Metal-forming Processes Research Articles

Influence of Metal Forming Process in the Fatigue life of Axle Housings & Failure Investigation

Abstract Axle Housings in the Heavy Commercial Vehicle Axles are mostly hot die formed at a temperature below re-crystallization to achieve the required designed section without any metallurgical cracks. Finished Axle beams when subjected to Indoor testing’s for Service loadings had a failure before the acceptance. CAE life analysis estimates a life higher than the actual failure by considering the axle housing tensile strength same as hot rolled plates supplied by steel mills. On Failure analysis of the component the actual tensile strength is 15∼17% lower than the raw material, this drop in strength has happened during hot forming process. Similar comparison has carried out with the forming process changed to cold forming for the same material at room temperature. Tensile strength at the similar section shows a tensile value, which is as same or higher by 2 to 5% in comparison with the raw material due to Strain hardening during cold working. But during the cold forming process, 10-15% of total numbers experiences forming cracks at the critical zones leading to manufacturing stoppages. So, design improvement has been carried out in the axle housings to overcome the failure due to tensile drop in hot forming process. In addition, optimization of hot forming parameters to reduce the losses of tensile strength is also under experimentation

Probability Distribution of Joint Point Loadings in Car Body Structures under Global Bending and Torsion

More than 6000 cylindrical joining points connect the individual sheet metal components of a current car body. Due to multi-material design, a large number of these points are currently realized by bulk-sheet metal-forming processes, such as clinching or self-pierce riveting. Today, the development and optimization of joining points takes into account tensile, shear and combined tensile-shear strengths of the joint. Although a load-optimized design can be used to increase the utilization of the joining points and to reduce weight and costs, the design of the joining points themselves is not adapted to the actual local load, since their predominant load distributions are hardly known. The aim of this paper is to determine the probability distribution of pure tensile, shear and combined tensile-shear loads at joining points of a body-in-white under realistic global loads. First, a body model is derived from a full vehicle, then the joining points are modeled, and the global loads are applied to the structure. The simulation results are then automatically evaluated. This data-driven approach thus enables an automated determination of the cross-sectional forces at the joining points and their statistical evaluation for load-compliant joint point design in product development.

Modelling and Simulation of Sheet Metal Forming Processes

Numerical simulation of sheet metal forming processes has become an indispensable tool for the design of components and their forming process, in industries ranging from the automotive, to the aeronautics, packing and household appliances [...]

Tribological studies on multi-coated forming tools

Processes of Sheet-Bulk Metal Forming combine operations of both sheet and bulk metal forming, enabling the production of closely-toleranced functional components. Locally differing friction conditions on a single tool surface are crucial to control the material flow and to reduce process forces and tool wear. In order to understand how different friction conditions on a multi-coated tool surface affect the material flow during forming operations, variants of amorphous carbon coatings (a-C:H:W) and Cr-based hard coatings (CrAlN, CrAlCN) were deposited in combinations side by side on punches of ring compression tests. Evaluating the rings’ shapes revealed the coatings’ effects on material flow in terms of ring inner contours with sections of varying curvatures. Characteristic friction mechanisms were observed, which allowed a local delimitation of friction conditions by selectively applied coatings.

Forming, fracture and corrosion behaviour of stainless steel 202 sheet formed by single point incremental forming process

This work aims to determine the forming limit of stainless steel 202 sheet having 0.8 mm thickness during Single Point Incremental sheet metal Forming (SPIF) process. A L18 orthogonal array was designed using taguchi method for performing SPIF. The process parameters used were spindle speed, feed rate and vertical step down having three levels each and ball diameter having two levels. A straight groove test was conducted for 18 samples and strain based Forming Limit Diagrams (FLD) and stress based FLDs were plotted. Stress triaxiality and strain triaxiality were determined. The fractographs were analyzed and dislocation density was measured from x-ray diffraction line profile analysis. The corrosion behaviour of both undeformed sample and deformed sample were also studied. It was found that the formability is increased with increasing the spindle speed, decreasing the vertical step down and feed rate. The sum of strain was found to be 0.91 which is twice greater than that of conventional forming process. It is also found that the dislocation density is 2.35 times greater for the sample possesses higher formability than the sample possesses least formability. The goodness of fit in strain based FLD and stress based FLD are found to be 0.989 and 0.968 respectively.

Influence of component design on extrusion processes in sheet-bulk metal forming

Nowadays, the functional integration of workpieces challenges existing forming processes. The combination of established forming processes – like sheet metal and bulk forming – offers the possibility to counter this issue. The application of bulk forming operations on sheet metal semi-finished products, also called sheet-bulk metal forming (SBMF), is an innovative approach. The potential of SBMF cannot be fully exploited, as there are no recommendations in terms of workpiece design and layout influence on the process result. Therefore, this paper focuses on the analysis of semi-finished products and component design parameters on resulting part and process properties in two extrusion processes in SBMF. The investigation is based on a combined numerical and experimental approach. It is shown that the investigated design parameters, in addition to the achievable dimensional accuracy, substantially influence the occurring tool loads as well as the required process forces.

Influence of varying sheet material properties on dry deep drawing process

Deep drawing is one of the most important processes in sheet metal forming. Conventionally, lubricants are used to reduce friction and wear. Demands for increased sustainability, environmental protection and resource efficiency motivate the realization of lubricant-free forming processes. The direct contact between tool and workpiece during dry deep drawing results in challenging tribological conditions, which cause an increase in friction and wear. Friction-reducing surface modifications of the tool such as carbon based coatings are being developed for the adaptation of the tribological conditions. The aim of this work is the simulation-based analysis of the stress spectrum for varying sheet properties for the qualification of wear-reducing surface modifications for a wide range of applications. By a simulation model for a rectangular cup, the influence of different batches of steel and aluminum materials with varying friction coefficients and mechanical properties is investigated within the framework of variant simulations. The tribological conditions in the simulation are described on the basis of friction coefficients from the strip drawing test. From the simulation results, the applicability of surface modifications for dry deep drawing is being evaluated depending on the sheet specific properties.

Optimal Bounds for the Probability of Failure of Sheet Metal Forming Processes of DP Steel

AbstractIn this contribution, the Optimal Uncertainty Quantification framework is extended to account for aleatory uncertainties, such that both epistemic and aleatory uncertainties can be quantified. The extended framework is demonstrated for an example of a forming process of a Dual‐Phase steel sheet, for which optimal bounds on the probability of failure are computed under polymorphic uncertainties.

Simulation of Structural Applications and Sheet Metal Forming Processes Based on Quadratic Solid–Shell Elements with Explicit Dynamic Formulation

In this work, nonlinear dynamic analysis of thin structures is investigated using quadratic solid–shell (SHB-EXP) elements. The proposed SHB-EXP elements are based on a fully three-dimensional formulation using an in-plane reduced-integration scheme along with the assumed-strain method in order to alleviate most locking phenomena. These developments consist of a 20-node hexahedral element, denoted SHB20-EXP, and its 15-node prismatic counterpart, denoted SHB15-EXP. The formulation of these elements is combined with fully three-dimensional behavior models, including elastic behavior as well as anisotropic plastic behavior for metallic materials. The resulting formulations are implemented into the ABAQUS explicit/dynamic software package in the framework of large displacements and rotations. First, to assess the performance of the SHB-EXP elements, four representative nonlinear dynamic benchmark tests have been conducted. Then, impact/crash problem and deep drawing of cylindrical cup have been performed to demonstrate the capabilities of the SHB-EXP elements in handling various types of nonlinearities (large strains, anisotropic plasticity, and double-sided contact). Comparisons with results obtained by ABAQUS elements as well as with reference solutions taken from the literature show the good capabilities of the developed quadratic SHB-EXP elements for the explicit dynamic simulation of thin structures.

Strengthening of cruciform sample arms for large strains during biaxial stretching

Material-forming abilities are crucial for the optimisation of sheet metal-forming processes. Among the many methods used for the evaluation of forming limits, those based on cruciform samples are very promising, mostly because of their frictionless character and access to a pure two-dimensional stress area. In contrary to punch or tubular test samples, they allow in-situ strain measurements on both sides of the gauge region. Nevertheless, they have some disadvantages. Namely, the arms of the sample crack at the gauge region before reaching the deformation limit. This reduces the mechanical insights that can be gained from a single specimen. The paper describes the development of cruciform specimens in which large strains can be achieved during bi-axial tensile testing. The experiments focus on the application of initial deformation on the cruciform sample arms prior to the test. Strain-induced hardening of the sample arms is shown to increase the maximum achievable strain within the gauge section. This allows the stress strain response of a given material to be characterised following large plastic deformation. The samples used in the bi-axial tensile tests each had one particular pre-deformed shape in the corners, whose degree of pre-deformation differed between them. The results demonstrate the increased strain characterisation capabilities, which can be determined from the addition of initial plastic deformation. Increased cold working was found to increase the maximum plastic deformation, and the associated data collection, which could be achieved within the test area. Selecting the correct degree of pre-deformation in the support region made it possible to increase the strain in the gauge section of the sample from ∼1% to about ∼11% without the need to build up the arms or reduce the thickness of the test area.

High Temperature Deformation and Microstructure Evolution Behaviours of 7075 Cast Aluminum Alloy under Multi-pass Loading

To analyse the effects of loading pass and heating temperature on the deformation behaviour and microstructure evolution of 7075 cast aluminium alloy, multi-pass high temperature loading experiments on Gleeble-3500 thermal simulation compressor were carried out. The results indicated that under each loading, all the true stress-strain curves are typical dynamic recrystallization curves. As strain increases, the stress increases sharply and then basically remains unchanged when it reaches a maximum value. As temperature rise, the peak value of flow stress slightly decreases when the temperature is less than 350°C, whereas it increases slightly when the temperature is larger than 350°C. The grain was elongated perpendicular to the axis. Only a small amount of fine recrystallized grains were found to nucleate and grow at grain boundaries at a lower temperature (250°C). As temperature increased, the recrystallized grain gradually increases, and its proportion gradually also increases until the recrystallization is basically completed. The achievements can provide a guideline to select processing parameters for the processes of metal forming of 7075 cast aluminium alloy, such as ingot blooming, spinning and extrusion.

Evaluating the Rheological and Tribological Behaviors of Coconut Oil Modified with Nanoparticles as Lubricant Additives

In metal-forming processes, the use of lubricants for providing desirable tribological conditions at the tool–workpiece interface is critical to increase the material formability and prolonging tool life. Nowadays, the depletion of crude oil reserves in the world and the global concern in protecting the environment from contamination have renewed interest in developing environmentally-friendly lubricants derived from alternative sources such as vegetable oils. In the present study, the rheological and tribological behavior of coconut oil modified with nanoparticle additives was experimentally evaluated. Two different nanoparticle additives were investigated: Silicon dioxide (SiO2) and copper oxide (CuO). For the two conditions, nanoparticles were dispersed at different concentrations within the coconut oil. The effects of concentration and shear rate on the viscosity were evaluated and the experimental data was compared with conventional models. A custom-made tribotester was used to evaluate the effect of concentration on the tribological performance of the nano-lubricants. The experimental results showed that wear volume loss was lowered by 37% and 33% using SiO2 and CuO nanoparticles, respectively. Furthermore, the addition of SiO2 and CuO nanoparticles decreased the coefficient of friction (COF) by 93.75% and 93.25%, respectively, as compared to coconut oil without nanoparticles.

On critical surface strain during hot forging of lubricated aluminum alloy

Abstract We present a new concept of critical surface strain to evaluate the lubrication-effective limit for process design in metal forming. Finite-element predictions obtained at various fixed Coulomb friction coefficients were compared in hot-forging experiments of a passenger car piston fabricated from short cylindrical aluminum alloy specimens well-lubricated with a solid film of water-dispersed lubricant. The Coulomb friction coefficient was formulated as a function of temperature, pressure, and material strain, and optimized by minimizing the difference between the predicted and experimental results. We established that the effect of surface strain dominated the metal-forming process, and that the optimized Coulomb friction coefficient changed abruptly at the critical surface strain at which the solid lubricating film used in the process is suddenly disrupted.

Constitutive Modelling of a New High-Strength Low-Alloy Steel Using Modified Zerilli–Armstrong and Arrhenius Model

Isothermal hot compressive deformation tests were performed on a new high-strength low-alloy (HSLA) steel designated as “Steel A” over a range of temperatures (950–1100 °C) and constant strain rates (0.0003—1 s−1). Using the hot deformation flow behaviour data, material constants to establish constitutive relations using revised Zerilli–Armstrong and phenomenological strain-included Arrhenius model were identified. The potential of the established constitutive equations to describe the high-temperature flow behaviour of the material was then compared with standard statistical parameters such as correlation coefficient (R) and average absolute relative error (AARE). The Arrhenius constitutive model proposed by Sellars and Tegart was found to describe the high-temperature flow behaviour of “Steel A” quite accurately, and hence, this model can be used in simulations of complicated metal-forming processes. The results obtained are presented and discussed here.

Influence of eccentricity of double eccentricity sleeves on the movements of swing head in rotary forging press

Abstract. Rotary forging is an innovative incremental metal forming process, In a rotary forging press with double eccentricity sleeves, the eccentricity of double eccentricity sleeves has significant effects on the movements of swing head. The internal and external eccentricity of the existing rotary forging machine is equal, except circular path, the rotation speed of internal and external eccentric sleeves for the rose curve, spirals curve and straight line is not equal, which will produce the oscillation centrifugal force during the forming process and cause the violent shaking on the machine. The shaking of the machine has an important influence on the life of the equipment parts machining accuracy and surface profile of parts, reducing the production efficiency. This paper proposes a method to reduce shaking by changing eccentricity and studied the influence of unequal eccentricity on the movements of swing head obtained the design relationship of internal and external sleeves eccentricity, which can reduce the shaking in rotary forging press. This study improving the working state of the rotary forging machine and economic benefits.

Modelling strengthening mechanisms in beta-type Ti alloys

An integral modelling approach for understanding the strengthening mechanisms in Ti alloys is presented and applied to alloys undergoing deformation via dislocation slip. The model incorporates contributions from solid solution, grain boundary, dislocation forest and strain hardening. The metal forming and thermomechanical processing factors influence both grain size and the stored strain energy. The strain hardening of Ti-Fe-Sn-Nb alloys was modelled by considering dislocation accumulation and annihilation terms. By tailoring the contribution of each strengthening effect, the yield stress and plasticity of advanced Ti alloys can be optimised.

Numerical Modeling Rolling Contact Problem and Elasticity Deformation of Rolling Die under Hot Milling

In metalworking, rolling is a metal-forming process in which slab is passed through one or more pairs of the rolling dies to reduce the thickness and to make the thickness uniform. Modeling of rolling die contact with the slab primarily needs to describe the Tribology of contact phenomena. The central concern of numerical modeling is used in this work to indicate a set of equations, derived from the contact principle, that transfer the physical event into the mathematical equations. Continuum rolling contact phenomena is considered to explain how a contact region is formed between rolling die and slab and how the tangential force is distributed over the contact area with coefficient of friction. At the end, elasticity stress behavior of rolling die contact with the slab for a number of cyclic loads is modeled. The model includes new proposed constitutive equations for discontinuity of the velocity–pressure distribution in rolling contact from the entry side to exit side of the neutral point. To verify the model, finite element simulation and experimental data from the literature are considered. The results show good agreement with finite element simulation and experimental data.

Continuum damage mechanics-based ductile behavior and fatigue life estimation of low carbon steels: AISI 1020 and AISI 1030

This paper presents an experimental estimation of the ductile behavior and low-cycle fatigue life for widely used structural steels AISI 1020 and AISI 1030 based on continuum damage mechanics approach. This method identifies the deterioration in stiffness of a material arising from micromechanisms of formation, growth, and coalescence of microvoids. This helps the characterization of the ductile flow behavior of metals through a damage variable D, evaluated via load–unload cyclic tensile test. The influence of strain hardening exponent, commonly treated as a constant in ductile flow characterization, is also explored in the current investigation. Its determination uses the Hollomon constitutive relation. Estimated D at different strain levels defines the corresponding effective stress. Application of this stress to the strain equivalence theory then enables the prediction of the stress–strain curve. The model-based results closely approximate the experimental stress–strain curve up to the onset of necking. The agreement of experimental results for fatigue life of the materials from low-cycle fatigue tests with damage-based low-cycle fatigue model demonstrates the correctness of the experimental findings. The damage-based model additionally helps in the prediction of microcrack nucleation and crack propagation life separately. Fractographic examinations of test specimen exhibit usually observed morphology of involved failure mechanisms. The present study emphasizes the experimental means of damage-based ductile flow assessment involving strain hardening exponent term and also the low-cycle fatigue life estimation. The significance of varying strain hardening exponent is further expressed in terms of the corresponding damage magnitude. The material data obtained from this study depicts the damage state at different levels of plastic strain that may serve as a useful information for metal-forming process design.

4.0 in metal forming – questions and challenges

The paper gives a view on perspectives for metal forming processes rising due to the industry 4.0 discussion and its consequences. The discussion starts with a view at aims pursued by introducing 4.0 into metal forming. From the results of this the needed data and required sensors are discussed as well as the potential of their introduction into current processes. At this point the processes in metal forming and their respective demands have to be taken into account as well. From here the step to the specific challenges, e.g. originating from the machine tools at hand, can be elaborated on.

Hot incremental forming of titanium human skull prosthesis by using cartridge heaters: a reverse engineering approach

The single-point incremental forming process is an emerging process, which presents an alternative to the conventional sheet metal-forming processes like stamping and drawing. It is known to be perfectly suited for prototyping and small series. The incremental forming process offers the possibility of manufacturing medical prosthesis or implants specific to each patient, which are more comfortable and guarantee better performance. A reverse engineering approach associated with single-point incremental forming process in order to produce a titanium prosthesis of human skull is developed. It allows guaranteeing the high degree of customization required. In this paper, several novel warm forming experimental setup equipped with instruments to measure efforts and temperature monitoring is proposed. This new warm setup is feasible and makes it easy to monitor force and temperature sheet at forming; it gives it the ability to be exploited in the industry of manufacturing titanium alloy medical shapes. The real geometry of a skull prosthesis is re-constructed from a laser scanning technique, and specific treatments are performed until a CAD model is obtained. From it, the forming punch trajectories have been defined, and skull prostheses are manufactured using the technology of single-point incremental forming in titanium material at different temperatures.