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The application of resistance projection welding is typically found in the automotive industry in which the screw fastener parts are joined to metal sheet components. Since the nuts and studs are very tiny accessories, the RPW process is the best welding method to be applied to fix the small pieces onto the metal sheets. The RPW is also used on day-to-day products such as shopping carts to which the welding sites are usually as tiny as a spot.
Welding refers to the process of melting a limited area of two metal pieces in order to join them together. The resistance welding process is commonly used when the budget is a concern because this type of welding includes no extra materials to join two pieces of metal together. There are multiple subtypes of resistance welding such as resistance projection welding, spot welding, etc.
Resistance projection welding (RPW) is one of the resistance welding processes which takes electricity, pressing force, and time to join metal pieces together. The parts to be forged together in the resistance projection welding are the raised segments, or called the projections, on the metal pieces. In an RPW process, only very confined and tiny parts will be heated and welded together.
The application of resistance projection welding is typically found in the automotive industry in which the screw fastener parts are joined to metal sheet components. Since the nuts and studs are very tiny accessories, the RPW process is the best welding method to be applied to fix the small pieces onto the metal sheets. The RPW is also used on day-to-day products such as shopping carts to which the welding sites are usually as tiny as a spot.
To begin with, welding is the process to bind two metal pieces together. Welding can only be performed on metal materials. The welding process is commonly known as fabrication. To fabricate two metal pieces together, the surface of the two pieces will be partly heated until it melts. The two pieces will then be engaged closely when the welding sites reach the plastic state. The melted welding sites will gradually cool down and harden as the two pieces forge into one.
The welding process sometimes involves a third material to achieve the fabrication. In the resistance welding process, additional material other than the two metal pieces is not required. The intermediate material is used in some cases to optimize the welding process or to fill the gap between the two welding sites. Though it is not exactly the major intention to introduce the agent material to a welding process, it sometimes involves reshaping the pieces to some extent.
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The resistance welding process refers to the fabrication of two metal pieces by means of applying not only heat but also pressure. In a resistance welding process, the heat for welding is obtained by the resistance to the electric current between the two welding sites; the process has its name consequently. To obtain enough amount of heat to melt the metal pieces, the metal pieces are exposed to the heat as well as the pressure for a controlled amount of time.
To pass the electric current to the welding sites, welding electrodes are needed. As the key component to release the current, the electrodes are usually made from copper-based alloys because it has a superior conductive property. Since the intermediate material is not required in resistance welding, the welding process is cost-effective.
There are three main factors to achieve a good quality resistance projection welding and they are force, power, and time. The force refers to the pressure to make a small indent at the tip of the projection, the welding site. A consistent amount of force is required during the RPW process. That being said, sometimes the force is increased when the welding process is close to the end in order to enhance the forging action.
In most cases, the time it takes to join two metal pieces together with RPW ranges from milliseconds to a second. The time is set based on the power it takes to finish the welding process. If the power is low and the time is short, the welds will be weak. On the other hand, with the power too high and the time too long, the ambient areas around the projections will be melted too and it is unwanted in an RPW process.
One of the advantages of resistance projection welding is that the heating, time, and welding sites are precisely controlled so that other areas of the metal pieces do not have to undergo unnecessary thermal damages. Excessive energy may influence the property and the rigidness of the metal pieces.
One of the challenges in resistance projection welding is the heat balance. The heat balance refers to the ability to deliver equal amounts of heat to both sides of the welding sites. If the heat is imbalanced on the two sides, the difference of the thermal mass, melting point, or conductivity makes the resistance welding harder. To balance the heat, the physical property of the two materials and the size of the welding sites should be considered.
The removal of plating is another important factor that affects the result of the resistance projection welding. Plating in metal is a thin coating of gold, silver, or other metal on the metal pieces to be coated. To successfully perform RPW, the removal of plating on the metal pieces is essential since the coating often interferes with the welding process. For example, the zinc coating on the surface of the steel is not conducive to welding, and cracks may be formed during the process and weaken the structural strength of the welding sites. As a result, before welding coated materials, the coating needs to be removed.
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