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Tack Welding Tips

Host Amy Devers shares tips and techniques for tack welding.

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The welding process was developed in the early 1940's for the aircraft industry. The TIG welder (TIG stands for tungsten inert gas) generates heat from an electric arc between the electrode at the tip of the torch, the filler rod and the metal part that is being welded. The electrode is made from tungsten. Tungsten is the same material in light bulbs, but instead of creating light, it's creating heat — enough heat to melt metal.

Basically, welding is the process of melting metal. There is also a grounding cable that clips onto the work piece itself, or to the welding table. It acts like the lightning rod on the top of a building. It takes the excess electricity, conducts it down the cable to the frame of the welder and neutralizes it.

In order to create a strong weld, you don't want any contaminants to get into the metal while it's in liquid form because that will weaken the weld and cause cracking over time. Inert gases are gases that don't combine easily with other elements — like metal. The inert, Argon gas in the tank is pumped through the welder to the tip of the torch where a small amount is released. This creates a gas shield around the weld keeping out any contaminates until the metal hardens.

TIG welders range in price from $1,000 to $3,500. You can rent one from an industrial rental supply for about $60 a day and that includes the safety equipment.

Welding has its own inherent dangers. You're dealing with an electric current that instantly generates 1,600 degrees of heat and a flash of light that’s so bright it could blind you. A welding mask not only protects your eyes from the flash of light, but it covers your entire face and part of your neck as well. This is important because that bright light can actually burn you just like sunburn. Protect your hands and arms with leather welding gloves and a long-sleeved leather welding jacket.

Some welders have a remote amperage control which allows one to adjust the amount of heat while welding using a foot pedal.

The welding process involves tack welding the metal pieces together, filling in the weld and then finally cleaning the weld.

Tack Welds
The purpose of a tack weld is to hold parts of an assembly in proper alignment temporarily until the final welds are made. Although the sizes of tack welds are not specified, they are normally between 1/2" to 3/4" in length, but never more than 1" in length. When determining the size and number of tack welds for a specific job, you should consider the thicknesses of the metals being joined and the complexity of the object being assembled.

Place small tack welds on one side of the joint with the filler rod. When the weld cools down, weld the other side of the joint. Tack welding involves welding two or more metal pieces together by merely applying pressure and heat to the area to be welded. Tack welding joins the two pieces of metal by using electrodes to send electrical current through the work pieces. The parts are locally heated. These small welds keep the work piece from over heating and warping until the permanent weld is made.

Filling Welds
The melted metal fills in the space between the joint creating a strong weld — hence the name filler rod. The welds used here are technically called fillet welds — metal fused into a corner formed by two pieces of metal whose welded surfaces are approximately 90 degrees to each other. A fillet weld is very common in welded furniture. It is also one of the most difficult to weld with consistency. Fillet welds require a high heat input. With novice welders, this can lead to a lack of penetration and/or fusion defects that can’t be visually detected.

Cleaning Welds
After each weld, take a wire brush and clean off the blue burn mark from the weld. This reduces the amount of polishing needed to remove the discoloration later.

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