Applied Mechanics and Materials Vols. 10-12

Abstract: In this paper a dynamic non-linear mathematics model is proposed to predict the surface roughness in optical ultra-precision machining, which can be automatically built by evoling computer program of genetic algorithm. The new model can improve the fitting and predicting accuracy, compared with the traditional linear regression model. The numerical simulation test proves the effectiveness and accuracy of new model.

Abstract: Prediction of temperature field is a key technology to achieve the groove design and reconstruction of milling insert, predictive model of neural network is a new way to achieve the prediction of temperature field. According to the non-steady state characteristic of temperature field of milling insert, the paper puts forward a predictive model of temperature field of milling insert with 3D complex groove based on Levenberg-Marquardt algorithm of BP neural network, and it overcomes the disadvantage that traditional neural network is easy to fall into local minimum. The predictive results show that this predictive model can converge quickly and predict accurately.

Abstract: Digital action mechanism of machining error propagation has been a hot research topic in recent years. A complicated machining system usually contains multiple stages. Basing on analyzing digital behaviors of machining process flow, a methodology of machining error monitoring and control is put forward, which is based on dynamic programming. Under this framework, state of machining feature is described with vector matrices, and then differential transition matrices are used to represent the influences of error sources on machining feature quality of workpiece. Basing on this, a general error propagation equation is derived. At last, an example of a three-stage machining processes is presented to illustrate the proposed methodology.

Abstract: A new optical manufacturing technology called bonnet polishing has been developed over last decade. During bonnet polishing, the puffed bonnet is flexible and self-reacting against the surface configuration of optical parts. So the same polishing tool can be used in machining the optical parts with different curvature. The mechanism of the bonnet polishing is described in this paper firstly. Since the optical workpiece has been polished in the “polishing spot”, the bonnet polishing experiments have been accomplished on the trial-manufacturing machine to study the effect of technological parameters on the size and shape of “polishing spot” and the material removal rate of optical workpiece. At last, the material removal rules of the bonnet polishing have been given in the paper.

Abstract: Laser forming is a technique of using the energy from a laser beam to modify and adjust the curvature of sheet metals or hard materials. 2-dimention (2D) laser forming can reasonably accurately control bend angles with various materials. To advance this process further for realistic forming applications in a manufacturing industry, it is necessary to consider larger scale controlled 3-dimention (3D) laser forming. On the base of mechanism of 2D laser forming, the deformation mainly depends on the temperature gradient between upper and bottom surface of sheet metal. The work presented in this paper shows that the temperature field of using the spider scanning path to transform the thin square sheet to spherical dome by 3D laser forming. The explicit thermal analysis on 3D laser forming is shown in the article. This paper discusses the interaction between moving laser beam and sheet, the varied temperature field on the sheet during laser scanning. In order to give the verification on the results of simulation, the correlative experiment has progressed and the results of experiments are in accord with the simulation.

Abstract: Effects of addition of glycerin in the electrolyte on the micro arc oxidation process have been investigated with a bipolar asymmetric pulse power supply, which involves peak value of pulse current, voltage, thickness and hardness of ceramic films of AZ61 magnesium alloy as well as surface roughness and structures. The results reveal that addition of a proper amount of glycerin helps to the decrease of positive pulse current peak and voltage, formation of a much dense ceramic coating with increase of the hardness, decrease of the surface roughness and good crystallization. When the amount of glycerin is more than 10ml/l, the growth of ceramic coatings begins to be inhibited and the performance of ceramic coatings seriously turns worse.

Abstract: Three dimension indenter model was established to replace the ideal shape indenter model in the study of nano-indentation simulation. The limitation of short of comparing to actual condition can be solved. Single crystal aluminum surface nano-indentation on the condition of arc indenter is researched by molecular dynamic simulation. The influences of different arc radius of indenter head to testing results are discussed and compared to experiment results. The results show that The measured hardness value increases with indenter head arc radius on the same indentation depth condition. With the increase of indentation depth, the difference between measured results with changed indenter head arc radius reduces gradually. When the indentation depth increase to a certain value, the arc effect of indenter head could be ignored, the measurement will be invariable.

Abstract: In the paper, the experimental study of grinding process of 2024Al/SiCp composites with the electroplated diamond wheel was conducted. The results indicate that the surface roughness of the workpiece is between 0.554 μm and 1.2 μm. Increment of the spindle speed, reduction of the cut depth and decrease of the feed speed make the surface roughness value reduce. After grinding, compressive stresses on the machined surface can be obtained. During grinding, the normal grinding force is greater than the tangent force and the grinding forces increase as the increase of the feed speed and depth of cut.

Abstract: Assembly sequences can be represented by a Petri net(PN) which characterizes dynamic system changes and provides a tool for obtaining optimal assembly sequences. In this study some assembly operation constraints are considered in order to obtain more practical sequences which are conformed to real situations. In order to enhancing the efficiency of the assembly sequence planning, knowledge-based Petri net, combining an usual Petri net with expert’s knowledge and experiences, is proposed to construct the assembly model. With the complexity of the product, the product’s assembly model size will be too large to analysis. So the basic subnets are used to reduce the large PN. And the reduced version can be used for the analysis of the original PN. To verify the validity and efficiency of the approach, a variety of assemblies including some complicated products from industry are tested, and the corresponding results are also presented.

Abstract: A design process of PMT virtual conceptual design is put forward, and a design platform of PKM virtual prototype is developed based on ADAMS; By analyzing topological structure and classifying the functional module of the existing PMTs, a modular component base are built. The management of component base and virtual assembly of PMT are realized. A method to analyze kinematic properties of parallel mechanism is introduced by taking screw theory as guidance and taking virtual prototype technology as verifying tool. With the method, DOFs of parallel mechanism are vividly depicted and rationalities of actuation scheme are judged.