should be four to six times the metal thickness for sheet metal and small-diameter tubing.
Lap joint Flanged butt joint Edge joint Solder Solder FIGURE 6-21. Silver soldering joints. FIGURE 6-22. Soldering copper and soldering iron.
The oxyacetylene flame for silver soldering should be neutral, but may have a slight exceas of acetylene. It must be soft, not harsh. During both prebeating and application of the solder, the tip of the inner cone of the flame should be held about ½ in. from the work, The flame should be kept moving so that the metal will not become overheated.
When both parts of the base metal are at the right temperature (indicated by the flow of flux), solder can be applied to the surface of the under or inner part at the edge of the seam. It is necessary to simultaneously direct the flame over the seam and keep moving it so that the base metal remains at an even temperature.
SOFT SOLDERING Soft soldering is used chiefly for copper, brass, and coated iron in combination with mechanical seams; that is, seams that are rivited, bolted, or folded. It is also used where a leakproof joint is desired, and sometimes for fitting joints to promote rigidity and prevent corrosion. Soft soldering is generally performed only in very minor repair jobs.
This process is also used to join electrical connections. It forms a strong union with low electrical resistance.
Soft solder yields gradually under a steadily applied load and should not be used unless the transmitted loads are very low. It should never be used as a means of joining structural members.
A soldering copper (called a soldering iron if it is electrically heated) is the tool used in soldering.
Its purpose is to act as a source of heat for the soldering operation. The bit, or working face, is made from copper, since this metal will readily take on heat and transmit it to the work. Figure 6-22 shows a correctly shaped bit.
To tin the copper, it is first heated to a bright red, then the point is cleaned by filing until it is smooth and bright. No dirt or pits should remain on its surface. After the copper has been mechanically cleaned, it should be re-heated sufficiently to melt solder, and chemically cleaned by rubbing it lightly on a block of sal ammoniac. (If sal ammoniac is not available, powdered resin may be used.)
Then solder is applied to the point and wiped with a The last two operations may be combined by melting a few drops of solder on a block of sal ammoniac (cleaning compound) and then rubbing the soldering copper over the block until the tip is well coated with solder. A properly tinned copper has a thin unbroken film of solder over the entire surface of its point.
Soft solders are chiefly alloys of tin and lead.
The percentages of tin and lead vary considerably in various solders, with a corresponding change in their melting points, ranging from 293° to 592° F.
"half-and-balf" (50-50) solder is a general purpose solder and is most frequently used. It contains equal proportions of tin and lead and melts at ap.
proximately 360° F.
The application of the melted solder requires somewhat more care than is apparent. The parts should be locked together or held mechanically or manually while tacking. To tack the seam, the hot copper is touched to a bar of solder, then the drops of solder adhering to the copper are used to tack the seam at a number of points. The film of solder between the surfaces of a joint must be kept thin to make the strongest joint.
A hot, well-tinned soldering copper should be held so that its point lies flat on the metal at the seam, while the back of the copper extends over the seam proper at a 45° angle, and a bar of solder is touched to the point. As the solder melts, the copper is drawn slowly along the seam. As much solder as necessary is added without raising the soldering copper from the job. The melted solder should run between the surfaces of the two sheets and cover the full width of the seam. Work should progress along the seam only as fast as the solder will flow into the joint.
ELECTRIC ARC WELDING Electric arc welding is a fusion process based on the principle of generating heat with an electric arc jumping an airgap to complete an electrical circuit.
This process develops considerably more heat than an oxyacetylene flame. In some applications, it reaches a temperature of approximately 10,000° F.
Variations of the process are metallic arc welding.
inert-gas (helium) welding, and multi-arc welding.
The metallic arc and helium processes have the widest application in aircraft maintenance.
The welding circuit (figure 6-23) consists of a welding machine, two leads, an electrode holder, an electrode, and the work to be welded. The electrode, which is held in electrode holder, is connected to one lead, and the work to be welded is connected to the other lead. When the electrode is touched to the metal to be welded, the electrical circuit is completed and the current flows. When the electrode is withdrawn from the metal, an airgap is formed between the metal and the electrode. If this gap is of the proper length, the electric current will bridge this gap to form a sustained electric spark, called the electric arc.
Welding cable connector Welding cable and the work to be welded. Under the intense heat developed by the arc, a small part of the base metal or work to be welded is brought to the melting point instantaneously. At the same time, the end of the metal electrode is also melted, and tiny globules or drops of molten metal pass through the arc to the base metal. The force of the arc carries the molten metal globules directly into the puddle formed on the base metal, and thus filler metal is added to the part being welded. By moving the metal electrode along the joint and down to the work, a controlled amount of filler metal can be deposited on the base metal to form a weld bead.
The instant the arc is formed, the temperature of the work at the point of welding and the welding electrode increases to approximately 6,500° F. This tremendous heat is concentrated at the point of welding and in the end of the electrode, and simultaneously melts the end of the electrode and a small part of the work to form a small pool of molten metal, commonly called the crater.
The heat developed is concentrated and causes leas buckling and warping of work than gas welding. This localization of the heat is advantageous when welding cracks in heat-treated parts and when welding in close places.
Generator Electrode holder Ground cable Ground cable connector Metal being welded FIGURE 6-23. Typical arc-welding circuit.
Metallic Arc Welding Metallic arc welding is used mainly for welding low-carbon and low-alloy steels. However, many nonferrous materials, such as aluminum and nickel alloys, can be welded using this method.
To form an arc between the electrode and the work, the electrode is applied to the work and immediately withdrawn. This initiates an arc of intense heat. To maintain the arc between the electrode and the work, the metal electrode must be fed at a uniform rate or maintained at a constant distance from the work as it melts.
Metallic arc welding is a nonpressure fusion welding process which develops welding heat through an arc produced between a metal electrode Gas Shielded Arc-Welding A good weld has the same qualities as the base metal. Such a weld has been made without the molten puddle being contaminated by atmospheric oxygen and/or nitrogen. In gas-shielded arc welding, a gas is used as a covering shield around the arc to prevent the atmosphere from contaminating the weld.
The original purpose of gas shielded arc welding was to weld corrosion resistant and other difficultto-weld materials. Today the various gas shielded arc processes are being applied to all types of metal. See fig. 6-24 for typical applications.
The ease of operation, increased welding speed and the superiority of the weld, will lead to shielded arc-welding and oxy-acetelyne welding being replaced with gas shielded arc welding.
Advantages of Gas-Shielded Arc Welding The shielding gas excludes the atmosphere from the molten puddle. The resulting weld is stronger, more ductile and more corrosion resistant. Also welding of nonferrous metal does not require the use of flux. This eliminates flux removal, and the possibilities of gas pockets or slag inclusions.
Shielding gas -Welding torch Shielding gas Molten weld Moiten weld - Nozzie metal metal - •Consumable - Tungsten Solidified weld metal (Machine fed) electrode Solidified weld • Arc electrode metal - Filler wire (Hand fed) Gas metal arc welding (MIG). Gas tungsten - arc welding (TIG).
FIGURE 6-24A. Gas-shielded arc welding process.
Figures 6-24, 6-25, 6-26, and 6-27 courtesy Hobart Bros.
Another advantage of the gas shielded arc is that a neater and sounder weld can be made because there is very little smoke fumes or sparks to control. The weld may be observed at all times.
Weld splatter is held to a minimum, therefore there is little or no metal finishing required. A gasshielded weld does not distort the base metal near the weld. The completed weld is clean and free of the complications often encountered in other forms of metallic-arc or gas welding.
FicuRE 6-24(C). One of the many types of automatic welders.
Tungsten Inert Gas Welding (TIG) In Tungsten Inert Gas (TIG) welding a virtually non-consumable tungsten electrode is used (figure 6-25) to provide the arc for welding. During the welding cycle a shield of inert gas expels the air from the welding area and prevents oxidation of the electrode, weld puddle and surrounding heataffected zone. In TIG welding the electrode is used only to create the arc. If additional metal FIGURE 6-24(B). A semi-automatic welder. is needed, a filler rod is used in the same manner as in oxy-acetylene welding.
Regulator with flowmeter Klectrole holder Tungsten betrole Filler metal held manually, if used Electrical conductor Insulating sheath Gas supply Gas passages Shickling gas Work Power source FIGURE 6-25. Typical TIG welding equipment.
Shielding gas Regulator with flosmeter Wire reel Wire drive may be located in welding gon handle or at wire reel Wire drive Pover saurce Controls for governing wire drive current gas fee:
and cooling water, if wed J Contactor FreURE 6-26. Typical MIG welding equipment.
The type gas used in TIG welding depends upon the metal being welded. Argon, helium or a mixture of the two gases is used. Argon is used more extensively than helium because it is cheaper.
Argon is preferred for several reasons besides the cost. It is heavier therefore provides better cover.
It provides better cleaning action wher welding aluminum and magnesium. The welding arc is quieter and smoother. Vertical and overhead welding arcs are easier to control. Welding arcs 268
are easier to start and for a given welding the weld produced is narrower with a smaller heat-affected zone.
Helium is used primarily in TIG machine welding or when welding heavy material having high heat conductivity. The arc voltage is higher when using helium, therefore a lower current flow is possible to get the same arc power.
Metal Inert Gas Arc Welding (MIG) With the substitution of a continuous feed consumable wire electrode for the non-consumable tungsten electrode used in TIG, the welding process becomes Metal Inert Gas Arc Welding (figure 6-26). The wire electrode is fed continuously through the center of the torch at pre-set controlled speeds, shielding gas is fed through the torch, completely covering the weld puddle with a shield of gas. This tends to complete automation of the welding process. Power, gas flow, wire feed and travel over the work piece are preset when using a welding machine. In semi-automatic welding, the operator controls the travel over the work.
Argon is the commonly used gas. Some metals use small amounts of helium or oxygen. Low carbon steel uses carbon dioxide or argon plus 2% Oz.
Plasma is often considered the fourth state of matter. The other three are gas, liquid, and solid.
Plasma results when a gas is heated to a high temperature, and changes into positive ions, neutral atoms and negative electrons. When matter passes from one state to another latent heat is generated In a plasma torch the electrode is located within the nozzle. The nozzle has a relatively small orifice which constricts the arc. The high-pressure gas flows through the arc where it is heated to the plasma temperature range. Since the gas cannot expand due to the constriction of the nozzle, it is forced through the opening, and emerges in the form of a supersonic jet. This neat melts any known metal and its velocity blasts the molten metal through the kerf (figure 6-27).
TUNCSTEN ELECTRODE
- OUTER (COOL) SHEATH Plasma Arc Welding
ARC CORE Plasma welding is a process which utilizes a - INNER (HOT) SHEATH central core of extreme temperature, surrounded by a sheath of coal gas. The required heat for fusion is generated by an electric arc which has been highly intensified by the injection of a gas into the arc stream.
The super-heated columnar arc is concentrated into a narrow stream and when directed on metal makes possible butt welds up to one-half inch in FicURE 6-27. Plasma welding uses a centrol core of exthickness or more in a single pass without filler treme temperature surrounded by a sheath of rods or edge preparation. cool gas.
In many respects plasma welding may be considered as an extension of the conventional TIG welding. In plasma arc welding the arc column WELDING PROCEDURES AND TECHNIQUES is constricted and it is this constriction that pro- The first step in preparing to arc weld is to make duces the much higher heat transfer rate. certain that the necessary equipment is available and that the welding machine is properly connected The arc plasma actually becomes a jet of high and in good working order. Particular attention current density. The arc gas upon striking the metal cuts through the piece producing a small should be given to the ground connection, since a hole which is carried along the weld seam. During poor connection will result in a fluctuating arc, this cutting action, the melted metal in front of the which is difficult to control.
arc flows around the arc column, then is drawn The electrode should be clamped to its holder at together immediately behind the hole by surface right angles to the jaws. Shielded electrodes have tension forces and reforms in a weld bead. one end of the electrode free of coating to provide 269
good electrical contact. The electrode holder should be handled with care to prevent accidental contact with the bench or work, since such contact may weld it fast.
Before starting to weld, the following typical list of items should be checked:
(1) Is the machine in good working order?
(2) Have all connections been properly made?
Will the ground connection make good contact?
(3) Has the proper type and size electrode been selected for the job?
(4) Is the electrode properly secured in the holder?
(5) Has sufficient protective clothing been provided, and is it in good condition?
(6) Is the work metal clean?
(7) Does the polarity of the machine coincide with that of the electrode?
(8) Is the machine adjusted to provide the necessary current for striking the are?
The welding are is established by touching the plate with the electrode and immediately withdrawing it a short distance. At the instant the electrode touches the plate, a rush of current flows through the point of contact. As the electrode is withdrawn, an electric are is formed, melting a spot on the base metal and the end of the electrode.
The main dificulty confronting a beginner in striking the are is freezing; that is, sticking or welding the electrode to the work. If the electrode is not withdrawn promptly upon contact with the plate, the high amperage will flow through the electrode and practically short circuit the welding machine. The heavy current melts the electrode which sticks to the plate before it can be withdrawn.
There are two essentially similar methods of striking the arc. The first is a touch method, illustrated in figure 6-28, and the second is a scratch method, shown in figure 6-29.
When using the touch method, the electrode should be held in a vertical position, and lowered until it is an inch or so above the point where the arc is to be struck. Then the electrode is touched Touch to work gently and swiftly Withdraw to long arc -1/8" to 3/16" FIGURE 6-28. Touch method of starting the arc.
Long arc immediately after striking 20°-25° Sweeping motion of electrode FIGURE 6-29. Scratch method of starting the arc.
very gently and swiftly to the work, using a downward motion of the wrist, followed immediately by withdrawing the electrode to form a long arc (approximately ⅛ to 16 in. long).
To strike the arc by the scratch method, the electrode is moved downward until it is just above the plate and at an angle of 20° to 25°, as illustrated in figure 6-29. The arc should be struck gently, with a swiftly sweeping motion, scratching the electrode on the work with a wrist motion. The electrode is then immediately withdrawn to form a long arc. The purpose of holding an excessively long arc immediately after striking is to prevent the large drops of metal, passing across the arc at this 270
time, from shorting out the arc and thus causing freezing.
To form a uniform bead, the electrode must be moved along the plate at a constant speed in addition to the downward feed of the electrode. The rate of advance, if too slow, will form a wide bead resulting in overlapping, with no fusion at the edges. If the rate of advance is too fast, the bead will be too narrow and have little or no fusion at the plate. When proper advance is made, no overlapping occurs, and good fusion is assured.
In advancing the electrode, it should be held at an angle of about 20° to 25° in the direction of travel, as illustrated in figure 6-30.
3 Crater FIGURE 6-31. Re-starting the arc.
Multiple-Pass Welding Groove and fillet welds in heavy metals often require the deposit of a number of beads to complete a weld. It is important that the beads be deposited in a predetermined sequence to produce the soundest welds with the best proportions. The number of beads is, of course, determined by the thickness of the metal being welded.
The sequence of the bead deposits is determined by the kind of joint and the position of the metal.
All slag must be removed from each bead before another bead is deposited. Typical multiple-pass groove welding of butt joints is shown in figure
6-32.
20° Techniques of Position Welding to 25* Each time the position of a welding joint or the type of joint is changed, it may be necessary to change any one or a combination of the following:
(1) Current value, (2) electrode, (3) polarity, (4)
- 1/16" to 1/8" arc length, or (5) welding technique. Current values are determined by the electrode arc length size as well as the welding position. Electrode size is FICURE 6-30. Angle of electrode. governed by the thickness of the metal and the joint preparation, and the electrode type by the welding position. Manufacturers specify the polarity to be a crater will be formed at the point where the are If the arc is broken during the welding of a bead, by a combination of the electrode size, welding used with each electrode. Arc length is controlled ends. The are may be broken by feeding the elec- position, and welding current.
trode too slowly or too fast, or when the electrode Since it is impractical to cite every possible variashould be replaced. The are should not be re-started tion occasioned by different welding conditions, in the crater of the interrupted bead, but just shead only the information necessary for the commonly of the crater on the work metal. Then, the electrode used positions and welds is discussed here.
should be returned to the back edge of the crater.
From this point, the weld may be continued by welding right through the crater and down the line of weld, as originally planned. Figure 6-31 illustrates the procedure for re-starting the arc.
Every particle of slag must be removed from the vicinity of the crater before re-starting the arc. This prevents the slag from becoming trapped in the wela.
Flat Position Welding There are four types of welds commonly used in flat position welding. They are the bead, groove, fillet, and lap joint welds. Each type is discussed separately in the following paragraphs.
Bead Welds Welding a square butt joint by means of stringer beads involves the same techniques as depositing 271
First pass-string bead,
- second & third-weave pattem Notice the variations of edge preparation and bead patterns as stock becomes progressively larger.
On plate thicknesses ¾" or more, double vee the edges and use multiple-pass welding FIcuRE 6-32. Multiple-pass groove welding of butt joints.
stringer beads on a flat metal surface. Square butt joints may be welded in one, two, or three pases. If the joint is welded with the deposition of one stringer bead, complete fusion is obtained by welding from one side. If the thickness of metal is such that complete fusion cannot be obtained by welding from one side, the joint must be welded from both sides.
When the metals to be welded are butted squarely together, two passes are necessary. Ii the metals must be spaced, three passes are required to complete the weld. In the latter case, the third pass is made directly over the first and completely envelops it It must be constantly kept in mind that beads, either the stringer or weave type, are used to weld all types of joints. Even though the bead may not be deposited on the same type of surface, its action in the different welding positions and joints is basically the same as its action on the surface of flat metal. The same fundamental rules apply regarding electrode size and manipulation, current values, polarity, and arc lengths.
Bead welds can be made by holding a short are and welding in a straight line at a constant speed, with the electrode inclined 5° to 15° in the direction of welding. The proper arc can best be judged by recognizing a sharp cracking sound heard all during the time the electrode is being moved to and above the surface of the plate. Some of the characteristics of good bead welds are as follows:
(1) They should leave very little spatter on the surface of the plate.
(2) The arc crater, or depression, in the bead when the arc has been broken should be approximately 16 in. deep.
(3) The depth of the crater at the end of the bead can be used as a measure of penetration into the base metal.
(4) The bead weld should be built up slightly, without any weld metal overlap at the top surface, which would indicate poor fusion.
Figure 6-33 illustrates a properly made bead weld.
Spatter Crater (A) Spatter
- Bead build up - Crater (B) 1/16" Penetration - Bead weld No overlap . •No overlap (C) 1/16" Penetration FIGURE 6-33. Properly made bead weld.
Groove Welds (Butt Joint) Groove welding may be executed in either a butt joint or an outside corner joint. A outside corner joint corresponds to a single vee butt joint, and the same welding technique is used for both. For this reason, these two types of joints are classified under the heading of grooved welding. There are certain fundamentals which are applicable to groove welds, regardless of the position of the joint.
Groove welds are made on butt joints where the metal to be welded is ¼ in. or more in thickness.
Butt joints with a metal thickness of less than ¼ in.
require no special edge preparation and can be joined with a bead weld on one or both sides.
Groove welds can be classified as either single groove or double groove. This is true whether the shape of the groove is a V, U, J, or any other form.
Regardless of the position in which a single-groove weld is made, it can be welded with or without a backing strip. If a backing strip is used, the joint may be welded from only one side. When a singlegroove weld is made without a backing strip, the weld may be made from one side, if necessary, although welding from both sides assures better fusion.
The first pass of the weld deposit may be from either side of the groove. The first bead should be deposited to set the space between the two plates and to weld the root of the joint. This bead, or layer off weld metal, should be thoroughly cleaned to remove all slag before the second layer of metal is deposited. After the first layer is cleaned, each additional layer should be applied with a weaving motion, and each layer should be cleaned before the next one is applied.
The number of passes required to complete a weld is determined by the thickness of the metal being welded and the electrode size being used. As in bead welding, the tip of the electrode should be inclined between 5° and 15° in the direction of welding.
Double-groove welds are welded from both sides.
This type of weld is used primarily on heavy metals to minimize distortion. This is best accomplished by alternately welding from each side; i.e., depositing a bead from one side and then from the other.
However, this necessitates turning the plates over several times (six times for 4-in. plate.)
Distortion may be effectively controlled if the plates are turned over twice, as follows: (1) Weld half the passes on the first side; (2) turn the plate over and weld all the passes on the second side;
and (3) turn the plates over and complete the passes on the first side.
The root of a double-groove weld should be made with a narrow bead, making sure that the bead is uniformly fused into each root face. When a few passes have been made on one side, the root on the opposite side should be chipped to sound metal to make the groove and then welded with a single-bead weld.
Any groove weld made in more than one pass must have the slag, spatter, and oxide carefully removed from all previous weld deposits before welding over them. Figure 6-34 shows some of the common types of groove welds performed on butt joints in the fat position.
Fillet Welds Fillet welds are used to make tee and lap joints.
In welding tee joints in the flat position, the two plates are placed to form an angle of 90° between their surfaces, as shown in figure 6-35. The electrode should be held at an angle of 45° to the plate surface. The top of the electrode should be tilted at an angle of about 15° in the direction of welding.
Light plates should be welded with little or no 273
Reinforcement of weld - Reinforcement of weld (A) (C) Square groove weld Double "V" groove weld Reinforcement of weld Reinforcement of weld (B) (D) Single "V" groove weld Single bevel groove weld FIGURE 6-34. Groove welds on butt joints in the flat position.
weaving motion of the electrode, and the weld is made in one pass. Fillet welding of heavier plates may require two or more passes. In that case, the second pass or layer is made with a semicircular weaving motion. In making the weave bead, there should be a slight pause at the end of each weaving motion to obtain good fusion to the edges of the two plates without undercutting them.
(A) The procedure for making the lap joint fillet weld ia similar to that used for making the fillet weld in a tee joint. The electrode should be held at an angle of 30° to the vertical. The top of the electrode should be tilted to an angle of 15° in the direction of welding. Figure 6-36 illustrates a typical lap joint. The weaving motion is the same as that used for tee joints, except that the hesitation at the edge of the top plate is prolonged to obtain good fusion with no undercut. When welding plates of different thickness, the electrode is held at an angle of 20° to the vertical. Care must be taken not to overheat and undercut the thinner plate edge. The arc must be controlled to wash up the molten metal to the edge of this plate.
Overhead Position Welding The overhead position is one of the most difficult in welding, since a very short arc must be maintained constantly to retain complete control of the molten metal.
Direction of The force of gravity tends to cause the molten
- 1/4' Leg size welding metal to drop down or sag on the plate. If a long are is held, the difficulty in transferring metal from FIGURE 6-35. Tee joint fillet weld. the electrode to the base metal is increased, and 274
FIGURE 6-36. Typical lap joint fillet weld.
large globules of molten metal will drop from the electrode and the base metal. The transfer of metal is aided by first shortening and then lengthening the arc. However, care should be taken not to carry too large a pool of molten metal in the weld. The procedures for making bead, groove, and fillet welds in the overhead position are discussed in the following paragraphs.
Bead Welds For bead welds, the electrode should be held at an angle of 90° to the base metal. In some cases, however, where it is desirable to observe the arc and the crater of the weld, the electrode may be held at an angle of 15° in the direction of welding.
Weave beads can be made by using the weaving motion. A rather rapid motion is necessary at the end of each semicircular weave to control the molten metal deposit. Care should be taken to avoid excessive weaving. This will cause overheating of the weld deposit and form a large pool of metal, which is hard to control.
Groove Welds (Butt Joints) Improved overhead groove welds can be made by using a backup strip. The plates should be prepared in a manner similar to preparing plates for welding butt joints in the flat position. If no backup strip is used and the plates are beveled with a featheredge, the weld will burn through repeatedly, unless the operator is extremely careful.
Fillet Welds When making fillet welds on overhead tee or lap joints, a short are should be held, and there should be no weaving of the electrode, The electrode should be held at an angle of about 30° to the vertical plate, and moved uniformly in the direction of welding.
The arc motion should be controlled to secure good penetration to the root of the weld and good fusion with the sidewalls of the vertical and horizontal plates. If the molten metal becomes too fluid and tends to sag, the electrode should be whipped away quickly from the crater ahead of the weld to lengthen the arc and allow the metal to solidify. The electrode should then be returned immediately to the crater of the weld and the welding continued.
Welding on heavy plates requires several passes to make the joint. The first pass is a string bead with no weaving motion of the electrode. The second, third, and fourth passes are made with a slight circular motion of the end of the electrode, while the top of the electrode is held tilted at an angle of about 15°.
Vertical Position Welding The vertical position, like the overhead position just discussed, is also more difficult than welding in the flat position. Because of the force of gravity, the molten metal will always have a tendency to run down. To control the flow of molten metal, a short arc is necessary, as well as careful are voltage and welding current adjustments.
In metallic arc welding, current settings for welds made in the vertical position should be less than those used for the same electrode size and type on welds made in the flat position. The currents used for welding upward on vertical plate are slightly lower than those used for welding downward on vertical plate. The procedure for making bead, groove, and fillet welds in the vertical position are discussed in the following paragraphs.
Bead Welds When making vertical bead welds, it is necessary to maintain the proper angle between the electrode and the base metal to deposit a good bead. In welding upward, the electrode should be held at an angle of 90° to the vertical. When weaving is necessary, the electrode should be oscillated with a "whipping up" motion. In welding downward, bead welds should be made by holding the top end of the electrode at an angle of about 15° below the hori.
zontal to the plate with the arc pointed upward toward the oncoming molten metal. When a weave bead is necessary, in welding downward, a slight semicircular movement of the electrode is necessary.
In depositing a bead weld in the horizontal plane on a vertical plate, the electrode should be held at 275
right angles to the vertical. The top of the electrode should be tilted at an angle at about 15° toward the direction of welding to obtain a better view of the arc and crater. The welding currents used should be slightly less than those required for the same type and size of electrode in flat position welding.
Groove Welds (Butt Joints) Butt joints in the vertical position are "groove welded" in a manner similar to the welding of butt joints in the flat position. To obtain good fusion with no undercutting, a short arc should be held, and the motion of the electrode should be carefully controlled.
Butt joints on beveled plates ¼ in. in thickness can be groove welded by using a triangular weaving motion, In groove welding butt joints in the horizonta. position on identical plates, a short arc is necessary at all times. The first pass is made from left to right or right to left, with the electrode held at an angle of 90° to the vertical plate. The second, third, and, if required, any additional passes are made in alternate steps, with the electrode held approximately parallel to the beveled edge opposite to the one being welded.
Fillet Welds When making fillet welds in either tee or lap joints in the vertical position the electrode should be held at an angle of 90° to the plates or at an angle of up to 15° below the horizontal, for better control of the molten puddle. The arc should also be held short to obtain good penetration, fusion, and molten metal control.
In welding tee joints in the vertical position, the electrode should be moved in a triangular weaving motion. The joint should be started at the bottom and welded upwards. A slight hesitation in the weave, as shown in figure 6-37, will improve sidewall penetration and allow good fusion at the root of the joint. If the weld metal overheats, the electrode should be lifted away quickly at short rapid intervals without breaking the arc. This will allow the molten metal to solidify without running down. The electrode should be returned immediately to the crater of the weld to maintain the desired size of the weld.
When more than one layer of metal is needed to make a vertical tee weld, different weaving motions may be used. A slight hesitation at the end of the weave will result in good fusion without undercutting the plate at the edges of the weld. When welding lap welds in the vertical position, the same pro- Hesitate Direction of welding For 1/4", 3/8", and 1/2" size fillets FICURE 6-37. Vertical tee joint fillet weld.
cedure is followed as that outlined for welding vertical tee joints, except that the electrode is directed more toward the one vertical plate. Care should be taken not to undercut either plate, or to allow the molten metal to overlap the edges of the weave. On heavy plate, lap joints require more than one layer of metal.
WELDING OF AIRCRAFT STEEL STRUCTURES Oxyacetylene or electric arc welding may be utilized for repair of some aircraft structures, since most aircraft structures are fabricated from one of the weldable alloys; however, careful consideration should be given to the alloy being welded since all alloys are not readily weldable. Also, certain structural parts may be heat treated and therefore could require special handling. In general, the more responsive an alloy steel is to heat treatment, the less suitable it is for welding because of its/tendency to become brittle and lose its ductility in the welded area. The following steels are readily weldable: (1) Plain carbon of the 1000 series, (2) nickel steel of the SAE 2300 series, (3) chrome/nickel alloys of the SAE 3100 series, (4) chrome/molybdenum steels of the SAE 4100 series, and (5) low-chrome/ molybdenum steel of the SAE 8600 series.
Aircraft Steel Parts Not To Be Welded Welding repairs should not be performed on aircraft parts whose proper function depends on strength properties developed by cold working, such as streamlined wires and cables.