Research On Online Monitoring Of Internal Thread Formed By Cold Extrusion

Internal thread formed by cold extrusion has good surface integrity, and the cold workhardening state on the thread surface and sub-surface after cold extrusion ensure its mechanicalproperties and fatigue life. Till now, technology of internal thread formed by cold extrusion hasbeen widely applied on many high-speed and dynamic load cases, such as marine, aerospace andhigh-speed train industries. However, it still lacks of the time-frequency analysis on vibrationsignal to reveal the vibration mechanism. In the paper, according to the non stationary of vibrationsignal of internal thread formed by cold extrusion, the Hilbert-Huang transform is applied to theanalysis on vibration signal in the forming processing of internal thread formed, in order to obtainits time-frequency characteristics. The major work and results are as follows:1. The vibration signal in forming process of internal thread formed by cold extrusion is atypical non stationary signal, traditional signal analysis methods do not suit any more. So, the allnew signal analysis method-HHT (Hilbert-Huang transform) is found, and applied to thetime-frequency analysis on vibration signal in forming process of internal thread formed by coldextrusion. And implementation steps of HHT are listed. Example proves that HHT have goodanalytic results.2. In the forming process internal thread formed by cold extrusion, extrusion tap squeezesinto different parts of the work piece, then the forming process could be divided into four periods,including non extruding period, extruding period, extruding with correcting period and correctingperiod. HHT are applied to the time-frequency analysis of vibration signal in forming process ofinternal thread formed by cold extrusion. The analytical results showed that high frequencyvibration emerged in the extruding period, and gradually became strong. With the exit of extrusiontap, high frequency vibration turned weak. It revealed variation of high frequency friction betweenextrusion tap and work piece, which laid foundation for the forming mechanism of internal threadformed by cold extrusion.3. Three parameters can impact the vibration signal in the forming process of internal ofinternal thread formed by cold extrusion: the bottom hole diameter of a piecework, the rotatespeed of lathe, kinds of lubricant. Vibration signals in the forming process internal thread formedby cold extrusion are studied by three groups. The analytical results show that, with the bottomhole diameter of a piecework increasing, high-frequency vibration decreasing, with the rotatespeed of lathe, high-frequency vibration first decreasing then increasing, and while rotate speed oflathe is25r/min, high-frequency vibration least; when PDMS is chosen as lubricant, high-frequency vibration is slightest.4. Three vibration parameters can impact vibration signals in the forming process of internalthread formed by cold extrusion based on low frequency vibration: exciting frequency, excitingforce and exciting arm. The vibration signals of internal thread formed by cold extrusion based onlow frequency vibration are divided into three groups by the rule of single variable. Then HHT areapplied to the time-frequency analysis of these vibration signals by group. The analytical resultsshow that: with the exciting frequency and exciting force increasing, high-frequency vibration firstdecreasing then increasing; with the exciting arm increasing, high-frequency vibrationincreasing.5. Multi-resolution analysis is applied on vibration signals in the forming process of internalthread formed by cold extrusion based on low frequency vibration which exciting frequency is thesingle variable. Basing on db5wavelet decomposition, the vibration signals are decomposed intothree layers, and we can obtain the three layer wavelet approximation of these signals. After that,the low frequency vibration signals are extracted by EMD and Hilbert transform.6. LabVIEW has a friendly user interface, and Access has strong memory function. LabSQLmakes link between LabVIEW and Access, which ensure the accuracy of the signal acquisitionand simplify the cumbersome manual operation process.