1、4ip American Welding Society I For CostmEff ective Welding 4jb American Welding Society STD*AWS DPW-ENGL L999 07842b5 0519498 938 I International Standard Book Number: 0-87 17 1-605-4 American Welding Society, 550 N.W. LeJeune Road, Miami, FL 33126 O 1999 by American Welding Society. All rights rese
2、rved Printed in the United States of America NOTE: Although care was taken in choosing and presenting the data in this guide, AWS cannot guarantee that it is error free. Further, this guide is not intended to be an exhaustive treatment of the topic and therefore may not include all avail- able infor
3、mation, including with respect to safety and health issues. By publishing this guide, AWS does not insure any- one using the information it contains against any liability or injury to property or persons arising from that use. Photocopy Rights Authorization to photocopy items for internal, personal,
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5、; online: http:/ 11 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Contents Section Page No . Primary Concepts of Weldablllty 1 Accepting Metal Fabrication Projects 5 Production Welding Cost Analysis 9 Modular Construction 17 Welding Process Selection 23 Primary Concepts of Welding Design . 33 Fatigue
6、 Considerations . 45 Welding Safety Considerations . 51 Weld Joint Design Considerations 57 Weld Distortion and Control . 63 Checklist for Sound Welding Decisions 71 Defects and Discontinuities of Welding 75 Nondestructive Examination . 93 Information for the Welder 103 Fitting Aids 109 Welding Meta
7、llurgy: Practical Aspects 119 Arc Stud Welding 129 Thermal Spray Fundamentals . 133 I . 111 Acknowledgment The original Manual was the result of a contract between Ingalls Shipbuilding and the Maritime Administration with support from the U.S. Navy. This project was performed by Puget Sound Naval Sh
8、ipyard for the Welding Panel, SP-7, of the Ship Production Committee of the Society of Naval Architects and Marine Engineers. Recognized contributors to the original project included the American Welding Society, the Lincoln Electric Foundation, Mr. Omer Blodgett, and New- port News Shipbuilding. In
9、 addition, Mr. Frank Gatto, Puget Sound representative to SP-7, was singled out for apprecia- tion. The Manual is meant to serve as a practical guide for engineers, planners, and hands-on professionals to improve scheduling and lessen rework. The Manual was released to the public in 1992. iv STDaAWS
10、 DPW-ENGL L777 m 038433h5 0527502 252 E I SECTION I Primary Concepts of Weldability Contents Weldability 2 Personnel Concerns about Fabrication Projects . . 2 Fundamentals of Welding Decisions 3 Coordination of Expertise 4 Education . . . . . ._. ._. ._. . _. . . , . . , . . . . . . . . . . . . . .
11、. . . . . . . 4 The Welder, Technician, and Production Supervisor . . ._. . . _. . . . . . . . . . . . . . . 4 The 100% Quality Weld and Weld-Associated Failures 4 Weldability Can Be Determined by the Manufacturer ._ . , . . . . . ._. . . . . . . . . . . . 4 Bibliography/Recommended Reading List . 4
12、 1 STD-AWS DPW-ENCL 1999 m 07842b5 0539502 m SECTION 1-PRIMARY CONCEPTS OF WELDABILITY Section I-Primary Concepts of Weldability Weldability Welding is used to make large and sometimes com- plex structures from smaller and simpler metal compo- nents. In general, a weld is a localized coalescence of
13、metal that is used to join or repair metal components. Filler metal may or may not be added to the weld. The capacity and ability to join these metal components with available resources help define the term weldability. The definition of weldability is: “The capacity of a metal to be welded under th
14、e fabrication conditions im- posed into a suitably designed structure, which will per- form the intended service.” When the definition of weldability is reduced to its lowest common denominator, this definition is “it.” To ensure weldability, interaction of countless groups and individuals with spec
15、ific needs may be involved. For a project to reach a successful conclusion, these needs must be identified, clarified, and, when in conflict, resolved. All metals may be considered weldable by the very fact that they exist as metals. Depending on whether you are the customer, the welder, the inspect
16、or, or the fabrica- tor your definition of weldability may be different. Gen- erally, it is the suitability for service, cost, and weldment aesthetics that determines weldability. With a fundamen- tal understanding of welding and a knowledge of the re- sources available, “lack of weldability” causin
17、g inservice failures, production failures, cost overruns, and schedule delays may be avoided. In common usage the term “weldability” is somewhat ambiguous and about as varied as the people who use it. The “degree” of weldability can be defined in terms of weld costs; the capacity of the fabrication
18、to perform its intended service; the ability of the weldment to meet fab- rication acceptance standards; or the difficulty of joining a material with a specific process. Personnel Concerns about Fabrication Projects Major concerns about a fabrication project and its weldability are expressed by thos
19、e involved as follows: From the customer: “Does the fabrication perform the intended service and will it last as long as intended? “Is the fabrication completed within cost and on schedule?” “Is it aesthetically pleasing?” From the engineer: “Does the weld and its heat-affected zone meet the critica
20、l base metal requirements that are necessaly for the intended service of the customer?” From the manufacturer: “How much money does it cost to make the weld (i.e., whats my profit) ?” “Are there any inspections or requirements associated with the weld that will prevent acceptance of my work?” “Am I
21、subject to any liabilities if my fabrication is not completed on time or fails in service? From the welder: “Do I have clearly defined instructions (such as draw- ings that specify weld size, joint design, material type, material size, stress relie$ and welding procedures)? “Is there adequate weld j
22、oint access? “Is there adequate environmental protection ?” “Do I have the proper equipment to accomplish the work?” “Are the fabrication requirements achievable from the standpoint of accessibility, position, distortion con- trol, weld size, inspection requirements and fabrica- tion sequence ?” “Am
23、 I trained and qualified to per$orm the welding required? 2 It is obvious, since the weldability of a metal inter- sects so many disciplines, that the solution to many weld- associated problems and the ultimate success of a project lies in afabricators ability to coordinate its available expertise.
24、There can be no question that people are still the most important resource in the fabrication enterprise. Because of this, it is recommended that a preacceptance bid re- view group, including production as well as technical personnel, be established to review projects prior to ac- ceptance. Formatio
25、n of this group may be the single most important action taken to ensure a successful and profit- able completion for all parties involved. Unless the same project is repeated over and over again, it is obvious that one person cannot resolve all the issues necessary for the project to be a success fo
26、r all the participants. Fundamentals of Welding Decisions One individual in a metals fabrication firm with a varying workload will find it difficult to make good welding decisions for all of the firms needs. The com- plexity of welding decisions is immense if the work var- ies. If an individual make
27、s enough welding decisions, expertise will be required beyond that of filler metals, base metals, and welding processes. This expertise will require a background in, and integration of the technical fields. Coordination of Expertise One person normally does not have expertise in all of the areas req
28、uired to make sound welding decisions. It will benefit a company to have a welding engineer to handle the majority of the welding problems that will arise. However, this individual will find it necessary to coordinate with other available expertise to make the best decisions for the company. If a co
29、mpany is small, this may require hiring a part-time consultant. Education There is no substitute for education of personnel in- volved in welding. Education is needed by the fabrica- tion shop superintendents, the design engineers, the planners and estimators, the production supervisors, and the wel
30、ding mechanics. Each has different needs. Often, a specification or procedural requirement will not be fol- lowed unless there is an understanding of why the re- quirement is necessary. Understanding the importance of preheats, postheat treatments, and filler metal selection SECTION 1-PRIMARY CONCEP
31、TS OF WELDABILITY and how they can affect the safety of personnel and the suitability of the part for service creates a desire by all in- dividuals to follow requirements. Knowing the basics of welding engineering can prevent a company from exten- sive rework or a customers refusal to accept a manuf
32、ac- turers product. The Welder, Technician, and Production Supervisor The resolution of many welding problems requires much more than technical solutions. Welding problems require practical solutions as well. For this reason, the practical expertise of the journeyman mechanic and his supervisor can
33、never be overlooked. They are absolutely essential if a company expects to remain profitable. It is for this reason the use of welding engineering techni- cians is quite common in larger companies. Technicians frequently are trained individuals with journeymen pro- duction experience. A balance of w
34、elding engineers and welding engineering technicians is most desirable for re- solving most welding problems. The 100% Quality Weld and Weld- Associated Failures Designers often mistakenly expect the welds they de- sign to have properties that equal or exceed the desired properties of the base metal
35、. The major error in this logic is that the base metal and the weld metal do not perform independently. Rarely does the weld improve the properties of the metal it joins. The base material, the weld, and the welds heat-affected zone are not homogeneous regions. They are, in effect, structural and me
36、tallurgical discontinuities within the weldment. This is due to the fact that the base materials usually have undergone significant mechanical and/or thermal treatments to optimize their properties, the weld usually performs its service in the as-cast condi- tion, and the heat-affected zone has unde
37、rgone widely varying heating and cooling rates. In many cases a weld joint lowers fatigue properties and lowers impact proper- ties; in some cases a weld joint also lowers the tensile and yield properties. However, large or complex struc- tures must be welded with high joint efficiency, since large
38、monolithic cast or wrought structures cannot be made in most cases. Since welds are usually located at changes of cross sections (commonly associated with highly stressed areas), the welds are often in areas where the structure fails. These failures may be wrongly attributed to welds that are percei
39、ved as inherently weak or flawed. These I I 3 STD-AWS DPW-ENGL 3999 M 0384265 0539504 Tb3 SECTION 1-PRIMARY CONCEPTS OF WELDABILITY failures are more likely caused by poor decisions on the part of engineers or company management due to a lack of knowledge or training. Improperly selected joint desig
40、ns, welding processes, locations of welds, and filler metals are frequently asso- ciated with weld failures. The root cause of these types of failures is in the decision-making process and not in the quality of the weld. Weldability Can Be Determined by the Manufacturer When a manufacturer designs a
41、nd fabricates a weld- ment, it can truly be said that the manufacturer deter- mines weldability. The manufacturer then controls most of the variables that determine weldability. The weldabil- ity of a metal, to a large extent, is determined by the manufacturers ability to: Recognize the cause of exi
42、sting and potential produc- tion problems. Properly utilize, coordinate, and develop cooperation of available expertise to make sound welding decisions. Often weld-associated failures are caused by lack of knowledge about welding and its effect on the base mate- rials. These failures are wrongly vie
43、wed as resulting from inherent weaknesses of welds. In most cases, with proper utilization of available expertise, the failures could have been avoided. Bibliography/Recommended Reading List Welding Handbook, 8th ed., vol. 1, Welding Technology (WHB-1.8). Miami, Fla.: American Welding Society. STD.A
44、WS DPW-ENCL 3999 m 07642b5 0539505 IT6 9 I SECTION 2 Accepting Metal Fabrication Projects Contents Background 6 Defining Special Projects 6 Establish a Prebid Review Group (Before Accepting Special Projects) . 6 Establish a Detail Planning Group (Prior to Issuing Job Orders) 7 Summary . . . . . ._._
45、. ._. . ._ . . . . . . . . . . . . . . 7 5 Section 2-Accepting Metal Fabrication Projects Background The critical question asked by a metals fabricator for a completed project to be considered successful is: Did the project make a profit and was it completed on time? When large or small companies ha
46、ve repetitive work, they are usually quite successful. They also know the pit- falls. They know what their minimum bid should be and what delivery or schedule times can be met. They proba- bly have experienced the normal day-to-day items that threaten their profit and the quality of their work. Know
47、- ing these pitfalls, they can make allowances for them. However, for a company to be successful when it accepts work that can be defined as a special project (meaning a different type of work for the company), the engineer, the fabricator, and the welder need a funda- mental understanding of the we
48、ldability of metals and the basics of sound welding decisions. During the accep- tance of work, many decisions that seem innocuous to welding end up jeopardizing the weldability of materials and the service suitability of the completed weldment. Defining Special Projects The critical first step for
49、a company is the ability to recog- nize a special project. Nearly all special projects require high up-front costs. There are increased costs in determining: Should the company bid on the project? What should the bid be? To what extent are production instructions required? What are the costs to establish these instructions? How and when to monitor the work in production? Are the company resources adequate? Do company equipment and personnel capabilities ad- equately meet project requirements? What additional training/equipment is re
