1、BRITISH STANDARD BS6944:1988 Specification for Flash welding of butt joints in ferrous metals (excluding pressure piping applications) UDC669.15194.55/.56/.57:621.791.762:620.1BS6944:1988 This British Standard, having been prepared under the directionof the Welding Standards Committee, was published
2、 under the authority ofthe Board of BSI and comes intoeffect on September1988 BSI04-1999 The following BSI references relate to the work on this standard: Committee reference WEE/33 Draft for comment86/77824 DC ISBN 0 580 16660 0 Committees responsible for this British Standard The preparation of th
3、is British Standard was entrusted by the Welding Standards Committee (WEE/-) to Technical Committee WEE/33, upon which the following bodies were represented: Associated Offices Technical Committee British Chain Manufacturers Association British Railways Board British Steel Corporation Electricity Su
4、pply Industry in England and Wales Water-tube Boilermakers Association Welding Institute Welding Manufacturers Association (BEAMA Ltd.) Amendments issued since publication Amd. No. Date of issue CommentsBS6944:1988 BSI 04-1999 i Contents Page Committees responsible Inside front cover Foreword iii 1
5、Scope 1 2 Definitions 1 3 Information and requirements to be agreed and to be documented 1 3.1 Information to be supplied by the purchaser 1 3.2 Requirements to be agreed 1 4 Welding equipment 2 5 Material to be welded 2 6 Process sequence: general 2 7 Process sequence: preparation 3 8 Process seque
6、nce: welding 3 8.1 Overhang 2 8.2 Clamping force 3 8.3 Alignment 3 8.4 Initial end squaring 3 8.5 Pre-heating 3 8.6 Flashing 3 8.7 Upsetting 3 8.8 Upset current time 3 8.9 Unclamping 3 9 Process sequence: finishing 3 9.1 Removal of upset metal 3 9.2 Post weld heat treatments 3 10 Procedure approval
7、3 10.1 General 3 10.2 Monitoring 4 10.3 Changes affecting approval 4 10.4 Heat treatment and finished condition 4 10.5 Sample preparation 5 10.6 Bend testing 5 10.7 Macro-examination 5 10.8 Tensile testing 6 10.9 Hardness testing 6 11 Statement of results of procedure approval 6 12 Production contro
8、l 9 12.1 Visual inspection 9 12.2 Mechanical tests 9 13 Parameter monitoring 9 14 Non-destructive testing 9 15 Weld acceptance criteria 10 Appendix A Welding equipment 11 Appendix B Generalized diagram illustrating monitoring variables 11 Appendix C Types of weld features 12BS6944:1988 ii BSI 04-199
9、9 Page Figure 1 Typical information to appear on a flash welding procedure record sheet 7 Figure 2 Typical information to appear on a flash welding procedure test report sheet 8 Figure 3 Generalized diagram illustrating monitoring variables 11 Figure 4 Flash welding features (diagrammatic only) 13 P
10、ublications referred to Inside back coverBS6944:1988 BSI 04-1999 iii Foreword This British Standard has been prepared under the direction of the Welding Standards Committee and is one of a series of British Standards concerned with the welding of metallic components of regular and irregular cross se
11、ction. This standard deals with the production of welds made by the flash welding process but excludes the flash welding of steel tubes for pressure applications which is covered in a separate standard (see BS4204). This standard follows the general pattern set by others in the series and is of the
12、“process” type. It embodies the currently accepted practice of initial procedure approval tests followed by periodical production control tests. This standard also details the various parameters specific to the flash welding process that are required to be determined in establishing the procedure. A
13、 list of the typical information to appear on a welding procedure sheet is given together with a typical test record sheet. An appendix gives guidance on typical flash welding imperfections. As the acceptance level of certain requirements, e.g.the contour and form of the weld profile, is related to
14、the service conditions of the joint, reference should be made for these details to the appropriate application standard, where such a standard exists. Where such guidance is not given, these aspects should be a matter of agreement between the contracting parties. It has been assumed in the drafting
15、of this British Standard that the execution of its provisions is entrusted to appropriately qualified and experienced people. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Complianc
16、e with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi toiv, pages1to14, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had ame
17、ndments incorporated. This will be indicated in the amendment table on theinside front cover.iv blankBS6944:1988 BSI 04-1999 1 1 Scope This British Standard specifies requirements for the automatic flash welding of ferrous metal sections excluding tubes, pipes and pipe fittings for pressure applicat
18、ions, which are covered in BS4204. In addition to the definitive requirements, it also requires the items detailed in clause3 to be documented. For compliance with this standard, both the definitive requirements and the documented items have to be satisfied. NOTEThe titles of the publications referr
19、ed to in this standard are listed on the inside back cover. 2 Definitions For the purposes of this British Standard the following definitions apply. For other terms the definitions in BS499-1 apply. 2.1 manufacturer the user of the welding equipment for the purposes of manufacturing welded products
20、2.2 automatic flash welding machine a welding machine that has an automatic sequence of events 2.3 inspecting authority the competent independent body or association that, where required, verifies compliance with this standard 2.4 upset current time the time after the commencement of upsetting durin
21、g which the current flows 2.5 pre-heating (flash welding) the resistance heating of workpieces to facilitate the onset of flashing by a series of current pulses with a cool time in between each pulse. The pulsing is achieved by moving the workpieces together and apart 3 Information and requirements
22、to be agreed and to be documented 3.1 Information to be supplied by the purchaser The following information to be supplied by the purchaser shall be fully documented. Both the definitive requirements specified throughout the standard and the documented items shall be satisfied before a claim of comp
23、liance with the standard can be made and verified. a) Specification of the material to be welded (see clause5) and of the required welded joint properties. b) Whether procedure approval tests are required and, if so, the necessary details (see clause10). c) The dimensional tolerances and surface fin
24、ish of the welded product. d) The number and title of the particular application standard; or where no application standard exists a statement of the quality and mechanical properties required. e) Whether production test specimens are to be retained for examination by the purchaser or his representa
25、tive. 3.2 Requirements to be agreed The following items to be agreed between the contracting parties, which are specified in the clauses referred to, shall be fully documented. Both the definitive requirements specified throughout the standard and the following documented items shall be satisfied be
26、fore a claim of compliance with the standard can be made and verified. a) Extent of dressing to remove upset (see9.1). b) Whether welded joints are to be subjected to any post weld heat treatment or controlled cooling (see9.2).BS6944:1988 2 BSI 04-1999 c) The type and number of welds required for pr
27、ocedure approval testing (see10.1). d) Limitations of the applicability of the welding procedure see10.3 b). e) Whether test specimens are to be subjected to any post weld heat treatment (see10.4). f) Bend testing: 1) test procedure where this does not comply with BS709 see10.6.1 a); 2) test procedu
28、re where entire section is used as test specimen see10.6.1 b); 3) test requirements see10.6.1 c); 4) variation in acceptable level of defects (see10.6.2). g) Tensile testing: 1) test requirements for component testing where no application standard exists see10.8 a); 2) variation in test specimen sha
29、pe see10.8 c). h) Number and type of production control tests (see12.2.1). i) Whether production control bend test specimens are to be retained for examination (see12.2.3). j) If parameter monitoring in production testing is required see clause13 b). k) If non-destructive testing of production welds
30、 is required (see clause14). l) Acceptance criteria for weld imperfections (see clause15). 4 Welding equipment All welding shall be done on a machine with an automatic flash welding sequence. NOTE 1Guidance on the choice of welding equipment is given in Appendix A. NOTE 2Where flash welding guards a
31、re used, they should be placed at such a distance from the clamped components as to minimize the possibility of particles thrown off during the flashing period richocheting into the weld. 5 Material to be welded It shall be demonstrated by the procedure approval tests (see clause10) that the materia
32、l or combination of materials selected can be satisfactorily flash welded. NOTE 1Certain features of the metallurgical structure such as laminations or non-metallic inclusions, can be detrimental to weld quality as can the presence of minor alloying elements naturally occurring or deliberately added
33、 to aid processing, e.g.to confer free cutting properties. NOTE 2Components to be joined should be of similar shape and cross-sectional area. 6 Process sequence: general The sequence shall consist of all or selected operations from those listed in clauses7, 8 and9 but the order in which the operatio
34、ns are carried out shall be as stated in the welding procedure (see10.1 and Figure 1) and not necessarily in the sequence given in these clauses. Where specific operations are used these shall be carried out according to the relevant requirements given in clauses7, 8 and9. 7 Process sequence: prepar
35、ation The procedure for component preparation, including the acceptable flatness and other characteristics of the surfaces to be welded, shall be established during the procedure development. Areas of electrical contact on the component and the machine shall be cleaned, as required, to give a consis
36、tent, low resistance interface. 8 Process sequence: welding 8.1 Overhang Where components are of the same nominal size and composition, they shall be positioned in the welding machine such that the welding interface is central to the contact dies as assessed by visual or mechanical means. The overha
37、ng for a particular application shall be determined and specified in the procedure. NOTEThe two components should be clamped wherever possible so that the overhang of each is equal. Where the composition or size of the two components is different it may be desirable for them to have different overha
38、ngs, either to achieve a heat balance or to permit effective work holding. The initial die opening (sometimes referred to as start gap or clamping distance) is equal to the sum of the overhang of the two components.BS6944:1988 BSI 04-1999 3 8.2 Clamping force Components shall be secured in the weldi
39、ng machine by clamps or a combination of clamps and end-stops. The clamping force exerted on the components shall not cause deformation or deleterious marking of the components. 8.3 Alignment The ends of the components to be welded shall be aligned such that the tolerances specified for the finished
40、 product can be achieved. 8.4 Initial end squaring If initial end squaring is carried out to reduce irregularities on the end of the workpieces by flashing, it shall not overheat the component such as to cause collapse or distortion. NOTEInitial end squaring is sometimes known in flash welding as bu
41、rnoff. 8.5 Pre-heating During pre-heating, the heating of the component ends shall be uniform when assessed visually. NOTEThere should be no evidence of gross local melting on the ends of the components during pre-heating. 8.6 Flashing Once initiated, flashing shall be continuous. NOTEWhere a monito
42、ring device is used, the record of flashing will assist in assessing whether significant breaks have occurred. 8.7 Upsetting Upsetting shall proceed immediately following flashing. Upsetting shall be sufficient to ensure that voids are closed and oxides are expelled from the weld interface. The weld
43、 interface shall extend into the upset metal. 8.8 Upset current time The upset welding current shall be maintained until after upsetting has commenced. NOTEThe current should not continue for so long that overheating occurs. 8.9 Unclamping The time between completion of welding and unclamping shall
44、be such that cracking is prevented and deformation is minimized. 9 Process sequence: finishing 9.1 Removal of upset metal Removal of the excess upset metal shall not cause mechanical or thermal damage in the parent metals. The surface of the trimmed area shall be free from cracking. The method of tr
45、imming shall be stated in the welding procedure record. The design thickness of the component shall not be reduced as a result of any dressing. NOTEIn general it is not necessary to remove the upset completely but, by agreement between the contracting parties, see3.2 a) dressing may be continued unt
46、il the weld is flush with the component surface. 9.2 Post weld heat treatments Any proposed heat treatment or controlled cooling associated with the welding process shall be stated in the welding procedure record and shall be the subject of agreement between the contracting parties see3.2 b). 10 Pro
47、cedure approval 10.1 General A procedure shall be established for each machine, for each size of component, and for each material or combination of materials to be used in production. Sufficient additional tests shall be carried out to define acceptable tolerance bands.BS6944:1988 4 BSI 04-1999 Repr
48、esentative welds shall be manufactured using the proposed procedure. These shall be subjected to testing to demonstrate their integrity. The form of the components for test welds and the number of components for test welds and the number and type of the test pieces required shall be in accordance wi
49、th the application standard, or in the absence of such an application standard, by agreement between the contracting parties see3.2 c). After the procedure has been approved, production shall be maintained within the acceptable tolerance bands, calibration of the equipment being carried out at regular intervals to ensure consistency of machine operation. NOTE 1It is recommended that the procedure approval tests carried out in accordance with this standard and approved by a purchaser or his representative should be accepted by other purchasers, or
