Design,Fabrication And Application Of CVD Dimond-coated Drawing Dies

CVD diamond films have the very similar characters with the natural diamond,such as high hardness,the high elastic modulus,the high thermal conductivity,the good selflubricating and chemical stability and so on.And the diamond films can be deposited on the inner surface of the substrate.Thus the CVD diamond films has currently become an important coating material to reduce friction and wear,prolong the working lifetime of the drawing dies and enhance performance.It can also facilitate machining technique development,reduce resource cost.This paper aims at solving three key problems:(1)study on tribological properties of polishing CVD diamond films;(2)optimization of diamondcoated drawing dies and(3)the design of the diamond-coated shaped drawing dies.The main innovations of this paper can be summarized as follows:1.Study on tribological properties of polishing CVD diamond films.CVD diamond films are deposited on the on WC-Co substrate.After deposition,the diamond films were mechanically polished using a diamond wheel.Four different kind of samples with different surface roughness are prepared.The unpolished and polished CVD diamond films are characterized with scanning electron microscope,atomic force microscope,surface profilometer,Raman spectrum and X-ray diffraction.The friction examinations were carried out by using a ball-on-plate type rotary friction tester.Low carbide steel,stainless steel,copper and aluminum materials were used as counterpart balls.The sliding tests were carried out under oil lubricating condition.The results show the diamond films have low friction coefficients.There is a clear trend of lowering the friction coefficient with decreasing roughness.While sliding against copper and aluminum balls,all the various diamond films give higher friction coefficients compare with the low carbide balls and stainless steel balls,attribute to the higher ductility of copper and aluminum causing larger amount of wear debris adhering on the sliding interface and higher adhesive strength between the contacting surfaces.The wear rate decreases while the roughness decreasing.Considering the friction coefficient,adhesion of the polished diamond films and wear rate of the metal,the roughness of polishing CVD diamond films are decided for different applications,to ensure the surface finish of the product while minimizing the polishing time and retain the adhesion between the diamond coating and the substrate.2.Design,fabrication and application of CVD diamond-coated wire drawing dies.Drawing processes of copper wire,aluminum wire,low carbon steel wire and stainless steel wire are simulated using finite element analysis software ANSYS Workbench.The stress distribution and drawing force are calculated.With the aim of studying the influence of the parameters of drawing die,a numerical simulation through the design of experiments method was carried out.Response surface methodology(RSM)is applied to obtain an approximation to a response function in terms of predictor variables.Optimal design is obtained.The result shows the optimal design can effectively reduce the axial stress of the wire,the stress on the die and drawing force.3.Design,fabrication and application of CVD diamond-coated shaped drawing dies.The ruled surface partition method is introduced to design the intermediate die profile of the multiple-pass cold drawing process.A FEM simulation approach is used to analyze stress and drawing force for the proposed process.The numerical compute drawing force of the six-pass drawing process is compared with the experimental ones.The results are very similar.Moreover,the influence of the number of the drawing passes is numerically assessed.The drawing force value and the Von-Mises stress value are lower when the number of dies is larger.From the FEM simulation results,the drawing force values decrease along the pass schedule.The six-pass drawing process is suggested to apply in a consideration of die cost.4.Design,fabrication and application of CVD diamond-coated tube drawing dies.Drawing processes of hollow sinking,float plug drawing and fix plug drawing are simulated using finite element method.The mechanism of diameter shrinkage in hollow sinking is discussed.The modified type drawing die is developed to minimized diameter shrinkage.The stress distribution and drawing force are calculated.With the aim of studying the influence of the parameters of drawing die,a numerical simulation through the design of experiments method was carried out.Response surface methodology(RSM)is applied to obtain an approximation to a response function in terms of predictor variables.Optimal design is obtained.The result shows the optimal design can effectively reduce the axial stress of the tube,the stress on the die and drawing force.5.Optimal design of multi-pass drawing processes based on artificial intelligence.Using the optimization method based on artificial neural networks and genetic algorithm,the optimal elongation of multi-pass drawing process is determined.Firstly,the optimal design of drawing dies and the object values for certain raw wires and elongation is calculated by FEM simulations.The results are used to train the artificial neural network.The genetic algorithm is introduced to optimize the elongation for each pass.The raw wire dimension and the elongation is mapped to the optimal design of drawing die using the artificial neural network.The FEM simulations are not necessary.Thus save amount of calculation time and improve the design efficiency.An optimization model of the elongation distribution is established using genetic algorithm.The trained artificial neural network is used to calculate the fitness.With powerful global optimization capability of genetic algorithm,the multi-pass drawing elongation allocation problem is solved efficiently.6.Diamond-coated drawing die database and FEM simulation platform based on web browser.According to specific engineering applications,a diamond-coated drawing die database and FEM simulation platform are developed based on web browser.The database and platform can be accessed via web browser.The drawing die design data can be queried using the drawing die database.Through the platform,optimal design parameters of drawing die can be calculated by artificial neural network.A convenient FEM tool is provided for engineers with FEM background to optimize the drawing die.