What is Tack Weld, Types, Symbol, Size, & applications

What is Tack Weld?

A tack weld is a small welding bead used to hold two pieces of metal together temporarily. It is typically used to hold the workpieces in place until the final permanent weld can be made.

Tack welds are usually made with the same type of welding process and filler material as the final weld. Tack Weld is not as strong as a regular weld, but it is strong enough to hold the pieces in place until the final weld can be made.

Tack welding is often used when welding large pieces of metal together, because it is easier to position the pieces correctly when they are only held together by a tack weld.

Tack welding is a common practice in many industries, such as automotive and construction. It allows for quick and easy attachment of two metal parts without the need for clamps or other fastening devices.

Tack Weld Symbol

Although there is no specified tack welding symbol given in AWS A2.4 or ISO 2553, a fillet weld symbol (for tacking T-Joints) or groove weld symbol (for tack welding in groove welds) can be used to show tack welds.

Such Tack weld symbols, or tack weld callouts shall specify the length of tack weld. Tail section can be used to mention tack weld only for such welding symbols.

Example of Tack welding symbols in T-Joints can be by using an intermittent fillet weld symbols and specifying the tack weld length and pitch (center to center distance of tack welds).

If you want to specify the tack weld symbol on your plans or drawings, be sure to mention Tack Weld in the tail section.

Tack Welding Size and Spacing

In welding during the part fitment stage, the appropriate size of tack welds is crucial in joining work pieces together. As per EN1011-2 recommendation, the appropriate size of tack weld in joining the workpiece is 2 inches (50 mm).

For thickness less than 12 mm (0.5 inch), tack weld shall be 4 times the thicker material (e.g., for 10 mm plate, tack weld length shall be 40 mm minimum).

Tacks should be no longer than 2 inches (50 mm) in length. In general, the size and spacing of tack welds should be determined by the thickness of the materials being joined.

stich welding symbol intermittent-fillet-weld

Tack welds in groove welds shall be minimum 0.5 inch (12 mm) away from outer edge of the groove weld as per AWS D1.1. EN 15085-3 standard specifies the minimum length of intermittent welds 50 mm (2 inches).

For example, when joining two pieces of thin metal together, such as sheet metal or tubing, use small tack welds spaced close together. This will help ensure a strong weld but less distortion.

Conversely, when joining thicker materials, such as plate steel or cast iron, use larger tack welds spaced further apart. If the workpiece is too thick, the spacing between tack welds can be increased to allow for proper penetration.

The spacing of the tack welds should be close enough so that the pieces being joined are held together securely, but not so close that they cause warping or other issues.

What is Bullet Tack Weld?

A Bullet tack weld is a type of tack weld in which small pieces of metal are used to bridge large gaps during root run welding. It is mainly used in piping jobs.

Small rod or triangle shapes of usually ¼ inch- ½ inch length are cut and placed in the groove of joint. This metal piece is tacked to both pipes.

Bullet tacks are removed before placing the root run, and they are never become part of the weld. Make sure to grind smooth after removal of bullet tack welds.

Importance of Tack Welds

Tack welds are an important part of many welding projects, as they play several key roles:

Alignment: Tack welds are used to temporarily hold parts in place and ensure that they are properly aligned before final welding. This helps to ensure that the final welds are accurate and strong.
Fixture: Tack welds can be used as a fixture, they help to position the parts in the right location and hold them firmly, this is particularly important when working on large structures where clamps alone may not be enough to hold the parts in place.
Distortion Control: Tack welding can help to distribute the heat of welding more evenly across the parts, which can help to reduce the amount of distortion or warping that can occur in the final welded parts.

Quality control: Tack welding can serve as a quality control step, where the alignment and fit-up of the parts can be verified before proceeding with the final welding, this help to detect and correct any issues before they become major problem.
Safety: Tack welding eliminates the need for clamps or other holding devices, which can reduce the risk of injuries.
Efficiency: Tack welding saves time and labor compared to other welding methods, it can be done quickly and efficiently, thus improving the overall productivity.

Cost-effective: Tack welding is a relatively fast and efficient process, it can save time and labor costs compared to other welding methods.

In summary, tack welds play a crucial role in ensuring the accuracy, strength and overall quality of the final welded product. Tack welding allows for precise alignment, distortion control, quality control, safety, efficiency and cost-effectiveness.

What is the specified length of tack welds on fillet welds?

If you’re wondering about the specified length of tack welds on fillet welds, the tack weld length should be 2 inches, or 4 times the material thickness, but usually maximum of a 2-inch (50 mm) tack weld length is sufficient.

Tack welds are used to temporarily hold two pieces of metal together until the final welding can be completed.

They’re usually made at the corners of the joint, and their main purpose is to keep everything in alignment while the welder works.

The size of a tack weld is important because it needs to be strong enough to hold the pieces together, but not so big that it’s difficult to remove later on.

That’s why the specified length is 2 inches, or 4 times the material thickness (whichever is greater).

This ensures that the tack weld will be strong enough to do its job without being too difficult to remove later.

Types of Tack welding

There are many different types of tack welding, each with its own unique benefits and drawbacks. Here are four of the most common types of tack welding:

Single pass Tack Weld
Multipass tack welds: should have cascade ends that allow their incorporation in final weld.
Bullet tack weld: explained above.

Bridge tack weld: Tack welds used to Bridge gap in weld joint.

How to ensure high quality of tack welds?

Follow these steps to ensure the high quality of tack welds:

Properly clean the surfaces to be welded: Removing dirt, oil, and other contaminants will ensure that the welds will properly fuse to the base metal.

Use the correct welding technique: Tack welds are typically made with a short arc, and using the correct technique will ensure that the welds are strong and consistent.
Use the appropriate welding equipment: Use a power source and welding wire that are appropriate for the thickness and type of metal being welded.
Adjust the welding parameters: The amperage, voltage, and travel speed should be adjusted according to the thickness and type of metal being welded.

Use proper tack weld size: Determine the size of tack weld according to the thickness of the parts being joined, The larger the thickness, the larger the tack weld size.
Inspect the tack welds: After completion, visually inspect the tack welds to ensure that they are of good quality, and make any necessary repairs or adjustments.
Use the right filler metals: it’s important to use the right type and size of filler metal to match the base metal, this will improve the compatibility between the base and filler metal, which will result in good quality of welds.

Advantages of Tack Welding

Tack welding has several advantages over other welding methods:

Speed: Tack welding is a quick and efficient way to temporarily hold parts in place before making a final weld. This saves time compared to clamps or other holding methods.
Precision: Tack welds allow for precise alignment of parts before final welding, ensuring that the final welds are strong and accurate.

Reduced distortion: Tack welding distributes the heat of welding more evenly, reducing the amount of distortion or warping that can occur in the final welded parts.
Flexibility: Tack welding can be used in a variety of positions, including overhead and vertical, which makes it suitable for a wide range of applications.
Cost-effective: Because tack welding is a relatively fast and efficient process, it can save time and labor costs compared to other welding methods.

Safety: Tack welding is relatively safe as it’s done in small quantity, meaning less heat and spatter, it also eliminates the need for clamps or other holding devices, which can reduce the risk of injuries.
Quality Control: Tack welding helps you to inspect the alignment of parts prior to final welding, thus reducing the risk of bad alignment, which can save time and cost.

Disadvantages of Tack Welding

Tack welding, like any welding method, also has some disadvantages:

Additional time required for tack welding: Tack welding requires an additional step of welding before final welding, which can add time to the overall process.
Extra cleanup: Tack welds need to be removed or ground down prior to final welding, which can add extra cleanup time and effort.
Risk of incomplete fusion: If the tack welds are not done properly, it can lead to incomplete fusion between the parts, which can weaken the final welded joint.

Extra cost for tack welding consumables: Tack welding requires additional welding wire and electricity, which can add to the cost of the final product.
Limited applications: Tack welding is limited to applications that require precise alignment or temporarily holding parts in place. It is not suitable for applications that require large fillet welds or complete penetration.
Risk of porosity in tack welds: Tack welding may cause porosity in the weld metal due to improper cleaning or poor welding techniques, which can weaken the joint.