| With the rapid development of aerospace,petrochemical,food and medical,civil nuclear power,marine industry,etc.,the demand for difficult-to-machine materials such as titanium alloy,stainless steel,etc.are also increasing rapidly.However,these highly versatile materials with high performance is facing serious challenges in the machining process,the harsh tool-chip interface environment,a large number of built-up edge formation,and severe tool wear together affect the machining efficiency.Therefore,it is significant to develop new cutting tools with reduction friction and augment the tool wear resistance,and the novel restricted contact design on the rake face is an essential way to improve the cutting performance.Nevertheless,up to now there are many problems in the research on the mechanism of restricted contact cutting and the actual application of restricted contact tool,the critical difficulty is that the traditional two-dimensional restricted contact theoretical analysis cannot be applied to variable restricted contact length cutting,while the use of the two-dimensional method to analyze the cutting forces generated by variable restricted contact cutting possibly results in inaccuracy,which is closely related to the lack of restricted contact cutting theory.In addition,there is still a lack of in-depth mechanistic studies on variable restricted contact length tools for cutting difficult-to-machine materials.Combined with the above mentioned points,this study takes 316 L austenitic stainless steel and carbide tools as the main object of study.With the aim of reducing the tool-chip interface temperature and extending the tool life,the design of variable restricted contact structure is carried out on the rake face under the premise of ensuring the applicability of the tool.Based on the metal cutting principle,the finite element analysis,and extensive cutting experiments,the force model in cutting process with variable restricted contact length is developed.The cutting performance,tool wear and surface integrity are further investigated,and the cutting mechanism of the variable restricted contact structure is clarified.The main contents are as follows:1.The analytical model was proposed for the cutting force components in turning with variable restricted contact length tool.Firstly,the force model of restricted contact tool was established during orthogonal cutting process.A three-dimensional model of the cutting force generated by the variable restricted contact length tool was then proposed based on the non-equal shear zone model,the metal cutting principle,and unified mechanics theory.The analytical model in the turning process was finally established by combining the experimental results and the discussion of the relationship between the restricted contact length and the proposed model.The accuracy of the proposed analytical model was verified after comparing extensive results.2.The finite element model with thermo-mechanical coupling was established to analyze the restricted contact cutting process.It includes: comparing and analyzing the difference between conventional cutting and restricted contact cutting;establishing the mathematical-mechanical model of restricted contact cutting;investigating the influence of cutting parameters and restricted contact parameters on the results such as cutting force,cutting temperature,effective stress,effective strain etc.in the restricted contact cutting process;exploring the influence of machining parameters,restricted contact length and restricted contact shape on tool-chip contact and chip curl during restricted contact cutting.3.The comprehensive and systematic evaluation methods for the cutting performance of conventional plane tool,tranditional restricted contact tool,and variable restricted contact tools were established under dry cutting conditions through the characterization of the experimental phenomena and results.Different analysis methods were applied to evaluate and investigate the cutting power,tool amplitude,cutting force,friction,cutting temperature,chip formation,tool wear,the machined surface roughness,machined hardness distribution,residual stress,surface texture as well as other surface integrity aspects;The cutting force,cutting temperature,chip formation and surface roughness were explore the improvement of the cutting performance of the restricted contact structure under different machining parameters.4.The variable restricted contact structure and its cutting mechanism to enhance the tool-chip interface performance are revealed through the analysis of the reduction of the thermal and mechanical load,friction,and tool wear during variable restricted contact cutting process.On the one hand,due to the existence of different restricted contact shapes,the tool-chip contact area is further decreased on the basis of the original rectangular restricted contact,which help to reduce the cutting forces and heat.Moverover,the variable restricted contact structure changes the stress distribution on the rake surface,which increases the average normal stress,reduces the apparent friction coefficient,and improves the tribological performance.On the other hand,the void area formed by the variable contact structure is more favorable for collecting hard abrasive particles,and the shorter tool-chip contact length contribute to declining the cold welding adhesion process and alleviating the damage of hard microparticles on the tool surface,thereby extending the tool life.The above study not only explore the cutting mechanism of variable restricted contact tool,but also contribute to the dry cutting technology progress for difficult-to-cut materials.It provides a solid foundation for the future development of high-performance tools and its design methods. |
