预应力淬硬磨削工件表面层质量试验研究

从抗疲劳制造与绿色制造的观念出发,融合预应力磨削与磨削淬硬技术原理,提出了将残余应力控制、表面淬火及磨削三者集成于一体的预应力淬硬磨削技术理论与方法。对45钢试件进行了预应力淬硬磨削加工试验,以工件淬硬层表面残余应力、硬度及粗糙度为研究对象,与相同条件下的磨削淬硬工艺试验结果进行了对比分析。结果表明：预应力淬硬磨削工艺可增大工件表面残余压应力,减小拉应力,其工件表面残余应力状态优于磨削淬硬工艺;预应力淬硬磨削工件表面硬度可以达到基体硬度的3倍左右,而工件表面粗糙度小于磨削淬硬工艺工件表面粗糙度。因此,在相同的加工条件下,预应力淬硬磨削工艺比磨削淬硬工艺具有更好的抗疲劳性、耐腐蚀性及表面完整性。     

硬态切削对GCr15耐磨性能影响的研究

针对硬态切削过程中工件被加工表面出现白层 ,表层组织和硬度均发生变化的现象 ,用PCBN刀具硬态切削和传统磨削的GCr15工件的耐磨性进行了对比试验。试验发现 ,在高相对滑动速率下 ,磨削加工的试件磨损量很小 ,耐磨性能明显优于车削加工的试件 ;而低相对滑动速率情况下 ,即使高速重载 ,车削加工试件与磨削加工试件的磨损量都很小 ,车削加工试件的耐磨性甚至优于磨削加工试件     

硬态干式切削机理及技术研究综述

介绍了硬态干式切削加工刀具材料的特性，工件材料的特点，淬硬钢切削时切屑形态及其形成机理，表面完整性如白层，残余应力分布和表面粗糙度等与切削参数的关系，讨论了最小量切削润滑液使用的概念和要求，综合国内外的研究进展论述了硬态切削机理和相关技术，有益于加速我国硬态切削的实施。     

硬态切削工件表面白层厚度预测方法

硬态切削过程中产生了高的机械载荷和热载荷,工件表面易产生白层组织,研究硬态切削工件表面白层的形成机理并对白层厚度进行建模预测,对于改善硬态切削加工技术具有指导意义。以探究白层形成机理为研究目标,综合运用弹塑性力学、热力学和材料相变理论,建立热力耦合的硬态切削模型,模拟了硬态切削过程中的温度场和应力场,分析了工件表面白层形成的组织转变过程,以热力影响下的材料相变温度作为白层形成的判据,建立了白层厚度的预测方法,并以轴承钢GCr15为研究对象,预测了不同切削参数下白层的厚度,对预测结果加以对比验证。研究结果表明:对于硬态切削工件表面白层的形成,基于相变理论的白层厚度预测方法是可行的。     

轴承圈加热切削加工表面质量研究

针对轴承圈易出现疲劳破坏的问题,提出采用预加热硬态切削加工轴承圈外表面的方法。普通硬态切削和预加热硬态切削试验结果表明,将工件内圈预先加热到160℃进行硬态切削加工,有助于减小加工表面的粗糙度,由于内圈加热减小了轴承圈内外表面的温度差,故加工后的表面残余应力显著减小,其值可达-50MPa,加工得到的表面纹理清晰,形貌光滑、规整,刀具进给运动轨迹清晰;加热切削得到的是均匀的锯齿形切屑,并且切屑形态呈螺旋状,与普通硬态切削相比,加热切削过程较为平稳,说明加热切削可获得良好的表面完整性,且不会引来额外的加工硬化。     

高速硬态切削工件表层显微硬度与白层研究

高速和硬态切削使得工件已加工表面及其表层中出现特有的现象.研究结果表明,切削速度和材料硬度是决定高速和硬态切削工件已加工表面及其表层结构形成的主要影响因素,切削热使被切削材料产生高温软化,刀具挤压摩擦使被切削材料变形加剧,工件表层材料显微硬度分布发生改变,出现了硬脆的白层组织,白层组织的出现将对零件的使用将造成不利影响.随着切削用量和材料硬度增大,切削变形增大,切削温度升高,白层厚度增大,工件表层材料显微硬度提高.抑制白层组织产生的措施是对工件降温.     

利用磨削热对工件表面热处理的研究

本文研究讨论能否利用磨削热对非淬硬钢进行表面热处理,即同时实现磨削加工与表面淬火两个工艺,既提高生产效率,又降低生产成本。选取齿条成形加工作为研究对象,综合考虑材料的热物性参数、对流换热、相变潜热等因素,通过数值仿真方式,计算加工过程中工件温度场分布情况。根据金属相变理论,推断出工件淬硬层深度。设计齿条成形磨削实验,对加工后的工件表面淬硬层深度进行测量,与计算结果具有较好的一致性,证明温度场仿真模型与淬硬层推断方法的正确性,同时验证了利用磨削热对工件表面进行热处理的可行性。     

碳化硅高速磨削表面完整性研究

针对碳化硅的应用日益扩大,但它质地硬脆,高效率高质量加工总遇到障碍的情况,采用高速磨削工艺,研究了砂轮速度对磨削力和材料去除率的演变规律,开展了磨屑形态、磨削表面和亚表面形貌观察,及表面粗糙度、残余应力等一系列试验。结果表明:高速磨削能降低磨削力和磨削热,减小磨削损伤层,成比例提高砂轮速度和工件速度能增进表面完整性和提升加工效率。基于磨削层表面粗糙度和深度残余应力的检测,表明:在碳化硅高速磨削中,存在脆-延性去除机理的转化过程;高速磨削有望成为高效率高质量磨削工程陶瓷碳化硅的一条有效途径。     

磨削白层厚度与磨削力的实验研究

高硬难加工金属材料在磨削加工过程中,工件表面通常会产生一些硬度很高的白层,白层在很大程度上影响了已加工表面质量和完整性.通过平面磨削淬硬GCr15钢,设计正交试验来研究磨削参数对磨削力和白层厚度的影响规律;分析磨削力与白层厚度之间的关系并对结果进行讨论;为降低并抑制白层的产生提供实验依据.     

超声振动螺线磨削表面微观形貌建模与仿真研究

为了实现高效率、高质量、低损伤的硬脆材料加工,对工件或砂轮同时施加砂轮轴向和径向的超声振动,该方法的显著特点是磨粒切削轨迹呈三维空间螺旋线型,将其定义为超声振动螺线磨削方法。在磨削工艺和二维超声振动的多参数共同作用下,材料去除机理产生复杂变化,表面微观形貌创出过程变得极其复杂。为此,提出一种超声振动螺线磨削加工表面数值仿真方法。基于超声振动螺线磨削几何映射关系,建立磨粒相对工件的空间螺旋线切削运动模型,进而给出超声振动螺线磨削加工表面生成模型,模拟出普通磨削和超声振动磨削的三维表面微观形貌,对比分析了超声振动对表面形成过程的影响规律。最后将仿真表面与磨削试验表面对比,发现两者微观形貌特征规律基本一致,验证了仿真方法的正确性和有效性。     

Surface Integrity and Machineability in Intermittent Hard Turning

Despite the large amount of research on hard turning, there are few results on intermittent hard turning. In this paper, the feasibility of internal intermittent hard turning has been investigated. First, the cutting tools with different cubic boron nitride (CBN) contents were evaluated, based on machineability: tool wear, surface roughness, and cutting forces. In the case of intermittent turning, low CBN content tools had better machineability than high CBN content tools. The depth of the machining damaged layer and the magnitude and distribution of residual stress were evaluated. The experimental results showed that intermittent hard turning can produce surface integrity which is good enough for replacing the grinding process.     

旋转超声磨削加工中刀具结合剂类型与加工性能的关系

实验分析了硬脆材料旋转超声磨削过程中刀具结合剂类型对加工性能的影响以便提高加工精度和加工表面的完整性.首先,采用能谱分析研究了铁基、陶瓷基和青铜基3种超声振动刀具中结合剂与金刚石颗粒的把持形式,并根据相同加工工艺条件下刀具磨损形式确定了把持力大小.然后,结合超声振动刀具特性,通过旋转超声磨削加工实验研究刀具结合剂类型与切削力、刀具磨损量、加工表面完整性的关系,并对实验结果进行了分析.实验结果表明:相对于陶瓷基和青铜基结合剂超声振动刀具,铁基结合剂超声振动刀具把持力最大,Z轴切削力平均值最小(为46.8 N);加工18 000 mm3材料后,刀具轴向磨损量最小(为0.1 mm);而陶瓷基结合剂超声振动刀具加工表面质量最好,表面粗糙度最大值为21.79 μm.结果证实铁基超声振动刀具适用于粗加工,陶瓷基超声振动刀具则适用于精加工.     

硬切削中刀具材料的选择

硬切削作为“以切代磨”的新工艺是一种高效的切削技术,其加工质量及加工精度应达到磨削的要求,这就对刀具提出了较高的要求。文中对硬切削中所用刀具材料及其选择进行了阐述。     

HARD TURNING PLUS GRINDING–A COMBINATION TO OBTAIN GOOD SURFACE INTEGRITY IN AISI O1 TOOL STEEL MACHINED PARTS

The establishment of adequate machining guidelines requires the study of several factors (residual stresses, roughness, hardness, microstructural changes, etc.) that define the surface integrity generated in the part by a machining operation. This work studies the surface integrity generated in AISI O1 tool steel by four hard turning (conventional, laser assisted, MQL and conventional with worn tool) and two grinding (production and finishing) processes, as well as by a combined machining process (conventional hard turning + finishing grinding). Hard turning generates tensile stresses and strong structural changes in the machined surface while grinding causes compressive stresses and negligible structural changes. Below the surface, grinding generates slightly tensile or nearly null stresses whereas turning generates strong compressive stresses. The results obtained show that an optimum machining process would imply the combination of hard turning plus a slight final grinding.     

HARD TURNING PLUS GRINDING-A COMBINATION TO OBTAIN GOOD SURFACE INTEGRITY IN AISI O1 TOOL STEEL MACHINED PARTS

The establishment of adequate machining guidelines requires the study of several factors (residual stresses, roughness, hardness, microstructural changes, etc.) that define the surface integrity generated in the part by a machining operation. This work studies the surface integrity generated in AISI O1 tool steel by four hard turning (conventional, laser assisted, MQL and conventional with worn tool) and two grinding (production and finishing) processes, as well as by a combined machining process (conventional hard turning + finishing grinding). Hard turning generates tensile stresses and strong structural changes in the machined surface while grinding causes compressive stresses and negligible structural changes. Below the surface, grinding generates slightly tensile or nearly null stresses whereas turning generates strong compressive stresses. The results obtained show that an optimum machining process would imply the combination of hard turning plus a slight final grinding.     

精密硬车加工轴承套圈的表面完整性试验研究

针对磨削加工中套圈精密加工存在的不足,进行精密硬车削加工轴承套圈新工艺的开发,通过加工试验分析了精密硬车加工轴承套圈的表面完整性,探究了基准面平面度、刀具磨损量等工艺参数与加工精度的对应关系。基于精密硬车削套圈试样的表面粗糙度、沟道圆度、显微硬度、热损伤、金相组织、残余应力分布、加工效率等方面的研究,得出了精密硬车削可达到磨削加工精度的结论,且金相组织稳定,不易存在热损伤,具有可控的残余应力分布和较高的加工效率,有利于产业化生产高精密轴承。利用磁性卡盘装夹套圈,分析试样基准面平面度对精密硬车削套圈沟道圆度的影响,发现提高基准面平面度可以有效提高加工套圈的沟道圆度;分析了刀具磨损对硬车削套圈加工精度的影响,得出在精密加工阶段刀具磨损量是控制套圈圆度的重要监控工艺参数的结论。     

超硬磨粒CBN砂轮的磨削性能

本研究的目的是评价三种砂轮在磨削高速工具钢时的磨削性能。采用ABWOOD平面磨床,在不同磨削条件下对材料去除率,比磨削能和磨削表面的热损伤进行了实验研究,同时借助专用装置采集了磨削过程中砂轮的动态磨损数据。研究结果表明,超硬磨粒CBN砂轮磨削M2高速钢时磨性能最佳,这种砂轮在硬铁族金属加工领域具有良好的应用前景。     

THE SURFACE INTEGRITY IN MACHINING HARDENED STEEL SKD11 FOR DIE AND MOLD

Milling cutters were evaluated by tool wear, cutting force and vibration. Surface integrity of grinding and milling were investigated by comparing residual stress distributions, metallurgical structure, hardened layer depth and surface roughness. And influence of cutting tool wear on surface integrity was investigated. Experimentations revealed that the preferable surface integrity would be obtained if the proper milling cutter as well as a small wear criterion were adopted to avoid the advent of tempered martensite. The research results pointed out the feasibility of taking milling as the finish machining process instead of grinding in machining hardened steel with high efficiency.     

THE SURFACE INTEGRITY IN MACHINING HARDENED STEEL SKD11 FOR DIE AND MOLD

Milling cutters were evaluated by tool wear, cutting force and vibration. Surface integrity of grinding and milling were investigated by comparing residual stress distributions, metallurgical structure, hardened layer depth and surface roughness. And influence of cutting tool wear on surface integrity was investigated. Experimentations revealed that the preferable surface integrity would be obtained if the proper milling cutter as well as a small wear criterion were adopted to avoid the advent of tempered martensite. The research results pointed out the feasibility of taking milling as the finish machining process instead of grinding in machining hardened steel with high efficiency.     

Tool-wear mechanisms in hard turning with polycrystalline cubic boron nitride tools

Hard turning is a turning operation performed on high strength alloy steels (45R_a0.1 μm). Extensive research being conducted on hard turning has so far addressed several fundamental questions concerning chip formation mechanisms, tool-wear, surface integrity and geometric accuracy of the machined components. The major consideration for the user of this relatively newer technology is the quality of the parts produced. A notable observation from this research is that flank wear of the cutting tool has a large impact on the quality of the machined parts (surface finish, geometric accuracy and surface integrity). For components with surface, dimensional and geometric requirements (e.g. bearing surfaces), hard turning technology is often not economical compared with grinding because tool-life is limited by the tolerances required (i.e. high flank wear rate).

The aim of this paper is to present the various modes of wear and damage of the polycrystalline cubic boron nitrides (PCBN) cutting tool under different loading conditions, in order to establish a reliable wear modeling. Flank wear has a large impact on the quality of the parts produced and the wear mechanisms have to be understood to improve the performance of the tool material, namely by reducing the flank wear rate. The wear mechanisms depend not only on the chemical composition of the PCBN, and the nature of the binder phase, but also on the hardness value and above all on the microstructure (percentage of martensite, type, size, composition of the hard phases, etc.) of the machining work material. The proposed modeling is in a generalized form of the extended Taylor’s law allowing to prediction of the tool-life as a function of the cutting parameters and of the workpiece hardness. The effects of these factors on tool-wear, tool-life and cutting forces are discussed in the paper.