Dong Van Pham

This study was performed to investigated the mechanism and stability prediction of flat-end milling process of SKD11 hard steel. The static milling force (MF) model, dynamic milling force (DML) model, milling vibration (MV) model, stability lobe diagram (SLD) model were developed and proposed in this study. The values of milling force coefficients (MLCs) and dynamic structure parameters (DSPs) were determined based on the combination of theoretical and experimental method. In static analysis, the relationship was very close to the linear regression with high determination coefficients (R2>97 %) in all three x, y, z directions. For experimental system of this study, the natural frequency of machine-tool system was almost half of natural frequency of machine-workpiece system. For the predicted results of SLD, the width of the stability region increased when the spindle speed increased. The machining processes were almost at the stable conditions with the axial depth of cut to be smaller than 0.3 mm at all values of spindle speed. The stable and unstable conditions in milling processes were verified with high precision for almost milling tests. With the points at the border between stable and unstable zones, the verified results had some differences between the predicted results using the proposed model and the analyzed results from experimental processes. These differences can be explained that there are many other parameters that have not been included in the predictive model such as heat, tool wear, friction, etc. In the applying of this study, it is the best way to choose the machining parameters at the absolute stable machining conditions.

In this study, in order to optimize the quality criteria of the machined surface based on the Archimedean spiral, the relieving grinding process (RGP) was performed to machine the material of HSS P18 in a 1Б811 machine with four input parameters including graininess of grinding wheel (G), grinding wheel hardness (Hd), velocity of grinding wheel (V), and feed rate (s) and with three quality criteria including surface roughness (Ra), hardening of surface layer (∆HRC), and hardened layer thickness (∆L). Taguchi-AHP-Topsis method was successfully applied to solve the Multi-Criteria Decision Making (MCDM) problem in this case. The optimized results of the output parameters are surface roughness of 0.21 µm, surface hardening of 1.45 HRC, and hardened layer thickness of 34.18 µm. These results were determined at the set of the input parameters includes G, V, s with their values of 120, 24 m/s, 2.08 m/min, respectively, and Hd at level 1. The optimal results were verified through the comparison between the calculated and the experimental results using this set of optimal parameters. The differences between the calculated results and the experimental results were quite small (maximum different value was 4.8 %) Thus, the results of this study can be applied to solve the multi-objective optimization problems in RGP of the GMT surface based on the Archimedean spiral

In the machining process, it is difficult to solve problems due to the relationship between productivity and quality, for example, as the productivity increases, the quality of reprocessing may decrease. Some methods only address specific objectives, such as the quality of the machining method, the machining productivity, the quality, or even the cost. Electrical discharge machining (EDM) and micro-EDM are most commonly used for processing the surfaces of die and moulds. The amount of electrode wear in micro-EDM has a direct effect on the dimensional accuracy of the machined hole. Therefore, improving the corrosion resistance of electrodes in micro-EDM is still of great interest. The effective coating of thin film for the micro tool electrodes in the case of micro – EDM can lead to minimize the electrode wear which eventually improve the productivity and machining quality. In the present study, experiments were performed on micro – EDM using carbon coated tool electrode and optimized using Taguchi-Topsis to investigate optimum levels of Depth of cut (Z) and overcut (OVC). It was concluded that optimum conditions had improved significantly using carbon coated micro tool electrode. Optimal levels of technological parameters include V=160 V, C=10000 pF, RPM=400 rpm, and Zopt=2,525 mm, OVCopt=72,856 μmm. The quality of the machined surface with the coated electrode at optimal conditions is analyzed and evaluated. The Topsis method is a suitable solution to this problem, and the steps to perform the calculation in this technique are simple

3D surfaces based on the Archimedes' spiral are widely used in mechanical engineering, especially in the manufacturing the gear milling cutters. The machining process to create this type of surface is usually performed in specialized machines. In this study, relieving grinding process was conducted to machine the Archimedes surface of HSS P18 workpiece material using a specialized machine (1Б811) to investigate the influence of the grinding wheel graininess (G), hardness of grinding wheel (Hd), grinding wheel velocity (V), and feedrate (s) on surface quality including surface roughness (Ra) and surface hardening (ΔHRC). The experimental plan with 27 experiments (L₂₇) was designed using the Taguchi method. Applying the analysis of variance (ANOVA), the influence of G, V, s, and Hd on Ra and ΔHRC was investigated. G, V, s, and Hd have different influences on Ra and ΔHRC in the relieving grinding process. V has the greatest influence on Ra and ΔHRC with 40.96% for Ra and 26.43% for ΔHRC. The grinding wheel hardness that has the lowest influence on Ra (0.82%), whereas the feedrate has a negligible effect on ΔHRC (7.01%). The interaction effect of the input parameters on Ra is not significant (2.91%). However, for ΔHRC, the interaction influence degree of these parameters on this criterion is quite high (33.77%). From the experimental data, Ra and ΔHRC were presented as a quadratic function of G, V, s, and Hd with high values of determination coefficient (R² = 92.75% for Ra and R² = 92.00% for ΔHRC). In the surveyed range of the input parameters, Ra decreases if G and V increase, and s decreases. Also in this survey range, the hardening increases if the values of the input parameters (G, V, and s) increase. This study also determined that there is no clear rule about the relationship between Ra and ΔHRC. Further studies need to be carried out to find the input optimal values ensuring the quality criteria of the relieving grinding process.

The combination of biopolymers with bioceramics plays vital role in development of artificial bone. Hydroxyapatite is extensively used as a material in prosthetic bone repair and replacement. In this paper synthesis of Hydroxyapatite- Polymethyl methacrylate – Zirconia (Hap-PMMA-ZrO2) composite by using powder metallurgy technique. The mechanical, morphological, In-vitro biocompatibility and tribological properties were characterized by universal testing machine, micro-vickers hardness tester, high resolution transmission electron microscope (HR-TEM), MTT assay and pin-on-disc setup. In-vitro cytotoxicity test on HeLa cell lines shows cell viability constant when doses concentration increases so material found non-toxic. Results show that micro Vickers hardness i.e. 520 approximately matches with natural human bone i.e. 400. Compressive strength is less as compared to human bone because of powder metallurgy route used for fabrication and is 74 MPa. Density of proposed composite artificial human bone i.e. 1.52 g/cc is less as compared to natural bone i.e. 2.90 g/cc. The Hap-PMMA-ZrO2 composite will be good biomaterials for bone repair and replacement work