Theoretical And Experimental Research On Small-Hole Vibration Tapping In Difficult-To-Cut Materials

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.