Advanced Materials Research Vol. 939

Abstract: Tensile tests of titanium alloy (Ti-6Al-4V) with different thickness of 0.4 mm and 0.3 mm, were performed to investigate thickness dependency of superplasticity. To keep the same inner microstructure between specimens with different thicknesses, electrochemical polishing method was applied to reduce thickness. By keeping the voltage for the electrochemical polishing as 30 V the thickness decreased as linear with respect to polishing time. Further, tensile tests of 0.4 mm with strain rate 9.310^-4 sec^-1 were conducted at room temperature and 850 °C. And the superplasticity of 450 % elongation was obtained at 850 °C. For quantitative measurement of superplasticity, strain rate sensitivity (m value) was calculated from the tensile test by changing strain rate. The m values of the unpolished 0.4 mm specimen and the polished 0.3 mm specimen were 0.52 and 0.43, respectively. Strain rates to calculate the m value were 510^-4 sec^-1 and 110^-3 sec^-1. Consequently the reduction of thickness resulted in the reduction of m value, which means less superplasticity for thinner sheets of Ti-6Al-4V.

Abstract: The importance of the effect of particle deformation under Micro-forming Fields Activated Sintering Technology (Micro-FAST) has been summarized in this paper. Micro-FAST is involved in the coupling of stress field, temperature field and electric field wherein these fields work simultaneously rather than independently. By using Gleeble-1500D thermal simulation instrument, the micro-cylinders with size of Φ1.0mm×1.0mm were formed from 316L stainless steel powders. It has been found that the maximum relative density of sintered samples reaches up to 99.2% close to the full density. Moreover, the microstructure of specimens has also been investigated. Especially, the metal powders have been simulated as globular plasticine particles in the structure to elucidate the deformation of particle under Micro-FAST.

Abstract: Electrochemical discharge machining (ECDM) is the preferred non-traditional process technology in recent years, The main processing is applied to machining non-conductive hard brittle materials. This study investigated the precision and stability of quartz fabricated by ECDM and explored the optimal processing parameters including size of electrode, machining speed as well as pulse-on and pulse-off duration. Microgrooves machined under the optimal processing parameters with adjusted rotational speed and feed rate were examined to understand the effect of different ECDM parameters on machining performance. The results indicate that micro-holes of better morphology could be obtained under pulse voltage of 40 V, electrolyte concentration of 5 M, electrode size of 125 μm. Moreover, rotational speed of 1500 rpm and pulse-on/pulse-off (ms) ratio of 1:0.6 gave higher machining accuracy with smaller hole diameter and shorter machining time. Finally, microgrooves machined under the optimal processing parameters showed the best accuracy in dimension and cross-sectional morphology at rotational speed of 2500 rpm, pulse-on /pulse-off (ms) ratio of 1:1.6, and feed rate of 3000 μm/min.

Abstract: Recently, with regard to global warming energy shortage, the saving energy has become a global issue. The demand for variety, variable production, high speed, high accuracy, and complex processing in the manufacturing fields has been emerged. Furthermore, automatic extinction of computer numerical control (CNC) screens and automatically hold of oil pressure pump in idling has been raise to do on research. On the contrary, there are few reports dealing with reducing power consumption based on existing machining tools system. The method presented in this report can be applied to various size and weight of machining tools. The experimental result of standby power and minimum power with emergency stop circuit of various machining tools is discussed in this research work. To expand the stage of the proposed method, a brand new system is developed. As a result, power consumption of a machining tool with the phase of idling can be effectively reduced through emergency stop circuit. By activating emergency stop circuit, power consumption can be equalized with the condition of main power-ON only. The standby electric power increases along with increasing weight of machining tools. Through the proposed original system, it is possible to set switching of servo ON and OFF to each section. Consequently, the methodology would be applied into many fields of precision processing.

Abstract: High powerCO₂(Carbon Dioxide,CO₂) laser cutting process not only attention to the type of material selected, the focus position of the laser beam and spot size (beam size) also plays an important role. In this paper, metal materials cutting through the wavelength of 10.6μm,CO₂ laser with the optical path length compensation techniquewith output power 4000W. We compare different focus position and spot size for processing quality to discussing the use of a constant optical path length system to maintain the stability of the cross-section of the metal material after laser cutting.Optical path length compensation is used with ABCD Law in metal (steel) laser cutting processing an indispensable technology.Finally, we verify that the cross-section of the optical path length compensation under laser cutting in different processing location, thicknessof 16 mmsteel with laser power 4000W, and cutting speed 0.9 m/minconditions observed area 3*1.5 m²workingstagefor optical path length of 7, 8.5, 10 and 11.5 m,the steel ofcross-section appearance almost identical.

Abstract: This study presents a new method for surface modification of polymeric materials by using pulsed UV laser welding technology. The bonding procedures including ablation treatment, Oxygen plasma treatment, adhesive layer bonding and cured by pulsed UV laser writing system was exhibited. The investigation of various parameters for UV laser writing system was performed and discussed by using water contact angle measurement. This technique has been successfully applied to bond dissimilar polymer substrates (polydimethylsiloxane (PDMS) to polymethylmethacrylate (PMMA)). The scanning electron microscopy (SEM) image reveals clearly that there was no clogging in the microchannel or deformation observed between PDMS and PMMA. The method was straightforward and the integrity of microfluidic features was successfully preserved after bonding.

Abstract: A finite element model (FEM) of an orthogonal metal-cutting process is used to study the influence of tool rake angle on the cutting force and tool temperature. The model involves Johnson-Cook material model and Coulomb’s friction law. A tool rake angle ranging from 0° to 20° and a cutting speed ranging from 300 to 600 m/min were considered in this simulation. The results of this simulation work are consistent optimum tool rake angle for high speed machining (HSM) of AISI 1045 medium carbon steel. It was observed that there was a suitable rake angle between 10° and 18° for cutting speeds of 300 and 433 m/min where cutting force and temperature were lowest. However, there was not optimum rake angle for cutting speeds of 550 and 600 m/min. This paper can contribute in optimization of cutting tool for metal cutting process.

Abstract: Chatter vibration in cutting processes usually leads to surface finish degradation, tool damage, cutting noise, energy loss, etc. Self-excited vibration particularly seems to be a problem that is easily increased to large vibration. The regenerative effect is considered as one of the causes of chatter vibration. Although the chatter vibration occurs in various types of processing, the end-milling is a typical process that seems to cause the chatter vibration due to a lack of rigidity of one or more parts of the machine tools, cutting tool, and work-piece. The aim of our research is to propose a simple method to control chatter vibration of the end-milling process on the basis of a coupling model integrating the related various elements. In this study, hammering tests were carried out to measure the transfer function of a machine tool and cutting tool system, which seems to cause vibration. By comparing these results, finite elemental method (FEM) analysis models were constructed. Additionally, cutting experiments were carried out to confirm the chatter vibration frequencies in end-milling with a machining center. In the hammering tests, impulse hammer and multiple acceleration pick-ups are connected to a multi-channel FFT analyzer and estimate the natural frequencies and natural vibration modes. A simplified FEM model is proposed by circular section stepped beam elements on the basis of the hammering test results, considering a coupling effect. In comparisons of the calculated results and hammering test results, the vibration modes are in good agreement. As a result, the proposed model accurately predicts the chatter vibration considering several effects among the relating elements in end-milling. Moreover, it can be seen that the chatter vibration is investigated from a viewpoint of the integrating model of the end-milling process.

Abstract: A biliary stent cutting system based on nanosecond fiber laser was designed in this study. In order to achieve the stent cutting, the main modules and the critical technologies were analyzed. Then with the cutting system, the kerf width size was studied for different cutting parameters including laser power, repetition rate, cutting speed and assisting gas pressure. Finally, a high quality of fabricated nitinol biliary stent was achieved.

Abstract: A simplified model for micro milling process is presented, as well as results on temperature on tool and work piece. The purpose is to investigate on finite element modelling of two flute micro end milling process of titanium alloy, Ti6Al4V with prediction of temperature distribution. ABAQUS/Explicit has been chosen as solver for the analysis. A thermo-mechanical analysis was performed. First model was created by selecting medium carbon steel, AISI1045, as workpiece material for model validation purpose. Second model was created by modifying the workpiece material from AISI1045 to Ti6Al4V. The model consists of two parts which are tungsten carbide micro tool and workpiece. Johnson-Cook law model has been applied as material constitutive properties for both materials due to its severe plastic deformation occur during machining. Prediction on forces was obtained during the analysis. Model validation was done by comparing results published by Woon et al. in 2008. The results showed a good agreement in cutting force. Once this was proved, the same model was then modified to simulate finite element analysis in micro milling of Ti6Al4V. Prediction of temperature distribution of micro end mill of Ti6Al4V was done in relation of different undeformed chip thickness. The findings showed that temperature increases as undeformed chip thickness increases. Temperature distribution of Ti6Al4V and AISI1045 under same machining conditions was compared. Results showed that the highest temperature was concentrated at tool edge for Ti6Al4V.