1、Designation: E751/E751M 17Standard Practice forAcoustic Emission Monitoring During Resistance Spot-Welding1This standard is issued under the fixed designation E751/E751M; the number immediately following the designation indicates the yearof original adoption or, in the case of revision, the year of
2、last revision. A number in parentheses indicates the year of last reapproval.A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This practice describes procedures for the measurement,processing, and interpretation of the acoustic emission (AE)re
3、sponse associated with selected stages of the resistancespot-welding process.1.2 This practice also provides recommendations for feed-back control by utilizing the measured AE response signalsduring the spot-welding process.1.3 UnitsThe values stated in either SI units or inch-pound units are to be
4、regarded separately as standard. Thevalues stated in each system may not be exact equivalents;therefore, each system shall be used independently of the other.Combining values from the two systems may result in non-conformance with the standard.1.4 This standard does not purport to address all of the
5、safety concerns, if any, associated with 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.1.5 This international standard was developed in accor-dance with inter
6、nationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2E543
7、Specification for Agencies Performing NondestructiveTestingE1316 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 Certifi-cation of Nondestr
8、uctive Testing Personnel2.3 AIA Standard:4NAS-410 Certification and Qualification of NondestructivePersonnel (Quality Assurance Committee)2.4 ISO Standard:5ISO 9712 Non-Destructive Testing: Qualification and Certi-fication of NDT Personnel3. Terminology3.1 DefinitionsFor definitions of terms relatin
9、g to acousticemission testing, see Section B of Terminology E1316.4. Summary of Practice4.1 The resistance spot-welding process consists of severalstages. These are the set-down of the electrodes, squeeze,current flow, forging, hold time, and lift-off. Various types ofacoustic emission signals are p
10、roduced during each of thesestages. Often, these signals can be identified with respect to thenature of their source. The individual signal elements may begreatly different, or totally absent, in various materials,thicknesses, and so forth. Fig. 1 is a schematic representationshowing typical signal
11、elements which may be present in theAE signature from a given spot-weld.4.2 Most of the depictedAE signal features can be related tofactors of weld quality. The AE occurring during set-down andsqueeze can often be related to the condition of the electrodesand the surface of the parts. The large, oft
12、en brief, signal atcurrent initiation can be related to the initial resistance, and thecleanliness of the part. For example, burning through of certainoxide layers contributes to the acoustic emission responseduring this time.1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-st
13、ructive Testing and is the direct responsibility of Subcommittee E07.04 onAcoustic Emission Method.Current edition approved June 1, 2017. Published June 2017. Originallyapproved in 1980. Last previous edition approved in 2012 as E751 - 12. DOI:10.1520/E0751-17.2For referenced ASTM standards, visit t
14、he 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 website.3Available fromAmerican Society for Nondestructive Testing (ASNT), P.O. Box28518, 1711 Arlingate Ln.
15、, 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-aerospace.org.5Available from International Organization for Standardization (ISO), ISOCentral Secretariat, BIBC
16、II, Chemin de Blandonnet 8, CP 401, 1214 Vernier,Geneva, Switzerland, http:/www.iso.org.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was de
17、veloped in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.14.2.1 During cur
18、rent flow, plastic deformation, nuggetexpansion, friction, melting, and expulsions produce AE sig-nals. The signals caused by expulsion (spitting or flashing, orboth) generally have large amplitudes and can be distinguishedfrom the rest of the acoustic emission associated with nuggetformation. Fig.
19、2 shows typical AE response signals duringcurrent flow for both d-c and a-c welding.4.2.2 Following termination of the welding current, somematerials exhibit appreciable AE during solidification whichcan be related to nugget size and inclusions. As the nuggetcools during the hold period, AE can resu
20、lt from solid-solidphase transformations and cracking.4.2.3 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 cosmetic condition ofthe weld.4.3 Using time, and amplitude or energy discrimination, o
21、rboth, 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 gives detailed consideration tothe AE generated by nugget formation and expansion,expuls
22、ion, and cracking.5. Significance and Use5.1 The AE produced during the production of a spot-weldcan be related 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 examina
23、tion method, and as a means forproviding feedback control.6. Basis of Application6.1 The following items are subject to contractual agree-ment between the parties using or referencing this standard.6.2 Personnel Qualification:6.2.1 If specified in the contractual agreement, personnelperforming exami
24、nations to this standard shall be qualified inaccordance with a nationally or internationally recognizedNDT personnel qualification practice or standard such asANSI/ASNT CP-189, SNT-TC-1A, NAS-410, ISO 9712, or asimilar document and certified by the employer or certifyingagency, as applicable. The p
25、ractice or standard used and itsapplicable revision shall be identified in the contractual agree-ment between the using parties.6.3 Qualification of Nondestructive AgenciesIf specifiedin the contractual agreement, NDT agencies shall be qualifiedand evaluated as described in Practice E543. The applic
26、ableedition of Practice E543 shall be specified in the contractualagreement.6.4 Procedures and TechniquesThe procedures and tech-niques to be utilized shall be as specified in the contractualagreement.7. Ordering Information7.1 If the spot-weld monitoring or process control methodsdescribed in this
27、practice are performed as a service, thefollowing items should be addressed in the purchasespecification, and are subject to agreement between the pur-chaser and the supplier:7.1.1 Description of the welded parts in terms of geometry,dimensions, number and position of welds, and materials.7.1.2 Desc
28、ription of the welding machine, type and dimen-sions of the electrodes, type of weld controller, weldingschedule, and distance between the welding head and thecontroller.7.1.3 Location and mounting method for the acoustic emis-sion sensors, and design of the mounting fixture, as appropri-ate.FIG. 1
29、Typical AE Response Signals During Resistance Spot WeldingE751/E751M 1727.1.4 In the event that the process is actually controlled byacoustic emission, the circuit requirements associated with theelectronic interface to the weld controller to ensure synchro-nous operation.7.1.5 The performance and l
30、imiting AE parameters whichwere predetermined.7.1.6 Method of recording or reporting (that is, form andcontent of the report), if applicable.7.1.7 Technical qualifications of the personnel performingthe examination. These should be based on a documentedprogram that certifies personnel for conducting
31、 AE examina-tions.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 with electrode vibrationsmay necessitate the use of sensors with a frequency response int
32、he 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 should be capable of performing time and amplitude orenergy discrimination. Using some
33、 timing reference, it isnecessary to detect the AE contained within a certain timeinterval and within a certain signal or energy amplitude range.This is required for each characteristic stage of the AE signalthat is to be separately measured. Thus, the instrument shouldcontain one or more signal amp
34、litude or energy level detectors,timing gates, and counters. It should also contain a comparatorand signaling output if it is used for on-line 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 appropriat
35、e control signal whenever this level isexceeded. This control signal should terminate the weldingsynchronously with the zero-crossing points of the weldcurrent.8.2 Support EquipmentA waveform recorder is normallyused for performing measurements. A means for detectingcurrent initiation independent fr
36、om the AE signals should beavailable.8.3 Data-Recording Devices (optional) If it is desired topermanently record processed AE data, the AE instrumentshould be capable of this function.8.4 Audio or Visual AlarmAn alarm can be used inapplications where the acceptability of individual spot welds isto b
37、e determined in real-time, and where no record of rejectedwelds is necessary.8.5 Report Output DeviceA report output device may beused to provide a permanent record or report, and it is usuallyemployed as follows:8.5.1 Whenever a permanent record is necessary to docu-ment the quality of individual w
38、elds, the AE system shouldprint out or display such information as is necessary tosegregate and identify rejectable welds.8.5.2 When the joined parts contain a large number ofspot-welds, and the integrity of the product does not depend onthe quality of individual welds but rather on the number ofuna
39、cceptable welds expressed as a percentage of the totalnumber of welds. The print-out should consist of a weldFIG. 2 Typical AE Response Signals During Current FlowE751/E751M 173sequence number and a running percentage of unacceptablewelds when the individual spot-welds are identifiable bysequence nu
40、mber.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 ofunacceptable welds and their location distribution.9. Procedu
41、re9.1 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 that it is periodically replenished and standard-ization of t
42、he 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 near the sensor. However, when the instrumentationis located
43、less than1m3ftfrom the sensor, the gainotherwise supplied by the preamplifier may be incorporatedinto the main amplifier of the instrument.9.2 Preliminary MeasurementsThe AE signal from asingle spot-weld should be displayed on a waveform recorder.A wire coil or Hall effect sensor positioned near an
44、electrodecan be used as a current sensor, thus providing a timingreference and trigger signal for viewing and measuring the AEsignal. This reference signal can be also obtained through anappropriate interconnection to the weld controller. Havingestablished a typical AE trace, characteristic stages s
45、hould 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 cracking.9.2.1 New ApplicationsIf the instrumentation was notpreviously applied to a specific welding problem, prelimi
46、narymeasurements must be made to determine the instrumentsettings and the conditions for monitoring. The weld controllersettings are determined from normal welding considerations.First, the complete AE response should be observed on thewaveform readout. Next, the amplification (gain) of theinstrumen
47、tation, if available, should be set to the maximumvalue where the AE signals, representing the selected exami-nation parameter, do not saturate the amplifier. This step willensure that the measurement will be made with the bestobtainable signal-to-noise ratio. Next, the detection thresholdlevel shou
48、ld be established at a value that is slightly above thepeaks of the AE signals, which are to be excluded from themeasurement. The timing control is referenced to the onset ofthe weld current and consists of a delay and a time interval.These time intervals should be selected so that the monitoringis
49、restricted to the time interval when relevant signals arepresent. The finalized settings of the weld controller and theAEinstrumentation should be recorded along with a waveform ofthe total acoustic emission signal. The AE or energy countsobtained from individual welds should also be recorded. Theserecords should be kept on file for future reference. Specialconsiderations associated with each of the various examinationparameters are discussed in 10.1 10.4.9.2.2 Repeated ApplicationsIf AE monitoring was previ-ously applied to a particular controlling
