1、Designation: E751/E751M 12E751/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,
2、 the year of 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 e
3、mission (AE)response associated with selected stages of the resistance spot-welding process.1.2 This practice also provides guidelinesrecommendations for feedback control by utilizing the measured AE response signalsduring the spot-welding process.1.3 UnitsThe values stated in either SI units or inc
4、h-pound units are to be regarded separately as standard. The values statedin each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining valuesfrom the two systems may result in non-conformance with the standard.1.4 This standard does not purp
5、ort to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.1.5 This international standard was developed in
6、 accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 A
7、STM Standards:2E543 Specification for Agencies Performing Nondestructive TestingE1316 Terminology for Nondestructive Examinations2.2 ASNT Standards:3SNT-TC-1A Recommended Practice for Nondestructive Testing Personnel Qualification and CertificationANSI/ASNT CP-189 Standard for Qualification and Cert
8、ification of Nondestructive Testing Personnel2.3 AIA Standard:4NAS-410 Certification and Qualification of Nondestructive Personnel (Quality Assurance Committee)2.4 ISO Standard:5ISO 9712 Non-Destructive Testing: Qualification and Certification of NDT Personnel3. Terminology3.1 DefinitionsFor definit
9、ions of terms relating to acoustic emission testing, see Section B of Terminology E1316.4. Summary of Practice4.1 The resistance spot-welding process consists of several stages. These are the set-down of the electrodes, squeeze, currentflow, forging, hold time, and lift-off. Various types of acousti
10、c emission signals are produced during each of these stages. Often,1 This practice is under the jurisdiction ofASTM Committee E07 on Nondestructive Testing and is the direct responsibility of Subcommittee E07.04 on Acoustic EmissionMethod.Current edition approved June 15, 2012June 1, 2017. Published
11、 July 2012June 2017. Originally approved in 1980. Last previous edition approved in 20072012 asE751 - 07.E751 - 12. DOI: 10.1520/E0751-12.10.1520/E0751-17.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM
12、Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 Available from American Society for Nondestructive Testing (ASNT), P.O. Box 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http:/www.asnt.org.4 Available from Aerospace Industries Association of Amer
13、ica, Inc. (AIA), 1000 Wilson Blvd., Suite 1700, Arlington, VA 22209-3928, http:/www.aia-aerospace.org.5 Available from International Organization for Standardization (ISO), ISO Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva,Switzerland, http:/www.iso.org.This docu
14、ment is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as
15、appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*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
16、 States1these signals can be identified with respect to the nature of their source. The individual signal elements may be greatly different,or totally absent, in various materials, thicknesses, and so forth. Fig. 1 is a schematic representation showing typical signalelements which may be present in
17、the AE signature from a given spot-weld.4.2 Most of the depicted AE signal features can be related to factors of weld quality. The AE occurring during set-down andsqueeze can often be related to the condition of the electrodes and the surface of the parts. The large, often brief, signal at currentin
18、itiation can be related to the initial resistance, and the cleanliness of the part. For example, burning through of certain oxide layerscontributes to the acoustic emission response during this time.4.2.1 During current flow, plastic deformation, nugget expansion, friction, melting, and expulsions p
19、roduce AE signals. Thesignals caused by expulsion (spitting or flashing, or both) generally have large amplitudes and can be distinguished from the restof the acoustic emission associated with nugget formation. Fig. 2 shows typical AE response signals during current flow for bothd-c and a-c welding.
20、4.2.2 Following termination of the welding current, some materials exhibit appreciableAE noise during solidification which canbe related to nugget size and inclusions. As the nugget cools during the hold period, AE can result from solid-solid phasetransformations and cracking.4.2.3 During the lift-o
21、ff stage, separation of the electrode from the part produces signals that can be related to the condition ofthe electrode as well as the cosmetic condition of the weld.4.3 Using time, and amplitude or energy discrimination, or both, theAE response corresponding to each stage can be separatelydetecte
22、d and analyzed. Although the AE associated with each stage of the spot-welding process can be relevant to weld quality,this practice only gives detailed consideration to the AE generated by nugget formation and expansion, expulsion, and cracking.5. Significance and Use5.1 The AE produced during the
23、production of a spot-weld can be related to weld quality parameters such as the strength andsize of the nugget, the amount of expulsion, and the amount of cracking. Therefore, in-process AE monitoring can be used bothas an examination method, and as a means for providing feedback control.6. Basis of
24、 Application6.1 The following items are subject to contractual agreement between the parties using or referencing this standard.6.2 Personnel Qualification:6.2.1 If specified in the contractual agreement, personnel performing examinations to this standard shall be qualified inaccordance with a natio
25、nally or internationally recognized NDT personnel qualification practice or standard such as ANSI/ASNTCP-189, SNT-TC-1A, NAS-410, ISO 9712, or a similar document and certified by the employer or certifying agency, as applicable.The practice or standard used and its applicable revision shall be ident
26、ified in the contractual agreement between the using parties.FIG. 1 Typical AE Response Signals During Resistance Spot WeldingE751/E751M 1726.3 Qualification of Nondestructive AgenciesIf specified in the contractual agreement, NDT agencies shall be qualified andevaluated as described in Practice E54
27、3. The applicable edition of Practice E543 shall be specified in the contractual agreement.6.4 Procedures and TechniquesThe procedures and techniques to be utilized shall be as specified in the contractual agreement.7. Ordering Information7.1 If the spot-weld monitoring or process control methods de
28、scribed in this practice are performed as a service, the followingitems should be addressed in the purchase specification, and are subject to agreement between the purchaser and the supplier:7.1.1 Description of the welded parts in terms of geometry, dimensions, number and position of welds, and mat
29、erials.7.1.2 Description of the welding machine, type and dimensions of the electrodes, type of weld controller, welding schedule, anddistance between the welding head and the controller.7.1.3 Location and mounting method for the acoustic emission sensors, and design of the mounting fixture, as appr
30、opriate.7.1.4 In the event that the process is actually controlled by acoustic emission, the circuit requirements associated with theelectronic interface to the weld controller to ensure synchronous operation.7.1.5 The performance and limiting AE parameters which were predetermined.7.1.6 Method of r
31、ecording or reporting (that is, form and content of the report), if applicable.7.1.7 Technical qualifications of the personnel performing the examination. These should be based on a documented programthat certifies personnel for conducting AE examinations.8. Apparatus8.1 Acoustic Emission System:8.1
32、.1 The AE sensor should be a contacting type having an appropriate frequency response within the range from 0.1 to 1.0MHz. Free resonances associated with electrode vibrations may necessitate the use of sensors with a frequency response in therange from 0.30 to 1.0 MHz.8.1.2 The electronic instrumen
33、t should contain adjustable amplification (gain) over the range from 40 to 100 dB, or anequivalent dynamic range and adjustable threshold. The instrument should be capable of performing time and amplitude or energydiscrimination. Using some timing reference, it is necessary to detect the AE containe
34、d within a certain time interval and withina certain signal or energy amplitude range. This is required for each characteristic stage of the AE signal that is to be separatelymeasured. Thus, the instrument should contain one or more signal amplitude or energy level detectors, timing gates, and count
35、ers.It should also contain a comparator and signaling output if it is used for on-line monitoring.8.1.3 If feedback control is to be used, the instrument should facilitate the selection of an optimum AE level, and it shouldgenerate an appropriate control signal whenever this level is exceeded. This
36、control signal should terminate the weldingsynchronously with the zero-crossing points of the weld current.FIG. 2 Typical AE Response Signals During Current FlowE751/E751M 1738.2 Support EquipmentA waveform recorder is normally used for performing measurements. A means for detecting currentinitiatio
37、n independent from the AE signals should be available.8.3 Data-Recording Devices (optional) If it is desired to permanently record processed AE data, the AE instrument should becapable of this function.8.4 Audio or Visual AlarmAn alarm can be used in applications where the acceptability of individua
38、l spot welds is to bedetermined in real-time, and where no record of rejected welds is necessary.8.5 Print-out Report Output DeviceA print-out report output device may be used to provide a permanent record, record orreport, and it is usually employed as follows:8.5.1 Whenever a permanent record is n
39、ecessary to document the quality of individual welds, the printerAE system should printout or display such information as is necessary to segregate and identify rejectable welds.8.5.2 When the joined parts contain a large number of spot-welds, and the integrity of the product does not depend on the
40、qualityof individual welds but rather on the number of unacceptable welds expressed as a percentage of the total number of welds. Theprint-out should consist of a weld sequence number and a running percentage of unacceptable welds when the individualspot-welds are identifiable by sequence number.8.5
41、.3 If weld identification is not possible, then the welding apparatus should be equipped with an automatic markingattachment. With the markings and the records, the acceptability of the welded part can be based on the percentage of unacceptablewelds and their location distribution.9. Procedure9.1 Se
42、nsor and Preamplifier AttachmentThe sensor should be mounted to the lower (grounded) electrode or electrode holder.If the measurements are to be made only as a periodic sampling of weld quality, a liquid couplant may be used provided that itis periodically replenished and standardization of the syst
43、em response is maintained. For sustained monitoring, such as on-lineAEexamination or control of each nugget, the sensor should be permanently mounted using an epoxy adhesive or a similar material.A preamplifier is usually positioned near the sensor. However, when the instrumentation is located less
44、than 1 m 3 ft from thesensor, the gain otherwise supplied by the preamplifier may be incorporated into the main amplifier of the instrument.9.2 Preliminary MeasurementsThe AE signal from a single spot-weld should be displayed on a waveform recorder. A wirecoil or Hall effect sensor positioned near a
45、n electrode can be used as a current sensor, thus providing a timing reference and triggersignal for viewing and measuring theAE signal. This reference signal can be also obtained through an appropriate interconnectionto the weld controller. Having established a typical AE trace, characteristic stag
46、es should be identified and one or more selectedas anAE examination parameter. For example, weld quality indicators may be obtained from theAE response to nugget formation,expulsion, or cracking.9.2.1 New ApplicationsIf the instrumentation was not previously applied to a specific welding problem, pr
47、eliminarymeasurements must be made to determine the instrument settings and the conditions for monitoring. The weld controller settingsare determined from normal welding considerations. First, the completeAE response should be observed on the waveform readout.Next, the amplification (gain) of the in
48、strumentation, if available, should be set to the maximum value where the AE signals,representing the selected examination parameter, do not saturate the amplifier. This step will ensure that the measurement will bemade with the best obtainable signal-to-noise ratio. Next, the detection threshold le
49、vel should be established at a value that isslightly above the peaks of the AE signals, which are to be excluded from the measurement. The timing control is referenced tothe onset of the weld current and consists of a delay and a time interval. These time intervals should be selected so that themonitoring is restricted to the time interval when relevant signals are present. The finalized settings of the weld controller and theAE instrumentation should be recorded along with a waveform of the total acoustic emission signal. The AE or energy countsobtained from indiv
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