AWS C7.1M/C7.1:2013 An American National Standard Approved by the American National Standards Institute February 5, 2013 Recommended Practices for Electron Beam Welding and Allied Processes 4th Edition Supersedes AWS C7.1M/C7.1:2004 Prepared by the American Welding Society (AWS) C7 Committee on High Energy Beam Welding and Cutting Under the Direction of the AWS Technical Activities Committee Approved by the AWS Board of Directors Abstract This document presents Recommended Practices for Electron Beam Welding and Allied Processes. It is intended to cover common applications of the process. Processes definitions, safe practices, general process requirements, and inspection criteria are provided. AWS C7.1M/C7.1:2013 International Standard Book Number: 978-0-87171-835-8 American Welding Society 8669 Doral Blvd., Suite 130, Doral, FL 33166 © 2013 by American Welding Society All rights reserved Printed in the United States of America Photocopy Rights. No portion of this standard may be reproduced, stored in a retrieval system, or transmitted in any form, including mechanical, photocopying, recording, or otherwise, without the prior written permission of the copyright owner. Authorization to photocopy items for internal, personal, or educational classroom use only or the internal, personal, or educational classroom use only of specific clients is granted by the American Welding Society provided that the appropriate fee is paid to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, tel: (978) 750-8400; Internet: <www.copyright.com>. ii AWS C7.1M/C7.1:2013 Foreword This foreword is not part of AWS C7.1M/C7.1:2013, Recommended Practices for Electron Beam Welding and Allied Processes, but is included for informational purposes only. Electron beam processing was initiated in the early 1900s, when an electron beam was used to produce tantalum metal by melting tantalum sponge. Since then, electron beam technology for materials processing has steadily advanced and is now commonly used. While electron beam processing encompasses a wide range of metal processing activities, this doc- ument focuses on welding and joining. The commercial application of electron beam welding (EBW) was first intro- duced in the late 1950s and subsequently gained rapid and widespread acceptance by the industrial community because of its ability to produce high aspect ratio (depth-to-width) welds and join dissimilar and difficult-to-weld materials. Welding speeds on the order of 760 mm/s [1800 in/min] and single-pass autogenous welds in metals of greater than 150mm [6 in] thickness have been achieved. It has been estimated that there are upwards of 3000 electron beam welders presently in operation throughout the world—of which approximately 35% are involved with automotive related tasks, 15% with both aircraft and aerospace related tasks, 10% with nuclear (either commercial or military) related tasks, 20% with a variety of job shop (contract welding) related tasks, and 20% with other industries (electronic, medical bimetal, Research and Development, etc.). It is also estimated that out of this total number of operating units, approximately 40% of those that were delivered during the’60s and’70s time frame (i.e., units having upwards of 35 years or more of operational time) are still being used on a regular basis—if not by the original purchaser, then by the 2nd or 3rd owner of the unit, thus attesting to the fact that equipment being supplied by the EBW manufactures has a demonstrated history of performing durably and reliably. The information contained in the Recommended Practices was compiled by the American Welding Society’s C7B Sub- committee on Electron Beam Welding and Cutting and has been carefully reviewed by a number of experts in the field, and should provide a helpful guide for use in applying the electron beam welding process. It must be noted that the oper- ating parameters specified in these recommended practices will not be the only possible parameter combinations that can be employed for successfully processing the materials and thicknesses shown. Changes in material composition, dimen- sional tolerances, and machine calibration will cause changes in the resulting welds. Therefore, the procedures contained herein are offered simply as a guide and are intended only for use in aiding the application of electron beam technology and increasing process consistency. AWS C7.1M/C7.1:2013, Recommended Practices for Electron Beam Welding and Allied Processes, is the third revision (4th edition) of the document issued initially in 1992. This edition adds three new practical examples and adaptations of the electron beam process, including electron beam braze welding (EBBW), electron beam cutting (EBC) and drilling, the deposition of supplementary weld metal (surfacing, cladding, and hard-facing), electron beam additive manufactur- ing (EBAM), surface texturing, and heat treating of components. Previous editions of the document are as follows: AWS C7.1-92 Recommended Practices for Electron Beam Welding AWS C7.1:1999 Recommended Practices for Electron Beam Welding AWS C7.1M/C7.1:2004 Recommended Practices for Electron Beam Welding Comments and suggestions for the improvement of this standard are welcome. They should be sent to the Secretary, AWS C7 Committee on High Energy Beam Welding and Cutting, American Welding Society, 8669 Doral Blvd., Suite 130, Doral, FL 33166. vii AWS C7.1M/C7.1:2013 Personnel AWS C7 Committee on High Energy Beam Welding and Cutting P. W. Hochanadel, Chair Los Alamos National Laboratory T. A. Palmer, 1st Vice Chair Applied Research Laboratory, Penn State K. W. Lachenberg, 2nd Vice Chair Sciaky, Incorporated B. C. McGrath, Secretary American Welding Society P. Blomquist Applied Thermal Sciences, Incorporated P. E. Denney The Lincoln Electric Company D. D. Kautz Los Alamos National Laboratory G. R. LaFlamme PTR—Precision Technologies, Incorporated E. D. Levert Lockheed Martin Missiles and Fire Control Advisors to the AWS C7 Committee on High Energy Beam Welding and Cutting R. D. Dixon Retired P. W. Fuerschbach Sandia National Laboratory R. W. Messler, Jr. Rensselaer Polytechnic Institute J. O. Milewski Los Alamos National Laboratory T. M. Mustaleski Retired D. E. Powers Retired R. C. Salo Sciaky, Incorporated AWS C7B Subcommittee on Electron Beam Welding and Cutting T. A. Palmer, Chair Applied Research Laboratory, Penn State B. C. McGrath, Secretary American Welding Society G. R. Gibbs Sandia National Laboratory P. W. Hochanadel Los Alamos National Laboratory D. D. Kautz Los Alamos National Laboratory K. W. Lachenberg Sciaky, Incorporated G. R. LaFlamme PTR—Precision Technologies, Incorporated E. D. Levert Lockheed Martin Missiles and Fire Control K. J. Zacharias Hamilton Sundstrand Space Systems Advisors to the AWS C7B Subcommittee on Electron Beam Welding and Cutting R. D. Dixon Retired D. R. Foster Pratt & Whitney G. S. Lawrence Retired J. O. Milewski Los Alamos National Laboratory J. C. Monsees Hi-Tech Welding & Forming T. M. Mustaleski Retired D. E. Powers Retired R. C. Salo Sciaky, Incorporated v AWS C7.1M/C7.1:2013 Table of Contents Page No. Personnel......................................................................................................................................................................v Foreword.....................................................................................................................................................................vii List of Tables................................................................................................................................................................xi List of Figures..............................................................................................................................................................xi 1. General Requirements........................................................................................................................................1 1.1 Scope..........................................................................................................................................................1 1.2 Units of Measurement................................................................................................................................1 1.3 Safety..........................................................................................................................................................1 2. Normative References.........................................................................................................................................2 3. Terms and Definitions.........................................................................................................................................2 4. Safety Considerations.........................................................................................................................................6 4.1 Scope..........................................................................................................................................................6 4.2 Potential Hazards........................................................................................................................................6 5. Process Fundamentals.......................................................................................................................................10 5.1 Description of Process..............................................................................................................................10 5.2 Areas of Application.................................................................................................................................12 5.3 Advantages and Limitations.....................................................................................................................12 5.4 Allied Processes........................................................................................................................................13 6. Description of Equipment.................................................................................................................................19 6.1 Introduction..............................................................................................................................................19 6.2 Modes of Electron Beam Welding............................................................................................................19 6.3 High- and Low-Voltage EBW Equipment................................................................................................22 6.4 Components of the EBW System.............................................................................................................22 6.5 EBW System Function and Performance Control....................................................................................26 6.6 EBW Equipment Specification.................................................................................................................27 7. Metallurgical Considerations...........................................................................................................................29 7.1 Introduction..............................................................................................................................................29 7.2 Heat-Affected Zone..................................................................................................................................29 7.3 Fusion Zone..............................................................................................................................................32 7.4 Metallurgical and Material Considerations..............................................................................................33 8. General Process Considerations.......................................................................................................................40 8.1 Overview..................................................................................................................................................40 8.2 Designing for Electron Beam Welding.....................................................................................................41 8.3 Joint Cleaning...........................................................................................................................................46 8.4 Welding Thin Metals................................................................................................................................48 8.5 Welding Thick Metals..............................................................................................................................49 8.6 Welding Dissimilar Thicknesses..............................................................................................................52 8.7 Fixtures.....................................................................................................................................................54 8.8 Controlling Parameters.............................................................................................................................54 8.9 Calibration and Verification.....................................................................................................................55 ix AWS C7.1M/C7.1:2013 Page No. 9. Inspection and Testing of Welds.......................................................................................................................56 9.1 Introduction..............................................................................................................................................56 9.2 Weld Characteristics.................................................................................................................................56 9.3 Inspection Processes.................................................................................................................................56 9.4 Special Inspection Techniques.................................................................................................................58 9.5 Acceptability Limits.................................................................................................................................58 9.6 Inspection Plans........................................................................................................................................59 10. Equipment Maintenance Program..................................................................................................................59 10.1 Preventive Maintenance Performed Daily................................................................................................59 10.2 Preventive Maintenance Performed Weekly.............................................................................................59 10.3 Preventive Maintenance Performed Monthly...........................................................................................60 10.4 Preventive Maintenance Performed Quarterly.........................................................................................60 10.5 Preventive Maintenance Performed Semiannually...................................................................................61 10.6 Preventive Maintenance Performed Yearly..............................................................................................61 11. Training and Qualification of Operators........................................................................................................61 11.1 Electron Beam Welding Equipment Operation........................................................................................61 11.2 Welding Operator Training Program........................................................................................................63 12. Weld Process and Procedure Development for Electron Beam Welding.....................................................65 12.1 Introduction..............................................................................................................................................65 12.2 Process Development Performance Requirements...................................................................................65 12.3 Structure/Properties Relationships...........................................................................................................65 12.4 Determination of Properties.....................................................................................................................66 12.5 Procedure Development and Qualification...............................................................................................66 13. Practical Examples............................................................................................................................................68 13.1 Example 1—Hermetic Seal on High Pressure Vessel..............................................................................68 13.2 Example 2—Electron Beam Welding of High Purity Niobium Superconducting RF Cavities...............70 13.3 Example 3—Electron Beam Deep Penetration Welding..........................................................................71 13.4 Example 4—Electron Beam Welding Fuel Elements for Space Reactor Test Components....................72 13.5 Example 5—Non-vacuum Electron Beam Welding of Torque Converters..............................................74 13.6 Example 6—Partial Vacuum Electron Beam Welding of Tangs of Planetary Gear Assemblies..............75 13.7 Example 7—Electron Beam Welding of Titanium Fin-to-Fuselage Brackets for the Eurofighter..........76 13.8 Example 8—Non-Vacuum Electron Beam Welding of Aluminum Structural Beams.............................80 13.9 Example 9—Partial Vacuum Electron Beam Welding of Speed Gear.....................................................81 13.10 Example 10—Titanium Chord Fabrication Using Electron Beam Free Form Fabrication Process.........81 13.11 Example 11—Electron Beam Welding of Dipole Vacuum Chamber for High Energy Accelerator........83 13.12 Example 12—Knife Edge Seal Using Electron Beam Additive Manufacturing Process........................87 14. Power Curves.....................................................................................................................................................89 Annex A (Informative)—Cross-Reference Chart for Various Pressure Units............................................................97 Annex B (Informative)—Format for the Specification of Electron Beam Welding Equipment................................99 Annex C (Informative)—Extended Glossary for Electron Beam Processing..........................................................101 Annex D (Informative)—Guidelines for the Preparation of Technical Inquiries.....................................................131 Annex E (Informative)—Informative References....................................................................................................133 List of AWS Documents on Electron Beam Welding and Cutting...........................................................................135 x AWS C7.1M/C7.1:2013 Recommended Practices for Electron Beam Welding and Allied Processes 1. General Requirements 1.1 Scope. These recommended practices present descriptions of electron beam welding equipment and procedures for welding a wide range of metals and thicknesses; allied processes, to include electron beam braze welding (EBBW), cut- ting, drilling, surfacing, additive manufacturing, surface texturing, and heat treating, are also discussed. The appropriate terms, definitions, and safety considerations are presented. Information is included on designing for electron beam weld- ing (EBW), welding dissimilar metals and thicknesses, fixturing, specifications, and operator training and qualification. Information regarding the safe practice of electron beam welding and allied processes can be found in Clause 4 of this standard. Highly technical and detailed descriptions of metallurgy and the physics of the EBW process, though important to the engineer and scientist, were considered beyond the scope of this publication. 1.2 Units of Measurement. This standard makes use of both the International System of Units (SI) and U.S. Customary Units. The latter are shown within brackets ([]) or in appropriate columns in tables and figures. The measurements may not be exact equivalents; therefore, each system shall be used independently. 1.3 Safety. Safety issues and concerns are addressed in this standard, although health issues and concerns are beyond the scope of this standard. Some safety considerations are addressed in Clause 4. Safety and health information is available from the following sources: American Welding Society: (1)ANSI Z49.1, Safety in Welding, Cutting, and Allied Processes (2)AWS Safety and Health Fact Sheets (3)Other safety and health information on the AWS website Material or Equipment Manufacturers: (1)Material Safety and Data Sheets supplied by materials manufacturers (2)Operating Manuals supplied by equipment manufacturers Applicable Regulatory Agencies Work performed in accordance with this standard may involve the use of materials that have been deemed hazardous, and may involve operations or equipment that may cause injury or death. This standard does not purport to address all safety and health risks that may be encountered. The user of this standard should establish an appropriate safety program to address such risks as well as to meet applicable regulatory requirements. ANSI Z49.1 should be considered when developing the safety program. 1 AWS C7.1M/C7.1:2013 2. Normative References The standards listed below contain provisions, which, through reference in this text, constitute mandatory provisions of this AWS standard. For undated references, the latest edition of the referenced standard shall apply. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. ANSI documents:1 ANSI/ASSE Z87.1, Occupational and Educational Personal Eye and Face Protection Devices; ANSI/HPS N43.3, For General Radiation Safety—Installations Using Nonmedical X-Ray and Sealed Gamma-Ray Sources, Energies up to 10 MeV; ANSI Z535.1, Safety Color Code; ANSI Z535.2, Environmental and Facility Safety Signs; ANSI Z535.5, Accident Prevention Tags. AVS documents:2 AVS M-1, Vacuum Hazards Manual. AWS documents:3 AWS A3.0, Standard Welding Terms and Definitions, Including Terms for Adhesive Bonding, Brazing, Soldering, Thermal Cutting, and Thermal Spraying; AWS A2.4, Standard Symbols for Welding, Brazing, and Nondestructive Examination. 3. Terms and Definitions For the purposes of this document, the following terms and definitions apply: accelerating potential. See beam voltage. alignment. Any mechanical or electromagnetic adjustment of the electron beam equipment that is made for the purpose of correcting the path or position of the beam. alignment coils. Electromagnetic deflection coils immediately below the anode used to deflect the beam so its axis coin- cides with the magnetic axis of the focus coil. anode. The more electrically positive element of the electron beam gun (usually at the ground potential of the machine) through which the electron beam passes. back-up bars. Material intended only to stop beam energy exiting the workpiece in full penetration welds. beam current. Measure of the quantity of electrons flowing per unit time in an electron beam, usually expressed in units of milliamperes (mA). beam deflection. The position of the beam spot on the workpiece is moved rapidly by small amounts, deflecting the beam back and forth. This oscillatory movement is superimposed on the steady movement along the weld path. The frequency of these oscillations can be from 10 Hz to 10 kHz, in one plane or in a circular, elliptical, or other pattern. beam deflection coils. Electromagnetic coils used to change the path of the electron beam. beam forming electrode. See bias cup. beam modulation. Any change in beam current (may be periodic). 1ANSI standards are published by the American Welding Society, 8669 Doral Blvd., Suite 130, Doral, FL 33166. 2AVS documents are published by the American Vacuum Society, 125 Maiden Lane, 15th Floor, New York, NY 10038. 3AWS documents are published by the American Welding Society, 8669 Doral Blvd., Suite 130, Doral, FL 33166. 2 AWS C7.1M/C7.1:2013 2. Normative References The standards listed below contain provisions, which, through reference in this text, constitute mandatory provisions of this AWS standard. For undated references, the latest edition of the referenced standard shall apply. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. ANSI documents:1 ANSI/ASSE Z87.1, Occupational and Educational Personal Eye and Face Protection Devices; ANSI/HPS N43.3, For General Radiation Safety—Installations Using Nonmedical X-Ray and Sealed Gamma-Ray Sources, Energies up to 10 MeV; ANSI Z535.1, Safety Color Code; ANSI Z535.2, Environmental and Facility Safety Signs; ANSI Z535.5, Accident Prevention Tags. AVS documents:2 AVS M-1, Vacuum Hazards Manual. AWS documents:3 AWS A3.0, Standard Welding Terms and Definitions, Including Terms for Adhesive Bonding, Brazing, Soldering, Thermal Cutting, and Thermal Spraying; AWS A2.4, Standard Symbols for Welding, Brazing, and Nondestructive Examination. 3. Terms and Definitions For the purposes of this document, the following terms and definitions apply: accelerating potential. See beam voltage. alignment. Any mechanical or electromagnetic adjustment of the electron beam equipment that is made for the purpose of correcting the path or position of the beam. alignment coils. Electromagnetic deflection coils immediately below the anode used to deflect the beam so its axis coin- cides with the magnetic axis of the focus coil. anode. The more electrically positive element of the electron beam gun (usually at the ground potential of the machine) through which the electron beam passes. back-up bars. Material intended only to stop beam energy exiting the workpiece in full penetration welds. beam current. Measure of the quantity of electrons flowing per unit time in an electron beam, usually expressed in units of milliamperes (mA). beam deflection. The position of the beam spot on the workpiece is moved rapidly by small amounts, deflecting the beam back and forth. This oscillatory movement is superimposed on the steady movement along the weld path. The frequency of these oscillations can be from 10 Hz to 10 kHz, in one plane or in a circular, elliptical, or other pattern. beam deflection coils. Electromagnetic coils used to change the path of the electron beam. beam forming electrode. See bias cup. beam modulation. Any change in beam current (may be periodic). 1ANSI standards are published by the American Welding Society, 8669 Doral Blvd., Suite 130, Doral, FL 33166. 2AVS documents are published by the American Vacuum Society, 125 Maiden Lane, 15th Floor, New York, NY 10038. 3AWS documents are published by the American Welding Society, 8669 Doral Blvd., Suite 130, Doral, FL 33166. 2 AWS C7.1M/C7.1:2013 beam oscillation. See beam deflection. beam power. A measure of the kinetic energy of the beam per unit time and equal to the product of the beam voltage times the beam current. In equation form, the beam power, P, in watts (W), is P = V × I (Eq. 1) where V = Beam Voltage, kilovolts (kV) I = Beam Current, milliamperes (mA) beam rastering. A method of high speed beam deflection (kilohertz range or higher) used for simulated multi-beam processing (joint detection, pattern generation, multi-welds, and in situ postweld heat treatment). beam spot. Apparent size of the beam impingement area on the surface of the workpiece (working spot size as opposed to focal spot size). See also focal spot. beam voltage. Magnitude of electrical potential employed to accelerate and increase the energy of the electrons in an electron beam gun (usually expressed in units of kilovolts). bias cup. Component of a triode gun, more electrically negative than the cathode, used as a grid to control the beam current and shape the beam. Also referred to as grid cup. See also triode gun. cathode. The source of electrons, commonly a segment of tungsten or tantalum, heated to a temperature where ther- mionic emission occurs. Other forms and materials used as thermionic emitters include buttons or rods of tungsten, tantalum, lanthanum hexaboride, and rare earth oxides. See also filament. CNC. An acronym for Computerized Numerical Control. cold shut. A form of weld discontinuity caused by material solidifying at an interface before the liquid metal on either side of the interface flows together to form a continuous structure. column valve. A vacuum valve between the electron gun and the work chamber, used to preserve vacuum and prevent contamination of the gun when the chamber is vented. Also referred to as gun valve. conduction mode. Welding at a power density below that required to form a keyhole, where the primary method of obtaining joint penetration is heat conduction in the material being welded. See also keyhole mode. convergence angle. The angle formed between the axis of the beam and the outermost electron trajectories as they approach sharp focus. corona clear. A technique for removing contamination from the electron beam gun by using a higher than normal beam voltage. Sometimes referred to as glow discharge cleaning or gun clearing. cosmetic pass. A partial penetration weld pass made primarily to enhance surface quality and appearance. defocus. To locate the focal spot above or below the workpiece level when welding. See also focus. degauss. To demagnetize a part or fixture in order to reduce unwanted magnetic fields. diode gun. An electron beam gun where the cathode and grid cup operate at the same electrical potential. downslope time. Period at end of weld during which the level of weld input power or other parameter is continuously decreased in a controlled manner. electron beam. Electrons accelerated and shaped into a directed stream by an applied electrical potential. Electron Beam Additive Manufacturing (EBAM). This process, also known as Electron Beam Free Form Fabrication (EBFFF) or Electron Beam Direct Manufacturing (EBDM), makes use of commercially available wire or powder as feedstock material that is melted by the electron beam. Parts are built layer by layer on a substrate until a targeted near net shape part is achieved. Electron Beam Braze Welding (EBBW). A hybrid process that employs an electron beam to simultaneously accom- plish welding and brazing, and which is sometimes used in performing T-joint welds in order to enhance the structural integrity of the joint being produced. 3