Low Formability Research Articles

Numerical modelling of forming high strength aluminium

In recent decades the developments of vehicle materials and technologies have been influenced by the environmental regulations. Reducing the mass of vehicles is important to reduce the air pollution emissions. In order not to break the safety standards with this reduction, the strength of the used materials should be increased. Nowadays the high strength steels have not enough formability, so the base materials of the vehicle need to be changed. The density of aluminium is significantly lower than that of steels, which is positive for weight reduction, but the strength of the traditional aluminium alloys is low, so it needs to be enlarged. However, due their different alloying elements and the rigid disperse precipitates phase they create, the ductility of high strength aluminium is not sufficient in most cases. The lower formability is a serious technical challenge for automotive engineers. The solution is in the newest dedicated FEM codes. With the help of these software the engineers can more easily plan the technical background of manufacturing a part, or making formability test in virtual environment without using specimen. Because of this, the objective of this paper is the numerical modelling of forming high strength aluminium.

Finishing Turning of Ni Superalloy Haynes 282

Nickel-based superalloys are widely used in the aeronautical industry, especially in components requiring excellent corrosion resistance, enhanced thermal fatigue properties, and thermal stability. Haynes 282 is a nickel-based superalloy that was developed to improve the low weldability, formability, and creep strength of other γ’-strengthened Ni superalloys. Despite the industrial interest in Haynes 282, there is a lack of research that is focused on this alloy. Moreover, it is difficult to find studies dealing with the machinability of Haynes 282. Although Haynes 282 is considered an alloy with improved formability when compared with other nickel alloys, its machining performance should be analyzed. High pressure and temperature localized in the cutting zone, the abrasion generated by the hard carbides included in the material, and the tendency toward adhesion during machining are phenomena that generate extreme thermomechanical loading on the tool during the cutting process. Excessive wear results in reduced tool life, leading to frequent tool change, low productivity, and a high consumption of energy; consequentially, there are increased costs. With regard to tool materials, cemented carbide tools are widely used in different applications, and carbide is a recommended cutting material for turning Haynes 282, for both finishing and roughing operations. This work focuses on the finishing turning of Haynes 282 using coated carbide tools with conventional coolant. Machining forces, surface roughness, tool wear, and tool life were quantified for different cutting speeds and feeds.

High strength aluminum alloys in car manufacturing

In recent decades, there are many requirements stated against car manufacturing both from the customers’ side and also as legal requirements to reduce harmful emissions to provide increased environment protection, as well as to achieve increased safety, higher comfort and more economical vehicles. To meet these often contradictory requirements, application of light weight design principles is one of the most widely applied solutions. There are two main trends for producing lightweight automotive structures with low cost manufacturing which are particularly valid for car body elements produced by sheet metal forming. Application of high strength steels is one of the main possibilities. Various generations of high strength steels (e.g. DP-steels, TRIP steels, XHSS and UHSS advanced high strength steels) were developed in the last decades which are already successfully applied in the automotive industry. The application of lightweight alloy materials – particularly various aluminum alloys – is regarded as the other possible solution to meet the requirements of lightweight car body constructions. Aluminum has even higher weight reduction potential than steel materials, but aluminium has lower formability than steel; replacing steel with lighter materials such as aluminum can be costly and is not simply straightforward. Aluminum sheet, in particular, has lower formability at room temperature than typical sheet steels. This is one of the main reasons that recently the hot forming of aluminum alloys came to the forefront of research activities. In this paper, some recent results obtained within a joint European project entitled Low Cost Materials Processing Technologies for Mass Production of Lightweight Vehicles will be introduced.

A study on forming process of AA5083 alloy with an infrared local heat treatment

Although the demand of aluminum alloys has been increasing to reduce vehicle’s weight in automotive industries, the low formability of aluminum alloys has made a limit on industrial applications. This work presents an infrared ray (IR) local heat treatment in the purpose of improving formability of aluminum alloys. The concept of the IR local heat treatment is focusing IR rays on target areas where the level of plastic deformation reaches the fracture level. The local heat treatment employs the intermediate heat treatment scheme that is conducted between two stages, 1st forming and 2nd forming. In the 1st forming, the blank is deformed until a part of the blank reaches 15% strain. Then, the part is locally heat treated. After the heat treatment, the 2nd forming makes the heat treated blank match the target shape. Authors recently conducted this heat treatment with an IR local heating method to resolve the formability problem of an AA5083 alloy [1]. However, in the paper, the IR heat treatment was applied to only a linear heating shape. Neither the heat treatment for a curved shape nor local heating effect in temperature distribution was discussed in the paper. In this work, the IR heat treatment is studied in three points of view. The first is to shortly introduce the IR heat treatment in the purpose of improving formability with the AA5083 alloy. The second is studying the local heating effects in temperature distribution and application of a curved shape. Finally, an industrial application of tailgate is discussed with reduction of heating energy. The results show that this focused IR heating can improve formability with reducing heating energy for industrial applications.

Effect of Heat Treatment Conditions on Mechanical Properties and Precipitates in Sheet Metal Hot Stamping of 7075 Aluminum Alloy

Due to the low formability at room temperature, the application of 7XXX aluminum alloy sheet is limited. The hot forming-quenching process is an effective technology for the forming of some complex-shaped aluminum alloy parts. In this study, heat treatment was integrated with sheet metal stamping to improve formability and strength of 7075 aluminum alloy sheet. The effect of different heat treatment parameters on the strength of 7075 aluminum alloy sheet was investigated under stamping and heat treatment integrated process, based on which the optimal heat treatment combination was determined. Furthermore, the evolution of precipitates with the variation of aging temperature and time was studied by transmission electron microscope. In addition, quenching under water-cooled dies was conducted for 7075 aluminum alloy sheet after solution heat treatment, in which the hardness under die quenching was compared with that of underwater quenching and air quenching. Finally, the tensile test illustrates that, after die quenching and successive artificial aging, the tensile strength of 7075 aluminum alloy sheet was achieved at around 548 MPa. Shear fracture with long strip step-shaped pattern was observed in aging state.

Fabrication of Microchannels and Evaluation of Guided Vascularization in Biomimetic Hydrogels.

The fabrication of microchannels in hydrogel can facilitate the perfusion of nutrients and oxygen, which leads to guidance cues for vasculogenesis. Microchannel patterning in biomimetic hydrogels is a challenging issue for tissue regeneration because of the inherent low formability of hydrogels in a complex configuration. We fabricated microchannels using wire network molding and immobilized the angiogenic factors in the hydrogel and evaluated the vasculogenesis in vitro and in vivo. Microchannels were fabricated in a hyaluronic acid-based biomimetic hydrogel by using "wire network molding" technology. Substance P was immobilized in acrylated hyaluronic acid for angiogenic cues using Michael type addition reaction. In vitro and in vivo angiogenic activities of hydrogel with microchannels were evaluated. In vitro cell culture experiment shows that cell viability in two experimental biomimetic hydrogels (with microchannels and microchannels + SP) was higher than that of a biomimetic hydrogel without microchannels (bulk group). Evaluation on differentiation of human mesenchymal stem cells (hMSCs) in biomimetic hydrogels with fabricated microchannels shows that the differentiation of hMSC into endothelial cells was significantly increased compared with that of the bulk group. In vivo angiogenesis analysis shows that thin blood vessels of approximately 25-30μm in diameter were observed in the microchannel group and microchannel + SP group, whereas not seen in the bulk group. The strategy of fabricating microchannels in a biomimetic hydrogel and simultaneously providing a chemical cue for angiogenesis is a promising formula for large-scale tissue regeneration.

The Current Status and Development of Practical Sheet Metal Forming Simulation

Sheet metal forming simulation is widely used for predicting formability and springback behavior of stamping parts. The increasing usage of low formability material such as high-strength steel and aluminum alloy has grown the importance of CAE technologies. JSOL responds to the expanding demand for CAE by developing and providing software JSTAMP (LS-DYNA). This presentation reports the current and development statuses of the practical use of CAE technologies. The current status is described by taking the springback simulation results as the example. The accuracy and the simulation time of springback prediction and springback compensation of the tool is presented. For the development effort, this presentation mentions the result obtained from different yield function to accomplish more accurate simulation, and the approach to optimizing CAE for hot forming. The technical development addressing the application of CAE for CFRP which are expected to become more common material for automobile part is also introduced.

A Review on Deep Drawing Process

Deep Drawing (DD) process is the one in which a punch forces a flat sheet metal blank into a die cavity. DD can also be described as the process which involves conversion of flat thin sheet metal blanks into parts of desired shape. Little work is available in the applications of DD processes at elevated temperatures which is going to be a very important manufacturing application in the coming decades. Deep Drawing (DD) is one of the sheet metal forming processes widely used in automobile, aerospace, electronics and allied industries to produce the hollow parts. The improvement in the deep drawing manufacturing process with latest methodologies leads to developments in the automobile and other sheet metal industries. Still today, this process of analysis and design is an art than science. Presently, the conventional deep drawing (CDD) operation is carried out at room temperature in industries. Although the deep drawing process of high strength / low formability metals has an extensive industrial application area, deep drawing at room temperature has serious difficulties because of the large amount of deformations revealed and high flow stresses of the materials. The present paper gives an overview of deep drawing process, its classification along with advantages, limitations and applications.

Strain-Induced Martensitic Transformation and Texture Evolution in Cold-Rolled Co–Cr Alloys

Co–Cr alloys have been used in biomedical purposes such as stents and artificial hip joints. However, the difficulty of plastic deformation limits the application of the alloys. During the deformation, Co–Cr alloys often exhibit strain-induced martensitic transformation (SIMT), which is a possible reason for the low formability. The distinct increase in dislocation density in the matrix phase may also result in early fractures. Since these microstructural evolutions accompany the textural evolution, it is crucial to understand the relationship among the SIMT, the increase in dislocations, and the texture evolution. To characterize those at the same time, we conducted time-of-flight neutron diffraction experiments at iMATERIA beamline at the Japan Proton Accelerator Research Complex (J-PARC) Materials and Life Science Experimental Facility (MLF), Ibaraki, Japan. The cold-rolled sheets of Co–29Cr–6Mo (CCM) and Co–20Cr–15W–10Ni (CCWN) alloys were investigated in this study. As expected from the different stacking fault energies, the SIMT progressed more rapidly in the CCM alloy. The dislocation densities of the matrix phases of the CCM and CCWN alloys increased similarly with an increase in the rolling reduction. These results suggest that the difference in deformability between the CCM and CCWN alloys originate not from the strain hardening of the matrix phase but from the growth behaviors of the martensitic phase.

Mechanical characterisation and modelling of randomly oriented strand architecture and their hybrids – A general review

A comprehensive review of the mechanical characterisation and modelling of randomly oriented strand material architecture and their hybrids with laminates is presented. Randomly oriented strand composites are long discontinuous fibre systems that exhibit excellent formability characteristics and stiffness properties comparable to quasi-isotropic laminates, allowing their use in the manufacture of intricate geometric parts for automotive and aerospace industries. Randomly oriented strand architecture complements out-of-autoclave methods such as compression moulding, thermostamping and resin-transfer moulding leading to cost-reduction. Their applicability is limited to non-structural and low-load bearing applications due to their low strength properties. Continuous fibre aerospace preforms exhibiting excellent mechanical performance possess low formability characteristics and are confined to simple shell-like geometries with minimal curvatures, while incurring high-costs and long manufacturing times. Hybridisation of randomly oriented strand and with other material architectures represents trade-off solutions of formability and performance characteristics often yielding synergistic effects. Seemingly simple, randomly oriented strand architecture is a complex material system that poses several structural and process challenges. This work categorises the pertinent research work from the literature on the mechanical characterisation into the framework of a formal characterisation environment of composite structures that includes the coupon, the part and structural levels. The manufacturing, dispersion methods and measurement techniques are qualitatively assessed with reference to the mechanical properties. The discussion on modelling involves the identification of crucial characteristics of significant analytical and numerical modelling techniques devised for the prediction of the mechanical behaviour of randomly oriented strand composites and their hybrids. Emphasis is on the methods of stiffness and strength prediction. Our perspectives on the effective use of randomly oriented strand composites and their hybrids are discussed. Process characterisation and process modelling of randomly oriented strand composites and their hybrids are beyond the scope of this article.

Cold Forming of Ni-Ti Shape Memory Alloy Sheet

Ni-Ti shape memory alloy has two specific properties, superelasiticity and shape memory effect, and thus is widely applied in diverse industries. To extend its further application, this study attempts to investigate the feasibility of cold forming its sheet blank especially under a bi-axial tensile stress state. Not only experiments but also a Finite Element Analysis (FEA) with DEFORM 2D was conducted in this study. The material data for FEA was accomplished by the tensile test. An Erichsen-like cupping test was performed as well to determine the process parameter for experiment setup. As a result of the study, the Ni-Ti shape memory alloy sheet has a low formability for cold forming and shows a relative large springback after releasing the forming load.

Effects of Pre-Strain on the Aging Behavior of Al 7075 Alloy for Hot-Stamping Capability

The present study investigates the significance of pre-strain on the T6 aging behavior of an Al 7075 alloy for evaluating the applicability of hot stamping. In practice, the alloy was pre-strained up to 15% during solution heat treatment at 480 °C prior to quenching, and artificial aging was conducted at 120 °C. The peak aging time and precipitation behavior were compared with the alloy with pre-straining at room temperature after quenching but immediately before the artificial aging. The results showed that increasing amounts of pre-strain tend to reduce the aging time up to 50% for achieving peak hardness, which is consistent with the alloy at the T6 condition. There is a limitation for the maximum attainable amount of pre-strain of 10% for the homogeneous distribution of strain when the alloy is strained at room temperature (RT) due to the low formability. The pre-strained alloy as hot stamping exhibited lowering of the peak reaction temperatures for dissolution and formation of Guinier–Preston (GP)-Zones and precipitated with increasing amounts of pre-strain towards 15% through the differential scanning calorimetry analysis, thereby confirming the shortening of the peak aging time. The present study confirms the excellent potential of the hot-stamping process to extend the capability of an Al 7075 alloy.

Optimizing the Heat Treatment Parameters of Al-6061 Required for Better Formability

Aluminium alloys are widely used in several engineering applications due to their high strength-to-weight, ease of availability, comparatively low cost and ease of machinability. These alloys are classified into heat treatable and non-heat treatable, among which the former have more applications. Al 6061 is one among them that has relatively higher strength and good formability. There are several tempers of Al 6061 available ranging from T1 to T9. However, tempers T4 and T6 are the ones with better mechanical properties and are hence more widely used. Al 6061-T4 has better formability (percentage of elongation of 18.8%) but lower yield strength whereas Al 6061-T6 has lower formability (percentage of elongation of 8.8%) but a higher yield strength. This paper aims at studying the properties of the different tempers of Al 6061 subjected to varying heat-treating parameters (such as artificial aging temperatures and durations, step aging temperatures and durations) and subsequently the determination of optimum parameters to strike a balance between strength and formability.

Influence of a local laser heat treatment on the bending properties of aluminium extrusion profiles

Driven by ecological and economical demands, lightweight design and in this context, the substitution of steel by aluminium has become a major trend in the automotive industry. However, design possibilities are limited by the low formability of aluminium alloys. One approach to overcome these limitations is the usage of tailor heat treated semi-finished products. By a local short-term heat treatment, distinct areas are softened, which can be used to improve the material flow into critical forming zones. Within this work, the influence of local short-term heat treatment on the formability of aluminium extrusion profiles is analysed by experimental bending tests. Aims are the enhancement of maximum reachable bending angles as well as the reduction of cross section deformations. Therefore, different heat treatment layouts are applied by laser irradiation. Finally, the bending results are evaluated and promising heat treatment strategies are derived.

Maximum Bulge Height and Weld Line Displacement in Hydroforming of Tailor Welded Blanks

Tailor welded blank (TWB) has many advantages over a traditional blank for manufacturing automobile sheet metal components, such as significant flexibility in product design, higher structural stiffness, and crash behavior. However, lower formability and weld line movement are some of the problems associated with forming of TWBs. Hydroforming is a potential technique to enhance formability. In this work, the effect of thickness ratio on maximum dome height and weld line movement in hydraulic bulging of laser welded interstitial-free (IF) steel blanks of different thickness combinations has been predicted using finite element (FE) simulations. The results are also validated with hydraulic bulging experiments on TWBs. It has been found that with increase in thickness ratio, the maximum bulge height decreased and weld line displacement toward thicker side increased. These results have been used to relocate the weld line toward the thinner side in the initial blanks and achieve a more uniform bulge profile of the dome. The peak pressure to achieve maximum safe dome height and percentage thinning has also been found out. The results showed huge improvement in uniformity of bulge profile with little reduction in dome height.

Enhancing plastic deformability of Mg and its alloys—A review of traditional and nascent developments

Abstract Mg and its alloys have continued to attract interest for several structural and super-sensitive applications because of their light weight and good combination of engineering properties. However for some of these applications, high plastic deformability is required to achieve desired component shapes and configurations; unfortunately, Mg and its alloys have low formability. Scientifically, the plastic behaviour of Mg and its alloys ranks among the most complex and difficult to reconcile in metallic material systems. But basically, the HCP crystal structure coupled with low stacking fault energies (SFE) are largely linked to the poor ductility exhibited by Mg alloys. These innate material characteristics have regrettably limited wide spread applicability of Mg and its alloys. Several research efforts aimed at exploring processing strategies to make these alloys more amenable for high formability – mediated engineering use have been reported and still ongoing. This paper reviews the structural metallurgy of Mg alloys and its influence on mechanical behaviour, specifically, plasticity characteristics. It also concisely presents various processing routes (Alloying, Traditional Forming and Severe Plastic Deformation (SPD)) which have been explored to enhance plastic deformability in Mg and its alloys. Grain refinement and homogenising of phases, reducing CRSS between slip modes, twinning suppression to activate non-basal slip, and weakening and randomisation of the basal texture were observed as the formability enhancing strategies explored in the reviewed processes. While identifying the limitations of these strategies, further areas to be explored for enhancing plasticity of Mg alloys are highlighted.

An Investigation and Prediction of Springback of Sheet Metals under Cold Forming Condition

Low formability and springback especially at room temperature are known to be major obstacles to advancements in sheet metal forming industries. The integration of numerical simulation within the R&D activities of the automotive industries provides a significant development in overcoming these drawbacks. The aim of the present work is to model and predict the springback of a Galvanized low carbon steel automotive panel part. This part suffers from both positive and negative springback which physically measured using CMM. The objective is to determine the suitable forming process parameters that minimize and compensate the springback through robust FE model. The analysis of the springback was carried out following (Isotropic model and Yoshida – Uemori model) which are calibrated through cyclic stress strain curve. The material data of the Galvanized low carbon steel was implemented via lookup tables in the commercial finite element software Pam-Stamp(TM). Firstly, the FE model was validated using the deformed part which suffers from springback problem at the same forming condition. The FE results were compared with the measured experimental trails providing very good agreement. Secondly, the validated FE model was used to determine the suitable forming parameters which could minimise the springback of the deformed part.

Press hardening of alternative materials: conventional high- strength steels

The increase in strength of new high strength steels (HHS) and advanced high strength steels (AHHS) has led to forming issues, such as high springback, low formability, increase of forming forces and tool wear. These problems increase thecosts of manufacturing and maintaining stamping tools in the automotive industry. The aim of this research was to analyse the advantages of applying the press- hardening process toconventional HSS and AHSS steel to increase their formability and therefore reduce the number of forming steps and productioncosts. With this aim in mind, the press-hardening process was used to manufacture an industrialcomponent using four different automotive steel grades: dual phase (DP),complex phase (CP), transformation- induced plasticity (TRIP) and martensitic (MS) grade. Springback measurements werecarried out, together with an analysis of the obtained final mechanical properties and microstructures. The results showed that the formability of all the materials increased. The mechanical properties of theCP800 and TRIP700 materials were maintained or even improved, whereas those of the MS1200 and HCT980X materials were significantly reduced. Weconclude that press hardening is a suitable manufacturing process forCP800 and TRIP700components.

Optimization of drilling parameters for drilling of TI-6Al-4V based on surface roughness, flank wear and drill vibration

Machining of titanium alloys is difficult due to their low elasticity, high formability and tendency of breakage. In drilling of TI-6Al-4V alloy, drill bits are subjected to chatter vibration and it causes poor surface finish and tool failure. In this study, effect of drilling parameters such as spindle speed, helix angle and feed rate on surface roughness, flank wear and acceleration of drill vibration velocity was investigated using Response Surface Methodology. A Laser Doppler Vibrometer (LDV) was used to measure vibration of drill bit in the form of Acousto Optic Emission (AOE) signal. And these signals were transformed into time domain with different time frequency zones using a high speed fast Fourier transformer. Experimental data were analyzed using Response Surface Methodology (RSM) to identify significant parameters on surface roughness, flank wear and acceleration of drill vibration velocity. A multi response optimization was performed to optimize drilling parameters for minimum surface roughness, flank wear and acceleration of drill vibration velocity. Optimum cutting parameters were found as 26.16 degrees of helix angle, 10.0 mm/min of feed rate and 600rpm of spindle speed.

A Study on Infrared Local Heat Treatment for AA5083 to Improve Formability and Automotive Part Forming

Automotive industries are increasingly employing aluminum alloys for auto parts to reduce vehicle weight. However, the low formability of aluminum alloys has been an obstacle to their application. To resolve the formability problem, some studies involving heat treatments under laboratory conditions have been reported. However, for industrial applications, the heat treatment sequence, heating energy efficiency, and a commercial part test should be studied. This work shows an infrared (IR) local heat treatment, heating only small areas where the heat treatment is required, for an aluminum alloy to improve the formability with a reduction of heating energy. The experiment shows that the formability drastically increases when the aluminum alloy is heat treated between two forming stages, referred to as intermediate heat treatment. The microstructures of the test pieces are evaluated to identify the cause of the increase in the formability. For an industrial application, an aluminum tailgate, which cannot be manufactured without heat treatment, was successfully manufactured by the IR local heat treatment with a reduction of energy. A simulation was also conducted with a stress-based forming limit diagram, which is not affected by the strain path and heat treatment histories. The simulation gives a good prediction of the formability improvement.