数控加工中的对刀方法

文章介绍了数控加工中对刀的基本原理,常见的对刀方法及特点,并分别举例说明了数控车床、数控铣床对刀问题的处理.     

纯铂的热塑性变形行为及微观结构演变规律研究

用热模拟试验机研究了纯铂在真应变量为0.9、变形温度为550℃～950℃和应变速率为0.01～1 s~(-1)的热塑性变形行为,并对热压缩后的样品进行了金相观察和显微硬度测量。结果表明,纯铂的流变应力随变形温度的升高和应变速率的降低而降低;其热压缩变形过程中软化行为由变形温度和变形速率共同作用决定,一般以动态回复为主,而在低应变速率和高形变温度下以动态再结晶为主,动态再结晶发生造成的软化使纯铂样品的硬度迅速下降。利用Zener-Hollomon参数方程获得了热塑性变形流变应力本构方程,得到纯铂的热变形激活能为208.51 kJ/mol,流变应力拟合公式计算值与实验值的平均误差为5.9%。     

Tensile overload-induced plastic deformation and fatigue behavior in weld-repaired high-strength low-alloy steel

The effects of tensile over-load (OL) on fatigue crack growth behavior of a weld-repaired high-strength low-alloy (HSLA) steel were studied by measuring both the fatigue crack growth rate and sample-thickness variation along the fatigue crack growth path. The thickness variation, indicating the degree of plastic deformation (PD), provided an indirect measurement of associated residual compressive stresses at the crack-tip. The applied tensile OL with one-hour holding period in each test generated a damage zone at the crack tip. Microscopic details of the crack-tip damage zone were characterized by scanning electron microscopy. Three groups of expanded compact-tension (E-CT) samples, 10 mm in thickness, were tested: weld-repaired HSLA without soft buffer layer (BL), and weld-repaired HSLA with 4 mm or 10 mm thick BL. The experimental results showed that the OL-induced PD, closely linked to the crack-tip residual compressive stresses, reduced the subsequent fatigue crack growth rate, and that the HSLA with a 10 mm BL had the lowest growth rate, indicating a soft BL with an adequate thickness could further improve the fatigue resistance.     

Prediction of cutting forces and chip geometry in oblique machining from flow stress properties and cutting conditions

An approximate theory of oblique machining is given in which the mean friction angle previously used to describe the frictional condition at the tool-chip interface is replaced by the shear strength of the chip material at the tool-chip interface. The shear strength is expressed as a function of strain-rate and temperature using a velocity-modified temperature. Good agreement is shown between theory and experiment.     

On prediction of tool life and tool deformation conditions in machining with restricted contact tools

This paper first reviews the recently developed semi-empirical method for predicting tool life in machining with restricted contact (RC) tools. The method uses Oxley’s machining theory to predict cutting forces, tool-chip contact length and cutting temperatures for the corresponding plane face tool i.e., tool having the same cutting edge geometry but no RC. These predicted parameters and a set of empirical relations are then used to calculate the cutting temperatures and tool life under RC conditions. In this paper additional experimental results are used to verify the above method and validate the predictions. An attempt is then made to use the above method to predict tool deformation under RC conditions. Finally, a comparison between experimental and predicted results and the modifications implemented to improve the predictive method are given.     

A study on the effect of tool nose radius in ultrasonic elliptical vibration cutting of tungsten carbide

Nowadays, ultrasonic elliptical vibration cutting (UEVC) technique is being successfully applied for ultraprecision machining of difficult-to-cut materials. Previous study reported that the tool geometry especially tool nose radius notably influences the performance of 1D ultrasonic vibration cutting (UVC). However, the effect of tool nose radius in the UEVC technique is yet to be studied. This study aims to investigate the effects of tool nose radius on the UEVC performance in terms of cutting force, tool wear and surface finish when machining a hard-to-cut material, sintered tungsten carbide (WC), using PCD tools. The experimental results show that the UEVC technique performs remarkably better in all aspects at a 0.6 mm nose radius compared to a lower (e.g. 0.2 or 0.4 mm) and a higher nose radius (e.g. 0.8 mm). When machining about 412 mm² surface area, an average surface roughness, R_a of 0.010 μm is achieved with a 0.6 mm nose radius. Analyses are conducted to justify the findings in this study.     

数控加工中对刀问题的处理

介绍了数控加工中对刀的基本原理和方法，对常见数控机床中对刀方法选择、NC指令选用和对刀参数设置等方面进行了详细讨论。     

Fe-14Co-10Ni合金的高温塑性变形及热加工图

利用Gleeble-3500热力模拟试验机,在温度为850～1150℃,应变速率为0.1～10s~(-1)的条件下,对具有高强韧性的Fe-14Co-10Ni基合金(16CoNi)在高温塑性变形过程中的动态再结晶行为及其热加工图进行了研究.试验结果表明,16CoNi合金的具有较高的动态再结晶温度,完全动态再结晶晶粒的平均尺寸随着Zener-Hollomon参数的增加而减小,并得到了动态再结晶晶粒尺寸与Z参数之间的定量关系.基于动态材料模型建立了16CoNi合金的热加工图(Processing Maps),当以0.1s~(-1)的应变速率,在1050℃变形时,合金的能量消耗效率达到最大值34%.     

5052铝合金板材热轧过程塑性变形及应力分布的三维热力耦合模拟

对5052铝合金板材热轧过程进行了三维热力耦合模拟,综合考虑热轧过程中轧制速度、变形温度、道次压下量和摩擦系数等因素对热轧过程中轧件变形区内塑性变形和应力分布的影响,建立了多参数的热力耦合热轧模型。结果表明,在轧件变形区内,因加工硬化与动态软化的综合作用,其流变应力呈典型的动态再结晶特征。在变形区内轧件表面因金属流动剧烈,其等效塑性应变和应变速率远远大于轧件心部,塑性变形显著。轧制速度是轧件温度场分布最重要的影响因素之一,轧制速度越大,轧件的温升就越高;而温度是影响等效应力大小的主要因素,温度升高和应变速率降低都使得流变应力降低。     

塑料盒模具型腔的数控加工

以一塑料盒注射模的设计与型腔的数控加工为例,详细地描述了运用CAD/CAM软件进行注射模设计和数控加工的工艺步骤及注意事项,缩短了模具制造周期,提高了模具的质量、尺寸精度和生产效率。     

新型Al-Zn-Mg-Cu合金高温塑性变形行为的加工图

采用Gleeble-1500热模拟机进行恒温和恒速压缩变形实验,变形温度为300～450℃和应变速率为0.001～1 s-1,研究了新型Al-Zn-Mg-Cu合金的高温塑性变形行为,并根据动态材料模型（DMM）建立了合金的加工图。结果表明,合金高温压缩变形均存在稳态流变特征且属于正应变速率敏感材料;在实验范围内,变形温度450℃、应变速率0.001 s-1的高温低应变速率变形区域的功率散耗率最大,约为0.61;合金热变形的最佳工艺参数为：热加工温度390～410℃,应变速率0.018～0.135 s-1。     

塑料模设计中的热切功能研究

介绍了塑料模设计中的热切功能,利用具有热切功能的模具加工的塑件无飞边,成型周期较短,对于大批量生产有非常重要的优势,不仅省去了后处理工具的使用,也节省了人力。     

Modeling of cutting forces in near dry machining under tool wear effect

A predictive model for the cutting forces in near dry machining, in which only a small amount of cutting fluid is used, is developed based on considerations of both the lubricating effect and the cooling effect. For the lubricating effect, with the material properties, lubricating parameters, and cutting conditions, the friction coefficient in near dry machining is calculated based on the boundary lubrication model for use in a modified Oxley's approach to determine the cutting forces. For the cooling effect in near dry machining, a moving heat source method is pursued to quantify the primary-zone shear deformation heating, the secondary-zone friction heating, and flank face air–oil mixture cooling. These two effects are considered collectively to estimate cutting forces under the condition of sharp tools. The predicted variables of flow stress, contact length, and shear angle obtained from the model are used to predict the cutting forces due to the tool flank wear effect based on Waldorf's model. Comparisons are made between predicted and experimental cutting forces for sharp tools and worn tools in the cutting of AISI 1045 with uncoated carbide tools. The results show that the proposed model provides average prediction errors of 14% in the tangential cutting force direction, 21% in the axial directions, and 30% in the radial directions within the experimental test condition range (cutting speeds of 45.75–137.25 m/min, feeds 0.0508–0.1016 mm/rev, and depth of cuts 0.508–1.016 mm). It is also found that the cutting forces in near dry machining are generally lower than those under dry machining condition. Under cutting speeds of 91.5 and 137.25 m/min, the deviations of the predicted forces between near dry machining and dry machining range from 5% to 39% for axial cutting forces, 3% to 36% for radial cutting forces, and 1% to 32% for tangential cutting forces. It suggests that the lubricating mechanism has a stronger effect on cutting forces than the cooling mechanism when cutting AISI 1045 with uncoated carbide tools.     

Study of cutting deformation in machining nickel-based alloy Inconel 718

During the process of high-speed machining nickel-based alloy the material presents serrated chips. An experiment involving quick-stop device was conducted. The chip root obtained in the experiment was presented in a metallographic graph. Through the analysis of metallographic graph, the physical features showed that shear angle is reduced and shear plane is converted into shear body when serrated chips formed were analyzed. Conditions under which a crack appeared and adiabatic shear that occurred were also analyzed. Based on the research, shear strain, shear strain rate and shear stress model in the adiabatic shear band were established. The effects of cutting parameters on character of the serrated chip were studied through observing chip metallographic graph.     

Upper bound analysis of oblique cutting: improved method of calculating the friction area

This paper describes further development of the upper bound analysis of oblique cutting with nose radius tools described previously by Adibi-Sedeh et al. [[1]] by incorporation of an improved method for calculating the friction area at the chip-tool interface. Previously, the friction area was obtained from the shear surface area assuming that the ratio of these areas is the same as in orthogonal machining. Our results showed that this led to overestimation of the effect of friction on the chip flow angle, thereby resulting in smaller changes in the chip flow angle with inclination angle as compared to experimental data. In the new approach, the chip-tool contact length is obtained from the length of the shear surface assuming that the ratio of the lengths is the same as in orthogonal machining and the friction area is calculated using this length. The chip flow angle predicted using the new approach shows much better agreement with experimental data. In particular, the dependence of the chip flow angle on the inclination angle is accurately reproduced. Upper bound analysis of oblique cutting using this new model for the friction area provides an elegant explanation for the relative influence of the normal and equivalent rake angles on the cutting force.     

大型"H"型钢压力矫直塑性变形失稳区域及侧压力的估算

针对国内首次研制的大型"H"型钢矫直机,提出了塑性变形区域及侧压力估算方法,并进行了分析与讨论,以供本行业科技人员参考与借鉴.     

On conversion of plastic work to heat during plastic deformation of tin-lead alloy and mild steel

The temperature rise caused by plastic deformation during the quick upsetting of tin-lead alloy and mild steel was investigated via experiments and numerical simulations aiming at a better understanding of the heat generation mechanism in friction welding. The results show that the compression amount and deformation temperature influence significantly the temperature rise during the upsetting of tin-lend alloy. The temperature rise increases with increasing the compression but decreases with increasing the deformation temperature. The simulation results are in good agreement with the experimental iaspection for Sn63A alloy. The simulation results of mild steel present a similar tendency with tin-lend alloy. Moreover, the temperature rise of mild steel at elevated temperatures is comparable to that of tin-lead alloy at low temperatures.     

镁合金铸造缺陷塑性变形弥合与修复过程

通过电子显微镜、透射电镜并结合塑性变形数值模拟,观察镁合金铸造缺陷(晶间缩松和缩孔)在变形过程中的形貌变化及缺陷附近应力分布,讨论塑性变形消除铸造缺陷的力学行为,提出镁合金铸造缺陷塑性变形弥合过程为:缺陷体积压缩→界面闭合→界面两侧基体相切变→界面附近再结晶→缺陷部分弥合.结果表明:变形过程中缺陷附近应力集中明显,变形后应力集中大大降低,部分铸造缺陷得以弥合与修复.     

高温塑性变形中孔隙性缺陷自修复机理

通过物理模拟研究20MnMo材料内部孔隙性缺陷的修复过程,建立了孔隙性缺陷高温修复的修复再结晶机理。将孔隙性缺陷修复分为3个阶段:修复再结晶晶粒形核准备、修复再结晶晶粒形核、修复再结晶晶粒长大和改建,其中修复再结晶形核主要存在3种方式。孔隙性缺陷修复再结晶机理的提出对深入研究塑性变形中缺陷修复以及塑性变形对性能的影响作用具有重要理论意义,对缺陷修复规律在生产实际中应用具有重要的实用价值。