考虑孔隙缺陷的CFRP微观切削仿真与实验研究

碳纤维增强树脂基复合材料(CFRP)在航空航天等领域应用广泛。在CFRP制造过程中难以避免会产生孔隙等缺陷,对后续的切削加工造成一定影响。在考虑了CFRP成型过程形成的孔隙缺陷基础上,运用有限元仿真模拟方法,从纤维-树脂-界面尺度建立了含孔隙缺陷的CFRP微观切削仿真模型,研究了不同孔隙率条件下不同纤维排布方向的CFRP微观切削行为,并通过实验验证了仿真模型的正确性。研究结果表明:孔隙的存在会增加刀具的“空切”现象,从而对CFRP切削过程的切削力、材料破坏及亚表面损伤、材料能量等产生影响。随孔隙率的增加,切削力呈下降趋势,孔隙边缘的纤维产生整体断裂的倾向增加;孔隙对0°、45°和135°纤维排布方向的CFRP切削加工的面下损伤影响不大,在纤维排布方向为90°条件下,孔隙率高于3vol%时对加工表面的面下损伤具有较大影响;在材料内部能量耗散方面,“顺切”(纤维方向角小于90°)时的总耗散能低于“逆切”,随孔隙率增加,总耗散能降低。      

刀尖圆弧半径加工误差解决方法探索

当实际车刀刀尖非理想点而是圆弧时,在加工圆锥和圆弧表面会产生过切削或欠切削的加工误差问题,本文根据不同功能的数控系统,介绍利用数控系统刀尖圆弧半径补偿功能及编程过程中计算刀位点坐标这两种方法解决加工误差进行探索。     

高速切削时摩擦系数对切削影响的数值模拟

高速切削加工中,刀屑间的摩擦系数对切削产生重要影响．由于刀屑接触的复杂性,它们之间的摩擦系数很难确定．为了探究高速切削时,刀具与切屑间摩擦系数对切削的影响,采用有限元通用程序ABAQUS／STANDARD对不同摩擦系数下切削过程进行数值模拟．通过对Mises应力和加工表面节点垂直方向位移的比较,得出刀屑间的摩擦系数对剪切角有较大影响,摩擦系数增大,剪切角随之减小．高速切削既能够提高切削效率,又能提高加工精度．     

切削式吸能热力耦合研究

据非线性动态模拟及热力耦合理论,利用有限元软件LS-DYNA对切削式吸能过程进行热力耦合研究。通过分析切削式吸能过程中切削力及能量耗散随切削行程的变化曲线,所得切削式吸能过程的力学特性十分稳定,撞击力未出现较大峰值;切削热耗散能量约占撞击总能量的21%,模拟中需考虑切削热影响。在热力耦合基础上分析撞击速度、切削截面参数及刀具参数对切削式吸能力学特性的影响规律。     

微细铣削加工过程中微毛刺形成机理的模拟与实验分析

研究了采用硬质合金微铣刀铣削加工硬铝合金微槽结构时微毛刺的形成机理．建立了三维微细铣削加工硬铝合金A12024-T6的有限元模型,利用该模型动态模拟微毛刺的形成过程．分析了不同进给量与切削刃钝圆半径比值下微毛刺的形成机理,动态模拟了微槽加工过程中切削参数及切削刃钝圆半径变化对微毛刺影响的变化规律．仿真结果表明,随着每齿进给量、背吃刀量及切削刃钝圆半径的增加,微毛刺的尺寸随之增大;切削刃钝圆半径与最大有效应力是影响微毛刺尺寸的主要因素．微细铣削加工过程中,毛刺顶端所受最大有效应变明显比常规铣削加工过程中的最大有效应变高,呈现出显著的尺寸效应．通过微细铣削加工微槽实验,获得了切削参数及切削刃钝圆半径变化对微毛刺形成的影响变化规律,验证了相应有限元模型的正确性．通过数值模拟与实验方法获得了切削刃钝圆半径与毛刺尺寸（毛刺高度和毛刺厚度）的关系曲线,实验与仿真结果最大误差不超过9．8％．进一步验证了所建立的三维有限元模型适于研究并预测毛刺形成机理及毛刺尺寸的变化规律．     

铝基碳化硅精密铣削刀具磨损实验研究

针对铝基碳化硅切削加工中刀具易磨损、寿命低、切削难度大和加工成本高等问题,选用不同材料的硬质合金铣刀及金刚石铣刀进行切削加工实验,并利用扫描电镜和工具显微镜对高体积分数铝基碳化硅铣削时刀具磨损形态进行了分析研究.研究表明:硬质合金刀具前刀面和刃口磨损主要形式为粘结磨损和微崩刃,后刀面磨损主要为刻划磨损,而金刚石铣刀加工时刀具磨损很小;YG6X铣刀材料微观组织致密,抗磨损能力较强,宜粗加工时选用;金刚石刀体的硬度远大于SiC颗粒,且金刚石与工件的摩擦系数小,金刚石铣刀寿命远大于硬质合金铣刀,宜精加工时选用.     

切削SiC增强铝基复合材料时刀具的磨损形态及机理

为研究切削SiC增强铝基复合材料时刀具的磨损形态和机理,采用硬质合金和聚晶金刚石(PCD)刀具进行了各切削工况下的切削试验。用爆炸式快速落刀装置获取切屑根,研究了前刀面的磨损部位。借助扫描电子显微镜(SEM)和原子力显微镜(AFM),检测分析了前、后刀面的磨损形态和成分组成,并进一步研究了磨损机理。结果表明:切削刀具的主要磨损部位发生在后刀面,磨损机理是磨料磨损;前刀面临近刃口区域首先产生由SiC增强相引起的磨料磨损,该区域随后由机械镶嵌生成积屑瘤,积屑瘤脱落后导致产生黏结磨损。黏结磨损的程度较轻,没有形成月牙洼型。前刀面离刃口稍远的区域(积屑瘤尾部后面)会同时产生由切屑底层SiC增强相引起的再次磨料磨损,磨料磨损的主要机理是"微切削"。     

单晶铜纳米切削过程的研究

采用分子动力学三维模型研究单晶铜纳米切削过程，工件原子间相互作用力和工件与刀具原子间相互作用力采用Morse势计算．通过分析切削过程中瞬间原子图像、切削力、单位切削力和轴向切削力与切向切削力比值。发现在整个切削过程中有位错产生，在加工表面发生弹性恢复，但未发生切屑体积的改变，切屑以原子团方式去除，单位切削力和轴向切削力与切向切削力的比值比传统切削时大得多．单晶铜纳米切削过程是位错在晶体中运动产生的塑性变形．     

硬质合金与结构钢钎焊刀具切削试验及数据分析

本论文以硬质合金与结构钢钎焊刀具切削试验及数据分析为研究对象,通过研究钎焊刀具切削试验过程,可以确定硬质合金与结构钢钎焊的刃具使用范围、使用方法、切削参数等问题进行说明,最终达到刀具能够在生产实际中使用。     

高速切削有限元模拟加工温度场分析

以高速切削条件下的数控车刀为研究对象,利用ANSYS有限元仿真软件对刀具的温度场进行模拟和分析,得出温度场的分布规律,验证切削速度对温度场的影响,为优化切削参数,延长刀具寿命提供一定的依据。     

Mathematical models to predict surface finish in fine turning of steel. Part II

This paper outlines further experimental development of mathematical models for predicting RMS surface finish in fine turning operation using TiC coated and cemented tungsten carbide throwaway cutting tools. The five independent variables included are: cutting speed, feed, depth of cut, time of cut of tool, nose radius. Using these five variables at different levels an experimental approach, predictive models for tungsten carbide and titanium coated tungsten carbide tools were developed. A sixth variable, 'the type of cutting tool,' was used to develop a single model for both the TiC coated and cemented carbide cutting tools. AIS1 4140 steel was used as workpiece specimen in the experimental work. Stepwise regression analysis was used in developing the models.     

An application of goal programming technique in metal cutting

This paper outlines the use of the goal programming technique in selecting levels of machining parameters in a fine turning operation on A1S1 4140 steel using cemented tungsten carbide tools. Goals that are proposed to be achieved are: (i) to finish turning the required depth in one pass, mid (ii) to finish turning within a stipulated time. Constraints used are: R.M.S. surface finish values, cutting horse power of the machine, ranges for cutting speed, feed and depth of cut. A predictive equation to predict the R.M.S. Surface roughness values from the machining variables, cutting speed, feed, depth of cut, and time of cut was used. This mathematical model was developed using stepwise regression analysis on the experimental data for 1/64 in. nose radius cemented tungsten carbide cutting tool. Experiment with the machining variables at different levels were performed to obtain the data. A statistically designed experiment called the rotatable design was used for the experimental design     

Cutting performance and failure mechanisms of a pure WC cutting tool in dry cutting of Cr12Mn5Ni4Mo3Al stainless steels and HT200 grey cast iron

A pure WC cutting tool material was fabricated by hot pressed sintering and treated by hot isostatic pressing (HIP). The cutting performance, failure modes and mechanisms of the pure WC cutting tools were investigated via dry cutting Cr12Mn5Ni4Mo3Al stainless steels and HT200 grey cast iron in comparison with those of YW2 cemented carbide tools. General view of the worn tool face was observed by light optical microscopy. Worn and fractured surfaces of the cutting tools were observed by scanning electron microscopy (SEM) and chemical analysis by energy-dispersive X-ray spectroscopy (EDS). The results of cutting process revealed that the wear mechanisms and failure modes of the pure WC cutting tool in cutting various workpiece materials were totally different due to the discrepant adhesion tendency of the workpiece materials to the pure WC material. The different wear behaviors of the pure WC cutting tools in cutting Cr12Mn5Ni4Mo3Al stainless steels and HT200 grey cast iron result in the completely opposite cutting performance and tool life.     

Machining of high performance workpiece materials with CBN coated cutting tools

The machining of high performance workpiece materials requires significantly harder cutting materials. In hard machining, the early tool wear occurs due to high process forces and temperatures. The hardest known material is the diamond, but steel materials cannot be machined with diamond tools because of the reactivity of iron with carbon. Cubic boron nitride (cBN) is the second hardest of all known materials. The supply of such PcBN indexable inserts, which are only geometrically simple and available, requires several work procedures and is cost-intensive. The development of a cBN coating for cutting tools, combine the advantages of a thin film system and of cBN. Flexible cemented carbide tools, in respect to the geometry can be coated. The cBN films with a thickness of up to 2 µm on cemented carbide substrates show excellent mechanical and physical properties. This paper describes the results of the machining of various workpiece materials in turning and milling operations regarding the tool life, resultant cutting force components and workpiece surface roughness. In turning tests of Inconel 718 and milling tests of chrome steel the high potential of cBN coatings for dry machining was proven. The results of the experiments were compared with common used tool coatings for the hard machining. Additionally, the wear mechanisms adhesion, abrasion, surface fatigue and tribo-oxidation were researched in model wear experiments.     

Chemical vapour deposition (CVD) diamond coated tools performance in machining of PEEK composites

This paper presents a study about the chemical vapour deposition (CVD) diamond coated tool performance in machining unreinforced PEEK and composite PEEK CF30 (reinforced with 30% of carbon fibres).

The experimental procedure consisted of turning operations, during which cutting forces and surface roughness obtained in composite workpieces were measured.

The obtained results showed a best cutting performance for CVD diamond coated tool in machining PEEK composites, particularly in terms of cutting forces and power consumption, when compared with polycrystalline diamond (PCD) and cemented carbide (K10) cutting tools. This fact is very important due to the minor production costs of CVD diamond coated tools in comparison with PCD tools.     

Characteristics of the wear process in the cutting of free-cutting steels

The paper brings some interesting results of the investigation of the cutting edge wear at cutting of free cutting steels by cemented carbide plates. These steels are characterized by the additions of sulphur and lead to increase machinability. The experimental results have shown that the additives of sulphur and lead can strongly affect not only chip generation but also the form and rate of wear. Previous investigations have indicated clearly that the criterion of wear on the clearance faces provides too little information on tool life. The experimental results have also shown that at equal wear on the clearance face the form and rate of wear on the rake face differ essentially.     

An experimental analysis of effective high speed turning of superalloy Inconel 718

Superalloy, Inconel 718 is widely used in the sophisticated applications due to its unique properties. However, machining of such superior material is difficult and costly due its peculiar characteristics. The present article is an attempt to suggest Taguchi optimization technique to study the machinability of Inconel 718 with respect to cutting force, cutting temperature, and tool life in high speed turning of Inconel 718 using cemented tungsten carbide (K20) cutting tool. Therefore, the objective of this work is divided into two phases: (i) to demonstrate a correlation between cutting speed, feed, and depth of cut with respect to cutting force, cutting temperature, and tool life in a process control of high speed turning of Inconel 718 in order to identify the optimum combination of cutting parameters; (ii) to show the effect of high speed cutting parameters on the tool wear mechanism and chip analysis. These correlations were obtained by multiple linear regressions. The confirmation tests were carried out to make a comparison between the experimental results and mathematical models proposed. The proposed models agree well with the experimental results.     

用立方氮化硼刀具对硬质合金材料进行延性超精密加工

对单相晶体结构和硬质合金的粘合特性的理论分析表明，对其进行延性超精密加工是可行的，并在普通加工中心上通过对切削力的监控，用立方氮化硼刀具实现了对硬质合金材料的延性超精密加工．研究结果显示，在用不同刀具进行的切削中，刀具的磨损都非常小；在对硬质合金的延性超精密加工中获得了纳米级表面粗糙度的平滑表面和层状切屑。     

Modelling the orthogonal machining process using coated carbide cutting tools

In this paper finite element methods were used to determine the influence of various coated and uncoated tungsten carbide cutting tools on the machining of a nickel-based super alloy Inconel 718. Disposable coated and uncoated carbide inserts were used both experimentally and as FEA models to study how the stress distribution within different coatings and carbide grades compared to each other, under a range of cutting conditions. Simulation of an orthogonal metal cutting process was performed using FORGE2, an elasto-visco plastic FEA code. All FE models were assumed to be plane strain. The results include the stress and temperature distributions through the primary shear zone, the chip/tool contact region and the coating/substrate boundaries. The tool wear and stress results from the FE modelling agree favourably with those obtained from experimental work.     

Development of diamond coated tool and its performance in machining Al-11% Si alloy

An attempt has been made to deposit CVD diamond coating on conventional carbide tool using hot filament CVD process. ISO grade K10 turning inserts with SPGN 120308 geometry were used to deposit diamond coating. This diamond coating well covering the rake surface, cutting edges and flank surfaces could be successfully deposited. The coatings were characterized by SEM, XRD and Raman spectroscopy for coating quality, morphology etc. Performance of diamond coated tool relative to that of uncoated carbide tool was evaluated in turning Al-11% Si alloy under dry environment. The diamond coated tool outperformed the uncoated carbide tool which severely suffered from sizeable built-up edge formation leading not only to escalation of cutting forces but also poorer surface finish. In contrast, the diamond coated tool, owing to chemical inertness of diamond coating towards the work material, did not show any trace of edge built-up even in dry environment and could maintain low level of cutting forces and remarkably improved surface finish. It has been further revealed that success of the diamond coated tool depends primarily on adhesion of the diamond coating with the carbide substrate and this is strongly influenced by the pre-treatment of the carbide substrate surface before coating.