Key Engineering Materials Vols. 554-557

Abstract: The effect of rotational and travelling speeds and down force on the torque in Friction Stir Processing (FSP) process are presented. To find a dependence combining the spindle torque acting on the tool with the rotational speed, travelling speed and the down force, the artificial neural networks have been applied. Studies have shown that the increase in the rotational speed causes decrease in the torque while the increase in the travelling speed and down force causes the increase in the torque at the same time. The relationship between parameters of the process and the temperature of the tool, based on measurement head TermSTIR, were presented. Tests were conducted on casting aluminium alloy AlSi9Mg. Application of FSP process resulted in a decrease in the porosity in the modified material and microstructure refining

Abstract: Unconventional production techniques became interesting and promising part of manufacturing methods. They provide complementary, to traditional loss methods, solutions enabling use of high - performance engineering materials for construction of machinery and industrial equipment. By using properly selected methods or their hybrids difficult to cut materials as steel, alloys, sintered materials and composites can be processed. Among the wide variety of unconventional methods of materials forming, particular attention should be given to electrochemical machining, which has been successfully used in various industries. This fact proves attractiveness and versatility of ECM. The method could be used on large scale and many variations was developed as each application requires an individual approach and has own requirements. One of the least known and described type of electrochemical machining is jet ECM where the electrolyte jet stream acts as a tool. In this kind of machining, the part is shaped only in the area where the electrolyte jet strikes the surface. This is due to the fact that the current density distribution is located just below the stream. In the area around the jet hitting the work piece thin electrolyte layer is formed. Thickness of that layer is growing rapidly. Since the electrolyte jet machining is an electrochemical process, the machined surface has all the benefits of ECM. There is no burrs and low temperature of the process prevents appearance of cracks and there is no heat-affected zone. Electrolyte jet machining can be used as well as in macro and micro drilling, turning, texturing, and electroplating. The process can be controlled by proper selection of such parameters as time, the current density and the diameter of the jet. Jet ECM can be used not only for material removal, but also for coloration (passivation) by means of anodic dissolution. 3D shaping of elements is also possible by controlling the current and the velocity of the electrolyte stream. In addition, by changing the polarity of the applied voltage it is possible to use this method in broadly considered electroplating. The paper presents results of the initial research on jet electrochemical machining (jet ECM) of acid proof steel and tungsten carbide. The material processing was carried in two ways – drilling holes and shaping grooves. Shaping was realized in milling and face turning regime. The influence of the two basic process parameters voltage and pressure was examined. In order to get rough information about the jet ECM process experiment planning method was applied. Obtained results enable planning of the further extended research.

Abstract: As other nonconventional machining methods, the electrical discharge machining is applied when the workpieces materials are difficult to be machined by classical machining methods or the surfaces could not be obtained in efficient conditions by classical machining methods. Such a situation could appear, for example, when test pieces must be separated from materials whose machining by classical methods is difficult. Taking into consideration the necessity to detach a cylindrical test piece from a workpiece made of a high resistance metallic alloy, the problem of using the electrical discharge machining was formulated. An initial experimental test by using the common work motion of the tool electrode from up to down highlighted high shape errors, due to the accumulation in the work zone of the particles detached from the workpiece and from the tool electrode, as a consequence of electrical discharge machining process. A second set of experiments were developed, placing the test piece over the electrode tool and ensuring a work motion of workpiece from up to down; in this situation, a diminishing of the shape error was noticed. The second set of experiments highlighted a relatively reduced conicalness of the machined surface and a low decrease of the machining speed. as the penetration depth of the tool electrode in the workpiece increases, too.

Abstract: The high investment cost and long lead-time to design and manufacture a forming tool is a major obstacle for local manufacturing of products in sheet metal. To minimize resource consumption large efforts are put into increase material efficiency by reducing the thickness of the sheet and move towards production methods with less scrap percentage. Nevertheless, the scrap portion is still high, in the automotive industry often as high as 50%. This paper discuss the possibilities of introducing knitting of metal wire into metal engineering industry to manufacture scrap free, light-weight three dimensional components in metal. Knitting could be a way of obtaining material efficient production within metal engineering industry especially for small and medium sized enterprises, SME. A knitting machine is able to produce large amounts of products at low price with moderate investments costs. For certain products knitting offer a simplified production of ready formed, 3D components. Experiments with knitting stainless steel wire were performed in order to establish the possibilities and limits of knitting today as well as identify development possibilities. The experiments covered improving the stiffness of the metal knit-wear by using different knitting techniques as well as introducing subsequent manufacturing steps such as surface treatment and joining. Demonstrators where produces for a number of geometries; squares, rectangles, boxes, hour-glass like in 2D and tubular, conical and T-tube shaped in 3D. For two geometries produced with knitting and sheet metal forming the material efficiency was compared. The first geometry used 32 % less material in the knitted product compared to the sheet metal component. The second geometry used 72 % less material in the knitted component compared to the sheet metal component. However, properties like strength and stiffness will be considerable less for a knitted component than for a sheet metal component. Today applications for the knitted materials have to be chosen carefully to take advantage of the potential of the material. With further development of both the knitting technique and subsequent operations the process will open new possibilities of material efficient and light-weight manufacturing.

Abstract: Traditionally forming tools for a press are machined with a CNC-machine. This is quite time consuming - calculating tool tracks, selecting cutting tools, cutting blanks, design fixation and finally machining - especially for a small batch of parts. One alternative method is to cut a die and a draw punch tools from a blank sheet and bunching the plates. Clamping plates together is fast and easy to implement by using for example studs and bars with a certain tolerance to ensure alignment. A laser, a water jet or a plasma cutter can be used for cutting plates. Especially the laser and the water jet cutting are precise methods giving a fine surface quality without a need for fine-tuning. The method saves material compared with machining because a die and a punch could be cut at the same time from a blank sheet as compatible pair as well as the needed amount of plates could be estimated depending of the length of a pressed product. University of Oulu, Oulu Southern institute, Future Manufacturing Technology -group has manufactured several forming tools within this technique and found it extremely suitable for experimenting different solutions and options fast. Furthermore, the method is likely to help especially SMEs in their R&D-phase by lowering production costs in a cost-efficiency way.

Abstract: This paper focusses on the statistical evaluation of process parameters in the mechanical surface treatments deep rolling (DR) and machine hammer peening (MHP) on the hardness increase. In MHP process a spherical hard metal tool is repeatedly accelerated onto the material surface. Just as the shot peening process MHP is an impact treatment although in MHP the impact area can be controlled, leading to the desired impact density. In DR the contact between spherical tool and work piece is quite different to MHP as the spherical is in sliding contact as it is moved along the surface. Although the material loading of both surface treatments vary, the resulting surface structure is the same. Both lead to a cold worked, smooth surface including compressive residual. Technically DR and MHP parameters have been part of researches but there still is a lack of statistical validation of every single process parameter leading to a hardened surface. This paper tries to close this gap. DR and MHP are conducted on different materials, containing tool steel 1.2379 and grey cast iron EN-JS-2070. Using a fractional factorial test design an experimental matrix was created able to examine the influence of every single process parameter. Which were for DR: rolling pressure, line spacing between hammer traces, diameter of roller ball and the travelling speed. For MHP the influence of the following process parameters was investigated: angle between hammering direction and surface normal, line spacing between hammering traces, diameter of hammering ball, hammering energy, travelling speed and hammering frequency. On every single sample ten Brinell hardness indents are made which give the statistical coverage needed to calculate the effect of every single process parameter within a confidence interval of at least 95 %. For all mentioned materials the effect of every single process parameter has been calculated with respect to hardening. It could be shown that especially the loading of the cast iron is quiet complex as a high amount of impact energy (MHP) or contact pressure (DR) can lead to overloading of the material leading to a degradation of the surface. At least an explanatory approach which describes the different influence of the tool diameter on the surface hardness is given using FEM simulations. These FEM simulations contain an advanced material model in which the Bauschinger-effect of 1.2379 is implemented. It can be clearly shown that a larger tool diameter in DR produces a higher amount of cold working in the material surface leading to harder surfaces compared to the smaller tool diameter. In contrast to DR the contact pressure in MHP is determined by the Hertzian pressure distribution. Here smaller tool diameters create larger Hertzian pressure and therefore a higher amount of cold working.

Abstract: The selective laser melting process (SLM), belonging to the family of additive manufacturing processes, can create complex geometry parts from a CAD file. Previously, only prototypes were created by SLM, but now this process is used to manufacture quickly and directly functional parts. For example, in the PEP (Pôle Européen de la Plasturgie), this process is used to fabricate tooling parts or injection molds with cooling channels that can’t be obtained by conventional routes. During the process, the laser beam generates violent heating and cooling cycles in the material inducing important thermal gradients in the consolidated part. The cyclic thermal expansions and contractions exceeding the maximum elastic strain of the material induce heterogeneous plastic strains and generate internal stresses the level of which can reaches the yield stress of the material and cracks may appear during the process. This paper deals with the measurement and analysis of residual stresses during the selective laser melting of a simple part in maraging steel. The objective of this study is the analysis of experimental results to validate the numerical model previously presented in [1]. Some authors have investigated the residual stresses produced in SLM parts using different experimental measurement methods such as the incremental hole drilling method in [2], the layer removal method see in [3] and [4] or the non-destructive method, by neutron diffraction in [5]. A new method is proposed to evaluate the residual stresses induced during the SLM process, a rosette is fixed on the bottom face of the support. The residual stresses in the created part are calculated from strain and temperature variations when the fused layer is consolidating during the cooling between two layers. Process parameters like the powder thickness or the time cooling between successive layers are studied in this paper. [1] L. Van Belle, G. Vansteenkiste, J.C. Boyer, Comparisons of numerical modeling of the selective laser melting, Key Engineering Materials Vols. 504-506 (2012) pp 1067-1072 [2] C. Casavola, S.L. Campanelli, C. Pappalettere, Experimental analysis of residual stresses in the selective laser melting process, Proceedings of the XIth International Congress and Exposition, June 2-5, 2008 Orlando, Florida USA [3] M. Shiomi, K. Osakada, K. Nakamura, T. Yamashita, F. Abe, Residual stress within metallic model made by selective laser melting process, CIRP Annals - Manufacturing Technology, Vol. 53, No. 1. (2004), pp. 195-198 [4] T. Furumoto, T. Ueda, M.S. Abdul Aziz, A. Hosokawa and R. Tanaka, Study on reduction of residual stress induced during rapid tooling process, influence of heating conditions on residual stress, Key Engineering Materials Vols. 447-448 (2010) pp 785-789 [5] M. Zaeh, G. Branner, Investigation on residual stresses and deformation in selective laser melting, Production Engineering, Volume 4, Number 1 (2010)

Abstract: Titanium and its alloys are nowadays widely used in many sectors: in the medical field (orthopedic and dental ones), in the architectural field, in the chemical plants field and in aeronautic [1]. In this last field it is more and more used both for its contribution to make lightweight and time durable structures and for its compatibility with new materials, first of all Carbon Fiber Reinforced Plastics (CFRP). Cutting of titanium sheets is one of the primary requirements in the fabrication of most of the components. Laser cutting offers several advantages over conventional cutting methods. It includes narrow kerf width (minimum material lost), straight cut edges, low roughness of cut surfaces, minimum metallurgical and surface distortions, easy integration with computer numerically controlled (CNC) machines for cutting complex profiles and importantly non-contact nature of the process (suitable for cutting in hostile environments and in areas with limited access) [2]. However, due to very limited literature available on laser cutting of titanium, it is very difficult to predict the cut surface quality and optimum process parameters for laser cutting, especially when dross-free cuts are required. Laser cutting of titanium and titanium alloys needs to be carried out with an inert gas, this due to the high reactivity of the titanium with the oxygen at high temperatures [3]. However when the available power is limited, as in the present case, the use of a reactive gas (air) can help to achieve cutting speed value reasonable for industrial applications. The aim of this work is to study the cutting of Ti-6Al-4V rolled sheets 1 mm in thickness, by means of a 100 W fibre laser, (SPI-Red Power) working at wavelength  = 1090 nm. The maximum cutting speed were measured in both CW and pulsed regime at different mean power and different duration. Furthermore, the kerf geometry and the heat affected zone (HAZ) were studied decreasing the cutting speed from the maximum to the 80 % of this values. The results obtained showed that both the power and the cutting speed influence the cutting kerf geometry and HAZ. In particular the synergy of power and speed, resulting roughly into the heat input, seems to rule the whole cutting process.

Abstract: The electrical dischargemachining (EDM) is known as the machining method in which the material removalis the result of developing electrical discharges having certain energetic andtemporal characteristics between the workpiece and the active surface of thetool electrode, while a dielectric liquid is circulated in the gap, essentiallyin order to remove debris. The last decades showed that in certain conditions,the dielectric liquid could be replaced by gaseous dielectric fluids, theprocess being named dry EDM. In the paper, some preliminary considerations areformulated about the material removal process for dry EDM drilling. Experimental researches were developed byconsidering the modifying of the values of some electrical characteristics(peak current, on time, off time and applied voltage) and determining thequantity of material removed from the test piece and the wear of the toolelectrode. The experimental results were mathematically processed and empiricalrelations were determined; these mathematical relations highlight the influenceexerted by the input parameters on the material removal rate.

Abstract: Rubber forming is a common process for the fabrication of flanged metallic parts in the aerospace industry. The process enables cheap tooling, which is important since the product series are limited. In the process a rigid and a soft tool are combined to form a metal blank into the required shape. Most components made in this way are “flanged parts”, i.e. parts with a rather flat web plate and curved flanges at the periphery of the web plate. For flanged parts the determination of spring back of the flanges, straight or curved, is important, since the forming dies compensated with the spring back, will result in accurate products. Like all metal forming processes elastic and plastic deformations are combined in the same process cycle. The elastic deformations result in spring back and residual stresses, the ratio between these two depends on the shape of the product and the distribution of the plastic and elastic deformations. In this research aluminum alloys were used. The low Young’s modulus of these alloys results in rather high elastic responses upon deformation. Other aspects that have been evaluated are the effect of processing parameters like friction and distribution of strains. For stretch flanges the strain is distributed evenly along the flange, but not for shrink flanges, where buckling plays a role. Experimental research shows that the spring back of the flanges depend on a number of variables like the thickness, flange geometry, and material parameters. The spring back of a flange is also a mixture of different contributions: spring back due to the bending over the bend line, spring back due to the curvature of the flange, and spring back due to in-plane deformations. The research performed focused on the different components of the spring back and their interaction. Analysis of the data resulted in a new parameter by which a number of variables could be captured. This improves the understanding of the spring back phenomena and is a generalization of the results.