1、RecommendedPractices forGas Metal ArcWeldingANSI/AWS C5.6-89RAn American National StandardKeywords Gas metal arc welding, joint ANSI/AWS C5.6-89Rdesign, arc spot welding, safety An American National StandardtrainingApproved byAmerican National Standards InstituteAugust 16,1989Recommended Practices f
2、orGas Metal Arc WeldingPrepared byAWS Committee on Arc Welding and CuttingUnder the Direction ofAWS Technical Activities CommitteeApproved byAWS Board of DirectorsAbstractThis standard is a recommended practice on the gas metal arc welding (GMAW) process. This document presents thebasic concepts of
3、this process and should enable the reader to obtain a fundamental understanding of this process andits variations, such as short circuit, spray, and pulse modes of metal transfer. It provides the specific technical datawhich will act as a guide in establishing optimum operation of the process.Americ
4、an Welding Society550 N.W. LeJeune Road, Miami, Florida 33126Statement on Use of AWS StandardsAll standards (codes, specifications, recommended practices, methods, classifications, and guides) of the AmericanWelding Society are voluntary consensus standards that have been developed in accordance wit
5、h the rules of theAmerican National Standards Institute. When AWS standards are either incorporated in, or made part of, documentsthat are included in federal or state laws and regulations, or the regulations of other governmental bodies, their provisionscarry the full legal authority of the statute
6、. In such cases, any changes in those AWS standards must be approved by thegovernmental body having statutory jurisdiction before they can become a part of those laws and regulations. In allcases, these standards carry the full legal authority of the contract or other document that invokes the AWS s
7、tandards.Where this contractual relationship exists, changes in or deviations from requirements of an AWS standard must be byagreement between the contracting parties.International Standard Book Number: 0-87171-301-2American Welding Society, 550 N.W. LeJeune Road, Miami, Florida 33126 1989 by Americ
8、an Welding Society.All rights reservedPrinted in the United States of AmericaReaffirmed: January 20,1994Reprinted: January 1997Note: The primary purpose of AWS is to serve and benefit its members. To this end, AWS provides a forum for theexchange, consideration, and discussion of ideas and proposals
9、 that are relevant to the welding industry and theconsensus of which forms the basis for these standards. By providing such a forum, AWS does not assume any dutiesto which a user of these standards may be required to adhere. By publishing this standard, the American Welding Societydoes not insure an
10、yone using the information it contains against any liability arising from that use. Publication of astandard by the American Welding Society does not carry with it any right to make, use, or sell any patented items. Usersof the information in this standard should make an independent, substantiating
11、investigation of the validity of thatinformation for their particular use and the patent status of any item referred to herein.With regard to technical inquiries made concerning AWS standards, oral opinions on AWS standards may be rendered.However, such opinions represent only the personal opinions
12、of the particular individuals giving them. These individualsdo not speak on behalf of AWS, nor do these oral opinions constitute official or unofficial opinions or interpretationsof AWS. In addition, oral opinions are informal and should not be used as a substitute for an official interpretation.Thi
13、s standard is subject to revision at any time by the AWS Committee on Arc Welding and Cutting. It must be reviewedevery five years and if not revised, it must be either reapproved or withdrawn. Comments (recommendations, additions,or deletions) and any pertinent data that may be of use in improving
14、this standard are requested and should be addressedto AWS Headquarters. Such comments will receive careful consideration by the AWS Committee on Arc Welding andCutting and the author of the comments will be informed of the Committees response to the comments. Guests areinvited to attend all meetings
15、 of the AWS Committee on Arc Welding and Cutting to express their comments verbally.Procedures for appeal of an adverse decision concerning all such comments are provided in the Rules of Operation ofthe Technical Activities Committee. A copy of these Rules can be obtained from the American Welding S
16、ociety, 550N.W. LeJeune Road, Miami, Florida 33126.Photocopy RightsAuthorization to photocopy items for internal, personal, or educational classroom use only, or the internal, personal, oreducational classroom use only of specific clients, is granted by the American Welding Society (AWS) provided th
17、atthe appropriate fee is paid to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, Tel: 508-750-8400; online: http:/ Committee on Arc Welding and CuttingE.R. Bohnart, ChairmanJ.R. Hannahs, 1st V. ChairmanB.L. Shultz, 2nd V. ChairmanW.A. Dierschow, SecretaryD.R. AmosW.L. BallisK.
18、E. BanksR.L. BennettLA. Colarossi*J.R. CondraN.A. FreytagR.H. FrostR. T. Hemzacek*G.K. HickenJ.E. HinkelD.B. HollidayL.C. Northard*N.E. LarsonE.R. PierreL.J. PrivoznikJ.S. SayreL.R. SoissonM.D. Stepath*E.P. VilkasG.K. Willecke*Miller Electric Mfg. CompanyMidmark CorporationTaylor-Winfield Corporatio
19、nAmerican Welding SocietyWestinghouse Turbine PlantColumbia Gas Distribution CompanyTeledyne MckayThermal Dynamics CorporationConsultantE.I. DuPont de Nemours a method usingmolding shoes to confine the molten weld metal forvertical welding electrogas welding (EGW); and amethod of controlled pulsatin
20、g current (GMAW-P)to provide a uniform spray droplet metal transferfrom the electrode at lower average current levels.The GMAW process uses either semiautomatic,machine, or automatic equipment and is princi-pally applied in high production welding. Mostmetals can be welded with this process and may
21、bewelded in all positions with the low energy varia-tions of the process. GMAW is an economical pro-cess that requires little or no cleaning of the weldmetal. Warpage and metal finishing are minimal.Each of the variations of GMAW provides spe-cific advantages, and standard process equipmentis normal
22、ly designed to permit the use of several ofthese variations. However, some equipment is de-signed for one specific mode only. Other variations,such as pulsed current or other processes such aselectrogas, require essentially special units whichare unique for these variations.The Committee has prepare
23、d these recom-mended practices as guidelines with the hope thatthey will serve as an incentive for industry to furtherdevelop the GMAW process. The Committee is con-tinuing its activities to provide data for additionalmaterials, designs, and equipment, and these rec-ommended practices will be revise
24、d as new infor-mation becomes available.2. Fundamentals2.1 Principles of Operation. GMAW is an arc weld-ing process which incorporates the automatic feed-ing of a continuous, consumable electrode that isshielded by an externally supplied gas. Since theequipment provides for automatic control of thea
25、rc, the only manual controls required by the welderfor semiautomatic operation are the travel speed,and gun positioning and guidance.Process control and function are achievedthrough these the basic elements of equipment (seeFigure 1).(l)Gun(2) Electrode Feed unit(3) Power SourceThe gun guides the co
26、nsumable electrode andconducts the electrical current and shielding gas tothe workpiece. The electrode feed unit and powersource are used in a system that provides automaticregulation of the arc length. The basic combinationused to produce this regulation consists of a con-stant voltage power source
27、 (characteristically pro-viding an essentially flat volt-ampere curve) inconjunction with a constant speed electrode feedunit. The arc length self-regulation produced by theconstant voltage power source, constant speedelectrode feed unit combination is described indetail in 3.2.5. Some GMAW equipmen
28、t, however,uses a constant current power source (characteristi-SHIELDING GASREGULATORELECTRODESUPPLYSHIELDING GASSUPPLYWORKPIECEFigure 1 - Basic GMAW Equipmentcally providing a drooping volt-ampere curve) plusan arc voltage-controlled electrode feed unit. Withthis constant current combination, arc v
29、oltagechanges, caused by a change in the arc length, willinitiate a response in the electrode feed unit toeither increase or decrease the electrode feed speedto maintain the original arc length setting. In someapplications, a constant current power source maybe coupled with a constant speed electrod
30、e feedunit. This combination will provide only a smalldegree of automatic self-regulation and can be quitedemanding in technique and set-up for semi-automatic welding.However, some users think this combination af-fords the range of control over the arc energy that isconsidered important in coping wi
31、th the high ther-mal conductivity of the aluminum base metal.2.1.1 The following are some advantages ofGMAW when compared to SMAW:(1) Can be used in all positions with the lowenergy modes(2) Virtually no slag to remove or trap in weld(3) Less welder training time than SMAW(4) No stub loss(5) Adaptab
32、le to semiautomatic, machine andautomatic welding(6) Low hydrogen process(7) Faster welding speeds than that used forSMAW2.1.2 The following are some limitations ofGMAW when compared to SMAW:(1) The related welding equipment is more com-plex, more costly, and less portable.(2) The shielding gas must
33、 be protected fromstrong winds and air drafts.(3) The cooling rates of the completed weld arehigher than slag producing processes.(4) The welding gun is larger than SMAW elec-trodes, making it difficult to weld hard-to-reachjoint locations.(5) The short circuiting welding arc is smallerthan the arc
34、produced with the SMAW process.Therefore, the possibility of incomplete fusion ex-ists on thicker weldments due to less heat input andbecause of arc outages.(6) The base metal must be cleaned before weld-ing while SMAW can tolerate some contamination.2.2 Characteristics. The characteristics of GMAWa
35、re best described by the three basic modes of metaltransfer which may occur with the process: axialspray transfer, globular transfer, and short circuitingtransfer. Axial spray and globular transfer are associ-ated basically with relatively high arc energy. Withthe occasional exception of the spray m
36、ode in verysmall diameter electrodes, both axial spray and glob-ular transfer are normally limited to the flat and hori-zontal welding positions with base metal thickness ofnot less than 1/8 in. (3.2 mm). Pulsed spray transfer,in which the average energy level is reduced, is an-other exception (see
37、2.3.1). Short circuiting transferis a relatively low energy process generally limited tobase metal thicknesses not more than 1/8 in., but isused in all welding positions.The physics of weld metal transfer are well under-stood. A combination offerees is responsible for de-taching the molten metal fro
38、m the electrode andpropelling it across the arc to the base metal. Two ofthese forces, gravity and “pinch effect,“ may be con-sidered in a simple description of the mechanism oftransfer and its three basic modes.Pinch effect is the momentary necking of the liq-uid drop from the current carrying elec
39、trode thatoccurs as a result of the electromagnetic effects ofthe current (Figure 2). It is the key to axial spraytransfer (see 3.2.6.2). In any conductor, the pincheffect force is proportional to the square of the cur-rent flowing through it; i.e., if the current is dou-bled, the pinch force will b
40、e four times as large. Thispinch effect can be made large enough to cause theelectrode to “neck down“ and finally to separate.The molten drop at the end of an electrode is easilypinched off at normal welding currents. Globulartransfer is characterized by the predominant effectof the force of gravity
41、.2.2.1 Axial Spray Transfer (Gas Shield with aMinimum of 90 Percent Argon). In this mode,metal transfer across the arc is in the form of drop-lets of a size equal to or less than the electrode diam-eter. The droplets are directed axially in a straightline from the electrode to the weld pool. The arc
42、 isvery smooth and stable.The axial spray transfer mode is established at aminimum current level for any given electrode di-ameter (current density). This current level is gener-ally termed the transition current (see Figures 3 and4). A well defined transition current exists only withgas shield cont
43、aining a minimum of ninety percentargon. At current levels below the transition cur-rent, the drop size increases larger than the diame-ter of the electrode (see Figures 4 and 5).The arccharacteristics are quite unstable in this operatingrange.CURRENT(A)A2ELECTRODEPINCH EFFECT FORCE. PFigure 2 - Ill
44、ustration of Pinch Effect2.2.2 Globular Transfer (Gas Shield with CO2 orHelium). In this mode, metal transfer across the arcis in the form of irregular globules randomly di-rected across the arc in irregular fashion (see Figure5), resulting in a considerable amount of spatter.Spatter is minimized wh
45、en using CO2 shield by ad-justing the welding conditions so that the tip of theelectrode is below the surface of the weld pool andwithin a cavity generated by the force of the arc. TheCO2 arc is generally unstable and characterized by acrackling sound. It results in a weld bead surfacethat is rough
46、in appearance (ripple effect) in com-parison to a bead obtained with axial spray transfer.Since most of the arc energy is directed downwardand below the surface of the weld pool, the weldbead cross section exhibits very deep fusion withless wetting at the weld bead extremities than thatobtained in t
47、he axial spray transfer mode. Relativestability of the CO2 arc can be established at highercurrent levels using a buried arc; i.e., wire melts be-low surface of base metal.When helium-rich gas mixtures are used, abroader weld bead is produced with a depth of fu-sion similar to that of argon, but wit
48、h a more desir-able cross section.1200“1000 800 tOLUICJ- 600 QLULUQ.COQ 400 - -200 -ALUMINUM WIREPOSITIVE ELECTRODE0.015 in.(0.4 mm)ARGON GAS 0.030 in.(0.8 mm)“ 30 20 i0.047 in.(1.2 mm)0.062 in.(1.6 mm)TRANSITIONCURRENT.25 K2toCELU 15-LUO_10OLULU5:LU-rtoLUOzQ11JJ1.QJJ1J_ISr1200 “1000 “800 -600 -400
49、-200 “0 -0.020 in.(0.5/4IA/ )/ iI111h-mm)1/IYA/0.025 in.(0./r/ /DROPNA/(-7 mm)/STEEL WIREPOSITIVE ELECTRODEARGON-2% 02/ 0.030 in./ (0.8 mm) / 0.035 in. / (0.9 mm) /0.045 in./ (1.1 mm)/ yASPRAY xs XO.062 in.f (1.6 mm)“TRANSITIONCURRENT1 1- 30- 25tif20 uiV)DC. . 10) 100 200 300 400CURRENT, A(A) ALUMINUM ELECTRODE DCEPARGON SHIELDED GAS100 200 300CURRENT, A400(B) STEEL ELECTRODE DCEPARGON - 2% ARGON SHIELDING GASFigure 3 - Melting Rates of Gas Metal Arc Electrodes2.2.3 Short Circuiting Transfer (GMAW-S).
