碳纤维复合材料小孔加工的试验研究

针对碳纤维复合材料小孔加工比常规尺寸的孔加工更困难,制孔质量和尺寸精度难易保证的问题,采用硬质合金麻花钻进行碳纤维增强树脂基复合材料直径3mm小孔的钻削试验,研究工艺参数、刀具磨损对切削力和制孔质量的影响。结果表明:转速和进给速度对制孔轴向力和孔径误差均有显著影响;回归分析得到了轴向力与转速和进给速度之间的关系式;转速对孔径误差的影响大于进给速度的影响;硬质合金麻花钻加工碳纤维复合材料的合格孔数为30个,孔径误差随刀具磨损量的增大而增大。研究结果可以对碳纤维复合材料小孔加工的切削力进行预测,为加工参数和刀具寿命的合理选择提供试验依据。     

T800级碳纤维复合材料螺旋铣磨制孔工艺研究

碳纤维复合材料由于具备强度高、各向异性、层间强度低等特点,加工时易产生毛刺、分层等损伤,是典型的难加工材料。本文针对碳纤维复合材料制孔出入口处易损伤的问题,对金刚石磨头端面进行锥角过渡改进设计,并采用螺旋铣磨工艺,探索T800级碳纤维复合材料轻量化低损伤加工方法,通过正交试验设计研究了刀具结构和工艺参数对制孔质量的影响。试验结果表明:与传统金刚石磨头相比,金刚石磨头端面锥角在60°时,轴向力从75N降至53.5N,降幅28.7%,径向力从35.5N升至128N,涨幅264%,并能获得较为理想的制孔质量,可以实现T800级碳纤维复合材料轻量化加工。     

复合材料叠层结构制孔技术

针对碳纤维复合材料与钛合金叠层制孔质量差、效率低的问题,通过有限元仿真计算和切削试验相结合的方法,研究了碳纤维复合材料与钛合金叠层制孔切削机理,分析了面向刀具结构、几何参数和制孔工艺参数等因素,建立刀具结构、切削力、刀具磨损等数学模型,实现了碳纤维复合材料叠层制孔的刀具设计技术。     

单向带复合材料ADU制孔刀具设计及验证

针对复合材料叠层ADU钻孔刀具开发测试周期长、样刀试制成本高以及制孔易损伤等问题,利用数控加工设备和ADU工具以相同的加工参数测试不同刃型的直柄硬质合金刀具,比较刃型结构对复合材料制孔质量的影响,确定最优结构后定制螺纹柄刀具开展ADU制孔验证,寻求一种便捷快速、成本较低的刀具开发路径,解决复合材料ADU制孔损伤问题,为复合材料叠层ADU钻孔刀具的选型测试提供参考,提高刀具开发效率,降低生产研发成本。     

TiSiC涂层钻头钻削CFRP/TC4钛合金叠层材料的研究

为解决碳纤维复合材料/钛合金叠层材料制孔刀具使用寿命短的问题,本文提出采用Ti Si C涂层来提高刀具耐用度,并研究了Ti Si C涂层钻头钻削碳纤维复合材料/钛合金叠层材料时的轴向力、刀具磨损和孔出口质量。结果表明,Ti Si C涂层刀具能减小钻削钛合金的轴向力,延长刀具寿命和改善孔出口质量,且制孔一致性良好,有利于提高钻孔质量和刀具寿命。     

C/E复合材料螺旋铣削制孔方法抑制缺陷产生的机理

传统钻削加工碳纤维/环氧树脂(Carbon/epoxy,C/E)复合材料时容易产生加工缺陷,而螺旋铣削作为一种新的制孔方法在航空材料的加工中逐渐受到关注。为分析螺旋铣削制孔方法抑制缺陷产生的机理,以传统钻削加工为参照,分别利用螺旋铣削及传统钻削两种方法对C/E复合材料进行制孔试验,并对螺旋铣削与传统钻削刀具的运动轨迹进行分析。在具有相同的加工效率及刀具切削速度的基础上,对两种加工方法的加工参数进行优化。进行制孔对比试验,并对制孔过程中的切削温度、切削力及加工质量进行检测与分析。结果表明,切削温度是影响C/E复合材料制孔质量的重要因素,且由于螺旋铣削制孔时的切削温度显著低于传统钻削制孔温度,因此螺旋铣削制孔质量明显优于传统钻削制孔质量。螺旋铣削制孔时的切削温度较传统钻削时降低69℃以上,降幅大于36%,因此有效避免了制孔出口处的撕裂及分层现象。     

复合叠层材料制孔过叠层阶段声发射分析

复合叠层材料钻孔加工时,伴随着刀具的磨损,会产生丰富的声发射信号。刀具在加工叠层材料接触面时会引起声发射信号突变,为研究该过程信号的突变规律,采用硬质合金钻头与碳纤维复合材料-铝合金叠层板件开展了一系列实验,采集制孔过程中刀具的声发射信号,对信号进行了时频域多分辨率分析。研究表明,在刀具从复合材料加工至铝合金过程中,信号强度逐渐降低,高频段成份逐渐增加。     

钻头几何角度对CFRP和钛合金叠层制孔的影响

针对碳纤维复合材料(CFRP)与钛合金叠层结构钻孔刀具寿命低、出入口质量不易保证、影响加工质量和制孔效率等问题。以钻头螺旋角、外缘后角和顶角为主要研究对象,进行试验方案设计,揭示钻头几何角度对叠层结构制孔切削力及出入口质量的影响规律,表明:碳纤维复合材料与钛合金叠层结构制孔的钻头最佳几何角度:螺旋角25°左右,顶角140°左右,外缘后角12°左右。     

复合材料成型分层缺陷在钻削横刃挤压阶段的扩展行为

碳纤维增强复合材料由于具有高比强度、高比模量等优异性能,广泛应用于先进装备的承力构件中。此类复材构件在铺放固化成型过程中易产生随机分布的分层缺陷,若缺陷区域与构件连接孔加工区域交叠,将使制孔损伤产生机制更加复杂、加工质量更难以保证。为保障碳纤维复合材料构件的加工质量,揭示成型分层缺陷对制孔质量的影响机制,针对钻削过程中成型分层缺陷的动态演化行为进行研究,得到其在钻削过程中轴向力最大的横刃挤压阶段发生扩展的临界条件以及扩展长度的计算方法。基于此,结合钻削试验对预埋分层缺陷在制孔过程中的扩展行为进行在线观测,最终获得刀具作用位置对缺陷扩展行为的影响。该研究成果将为后续有关复材成型缺陷在钻削过程中扩展的抑制方法研究提供基础,也将为丰富复材损伤抑制理论作出贡献。     

航空叠层材料制孔技术研究现状与发展趋势分析

为有效的减轻飞机质量和燃料成本,复合材料/金属叠层材料已广泛应用于现代飞机的高科技部件。综述了包括CFRP/铝和CFRP/钛叠层材料制孔技术的最新进展,主要涵盖了制孔加工刀具、金属切屑排除、金属材料毛刺、切削温度等方面。文献综述表明,有多种方式可改善加工品质:1)改善航空叠层材料的制孔刀具;2)有效的排除金属切屑,减少对复合材料的损伤;3)预防和减少钛合金和铝合金毛刺的形成;4)有效的冷却方式,减少复合材料的热损伤。     

高速数控加工中NURBS曲线拟合及插补技术的研究

通过分析现代数控系统中自由曲面插补算法的特点,提出了基于最小二乘法的NURBS曲线拟合算法和基于弧长参数补偿的NURBS插补技术。采用最小二乘法拟合NURBS曲线,能获得光滑的刀具加工路径,并且在一定范围内能复原曲线的设计轮廓。参数补偿的NURBS插补方法,以泰勒展开法得到的插补参数作为临时插补点,利用该插补法能显著减小速度波动,可将速度控制在理想的范围内,可进一步提高加工精度并减小数控机床的振动。仿真实验表明：该算法简明高效、易于实现,能够满足现代数控系统的要求。     

基于粗糙集属性约简和贝叶斯分类器的故障诊断

利用改进的小波包对收集的信号进行特征提取,解决了小波包分解的频率混叠问题;针对故障信息中的冗余属性问题,提出了基于类差别矩阵改进属性重要度的属性约简算法,根据各条件属性在类差别矩阵中出现1的频次定义新的属性重要度,提高属性约简的效率;通过考虑条件属性与类属性间的关联性,提出了基于熵权法的属性加权朴素贝叶斯分类器算法,提高故障分类精度。通过对滚动轴承故障数据的对比分析,验证了所提组合方法在提高故障诊断正确率、快速性方面所具有的优势。     

Studies of high temperature sliding wear of metallic dissimilar interfaces II: Incoloy MA956 versus Stellite 6

The development of wear surfaces formed during limited debris retention sliding wear of Incoloy MA956 against Stellite 6 between room temperature and 750 °C, and sliding speeds of 0.314 and 0.905 m s⁻¹ (7 N applied load, 4522 m sliding distance) were investigated. At 0.314 m s⁻¹, mild oxidational wear was observed at all temperatures, due to oxidation of Stellite 6-sourced debris and transfer to the Incoloy MA956; this debris separated the Incoloy MA956 and Stellite 6 wear surfaces. Between room temperature and 450 °C, the debris mainly took the form of loose particles with limited compaction, whilst between 510 °C and 750 °C the debris were compacted and sintered together to form a Co–Cr-based, wear protective ‘glaze’ layer. The behaviour was identical to that previously observed on sliding Nimonic 80A versus Stellite 6 at 0.314 m s⁻¹.At 0.905 m s⁻¹, mild oxidational wear was only observed at room temperature and 270 °C and dominated by Incoloy MA956-sourced debris. At 390 and 450 °C, the absence of oxide debris allowed ‘metal-to-metal’ contact and resulted in intermediate temperature severe wear; losses in the form of ejected metallic debris were almost entirely Incoloy MA956-sourced. This severe wear regime was also observed from 510 up to 630 °C, but increasingly restricted to the early stages of wear by development of a wear protective Incoloy MA956-sourced ‘glaze’ layer. This ‘glaze’ layer formed so rapidly at 690 °C and 750 °C, that severe wear was all but eliminated and wear levels were kept low.The behaviour observed for Incoloy MA956 versus Stellite 6 at 0.905 m s⁻¹ contrasts sharply with that previously observed for Nimonic 80A versus Stellite 6, in that the Incoloy MA956-sourced high Fe–Cr debris formed a protective oxide ‘glaze’, whilst the Nimonic 80A-sourced Ni and Cr oxides formed an abrasive oxide that at high sliding speeds assisted wear. The data indicates that the tendency of oxide to form a ‘glaze’ is readily influenced by the chemistry of the oxides generated.     

基于敏感参数分析的变矩器叶片参数研究

运用试验设计技术,研究了叶片进出口角、液流偏离角和损失系数等液力变矩器敏感参数,综合考虑这些敏感参数对最高效率、启动变矩比系数和力矩系数的影响,得到了它们之间的影响趋势,确定了影响因素的特定范围。改变泵轮的入口角度后,通过相关试验验证了效率变化的趋势。     

The estimation of the diameter error in bar turning: a comparison among three cutting force models

Machining accuracy is considerably affected by the deflection of the machine-tool-workpiece system under the action of the cutting force. A new model to estimate a bar diameter error due to the deflection of the tool, of the workpiece-holder and of the workpiece was defined by the authors, starting from a cutting force model. This work deals with a comparison among the bar diameter errors that are calculated by means of the developed model involving three different cutting force models. The considered cutting force models were the specific cutting resistance, the Kronenberg cutting force and the unified-generalised mechanics of the cutting force model developed by Armarego. The numerical results were compared with those obtained by experimental tests carried out through a parallel lathe. The results show that the Armarego's cutting force model provides values of the force components and, therefore, the values of the resulting bar diameter errors are closest to the experimental ones.Nomenclature a The longitudinal position of the tool, [mm] - a_pn The nominal depth of cut, [mm] - a_p The real depth of cut, [mm] - b The width of area of cut, [mm] - A The tool-workpiece interference area of cut, [mm²] - AB The generalised cutting edge vector - A_r The area of the workpiece cross section, [mm²] - c_s The spindle compliance, [mm/N] - c_t The tailstock compliance, [mm/N] - c_tht The tangential toolholder compliance, [mm/N] - c_thr The radial toolholder compliance, [mm/N] - D The workpiece diameter, [mm] - E The modulus of elasticity, [N/mm²] - f The feed, [mm/r] - F_rad The radial component of the cutting force, [N] - F_feed The feed component of the cutting force, [N] - F_{tan g} The tangential component of the cutting force, [N] - F_i The resultant of F_feed and F_{tan g}, [N] - G The shear modulus, [N/m²] - h The thickness of the area of the cut, [mm] - I The workpiece moment of inertia, [mm⁴] - L The workpiece length, [mm] - P_i The plane containing the inflected curve of the workpiece - P_f The tool assumed working plane - P_n The cutting edge normal plane - P_nG The generalised cutting edge normal plane - P_r The tool reference plane - r_l The chip length ratio - R The workpiece radius, [mm] - R_b The tailstock reaction force, [N] - R_s The spindle reaction force, [N] - S The shape factor - v_c The cutting speed, [mm/min] - v_e The resultant cutting speed, [mm/min] - v_f The feed speed, [mm/min] - v_ch The chip speed, [mm/min] - v_sh The shear speed, [mm/min] - w(z) The total deflection of the workpiece axis, [mm] - w_a The total displacement of the workpiece axis from z reference axis measured in P_i plane, [mm] - (z) The orientation of P_i with respect to F_rad and F_{tan g}, [degree] - The friction angle, [degree] - _n The normal friction angle, [degree] - _nG The generalised normal friction angle, [degree] - The shear factor - _n The normal shear angle, [degree] - _NG The generalised normal shear angle, [degree] - _f The tool side angle, [degree] - _n The tool normal rake angle, [degree] - _nG The generalised tool normal rake, [degree] - _P The tool back angle, [degree] - _c The chip flow angle, [degree] - _cG The generalised chip flow angle, [degree] - _r The tool cutting edge angle, [degree] - _rG The generalised tool cutting edge angle, [degree] - _s1 The tool cutting edge inclination, [degree] - _s2 The inclination of the secondary tool cutting edge [degree] - _sG The generalised tool cutting edge inclination, [degree] - The friction coefficient - The work material shear stress, [MPa] - _r The tool approach angle, [degree] - The approach angle of the secondary cutting edge, [degree]     

Frictionally-excited thermoelastic contact of rough surfaces

Frictional sliding contact between two elastically similar half-planes, one of which has a sinusoidally wavy surface, is studied in the full-contact regime. The steady-state regime is evaluated, within the limits imposed by the well-known phenomenon of thermo-elastic instability (TEI). TEI gives a critical speed whose value depends on the wavelength of the perturbation, and above which the perturbation itself grows arbitrarily with time. It is found that the TEI critical speed, V_cr, is clearly identified by the steady-state solution only in the special and limiting case when the flat half-plane is non-conductor; in that case, V_cr is the speed for which the steady-state predicts infinite amplification. In all other cases, V_cr (appropriate to the wavelength of the profile) does not correspond to infinite amplification, nor to the maximum one, V_M. In the limiting case of thermoelastically similar materials, not only the system is unconditionally stable (V_cr=∞) for f H₁<0.5, where f is the friction coefficient and H₁ a certain thermoelastic constant, but the regime at the maximum amplification is also always stable, and arbitrarily large amplification is obtained for f H₁ tending to infinity. However, it is found that in most practical cases of braking systems, V_crV_M, and so the limiting conditions are reached at V_cr. At this speed, the amplification is typically not extremely high.