Deep Drawing Steel Research Articles

Modeling of anisotropic hardening and grain size effects based on advanced numerical methods and crystal plasticity

Modeling of anisotropic behavior as well as hardening behavior based on micromechanical quantities in combination with a spectral solver is the focus of this study. A deep drawing steel as well as two different aluminum alloys are investigated. Prediction capabilities of the proposed modeling strategy are discussed and the benefits of the micromechanical model are highlighted. Further, a comparison of the crystal plasticity (CP) results with the well established macroscopic model YLD2000-2d underlines the importance of the CP as a complementary modeling technique to the macroscopic modeling. Both models – the microscopic as well as the macroscopic – are validated on experimental data mainly gained from uniaxial and biaxial tests. In the second part of this study, strong inhomogeneous microstructures are investigated from a modeling point of view. For this purpose, a Hall–Petch phenomenological model is implemented in the CP open-source code DAMASK to take the grain size effects into account. Appropriate combinations of the grain sizes in a bimodal microstructure are presented in order to increase the strength as well as ductility of a generic aluminium alloy. The proposed numerical strategy of coupling the CP and efficient FFT-based spectral solver supports the development of new materials in an optimal way.

Research on manufacturing of pyramidal frustum parts using single point incremental forming process

The incremental sheet metal forming is a flexible “die-less” process used to manufacture sheet metal parts in cold pressing domain. Especially talking about single point incremental forming, it is a process which does not require a special die to allow the sheet metal forming. To implement this process, a fixing device and a simple rounded tool are needed. The paper presents some research on the influence of a support plate upon the parts dimensional precision. Because, the main advantage of single point incremental forming process is the flexibility, in experiments, a fixing device that it was initial designed for incremental deformation of frustum cone parts, is used to deform pyramidal frustum parts. Different configurations of pyramidal frustum parts are simulated using a finite element method and a special software tool named TMPG, to check if the sheet material, deep drawing steel DC05, can be deformed without fracture. The manufactured parts are measured using a 3D scanner, and a comparison with the 3D CAD models of the original parts is made.

Stability of structured sheet metals during buckling

Abstract Structured materials can be a progressive alternative to commonly used flat sheets. There is an enormous range of possibilities for using structured sheet metals due to their better stability. However, the effective use of these materials as well as their implementation in production requires precise knowledge about specific properties of structured sheet metals. The aim of this work is to obtain new knowledge about stiffness and stability during the deformation of this material. The structured sheet metals were investigated by means of buckling tests. The steel type investigated is a commonly used deep-drawing steel DC04. Six types of structure arrangements were compared to non-structured (flat) specimens as a reference. The influence of the type of structure arrangement as well as the deformation speed on the mechanical properties was investigated.

Development of Damage-Tolerant and Fracture-Resistant Materials by Utilizing the Material Inhomogeneity Effect

AbstractThe improvement of fracture strength by insertion of thin, soft interlayers is a strategy observed in biological materials such as deep-see sponges. The basic mechanism is a reduction of the crack driving force due to the spatial variation of yield strength and/or Young's modulus. The application of this “material inhomogeneity effect” is demonstrated in this paper. The effectiveness of various interlayer configurations is investigated by numerical simulations under application of the configurational force concept. Laminated composites, made of high-strength tool steels as matrix materials and low-strength deep-drawing steel as interlayer material, were manufactured by hot press bonding. The number of interlayers and the interlayer thickness were varied. Fracture mechanics experiments show crack arrest in the first interlayer and significant improvements in fracture toughness, even without the occurrence of other toughening mechanisms, such as interface delamination. The application of the material inhomogeneity effect for different types of matrix materials is discussed.

Dynamic Behavior of Self-Piercing Riveted and Mechanical Clinched Joints of Dissimilar Materials: An Experimental Comparative Investigation

The present work compares the dynamic effect of a self-piercing riveted (SPR) joint with that of a mechanical clinched joint having the dissimilar materials combination. The substrates used in this investigation are aluminum alloy AA5182-O and deep drawing steel DX51D+Z. The static and dynamic behaviors and the failure modes of the SPR and clinching joints are characterized by lap-shear, cross-tension, and coach-peel tests. The influence of the strain-rate-dependent mechanical behavior of the substrates on the joints is examined; this can help improve prediction of the energy absorption of the joints under impact loading. Considering the realistic baking process in a painting shop, the deforming and hardening effects on the SPR and the clinched joints induced by baking are also studied. The specimens are heated to 180°C for 30 min in an oven and then cooled down in air. The SPR and the clinched joints before and after the baking process are compared in terms of the mechanical behavior.

Experimental studies on incremental hole flanging of steel sheets

ABSTRACTIncremental Hole-Flanging (IHF) process has various applications in rapid prototyping and low volume production of conical and vertical flanges in sheet metal parts. Therefore, understanding mechanics and failure strategies in IHF is very important for successful forming without cracks. In this paper, Deep Drawing (DD) steel blanks with pre-cut hole of 40 and 70 mm diameter are used for multistage conical hole flanging. Conical hole flanges are formed on CNC milling machine with starting angle 60° to final angle 90° with an increment of 10°. The experimental results showed a crack at 80° flange angle with the blank of 40 mm pre-cut hole. The blank with 70 mm-pre-cut hole has no such crack behaviour even at 90° flange angle. The paper also discusses the variation of flange height, surface roughness and forming forces in IHF of DD steel sheets.

Strain Localization Behavior of Cold-Rolled Deep-Drawing Steels

With the purpose of defining optimal microstructure and texture for higher quality in deep–drawing operations of cold-rolled steels; this study monitors and analyses the micro- and macro-scale deformation behavior of DC04 grade cold-rolled steel sheets under uniaxial tension and biaxial stretching. An in-plane biaxial test setup capable of observing and measuring the deformation is utilized for obtaining strain maps at the micro- and macro-scale. Strain maps at the micro-scale are then compared with texture and microstructure data obtained before and after the deformation. Results show strain localization to the interior of grains under both strain paths, as opposed to the common grain boundary localization observed in the literature. Remnants of the α fiber components in the initial γ fiber texture, especially grains with {100}<110> orientations, are the likely sources of the localizations as they allow deformation in the sheet thickness direction. While these localizations do not appear to be critical for macro-scale formability, their suppression should be helpful in preventing surface defects and local fracture. Total elimination of α fiber components from the initial texture is proposed as a way preventing micro-scale localizations

Modified fine blanking of cam-shaped profile using a double-action hydraulic press

ABSTRACTBlanking is a single stroke sheet metal cutting process that produces blanks with closed contour profiles. Fine blanking is a more precise version of this process that produces near-net products that require minimal post-forming finish machining operations. The process of fine blanking generally requires a triple action press. In the present work, fine blanking of a non-rotational symmetric profile using a double-action press while using rubber to apply counterforce has been investigated for four commonly used sheet metals viz. commercially pure aluminum, α-brass, extra deep drawing (EDD) steel and 304 grade stainless steel (SS304). Edge quality and product flatness while using rubber to apply counterforce were found to be meeting fine blanking quality standards. Percentage smooth shear and burr were found to be independent of material properties. Die roll, dishing and tearing behavior were found to be dependent on material properties. The effect of counterforce on the product quality was investigated by conducting experiments without counterforce. An empirical relation that relates the dishing tendency of a material (in the absence of counterforce) to its mechanical properties was developed.

Determination of the Hole-flangeability for thin Sheets

Sheet metal stretching is one of the most frequently applied sheets forming operation in the industry. Hole flanging is a common sheet forming operation to produce structural sheet metal components. Flanges are used for appearance, rigidity, hidden joints, and strengthening of the edge of sheet metal parts. Trial-end-error is the most common approach for tooling and process design in flanging operations. This paper presents some experimental results of hole-flanging process performed on flat deep drawing steel sheets with circular hole drilled or punched in the centre of blank. Three punches of different geometry i.e. cylindrical, hemispherical and conical were used in this experiment. The effect of both the punch geometry and material mechanical parameters (especially strain hardening and plastic anisotropy) on the limit expansion of the hole, limit strain dependence on hole performing technology as well as sheet thickness distribution along collar formed was determined.

Numerical analysis and experimental investigation of surface defects in die hemming process

Hemming is the main assembly process used for auto-body panels. Surface defects resulting from the hemming operation may significantly influence the appearance aesthetics of an automobile. The formation of surface defects can be forestalled, and the process can be optimized and compensated by the numerical simulation method during the process design stage. In this study, the hemming assembly of a fuel tank cap is chosen as the research object, and the specimen is made of DX54D + Z deep drawing steel sheet. Numerical simulation and forming experiments have been carried out. It was found that the surface defect index can be expressed as the weighted sum of the design variable effects by simulation and orthogonal design. In addition, the magnitude of each effect can be ranked from the most significant to the least significant. Using this information helps to obtain an optimal hemming process plan. However, process parameter optimization cannot completely eliminate surface defects. The surface compensation of tool geometry based on the continuity of curvature was used to eliminate the surface lows and the hemming test results indicated that the obtained component was of the required quality.

Refinement of a material model for springback after press forming

.The best tool for characterizing the behaviour of sheet metal during press forming is numerical modelling based on the finite element method (FEM). Using this technique, the response of the press-formed part can already be predicted during the process design stage. The main input data for the process simulation include the tool geometry and materials properties and process conditions, such as temperature, pressing velocity, lubrication and others. The resultant shape of the press-formed part is governed predominantly by the shape of the tools and the workpiece material. The input information on the workpiece material has the form of a material model whose accuracy dictates the accuracy of results. Where high-strength steels are used in the automotive industry, one should focus on springback which alters the shape of press-formed parts. Springback is an undesirable change to the part’s shape caused by residual stresses being released after its removal from the tool. Tooling designers need to take springback into account by choosing an appropriate material model. Conventional hardening models, such as kinematic and isotropic hardening rules, are not adequate for modelling springback. Instead, more sophisticated models, such as the one introduced by Lemaitre and Chaboche are a better choice. In this paper, the options for measuring and FE modelling of the Bauschinger effect are discussed. The proposed idea was tested on a 1.5 mm sheet of DC01 deep-drawing steel.

Comparison of Common Deep Drawing Steel Sheets in terms of Blank Holder Force and Friction Conditions

In this study, it is aimed to make comparison of four different steel sheet materials that are widely used in deep drawing applications by taking blank holder force and friction conditions into account. Comparison is made between a standard steel which is generally used in white goods manufacturing (DC01), an ultralow carbon steel (DC04), a deep drawing steel suitable for cold forming (DD13) and an extra deep drawing steel resistant to ageing (DD14), which are preferred when manufacturing a part by deep drawing, if there is not any special material requirements. The purpose of this study is to make selection between these mentioned materials easier. Simufact.forming, a plastic deformation analysis software based on finite element method, and material database of the software was used in the conducted analyzes. Various blank holder forces were applied and friction conditions were changed for each material. By investigating obtained results, it was seen that there is a significant difference between deep drawing behavior of these materials and DD14 has high deep drawability even under high blank holder forces with low energy. Moreover, it was observed that friction conditions have a significant influence on effectiveness of deep drawing process.

Experimental setup to characterize flow-induced anisotropy of sheet metals

For many metals, a transient variation of the yield stress can be observed when changing the orientation of a load-path. Such behavior affects the manufacturing process itself, e.g. by increasing forming forces, altered material properties or springback of the manufactured components. Hence, the aim of this work is to develop a novel experimental setup to characterize hardening effects due to flow-induced anisotropy for sheet metals. The proposed experiment consists of two subsequent forming operations. Initially, a hydraulic bulge test is conducted, followed by torsion of the hemispherical preformed sheet. Such approach captures the effects of flow-induced anisotropy like cross hardening as could be proved for the example of the conventional deep-drawing steel DC04. The benefits of the presented setup are (i) high plastic strains in the pre-loading step and (ii) determination of several combinations of pre- and subsequent loading.

Tribological Behavior of Carbon Based Coatings Adapted to Lubricant-Free Forming Conditions

In conventional deep drawing lubricants are applied to achieve low friction and wear. However, most lubricants contain environmental harmful ingredients. Global trends like sustainability and efficient resource usage motivate the development of lubricant-free deep drawing. However, dry contact conditions lead to intensive interaction between tool and workpiece especially for aluminum alloys with high adhesion tendency towards tool steel. First investigations revealed promising results for diamond like carbon (DLC) coated tools in lubricant-free tests. Therefore, in this study the lubricant-free friction and wear behavior of DLC coatings is investigated in strip drawing tests. To ensure industrial-like conditions commonly used deep drawing steel with zinc coating and an aluminum alloy were selected as sheet material. The properties of DLC coatings were modified at different scales to attain tailored tribological conditions. A laser based heat treatment achieved an increase of sp2 hybridization and thus leads to increased friction. Different mechanical pre- and post-treatment strategies like polishing and brushing proved that a smooth tool surface is beneficial for the tribological conditions in dry contacts. With laser generated structures a modification of friction was realized with varying degree of coverage for DC04. In contact with AA5182 the application of structures is limited due to adhesion.

Developing a progressive draw with ironing tool for manufacturing a solenoid casing

The present paper focuses on developing a progressive draw with ironing process for production of solenoid casings with the main aim of reducing the number of presses required to form the component thereby reducing the cost of the component and enhancing the productivity rate. The material used for the present study is extra deep drawing (EDD) steel. In progressive draw with ironing tool, the first draw operation takes place followed by the ironing operation in a single tool. The progressive draw with ironing tool consists of three different die inserts planned one below the other in single station. The solenoid casing is manufactured by using this progressive draw with ironing tool and the thickness is measured at the dome and wall regions using an ultrasonic thinning measuring device. Tensile tests were performed for EDD steel according to ASTM standards and mechanical properties were evaluated. Finite element method (FEM) simulations were performed using the mechanical properties evaluated from tensile tests to predict the thickness at the dome and wall regions by using the progressive draw with ironing tool. It is found that the simulated thickness is close to experimental results. It is also found that the surface finish on the component has improved and die life has increased due to use of internal lubrication with coolant supplied.

Study of the Technology Preventing the deformation area of the Hot -Dip Zn -Al Galvanizing steel Blackening

In order to prevent the deformation area of the hot -dip Zn -Al Galvanizing extra deep drawing steel blackening during the drawing process, the microstructure and composition of the blackening area was researched by SEM and EDS. The blackening during the drawing process was caused by Zn -Al coating corrosion after the damage of passive film. And the effective measures that the surface passive film on Zn -Al coating had self-lubrication and the friction factor of the surface below 0.2 to prevent the blackened was determined. Then a self-lubricating hot -dip Zn -Al Galvanizing extra deep drawing steel was developed. After the application of Technology about the self-lubricating hot -dip Zn -Al Galvanizing, the blackening did not appear again.

Analysis of Anisotropic Effects in Single Point Incremental Forming

Incremental Sheet Forming (ISF) has great potential to form complex sheet metal parts without using component specific tooling. Formability in ISF process is higher than the conventional forming processes but achieving good geometrical accuracy is a challenging task. Anisotropy of material causes variation of thickness with respect to rolling direction, which effects stiffness, spring-back and accuracy. Variation of thickness and spring-back with rolling direction is studied using experimental and numerical analysis for a conical geometry formed using extra deep drawing steel having high anisotropy. Comparison of anisotropy and isotropy is done using numerical analysis. Results showed that, thickness is low in the direction with low ratio of width to thickness strain (r-value), resulting in higher spring-back. This directional property has to be considered in tool path design to enhance the accuracy. When material is assumed to be isotropic, variation of thickness and spring-back with respect to direction is insignificant.

The effect of sheet metal anisotropy on the calibration of an equivalent model for clinched connections

Clinching is a mechanical joining technique that involves severe local plastic deformation of two or more sheet metal parts using a punch and die. The local deformation results in a permanent mechanical interlock. It is widely applied as a reliable joining technique in automotive, heating, ventilation, air conditioning (HVAC) and general steel constructions and is still gaining interest. In FEA models of structures containing a large number of clinched joints, it is not computationally feasible to use detailed sub models of the joint. Therefore an equivalent model was proposed by Breda et al. to predict the force-displacement behaviour. This equivalent model was calibrated using a simple shear-lap and pull-out test. During the calibration step, some local effects due to the material properties are captured in the calibration parameters. This paper investigates the impact of the plastic material properties on this calibration method. The effect of strain hardening due to the bending process prior to pull-out testing, potential plastic anisotropy of the base material and their relation to the calibration parameters are investigated. This research has been validated with experimental results on mild deep drawing steel.

Effect of Alloying Elements on Growth Behavior of Intermetallic Compounds at the Cold-Sprayed Coating/Steel Interface During Immersion in Aluminum Melt

The formation of the intermetallic compounds at the interface between cold-sprayed coatings and steel as well as interaction between coatings and aluminum melt was investigated. Coatings of AA7075 (AlZn5.5MgCu) and AA4145 (AlSi10Cu4) were deposited on the sheets of the deep drawing steel DC04. The coated samples were then immersed in the aluminum melt AlSi9Mn at the temperature of T = 610 °C for different durations in the range 30 s < t < 10 min. The reaction layer growth was examined metallographically and by means of scanning electron microscope with energy-dispersive spectroscopy. Furthermore, the intermetallic phases were identified by X-ray diffraction analysis and characterized by microhardness measurements. For both coatings, β-AlFeSi phases were shown to be the major constituent in the reaction zone. The growth kinetics of the intermetallic phases appeared to be similar for AA4145 and AA7075 coatings, while their morphology was completely different.

Deep Drawing of constrained groove pressed EDD steel sheets

Constrained groove pressing (CGP) is a severe plastic deformation process for producing ultra-fine grained sheet metal without any change in the initial dimensions. CGP works on the principle of repetitive shear deformation of the material by alternate pressing by using asymmetrically grooved die and flat die constrained tightly by boundaries of the die. In this study, CGP, up to two passes has been performed on Extra deep drawing (EDD) steel specimens. To study the formability, the CGPed steel specimens have been deep drawn using a typical deep drawing setup and the limiting draw ratio (LDR) has been calculated. This LDR of CGPed material has been compared to the LDR of cups drawn using as-received EDD steel blanks. The formability of the CGPed material is almost the same as that of the as-received material. Apart from this, micro-hardness study of the cups has also been done on a similar comparative basis. These investigations show a slight improvement in the hardness values. It is found that by doing two passes of CGP on EDD steel, stronger cups can be produced without sacrificing much of the formability.