Study On Preparation And Technology Of CVD Diamond Coating For Small Diameter Wire Drawing Die

The diamond can be deposited on the inner hole surface of the YG6 carbide wire drawing die by hot wire chemical vapor deposition,which greatly improves the wear-resisting property and service life of the wire drawing die.However,due to the limitation of technological conditions,such as the distribution of temperature field in the inner hole,CVD diamond coating is only widely used in the wire-drawing die with an aperture of 3mm or more.In this paper,simulation and experiment are combined to explore the technique of preparing diamond coating in the inner hole of cemented carbide wire drawing die with an aperture of 1.2mm.The main research contents and results are as follows:（1）According to the actual deposition process,a three-dimensional simulation model was established.Comsol Multiphysics simulation software was used to discuss the mold temperature fields under three hot wire distribution modes,a more uniform temperature distribution of the inner hole can be obtained by the two-sided cross-thread method.L₉（3⁴）orthogonal simulation experiments were designed to optimize the process parameters of hot wire by taking the diameters of two hot wires and the distances between hot wire and die as factors.（2）After using simulation optimization of process parameters on the two-sided cross-thread method,the experiment of preparing diamond coating in the wire drawing die hole with small diameter was carried out,and the thermal resistance was used to measure the temperature to verify the simulation effect.The results show that the simulation error is 1.25%,which is helpful to the experiment.The diamond composition is detected in the inner hole of the mold,and the uniform temperature distribution of the inner hole make the diamond coating thickness in the three key areas more uniform.（3）In order to further improve the quality and thickness of the diamond coating,the cathode DC bias voltage of the die was introduced on the basis of the cross-wire distribution method,and three bias voltage sizes of-50V,-100V and-150V were selected for the comparison experiment.With the increase of bias voltage,the amorphous carbon content of diamond coating decreases,and the crystal surface（100）becomes more significant,the grain size and coating thickness increase accordingly,and the coating binds to the substrate more strongly.Comparing the experimental results of the three groups,the optimal bias parameter is-150V.（4）The diamond coated wire-drawing dies without bias voltage and with bias voltage of-150V were polished by using consolidated abrasive wire polishing.During the polishing process,the diamond coating mold without bias occurred to fall off,while the diamond coating prepared by HFCVD with bias voltage have better bonding force with the mold.Then dissociating abrasive was used for the latter semi-finishing polishing,and the final surface roughness Ra of diamond coating is0.1μm,which reach the wire drawing requirement.