Advanced Materials Research Vols. 83-86

Abstract: In this study the performances of some commercially available carbide inserts when machining Hastelloy C-22HS was investigated under scanning electron microscopy (SEM) for wear mechanisms and other microstructure defects. Carbide inserts coated with TiCN/TiN and TiALN/ TiN experienced severe intergranular fractures and cracks. High temperature causes the layer of the coating to wear off and subsequently the inserts damaged at fast rates. Both types of inserts suffered from high crater wear and thermal cracking. Most of the wear occurred at the nose and flank of the inserts. Generally, it was observed that carbide coated with TiALN/ TiN cutting tool performed better than carbide coated TiCN/TiN cutting tool when milling Hastelloy C-22HS

Abstract: The focus of this study is to investigate the effects of cutting speed, feed rate, hardness and cutting tool material on cutting region temperature and surface finish in hard turning process. A L36 Taguchi's standard orthogonal array was applied as experimental design. Machining tests were conducted under controlled conditions. AISI 4340 alloy steel which has numerous industrial applications was used to perform machining experiments. CBN, ceramic and cermet tools were employed to accomplish 36 tests with three random repetitions, resulting in 108 experiments. Main effects of the factors and their interactions are considered in this study using ANOVA (Analysis of variance) method. Also predictive models are derived by regression. Furthermore, optimal factor levels are obtained through S/N (signal to noise) ratio analysis in order to increase the machining efficiency. Finally, the results of confirmation tests are presented to verify the adequacy of the predictive models.

Abstract: The single point cutting tool in ultrasonic vibration-assisted turning (UAT) is made to vibrate under ultrasonic frequency. In present study, the influence of various parameters such as vibration amplitude, depth of cut, feed rate and cutting velocity on the machining force and workpiece's surface roughness in UAT of Al7075 has been investigated. Full factorial experiments were carried out with an ultrasonic frequency range of 20±0.5 kHz. ANOVA was conducted on the experimental results and regression models were obtained for predicting the machining force, surface roughness and cutting temperature. The proposed models were verified by further experiments. The robustness of the proposed models was then investigated whence the optimal parameters were estimated. Similar full factorial experiments were also carried out with conventional turning (CT) in order to compare the results with those of UAT.

Abstract: In present study, neural networks have been employed for studying the ultrasonic vibration-assisted turning (UAT) process and for predicting the machining force and workpiece's surface roughness. Extensive experiments were carried out using different values of UAT parameters such as vibration amplitude, depth of cut, feed rate and cutting speed. The tests were implemented on the basis of full factorial design of experiments for three different levels of each UAT parameter. The machining force and workpiece's surface roughness were measured as the responses of the experiments and were subsequently modeled with the aid of back propagation multilayer perceptron neural network for 1.1191 steel. The nonlinear relation existing between the aforementioned UAT parameters and the machining force and workpiec's surface roughness could effectively be modeled by the developed networks and the responses error could be kept less than ten percent. This was verified by further experiments different from those carried out for developing the network.

Abstract: In this study, machinability of Zr-based bulk metallic glass (Zr52.5Ti5Cu17.9Ni14.6Al10) (BMG) material was investigated by conducting a set of milling and drilling experiments. In milling, two different tool paths, spiral and slot milling, were used. To investigate the behavior of BMG in drilling by two different tools at different feed rates, two sets of drilling experiments are conducted. Crown shaped exit burr formation are observed in drilling of BMG. Best results on thrust force, exit burr formation and hole surface roughness is obtained while using micrograin WC tool on BMG drilling. No chip light emission was observed during all tests. This study concludes that BMG can be achieved machining with good surface roughness, (Ra=0.113 µm), using conventional cutting tools.

Abstract: Rapid prototyping (RP) is being widely used in diverse areas, from the building of aesthetic and functional prototypes to the production of tools and moulds for prototypes. Many RP techniques like stereo lithography, laminated object manufacturing, three dimensional printing etc. are commercially available. The implication of these technologies revealed that the time and cost of developing new foundry tools could be greatly reduced. The purpose of the present research paper is to review three dimensional printing for generation of prototype for casting applications.

Abstract: A methodology of formulating an elasto-plastic three-dimensional finite element model, which is based on Prandtl-Reuss flow rule and von Mises yield criterion respectively, associated with an updated Lagrangian formulation. An extended r-min algorithm is proposed to formulate the boundary conditions, such as the yield of element, maximum allowable strain increment, maximum allowable rotation increment, maximum allowable equivalent stress increment, and tolerance for nodes getting out of contact with tool. In order to verify the reliability and accuracy of the FEM code, the fractured thickness of a specimen in the simple tension test is adopted as the fracture criterion of forming limit in simulation. A set of tools was designed to perform the elliptical cup drawing experiment on the hydraulic forming machine. According to the simulation and experimental results, the minimum thickness is concentrated on the contact regions between work-piece and punch major axis, because the camber radius is relatively large along the minor axis, the ones that bear are relatively small to the circular tensile stress, so the thickness does not change much. The limit drawing ratio (LDR) amounts to about 2.136 for penetration in the elliptical cup drawing process of this study. According to the definition of LDR, when the die radius is increased from R3.0mm to R9.0mm, the LDR would increase from 2.11 to 2.157. When the punch radius is increased from r3.0mm to r9.0mm, the LDR would increase from 2.07 to 2.181. This paper has provided a better understanding of the elliptical cup drawing process for improving the manufacturing processes and the design of tools.

Abstract: Microstructure and mechanical properties of high Si bainitic steel, before and after two passes of equal channel angular pressing (ECAP) at room temperature were investigated. SEM and TEM microscopy were used for microstructural study. Shear punch test and Vickers hardness test of as received and ECAPed samples were carried out to measure the influence of ECAP process on the mechanical properties of the samples. The results showed that tensile strength and shear strain were increased as a consequence of ECAP processing.

Abstract: The compounding of rice husk and high density polyethylene (HDPE) was undertaken on a Sino PSM 30 co-rotating twin screw extruder. Four sizes of rice husk were studied at various compositions. The size ranged from 500 μm and below (coded A, B, C and D) while the content of rice husk in the composite varies from 30, 40 and 50 percent of weight. A fixed amount of Ultra-Plast TP10 as a compatibilizer and Ultra-Plast TP 01 as lubricant, were added into the bio-composite compound. The injection molding process ability of the bio-composite was studied through flow behavior on melt flow indexer and analyzed on JSW N100 B11 Injection Molding. Size A which has the largest particle is the most appropriate size as the bio-composite filler based on thermal stability test. The melt flow rate of rice husk/HDPE (RHPE) decreases with the increased in rice husk compositions and apparent viscosity also increases with composition for all filler size. Melt flow rate above 4g/10 min was found to be the lower limit for injection molding process. The smaller the filler size, the lower is the impact strength and the increased in the filler composition lowers the impact strength. A bio-composite at 30 weight percent rice husk size A (RH30PEA) was found to have optimum rheological properties with respect to impact strength.

Abstract: The present paper is focused on the Finite Element modeling of the Marciniak stretch-forming test in warm condition. Such a test was proposed by the authors for evaluating the warm formability of the Mg alloy AZ31 according to the most important parameters: the temperature and the strain rate. Tensile tests confirmed the large influence of the strain rate on the deformation of the AZ31, especially when the test temperature is over 200°C. Three dimensional FE simulations were thus carried out in order to analyze the strain and strain rate evolutions during the formability test at the temperature of 200°C. In particular, simulations were aimed at investigating the effect of the specimen’s geometry on the strain rate evolution in the central region, where failure occurs during the Marciniak stretch-forming test. An equation for calculating the punch speed profile able to keep a constant equivalent strain rate in the central region of the specimen has been furnished according to the geometry of the specimen. Its efficiency was validated by means of additional simulations implementing the punch speed profile calculated using the proposed approach.