurred in one specimen. This shows that the compression of elastomers is able to generate very high loads comparable to the cold forging of steel.
Consistent and reasonable characterization of the material behavior under the coupled effects of strain, strain rate and temperature on the material flow stress is remarkably crucial in order to ...design as well as optimize the process parameters in the metal forming industrial practice. The objective of this work was to formulate an appropriate flow stress model to characterize the flow behavior of AISI-1045 medium carbon steel over a practical range of deformation temperatures (650⁻950 ∘ C) and strain rates (0.05⁻1.0 s - 1 ). Subsequently, the Johnson-Cook flow stress model was adopted for modeling and predicting the material flow behavior at elevated temperatures. Furthermore, surrogate models were developed based on the constitutive relations, and the model constants were estimated using the experimental results. As a result, the constitutive flow stress model was formed and the constructed model was examined systematically against experimental data by both numerical and graphical validations. In addition, to predict the material damage behavior, the failure model proposed by Johnson and Cook was used, and to determine the model parameters, seven different specimens, including flat, smooth round bars and pre-notched specimens, were tested at room temperature under quasi strain rate conditions. From the results, it can be seen that the developed model over predicts the material behavior at a low temperature for all strain rates. However, overall, the developed model can produce a fairly accurate and precise estimation of flow behavior with good correlation to the experimental data under high temperature conditions. Furthermore, the damage model parameters estimated in this research can be used to model the metal forming simulations, and valuable prediction results for the work material can be achieved.
In forming processes, friction is a local phenomenon influenced by the contact conditions at the tool-sheet metal interface. A multi-scale friction model applicable for coated sheets is developed for ...the boundary lubrication regime which accounts for the physical behavior of coating and measured surface topographies of sheet and tools. The contact patches and therefore the real area of contact is determined at the tool-sheet metal interface for different contact loading conditions. A single asperity micro-scale ploughing model is adapted at each contact patch to determine the friction force from which the overall coefficient of friction is determined. The friction model is validated using different sets of lab-scale friction tests and cup drawing experiments on zinc coated (GI) steel sheets.
•1.A multi-scale friction model is developed for the boundary lubrication regime.•2.Applicable for coated sheets and accounts for physical behavior of the coatings.•3.Surface topographies of sheet and tools are used as the input in the model.•4.Single asperity ploughing model is adopted at macro-scale deformed sheet surface.•5.The model is validated using lab-scale friction tests and cup drawing experiments.
Numerical process design leads to cost and time savings in sheet metal forming processes. Therefore, a modeling of the material behavior is required to map the flow properties of sheet metal. For the ...identification of current yield criteria, the yield strength and the hardening behavior as well as the Lankford coefficients are taken into account. By considering the anisotropy as a function of rolling direction and stress state, the prediction quality of anisotropic materials is improved by a more accurate modeling of the yield locus curve. According to the current state of the art, the layer compression test is used to determine the corresponding Lankford coefficient for the biaxial tensile stress state. However, the test setup and the test procedure is quite challenging compared to other tests for the material characterization. Due to this, the test is only of limited suitability if only the Lankford coefficient has to be determined. In this contribution, a simplified test is presented. It is a reduction of the layer compression test to one single sheet layer. So the Lankford coefficient for the biaxial tensile stress state can be analyzed with a significantly lower test effort. The results prove the applicability of the proposed test for an easy and time efficient characterization of the biaxial Lankford coefficient.
Modelling of metal forming processes is an essential task of production engineering. Due to the latest technological developments, a huge variety of models is already available and extending ...continuously. Thus, it is important to find a suitable model. This paper gives an overview on the common classification and characterization of modelling and models in metal forming, as well as introduces a model selection procedure. Based on this classification, various relevant process limits for metal forming are investigated regarding existing models. The conclusion of the paper shows open topics as well as upcoming challenges in modelling process limits in metal forming.
This paper reviews studies on the prediction of ductile fracture during metal forming using an ellipsoidal void model and some other models proposed by the author and some relevant studies. Section 2 ...discusses the research on the theory of voids for predicting ductile fracture during metal forming. Section 3 summarizes the simulation method for predicting ductile fracture during metal forming using the ellipsoidal void model, and Section 4 summarizes the simulation result on the ductile fracture prediction during metal forming using the ellipsoidal void model. Section 5 shows the applicability of the ellipsoidal void model and the simulation result on the ductile fracture prediction during metal forming using some other models.
This paper reviews studies on the prediction of ductile fracture during metal forming using an ellipsoidal void model and some other models proposed by the author and some relevant studies. Section 2 ...discusses the research on the theory of voids for predicting ductile fracture during metal forming. Section 3 summarizes the simulation method for predicting ductile fracture during metal forming using the ellipsoidal void model, and Section 4 summarizes the simulation result on the ductile fracture prediction during metal forming using the ellipsoidal void model. Section 5 shows the applicability of the ellipsoidal void model and the simulation result on the ductile fracture prediction during metal forming using some other models.
In this paper, a multi-scale model for AA3104-H19 and AA2024-T3 aluminium alloy with strong cold rolled crystallographic texture is proposed. This model consists of two components: (i) a full-field ...crystal plasticity spectral method using fast Fourier transformation (CPFFT) that can be used to predict anisotropic mechanical properties in both the in and out-of-plane uniaxial and multi-axial stress states and (ii) a 3D new phenomenological anisotropic yield function with enough flexibility to describe the in and out-of-plane mechanical anisotropies of strongly textured aluminium alloy sheet. This multi-scale model was implemented into a commercial finite element (FE) software Abaqus via a user-defined material subroutine UMAT to predict the anisotropic plastic deformation in a multi-step forming process (deep drawing). Results showed that this new modelling approach is able to accurately predict earing profiles with multiple ears in deep drawn cups based on the crystallographic texture information data obtained from orientation density functions (ODFs).
Damage in metal forming Tekkaya, A.E.; Bouchard, P.-O.; Bruschi, S. ...
CIRP annals,
2020, 2020-00-00, Letnik:
69, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Physical mechanisms of ductile damage in metal forming, experimental characterization methods for damage, and models predicting the damage level in formed components are reviewed. Applications of ...damage analysis in metal forming processes reveal that damage in metal formed parts is not failure, but a product property that accumulates between processes. Various metal forming process designs demonstrate that damage in formed products can be reduced and their performance can be increased. Static and fatigue strength, impact toughness, stiffness, and formability are typical examples of performance indicators that can be improved by damage-based process design. Potential scientific and technological challenges are addressed to realize damage-controlled metal forming processes.
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