Advanced Materials Research Vols. 83-86

Abstract: The benefits of applying advanced coatings on both single point and multipoint cutting tools such as improvement of productivity, tool life, machined surface quality etc. have been realised by the surface engineering researchers [1], commercial coaters [2-4] and end users [5]. The demand for advanced coatings in cutting tool industries is continually growing to meet the challenges of high speed machining, dry machining, near net-shape machining, machining of hard-to-cut materials etc.. Advanced coatings with excellent properties on flat coupon in a laboratory deposited by modern deposition technologies should not be taken for granted in improving the performance of complex shaped cutting tools [6] in aggressive cutting environments. This is because the end performance of coated cutting tools is not only dependant on the coating itself but also on the tool substrate material, geometry, surface finish and cutting edge conditions prior to coating deposition. The paper presents case studies with examples of successes and failures of advanced coatings on different multipoint cutting tools (e.g., milling cutters, bandsaws, circular saws, holesaws etc.). The future strategy for developing successful coating technology for cutting tools should be directed towards adopting a systems approach to bridge the communication gap amongst the cutting tool manufactures, tool coaters and end users.

Abstract: Meso-scale structures are formed on a silicon surface using a sulphur hexafluoride (SF6) based dry etching process. Etched feature parameters, including etch rate, trench profile, and selectivity are explored using an optical emission spectroscopy and a resonance hairpin probe. With increasing process power, the etch rate was observed to increase, which was correlated with an observed increase in intensity of fluorine emission. Damage of the photoresist with increasing power was observed and a marked increase in hydrogen (H) emission was found to indicate this fault. The electron density and the sidewall roughness were also found to increase with higher reactor power. The e-SF6 collisions contribute to the production of atomic fluorine, which etches the silicon by the dissociative ionization (SF+5 and F or SF+3 and F) and electron impact dissociation (SF5 and F).

Abstract: In this paper, the surface integrity is studied when machining the aeronautical titanium alloys. Surface roughness, lay, defects, microhardness and microstructure alterations are studied. The result of surface roughness judges that the CVD-coated carbide fails to produce better Ra value than the uncoated. Lay is characterized by cutting speed and feed speed directions. Feed mark, tearing surface, chip layer formation as built up layer (BUL), and deposited microchip are the defects. Microhardness is altered down to 350 microns beneath the machined surface. The first 50 microns is the soft sub-surface caused by thermal softening in ageing process. Microstructure alteration is observed in this sub-surface. Down to 200 microns is the hard sub-surface caused by the cyclic internal work hardening and then it is gradually decreasing to the bulk material hardness. It is concluded that dry machining titanium alloy is possible using uncoated carbide with cutting condition limited to finish or semi-finish for minimizing surface integrity alteration.

Abstract: Semiconductor nanostructures are interesting objects for many microelectronic and optoelectronic applications. Nevertheless, to use them, it is necessary to control their size, their density and their spatial distribution. In the last decade, many researches have been done to control these parameters. One of these researches is the elaboration of a functional substrate inducing a lateral self-organization of nanostructures. The organization driving force is the strain field induced on the surface by a buried dislocations network. The purpose of this work is the numerical resolution, in the case of anisotropic elasticity, of the problem of a misfit dislocation located between an infinite substrate and two-layer composite. The elastic fields of stresses are calculated for various orientations of the Burgers vector, by inversion of 30x30 arrays of linear equations. The composite NiSi2/Si / (001) GaAs, that made the object of several investigations, is treated like example.

Abstract: Metal forming by a laser source is an efficient and economical method for forming sheet metal into straight bend and doubly curved shape. It can be most useful in the automation of sheet metal forming. This paper presents an FEM model for three dimensional thermo-mechanical simulation of the laser forming. The aim of this simulation and experimental study is to identify the response related to deformation and characterize the effects of process parameters such as laser power, beam diameter, scans velocity and pulse duration, in terms of bending angle for a square sheet part. Extensive experimentation, including a design of experiments, is performed to address the above-mentioned aims. From these experiments it has been determined that laser forming using Nd:YAG laser is a flexible manufacturing process for steel sheet bending.

Abstract: Some new sheet hydroforming processes have been introduced during the last few years to increase the application and to overcome some of the limitations in conventional deep drawing. In recent years, the applications of sheet hydroforming have become increased. Nowadays, this technology has been largely accepted by industries for the production of different components with specific characteristics. Despite the advantages of the sheet hydroforming techniques, they have their own disadvantages. In this paper, a new sheet hydroforming technique is presented that improves the applications of the current sheet hydroforming processes. The proposed technique is applied to two complex non-symmetrical industrial parts. It is shown that the new technique can produce the products very well. In addition, it is shown that the forming pressure and load are very low compared with those of other hydrofoming methods.

Abstract: This study investigates the effects of grain size on the micro backward extrusion of copper cups. An equal channel angular extrusion (ECAE) technique was applied to refine the grain size in copper. Commercial available copper was annealed, deformed by six-pass ECAE at room temperature and then heat treated to obtain a microstructure with a grain size of about 4μm. Microstructure was examined and mechanical properties including hardness and stress-strain relationship were also investigated. The processed copper was then used in a micro backward extrusion of cups with the diameter of 3 mm and the wall thickness of 0.1 mm. The extruded cups were compared with those resulting from the coppers with larger grain size prepared by different heat treated processes. This study shows that the quality of the micro extruded cup increases as the grain size decreases. By using the refine-grained coppers for the micro backward extrusion, the cups with even rim height and uniform wall thickness can be easily produced.

Abstract: In cold working metal forming process, severe plastic deformation results in changes in the material properties. Earlier researches mainly investigated the rolling and equal channel angular extrusion (ECAE) processes. This study focuses on the fine-blanking process, specially the increasing material hardness on the fineblanked sprocket part. The microstructure around the cut surface is observed and the finite element analysis is done to clarify the mechanism of the increasing hardness as well. The microstructure revealed increasingly compressed and elongated grain structure of the contributed grain flow and orientation, as the blankholder and counterpunch forces increased. This resulted in the increased material hardness around the cut surface. Thus, these results theoretically clarified the mechanism of the increasing material hardness in the fine-blanking process regarding microstructural evolution, with the associated finite element analysis. Therefore, the special characteristic features in the fine-blanking process, result in the pronounced hardening around the fineblanked surface.

Abstract: The aim of this paper is to survey thin-walled tube bending process (without use of mandrel and booster). In tube bending process there are several effective parameters such as wall thickness, outer diameter-to-wall thickness ratio, and centerline bending radius-to-outer diameter ratio. Any mismatch in selecting these parameters would cause defects like wrinkling, variation in wall thickness, and cross section distortion. Firstly, the effects of these parameters on the initiation of the wrinkle, depth of wrinkling, change in wall thickness, and cross section distortion are studied. For this purpose, an FE commercial code has been used to simulate the process. Then, a series of experimental tests have been carried out to verify the results simulation. A comparison between analytical and experimental results shows a reasonable agreement with each other. Based on this comparison, it has been observed that there is a critical bending radius for any tube with a certain radius and thickness, in which the wrinkling begins to occur. For a certain bending angle and radius, it have been observed that the depth of wrinkling, change in wall thickness, and cross section distortion increase with reduction in wall thickness and outer diameter-to-wall thickness ratio

Abstract: In this paper, spring-back and its effect on geometrical and dimensional accuracy of incremental sheet metal forming (ISMF) process has been studied. The influence of process parameters such as: vertical step size, sheet thickness, tool diameter, feed rate and spindle speed have been investigated. A series of experimental tests have been carried out for a straight groove bead-shape part made of aluminum sheets. A reliable statistical analysis has been carried out to extract the importance of each parameter. The obtained model permits to select appropriate process parameters to reduce spring-back effectively.