Home

This is the simple HTML-Text version of the PDF file 271 KB. It serves as a quick to access preview of the PDF file. EWGAE 2004 Proceedings SESSION: Other Industrial Applications Full-Text PDF (KB) 271 KB

Home

Condition monitoring using of AE method Authors: Ron Murray, Vaclav Svoboda, Pavel Svec Application of Acoustic Emission Method during the press monitoring process is used to diagnose and evaluate crack initiation.. Simple method of permanently fixed AE sensors on the machine tools are described. During the cycling working process the AE signals are detected and compared with threshold level. Special electronic device - CoMo is used for determination crack detection in every cycle. Whole process is controlled automatically and as a results the bad and good parts are sorted. 1) Principle of Basic Single Level Detection On Fig. 1 is schematically shown basic principle of signal detection. Practical shape of real signal RMS is shown on Fig. 2 which is done through converter. Fig. 1 Fig. 2 5125/5127 - Broad-band (raw) signals are converted to RMS representation. These are the only Kistler products capable of RMS conversion. 297 DGZfP-Proceedings BB 90-CD Lecture 28 EWGAE 2004 RMS represents the amount of broadband AE "energy" present ... * RMS signal is compared to a preset user defined voltage level * When RMS Output exceeds preset level, an optocoupler will provide a digital output, and hold it until 1.3 seconds after signal returns below the pre-set level. Fig. 3 Live Acoustic Signal RMS representation * Surface waves propagating from a point source event, traveling along an objects surface. The waves have a relatively low signal intensity, but very high frequency, from 50 kHz to 1 MHz. Fig. 4 2) Practical Configuration of experimental equipment There are two ways of fixing the AE sensors to the object surface: a) magnetic mounting b) tapped hole mounting Both configuration are shown on Fig. 5 and 6. 8443 Magnet Mount Tapped Hole Fig. 5 298 DGZfP-Proceedings BB 90-CD Lecture 28 EWGAE 2004 Ground surface Rough surface Fig. 6 3) Influence of mounting conditions on RMS AE signal On Fig. 6 is shown mode of mounting the sensors on ground and rough surface. On Fig. 8 are graphs showing influence of different mode of sensor fixing on level of output signal. AE-Sensors 8152B... RMS-Signal AE-Coupler 5125B2 (Filter: 50kHz high pass, 1MHz low pass, time constant τ=1.2ms, gain 1X (20dB)) magnetic clamp, without silicone grease, rough surface M6 screw, without silicon grease, rough surface magnetic clamp, silicone grease, rough surface M6 screw, with silicon grease, rough surface magnetic clamp, without silicone grease, grinded surface M6 screw, without silicon grease, grinded surface magnetic clamp, silicone grease, grinded surface M6 screw, silicon grease, grinded surface 0.9 0.8 0.7 0.6 0.5 signal (VRMS) 0.4 0.3 0.2 0.1 0 -0.1 -2 0 2 4 6 8 10 12 14 16 18 time (ms) Fig. 7 299 DGZfP-Proceedings BB 90-CD Lecture 28 EWGAE 2004 Set DC level to provide output if RMS exceeds set level ... Limit set at 2.0 volts. 5125 will provide indication when AE RMS exceeds 2.0 volts. The indication will last approx. 1.3 seconds after level falls below limit. 4) AE - Application Types * Crack detection - Detect cracks when they form ... * Fatigue testing - collect data and give notification to a cyclic fatigue event occurrence. ( plastic deformation ) * Chip detection - Detect the presence of a chip in a tool... also detect chipping as it occurs... * Tool Breakage Detection - Instantly shut down a process when the tooling breaks ... * Deep Drawing - determine defects when they occur during drawing, stop draw press during "necking". * Stamping - Determine Good vs. Bad stamping operation ... * Piercing - Indicate the presence of a missing or malfunctioning punch ... * Scoring - detect scratches and gouges as they occur in metal ... 300 Fig. 8 DGZfP-Proceedings BB 90-CD Lecture 28 EWGAE 2004 No Cracks ... Many micro - cracks... Fig. 9 5) Application Example: Detect a housing crack as occurs in a press fit operation. No crack occurred ... RMS Output ... Crack occurred during assembly ... Fig. 10 6) Conclusion: In the presented paper is shown one simple monitoring method using AE technology. As stated the main field of this application is in production process like stamping, fitting, forming, etc. AE method used in these monitoring processes conduce to improve product quality and to decrease costs by scraps elimination. Another advantage is based on simple installation without changes of the production machine. 301

© NDT.net