基于C＋＋Builder的切削热预测

切削热及由此产生的切削温度,是造成刀具磨损和粘结破损的直接原因.切削温度直接影响刀具体内的热应力分布;尤其在切削过程中,刀具受到周期性的热冲击,易使硬质合金刀片产生热裂纹而导致破损,对车削加工过程中的切削热进行仿真具有重要的理论研究与实际应用价值.为此,基于C+ +Builder软件仿真了工件的实际加工过程,并对切削热进行了动态仿真.为数控车削中切削热仿真的进一步研究提供了理论指导依据.     

刀具补偿与数控工艺分析

系统地论述了刀具半径补偿问题,结合下刀、切入、切出、抬刀等数控铣削加工工艺,详细阐述了刀具半径补偿建立、启用和取消的基本方法和注意事项,分析了刀具半径补偿类别和顺铣逆铣工艺与走刀路线关系,并从运动学、刀补理论说明了刀具大小选取原则。     

端铣边缘毛刺生成机理的研究

研究了高效率端铣边缘毛刺的生成机理，分析讨论了毛刺类型及其与切削参数、几何角度、刀具磨损因素的关系后，指出端铣边缘毛刺的生成与端铣刀齿切入、切出方式有关，并提出了减少和控制毛刺形成的工艺措施。     

基于声信号小波分析的刀具破损监测

提出了基于切削声信号的刀具破损监测方法。通过对破损声信号进行小波分析,提取出了与刀具破损具有相应关系的特征频带,去除了冲击声信号、刀具切入声信号等与刀具破损具有相似特征的声信号干扰,通过设定合适的阈值,能够较好地监测刀具的破损。这种监测方法为刀具的破损监测提供了一种新的途径。     

新型陶瓷工具LD-1的抗破损性能研究

研究了新型陶瓷工具LD－1端铣淬硬钢时的抗破损性能。结果表明：热裂纹是造成刀具破损的重要原因之一。这种刀具材料的抗破损性能明显优于其它Al2O3－TiC系陶瓷刀具材料。     

WC颗粒增强钢基复合材料热疲劳裂纹扩展方式与机理研究

以复合电冶熔铸技术制备的WC颗粒增强钢基复合材料为研究对象,通过热震试验,研究热裂纹的扩展方式、途径和基本规律,并分析了热疲劳机理。结果表明,萌生热裂纹需要一定的孕育期,五至十次循环后,裂纹就会萌生在缺口根部倒角圆弧与两边的切点处。热疲劳裂纹的扩展方式分为通过碳化物和钢基体的分界面扩展、贯穿大颗粒WC和大块碳化物扩展、沿网状碳化物链扩展、穿越WC小颗粒聚集区扩展、穿过鱼骨状碳化物扩展和穿越钢基体扩展。热疲劳裂纹的扩展可分为弯曲扩展或分岔扩展,裂纹扩展前方的孔洞、微裂纹和热应力聚集共同作用导致了热疲劳裂纹的延伸。热疲劳裂纹扩展机理是增强颗粒、钢基体、组织缺陷和热应力的综合作用结果。     

用球头铣刀加工模具曲面时刀具路径的优化

以球头铣刀产生平行走刀精加工刀具路径为例,从行距、步长、曲面分区加工、切入切出点确定、行间和层间附加圆滑转接等方面对刀具路径的优化进行研究,指出行距和步长的选择应综合考虑,以兼顾生产效率和曲面质量。当曲面曲率半径变化较大时,应分区确定行距和步长。切入切出点以及刀路间圆滑过渡不仅能避免刀具过早失效,且能提高模具表面质量。     

PCD刀具高速干式切削铜合金的磨损研究

使用PCD刀具对锡青铜合金材料进行高速干式切削试验,分别采用扫描电镜（SEM）、X射线能谱仪（EDS）对刀具的磨损形貌进行观察和磨损区域化学成分进行分析,并以此研究了PCD刀具的磨损机理。结果表明:在高速干式切削条件下,PCD刀具主要表现为前刀面的片状剥落和后刀面的轻微破损;同时还伴随着机械应力和热应力冲击下的脆性破损,出现崩刃、切削刃整体断裂以及前后刀面的大面积剥落。刀具磨损的主要原因是高温作用下的氧化磨损和扩散磨损。      

高铬铁素体耐热钢的热疲劳与相变

试验研究了高铬铁素体耐热钢的热疲劳与γ、α相变的关系，发现有相变的热循环热疲劳裂纹发生在试样外缘，裂纹长度及变形量均较小，无相变的热循环疲劳裂纹发生在试样中心，裂纹长度及变形量均较大，无相变的Ｃｒ２６钢表面呈严重的龟裂现象，试验证明，相变并不加剧高铬铁素体耐热钢的热疲劳破坏，其机理是相变应力部分抵消热循环过程中产生的热应力。     

金属凹模中半埋藏环形裂纹电磁热止裂的数值模拟

采用有限元方法研究了带半埋藏环形裂纹的Cr12MoV圆筒形凹模的电磁热止裂问题 ,建立了超强脉冲电流放电瞬间 ,环形裂纹尖端附近电场、温度场和热应力场的藕合关系。数值模拟分成热—电藕合 (焦耳热问题 )和热—机械藕合两个过程来实现 ,通过数值解析轴对称模型 ,给出了脉冲放电瞬间Cr12MoV凹模中电流—温度—热应力的求解过程 ,得到了脉冲放电瞬间带半埋藏环形裂纹凹模的温度场和热应力场。     

陶瓷刀具断续车削淬硬钢失效形态研究

采用Al_2O_3/Ti(C,N)陶瓷刀具进行淬硬钢的断续车削正交试验,对不同切削速度下刀具的失效形态进行了对比。结果表明,低速时,刀具的失效形态主要是崩刃和前刀面剥落,疲劳破损影响较小。随着切削速度的增加,疲劳破损对刀具的影响逐渐增大。高速时,疲劳裂纹扩展引起的破损成为刀具主要失效形式。在不同切削速度下,刀具内部的应力水平不同,导致裂纹扩展速率及裂纹方向有所差异,疲劳特征则表现出不同形式。低速时疲劳特征表现为疲劳条带,而高速时的疲劳特征通常为疲劳弧线。     

板坯火焰切割机故障分析及改造

某钢厂连铸车间K7043火焰切割机机械系统常见故障表现为提升机构传动箱体断裂;介质系统常见故障表现为管道元器件堵塞、切割枪堵塞;电气系统常见故障表现为编码器故障、电缆损坏、接近开关故障。对切割机常见故障进行分析,表明提升机构传动箱体断裂为箱体存在应力集中造成;管道元器件堵塞为煤气中焦油析出造成,切割枪嘴堵塞为切割热态板坯渣子飞溅堵塞造成;电气系统常见故障多由于切割机工况复杂造成。随后对火焰切割机进行了适应性改造,提升机构传动箱体应力集中现象得到消除,介质系统管路元器件堵塞情况得到改善,缩短了切割枪嘴更换时间,降低了电气元件故障率。对其实际运行情况进行观察,切割机故障率得到明显降低。     

Study of the mechanism of nanoscale ductile mode cutting of silicon using molecular dynamics simulation

In cutting of brittle materials, it was observed that there is a brittle-ductile transition when two conditions are satisfied. One is that the undeformed chip thickness is smaller than the tool edge radius; the other is that the tool cutting edge radius should be small enough—on a nanoscale. However, the mechanism has not been clearly understood. In this study, the Molecular Dynamics method is employed to model and simulate the nanoscale ductile mode cutting of monocrystalline silicon wafer. From the simulated results, it is found that when the ductile cutting mode is achieved in the cutting process, the thrust force acting on the cutting tool is larger than the cutting force. As the undeformed chip thickness increases, the compressive stress in the cutting zone decreases, giving way to crack propagation in the chip formation zone. As the tool cutting edge radius increases, the shear stress in the workpiece material around the cutting edge decreases down to a lower level, at which the shear stress is insufficient to sustain dislocation emission in the chip formation zone, and crack propagation becomes dominating. Consequently, the chip formation mode changes from ductile to brittle.     

Fatigue failure of coated carbide tool and its influence on cutting performance in face milling SKD11 hardened steel

Failure patterns of coated carbide tool were investigated by high-speed face milling of the hardened steel SKD11. Tool failure surface morphology, cutting force and machined surface roughness were also analyzed to reveal the failure mechanisms. The results indicated that the dominant failure pattern of coated carbide tool was breakage. The primary mechanism of tool breakage was fatigue fracture. Under different cutting speeds, the distinctive morphologies of fatigue fracture were presented on the failure surfaces. At low cutting speeds, many fatigue sources were observed on the rake face. The distance between fatigue sources and tool nose was approximately two times of the depth of cut. With the increase of cutting speed, the fatigue striations and riven patterns were observed at the fracture surface. In addition, the fatigue steps and crack deflection were found under high cutting speeds. The main fracture mode was intergranular fracture at lower cutting speeds. However, it was transgranular fracture at higher cutting speeds. Furthermore, the irregular fracture surfaces at low cutting speeds and at high cutting speeds contribute to a larger cutting force increment compared with the medium cutting speeds. The increment of surface roughness in the initial and severe wear stages was lower than that in the steady wear stage, while the deviation of surface roughness was relatively large.     

Molecular dynamics modelling of brittle–ductile cutting mode transition: Case study on silicon carbide

The mechanism of brittle–ductile cutting mode transition has received much attention over the past two decades. Due to the difficulties in directly observing the cutting zone during the brittle–ductile cutting mode transition by experimental techniques, many molecular dynamics (MD) studies have been conducted to investigate the atomicscale details of the phenomena, e.g. phase transformation, stress distribution and crack initiation, mostly under nanoscale undeformed chip thicknesses. A research gap is that direct MD modelling of the transition under practical undeformed chip thicknesses was not achieved in previous studies, due to the limitations in both computation capability and interaction potential. Important details of the transition under practical undeformed chip thicknesses thereby remain unclear, e.g. the location of crack formation and the stress distribution. In this study, parallel MD codes based on graphics processing units (GPU) are developed to enable large-scale MD simulations with multi-million atoms. In addition, an advanced interaction potential which reproduces brittle fracture much more accurately is adopted. As a result, the direct MD simulation of brittle–ductile cutting mode transition is realised for the first time under practical undeformed chip thicknesses. The MD-modelled critical undeformed chip thickness is verified by a plunge cutting experiment. The MD modelling shows that tensile stress exists around the cutting zone and increases with undeformed chip thickness, which finally induces brittle fractures. The location of crack formation and direction of propagation varies with undeformed chip thickness in the MD simulations, which agrees with the surface morphologies of the taper groove produced by the plunge cutting experiment. This study contributes significantly to the understanding of the details involved in the brittle–ductile cutting mode transition.     

优化硬质合金涂层微槽车刀后刀面磨损失效对比研究

后刀面磨损量是衡量刀具寿命的重要指标,对刀具寿命其决定性作用。针对前期研制的优化硬质合金涂层微槽车刀,文章通过切削实验和理论分析,研究了优化微槽车刀和原车刀在切削过程中刀具后面磨损情况。从两车刀后刀面磨损失效现象的对比分析发现,在相同的切削时间内,微槽车刀后刀面磨损程度低于原车刀,在达到几乎相同的磨损程度情况下,微槽车刀经历的切削时间长于原车刀,即原车刀相较于微槽车刀更容易出现后刀面磨损失效。研究结果为优化硬质合金微槽车刀磨损失效机理的深入研究提供理论依据。     

DLC膜涂层硬质合金刀具的研究进展

类金刚石(DLC)膜涂层刀具的硬度高、摩擦系数低、耐摩擦和耐腐蚀性能强、抗粘结性能好,并且可以用来制作复杂、异型刀具,是未来刀具的一个重要发展方向。本文介绍了DLC膜的表面显微结构和Raman光谱并列举了DLC的制备方法 (包括磁控溅射、离子束沉积、脉冲激光沉积、真空阴极电弧沉积、等离子体增强型化学气相沉积)与分类。从酸蚀法、施加过渡层、表面微喷砂处理和掺杂4个方面分析如何提高膜基结合力,探讨了DLC膜的摩擦性能受湿度、温度和加工条件的影响。例举了几个国内外DLC涂层硬质合金刀具的使用范例,指出了目前研究工作的不足之处,提出了下一步研究工作的重点是优化DLC膜的制备工艺、提高膜基结合力和热稳定性以及加强DLC涂层硬质合金刀具的磨损机理研究。     

碳纤维增强热塑性复合材料螺旋铣磨制孔损伤研究

目的 研究碳纤维增强热塑性复合材料(CFRTP)螺旋铣磨制孔的切削温度和切削力的变化趋势,以及典型制孔损伤的特点,并分析切削温度的下降对制孔损伤的影响。方法 采用螺旋铣磨的方法开展CFRTP的制孔试验研究,通过改变工艺参数研究切削温度、切削力的变化趋势,分析各类典型制孔损伤的特点、形成原因及随工艺参数的变化情况,并研究添加冷却辅助降低切削温度对抑制制孔损伤的效果。结果 随着刀具自转转速、公转转速和螺距的升高,切削温度分别升高了约46.43%、12.06%和95.97%;切削力随着自转转速的升高而降低,随着公转转速和螺距的升高而增大。当螺距达到0.45mm时,轴向力会有所下降。入口损伤和出口损伤主要以毛刺为主,损伤会随着各工艺参数的升高而加剧,孔壁损伤主要表现为涂覆、变形、裂纹等3种形式。添加冷却辅助后,制孔质量得到显著提高,高温下的刀具涂覆问题基本解决。结论 切削温度是影响CFRTP制孔质量的主要因素,切削温度的升高导致树脂基体软化,使得切屑形貌从粉末状转变为连续薄片状,进而对切削力产生影响,树脂软化对制孔损伤有着明显的影响。冷却辅助能够明显地降低切削温度,从而起到抑制损伤的作用。     

陶瓷刀具断续车削淬硬钢切削力和切削温度的有限元分析

为揭示Al2O3/(W,Ti)C陶瓷刀具断续车削淬硬钢时的切削力、刀具温度以及刀具应力的变化规律及相互关系,采用有限元方法进行金属切削仿真。仿真结果表明,断续车削过程中,刀具承受十分明显的周期性机械载荷冲击与热载荷冲击;单个切削周期内机械载荷与热载荷的变化规律体现了两者的密切相关性以及时间上的不一致性;由于剪切角偏转的影响,刀具最大主应力显著增大,所以切出过程对刀具破坏的作用尤为严重。     

Crack initiation in relation to the tool edge radius and cutting conditions in nanoscale cutting of silicon

In cutting of brittle materials, experimentally it was observed that there is a ductile–brittle transition when the undeformed chip thickness is increased from smaller to larger than the tool cutting edge radius of the zero rake angle. However, how the crack is initiated in the ductile–brittle mode transition as the undeformed chip thickness is increased from smaller to larger than the tool cutting edge radius has not been fully understood. In this study, the crack initiation in the ductile–brittle mode transition as the undeformed chip thickness is increased from smaller to larger than the tool cutting edge radius has been simulated using the Molecular Dynamics (MD) method on nanoscale cutting of monocrystalline silicon with a non-zero edge radius tool, from which, for the first time, a peak deformation zone in the chip formation zone has been found in the transition from ductile mode to brittle mode cutting. The results show that as the undeformed chip thickness is larger than the cutting edge radius, in the chip formation zone there is a peak deformation depth in association with the connecting point of tool edge arc and the rake face, and there is a crack initiation zone in the undeformed workpiece next to the peak deformation zone, in which the material is tensile stressed and the tensile stress is perpendicular to the direction from the connecting point to the peak. As the undeformed chip thickness is smaller than the cutting edge radius, there is no deformation peak in the chip formation zone, and thus there is no crack initiation zone formed in the undeformed workpiece. This finding explains well the ductile–brittle transition as the undeformed chip thickness increases from smaller to larger than the tool cutting edge radius.