1、Designation: E 751 07Standard Practice forAcoustic Emission Monitoring During Resistance Spot-Welding1This standard is issued under the fixed designation E 751; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revis
2、ion. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice describes procedures for the measurement,processing, and interpretation of the acoustic emission (AE)response ass
3、ociated with selected stages of the resistancespot-welding process.1.2 This practice also provides guidelines for feedbackcontrol by utilizing the measured AE response signals duringthe spot-welding process.1.3 This standard does not purport to address all of thesafety concerns, if any, associated w
4、ith its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 543 Specification for Agencies Performing Nondestruc-tive Testi
5、ngE 1316 Terminology for Nondestructive Examinations2.2 ASNT Standards:3SNT-TC-1A Recommended Practice for NondestructiveTesting Personnel Qualification and CertificationANSI/ASNT CP-189 Standard for Qualification and Certi-fication of Nondestructive Testing Personnel2.3 AIA Standard:4NAS-410 Certif
6、ication and Qualification of NondestructivePersonnel (Quality Assurance Committee)3. Terminology3.1 DefinitionsFor definitions of terms relating to acousticemission testing, see Section B of Terminology E 1316.4. Significance and Use4.1 The AE produced during the production of a spot-weldcan be rela
7、ted to weld quality parameters such as the strengthand size of the nugget, the amount of expulsion, and theamount of cracking. Therefore, in-process AE monitoring canbe used both as an examination method, and as a means forproviding feedback control.5. Basis of Application5.1 The following items are
8、 subject to contractual agree-ment between the parties using or referencing this standard.5.2 Personnel Qualification:5.2.1 If specified in the contractual agreement, personnelperforming examinations to this standard shall be qualified inaccordance with a nationally or internationally recognizedNDT
9、personnel qualification practice or standard such asANSI/ASNT CP-189, SNT-TC-1A, NAS-410, or a similardocument and certified by the employer or certifying agency,as applicable. The practice or standard used and its applicablerevision shall be identified in the contractual agreement be-tween the usin
10、g parties.5.3 Qualification of Nondestructive AgenciesIf specifiedin the contractual agreement, NDT agencies shall be qualifiedand evaluated as described in Practice E 543. The applicableedition of Practice E 543 shall be specified in the contractualagreement.5.4 Procedures and TechniquesThe procedu
11、res and tech-niques to be utilized shall be as specified in the contractualagreement.6. Ordering Information6.1 If the spot-weld monitoring or process control methodsdescribed in this practice are performed as a service, thefollowing items should be addressed in the purchase specifi-cation, and are
12、subject to agreement between the purchaser andthe supplier:6.1.1 Description of the welded parts in terms of geometry,dimensions, number and position of welds, and materials.6.1.2 Description of the welding machine, type and dimen-sions of the electrodes, type of weld controller, weldingschedule, an
13、d distance between the welding head and thecontroller.1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is the direct responsibility of Subcommittee E07.04 onAcoustic Emission Method.Current edition approved Feb. 15, 2007. Published March 2007. Originallya
14、pproved in 1980. Last previous edition approved in 2001 as E 751 - 01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM
15、 website.3Available fromAmerican Society for Nondestructive Testing (ASNT), P.O. Box28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http:/www.asnt.org.4Available from Aerospace Industries Association of America, Inc. (AIA), 1000Wilson Blvd., Suite 1700,Arlington, VA22209-3928, http:/www.aia-aero
16、space.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.6.1.3 Location and mounting method for the acoustic emis-sion sensors, and design of the mounting fixture, as appropri-ate.6.1.4 In the event that the process is actually cont
17、rolled byacoustic emission, the circuit requirements associated with theelectronic interface to the weld controller to ensure synchro-nous operation.6.1.5 The performance and limiting AE parameters whichwere predetermined.6.1.6 Method of recording or reporting (that is, form andcontent of the report
18、), if applicable.6.1.7 Technical qualifications of the personnel performingthe examination. These should be based on a documentedprogram that certifies personnel for conducting AE examina-tions.7. Principles of Application7.1 The resistance spot-welding process consists of severalstages. These are t
19、he set-down of the electrodes, squeeze,current flow, forging, hold time, and lift-off. Various types ofacoustic emission signals are produced during each of thesestages. Often, these signals can be identified with respect to thenature of their source. The individual signal elements may begreatly dif
20、ferent, or totally absent, in various materials, thick-nesses, and so forth. Fig. 1 is a schematic representationshowing typical signal elements which may be present in theAE signature from a given spot-weld.7.2 Most of the depictedAE signal features can be related tofactors of weld quality. The AE
21、occurring during set-down andsqueeze can often be related to the condition of the electrodesand the surface of the parts. The large, often brief, signal atcurrent initiation can be related to the initial resistance, and thecleanliness of the part. For example, burning through of certainoxide layers
22、contributes to the acoustic emission responseduring this time.7.2.1 During current flow, plastic deformation, nugget ex-pansion, friction, melting, and expulsions produce AE signals.The signals caused by expulsion (spitting or flashing, or both)generally have large amplitudes and can be distinguishe
23、d fromthe rest of the acoustic emission associated with nuggetformation. Fig. 2 shows typical AE response signals duringcurrent flow for both d-c and a-c welding.7.2.2 Following termination of the welding current, somematerials exhibit appreciable AE noise during solidificationwhich can be related t
24、o nugget size and inclusions. As thenugget cools during the hold period, AE can result fromsolid-solid phase transformations and cracking.7.2.3 During the lift-off stage, separation of the electrodefrom the part produces signals that can be related to thecondition of the electrode as well as the cos
25、metic condition ofthe weld.7.3 Using time, and amplitude or energy discrimination, orboth, the AE response corresponding to each stage can beseparately detected and analyzed. Although the AE associatedwith each stage of the spot-welding process can be relevant toweld quality, this practice only give
26、s detailed consideration tothe AE generated by nugget formation and expansion, expul-sion, and cracking.8. Apparatus8.1 Acoustic Emission System:8.1.1 The AE sensor should be a contacting type having anappropriate frequency response within the range from 0.1 to1.0 MHz. Free resonances associated wit
27、h electrode vibrationsmay necessitate the use of sensors with a frequency response inthe range from 0.30 to 1.0 MHz.8.1.2 The electronic instrument should contain adjustableamplification (gain) over the range from 40 to 100 dB, or anequivalent dynamic range and adjustable threshold. The instru-ment
28、should be capable of performing time and amplitude orFIG. 1 Typical AE Response Signals During Resistance Spot WeldingE751072energy discrimination. Using some timing reference, it isnecessary to detect the AE contained within a certain timeinterval and within a certain signal or energy amplitude ran
29、ge.This is required for each characteristic stage of the AE signalthat is to be separately measured. Thus, the instrument shouldcontain one or more signal amplitude or energy level detectors,timing gates, and counters. It should also contain a comparatorand signaling output if it is used for on-line
30、 monitoring.8.1.3 If feedback control is to be used, the instrument shouldfacilitate the selection of an optimum AE level, and it shouldgenerate an appropriate control signal whenever this level isexceeded. This control signal should terminate the weldingsynchronously with the zero-crossing points o
31、f the weldcurrent.8.2 Support EquipmentA waveform recorder is normallyused for performing measurements. A means for detectingcurrent initiation independent from the AE signals should beavailable.8.3 Data-Recording Devices (optional)If it is desired topermanently record processed AE data, the AE inst
32、rumentshould be capable of this function.8.4 Audio or Visual AlarmAn alarm can be used inapplications where the acceptability of individual spot welds isto be determined in real-time, and where no record of rejectedwelds is necessary.8.5 Print-out DeviceA print-out device may be used toprovide a per
33、manent record, and it is usually employed asfollows:8.5.1 Whenever a permanent record is necessary to docu-ment the quality of individual welds, the printer should printout such information as is necessary to segregate and identifyrejectable welds.8.5.2 When the joined parts contain a large number o
34、fspot-welds, and the integrity of the product does not depend onthe quality of individual welds but rather on the number ofunacceptable welds expressed as a percentage of the totalnumber of welds. The print-out should consist of a weldsequence number and a running percentage of unacceptablewelds whe
35、n the individual spot-welds are identifiable bysequence number.8.5.3 If weld identification is not possible, then the weldingapparatus should be equipped with an automatic markingattachment. With the markings and the records, the acceptabil-ity of the welded part can be based on the percentage ofuna
36、cceptable welds and their location distribution.9. Procedure9.1 Sensor and Preamplifier AttachmentThe sensorshould be mounted to the lower (grounded) electrode orelectrode holder. If the measurements are to be made only as aperiodic sampling of weld quality, a liquid couplant may beused provided tha
37、t it is periodically replenished and standard-ization of the system response is maintained. For sustainedmonitoring, such as on-line AE examination or control of eachnugget, the sensor should be permanently mounted using anepoxy adhesive or a similar material. A preamplifier is usuallypositioned nea
38、r the sensor. However, when the instrumentationis located less than 1 m from the sensor, the gain otherwisesupplied by the preamplifier may be incorporated into the mainamplifier of the instrument.9.2 Preliminary MeasurementsThe AE signal from asingle spot-weld should be displayed on a waveform reco
39、rder.A wire coil or Hall effect sensor positioned near an electrodecan be used as a current sensor, thus providing a timingFIG. 2 Typical AE Response Signals During Current FlowE751073reference and trigger signal for viewing and measuring the AEsignal. This reference signal can be also obtained thro
40、ugh anappropriate interconnection to the weld controller. Havingestablished a typical AE trace, characteristic stages should beidentified and one or more selected as an AE examinationparameter. For example, weld quality indicators may beobtained from the AE response to nugget formation, expulsion,or
41、 cracking.9.2.1 New ApplicationsIf the instrumentation was notpreviously applied to a specific welding problem, preliminarymeasurements must be made to determine the instrumentsettings and the conditions for monitoring. The weld controllersettings are determined from normal welding considerations.Fi
42、rst, the complete AE response should be observed on thewaveform readout. Next, the amplification (gain) of the instru-mentation, if available, should be set to the maximum valuewhere the AE signals, representing the selected examinationparameter, do not saturate the amplifier. This step will ensuret
43、hat the measurement will be made with the best obtainablesignal-to-noise ratio. Next, the detection threshold level shouldbe established at a value that is slightly above the peaks of theAE signals, which are to be excluded from the measurement.The timing control is referenced to the onset of the we
44、ldcurrent and consists of a delay and a time interval. These timeintervals should be selected so that the monitoring is restrictedto the time interval when relevant signals are present. Thefinalized settings of the weld controller and the AE instrumen-tation should be recorded along with a waveform
45、of the totalacoustic emission signal. The AE or energy counts obtainedfrom individual welds should also be recorded. These recordsshould be kept on file for future reference. Special consider-ations associated with each of the various examination param-eters are discussed in 10.1-10.4.9.2.2 Repeated
46、 ApplicationsIf AE monitoring was previ-ously applied to a particular controlling or monitoring problem,the purpose of the preliminary measurement is to reestablishthe known and recorded original test conditions. The heat andthe weld time settings on the weld controller, and the gain,threshold level
47、 timing, and other settings on the AE instru-mentation should be made identical to those on record. A fewsample welds should be made to verify that the generalappearance of the total AE signal exhibits the expectedcharacteristic features, and that the average count falls withinthe range of past mea
48、surements.10. Weld Quality Parameters That Produce AE10.1 AE During Nugget Formation:10.1.1 When the material in the welding zone is heated, thepressure applied by the top electrode will plastically deform thematerial and AE will be generated. The amplitude of the AEsignals associated with this proc
49、ess is affected by both elec-trode pressure and the “cleanliness” of the parts. These AEsignals may be gated out since they provide no useful infor-mation relative to the quality of the weld.10.1.2 Further heating results in melting within the weldingzone and growth of the nugget. Nugget formation and expan-sion produceAE signals that can be correlated with the strengthof the weld.10.1.3 As soon as the welding current starts to decrease, thenugget begins to solidify and residual stresses will be presentin and around the weldment. If these residual stresses aresevere, hot c
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