What Is a Tack Weld and What Are the Pros and Cons?
Tack welding is a fundamental skill and a staple in the welder’s arsenal, used in almost all welding jobs — particularly in manufacturing complex joints and parts.
The tack weld is created by creating small, dot-like welds along the joint's length. They're designed to temporarily hold metal parts in place. The number of tack welds required will depend on the geometry, measurements, material thickness and type of metal used.
As a temporary fastening method, tack welding offers several pros and cons. We’ll explore them in this article while also covering the following:
- What Is a Tack Weld?
- Types of Tack Welding
- The Four Forms of Tack Welds & When to Use Them
- Tack Welding: The Pros and Cons
- Tack Welding vs. Spot Welding
- Alternatives to Tack Welding: Self Clinching Fasteners
- Discover the Benefits of Self Clinching Fastener Technology
What Is a Tack Weld?
Tack welding plays a vital role in the sheet metal welding process. It uses low heat and a concise arc to temporarily fix two pieces of metal together.
As such, this method usually uses a pre-final weld and holds all the components in place, allowing engineers to complete the final weld to strict alignment specifications.
As it’s possible to undo this type of weld, tack welding allows engineers to test the assembly before committing to the final weld, thereby ensuring high quality and precision in the final product.
Types of Tack Welding
While there are several approaches to tack welding, the three most common methods are:
- Standard tack weld
- Bridge tack weld
- Hot tack weld
What Is a Standard Tack Weld?
Standard tack welds sit within the joint and are intended to be consumed by the final weld. A standard tack weld will hold the pieces together in the proper fit throughout the final welding process.
What Is a Bridge Tack Weld?
Bridge tack welding is used when a gap exists between two materials after they fit together. The gap may be intentional, such as a root opening in a pipe, or it may be a gap created by mistake due to the materials being miscut.
When bridge tack welding, the engineer must apply small tacks on each component alternately so that each side has time to cool down before re-tacking.
Bridge tack welding can be challenging, as it’s easy to apply excess heat in the process, which can widen the gap on the opposite side of the joint.
It’s also important to remember that bridge tacks don’t penetrate the root of the joint. As a result, they can be ground off after the first root pass is complete.
What Is a Hot Tack Weld?
A hot tack weld is formed by depositing excess filler metal into the gap between metal parts and then using a hammer to close it up.
The hot tacks are known as cleats or dogs. While this is a quick and efficient method of closing a gap between two metal parts, products that use this method are unlikely to pass quality checks.
The Four Forms of Tack Welds & When to Use Them
There are four key applications of the tack welding method. They are:
Perhaps the strongest weld formed by tack welding, this method involves making tack welds in a square pattern and is typically used for joining two parts at a right angle.
Used in instances where there are two metal pieces that you want to align vertically, this involves applying a tack weld between them so it runs from top to bottom.
This type of tack weld can be used when the metal pieces you want to join sit perpendicular to one another. Usually, the tack weld will be applied to the bottom piece.
In cases where joining two perpendicular pieces of metal together will result in a T-shape, the engineer can use this method to join the pieces at their 90-degree point.
Tack Welding: The Pros and Cons
Tack welding presents a range of advantages and disadvantages, which may eliminate this joining method from your toolbox, depending on your requirements.
Advantages of Tack Welding
- It allows you to test your design before committing to a permanent weld
- The tack welding process is quick, easy and cheap to carry out
- It allows for quick disassembly if required
- The joint can be held together in tight spaces
- It quickly sets and maintains the joint gap
- It prevents distortion during welding
- It can be used with most materials
- It can provide a reliable alternative to work clamps for holding parts together
Disadvantages of Tack Welding
- It’s temporary and produces weak bonds
- Joint quality can be impaired if tack welding isn’t carried out correctly
- It exacerbates the build-up of oxides
- Parts will need to be cleaned afterward
- When tack welding some materials, such as hard and brittle steel, specialist knowledge and skill is required, as it can leave some spots vulnerable to cracking
- Some materials don’t handle the rapid, localized heating and cooling of tack welding very well
- It isn’t easier to carry out on large parts or areas near the edge of parts
Tack Welding vs. Spot Welding
There are several key differences between tack welding and spot welding, namely:
- Tack welding forms a temporary pre-weld, whereas spot welding is a method used to fuse two metals together permanently
- Tack welding uses filler material when joining metal pieces, whereas spot welding is carried out through a combination of electrical current and pressure being applied to the metals being fused
- Tack welding can be used on a range of metals, each with varying thicknesses, while spot welding is ideally suited for joining thin metal materials, like wire mesh and foil
Alternatives to Tack Welding: Self Clinching Fasteners
As a solution that can create temporary and permanent joints, self clinching fasteners offer a viable alternative to tack welding.
Unlike tack welding or any other type, a fastener can be adjusted, removed, replaced and repaired at any point without causing any damage to the fastened components.
Some other advantages afforded by the use of self clinching fasteners include:
- Fastened joints allow for more movement with less structural stress
- Fasteners are relatively simple to install without the need for specialized equipment
- There are no specific safety risks associated with fastener installation
- The cost of producing fastened joints, including parts and labor, is usually less expensive than producing welded joints
While tack welding shouldn’t be considered a permanent method of joining sheet metal and other materials, there are several advantages to using this method as part of the process.
Tack welding can secure the appropriate gap and alignment for a fixture before the final welding process takes place, and it’s instrumental in applications where only one side is accessible.
If you're considering alternative approaches to joining sheet metal, read our article on the subject and get a comprehensive overview of the benefits and drawbacks of welding when compared with self clinching fastener technology.
Discover the Benefits of Self Clinching Fastener Technology
Design flexibility, a reduction in costs and a simple installation process are among the many reasons design engineers are moving away from welding and adopting versatile PEM® self clinching fastener technology.