Spot Welding vs Tack Welding: What's the Difference and When to Use Each

Welding is not always about making long, continuous welds. Sometimes, welds appear as small dots, often referred to as spots or tacks.

Spot welding and Tack welding are two commonly used techniques in metal fabrication. They both produce small, dot-like welds. However, depending on the application, each serves a distinct purpose.

Understanding the differences between these methods is essential for selecting the proper welding technique. Therefore, we will explain the differences and applications of Spot welding vs. Tack welding.

Spot Welding vs. Tack Welding
Photo by @TimWelds (YouTube)

Similarities Between Spot Welding and Tack Welding

Many new or less experienced welders mix spot welding and tack welding. That's nothing new, as these techniques share some similarities, especially in the context of metal fabrication.

Both welding processes create small, dot-like welds, which differ from the long, continuous welds produced by most arc welding techniques. Small welds involve localized heating of metal surfaces to form a bond, minimizing distortion over larger areas.

Tack Welds vs. Spot Welds
Source: https://www.rapiddirect.com/blog/what-is-tack-welding/

Welders use spot welding and tack welding to join metal parts together, either permanently or temporarily during assembly, and further multi-step procedures. Both are widely used in metal fabrication, including industries like automotive, construction, and machinery, to produce quick welds.

Essentially, spot welding and tack welding are both critical for efficient, accurate, and safe metal assembly. They particularly shine in applications where operators must secure parts before or during final joining processes.

However, these are two fundamentally different welding processes. To help you make an informed choice, we will first explain the basics and working principles behind both.

What Is Spot Welding and How Does It Work?

Spot welding is a resistance welding method that utilizes pressure and heat generated by the electrical resistance of the metals to create small, spot-like welds. In most cases, a copper electrode conducts current in spot welding. Copper has high thermal conductivity and low electrical resistance, which makes it highly helpful for these applications.

To produce welds, copper electrodes firmly clamp two metal sheets you are about to join. Once you press the button, the electrodes apply pressure to the parts, and the electrical current starts.

Source: https://www.youtube.com/shorts/fQYkdNaV930

Due to the properties of the copper electrodes, the current freely passes through them. But once the current meets the weld pieces, it creates resistance. Due to resistance, the current can reach up to 5000 amps, which generates extreme heat. This high heat melts the sheets, and with applied pressure, two pieces fuse.

This entire procedure passes through 4 phases: alignment, pressure, current, and release. Each phase affects the quality and strength of the weld, but everything happens super fast. Welds are done in 1/2 or 3/4 of a second, so you can quickly move forward.

Spot Welding Principle
Source: www.insajo.edu.co

Applications and Advantages of Spot Welding

Welders use spot welding to join practically any metallic material. However, due to the working principle, the most suitable metals are the ones with high electrical resistance and low thermal conductivity. Some typical examples include carbon steel, galvanized steel, aluminum, stainless steel, titanium, copper, or nickel.

Spot Welding Aluminum
Source: https://www.youtube.com/shorts/WnpnqWnrYlk

Although you can use it on various metals, spot welding has thickness limits. This method works best with 1/8-inch or lower gauge metals. The weld strength on the thicker metal is much lower. As a result, the most common applications of spot welding include:

• Welding sheet metal parts in the automotive industry, including car doors, hoods, and frames.

• Joining thin sheets of aluminum and other alloys in the aircraft industry, as well as parts such as fuselages and wings.

• Assembling parts of refrigerators, washing machines, and air conditioners.

• Connecting battery packs in laptops, smartphones, electric vehicles, etc.

• Joining metal sheet parts in chairs, tables, and cabinets.

• Fusing metal sheets and components in train carriages and other railway vehicles.

Spot Welding Car Body
Source: https://www.youtube.com/watch?app=desktop&v=rjpuufjrCis

Advantages of Spot Welding

• You can join most metallic materials (mild steel, galvanized steel, aluminum, stainless steel, copper, etc.).

• Spot welders are fast and efficient. They utilize much less power than arc welders to produce high-strength welds.

• Spot welding is a relatively straightforward method that is easy to learn.

• Resistance spot welding produces the highest-quality welds on sheet metal with a low risk of thermal defects.

• With pre-customized parameters, spot welding can yield controlled and repeatable welds every time.

• Spot welding equipment is affordable, with cheap operating and maintenance costs.

If you wish to learn more, check our article that thoroughly explains Spot welding and its working principle.

Image credit: wi6995 / Shutterstock

What Is Tack Welding and How Does It Work?

Tack welding is a technique that uses regular arc welding methods (MIG, Stick, or TIG welding) to produce small welds, which hold pieces before the final weld. Making tack welds allows you to align, hold in place, and maintain the equal joint gap on pieces you will later weld.

Tack welding produces small, temporary weld beads inside the joint. You can use any desired welding method, but it should preferably be the one you will use later to join pieces permanently. Tack welds should be strong enough to hold the aligned pieces and should not degrade the quality of the finished weld. Most commonly, welders use the same materials and technique for final welds, but with higher overall heat than tacks.

Therefore, tack welding is not a standalone metal joining process. It is a welding technique used to ensure the workpieces are correctly and rigidly aligned for the final welding procedure. A practical explanation is that of a tailor who uses pins to hold two pieces of material together before sewing them.

What is Tack Welding?
Source: https://mechlesson.com/tack-welding/

Applications and Advantages of Tack Welding

Due to the working principle, tack welding is beneficial in various metal fabrication applications. The most common uses of tack welding include:

• Temporarily holding parts in position before final welding in construction, automotive, shipbuilding, and machinery manufacturing.

• Providing accurate alignment of metal parts during setup and before applying full welds.

• Securing components to jigs or fixtures, especially in custom or prototype builds.

• Keeping large steel members in place for bridges, buildings, or frames prior to complete weld passes.

• Aligning pipes or tubes precisely before orbital or full seam welding.

Tack Welding for Aligning Pipes before Welding
Source: https://www.zintilon.com/blog/tack-welding/

Advantages of Tack Welding

• Ensures parts stay correctly aligned and positioned throughout the welding process.

• Speeds up fabrication by allowing quick assembly before final welding.

• Small tack welds limit heat input, reducing the risk of distortion and warping in thin or heat-sensitive materials.

• Easy to remove or adjust if needed during setup.

• Improves the safety and reduces the risk of movement or collapse during welding.

• Provides a stable base for consistent, high-quality final welds.

To learn more, check out our detailed article on Tack welding, its applications, and advantages.

MIG tack welding for positioning workpieces before final welding.
Photo by @tywelds (TikTok)

Spot Welding vs Tack Welding: Detailed Breakdown

Understanding the fundamentals of spot welding and tack welding is crucial in making the right choice for your further welding applications. Although we could've deduced the essential differences between these two techniques, we will include a detailed breakdown of the differences between spot welding and tack welding.

To completely understand the difference between spot welding and tack welding, we will discuss major aspects, including:

• Process fundamentals

• Required equipment

• Purpose and applications

• Strength of the weld

• Appereance

Basics of Process

Spot welding is a resistance welding method. It uses the pressure of electrodes and the heat caused by the electrical resistance of the metals you are joining. Fundamentally, spot welding is a specific and individual welding method, part of the larger group of processes called Resistance welding. It has particular equipment and operator training.

Tack welding, on the other hand, is a technique you can perform using one of the most common Arc welding methods, such as Stick, TIG, or MIG welding. Tack welding is not a special welding process; it is a technique welders use to clamp, fixate, and align pieces before further welding. You can perform it with regular Arc welding equipment.

TIG Tack Welding to Hold Sheet Metal in Position
Photo by @vanthefabricator (TikTok)

Process Equipment

As a standalone method, Spot welding uses dedicated spot welding machines. These relatively straightforward welders transform high voltage/low current from the outlet into high current/low voltage power. On home machines, you manually adjust current, pressure, and weld time, but there are also large automated systems for mass production.

You can recognize Spot welders by their distinctive look. They feature a small housing and two copper tongs (they can also be made of tungsten or molybdenum). These tongs are actually electrodes that carry the current and clamp the overlapping pieces. Electrodes can have adjustable lengths and tips sharpened to 3/16″ to transfer enough current and reach desired temperatures.

To tack weld, you can use any arc welder you would use for your welding applications, such as the YesWelder DP200 Dual Pulse MIG welder. You should use the same filler as the other equipment you will use later to finish the welds. However, you should reduce the heat.

Firstess DP200 Multi-Process MIG Welder

The considerable confusion comes from the feature called Spot timer. Some arc welders designed for automotive work have this feature, which can make you think it is capable of doing spot welding. Nonetheless, this feature will help you adjust weld time to make repetitive tack welds, not spot welds.

Firstess DP200 Welder Features Spot Timer  

Purpose and Applications

Spot welding produces permanent welds on metal sheet pieces, such as car body panels, doors, or hoods. These welds are strong and everlasting, and they often take less than a second to complete.

In general, spot welding is helpful in all applications that involve seamlessly welding sheet metal. Its localized heat reduces the risk of burn-through, distortion, or warping on delicate metals. In automated applications, spot welding can yield controlled, repeatable welds.

Automated Spot Welding
Source: https://www.thefabricator.com/thefabricator/article/automationrobotics/automating-spot-welding-to-win-fabrication-work-maintain-culture

Tack welding creates temporary welds, with the sole purpose of holding parts in place before final welding. Although not permanent, these welds can significantly increase the accuracy, consistency, and safety during the final procedure. The number and position of tack welds you need depend on the size of the materials. Later, you can grind out the tacks, but you don't need to remove all the metal and lay your weld on top.

This technique is invaluable in pipe welding. Aligning the pipes and providing a consistent gap between them helps welders produce high-quality results in root pass welding. Root pass serves as a foundation for the following passes, and producing high-quality results is crucial.

Tack Welds on Pipes
Source: https://bakersgas.com/blogs/tig/how-to-make-high-powered-tack-welds-tig-welding-tip

Strength of the Weld

Both spot welding and tack welding must produce strong welds. However, multiple spot welds are enough to hold the entire weldment permanently, while tacks are just temporary.

Spot welders can produce extreme current up to 5000 amps. Heat, combined with pressure, makes very strong welds on sheet metal. These localized welds provide the strength and durability required to withstand regular use of the parts.

Spot Welding Using a Spot Welder
Photo by @makeitextremeofficial (TikTok)

Fundamentally, tack welds are not weaker than spot welds. They need to be strong enough to hold the workpieces together and provide the mechanical strength of the assembly, whether hoisted, moved, or turned. In one direction, tacks can take a surprising amount of weight.

However, tack welds cannot offer the same tensile strength or yield strength as the finished welds. When exposed to high pressure under twisting and other directional stresses, tack welds can crack, which is expected as they are not designed to withstand harsh conditions like final welds. Simply put, tack welds are not made for strength and durability. They are intended for support, alignment, and fixture.

Tack vs. Spot Welds: Strength Comparison
Source: https://www.basicwelding.co.uk/blogs/news/whats-stronger-a-spot-weld-or-a-mig-weld

Appearance and Location

Spot welding does not produce a typical weld bead. Force and localized heat yield a molten nugget that looks like a spot, hence the name spot welding. These small, round spots or dimples have a distinguishing appearance, but they can be barely visible on thin pieces or batteries.

Appearance of Spot Welds
Source: https://rime.de/en/wiki/spot-welding/

Tack welds are small welds spaced out along the workpieces. They have a dot-like appearance, and fundamentally, they are just short weld beads.

Although both procedures create small dot-like welds, the main difference is the location of the weld. Tack welds are spaced along the weld joint, holding the pieces for future welding. You can see spot welds on top of the two overlapping pieces.

MIG tack welds secure parts for final welding.
Source: https://www.youtube.com/watch?v=yyTv8dXZwTM&t=8s

Summary Table of Tack Welding Vs Spot Welding

Instead of a regular summary of everything we learned today, we compiled a quick table of differences between spot welding and tack welding.