High Strength Steels - Welding Procedures
83ford12 Article No. 83-13-4SHEET METAL - WELDING PROCEDURES FOR HIGH STRENGTH STEELS
FORD ALL CARLINES - ALL MODEL YEARS
LINCOLN-MERCURY ALL CARLINES - ALL MODEL YEARS
Due to numerous inquiries relating to welding high strength steels utilized in Ford Motor Company vehicles, the following Article is reproduced from the December, 1980 issue of Body Repair Tips.
OTHER APPLICABLE ARTICLES: None
WARRANTY STATUS: "INFORMATION ONLY"
BACKGROUND ON THE NEW HIGH STRENGTH STEELS (HSS) Losing weight is the name of the game with Ford Motor Company. This trend will continue to accelerate in the future as engineers seek better fuel economy from all their models.
As a result, body engineers are turning more and more to lightweight plastics, aluminum and High Strength Steels (HSS). These new steels look the same as any other mild steels that you are familiar with and have welded, cut and formed over the past twenty years or more. However, these new steels ARE DIFFERENT! For one thing, they are THINNER, they have a low alloy content and are heat sensitive.
They cannot be welded or repaired by following commonly used methods and techniques that you have used in the past.
NEW REPAIR PROCEDURES APPLICABLE TO VIRTUALLY ALL STEELS New repair procedures and new techniques for welding and common body shop repairs have been developed for HSS in order to maintain the original strength and durability built into Ford Motor Company cars.
However, procedures and techniques outlined in this article are also applicable to virtually all steels including mild steels. Good quality welds will result even on low carbon steels. Note that as you review the information on the following pages, all commonly known methods for heating/welding metal car components have been replaced by new repair procedures . . . with one exception:
Outer body skin panels may still be repaired using previously accepted methods and techniques.
And, as pointed out in articles published over the past few years, door intrusion beams are NEVER TO BE REPAIRED. When they become damaged, complete beam replacement is the only acceptable service.
WHERE THE INDUSTRY IS HEADED From what body engineers at Ford Motor Company tell us, "you haven't seen anything yet" when it comes to HSS applications. And, to give you an idea of how far engineers have gone at this date, body components of Ford's new Escort/Lynx models are constructed with up to 200 pounds of HSS in over 30 individual parts. Fourteen HSS parts help make up the floorpan assembly. This represents a new standard for the use of this metal in sub-compact type models. As they plan ahead to the mid 1980's their predictions point to far wider use of HSS in more and more areas of the total body structure. Of course, plastics and lightweight metals such as aluminum will also gain increased prominence. Weight savings may amount to hundreds and hundreds of pounds with more widespread use of those materials and yet vehicles will still be designed and constructed to retain their ability to package drivers and passengers safely. What this all means to body/paint shop owners and professional repairmen has great significance when it is necessary to heat or weld high strength steels.
NOTE: Most of the applications of HSS are confined to body structures, reinforcements, gussets, brackets and supports rather than large panels or outer skin panels.
WORKING & WELDING HSS Now is the time to become familiar with HSS . . . how to work with it and how to perform proper heating/welding procedures using MIG (Metal-Inert Gas) welding equipment. And good news! It doesn't take a 10-week training course to become competent! In just a few short hours (or less) of practice, you'll find that working and welding HSS is not that much different than with conventional mild steels. But, we suggest getting started right now (that is ... if you haven't done so already). You'll have a headstart! And here in this issue of Body Repair Tips we have presented guidelines to help clear up any misunderstandings you may have on HSS and MIG welding.
NOTE: MIG welding is also known as GMAW (Gas Metal Arc Welding).
MIG WELDING-THE PREFERRED METHOD
Metal-Inert Gas Welding (MIG) is preferred over conventional Arc Welding when welding High Strength Steels (HSS). Oxyacetylene should not be used. Local welding suppliers can advise you on the type of MIG equipment best suited to your body repair shop needs.
NOTE: The procedures using one type of rod was developed especially for this purpose.
MATERIALS NEEDED - MIG WELDING MIG WELDING WIRE (Meeting American Welding Society Standards: AWS-E-70S-6) .030"-.035" Diameter. WELDING
SUPPLIERS: WIRE CODE AIRCO WELDING PRODUCTS . . . . . . . . . . . . A-681 AMERICAN CHAIN AND CABLE . . . . . PAGE AS-28 OR AS-18
CHEMTRON CORP. . . . . . . . . . . . .SPOOL ARC-88
WELDING
SUPPLIERS: WIRE CODE NATIONAL STANDARD CORP. . . . . . . . . . . . . . . . NS-115 REID AVERY COMPANY . . . . . . . . . . . . . . . . . . 70S-G UNION CARBIDE CORP. . . . . . . . . . . . . . . . . LINDE-86 ALTERNATE METHOD
ARC WELDER WELDING RODS (3/32" Diameter). . . . . AWS-E-7014 TEMPERATURE INDICATING CRAYON . . . . . . . . . . . . . . . LOCAL WELDING SUPPLIERS
FIGURE 1 - Typical layout of a MIG welding unit showing the placement of major components.:
COMPONENTS OF A TYPICAL MIG WELDING UNIT
ADVANTAGES OF MIG WELDING Essentially, MIG WELDING can economically replace all resistance spot welding, gas welding and manual arc welding repair jobs in body shops. And, one of the outstanding characteristics of MIG welding is its capability of producing 100% fusion into the parent metal. Therefore, grinding flush does not detract from weld quality or weld strength.
JUST WHAT IS FINE WIRE MIG WELDING ANYWAY?
FIGURE 2 - Carbon dioxide (CO2) protects the molten metal from contamination by the atmosphere.:
FIGURE 3 - Here is the typical action of the welding wire as it "burns back" from the work during the MIG welding process.:
For those of you who are not completely familiar with the process, here's a brief explanation: Fine wire MIG (Metal Inert Gas) is an arc welding process whereby joining together of metals is produced by heating with an arc between a continuous fine wire filler metal and the work. And, a "shielding" gas such as Carbon Dioxide (CO2) or other inert gases (Argon-Helium) protect the fluid metal from contamination by the surrounding atmosphere and helps to stabilize the arc. See Illustrations 2 and 3. The fine wire electrode is automatically fed at a predetermined rate into the molten puddle.
MIG Welding Equipment consists of these components:
^ MIG type of welder machine connected to an electrical power supply, ^ A wire/feed control to feed the wire at the required speed.
^ A welding gun that the welder holds to direct the wire to the weld area.
^ A shielding gas to protect the molten weld pool from contamination.
^ A spool of electrode wire of a specified type and diameter. Wire diameter should be .030" to .035". The thickness and type of base metal, (material being welded) and the wire diameter will govern the setting of the welding machine used to deliver power to the welding arc.
FIGURE 3 - Here is the typical action of the welding wire as it "burns back" from the work during the MIG welding process.:
As shown in Illustration 3, the electrode advances to contact the work (A) and a short circuit occurs. Resistance heating of the electrode (fine wire) causes it to burn down and melt. The wire burns back at a faster rate than it is being fed (C) and the arc force flattens the molten metal (D). Wire feed then overcomes burn back (E) and the electrode (fine wire) advances to contact the work once again. This cycle all takes place in a fraction of a second. Generally, this process is restricted to metals less than 1/4-inch thick while arc voltages seldom exceed 20 volts.
BASIC REASONS FOR MIG WELDING There are several benefits resulting from MIG welding that lend itself to professional work, especially with the lighter gauges of either high strength steels or mild steels. In short, here are a few of the major ones:
^ Welds are made fast on all types of steel.
^ Low current can be used when welding and as a result, distortion of the thin metals is reduced.
^ No extensive training is necessary.
^ The equipment does not take up much more room than a set of cylinders used in oxyacetylene welding.
^ MIG spot welding is more tolerant of gaps and misfits of the metals being welded.
^ Severe gaps can be spot welded by making several spots on top of each other.
^ It's simple to weld vertically and overhead.
^ Metals with different thicknesses can be easily welded with the same diameter wire.
^ Almost all steels can be welded with one common type of weld wire.
HEATING WITH OXYACETYLENE EQUIPMENT Oxyacetylene equipment CANNOT BE USED ON HSS components for welding or cutting. Ford Motor Company body engineers stress this point. Frankly, there is just too much heat build-up which can reduce structural strength in HSS. However, in some instances an oxyacetylene torch may be used to HEAT HSS components or parts ("hot working") provided the critical 1400 degrees F. temperature IS NOT EXCEEDED. At that level (1400 degrees F.) heated steel appears a cherry red (dark red) color. Under no circumstances should HSS be heated to a bright red color (1500 degrees F.) or to a red-orange color which indicates a heat level of around 1600 degrees F.
HEATING TIME OF HSS
FIGURE 4 - DISCOLORATION OF HSS HEAT-AFFECTED AREA.:
High strength steels should only be exposed to high temperatures from an oxyacetylene torch for a very short period of time. Three minutes is the recommended maximum time span for exposing HSS to a 1400 degrees F. temperature in order to reduce the amount of "scaling" that normally takes place on the metal surface. High temperature exposure causes discoloration as shown in Figure 4.
FIGURE 5 - THIS IS A TYPICAL HEAT INDICATING CRAYON THAT CAN BE PURCHASED LOCALLY FROM YOUR AUTOMOTIVE SUPPLIER OR WELDING OUTLET.:
TEMPERATURE CONTROL RECOMMENDATIONS In order to determine and control temperatures of high strength steel parts and components, being "heat worked" with oxyacetylene equipment, Ford engineers recommend temperature indicating crayons. See Figure 5.
They can be purchased from local welding supply outlets and are available in various temperature indicating heat levels. The metal should be marked closely adjacent to the area being worked with a crayon rated no more than 1400 degrees F. Using such a crayon will indicate to the welder whether or not an excessive amount of heat is being applied. Thus metal temperatures can be controlled within safe levels and HSS damage easily prevented.
FIGURE 6 - NEVER WELD HSS WITH OXYACETYLENE EQUIPMENT.:
CONVENTIONAL ARC WELDING EQUIPMENT SPECIAL NOTE:
If MIG welding equipment is not available, then the only other acceptable method is the use of conventional arc welding equipment. Oxyacetylene welding must never be used on HSS. But . . . and this is a big point, ONLY if the following precaution is followed exactly as stated:
Manual arc welding must only be performed with 3/32-inch weld rods that conform to the American Welding Society (AWS) SPECIFICATION E-7014. When you purchase weld rods, be sure your welding supplier understands E-7014 and fills your order correctly! No substitutes please. Rods meeting that specification will:
1. Meet all requirements for welding HSS.
2. Retain the tensile strength of HSS.
3. Assure good welding repairs of HSS.
PRECAUTION: It is advisable to store weld rods in a moisture-free atmosphere. The minute they get unpacked they get "thirsty" and start absorbing moisture. Ideally, they should be placed in a warming oven before being used to remove moisture absorbed by the mineral coated rods.
CUTTING HSS FOR SALVAGE PURPOSES
IMPORTANT: Cutting salvage components must be done with a grinding wheel disc . . . an air chisel and/or metal cutting saws.
If use of a torch is necessary when cutting HSS sheet metal components for salvage purposes or cutting a body structure for a "front/rear clip", Ford engineers advise the following approach:
^ Cut the metal structure at least two inches (2") away from the desired cut line. Sheet metal within the heat affected area will lose strength when subjected to the high heat levels of a torch, ^ After torch cutting, use a grinding wheel disc, an air chisel or a metal saw to make the final cut at the originally intended dimension line. HSS damage will then be "cut out" of the salvaged part.
FIGURE 7:
FIGURE 7 - APPROVED WELDING SHIELDS AND FLASH GOGGLES FOR WELDER PROTECTION IS FOR YOUR PERSONAL SAFETY. SEE THE SUGGESTED "SHADE" FOR THE EYE PIECE IN THE CHART BELOW.
SAFE PRACTICES
USING MIG WELDING EQUIPMENT
SAFE HANDLING OF SHIELDED GAS CYLINDERS Carbon Dioxide gas cylinders (CO2) weigh approximately 185 pounds when filled with 50 pounds of (CO2) and are pressurized with up to 1000 psi at 70~F. Handle them carefully!
PROTECTION FROM RADIANT ENERGY The suggested filter glass shields for welder protection when using MIG welding equipment are listed here as a guide:
Shade
^ When welding ferrous metals . . . . . . . . . . 12
^ When welding nonferrous metals . . . . . . .11
^ Flash goggles . . . . . . . . . . . . . . . . . . .2
NOTE: All welders should be familiar with safe practices and potential hazards in ALL welding and cutting operations. Often a review of the precautions that are necessary should be made to be absolutely sure of personal and shop safety. The American Welding Society offers a "Publications Catalog" listing hundreds of hand books, pamphlets and other literature at varying prices.
Write to: American Welding Society 2501 N.W. 7th Street Miami, Florida 33125