Thermomechanical modelling of oblique cutting and experimental validation

An analytical approach is used to model oblique cutting process. The material characteristics such as strain rate sensitivity, strain hardening and thermal softening are considered. The chip formation is supposed to occur mainly by shearing within a thin band called primary shear zone. The analysis is limited to stationary flow and the material flow within the primary shear zone is modelled by using a one-dimensional approach. Thermomechanical coupling and inertia effects are accounted for. The chip flow angle is determined by the assumption that the friction force on the tool face is collinear to the chip flow direction. At the chip–tool interface, the friction condition can be affected by the important heating induced by the large values of pressure and sliding velocity. In spite of the complexity of phenomena governing the friction law in machining, a reasonable assumption is to consider that the mean friction coefficient is primarily function of the average temperature at the tool–chip interface. Comparisons between model predictions and experimental results are performed for different values of cutting speed, undeformed chip thickness, normal cutting angle and inclination angle. A critical study is presented in order to show the influences of the input parameters of the model including the normal shear angle, the thickness of the primary shear zone and the pressure distribution at the tool–chip interface. The model permits to predict the cutting forces, the chip flow direction, the contact length between the chip and the tool and the temperature distribution at the tool–chip interface which has an important effect on tool wear.     

刀具几何参数对金属钛纳米切削影响的分子动力学研究

基于分子动力学的基本原理,构建了钛的纳米切削分子动力学仿真模型。工件原子间采用嵌入原子势EAM（Embedded atom method）,工件原子与刀具原子间采用Morse势函数,研究了在不同刃口半径和刀具前角条件下,钛纳米切削过程中工件形态、系统势能、切削力以及工件温度等的变化规律。结果表明：随着刀具刃口半径增大,加工表面粗糙度增加,切削力和工件温度降低,切屑变薄;当刀具前角由负值增加到正值,钛工件承受的压应力逐渐变为剪应力,正前角刀具更有利于切削,同时在不同的刀具前角下,切向力和法向力的大小也有显著变化。     

Experimental investigation to study the effect of solid lubricants on cutting forces and surface quality in end milling

Milling is a widely employed material removal process for different materials. It is characterized by high material removal rate. Machining leads to high friction between tool and workpiece, and can result in high temperatures, impairing the dimensional accuracy and the surface quality of products. Application of conventional cutting fluid may not effectively control the heat generation in milling. Besides, cutting fluids are a major source of pollution. Solid lubricant assisted machining is an environmental friendly clean technology for desirable control of cutting temperature. The present work investigates the role of solid lubricant assisted machining with graphite and molybdenum disulphide lubricants on surface quality, cutting forces and specific energy while machining AISI 1045 steel using cutting tools of different tool geometry (radial rake angle and nose radius). The performance of solid lubricant assisted machining has been studied in comparison with that of wet machining. The results indicate that there is a considerable improvement in the process performance with solid lubricant assisted machining as compared to that of machining with cutting fluids.     

Re-evaluation of the basic mechanics of orthogonal metal cutting: velocity diagram, virtual work equation and upper-bound theorem

This paper re-evaluates the known velocity relationships expressed in the form of a velocity diagram in orthogonal metal cutting, arguing that the metal cutting process be considered as cyclic and consisting of three distinctive stages. The velocity diagrams for the second and third stages of a chip-formation cycle are discussed. The fundamentals of the mechanics of orthogonal cutting, which are the upper-bound theorem applied to orthogonal cutting and the real virtual work equation, are re-evaluated using the proposed velocity diagram and corrected relationships are proposed. To prove the theoretical results, the equation for displacements in the deformation zone is derived using the proposed velocity relationships. To prove that the displacements in the deformation zone follow the derived equation and that this zone consists of two unequal parts, a metallographical study of chip structures has been carried out. To estimate the variation of stress and strain in the deformation zone quantitatively, a microhardness scanning test was conducted.Because it is proved that the chip formation process is cyclic, its frequency is studied. It is shown that when the noise due to various inaccuracies in the machining system is eliminated from the system response and thus from the measuring signal, and when this signal is then properly processed, the amplitude of the peak at the frequency of chip formation is the largest in the corresponding autospectra.     

Prediction of the cutting conditions giving plastic deformation of the tool in oblique machining

A method is described for predicting cutting conditions at which the cutting edge starts to deform plastically when machining with oblique nose radius tools. It is shown how tool stresses and temperatures determined from machining theory can be used together with experimental high temperature compressive strength data for the tool material to make these predictions. A comparison made between predicted and experimental results for two plain carbon steel work materials and a range of cutting conditions shows good agreement.     

减载缓释机构缓释特性的上限法分析

为了提高发射可靠性,我国未来的运载火箭中拟采用牵制释放系统。文章以一种新型强制式牵制释放系统为例,建立了分析该系统中减载缓释机构缓释特性的上限模型。该模型可以考虑缓释销拉拔过程中截面缩减率的变化、拉拔模芯表面的摩擦、缓释销材料的硬化以及死区的形成等因素对缓释力曲线的影响。所得上限解与实验数据符合较好,可为减载缓释机构的合理设计提供理论依据。     

Cutting forces compatibility based on a plasticity model.: Application to the oblique cutting of the AA2024 alloy

In this work, a compatibility model for cutting force components is proposed. This model has been built by considering the plasticity hypothesis and cutting–shear force bond conditions. Its formulation gives rise to the Cutting Forces Compatibility Equation. This equation suggests that the cutting force components are related and, therefore, that they cannot be considered independent. An experimental study of AA2024 alloy has been achieved in order to determine the consistency of the model. This study was carried out by acquiring the orthogonal cutting force components through a piezoelectric dynamometer placed in the revolver of a computer numerically controlled lathe. The results obtained are in good agreement with the proposed model within the pre-established limits.     

Analysis of fuzzy dynamic characteristics of machine cutting process: fuzzy stability analysis in regenerative-type-chatter

This paper deals with the influence of fuzzy uncertainty factors on the analysis of chatter occurring during the machine tool cutting process. Using fuzzy mathematical analysis methods, the present work discusses the fuzzy stability analysis problems related to the regenerative-type-chatter with respect to intrinsic structure fuzzy factors and gives the possibility distribution of the fuzzy stability cutting range and the confidence level expressions. Finally, on the basis of the theoretical analysis, this paper gives a fuzzy coefficient of merit definition, and a discussion on application problems of this theoretical analysis both in machine tool chatter resistance's capability and in CAD/CAM.