When it comes to spot welding vs arc welding comparison, it can be hard for beginners and those with a passing knowledge to understand them. After all, both processes can join metals together and yet they each have their own unique advantages and disadvantages to consider. In this article, we will look at the difference between spot welding vs arc welding to help you make an informed choice for your next project.
Spot Welding Basics
This is a resistance welding process that uses an electric current to generate heat to fuse metal pieces together. This is a common process used in the automotive industry to weld body panels together and it’s ideal for thin sheets of metal. The generated heat melts the metal to create a strong weld that’s resistant to stress and vibration.
Arc Welding Basics
This process uses a wire electrode to create the electrical arc to the work-piece. Which causes the metal to melt into a molten pool which cools rapidly to form the weld joint. Arc welding is hard to master in comparison to spot welding, it’s a complex process and the sparks that are generated can be dangerous.
Technique Comparison of Spot Welding vs Arc Welding
A direct spot welding vs arc welding comparison is hard to make because these are very different welding processes with key differences in the techniques and applications.
The Process of Spot Welding
This process is used to join together metal pieces of sheets at specific “spots” along a joint at regular intervals. Electrical resistance is used to generate the required heat with a high current passed through the work-piece at the contact points. This creates precise localized fusion at the spots where a weld is required.
A pair of electrodes with special tips are placed into direct contact with the work piece to facilitate fusion. The electrodes are usually made of copper or some other conductive material to handle the heat and high electrical current.
To facilitate the join, pressure is applied at the electrodes to ensure that the weld quality is uniform, consistent, and high-quality. The current flows through the work-piece for a preset length of time and this is usually mere milliseconds. Spot welds can be inspected for size, strength, and uniformity and destructive or non-destructive testing can be used to verify weld quality.
The Process of Arc Welding
This process fuses metals together along the entirety of a seam or joint. A continuous weld bead is created with an electric arc heat source that uses a consumable or non-consumable electrode.
Consumable electrodes are used in Shielded Metal Arc Welding (SMAW) or Gas Metal Arc Welding (GMAW), Non-consumable electrodes are used in Gas Tungsten Arc Welding (GTAW) processes.
The electrodes will vary depending on the process, MIG wire and stick electrodes melt into a weld pool and TIG welding uses tungsten electrodes.
During arc welding, controlled electrode movement along the entire joint is required to make the weld joint. The correct arc length and an appropriate travel speed must be maintained to create a high-quality weld.
There is no specific welding time, unlike spot welding the process continues until the entire length of the joint is welded. These welds are inspected for penetration depth, proper fusion, and bead appearance along the length of the weld joint.
Advantages of Spot Welding
- Consistency: Spot welding will produce repeatable and consistent welds that are critical for certain applications where precision and uniformity are needed.
- Efficiency: The setup time between welds is minimal, the process is fast and these factors reduce production costs.
- High-Speed: This is a fast welding process, multiple welds can be created in a very short period which makes this a popular choice for assembly lines and mass production.
- Clean and Neat: Spot welds are clean and neat which makes them an ideal choice in applications where aesthetic appeal is important.
- Strong Joints: A well executed spot weld is a strong and reliable way to join steel and certain other non-ferrous metals.
- Minimal Distortion and Warping: Spot welding uses fast localized heat to create fusion which minimizes the risk of distortion and warping. This is especially true if thin metals are joined together.
- No Filler: This welding process requires no filler materials which simplifies the process and reduces the material costs.
Disadvantages of Spot Welding
- Calibration and Setup: A spot welding machine must be properly calibrated and set up which is a complex procedure. Adjusting and maintaining the machine for a variety of different applications is the realm of skilled technicians which raises the costs.
- Joint Limitations: This process is well suited to lap joints between two or multiple metal sheets, but it’s less useful for complex joint types and configurations.
- Thickness Limitations: Spot welding works well with thin to medium materials, but thicker materials tend to require multiple welds.
- Material Limitations: This process is ideal for materials that have good electrical conductivity, including stainless steel, steel, and certain aluminum alloys. But, it’s not suitable for highly resistive or non-conductive materials.
- Reach Limitations: The reach of spot welding is limited to the electrode arm or tip lengths. This can be a significant drawback if the access to a prospective joint is restricted in some way.
- Constant Electrode Maintenance: The electrodes wear out quickly because they are subjected to significant thermal stress and high electrical current. So, regular electrode maintenance and replacement is a requirement to maintain weld quality.
- Proper Quality Control: Regular inspections are essential to ensure that the welds are consistent, free from defects and that the weld integrity is maintained.
- High Energy Consumption: This process consumes a lot of energy and this is especially true in the high-production settings.
Advantages and Disadvantages of Arc Welding
- Highly Effective Welds: This process can create extremely strong and durable welds that can withstand high stresses and loads.
- Precision and Control: A skilled welder has full control over the welding process, they can adjust variables, such as voltage, current, and travel speed for any given application.
- Portability: Certain welding processes, such as Gas Metal Arc Welding (GMAW) known as “MIG Welding” and Shielded Metal Arc Welding (SMAW) known as “stick welding” are portable and they can be used in a wide variety of locations.
- No Need for Gas: A welding process such as SMAW requires no shielding gas which simplifies the setup and reduces operating costs.
- Positional Welding: Arc welding can be performed in multiple positions, including flat, vertical, horizontal, and overhead. This makes welding complex structures and joints possible.
- Welding Outdoors: Arc welding processes can be used outdoors with no need for extra shielding.
- Versatility: This process can join together a wide variety of metals, such as aluminum, steel, stainless steel, and cast iron.
- Skills and Training: Arc welding requires significant training to learn how to produce high-quality welds. Until they gain experience novice welders will produce subpar welds and regular practice is essential to progress.
- Excess Weld Spatter: Arc welding can produce spatter which can create additional safety hazards and lead to extra cleanup.
- Electrode Handling: The arc weld processes that use MIG wire and stick electrodes require proper storage and handling. If consumables electrodes are exposed to moisture they can compromise the weld quality.
- Limited Access to Joints: This process may not be the best option for joins in confined or tight spaces due to the bulkiness of the equipment, shielding gas and electrode holders.
- Electrical Hazards: Arc welding uses high electrical current which can present a safety risk if the safety precautions are ignored.
- Thin Material Suitability: Welding thin materials can cause burn-through and/or excessive distortion.
- Heat-Affected Zone (HAZ): Arc welding may cause a HAZ near the weld which can affect the properties of the material, including toughness and hardness.
- Slag Removal: Certain arc welding processes such as SMAW can form slag on the weld bead which must be manually removed.
- Consumables: If the arc welding process uses consumable electrodes, filler materials, and shielding gasses this will drive up the final welding costs.
Spot Welding vs Arc Welding– Which is Best?
Now that you have a better understanding of the difference between spot welding and arc welding, it’s easier to notice that there is no definitive answer.
Which is best, is subjective and both processes are useful in specific applications. If you need to make fast, efficient, and repeatable welds on thin sheet metal, spot welding is the go-to solution.
But, if you want to weld thicker materials with less heat damage from excessive heat and a lower distortion risk, then arc welding is better.
The most common spot welding applications include automotive, sheet metal industries, electronics, and manufacturing. When it comes to arc welding processes, they can be commonly found in aerospace, heavy machinery, construction, and pipelines.
Conclusion: Spot Welding vs Arc Welding
As you can see, spot welding vs arc welding is a tricky comparison to make because these are very different processes. Spot welding is faster and more efficient if you need strength and consistency in thinner or sheet metal applications. However, there are significant limitations in the thickness, joint types, and material compatibility.
Arc welding is effective and versatile for many applications, but there is a steep learning curve to deal with slag, weld spatter and other issues. Understanding the welding project requirements and the materials that are being joined together is essential to choosing the right welding process.