Key Engineering Materials Vols. 504-506

Abstract: The increased demand for manifold industrial goods requires superior manufacturing techniques. In the field of steel products, cold forging has gained importance for the last sixty years. Within cold forging the tool takes a key role as it determines both accuracy and efficiency of forming process. For forming processes with high demands regarding wear resistance WC-Co cemented carbides are increasingly used as tool materials. The manufacturing process of the tool requires a combination of hard and fine machining. In order to reduce the effort of subsequent fine machining process, surfaces with low roughness are preferred. As grinding leads to high surface qualities, it is a common method in tool machining. Grinding is accompanied by compressive residual stresses in the surface which have a positive influence on the tool life. The absolute value of residual stresses is determined by the machining parameters. The present study investigates the influence of feed and in-feed on the topography and the near surface residual stresses. While the surface roughness is correlated with both parameters, the feed has a major influence on the residual stresses in the surface of cemented carbides.

Abstract: Extremely high strength of the ultra-high-strength steels leads to increased load factors on the tooling machines and punching tools. This experimental study examines how much convex punch geometry affects cutting forces when punching ultra-high-strength steels. Tools used in punching tests were four different convex sheared rooftop punches and one conventional flat end punch, to which rooftop punches were compared to. The material in punching tests was ultra-high-strength steel Ruukki Optim 960 QC, with a thickness of 4 mm. The test material in punching tests was sheared with rooftop punches and a flat end punch and occurred cutting forces were measured. The qualities of punched holes were evaluated visually and the roundness measurements were also performed. The results show that the cutting forces of Optim 960 QC can be reduced radically with optimal convex punch geometry. With using 14-degree shear angle of the punch end, the cutting forces reduced up to 57 % compared to forces of the conventional flat end tool. However, largest tested shear angles caused several negative effects on the cutting quality of the holes and therefore they are not suitable in all applications. Punching tests proved that the cutting clearance had no appreciable effect on cutting forces when punching ultra-high-strength steel. Instead there was a noticeable effect on the quality of the punched hole, especially when large shear angles were used.

Abstract: The paper presents a predictive cutting force model in drilling of anisotropic materials. Three dimensional chip flow in drilling is interpreted as a piling up of the orthogonal cuttings in the planes containing the cutting velocities and the chip flow velocities. The cutting models in the chip flow are determined to calculate the cutting energy using the orthogonal cutting data. Then, the chip flow direction is determined to minimize the cutting energy. The cutting force can be predicted in the determined chip flow model. The cutting force with anisotropy in the material is modeled as the change in the shear stress on the shear plane. The shear stress changes with the rotation angle of the cutter. The cutting force prediction is verified in drilling of a titanium alloy. The anisotropic parameters are identified to minimize the model error between the measured and the predicted cutting forces. The periodical oscillation of the cutting force is also predicted by anisotropy in the shear stress.

Abstract: Abrasion resistant (AR) steels offer excellent hardness and strength properties in applications as mining and earth moving machines. As an outcome of high hardness AR steels can be used to produce durable, light-weight and energy saving products. However, their mechanical processing can be challenging as the hardness of the material approaches the hardness of the tooling used. This places high forces on cutting tools and machines, which, in turn, increases wear and causes early breakdown. This research examines whether the laser treatment of AR steels can be used to aid guillotine shearing. The tested material was abrasion resistant steel with hardness of 400 HBW. Two different laser treatments were examined: local laser heat treatment and laser milling. The aim of laser heat treatment was to change the original martensitic microstructure locally into weaker structure, beneficially for shearing. Narrow grooves were made along the cut line by laser milling, and then the plate cut along them. The effect of local laser heat treatment and the fracture initiating effect of the groove was evaluated from the cutting force. Microhardness tests and micro photos were taken after laser heat treatments. The results indicated that the shearing force of AR steels can be reduced up to 25% with the aid of laser heat treatments. Laser milling had only a slight effect to the shearing force of up to about 8%. In addition, the relative depth of the laser milled groove is estimated at the same range, thus force reduction is mainly due to reduction of material thickness.

Abstract: Obtaining to high quality surfaces of industrial parts is an important manner for manufacturing involves. Different finishing process are capable to providing the require surface roughness in most cases, considering that, in some special parts, depending on shape, material and dimension of parts, the prevalent methods are limited, especially in finishing of sculptural and curvilinear surfaces. In this research, a new applied apparatus is represented based on magnetized abrasive grains finishing process. In this way, abrasive grains gathering around a rotational cylindrical tool thanks to a permanent magnetic field and work-piece, which usually is a formed thin metal sheet, located on a rotary table. Therefore, coinciding of those motions providing the require machining forces for finishing of surface without any physical contact between tool and work-piece. Presented process may carry out dry and wet in case of changing the main machining parameters such as: material and size of abrasive grains, tool and work-piece surface gap distance, tool and/or table rotational speed (r.p.m) and work-piece material. The recommended process has remarkable advantages such as: non-contact surface finishing, high finishing of non-flat surfaces, no need to clamping for work-piece because of low machining forces, responsibility for finishing of a wide range of materials except magnetizable parts, low machining costs and easy set up. This method has a lot of applications in production of optical lens, orthopedic prosthetic components and jewellery. For approve of the designed apparatus advantages, relative to other existed MR fluid machining system, some samples of very thin complex formed sheet have been successfully polished.

Abstract: The application of mechanical vibration has been known for many years, but some controversy still exists. According to some ideas the mechanical vibration reduces the technological stresses by summation of technological stress and stress from external loads (vibration). But on the other hand, the mechanical vibration causes more complicated phenomena (micro-relaxation) resulting in dimensional stability close to natural seasoning effects. In the present study authors present results of research into mechanical vibration from the experimental and practical point of view, proving that this process can be used to obtain dimensional stability. The results has also indicated that the reduction of the technological stresses is highly questionable.

Abstract: This contribution presents computational concepts and algorithmic techniques for simulation and gradient-based optimization of geometrically nonlinear and large-scale finite element models of composite structures. Several industrial application examples illustrate the methods, show the applicability to large problems, and prove the high parallel efficiency.

Abstract: Stiffened panels are composed of a base plate with stiffeners in one or more directions, leading to lightweight structures with high resistance. The structural design, in most cases, focuses mainly on the longitudinal compressive loads that the panels are subjected and can safely withstand. In the present work, a set of Finite Element Method Analyses (FEA) were carried out, using ABAQUS commercial simulation software, and compared with experimental data in order to infer about the sensitivity of the results to the initial geometrical imperfections (either in magnitude and shape). The developments in the present work aim to provide a range of models able to properly reproduce the experimental behaviour of aluminium stiffened panels subjected to compressive loads. It was shown that FEA using shell finite elements were able to obtain accurate predictions of the ultimate load, considering large deformation and elasto-plastic behaviours. The effect of using different shapes and magnitudes of the initial geometrical imperfections on the numerical simulation of the panels was also inferred and tested using previously obtained eigenvalue (EV) buckling modes.

Abstract: During the pressing step, the clay tiles undergo stresses which result in the appearance of defects. A rheological study, based on free compression tests, allowed to confirm the Elasto-visco-plastic behaviour of the clay. The different constitutive parameters were estimated by fitting the force-displacement experimental curves using the optimisation algorithm (ES Metamodel) implanted in the commercial software Forge 2009®. The influence of the tribological parameters was studied using squeezing numerical simulations of a full tile. The numerical model was validated with experimental squeezing test of technological specimen with a tile lug. Then, we have compared experimental force with the numerical one and deduced that the clay/tool interface is not perfectly sliding. A friction Tresca’s law was used to model the clay/tool interface. Numerical results showed that the actual geometry of tile lug didn’t allow to form correctly the tile. Several areas undergo tensile stress, air traps ,... A new geometry of tile lug was proposed in order to limit this phenomenon. Using a simplified defect criteria (Latham and Cockroft), the numerical model allowed to locate the areas where there is a risk of crack.