Simulation Of Physical Fields And Experimental Study In The Preparation Of HFCVD Diamond Coated Tools With Complex Shape In Quantities

CVD diamond coated tools is a type of new high-performance cutting tool whichis prepared by CVD method. Through this method a layer of diamond film which hashigh strength and high toughness is deposited on the substrate. The diamond films onthe surface of the tools has excellent properties close to natural diamond, such as highhardness, elastic modulus and thermal conductivity, low friction coefficient andoutstanding wear and chemical stability, etc. All the advantages make it widely used inthe aerospace, automotive, mold, medical and other processing industry. Hot filamentCVD (HFCVD) is practically applied for its advantages such as geometricsimplification, operational convenience and low cost. Particularly, the diamond filmscan be deposited directly onto complex shape tools by HFCVD method. However, theinconsistent film quality and film thickness during the diamond films growth on thecomplex shape tools have been the key issues remained to be resolved. A large numberof experimental and theoretical studies have showed that the temperature field and gasflow field in the reaction chamber play determinate roles in the homogeneity andsurface quality of deposited diamond flms. So the study aimed at obtaining moreuniform temperature and gas flow field during the deposition, which are more necessarywhen preparing diamond coated in large quantities, has important theoreticalsignificance and practical value.In the thesis, the ordinary twist is selected as the example to establish thesimulation model and the CFD (Computational Fluid Dynamics) software which usesfinite volume method (FVM) is applied to calculate the physical field distribution. Alot of temperature tests were also conducted to verify the correctness of the simulation.Then the research and optimization of the temperature field under the cases of theordinary cutting edge length drill and the long cutting edge length drill were completed.The analysises and optimizations on the inlet and outlet parameters were also carriedout to get an uniformity flow field around the filament and the tools. Finally, thepreparation test under the optimized conditions, characterization tests and cutting testswere carried on to validate the correctness of the simulation results further. The mainresearch contents of the thesis are as following：1. Considering the heat radiation, conduction and convection, the simulation method and conditions were determined and the FVM method was used to simulate thetemperature field and gas flow field in the HFCVD chamber. In order to verify thecorrectness of the simulation methods, a platform for multi-point temperaturemeasurement was established and the temperature measurement were conducted underthe model of large quantities, one single line and one single row. The comparationbetween the results of the temperature measurement and simulation showed that thesimulation reflect the actual substrate temperature distribution trends nicely.2. The filament arrangement of the two types of drills with different cutting edgelength were studied. The result shows that for drills with ordinary cutting edge lengththe necessary temperature condition can be guaranteed by arranging one layer offilaments over the drills, but it is needed to place two layer of filaments to obtain theappropriate temperature field for the drills with long cutting edge. Firstly, the effect ofthe parameters (including filament length, filament diameter, filament separation,filament height, filament temperature, the material of support block and the flowcooling water) on the temperature values and temperature uniformity on the surface ofthe large quantities of drills in the case of equidisant arrangement of the filaments wereanalyzed and optimized. Then a novel unequal spacing filament arrangement methodwas proposed to obtain a more uniform temperature field and the difference of thetemperature on the top side of the drills were reduced to36℃.For drills with long balde,the research started with orthogonal test to obtain the optimized filament parameters inthe one single row model. Then using the unequal spacing filameng arrangementmethod to get each optimized parameters in medium and large batch.3. A systemic study of the form of inlet and oulet on the effect of the velocity anddensity fields were analyzed and the optimization were also conducted to improve theuniformity of the gas flow fields. The parameters discussed were the height of the inlet,the area of the inlet, the velocity of gas from the inlet, the structure of the inlet, the areaof the outlet, the placement of the outlet.4. Taking the ordinary cutting edge length drill as example, the deposition test in largequantities under optimized conditions was done and the surface morphology and qualityof diamond films were analyzed by Scanning electron microscopy (SEM) and Ramanspectra (Raman). Furthermore, the cutting performance of the diamond coated drill indifferent place and the uncoated drills were studied by cutting tests of high siliconaluminum alloy. All the tests results showed that the optimized parameters met therequirement of the preparation of the diamond coated drills in large quantities.