Research On Ultra-fine Ti(C, N) Based Cermet Cutter And Its Cutting Behavior

With the development of high speed precision cutting and numeric control technique, the needfor the cutter with high performance is increasing everyday. There are some advantages in cermetcutter, such as good wear resistance and high temperature mechanical properties and so on, but itsapplication has been limited for its brittleness. Many research works have been done in order toincrease the toughness. Based on the previous studies, ultra-fine grade Ti (C,N)-based cermet cutterwas prepared and its machinability was studied. Finite element cutting models were built and thecutting progress was simulated by using finite element software. Calculating results such as the cutstatus, wear resistance as well as the distribution of cutting force and temperature between the tooland work-piece were obtained.In the first part, the importance of machining in national economy, the need for cutting-tool, thedevelop-background of cutter, problems existed, as well as the developing trend of cermet wereintroduced. The development process, microstructures and properties of Ti(C,N)-based cermet andits application in cutting-tool area, development status and trend of nano cermets was outlined,Complexity of metal-cutting technique, development history and status of simulation technique ofmachining process and problems presented are also outlined.Next, the manufacturing process, mechanical properties and microstructure of ultra-fine grainedTi(C, N)-based cermets have been discussed in detail. A special attention is paid to the relationshipbetween the composition, microstructure and macro-mechanical property, the influence of rawpowder size on the microstmcture and mechanical property of material as well as the addition of TiC,TiN, Mo, Co on materials was studied. The results denote that: 1) The hardness of cermet increaseswith the decrease of ceramic particle size while its bending strength and fracture toughness shows anopposite trend to hardness. 2) If the raw material contains too much oxygen or too much TiN, it willlead the decarbonization. A new compound appeared in cermets which can be written as(Ni₂Mo_2.5W_1.3)Cx. The presence of this phase seems to be beneficial to hardness, however, harmfulto strength and toughness. 3) A new type "white core-grayish rim" grain appeared in cermetsfabricated from sub-micron sized Ti(C,N) starting powders. It was believed that promoteddiffusional reaction caused by ultra-fine raw powders led to the formation of this new core/rim grainwhich helps to improve the strength and toughness of the material. 4) Mo addition played animportant role in determining the microstructure of the cermets. Since the wettability of Co toTi(C,N) is better than that of Ni, the interface strength between ceramic phase and binder phasecould be strengthened when binder phase is composed of Ni+Co. 5)There are lots of typical grains,i.e. "black core-grayish rim" grains in cermets which prepared with micro-sized TiC powders. Incermets prepared with sub-micron Ti(C,N) raw powders, except typical grains, some exhibit coreless grains. At the same time, a new kind of grains with white core-grayish rim was found. It was foundthat the white core mainly is (W, Mo,Ti)(C,N) solid solution.The machinability of two group experimental cutter inserts against AISI 1045 carbon steel wasstudied. Effect of cutting force and feed rate on the tool life as well as wear mechanism was alsodiscussed. Results show that in high speed turning, oxidative and diffusion wear are two main wearmechanisms.Based on rigid-plastic finite element method, thermal coupling finite element models of 2D and3D were built, the key problems existed such as friction model, separate, break criterion betweenchip and work-piece, wear model and composite model of new cutter were analyzed. The results ofsimulation correlate well with the experiment. Some dates, for example, the distribution ofstress-strain, temperature, the change and magnitude of cutting force, are obtained through analogcomputation. Based on above works, the phenomenon can be explained more reasonable. The worksprovides the basis to better understand the internal phenomenon during cutting process. Based on 3Dcutting simulation, the changes of time, the cutter wearing capacity and the total value of the weartrend were obtained. The finite element cutting model with different rake angles was simulated.The works above-mentioned shows that: ultra-fine grade Ti (C,N)-based cermet will be apromising cutter material if appropriate geometry and cutting parameters were adopted.Three-dimensional numerical simulation can provide the basis for studying cutting-tool wear,optimizing the geometry and cutting parameters, reducing the cost and improve the efficiency.Finally, the whole works were summarized and some suggestions on future works wereproposed.