What is Spot Welding? Understanding it Thoroughly

Last Updated: June 21, 2021

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Spot welding, also known as electrical resistance welding, is ranked among the oldest forms of welding. Welders consider this method as the most efficient process to use when merging two or more metal sheets. The technique involves the application of immense pressure, heat, and electrical current through the metal sheets. By doing this, you will be eliminating resistance from the metal sheets, leading to fusion. 

Over the years, spot welding has been used in various sectors of the economy. Businesses such as automobile development in the manufacturing industry use spot welding for sheet metal. Upon completion of the sheeting, the joint weld produced is used to manufacture vehicle bodies. 

How Does Spot Welding Work?

First, let us understand the steps used in the spot welding process. Here is an overview. 

1. Aligning of Workpieces and Metallic Sheets

Before welding begins, all the workpieces and metallic sheets are lined up accordingly. This activity is critical since once the sheets are welded together, detaching them will not be possible. Failure to align your workpieces correctly may force you to repeat the procedure afresh using new metallic sheets.

2. Pressing Electrodes

The process of passing electrodes involves choosing suitable electrodes for welding your workpieces. Most welders prefer using pure refractory copper electrodes due to their enhanced ability to resist oxidation and retain heat. These electrodes are also ideal since they contain portions of molybdenum (Mo). MO is known to have a high melting point, which is sufficient to prevent delamination.

3. Allowing Current to Flow through the Electrodes 

In this process, you are required to position your electrodes in their correct designated areas. Step on the legal pad on your welding machine to generate the necessary electric current. The stepping will generate a high voltage electric current. The current then flows through the electrodes and metallic rods into the metal sheets. As a result of the metal’s base resistance to the electric current, heat is generated to melt the metal sheet, and a weld is formed.

The heat produced will only be limited to the area of contact between the electrode and the weld. Use reasonable force when squeezing the electrodes to the metal sheets to get quality yields. At the holding stage, switch off the current while maintaining the pressure to allow the welded nugget to cool down. 

The type of workpieces you’ll be working on during spot welding will determine the type and amount of current to use. For instance, the amount of time allowed for current to flow is determined by the workpieces’ thickness. Once all your sheets are welded accurately, remove and reposition the electrodes in readiness for a new welding session.


Materials Used During Spot Welding

There are different types of raw materials for spot welding. Other than metallic ones, you can use steel, nickel alloys, titanium, and wire mesh. Steel is extensively used in the automotive industry due to its high electrical resistance and poor conductivity. Automotive mechanics prefer low carbon steel to high carbon steel because it doesn’t crack easily.

Spot welding can also be difficult due to various factors. The most common ones include using galvanized steel and aluminum. These materials require high electric current levels to weld and a longer welding time, unlike welding steel.

The other factor is the inappropriate thickness of the welding materials. Spot welding requires using materials with a thickness close to 3 mm. If you are using sheets with different sizes, always maintain a ratio of 3:1 to get quality welds.

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Credit: Fusionstudio, Shutterstock

The Parameters of Spot Welding

1. The Force of the Electrodes

The electrodes’ force refers to the amount of energy required to merge or fuse your metal sheets. The higher the amount of energy, the more heat will be generated. In this case, engineers need to be extremely cautious not to compromise on the weld’s quality.

Occasionally the welding current needs to be increased to enhance the welding force. Ensure the increase is on a moderate level to mitigate spatter formation between the sheets and the electrodes. Should spatter form, the electrodes will adhere to metal sheets and ruin the final weld. 

Spot welding also requires the application of minimal pressure. Minimal pressure helps in conserving the electric current and heat generated from the metal sheets and electrodes. Applying a lot of pressure creates a small spot, which reduces the weld’s penetration power.

2. Squeeze Time

Squeeze time, also referred to as programmed squeeze time, is the difference between applying the initial electrode force and the initial current on a workpiece. This parameter functions by stabilizing the welding tip before an electric current is applied to it. Skipping this step may lead to arching, premature electrode wear, or interfacial expulsion. 

Extending the squeeze duration is essential to getting quality welds. On the other hand, this extension can also lead to increased operating costs and fewer welds per session. Limiting the squeezing time may cause metal expulsion or production of low-quality welds. Ensure you program the squeeze time prematurely before beginning to weld. Programming is done from the power supply to allow the electrode’s force to stabilize effectively. 

3. The Weld Time

Welding time is the duration for applying electric current to the workpieces or metal sheets. This time is usually computed using line voltage cycles. However, it is challenging to calculate welding time accurately. It relies heavily on the activity conducted around the welding spot. 

In determining the welding time, here are the factors to consider:
  • The type and amount of current to use should generate a quality weld
  • Ensure the weld time is very brief
  • When welding thick sheets, the weld time needs to generate a nugget with a large diameter
  • Choose parameters that reduce the chances of electrodes wearing down
  • Change the weld’s duration during an automatic tip dressing and maintain a constant value for the electrode’s contact surface 

4. Hold Time

Hold time is the period after a welding session. During this time, the electrodes remain attached to the metal sheet to gradually cool down the welded area. Once the fused mass has solidified, remove the welded parts from the welding surface before starting a new session. 

Overstretching the hold time will allow heat to spread on the weld unnecessarily. This heat spread may cause electrodes to heat up and begin wearing out. High carbon materials require little holding time. Such materials start developing cracks and become brittle when subjected to long sessions of holding time. Removing electrodes before the nuggets solidify may result in the welds pulling apart or producing weak welds.

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Credit: Praphan Jampala, Shutterstock

Applications of Spot Welding

1. Manufacturing Electronics

Spot welding is widely used to manufacture items such as gas sensors, solar panels, switches, high voltage cables, and circuit boards. The method is known to have high electrical resistance, making it ideal for manufacturing complex and delicate electronic items. 

2. Fusing of Nails

A significant part of the population is not aware that spot welding is among the methods used to join rolls of nails. Welding steel wires to nails is usually done at high speeds using pneumatic nail gun magazines. To increase the number of nails to be produced, welders can use seam welding wheels. Using these wheels guarantees a production rate estimated at 1,200 nails per minute.

Before beginning the process of fusing nails, ensure the electric current applied is precise. Your electric current’s focus should be majorly at the point where the nail is under the welding wheel. Focusing intently on the electric current will lead to securing the nails accurately in readiness for fusion. 

3. Automobile Industry

Spot welding is renowned in the car manufacturing sector since the cost is pocket-friendly and readily available. The method is also fast and provides an efficient and straightforward way for welding sheet metals to manufacture cars. Manufacturers can also capitalize on the little time spent using this method and develop more cars per shift, leading to profit maximization.

Spot welding requires little skill to operate. The method can be utilized effectively by rudimentary trained staff or programmed robots, consequently making the production process flow smoothly. 

4. Dental Treatment

Spot welding is applied in dental laboratories for several treatments. The method is used to heat or repair orthodontic materials via electro soldering. A spot welder may be used by an orthodontist to anneal wire used in fastening dental implants.

5. Manufacture of Batteries

Electrical resistance is used to spot welding straps to nickel-metal hydride, lithium-ion batteries, or nickel-cadmium cells when manufacturing batteries. Spot welding fuses thin nickel straps to the battery’s terminals. The method is widely preferred to the conventional soldering process since it prevents frequent heating of the battery. 

Advantages of Using Spot Welding
  •  The Method is Quick

Spot welding is known to have a short turnaround time in yielding results. During spot welding, the heat produced is sufficient to adhere two pieces of metal sheets uniformly and in quick succession. Despite the method’s swiftness, workpieces are never distorted.

  • Easy to Understand 

Spot welding is among the oldest and well-known forms of welding. This method is well defined and easily applicable in welding various thin metals such as nickel and stainless steel. Since it’s easy to understand and apply, the technique is widely used in several sectors such as aviation, automotive, building, and construction. 

  • Proven and Tested

Spot welding has high compatibility with efficiency and uniformity. To this day, there has been a lot of work put in by all stakeholders in spot welding to test and prove that the method is the best. 

  • Energy Efficiency

Welding using the electrical resistance method requires a minimal amount of energy and electricity. This method provides a much more efficient way of utilizing electricity and energy than other welding methods such as MIG and TIG. 

  • Economical

Spot weld saves engineers’ production costs since it is relatively cheap to operate. This process also allows you to incorporate robots that enhance the production capacity. For this reason, spot welding has blended easily with other complex production methods, especially in areas such as the assembling line of production. 

Disadvantages of Friction Welding
  • Requires a Large Working Area

Spot welding cannot be done in a small or confined working space. The method involves using a lot of heat and hazardous gases. As such, this method requires you to have a large and well-ventilated working area.

  • Can be Dangerous

The welding guns used in spot welding are heavy and require great strength when using them. Such characteristics make the method very dangerous, especially to the aged welders. The high amounts of heat produced during welding can cause severe burns if they contact a welder’s skin.

Welders are also always around hazardous fumes and sparks, which pose a significant risk to their health. Other risks posed to welders include crashing and injuring themselves, especially hands and fingers.

  • Spot Welding Can be Weak 

Spot welding is not suitable for welding thicker materials. The final weld will be of low quality since the spot weld will not penetrate appropriately. By this weakness, projects done using spot welding easily break apart, requiring you to do repairs regularly. 

FAQs

1. Is it Possible to Spot Weld Thick Materials?

Spot welding is primarily used to join thin materials with thicknesses of around 3 millimeters. When welding components with different sizes, ensure the ratio of thickness is not greater than 3:1. The strength of the final weld will depend on the quantity and size of each material. Your final product should have a spot-weld diameter ranging from 3 mm to 12.5 mm. 

2. Can You Spot Weld Aluminum?

Over the years, the welding industry has gradually shifted from using steel to the use of aluminum. This replacement has happened in numerous applications such as car manufacturing, where weight is a significant component. Most welders prefer taking advantage of the three-phase electric power to spot-weld and manufacture lightweight aluminum products.

The high amount of electricity needed in such welding makes spot welding the most suitable method. The turnaround time in which spot welding supplies electric current is 0.1 seconds or less. 

3. How Does a Spot Welding Machine Work?

Resistance welding involves the resistance caused by the material to the flow of current. In this process, the final weld is formed by combining pressure, time, and heat. The material’s resistance will cause the formation of localized heat to fuse the materials. The welded parts are usually held down by the pressure exerted by the electrode tips and tongs.

The electrode tips and tongs also work as conductors through which electric current flows during the welding cycle. Several factors usually determine the welding duration. These factors include:
  • The material’s thickness
  • The cross-sectional area of the welding tip’s contact surfaces
  • The type and amount of current flow

Conclusion

Spot welding is best applied when you require small cross-section welds. Welders can also repeat the method as many times as they wish. They only need to check on the size of the workpiece. Repeating spot welding will reinforce your weld’s strength, making them last longer. The reinforcement is guaranteed due to the method’s high degree of stability. Welders can also enhance the welding quality by setting the splash’s conditions close to the welding parameters.


Featured image credit: Nordroden, Shutterstock

Cameron Dekker
 

Cameron grew up in Allentown, Pennsylvania, a once-proud steel town on the Lehigh River, where he got a taste of TIG welding in his high school shop class. He holds certificates for Certified WeldingEducator (CWE) and Certified Resistance Welding Technician (CRWT) from the American Welding Institute. His interests include scuba diving, sculpture, and kayaking.