Advanced Materials Research Vols. 966-967

Abstract: Tribological surface textures are considered in this paper as a non-traditional friction control solution for microforming. Textured pads fabrication techniques are first evaluated and load-controlled micro-embossing is chosen as the optimal method to produce repeatable textured patterns on metallic pads. Using tribometer experiments and finite element simulations of dry contact between untextured and textured surfaces for pressure levels representative of microforming conditions, it is shown that there are competing mechanisms creating a sinusoidal-like friction reduction behavior when surface textures are present. Ultimately, it is concluded that a proper design of surface textures and loading conditions can be used for friction reduction in microforming.

Abstract: This paper proposes a new method of 3D roughness peaks curvature radius calculation and its application to tribological contact analysis as a characteristic signature of tribological contact. This method is introduced through the classical approach of calculation of radius of asperity in 2D. Actually, the proposed approach provides a generalization of Nowicki's method [], depending on horizontal lines intercepting the studied profile. Here, the basic idea consists in intercepting the rough surface by a horizontal plane and to calculate the cross section area without including “islands into islands”, i.e. the small peaks enclosed in bigger ones. Then, taking into account the maximal value of the height amplitude of the roughness included into this area, an appropriate algorithm is proposed, without requiring the classical hypothesis of derivability, which may be unstable when applied to engineering surfaces. This methodology is validated on simulated surfaces, and applied to engineering surfaces created experimentally, with a laboratory aluminium strip drawing process. The regions of the textured and lubricated specimens surface are analysed, and the results gives interesting prospects to qualitatively identify the local lubrication regimes: regions with high curvature radii correspond to severe contact (boundary/mixed lubrication regime) while regions with low curvature radii correspond to hydrodynamic lubrication regime.

Abstract: In this paper, machining tests of silicon wafer under high hydrostatic pressure are reported. A lathe type machining tester was developed, and machining tests were conducted on the upper surface of silicon wafers whose crystal orientation was (001). Roughness of the finished surface was measured by using AFM, and the effect of hydrostatic pressure on roughness was studied. It was found that roughness decreases with increase of hydrostatic pressure. It was also found that the roughness depends on the cutting direction. The roughness is large when the cutting direction is parallel to the <100> direction, but it is small when the cutting direction is parallel to the <110> direction. Mechanism of effects of hydrostatic pressure and crystal orientation are discussed.

Abstract: Generally in the drilling of new engineering materials such as metal matrix composites, problems frequently occur in terms of poor finished surface, tool stress, tool wear, high drilling forces as well as low process reliability. A useful and promising method to overcome these problems is the use of ultrasonic vibration as an assistance, where high-frequency and low amplitude vibration are added to the conventional movement of cutting tools or workpieces. This research presents the new design of an ultrasonic assisted system and the experimental investigation of ultrasonically assisted drilling of Al/SiC metal matrix composites under different cutting conditions. The effect of cutting conditions and ultrasonic amplitude on the circularity, cylindericity, and hole oversize of the ultrasonically and conventionally drilled workpieces were investigated. The obtained results show that the ultrasonic vibration can improve the hole quality.

Abstract: A micro dimple machining is presented to control the surface functions with the micro-scale structures on the solid surfaces. The micro dimples are machined in milling with the inclined ball end mill. When an inclined two flutes end mill removes the material in a depth of cut less than the tool radius, the air cutting time during neither edges contact with the workpiece appears in a rotation of cutter. When the tool is fed at a high feed rate so that the removal areas of an edge and another edge do not overlap each other, the concave dimples are machined. A mechanistic model is presented to control the shape and the size of the dimples to be machined. The micro dimples were machined to verify the mechanistic model in milling. The micro asperities were also formed in molding using the dimpled surface. As applications of the functional surfaces, wettability and friction coefficient were measured on the surfaces with the dimples and the asperities. The surface functions change with the alignments of the dimples and the asperities.

Abstract: The wear of TiCN coating carbide cutting tools (Sandvik® Grade 1010 and 4220) in different hard-milling machining conditions was monitored, analyzed, and discussed for AISI H13 steel. This material is commonly used in the forge industry in order to optimize the manufacturing process according to a qualimetry/cost compromise criterion. AISI H13 steel generally is used in modern production for high wear-resistant dies and molds. One of the most basic and primary geometric shapes in the manufacture of molds and die cavities is the geometry known as "inclined plane." Experimental investigations were carried out on a "mold model" design with the aim of analyzing and optimizing the principal manufacturing conditions. The tests are dependent on manufacturing factors, particularly their impactin a complex tribological process. Five clearly defined different surfaces of the hardened AISI H13 steel model mold, with appropriate geometries were studied; i) vertical downward; ii) curved downward; iii) horizontal; iv) curved upward; and v) vertical upward.The analysis of cutting tool wear during this process was based on computerized measurements of visually observable wear and power consumption. Morphological investigations of the surface topography for the cutting tool, as well as of the work-piece surfaces, were systematically carried out. Moreover, the interactions with simultaneously measured energy consumption during the process are also explicated in the present study and therefore tentative methods to optimize hard-milling machining are offered.

Abstract: To determine the impact of dynamic recrystallization on frictional behaviour in the tool-chip interface, a specific friction test called the Warm and Hot Upsetting Sliding Test (WHUST) is implemented. This friction bench simulates tests with contact pressure, sliding velocity, contactor and specimen temperatures similar to industrial ones. Several tests are performed on specimens at different sliding speed, penetrations and work-piece temperatures to reach different dynamically recrystallized states. A numerical model of this test using Arbitrary Lagrangian Eulerian (ALE) method is implemented. Thanks to a specific rheological model, we are able to predict the evolution of the volume fraction of recrystallized grains.

Abstract: The cylinder liner surface texture, widely generated by the honing technique, contributes a lot on engine functional performances (friction, oil consumption, running-in, wear etc.). In order to improve these functional performances, different honing processes are being developed. These different honing processes generate surfaces with various texture features characteristics (roughness, valleys depth, valley width, cross hatch angle, etc.). This paper addresses a comparison of ring-pack friction for cylinder texture with different cross-hatch angles and valley sizes. It takes in consideration the mutual effect of valley depth and honing angle. A numerical model is developed to predict friction within the cylinder ring-pack system in mixed lubrication regime and a morphological method is used to characterize groove depth. The results show the effect of different honing variables (rotation speed, stroke speed and indentation pressure) on cylinder bore surface textures and hydrodynamic friction of the ring-pack system.

Abstract: Sheet metal shearing takes place immediately after hot rolling of steel. Due to the extreme operating conditions, flying shear blades suffer from severe wear and need frequent repair, significantly increasing the maintenance costs for steel producers. In order to optimise the shearing process and increase the tool lifetime, a finite element model was applied for performing a systematic variation of the blade geometry and process parameters. In the model, friction is taken into account by implementing a hybrid friction equation, which is suitable for the simulation of metal forming processes. Tool geometry and process parameters such as the vertical overlapping between the two shearing blades were varied in the simulation, in order to identify optimum process parameters. The results obtained show in particular that the variation of the vertical overlapping between both blades has a limited influence on the maximum calculated stresses, leading to the assumption that no significant changes in tool wear may be achieved by modifying it. On the other hand, it was found that higher cutting edge radii lead to significantly lower stresses for both flying shear blades, thus suggesting the possibility of decreasing tool wear through increasing values of the cutting edge radius.

Abstract: An experimental investigation of the rheological properties for abrasive Metal Injection Moulding feedstocks is presented for different materials with dissimilar particle sizes and shapes. Tribological issues are inevitable since feedstock has up to 93 wt. % powder loading in the feedstock. In this study, each of the relatively soft carbonyl iron powder and the hard, abrasive Iron oxide powder are mixed with binder system, consisting of HDPE (High-density polyethylene), Paraffin Wax and S.A. (Stearic Acid) at different magnitudes of volumetric powder loading. The rheological properties such as flow rate (cm³/s), shear rate (s^-1) and viscosity (Pa.s) are investigated for varying conditions of temperature and pressure. The properties of the feedstocks made from the two materials showed significant variation in flow behaviour (due to difference in inter-particle frictional behaviour) with changing process parameters as well as material parameters. Furthermore, to study flow behaviour of feedstocks apparent viscosity is plotted against temperature and shear rate in order to establish the sensitivity of temperature and pressure. Flow behaviour index was determined by analysing variation of viscosity with shear rate of feedstock. As expected, results show that the feedstock having iron oxide powder with hard irregular shaped particles exhibits a higher viscosity if compared to the spherical particles in the Carbonyl iron powder feedstock. It was observed that the feedstock containing iron oxide powder (75 wt. % powder loading) gives higher shear rate but the feedstock dissociates faster with increasing temperature, whereas carbonyl iron powder feedstocks (90 wt. % powder loading) were found to be more stable (dissociate less) at higher temperatures and flowed at a smaller shear rate. Additions of graphite powder to the hard and abrasive iron oxide powder (to facilitate reduction of the iron oxide during sintering) would also be expected to improve the flow behaviour of the iron oxide feedstock on account of the superior lubricating properties of the graphite powder.