【作者】 殷宝麟；

【导师】 韩荣第；

【作者基本信息】 哈尔滨工业大学 ， 机械制造及其自动化， 2008， 博士

【摘要】 攻丝几乎是小螺孔加工唯一完全可行的工艺方法。由于攻丝是半封闭容屑的多刀齿切削过程,切削液不能有效进入切削区,排屑又困难,故切削条件十分恶劣。难加工材料小孔攻丝,由于攻丝扭矩大,丝锥易崩齿和折断导致攻丝无法进行。随着现代工业对零件性能要求的提高,高性能材料大量被采用,迫切需要解决难加工材料小孔攻丝难题。而振动攻丝具有攻丝扭矩小、螺纹精度高以及丝锥使用寿命长等特点,故在难加工材料攻丝领域得到了广泛应用。但对其机理及应用的研究还不够十分充分,因此对振动攻丝机理及实际应用进行深入系统研究,具有重要的理论意义和应用价值。首先,在综述国内外振动攻丝技术的基础上,对攻丝过程中切削扭矩在攻丝扭矩中所占的比率进行了试验研究,可以认为切削扭矩是影响加工难易的重要因素之一。基于动态断裂力学理论,分析了振动攻丝中丝锥刀齿对切削区中随机分布的微裂纹呈三维脉冲力的作用导致应力出现了跃动,这种跃动随作用时间的持续将趋于静载荷作用的效果,且还随作用距离的增大呈减弱趋势,从而给出了振动攻丝中切削扭矩的减小使攻丝扭矩减小的机理。通过对试验所获得振动攻丝扭矩波动的分析,验证了上述机理研究的合理性。并基于此机理研究的结论,理论分析了工艺参数对攻丝扭矩的影响规律。然后,为了进行振动攻丝试验,研制了单片机控制的步进电机式低频振动攻丝试验系统SZ48-HIT,它包括攻丝机的机械系统、控制系统及扭矩测量系统。控制系统采用单片机来控制步进电机,用汇编语言编制了振动攻丝需要的各功能子模块及其服务程序,对各子功能模块的控制模型进行了分析,并对软、硬件进行了综合测试。还设计了不同放大倍数、不同滤波频率的滤波放大电路,建立了可以同步存储并实时显示的扭矩测量系统。再后,在SZ48-HIT试验系统及原试验系统下对奥氏体不锈钢1Cr18Ni9Ti、钛合金TC4、镍基高温合金GH4169及45钢(淬火50HRC)4种典型难加工材料,进行了大量的小孔(M3)振动攻丝试验。用单因素法的振动攻丝试验,研究了各工艺参数对攻丝扭矩的影响规律,所得结果与前述扭矩减小的机理分析是一致的。用正交设计法的振动攻丝试验,研究了各工艺参数对攻丝扭矩影响的显著性问题。还探讨了不同物理力学性能的典型难加工材料振动攻丝中,工艺参数对扭矩影响的差异。从而为振动攻丝技术在难加工材料小孔攻丝中的应用提供了依据。最后,对不同材料及螺孔尺寸参数进行了振动攻丝试验研究,尺寸范围M3～M8,材料为45钢(正火)、1Cr18Ni9Ti、TC4及GH4169。并基于神经网络技术,建立了多参数的振动攻丝扭矩模型,对其进行了数值计算,分析了工艺参数、螺孔尺寸和材料力学性能对振动攻丝效果的影响。还基于该扭矩模型,采用遗传算法,以扭矩最小为目标函数,进行了工艺参数优化。大量试验的结果表明,对于物理力学性能不同的难加工材料及尺寸不同的螺孔,振动攻丝均获得了良好效果,所攻螺纹齿形平直、完整且精度高。故振动攻丝是解决难加工材料小螺孔加工的有效手段。更多还原

【Abstract】 Internal thread tapping is one of the most demanding machining operation. Inthe tapping process, multiple cutting edge cut workpiece at the meantime with thechip in the tap pocket. Process can’t continue result from cutting ?uid penetratinginsufficiently and chip clogging. Tapping small-hole in difficult-to-cut materials, tapbreakage appears to be one of the major problems in the process, possibly due toexcessive torque and tap tooth tipping. With the rapid development of modern man-ufacturing technologies, superalloys are frequently used for components, it is clearthat conventional process could not fulfill the requirement of small-hole tapping insuch materials. Vibration tapping has been applied to difficult-to-cut materials to in-crease the tapping efficiency, reduce the overall tapping torque and improve threadquality. However, theoretical analysis and experimental research on vibration tappingare insufficiency. A systematic investigation is therefore of great importance.Firstly, the present status of investigation on vibration tapping is analyzed. Ex-perimental results indicate that the effect of cutting torque is one of most vital rolein tapping processing. The mechanism impulsive force of cutting tooth generation invibration tapping is shown. Theoretical analysis the three-dimensional stress-intensityfactor history with fracture mechanics. The analysis is performed for a solid contain-ing a half plane crack subjected to suddenly applied concentrated point forces actingat a finite distance from the crack edge. Upon sudden force application, the stress-intensity factor is of the singularity. Thereafter, the transient stress-intensity factordecays gradually towards its equilibrium stress-intensity. And the singularity decayswith range of action. And the impulsive force in vibration tapping leads to reducedcutting forces and a much lower tapping torque. Tapping torque wave is measuredin vibration tapping, and the theoretical results are confirmed by experiments. Basedon the theoretical results, a simulation is proposed to describe the relation betweenvibration tapping torque and processing parameters.Secondly, in order to expand the experimental research, the low-frequency vi-bration tapping system SZ48-HIT is developed successfully. Strength and rigidity ofmachine key component are checked, and the spindle circular runout is measured. On the vibration tapping machine, a torsional vibration is imposed on the spindle by astepping motor under the control of a microcomputer. A simulation is carried out toverify the mathematical model. The service module and control programming moduleare developed with assembly language. Hardware and software of the control systemare tested integrally. With the amplifier-filter circuit, the torque transducer is used tomonitor tapping torque.Thirdly, experimental research on vibration tapping small-hole(M3) in typicaldifficult-to-cut materials, such as austenlitic stainless steel(1Cr18Ni9Ti),α+βphasetitanium alloy(TC4), nickel-base superalloys(GH4169) and hardened steel(hardness50HRC). With single factor trial of vibration tapping, the tapping torque variationby processing parameters changed is investigation. And the experimental results areconfirmed by theoretical analysis. With orthogonal design trial, it is shown that, vari-ation of decreasing vibration tapping torque results from diversity material. So that itprovides fundamental application of vibration tapping.Lastly, large quantity trial of vibration tapping in different materials with differ-ent thread dimension are researched. The thread dimension range from M3 to M8, andmaterials of test include C45 steel, 1Cr18Ni9Ti, TC4 and GH4169. Neural networkwith back propagation algorithm has been applied to predict the tapping torque modelin vibration tapping. A numerical calculation of the tapping torque is carried out. Thevariable regular is researched, which of varied result from varied of processing param-eters, thread dimension and mechanical properties of the materials. Based on tappingtorque model, the study investigated the application of genetic algorithm for tappingtorque minimization.The experimental results show that, complete machined teeth are acquired, andthe screw fulfils the requirement of a screw plug gauge. According above, vibrationtapping is proved to be a practical solution to the problem of small-hole tapping indifficult-to-cut materials.更多还原