Key Engineering Materials Vols. 611-612

Abstract: Bending is a commonly used forming technology in metal forming. The occurring springback and low forming limits of high-strength steels especially during air bending are the main disadvantages. In this paper, the conventional air bending process is applied with a hydrostatic pressure in the bending zone. This was done using an elastomer tool. The advantage of this method is that the flexibility of air bending is maintained by reducing the springback while the forming limits are extended. Furthermore, different geometries for the elastomer tool were investigated by means of a FEM simulation. The investigation leads to a reduction of the process forces by minimizing the springback and to an extension of the forming limits.

Abstract: In this paper the effects of shape and tool material on the output parameters on spinning of aluminum sheets are investigated. To achieve this purpose, four kinds of roller tools with the same shapes and with different materials including mild steel, ertalon, polyamid and caoutchouc were used and some parts were spun by the same geometric form; moreover, in order to investigate the effects of roller nose radius on output parameters such as surface smoothness and thickness distribution, three caoutchouc roller tools with different nose radius were used at the same condition. The results show that using a caoutchouc roller tool for spinning of aluminum sheets leads to the best surface smoothness, while using a steel tool because of its roughness is not suitable. Ertalon and polyamid roller tool have a high rate of wearing. Furthermore, in the constant feedrate by increasing of roller nose radius the contact area between roller and workpiece is increased and surface smoothness is followed, relatedly.

Abstract: Electromagnetic forming (EMF) is a typical high speed forming process using the energy density of a pulsed magnetic field to form work sheets made of metals with high electrical conductivity like aluminium alloys, which have low formability at low strain rate. Under high velocity forming, metallic materials exhibit an increase of flow stress and ductility with increasing deformation rate. Therefore, materials of lower ductility can be deformed to higher strains using high strain rate deformation processes such as electromagnetic or explosive forming techniques. In this paper analysis of an electromagnetic sheet metal forming process is carried out by using commercial finite element software LS-DYNA^®, which incorporates a sequential coupling method involving electromagnetic field, structural and thermal solutions. Study of process parameters for forming aluminium ice tray (used in refrigerator) by Electromagnetic forming process has been carried out, simulation was done involving a die, Al worksheet and a spiral coil.

Abstract: The preforming stage in hydroforming of an aerospace generic shape was investigated using a combination of experimentation and numerical modeling. The preform die was manufactured using a rapid prototyping method, namely the selective laser sintering (SLS) process. The preforming experiments were conducted on 0.9 mm and 1.2 mm thick stainless steel 321 (SS321) tubes. To evaluate the preforming process, an automated deformation measurement system, ARGUS^®, was used to measure the 3-dimensional (3D) strains on the deformed tubes. Data collected from the experiments were used to validate the simulation of the preforming stage. The simulation and experimental results were found to be in good agreement, indicating that the preform model can be used as a starting point for simulating the tube hydroforming (THF) process. In addition, the SLS approach was found to be very promising, as it reduced greatly the lead time and cost of process development for THF.

Abstract: The rapid application of alternative materials is vital to the environmental and sustainable development of the European manufacturing industry. In many cases, companies seek using ‘old’ materials, such as aluminum alloys, magnesium, titanium, composites and plastics, for new applications in order to improve customer value; i.e., the perceived product benefits subtracted its price. For a subset of manufacturing companies, one of the most viable strategies is to offer weight savings at an affordable price by replacing steel with aluminum alloys, typically providing added value in the 0.25 - 0.5 kg/€ range, depending on application. Hence, weight savings shave to come with minimum cost penalty, which calls for a balanced optimization of manufacturing process and material consumption. For formed products, the latter optimization is driven by the performance characteristics of the final product as well as its quality capabilities relating to dimensional accuracy. The former is closely related to the attributes of the particular forming method. In this study, an industry-like rotary stretch bending set-up has been equipped with two different modular die inserts to determine how process characteristics impact dimensional accuracy of the product, as represented by local cross-sectional distortions and global elastic springback in industrial practice. A number of cross-sectional profile geometries with different wall thickness, depth, width and number of internal chambers have been simultaneously stretched and bent into the shapes provided by two die different configurations. The extruded profiles were made in different heat treatable alloys within the AA6xxx and AA7xxx series and formed according to industrial practices, which for the latter included solution heat-treatment immediately before forming. The results show that the slenderness of the external flange of the cross section is the main parameter with regard to the magnitude of local cross-sectional distortions. In practice, therefore, wall-thickness is the critical quality control parameter. The material’s yield characteristic proved to have limited impact on local distortions, although this is usually a major concern with regard to springback variations. The results from the experimental series have been structured into a design relationship for assessment of local distortions where the problem is reduced to the use of a proposed dimensionless bendability parameter as input.

Abstract: Recently, to construct an airframe 2-layer composite materials consisting of carbon fiber reinforced plastic (CFRP) laminates an TiAl6V4 still need to be machined, whereby drill holes are frequently machined. Special attention has to be paid to the machining quality, which implies hole dimensional accuracy, defect free peripheral zone, edge quality at inlet and outlet of hole and so on. In this research, first by using a high performance CNC machine tool equipped with potent control unit, drilling and circular milling are compared for hole making in CFRP laminates and it is ascertained that circular milling is superior to drilling in defect free peripheral zone and also tool life [. Second, from comparing drilling and circular milling in hole making of 2-layer composite materials consisting of CFRP laminates and TiAl6V4, the superiority of circular milling caused by lower thrust force and lower thermal load than those of drilling has been made clear [. Third, the author has devised a new spindle designed based on double eccentric mechanism so that circular milling can be executed at an airframe assembly site. By using a new handy type apparatus having the spindle driven by air motors, hole making tests were executed to 2-layer composite materials consisting of CFRP laminates and TiAl6V4 with cemented carbide endmill [.

Abstract: In aeronautics weight reduction of aircrafts has become one of the main objectives. This has led to the fact that a majority of the aeronautical parts made from aluminium are large monolithic parts (to avoid the use of assembling systems like rivets and screws). The manufacturing of these aeronautic parts, especially the structural parts, is usually performed by machining. On large aluminium aeronautical parts, the main factor which can lead to non-compliance of a part is the re-equilibrium of the initial residual stresses inside the workpiece during the machining process. In this paper, an example of multi-sided machining of a part made of AIRWARE^® 2050 alloy is realised. Simulations of the machining of this part have been performed using a specific finite element tool which has been specially developed to predict the distortion due to the redistribution of these initial residual stresses during machining. Results numerically obtained are then compared with experimental results, showing a good agreement.

Abstract: The demand of carbon fiber reinforced plastics (CFRP) has been increased in aircraft and automobile industries. In milling of CFRP, the cutting parameters should be determined to finish the machining surfaces without delamination. The tool wear is also a critical issue to finish good surfaces. The paper presents a force model to study the milling process of CFRP. In order to investigate the anisotropy in milling of CFRP, the cutting tests were conducted for unidirectional CFRPs with changing the feed direction of the milling tool. The cutting force and the surface finish depend on the feed direction with respect to the fiber orientation. A force model based on the minimum cutting energy is applied to milling of CFRP. The orthogonal cutting data used in the force model is associated with the relative angle of the cutting edge rotation angle to the fiber orientation. The model was verified in comparison between the predicted and the measured cutting forces. The model also estimates the effect of the feed direction with respect to the fiber orientations on the cutting force in terms of anisotropy in the orthogonal cutting data.

Abstract: Titanium alloys, mainly because of their poor thermal conductivity, need to be cut at relatively low cutting speeds to avoid a severe diffusion wear, with obvious negative consequences on the profitability of machining. An important amount of research activities has been done in order to increase productivity in titanium machining operations and one of the most promising solutions is represented by the use of liquid nitrogen as a coolant during the machining operation. The aim of this paper is to compare traditional and cryogenic turning of Ti6Al4V in a region of cutting parameters particularly relevant to the aerospace industry where no previous data are available. The cutting parameters are those typical of titanium alloys rough machining which is considered, cost-wise, the most important operation because, for aerospace components, the so-called Buy-To-Fly ratio can reach values up to 20:1. The experiments have been performed using a full factorial design in order to statistically evaluate, using ANOVA and regression analyses, the significance of the input factors on the process most interesting outputs. The considered input factors are: type of cooling method, cutting speed and feed rate. The main analysed responses are: tool wear, surface roughness, cutting forces, coefficient of friction and chip morphology. The results show the significance of the cooling method on the tool life and that cryogenic machining is able to increase the tool life with respect to wet cutting. On the other hand, the beneficial effect of the liquid nitrogen cooling is reduced at high cutting speed and feed rate. Besides, the results showed that a small but significant reduction can be achieved for both the repulsion force and the coefficient of friction at the tool-workpiece interface.

Abstract: Electron Beam Melting (EBM) is attracting large interest among the manufacturers of surgical implants as a near-net shape technology. Titanium alloy Ti6Al4V is widely used in the biomedical field thanks to its high biocompatibility, corrosion resistance and mechanical properties. The chemistry and microstructural features of EBM Ti6Al4V indicate lower machinability in comparison with wrought Ti6Al4V. Aim of the paper is to present a comparison between the machinability of wrought and EBM Ti6Al4V in semi-finishing external turning, by quantifying the effects of the cutting speed and the feed rate. Tool wear, surface integrity, chip morphology and microstructural analysis have been used to compare and assess the machinability of Ti6Al4V delivered in the two conditions.