Applied Mechanics and Materials Vols. 217-219

Abstract: In this paper, a FEM mode was developed to study the feasibility of the plasma arc bending of the laminated clad metal sheets (LCMS) containing defects. The three layer LCMS of stainless steel/mild steel/stainless steel was selected as the sample. The influences of the defects on the temperature field and deformation field were investigated. Besides, the bending experiments were performed to examine the feasibility. The results show that there is a sharp rise of temperature around the defect due to the lower thermal conductivity which causes the possible partial melting of the formed parts. The existence of the defect exacerbates the unevenness of the thickness along the heating line. But the delamination of the interface does not occur because of the instantaneous variations of the stress under the high temperature, which is consistent with the experiments.

Abstract: This article constructs the characteristics equation of negative pressure nozzle (for DF), and on this foundation, analyses the separating flow ratio of NP equipment detail, thus obtaining its reasonable scope. Also the paper attempts to find relationship between section area ratio and separating flow ratio from the perspective of the characteristic equation of the nozzle. Based on the combination of the analysis and the principle of hydomechanics, the structure of traditional NP nozzle is modified according to the negative pressure gap, spray angle and separating flow ratio.

Abstract: This paper concentrates on the practical applications of game theory in the field of aviation security system. The purpose of this analysis is to demonstrate the use of mathematical device in an interactive decision-making environment in order to analyze real-world problems: terrorism threats. Making the link between game theory and linear programming effectively supports the decision making process in resolving conflict situations that may arise between the attacker aviation system, situations which are characterized by low probability of occurrence and serious consequences. Modeling such phenomena as a result has a systematic and effective risk assessment of such attacks. To demonstrate this approach, two simple examples of a terrorist attack against an airport infrastructure are modeled and analyzed.

Abstract: Chatter is detrimental to turning operations and leads to inferior surface topography, reduced productivity, dimensional accuracy, and shortened tool life. Avoidance of chatter has mostly been through reliance on heuristics such as: limiting material removal rates or selecting low spindle speeds and shallow depth of cuts. But, modern industries demand increased output and not steady operational limits. Various research efforts have therefore focused on developing mathematical models for chatter formation. However, as yet there is no existent model that meets all experimental verification. This research employed a novel technique based on the synergy of statistical modeling and experimental investigations in order to develop an effective empirical mathematical model for chatter amplitude and to subsequently find optimal machining conditions. Ti-6Al-4V, Titanium alloy, was used as the work-piece due to its increased popularity in applications related to aerospace, automotive, nuclear, medical, marine etc. A sequence of 15 experimental runs was conducted based on a small Central Composite Design (CCD) model in Response Surface Methodology (RSM). The primary (independent) parameters were: cutting speed, feed, and depth of cut. The tool overhang was kept constant at 70 mm. An engine lathe (Harrison M390) was employed for turning purposes. The data acquisition system comprised a vibration sensor (accelerometer) and a signal conditioning unit. The resultant vibrations were analyzed using the DASYLab 5.6 software. The best model was found to be quadratic which had a confidence level of 95% (ANOVA) and insignificant Lack of Fit (LOF) in Fit and Summary analyses. Desirability Function (DF) approach predicted minimum vibration amplitude of 0.0276 Volts and overlay plots identified two preferred machining regimes for optimal vibration amplitude.

Abstract: Chatter is detrimental to all machining operations. In metal turning operations it leads to inferior surface topography, reduced productivity, and shortened tool life. Various researchers have thus tried to develop mathematical models and theories for chatter formation in order to find optimum ways of chatter suppression. This research investigated the chatter phenomenon in turning of stainless steel AISI 403 in the light of vibration amplitude. Central composite rotatable design of experiments under Response Surface Methodology (RSM) was employed to create a second order mathematical model, and the adequacy of the model was verified using analysis of variance (ANOVA). Machining operations were carried out on a conventional engine lathe (Harrison M390, England) with rated power of 5.5 kW and maximum spindle speed of 2000 rpm. Cemented Tungsten Carbide (WC-Co) inserts were used to machine a stainless steel cylinder. The data acquisition system consisted of a vibration sensor (KISTLER accelerometer Type 8774A50) and a signal conditioning unit, which was connected to the computer via a data acquisition (DAQ) card. Analog input signals were fed into the DAQ card and evaluated using the DASYLab 5.6 software. The vibration results were analyzed in the frequency domain (FFT) plots. It was observed that the uncontrolled vibration of the tool holder was the largest contributor to chatter formation.

Abstract: The article aimed at mold parts surface machining, has been studied high speed wire cutting technology. Explored the process evaluation factors which impact wire cutting mold based on the theoretical analysis of the wire cutting discharge gap and the surface processing finish of the mold parts. By studying the two main elements which affect the mold parts surface roughness processing, measures of improve and enhance wire cutting mold surface roughness are proposed. Only the comprehensive account of various factors can obtain mould parts processing good surface quality. The research methods and conclusion have provided reference on solving the problem of mold parts surface roughness by WEDM.

Abstract: The present work shows an experimental study for selecting the best tools to use in the intermittent turning of pieces of UNS M11917 magnesium alloy under low performance conditions based on the surface roughness. Namely, two types of tools are considered: one, specific for non-ferrous materials, and the other, for materials usually combined with the magnesium to form hybrid parts such as titanium or steel. In order to carry out this study, a combined design of experiments (DOE) L4x32 is established. Concretely, the factors that are taken into account in the design, in addition to the type of tool, are considered the next ones: depth of cut, feed rate, spindle speed, quantity of lubrication, type of interruption, and measurement zones of the surface roughness in terms of the measurement length and of the measurement generatrix. Obtained data are analysed by means of the analysis of variance (ANOVA) method. In this case, feed rate is the most influential factor on the variability of surface roughness followed, although at a large distance, by: type of interruption, interaction feed rate-quantity of lubrication, type of tool, quantity of lubrication, interaction type of tool-type of interruption and spindle speed. As conclusion, it is possible to affirm that, in general, the surface roughness is slightly lower when using non-ferrous tools than when using the other types tried.

Abstract: Austenite 0Cr18Ni9Ti stainless steel is one of difficult-to-cut materials. It has poor dilling process, especially for micro-hole machining. The main reasons are the tiny drill, poor rigidity, easy to deviation. Moreover, the chip is difficult to discharge, so the drilling force is increased and the drill bit is easy to break, or even it is impossible for micro-hole drilling. In this paper, the vibration drilling process is adopted. The vibration drilling 0Cr18Ni9Ti stainless steel micro-hole process mechanism is researched. The stainless steel micro-hole drilling experiments are conducted. The results show that the vibration drilling can be a better solution for 0Cr18Ni9Ti stainless steel micro-hole processing.

Abstract: Aluminum alloys have limited usage because of their limited formability at room temperatures. In order to design and develop more parts made of aluminum, new forming techniques such as hydroforming, warm forming and warm hydroforming have been researched to overcome the low formability issues. This, in turn, necessitates understanding and modeling the behavior of aluminum alloys at different temperatures and strain rates. This paper deals with the investigation of the effect of temperature and strain rate sensitivity on the formability of AA 5754 aluminum alloy. Tensile tests were carried out at temperatures of 20,100,180 and 260°C and forming rates of 25, 100 and 250 mm/min. The mechanical properties and flow curves were obtained and the strain rate sensitivities were calculated at different strains and temperatures. The effects of temperature and strain rate sensitivity on the formability were introduced.

Abstract: Formability of sheet metals can be increased by Hydromechanical Deep Drawing (HDD) process. Formability of the deep drawn cups is generally assessed by Limiting Drawing Ratio (LDR) which is the ratio of the blank diameter to punch diameter. In order to increase LDR by HDD, process parameters of the HDD should be arranged properly. Arranging of the process parameters requires a great knowledge about the effects of the process parameters to certain performance criteria of the process. Determining of the effects of the process parameters by full factorial experiments is a hard duty. Hence certain statistical methods that decrease the number and the cost of the experiments and reduce the time should be used to find effective parameters and their appropriate levels. In this study orthogonal experimental array was applied and effective process parameters were determined by analyzing predicted data with Taguchi's robust parameter design method and ANOVA method. Then the results were compared with each other to evaluate differences between the methods. By using the appropriate levels of the parameters the LDR of AA 5754 aluminum alloy which uses in automotive industry intensely was determined.