IN THIS CHAPTER

Hammering it together

Leveraging electricity

Spotting and sounding off

Shielding the fire

Reading the symbols of welding

Learning about weld safety

Great works are performed not by strength but by perseverance.

— SAMUEL JOHNSON

So far, this book has been concerned with the various ways in which metal is chopped up, bent, and formed into little pieces — making parts, in other words. But until the day we can build one-piece toasters, bridges, airplanes, and millions of other assemblies, most parts must be joined one to the other if they’re to do anything useful.

Fasteners such as nuts, bolts, screws, and rivets may be used. Adhesive bonding — a fancy way to say glue — is an increasingly popular way to join metals in the automobile industry. Sometimes parts are made with clever stamped-metal tabs that snap together, not unlike a high-tech version of a model airplane. And then there’s welding. Let’s talk about that for a while.

Wondering About Welding

Several dozen unique welding technologies exist, each labeled with confusing acronyms such as FOW (forge welding), FRW (friction welding), AHW (atomic hydrogen welding), EBW (energy beam welding), and lots more. There’s nowhere near enough space to give each of them fair coverage, so feel free to check out Welding For Dummies if you want to learn more about the topic (or decide to pursue a career as a manufacturing engineer). For now, at least be aware that most experts lump all the different welding methods into one of the following categories:

• Arc welding relies on an alternating or direct-current power source to generate an arc of high temperature, metal-melting electrical energy between two workpieces.
• Energy welding uses a beam of collimated light (you might know it as a laser) or high-energy electrons (the same technology that once powered your grandparent’s TV set) to heat and fuse metal.
• Gas welding is one of the oldest known forms of welding and uses nothing more than a gas-powered torch and some “filler metal” to join two pieces of metal.
• Resistance welding is sort of like arc welding but without the arc, using electrical current to melt two pieces of tightly-clamped metal together. Most of your car was resistance welded, as was your refrigerator, your toolbox, the door on the vending machine where you once got your arm stuck and had to call 911 … the list goes on.
• Solid-state welding is performed on metal while it’s still in the “solid” state, heating it just enough to make it pliable like a warm candy bar. Sometimes it is performed by not heating it at all, relying instead on the seeming affability of atomic materials.

Of these, arc welding is easily the most common, although some of the others listed here are certainly no less important. In some cases, relatively new technologies such as friction stir welding and laser welding (both discussed a bit further along in this chapter) are leading the pack in a variety of high-performance welding applications, displacing their more mature peers in favor of higher speed and improved weld quality.

However it’s accomplished, all welding methods share one thing in common: They join metal (Figure 10-1). Some aren’t all that different from a hot glue gun, using heat to melt filler material that then bonds with the edges of adjoining metal pieces — filling the gap — to create a welded assembly. Others rely on friction to heat and join two pieces of metal, while still other welding techniques are “cold” processes, using nothing more than atomic attraction to bond metals together. (See the sidebar “A dish best served cold” for more.)

Doing Me a Solid (State)

Welding is not a new technology. Several thousand years ago, some brawny blacksmith with plenty of time on his (or her) hands discovered that if you stack two pieces of heated metal and pound on them long enough, they’ll become one. Maybe he was mad over not being invited to the Pharaoh’s birthday party, or maybe his girlfriend just broke up with him — whatever the reason, this unsung hero of metallurgy discovered that forge welding is a surprisingly effective (albeit tiring) way to make metals stick to one another. If you want to try it for yourself, just fire up the barbecue, break out your favorite hammer and a handful of nails, and get pounding.

Unfortunately, the low-carbon steel used to make most nails is about the only metal suitable for forge welding, limiting its use. Though older than dirt even in dog years, it can be considered a subset of a much more modern welding technology, solid-state welding. It’s called that because the temperatures used aren’t high enough to actually melt the metal, but rather soften it up sufficiently to make it pliable, sort of like buying your spouse something nice before breaking the news that you quit your job and bought a car wash.

In the case of forge welding, operating temperatures are around 1,800 °F (1,000 °C). This may seem pretty hot to those of us used to baking pot pies and frozen pizzas, but in metallurgical speak, those temperatures are no warmer than an early spring day. In comparison, arc welding achieves 11,000 °F (6,000 °C) or higher, and PAW (plasma arc welding) reaches five times that temperature. Now that’s hot.

Hot or not, solid-state welding covers a broad range of technologies:

• Diffusion welding (DFW): Also known by its moniker diffusion bonding, DFW relies on the same atomic love-fest that drives cold welding. What’s different is that diffusion welding is performed at higher pressures and temperatures, approaching those used in forge welding. But where forge welding needs a hammer and plenty of upper-arm strength, diffusion welding is about as exciting as watching paint dry. An inert gas might be present to limit oxidation, it may be done in a vacuum, and there may be a sandwich-like “interlayer” where material incompatibility is a concern (hey, it happens), but all types of diffusion welding form a strong, durable bond.
• Explosion welding (EXW): In Chapter 8, I devote an entire section to the use of explosives to form complex metal parts. This was done not because it’s a widely used process, but rather because explosives — like fireworks — are cool, especially when detonated underwater. Explosion welding works the same way, relying on the force of high-energy explosives to accelerate one metal into another, thus bonding the two together. As with friction welding, it is often used to join dissimilar materials, something that is difficult to achieve with many welding processes.
• Friction stir welding (FSW): The new kid on the welding block, friction stir welding was invented in 1991 by The Welding Institute (TWI), a UK-based welding research and technology organization (and a good club to join if you’re a welder). It’s a devilishly simple process — clamp two pieces of metal alongside one another, force a rotating tool shaped a little like a short, stubby screwdriver into the gap until buried against the “shoulder,” and then slowly drive the tool down the length of the workpiece. As it passes, the tool’s shoulder riding along the surface heats the metal to near forging temperatures while the smaller probe sitting between the two pieces of now-softened metal “stirs” the halves together.
• Friction welding (FRW): Sometimes metals can be welded by pure friction. No, this isn’t the friction felt by you and your significant other when disagreeing over which movie to see this weekend (I prefer war movies myself), but rather the friction caused when two objects are rubbed against one another very quickly. For example, take two metal cups, place them rim to rim, and spin them in opposite directions. You’ll soon have a sealed container that’s good for … well, nothing really, although it will have a strong weld that you can show off to your friends. This is called, appropriately enough, spin welding. It can also be done linearly, in which case it’s called linear friction welding, or LFW. Both are widely used in the aerospace, power generation, and any other industry requiring a robust weld, often between dissimilar materials.
• Ultrasonic welding (USW): Place two or more sheets of thin metal one on top of the other and blast them with a high-frequency soundwave. There’s little heat, it’s fast, and it produces a darned strong weld in the right application. Ultrasonic welding uses a tool called a sonotrode — more often called a horn — to transmit a pulse of sound in the 20- to 75-kHz range (high enough that you should probably leave your dog at home), thereby joining the thin layers of metal used to make batteries, heat sinks, electrical contacts, and more.

There are more. Hot-pressure welding, roll welding, electromagnetic pulse — as with most types of welding, the term “solid state” encompasses a wide variety of technologies, each designed to address specific joining challenges. Despite their differences, all are effective ways to bond metal via vibration, pressure, friction, or a combination of the three, and do so at temperatures well below the melting point of the material being welded.

Firing Up

“Fire bad!” Frankenstein’s monster learned this the hard way, just before the ignorant villagers burned him alive. It’s tough to be a monster. In a welding shop, however, fire is your friend. That’s because mixing bottled oxygen with a fuel gas such as acetylene, propane, or hydrogen creates a flame hot enough to melt steel and iron.

One of the oldest of all welding processes, oxy-fuel welding — also known as oxy-acetylene welding or oxy-hydrogen welding or even oxy-gasoline welding or just gas welding (yikes) — creates a “localized melting” pool of molten material that, when cooled, does a nifty job of joining two pieces of material. Filler metal might be used to further strengthen the bond and replace lost material, although this is not mandatory.

Oxy-fuel welding is simple and inexpensive. For a few hundred bucks, you could be welding yard ornaments by this afternoon. But for most industrial uses, oxy-fuel welding has largely been replaced by the faster and more effective arc welding (don’t worry, I’m getting to it next), except in those places where electricity may not be readily available — northern Greenland, perhaps, or deep in the Australian Outback.

As I discuss in Chapter 4, there’s one industrial application of oxy-fuel welding that remains quite common: By applying a blast of pure oxygen to an oxy-fuel flame, the flame can be made to cut rather than join and does so with a fury greater than the proverbial woman scorned (see Figure 10-2). Computer numerical control (CNC) oxy-fuel tables are widely used to cut shapes and punch holes in steel plate up to a foot thick. And by equipping the same machine with a plasma head, aluminum and stainless steel can also be cut quickly and accurately.

Arcing Across

I once neglected to turn off the circuit breaker before replacing an electrical outlet in my basement. Once the smoke cleared and sparks subsided, I discovered that my screwdriver had been permanently joined to one of the terminals. That’s the power behind arc welding.

Step into any garage, hobby shop, or fabricating company and you’re sure to find an arc welder there (no, I don’t mean the tall gal in the corner with the name Brenda stenciled on her welding helmet). I mean a piece of welding equipment that channels electrical energy through an electrode and into a workpiece, heating the heck out of the joint and allowing the now molten metal to flow together. Here are the most common types of arc welding methods in use today, although there are plenty more where these came from (see Figure 10-3):

• Metal inert gas (MIG) welding: Also known as gas metal arc welding (GMAW), or more often as simply wire-feed welding, MIG welding is one of the most common welding processes in use today. It works by sending an electrical current through a gas-shielded spool of wire, which serves as both electrode and filler material. As the wire touches the workpiece, it short-circuits, simultaneously melting the electrode and the surrounding metal. MIG welding is suitable for joining mild steel, stainless steel, and aluminum, and it is easy to learn, an attribute that kept me from being fired when I was a teenager.
• Shielded metal arc welding (SMAW): Because welders are by nature laid-back people averse to using lofty acronyms, most refer to SMAW as simply arc welding (even though the competing methods listed here are all technically considered arc welding) or even stick welding, as in “how’s the stick treating you today?” Similar to wire-feed welding but even simpler to operate, it uses a consumable metal electrode that looks a lot like one of the sparklers you enjoy lighting during Fourth of July celebrations. The outer coating of this electrode is called flux, a mysterious material that disintegrates during the welding process to clean the metal and form a shielding gas, thus protecting the weld from atmospheric contamination. (For more on flux, see “In flux over flux” later in this chapter.)
• Flux-cored arc welding (FCAW): By replacing the solid metal wire electrode used in MIG welding with a flux-filled metal tube, there’s less need and sometimes no need at all for shielding gas. This makes FCAW perhaps the easiest of all welding processes to learn and inexpensive to operate, besides. And even though the resulting weld bead (the swirly-looking area where the two pieces of metal are joined) is perhaps less pretty than other welding methods (depending on the skill of the operator), FCAW is quite fast, making it a favorite on construction sites or to make quick repairs out in the field.
• Tungsten inert gas (TIG) welding: Where MIG welding and FCAW are the simplest types of welding to learn, TIG welding (also called GTAW, for gas tungsten arc welding) requires a skilled craftsman to produce high-quality, aesthetically-pleasing welds. TIG welding uses an electrically charged tungsten electrode to strike an arc between it and the workpiece, heating it enough to create a “puddle” of molten material. The welder (meaning the person under the welding helmet) then feeds a piece of filler material into the weld joint, permanently bonding the two materials. When done properly, the weld will be stronger than the base material (as is true for many welding technologies).

But wait, there’s more! Thermite welding (TW) is an exothermic process used to butt-weld railroad tracks. Ship builders and structural steel firms use electroslag welding (ESW) to join thick steel plates and beams. There’s also submerged arc welding (SAW), called that because the weld bead is submerged beneath a layer of flux, not because it’s done underwater. Pipeline builders use magnetically impelled arc butt (MIAB) welding, and pressure vessel manufacturers use magnetic pulse welding (MPW). It’s clear that welding scientists enjoy their acronyms even more than computer geeks do, but that’s okay — without welding, the world would quite literally fall apart.

Marking the Spot

Here comes another acronym: RSW. It’s short for resistance spot welding, and it’s used extensively to join metals too thin or otherwise unsuitable for arc or friction welding. If you have a spare C-clamp in the garage, you might give it a try — just strip the end off of an old extension cord and attach the two wires within it to opposite sides of the clamp. Stick a couple hunks of sheet steel or aluminum between the anvils, tighten the clamp, and plug ’er in for a second. Assuming you didn’t blow the door off your electrical cabinet or start the house on fire, the two pieces of metal should now be one.

Actually, that’s a really bad idea. Forget I ever said it. But resistance welding itself — properly done — is used to produce vehicle chassis, weld wires to electrical assemblies (maybe the ones in the extension cord you just ruined), join threaded studs to sheet-metal components, replace rivets and other fasteners with welded joints, attach nails to nail gun magazines, and so on.

Getting Gassed Up

Think about it: Permanently joining two pieces of metal requires lots of energy. And while this energy is often generated by electricity, friction, flame, and even explosives will do. Yet there’s far more to the wonderful world of welding than the energy source used to bring metals together. There’s also the type of joint used, whether a shielding gas or filler material is needed, what kind of surface preparation is required to create a strong weld, and how much cleanup will be needed afterward.

Shields up, Captain!

Let’s take a peek at shielding gases. When the Romulans attacked the Starship Enterprise, the only thing that saved Captain James T. Kirk and his brave crew from certain death was the energy shield surrounding the ship. Certain types of welding also require a shield, although it doesn’t require an antimatter-powered warp core to generate it, but rather a bottle of argon or carbon dioxide.

Why is this necessary? Because the nitrogen, oxygen, and water vapor in our environment tend to degrade weld quality, causing cracks and porosity to form. But by displacing those nasty intruders with an inert or semi-inert gas, welds are improved and welding throughput is increased. The question then becomes which type of gas to use, along with when and how to apply it.

There are many kinds of shielding gases, as well as dozens or even hundreds of custom gas mixtures designed specifically for the metal being welded, the type of welding, where it will be performed (inside a welding shop or out on a windy job site), the final use of the product being welded, and so on:

• Argon: An inert, colorless, and odorless element, argon is one of the noble gases. Noble gases are those whose outer electron shell is completely full, eliminating their desire to interact with other, less lofty gases. Welders couldn’t care less about molecular structures, however. All that’s important to them is the fact that argon’s inert nature makes it an excellent shielding gas for welding aluminum, magnesium, and titanium.
• Carbon dioxide: Welding can be expensive, so when manufacturers see a viable way to reduce operating costs, they’re going to jump on it. One of these ways is to use carbon dioxide, which is cheap, ubiquitous, and does a decent job as a shield gas, especially on thick materials where a deep weld is needed.
• Helium: Also noble, helium is a lot of fun at birthday parties, as sucking on the balloon tank and singing “For He’s a Jolly Good Fellow” leads to hysterical laughter from all involved. On a more serious note, though, helium and helium blends help improve weld quality in non-ferrous metals such as aluminum and stainless steel.
• Hydrogen: To anyone who’s watched videos of the hydrogen-filled Hindenburg crashing to the ground, the suggestion that this extremely flammable gas should be brought anywhere near a welding arc might be met with incredulity. But it’s true: Adding a small amount of hydrogen to argon and helium makes a nifty shielding gas — one might literally say, “It’s the bomb!”
• Nitrogen: The Earth’s atmosphere is 78 percent nitrogen, and it’s one of the bad actors that make shield gases necessary in the first place. However, a smidge of nitrogen in your argon mix helps weld quality on duplex steels (mainly used for pipelines). And if your shop owns a fiber laser, chances are good there’s plenty of it around, as nitrogen is often used as an “assist gas” on laser cutters.
• Oxygen: Yes, I know that I called oxygen a “nasty intruder,” but as with many things in life, a small amount in moderation is a good thing. Mixing a few percent by volume of oxygen with argon tends to increase arc stability and decrease the surface tension of the weld pool, making it flow better. Too much oxygen, however, and weld brittleness can occur.

Check out any welding gas supply company’s website and you’re sure to find a broad assortment of special blends using these gases as well as crazy additives like nitric oxide (which reduces ozone creation during welding), sulfur hexafluoride (which helps with aluminum welding), and dichlorodifluoromethane (used when welding aluminum-lithium alloys). I told you earlier that welding is complicated.

The good news is that shield gases are limited to arc welding. The bad news is that TIG and MIG arc welding are among the most common of all industrial welding processes. (Check out Figure 10-4 for a picture of high-volume robotic welding.) The takeaway is simple: If you’re an arc welder, it’s important to work closely with your weld gas and equipment suppliers to find the right mix of shield gases for your application.

Choosing a Good Joint

Check out Figure 10-5. It illustrates the five basic types of weld joint. There are, of course, a huge number of variations, but understanding these will get you pointed in the right direction:

• Butt joints are used to join two flat pieces of metal that are aligned in the same plane.
• Corner and tee joints allow two pieces of metal to be joined at right angles to one another.
• Lap joints are most often seen in spot and resistance welding, although there’s nothing stopping you from using one when arc welding. A good rule of thumb is to overlap the two pieces by three times the material thickness.
• Edge joints are like a metal sandwich. Stick the two halves together, weld all around the periphery, and the thing is never coming apart.

Unless the weld is made via friction or some other method of solid-state welding (meaning no filler metal is needed), the edges of each piece will usually be prepared in advance by machining a small chamfer or grinding a bevel to leave room for the weld bead. Doing so provides a stronger, more accurate, and more aesthetically pleasing weld (and everyone likes a pretty weld).

It’s important to understand each of these weld types, as well as the various ways to prepare the surface before welding — rather than a simple 45-degree chamfer, some manufacturers specify J or U shapes, with clearly defined starting distances (called root openings) between mating pieces. The type of weld is also called out on the drawing, perhaps using one of the symbols shown in Figure 10-6.

As I allude to earlier in this chapter, welding has oodles of science and technology behind it, and it usually requires years to master. So even though you might need a shower after a day spent under a welding helmet, remember this: Welding is a complex but deeply important manufacturing skill. Your parents should be proud of you.

Learning Safety with Jimmy

Early in my manufacturing career, my boss tasked me with operating “the notcher,” a machine not unlike a punch press that took neat, perfectly square bites out of metal blanks that would then be sent to a press brake where they were bent into chain covers for the massive cereal processor my employer was constructing.

It was mind-numbing work for anyone, but especially so for a 16-year-old boy concerned with only two things: whether his girlfriend’s parents would let her go to the concert on Friday night, and what kind of third-degree my Mom would give me for staying out past curfew again. Long story short, I wasn’t paying attention, and several hours of daydreaming later, the once-square notches in the chain covers had become decidedly rectangular. That’s when my now red-faced boss introduced me to Jimmy, the head of the welding department.

Actually, Jimmy was the welding department, but as he frequently explained to me during our time together, that made him the “de facto” supervisor (he actually used that term). No one argued the point — Jimmy was a little off, prone to sudden temper tantrums during which he would throw metal objects across the shop floor, but that didn’t stop him from being a good welder.

Over the next three weeks, the chain-smoking Jimmy taught me how to wire feed (I didn’t know at that time that it’s also called MIG welding). I’d pick an irregularly-shaped chunk of metal from the notcher’s scrap bucket, set it into one of the misshapen corners of a chain guard, and weld the thing into place. Every hour or so, I’d smooth down the edges of the now whole chain guards with a grinding wheel, then carry the stack over to the notcher for re-notching (by one of my coworkers — my days on that machine were over).

I learned a great deal during my brief time with Jimmy:

• When an emergency physician attempts to remove grinding grit from your eye by scraping it with a metal instrument and repeatedly flushing the affected area with saline solution — a process known as irrigation — it hurts. A lot. Always wear your safety glasses, preferably ones with side shields.
• Looking directly at the pretty blue glow generated by an arc welder leaves phantom black spots floating about in your field of vision that don’t disappear for several days afterward. Never look at the arc, and always wear appropriate eyewear for welding.
• Handling parts immediately after welding them together can lead to burned fingers and bountiful cussing. Despite my previous warnings elsewhere about wearing gloves in a manufacturing shop, welding gloves should always be used.
• Dropping sharp, heavy workpieces on your toes hurts almost as much as having your eye irrigated by an overworked emergency-room physician. Always wear steel-toed shoes. Not only will they prevent you from walking with a limp for the rest of your life, but also, they’re tax deductible.
• Welding is often a little stinky, and the fumes can give you a headache (even more so than Jimmy’s endless cigarette smoking). Always use good ventilation.
• When welding and especially grinding metal, hot sparks fly everywhere. These will burn little holes in your pants and leave scars on your arms that your grandson will one day remark upon. Always wear your leathers when welding (or when riding a motorcycle).

All of these warnings might make it sound as though welding is a dangerous occupation. Nothing could be further from the truth. Cooks wear aprons and funny hats, seamstresses wear thimbles, truck drivers wear kidney belts and sit on inflatable donuts. All professions carry some level of hazard, and welding is no different. If you want to stay safe (and who doesn’t?), you need to follow the rules, own and maintain the right safety equipment, and above all, pay attention to what you’re doing.