Fabricating Railcars with Resistance Welding

An overview is provided on the history, base materials, equipment, and standards regarding the use of resistance welding in creating stainless steel passenger railcars

. BY W!.ADYSt.AW JAXA-ROZEN Bombardier Transportation's facility in La Pocatiere, Quebec, Canada, produced cal'shells of the Eurotunnel shuttle cars, the largest stainless steel cars ever made, The locomotive is of the standard size. (Photo coU/tesy of the Nickel Institute.)

The application of resistance welding ward Budd became fascinated with stain­ process featured a welding time that was in the production of transportation vehi­ less steel. At the same time, Ralph Budd shorter thim the dwell time causing the cles has traditionally been associated with (no relation), president of Burlington development of chromium carbides. automobiles. However, there is a lesser Railway, had the idea of applying stain­ known area where the process has been less steel in railway car design and fabri­ The Creation of Zephyr Trains used with success and to its full potential cation. Two important developments fol­ since the 1930s - fabrication of stainless lowed: the mastery of producing 18-8 cold­ As a result, a new kind of passenger rail steel passenger railcars. worked, high-strength austenitic stainless vehicle was manufactured and put into steel by the Allegheny Steel Co., and the service in 1934. This was the birth of the History growing experience and competence of Burlington Zephyr trains - Fig. 2. The the Budd Co. regarding formability of the conjunction of stainless steel, resistance The use of resistance welding for stain­ material and spot welding technology. welding, creative minds, and bold manage­ less steel railcar fabrication was a fasci­ Stainless steel used by the Budd Co. ment brought a major paradigm shift. nating feat of engineering linked to the had tensile strengths up to 160 ksi (1100 Compared with existing railcars, the stain­ creativity and vision of Edward Gowan MPa) and yield strength of 120 ksi (830 less steel train was much lighter, which in Budd (1870-1946), founder of the Edward MPa). Its weld ability with both fusion and turn made the first application of a diesel­ G. Budd Manufacturing Co., Philadel­ resistance processes was impaired by a rel­ electric propulsion unit practical. phia, Pa. - Fig. 1. His company was the atively high carbon content that caused In a display of its speed, the first first to produce all-steel automobile bod­ chromium carbide precipitation in the Zephyr made a lOIS-mile nonstop run ies and also one of the first to use resist­ heat-affected zone (HAZ). Budd's chief from Denver to Chicago at the record av­ ance spot welding. engineer, Col. Earl J. W. Ragsdale, found erage of 77 miles/h. Soon after, the first During his visit to Europe in 1930, Ed- the remedy. His 'shotweld' spot welding disc brakes were introduced. The sleek sil-

WL4DYSLAW JAXA-ROZEN ([email protected]) is a senior expert engineer with Bombardier Transportation - North America, St-Bruno, Quebec, Canada. Based on a paper presented at the AWS Detroit Section's Sheet Metal Welding Conference XIv, Livonia, Mich., May 12-14, 2010.

141 DECEMBER 2010 very train was a forerunner in streamlined Table 1 - Chemical Composition of industrial design. Selected Austenitic Stainless Steels The Zephyrs changed railway travel, due to their speed, comfort, and ameni­ Element Stainless Steel Grades ties such as attractive interior design, air­ conditioning, and an audio system broad­ Allegheny 304 301L 201L <;asting radio, public addresses, and music 18-8 from wire recorders. A popular feature C 0.12 0.08 0.03 0.03 was the domed observation lounge. Cr 17.0, 18.0- 16.0 - 16.0- min 20.0 18.0 18.0 Progress Ni 7.0, 8.0- 6.0- 3.5 - mm 10.5 8.0 5.5 Budd's example was followed by the Mn 0.2- 2.0 2.0 5.5 - St. Louis Car Co. and Pullman-Standard 2.5 7.5 in the United States. Together, they pro­ Si 0.2-1.5 0.75 1.0 0.75 duced thousands of stainless steel passen­ Cu 0.5 ger railcars. N 0.10 0.20 0.25 The next important development oc­ Contents: wt- %, maximum values unless oth- curred in Japan, where stainless steel pas­ erwise specified. senger railcars, mostly for subway and Fig. 1 - Edward Gowan Budd. (Photo commuter trains, have been mass pro­ courtesy of the Hagley Museum and Libra/Y·) duced since the end of the 1950s. In Asia, steels caused by welding, either with re­ stainIess steel railcars are also produced sistance or fusion processes. Because of in India and South Korea. recent increases in the price of nickel, the In North America, Bombardier Trans­ 200 series of stainless steels is currently portation entered the rail transit industry (2008-2010) regaining interest. in the mid-1970s and has grown to be a The chemical compositions of selected global producer of subway, commuter, austenitic stainless steels are presented in and intercity railcars. Its La Pocatiere, Table 1. Quebec, facility in Canada has specialized With regard to other groups of stain­ in stainless steel since the beginning of the less steels, duplex steels have the poten­ 1980s. This plant also produced cars hells tial for application, especially because of of the Eurotunnel shuttle cars, the largest their high strength in larger thicknesses. stainless steel cars ever made - see lead However, they probably will not become photo. In Europe, for reasons associated popular in the production of railcars. They with a traditional requirement for car bod­ are more expensive than austenitic steels, ies to be entirely painted, stainless steel and in lower thicknesses (up to about 5 cars gained only limited popularity. This mm), cold-worked austenitics are stronger Fig. 2 - The Burlington Zephyr train came is not the case in Australia, where stain­ than duplex steels. Where larger thick­ less steel cars are produced and used. into se/vice in 1934. It was a forerunner in nesses are required, high-strength, low­ streamlined industrial design. alloy (HSLA) steels with yield strengths Materials Used for up to 700 MPa are commonly used. The Railcars Construction use of martensitic and ferritic steels is lim­ ited to nonstructural applications. In the remaining part of this article, Chemistry only austenitic steels are considered.

The first stainless steel railcars were Mechanical Properties made from an austenitic alloy produced by Allegheny and classified by Budd as 18-8 In typical descriptions of austenitic steel consisting of 18% chromium and 8% stainless steels, their mechanical proper­ nickel. Relatively high carbon content made ties are those in the annealed condition. Fig. 3 - Only 20 of the RB-1 Conestoga this steel susceptible to chromium carbide However, the strength of these materials cargo planes were produced. (Photo cour­ precipitation in the HAZ of welds and to may be significantly increased by cold de­ tesy of Wikipedia.) subsequent intergranular corrosion. The formation, such as thickness reduction in need to limit dwell time in the critical tem­ cold rolling, forming, or bending. perature range inspired the motivation for Deformation strengthening of auste­ Budd's experts to invent the short -time spot nitic steels results from partial transfor­ welding process ('shotweld'). mation of austenite into martensite. In the 1950s, 201 and 202 steels were Strength levels of cold-worked stainless also applied. In their chemistries, a sub­ steels are covered by ASTM Interna­ stantial part of the nickel is replaced with tional's A666, Standard Specification for manganese. Later, 17-7 Type 301 steel was Annealed or Cold-WorkedAustenitic Stain­ introduced. In the 1980s, the advent of less Steel Sheet, Strip, Plate, and Flat Bar, argon-oxygen decarburization allowed the and British Standard EN 10088-2, Stain­ fabrication of low-carbon stainless steels less Steels: Technical Delivery Conditions Fig. 4 - A spot weld in a thick assembly, containing less than 0.03% C. This carbon for Sheet/Plate and Strip of Corrosion Re­ totaling 15.6 mm, is shown. (Photo cour­ level prevents sensitization of stainless sisting Steels for General Purposes. tesy of Bombardier.)

WELDING JOURNAL fM Main stainless steel carbody materials

Cant line Carline Roof sheet Purline End plate sus 301LHT SUS301 LST SUS 301LMT SUS 301LST SUS301LDLT

Gutter S 30400

Roof skirting SUS 301LHT

Frieze board SUS 301LDLT

Window head Stud SUS 301L HT SUS301LHT i Gusset SUS 301L HT Belt rail SUS 301 LHT I Belt rail, outside SUS 301 LLT

Wainscot panel SUS 301 LST I Bottom panel SUS 301LHT A Door end post, I SUS301LHT ,

Rocker rail B Outside plate stiffener, SUS 301L HT SUS301LHT i C Outside post, I Side sill SUS 301L HT I SUS 301L HT Gusset Cross beam Floor board I SUS 301L HT SUS301LHT SUS 301L MT o Gusset, SUS301LHT I

Code: LT, low tensile; DLT, dead lite panel; ST, special tenSile; MT, medium tensile; and HT, high tensile. I

Fig. 5 - A sketch of a stainless steel railcar detailing its key components. (Photo courtesy of the Nickel Institute.)

The strengthening efficiency of cold Technological Properties bon steels, austenitic steels have a resis­ rolling depends on the material thick­ tivity five times higher, thermal conduc­ nesses. As an example, in thicknesses up Austenitic stainless steels can be bent tivity three times lower, and coefficient of I to 1 mm, tensile strength close to 1300 with ease. Even in the cold-worked con­ thermal expansion one-third higher. I MPa and yield strength (0.2% proof) close dition, material may be safely bent with a to 1000 MPa may be achieved. For 5-mm­ radius equal to twice its thickness. Weldability thick materials, the achievable values are Formability of austenitic steels is I­ 1000 and 750 MPa, respectively. The high strongly dependent on the initial condi­ Austenitic stainless steels do not un­ strength-to-weight ratio allows for consid­ tion of the material. Annealed material dergo the y-a transformation, which en­ ering cold-worked stainless steel as light­ can be formed without difficulty, while the sures their good metallurgical weldabil­ I weight material. forming potential of cold-worked materi­ ity. A limited recrystallization occurs in ! The first stainless steel moving object als is limited. If material is to be formed, the HAZ, leading to some softening. manufactured by Budd was the Pioneer its final properties resulting from defor­ However, this has practically no conse­ amphibious plane launched in 1931. It was mation may be considered for design. quence on the strength of resistance followed 12 years later by the RB-1 Con­ welds. The HAZ remains ductile in all estoga cargo plane, 20 of which were built Physical Properties cases. In either a peel or chisel test of spot - Fig. 3. welds, a well-defined button is always An important characteristic of cold­ Three properties of austenitic steels obtained. worked austenitic steels is· the absence of are important for resistance welding - High resistivity of austenitic steels al­ yield point in tensile deformation. In de­ electrical resistivity, thermal conductivity, lows for rapid obtaining and growth of the sign, 0.2% proof stress is typically used as and coefficient of thermal expansion. In weld nugget. This is further enhanced by the reference value. comparison with the properties for car- the low thermal conductivity, which lim-

'1:' DECEMBER 2010 Intensifier Port

High Pressure Seal Working Piston

Fig. 7 - An air-aver-oil intensifier cylinder is shown. (Photo courtesy of CenterLine Windsor.)

Fig. 6 - A large C-type gun. Welding guns cars, is possible, and restoration of the requirements. An optimal solution is rep­ should have a rigid structure, preferably original finish is difficult. Also, spot weld resented by a cylinder using both media made of a nonmagnetic material. (Photo indentations should be shallow and defect with an internal intensifier. The device courtesy ofBombardier.) free, and no discoloration on visible sur­ makes a quick "soft touch" approach using faces is permitted. The answer to these compressed air. Upon the contact be­ challenges is the use of protective plastic tween electrodes and the assembly, the air its heat sinking into surrounding material. foil, which is removed just before weld­ pressure is converted into a high hydraulic As a result, relatively low amperages are ing; appropriate welding schedules and force - Fig. 7. Electric servo-guns repre­ required, and spot welding multiple part sequences; and the use of shielding gas. sent an interesting application potential, combinations of a large total thickness is Contact surfaces of electrodes should be especially when their squeezing force possible - Fig. 4. maintained in a perfect state, and the reaches the required level. The high coefficient of thermal expan­ schedules of electrode dressing and re­ sion results in a tendency to produce placement should be rigorously respected. Electrodes nugget shrinkage discontinuities as well as high residual stresses in welds and dis­ Equipment Resistance Welding Manufacturing Al­ tortion of assemblies. To prevent both oc­ liance (RWMA) Class 3 electrodes are currences, high forging forces are applied. General Requirements used. This class primarily includes UNS C175l0 beryllium copper and UNS C18000 nickel-silicon copper, the latter Design Resistance welding equipment should commonly referred to as beryllium-free have the following characteristics: Class 3. Beryllium copper provides re­ A typical car body is of m_onocoque de­ • Large length and width coverage sign - Fig. S. The sides and roof consist markable performance; however, use of • High forces up to 20 kN (4500 lbf) this alloy for electrodes has become com­ of cold-formed member frames to which • Moderate amperages with an order skin is attached. The floor structure is maximum of 15 kA for spot welds and 30 plicated because of restrictions related to beryllium toxicity. As a result, C18000 is composed of crossbeams, which are fixed kA for seam welds to side sills. A center sill is rarely used. now the preferred alloy for electrodes. A • High reliability. The design strength of spot welds is de­ A description of the particular equip­ spherical contact surface of a 75 mm (3 fined in standards such as the AWS C1.l, ment elements follows. in.) radius, recommended by the AWS Recommended Practices for Resistance C1.l standard, represents an optimal Welding, and AWS D17.2, Specification for shape. Large electrode diameters around Resistance Welding for Aerospace Applica­ Stationary Machines and 20 mm (0.750 or 0.875 in.) are preferred. tions. Minimum distance between spot Mobile Guns welds is limited by shunting current. The Gun POSitioning typical maximum center-to-center distance Stationary machines and C-type mo­ in North American practice is 50 mm + 2 bile welding guns should have rigid struc­ Guns for welding large structures are d, where d represents the nugget diameter. tures - Fig. 6. Rectilinear movement of displaced by gantry systems, the level of These design principles have ensured struc­ electrodes is preferable to rotational mechanization of which varies from man­ tural integrity of the cars through the movement. For gun structures, nonmag­ ual to fully automatic. In manual mode, decades. In addition, the strength of seam netic stainless steel is the material of spot welds are positioned with the help of welds is comparable to that of base metal choice. templates. and is not a design consideration. The opposite side of the spectrum is Cylinders represented by robotic gantry systems, Fabrication which are typically used for welding side Cylinders should ensure rapid advance and roof frames. For better flexibility, the The external surfaces of stainless steel movement, high forces, and soft contact welding head is equipped with a gun car bodies should be scratch free and flat. with welded assembly. They should also exchanger. No thermal straightening, such as that have a limited size. Hydraulic and pneu­ Welding the roof and side skins to their used in the fabrication of carbon-steel matic cylinders only partially meet these structures represents a special challenge.

WELDING JOURNAL 'f' Aluminum, is also used. This standard de­ fines conditions regarding personnel, equipment, and quality systems, which must be met by a company to be certified by the Canadian Welding Bureau. The European Committee for Stan­ dardization and International Organiza­ tion for Standardization have published numerous standards for resistance weld­ ing. Typically, they are short documents linked through cross references, describ­ ing test procedures, rather than specify­ ing precise acceptance criteria. Japanese Industrial Standards pub­ lished by the Japanese Standards Associ­ ation resemble North American codes.

Welding Procedure Specification Establishment and Qualification

Fabricating car bodies requires a large number of spot welded thickness combi­ nations. Combinations may include three, Fig. 8 - Specialized gantly machines with separate but synchronized mechanical systems for four, and even five thicknesses of varying top and bottom electrodes are the solution for welding roof and side skin to their structures. gauges. In large stations, dozens of differ­ (Photo courtesy of Bombardiel:) ent combinations must be welded, and their number is by far larger than that of available schedules. This represents a challenge for resistance welding techni­ Up to a certain width, mobile C-type guns Resistance Welding Controls cians. Another difficulty is a need to ver­ may be used. In some cases, guns may be ify the shear strength qualification assem­ introduced through window and door Because of the required quality of the blies totalling up to four faying surfaces. openings. However, this solution is labo­ welds, as well as ofthe multitude and com­ rious, and not always possible. In the case plexity of schedules, the most advanced Production Control of roofs, the situation is further compli­ resistance welding controls are sought. cated by their curvature. A possible solu­ Monitoring capability of the controls is Every weld is important to the struc­ tion consists of using specialized gantry used for a signature verification of each tural integrity of the car. Consequently, machines with separate but synchronized weld. rigorous quality control is necessary dur­ mechanical systems for top and bottom ing fabrication. Monitoring parameters electrodes - Fig. 8. Quality combined with application of threshold values for essential variables allows for Power Sources real-time verification of the process. On General Requirements automatic equipment, position and signa­ All kinds of systems may be used to pro­ ture records for each weld are used for vide welding current. For large spot weld­ The requirements for weld integrity traceability. Also, frequent testing is per­ ing machines, direct current is the pre­ and appearance necessitate stringent weld formed on samples, namely chisel tests ferred logical choice. As in the whole re­ quality criteria. There can be no nugget and periodic verification of weld charac­ sistance welding industry, medium fre­ expulsion. Indentation must be shallow teristics, which were determined in pro­ quency inverters have made their entrance. and uniform. Discoloration at surfaces ex­ cedure qualification. The equipment op­ posed to users is not permitted. There are erators' involvement and constant vigi­ Seam Welding Machines precise limits of nugget strength, diame­ lance represent equally important factors ter, penetration, and discontinuities. in ensuring quality of production welds. Seam welding is used to assemble the roof and sometimes the side skin panels. Standards Conclusion The considerable size of both assemblies requires large installations. Fixed-ma­ The two basic standards used in North In the fabrication of stainless steel rail chine stations have a length that is twice America are AWS D17.2, Specification for cars, resistance welding ensures high-pro­ that of a railcar. This is not the case of sta­ Resistance Welding for Aerospace Applica­ ductivity, structural integrity, and aes­ tions using mobile machines. However, tions, which replaced the military specifi­ thetic quality, while taking advantage of while sparing a lot of floor surface, this cation MIL-W-6858D, Welding, Resist­ the characteristics for austenitic steels. solution represents considerable chal­ ance: Spot and Seam, and AWS CI.I, Rec­ More than 75 years after introducing lenges, not least of which is the accurate ommended Practices for Resistance Weld­ resistance welding in passenger railcar movement of heavy cantilevered equip­ ing. AWS Cl.I covers a larger range of fabrication, the legacy of Edward G. Budd ment. Weld discoloration is prevented or thicknesses, whileAWS D17.2has require­ and his companions is still alive and well. + limited by water jets from the top and bot­ ments for multiple thicknesses. tom sides. The current used is direct with In Canada, the Canadian Standards Acknowledgments polarity changing from one pulsation to Association's W55.3, Celtification ofCom­ another. panies for Resistance Welding of Steel and The technical and editorial assistance

DECEMBER 2010 of David Beneteau, Jim Dolfi, Michael Karagoulis, Mark Sapp, Don DeCorte, Serge Martellini, Gaston Morneau, Nigel Scotchmer, Harold Cobb, and Maryanne Roberts is gratefully acknowledged. Add Wafer To A Promising New Career Today Bibliography In Commercial Diving Encyclopedia ofAmerican Coachbuilders The Highest Level of Certifications at & Coachbuilding. www.coachbuilt.com. The Most Prestigious Academy With www.coachbuilt.com/bui/b/budd/budd.htm. A 35 Year Reputation. The ESRC Centre for Business Rela­ tionships, Accountability, Sustainability Aim High, Dive Deep, Train In 5 Months for and Society. Cardiff University, UK: Did . A Rewarding And Unique Career. c Ford really invent mass production? c www.brass.cfac.uk/uploads!cafordPN0603 Financial aid available to ~~ IVERS .pdf. those who qualify c_ACADEMY U.S. Patent 1 944 106. 1934. Method ~p INTERNATIONAL and product of electric welding. Earl J. W. Li Ragsdale (Edward G. Budd Mfg. Co.). Watter, M. (Edward G. Budd Mfg. Co.) 1940. Stainless Steel in Aircraft, SAE. Sapp, M. A history of welding. www. weldinghistOlY. org, http://weldinghis tOlY. org/whistOlyfolder/welding/wh j 900- 1950.html. PBS. American experience, streamlin­ ers, people & events - Edward G. Budd. www.pbs.olg/wgbh/amex/sh·eamliners/peopl eevents/p _ebudd.html. Wikipedia: Pioneer Zephyr. Coel, M. 1986. A silver streak, American heritage. Vol. 2, No.2. www.americanheritage.com/a/1icles/magazi For info go to www,aws,orglad-index ne/it/1986/2/1986_2jO.shtml. Reutter, M. 2004. On the wings of the Zephyr, Indiana Historical Society Press. www.indianahistory.org/ ihs-press/ web "'publications/railroad04/reutter. html. Houska, C. 1996. Stainless steel pas­ senger rail cars in North America: 60 years of experience. International Congress Stainless Steel '96. DiisseldorflNeuss. Hatono, 1. 1991. Development of stain­ less steel railroad cars in Japan. Nickel Development Institute. Cobb, H. M. 2010. The HistOlY of Stain­ less Steel. Materials Park, Ohio: ASM International. ASTM A666-02, Standard Specification for Annealed or Cold-Worked Austenitic Stainless Steel Sheet, Strip, Plate, and Flat Bar. EN 10088-2:2005, Stainless Steels: Technical Delivery Conditions for Sheet/Plate and Strip of Con'osion Resist­ ing Steels for General Pwposes.

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