welding basics an introduction to practical and ornamental welding pdf
Introduction to Welding
Welding is all about heat, about using heat to melt separate pieces of metal so
they will flow together and fuse to form a single, seamless piece.
the welding or cutting process, your ability to control the heat generated by the
flame or arc determines the quality of your welds and cuts.
Certain terms are used to describe the heat and action of all the welding
The parts being welded together are referred to as the base metal.
Additional metal, called filler, is often added to the weld.
The molten puddle is
the area of melted base metal and filler metal that you maintain as you create
To have fusion of metals, the base metal and filler metals must be the
Methods for joining metal without fusion are called
soldering, brazing, and braze welding.
These methods can be used to join similar
or dissimilar metals.
Oxyacetylene welding and cutting use flames to generate the heat to melt the
Shielded metal arc, gas metal arc, and gas tungsten arc welding and
plasma cutting use an electric arc for heat generation.
welding, you have time to watch the puddle develop as the metal turns red, then
glossy and wet looking, then finally melts.
With the arc processes, the puddle
forms quickly and may be difficult to see because of the intensity of the arc. It is
important to have ample lighting and clear vision so you can watch the puddle
and move it steadily.
Welding can be a dangerous activity. Possibilities exist for getting cut, burned,
electrocuted, and causing fires or explosions.
Preparations for welding—
grinding, burnishing, and sawing—are also dangerous. That said, it is absolutely
possible, with a little care and diligence, to weld for years and never suffer more
than a burnt thumb from being too eager to examine a just-completed weld.
It is very important to follow manufacturer’s specific instructions and
recommendations for equipment and product use and to follow general welding
Whether you are welding in a dedicated welding shop or have set up
your own shop at home, you need to be aware of a number of specific safety
Fumes. Welding produces hazardous smoke and fumes. It is always important to
keep your face out of the weld plume. Welding indoors requires either a
ventilation fan, exhaust hood, or fume extractor.
Wear an OSHA approved N99
particle mask or a respirator.
If you are pregnant or plan to become pregnant, a
respirator is a necessity.
Burns. Hot sparks and flying slag can cause burns.
Protect your hands, head,
and body with natural fibers—leather, wool, or cotton.
Manufactured fibers such
as nylon and polyester melt when ignited, which causes serious burns. Wear
leather slip-on boots, and make sure your pant legs fall over the top of your
Cuffed pants and pants with frayed edges are fire hazards. Also,
welding sparks will find tiny holes, so don’t wear holey jeans. Wear a welding
cap and tie back long hair and keep it tucked under your shirt or cap.
Welding arcs produce ultraviolet and infrared light. Both of these can
damage your eyes permanently, burn your skin, and potentially lead to skin
A welding helmet with a filter lens protects your eyes and face, while
long sleeve shirts and long pants protect your skin. Remember, you are also
responsible for protecting the vision of curious neighbors, passersby, and pets.
Use welding screens and have an extra helmet on hand for observers.
The area you’re working in should be cleared of any flammable items such
as lumber, rags, dropcloths, cigarette lighters, and matches. Absolutely do not
weld or grind metal in a sawdust-filled shop. Sparks from welding and grinding
can ignite airborne dust or fumes, or travel across the floor and come to rest
against flammable materials.
A fire extinguisher rated ABC is a must—mount it
next to a first aid kit so you know where both are.
Check your welding area one
half hour after welding to make sure no sparks have found a place to smolder
Even non-flammable gases such as carbon dioxide are stored in
cylinders at such high pressure that they can easily become dangerous missiles.
Keep the cylinder’s protective cap on if regulators are not installed, and keep
cylinders chained or strapped at all times. Cylinders should never be used as
rollers or supports, and cylinders and protective caps should never be welded on.
Shut acetylene and oxygen cylinder valves if you’re away for more than 10
minutes. Cylinders must be transported right side up and chained, even if empty.
Setting Up Shop
If you plan to weld on a regular basis, it makes sense to set up a welding shop.
The primary concern with welding is containing the hot sparks or slag and the
flammable elements while exhausting dangerous fumes.
It is possible to weld
outside, but not all processes allow that.
Gas metal and gas tungsten arc welding
require that the surrounding air be still so the shielding gas is not disturbed. All
the arc processes must be done in dry conditions to prevent electrical shock.
Cold metals do not respond as well as metals at 70° F and may not be weldable
using certain processes. A heated garage or outbuilding is best suited for a
A basement is not suitable due to the dangers of fire and
compressed gases next to living spaces. Additionally, your homeowner’s
insurance may not cover a welding shop if it is inside your living area as
opposed to in a detached garage or shop building.
Power tools such as the reciprocating saw, angle grinder, portable band saw, and
chop saw are useful when cutting and fitting metal parts to be welded.
A drill press and metal cutting band saw are also useful tools for welding.
Weldability & Cutability
Different metals have different characteristics that affect their ability to be
welded or cut with any of the processes described in this book.
In general, only
metals of the same type are welded together because welding involves melting
the base metal parts and adding melted filler metal.
In order to accomplish this,
the parts and filler must have the same melting temperature and characteristics.
Dissimilar metals can be joined by brazing and braze welding because these
processes do not actually melt the base metal.
Finding a metal supplier can be a challenging task. The materials that are readily
available may not be the sizes and shapes needed for a project and may be
expensive. Metal dealerships may not be friendly to small accounts.
Because steel is so heavy, Internet or catalog shopping carries prohibitive shipping costs.
With some searching, however, most necessary materials can be found.
Preparing Metal for Welding
A successful weld begins with a well-prepared piece of metal. The cleaner the
pieces to be welded, the better the weld quality and appearance. When working
with mild steel, it is possible to clean batches of parts ahead of time.
When working with aluminum, parts need to be cleaned immediately before welding
due to aluminum’s nearly instant formation of a protective layer of oxidation.
Mild steel is usually covered with mill scale and, often, oil or grease.
square tubes are usually thickly coated with oil, which helps in the
This oil can be removed with denatured alcohol, acetone,
or a commercial degreaser.
Though most commercially available metal items—patio furniture, indoor
furniture, and garden accessories—have rough welds and spatter still present, it
is nice to grind these down on your projects. An angle grinder is good for flat
area welds, and a small rotary grinding tool can get into nooks and crannies.
You’ll be pleased with the results of a nicely ground, good weld because it looks
like a solid piece of metal.
Wire brushing, sanding, or sandblasting the entire
piece will further prepare it for finishing.
Metal Shaping Techniques
There are a number of ways to bend and shape mild steel.
Bending tools for
creating right angle bends are called metal brakes.
Rollers create circles, punches
make holes, and shearers make cuts. You can purchase simple hand-powered
metalworking tools, though they can be costly—the higher the quality or larger
the capacity, the higher the price.
The basic joints in welding are the butt joint, lap joint, corner joint, T-joint, edge
joint, and saddle joint.
The butt joint is two pieces in the same plane butted against each other. The gap
between the pieces is determined by the thickness of the pieces.
Whether or not
the surfaces need to be ground down (beveled) is also determined by the plate
thickness. The type of weld used for a butt joint is a groove weld.
The butt joint
is a weak joint and should be avoided if at all possible.
A lap joint is two pieces in the same plane overlapped. The type of weld used
for a lap joint is called a fillet weld.
The strongest lap joint has welds on both
A corner joint is two pieces coming together to make a right angle at a corner.
The joint can be open, partially open, or closed. An open corner takes a fillet
weld, but other corner joints may take groove welds.
For hobby welding on
metal 3/16″ and thinner, an open corner joint is stronger and allows more
A closed corner joint may be weakened if the weld is ground.
A T-joint is two pieces placed together to make a right angle T shape. Again, it
is welded with a fillet weld.
A T-joint is stronger if both sides are welded.
The edge joint, or flange joint, as it is sometimes called, is predominantly used
to join thin sheet metal components.
The turned up edge lessens the heat
distortion to the thin sheets. With the advent of cooler welding processes, the
need for the edge joint has diminished.
The saddle joint, or fishmouth joint, is used to join structural tubing. The tubes
may join at any angle, and more than two tubes may be part of the joint. A fillet
weld is used, most often all the way around the joint.
Weld Symbols & Weld Types
Welding blueprints use specific symbols to denote weld types, locations, and
other factors. The basic symbol consists of an arrow and a reference line with
The weld symbol is placed above the reference line if the weld is
located on the side opposite the arrow, and below the reference line for a weld
located on the same side as the arrow.
Weld symbols above and below the
reference line indicate to weld both sides. A circle at the junction of the arrow
line and reference line means to weld all around.
Most hobby welders will not
encounter these symbols.
The most common weld types used for home welding are the fillet and groove
The fillet weld is roughly triangular in shape. It is made when welding most 90°
angle joints. T-joints, open corner joints, lap joints, and saddle joints all take
The groove weld is made in a groove between pieces. The groove may be square
grooved (straight sides), beveled (flat angled sides), or U shaped.
weld is used for butt joints, edge joints, and closed corner joints.
Once you begin welding, you will encounter numerous opportunities to repair
When your friends and neighbors discover you can do repairs, even more
challenges will come your way.
Performing welded repairs can be very tricky.
It is important to assess your
welding skills, the difficulty of the repair, and the intended use of the repaired
Any structural or vehicle repairs, such as stairways, ladders, trailers, or
truck chassis, need to meet the same safety standards as they did in their original