Key Engineering Materials Vols. 291-292

Abstract: Selective Laser Sintering (SLS) has many advantages such as fast building speed, wide range of materials, complicate shape of prototype and simple post-treatment. However, the shrinkage and mechanical stresses result in lost of the accuracy. This paper investigates the dimension precision of polymer SLS prototypes and proposes methods to control dimensions in suitable degree. The influencing factors of dimensional precision in the file preparation of CAD model, manufacturing system of SLS prototype and sintering process are analyzed. It indicates that the sintering shrinkage in sintering process is the main reason of dimensional changes. To improve the dimensional precision, the measures are proposed to diminish the shrinkage: improving material of prototype, optimizing the sintering process and compensating the lost of dimension. After analysis the experimental results, the rule of error changes is summarized by fitting equations and feedback to controlling software of SLS system to improve the dimensional precision effectively. The SLS prototype could be controlled in 100±0.20mm through compensation.

Abstract: In order to improve the lifespan and performance of the forming mould with low melting point, arc spray forming of stainless steel mould has been advanced. The technical process of spray mould has been investigated, and the correlations among the spray parameters, in-flight characteristics of molten particle and the forming quality have been analyzed in detail. Meantime, the influence of the preheating temperature of the spray mould and the spray angle on the morphology of the splashing particles has been also investigated. The research results indicate that the atomization pressure greatly influences the velocity and granularity of the in-flight particles. The working current greatly influences the particle temperature, and the spray distance influences the temperature and velocity to some extent. A compact spray layer, with a low porosity, little oxide content, and high microhardness, can be obtained by increasing the atomization pressure. The research has a great significance to optimize and control the forming quality of rapid tooling by arc spraying.

Abstract: There is the advantage of continuity in organic structure and mechanical property for functionally gradient materials (FGMs), but it is unable to be used in the mould industry for the difficulty of the second machining up to now. In this study, a novel technology of FGM mould with fine veins fabricated by plasma spraying has been developed, which can easily realize the integration of FGM forming and deep machining of the mould. According to applied characteristic of plastic injection mould, WC-12%Co/NiCrAl powders are selected and the reasonable FGM coating has been prepared. Spraying processes have been investigated, such as fabrication of spray mould with fine veins, FGM forming, backing and demoulding, etc. At the same time, the metallography, porosity and microhardness of the spraying layer have been analyzed. The results show that the service performance of the FGM mould is much more excellent than that of the traditional mould, and the life span can also be greatly improved. The research will have a significant influence on the material development in the mould industry.

Abstract: Flexible forming using plasma arc (FFUPA) is a newly developed method of sheet metal forming. It makes the forming by means of thermal stress and thermal strain without mould and die, and is recognized as a promising forming method in developing new products. But the forming effect of FFUPA is determined by many factors, which compose a highly nonlinear system due to their complicated interact. As a result, it is difficult to predict the forming results and choose the processing parameters in FFUPA. In this paper, BP neural network is applied to solve this problem. After introducing the mechanism of FFUPA and analyzing the influence of processing parameters on the forming result, BP neural network is established, which include an input layer, an output layer and a hidden layer. When inputs and outputs are properly chosen, the BP neural network can be used to predict the forming results and to select the forming parameters. To verify the validity of this network, the results obtained by the BP neural network are compared to those obtained by experiments, and the results show that the former is close to the later, which indicates it is feasible to apply BP neural network in determining the processing parameters and forecasting the bending effects in FFUPA.

Abstract: Plastic profiles produced by extrusion die are cooled down and calibrated by calibrators, so it is an important basis to solve design problems of calibrators that how to obtain the transient temperature field of cooling process of hot plastic profiles. Based on the analysis of heat transfer ways during the cooling process, computation model, initial and boundary conditions are studied deeply, and then ANSYS is applied to simulate the cooling process of plastic profiles. Lastly, the transient temperature field of the cooling process is gain. Results of the numerical simulation show that the temperature drops of functional blocks, main-walls and inner-ribs are reduced in order of priority. Based on the results, the cooling water channels can be adjusted in order to improve the distributing uniformity of temperature field. All this is effective to the calibrators’ design.

Abstract: Sculptured surface machining is a critical process commonly used in die and mold industries. Since there is a lack of scientific tools in practical process planning stages, feedrates of CNC machining are selected based on previous experiences. In the selection of feedrate, the feedrate is set an individual conservative constant value all along the die cavity roughing processes in order to avoid undesirable results such as chipping, cutter breakage or over-cut due to excessive cutter deflection. Usually, volumetric models or vector force models used for optimizaton of feedrates must be created to get the variable feedrates along the tool path. Considering the die cavity roughing being a 2.5D cutting, a novel cutting force surface model is created based on orthogonal cutting tests to adjust the feedrates. The model is tested by a typical die-cavity roughing, thinning down machining time and balanced cutting-load can be attained. The presented feedrate scheduling characterized by balancing the cutting-loads in die-cavity roughing will be more significative in high speed machining.

Abstract: Finite element (FE) analysis is very useful in the early stage of a fixture development in order to reduce or eliminate design problems. Accurate prediction of fixture-workpiece deformation requires an appropriate representation of the contact relationship between fixture elements and workpieces. The paper addresses the special features of the deformation analysis between complicatedly shaped components and fixture elements. The effectiveness and the scope of applicability of commonly used methods are analysed. The verified FE analysis is used to predict surface error arising from deformations, and to evaluate the deformation distributions from fixture elements and workpiece. Based on the FE analysis, the tolerance can be allocated to the fixture elements and the workpiece. The development of a turbine blade fixture is provided as case study.

Abstract: Graph-analytic modification of the known method of upper estimation is presented here. This method gives possibility to get easily and quickly the result of graphic design of process and speed godograph (locus). The given modification allows realize graphic calculation of speeds and efforts of deformation through ratio l/h excluding design of speed godograph. This process does not only simplify and formalize all solutions but also gives possibility to optimize results and find defined parameters. Depending on the type of presented ratio l/h the given modification of this method attracts different kinds of graphic and analytic solutions. The results of calculation according to specific efforts coincide with known graph-analytic solution attained by the method of upper estimation with identical representation of the center of deformation. The usage of graphanalytic method in solution of energy expenses on the bases of geometric ratio allows find ways to the definition of conformity deformation processes applying to as forging as other fields of mechanics. The given method of defining energetic expenditure during the process of deformation gives the possibility of seeing interaction between some parts of deformed body, caused by selforganization of the process. Stating laws of self-organization of deforming processes is the necessary task of mechanic as a whole, mechanics of a solid deformed body and its appliances.

Abstract: Features of application of laser trimming for normalization of accuracy of resistance of resistive elements (REs) of hybrid integrated circuits (ICs) are considered. Limitations of the applied method are determined and decisions on its development are offered on the basis of application of means of the automated designing and modelling. Application of the method of the analysis of hierarchies (MAH) and the theory of indistinct sets for an estimation and optimization of projects of normalization is proved.