For many years, surface has quality received a serious attention due to its influence on various mechanical properties. The main contribution made in this scientific paper is the performance of actual experiments, as well as the experimental processing obtained in order to develop a model for predicting the surface roughness based on the optimization of cutting parameters. The novelty of this paper is brought by the method of obtaining the regression equation of the surface roughness, resulted from a standard end-milling process (standard milling tools, standard milling parameters, recommended by the tool manufacturer, 3 axis CNC machine and standard vice), on aluminum alloy 7136 in temper T76511, through two statistical methods of data analysis. This material is used for the production of extruded parts and is poorly understood for the proposed line of research. This study’s aim is to determine the surface roughness equation obtained by the milling of aluminum alloy 7136 in two ways: using Taguchi′s experimental design once and the other, using the central composite design. The Taguchi method and the central composite design are used to develop an efficient mathematical model to predict the optimal level of certain processing parameters. Using ANOVA analysis, a comparative study of calculated and experimental surface roughness values is carried out. The initial characteristics (surface roughness) and the controlled factors (cutting speed, depth of cut and feed) are analyzed with the Minitab program. Finally, an analysis of the advantages and disadvantages of the two methods used is presented. This study has a great industrial application, since the main task of every manufacturer is to achieve a better quality of the final product with minimal processing time.
The precision of the thread processed by tapping is closely related to the precision of the pre-drilling of the blank. Currently, the technologies for processing threads with the tap in the case of metals are well established. In this sense, there are tables and clear recommendations about the tool pairs—helical drill-tap, depending on the size of the thread, but in the case of plastics, no correlations or recommendations have been found. A well-known aspect concerns the fact that the hole made in plastics is obtained with a smaller diameter than the diameter of the drill bit used. To determine the differences between the drill bit and the diameter of the resulting hole, and its precision on different types of plastic materials, experimental research was started. At the same time, the tolerance of the resulting hole was checked and the influence of the cutting regime on the processing precision was studied. During the experiments, plastic materials often used in the aeronautical and car-building industries were used: POM-C, PA6, PEHD1000, Sika Block 700, Sika Block 960, and Sika Block 980. Following the experiments, differences in the diameter of the holes processed were found according to the plastic mass of even 0.3 mm, which is 4.4% of the diameter of the hole. Based on the experimental results and the design of the experiment, recommendations could be made about the diameter of the drill to use to obtain the desired diameter of the hole after processing.
The paper addresses the problem of urban road noise, in the context of the European legislative requirements regarding noise pollution. The second noise mapping in Pitesti city, revealed that despite the proposed action plan after the first noise mapping, the noise pollution increased instead of decreasing. Considering that the proposed measures were insufficient to control road noise in the conditions of the estimated increase in road traffic, the authors developed complex research to identify how the road noise level is determined by the way of regulation of road traffic at intersections of the residential zone. Thus, noise and traffic measurements are made at the main road intersections in the central part of the city, determining the most relevant noise indicators for the specifics of urban traffic and residential areas. The results obtained lead to the conclusion that roundabouts bring a reduction in noise pollution compared to traffic light intersections only if the speed of vehicles in the roundabout is predictable: on preselected lanes and with speed timing.
Abstract. To ensure customer satisfaction, the products made by aviation, space and defense organizations need to be continuously improved from the point of view of safety, security, reliability and maintainability. The improvement goal is to be at the customers' requirements and legislations level, if not even to overcome it. The occurring problem with the final products is the challenge to ensure their quality in a shorter time. In this research the importance of implementing the APQP concept in the aeronautical industry is highlighted. To achieve this purpose, the methodologies needed to ensure that the product development processes of the aviation, space and defense industry are fully integrated processes ranging from concept and design to planning, manufacturing and production, aiming the product good use, a quality service and finally getting a positive customer feedback. The final goal of this concept implementing is the Production Part Approval Process (PPAP), which is actually the main result of APQP confirming that the manufacturing process has demonstrated the potential to achieve products that consistently fulfil absolutely all the expressed and not expressed customer requirements.
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