Lec 2.pptx industrial electronics mid exam

Spot welding (or resistance spot welding[1]) is a type of electric resistance welding used to weld various sheet metal products, through a process in which contacting metal surface points are joined by the heat obtained from resistance to electric current.
The process uses two shaped copper alloy electrodes to concentrate welding current into a small "spot" and to simultaneously clamp the sheets together. Work-pieces are held together under pressure exerted by electrodes.
Seam welding is a welding technique in which two similar or dissimilar metals are connected by supplying an electric current and in this process a nugget formation takes place. Mostly, these nuggets are formed in the form of a butt or overlapping welding components. Do you know the meaning of these nuggets? Well, the nuggets are nothing but small pools of molten metal which are formed at the location with high electrical resistance. Seam welding is one of the types of Resistance welding.
Seam welding is a welding technique in which two similar or dissimilar metals are connected by supplying an electric current and in this process a nugget formation takes place. Mostly, these nuggets are formed in the form of a butt or overlapping welding components. Do you know the meaning of these nuggets? Well, the nuggets are nothing but small pools of molten metal which are formed at the location with high electrical resistance. Seam welding is one of the types of Resistance welding. Spot welding and seam welding are two of the most commonly used welding processes in the manufacturing industry. Spot welding is a process that uses heat and pressure to join two metal pieces together. It applies an electric current between two electrodes, creating an electrical arc that melts the metal at the point of contact. Seam welding is a similar process. But instead of using two electrodes, it involves running a continuous wire along the seam of two metal pieces to join them together. Both are used in automotive and aerospace manufacturing for joining sheet metal components.Spot welding is better utilized for welding materials that’re smaller and are overlapping. Spot welding has a manual mode while seam welding does not. Seam welding is great for welds that need an air-tight seal (remember that spot welds tend to not be the best overall. It’s also great for welds that must be continually done such as for placing strings of spot welds. What are the best uses for spot vs. seam welding? Spot welding is ideal for joining thin sheets of metal. Making it ideal for light duty applications including electronics and battery manufacturing. It is also widely used in the automotive sector, due to it’s ease of automation in high-volume production lines.
While seam welding is best suited for joining thicker materials, or creating a continuous weld along a seam. Thus making it ideal for the fabrication of tanks and vessels, as well other pipe and tube welding applications.
Spot and seam welding are both important met

1. RESISTANCE WELDING Resistance welding is the method used to join two plain metal work pieces together by running an electrical current through them. The necessary welding heat is generated by the electrical resistance of the metals, by the contact resistance in between them and by the electrical current . Resistance welding is a property of conductor by which it opposes the flow of electrons and friction and heat is produced.

2. RESISTANCE WELDING The heat is used to join two similar or dissimilar metal plates by melting and forms a bound between them.

3. WORKING Heat required to weld the two metal plates is generated by the flow of current. The welding electrodes are made-up of copper. The metal plates are held under pressure with one movable and one fixed tong. When the current flows it experiences resistance between electrodes and metal plates and generates heats which causes the metal plates to melt and join together and forms solid bound.

4. Equipment Spot welding equipment consists of welding machine. Tongs also known as electrodes

5. WORKING When the power is turned on the transformer provides low voltage high current to the electrodes made-up of Copper. Theses electrodes are held in pressure against the pair of metal plates to be spot welded with the help of tongs. The current flows from the tong to the electrodes as Copper good conductor of electricity which faces resistance at the point of contact between the two work pieces. This resistance generates heat and cause metal to metals in contact to melt and the pressure cause the melted plates to fuse together thus a solid bound is form.

6. Materials for spot welding The material’s resistivity influences heat generation. The thermal conductivity and the heat capacity influence the heat transfer. Generally, high resistance and low thermal conductivity metals are the best for spot welding.

7. Steels and AHSS Low-carbon steels, stainless steels and the new generations of advanced high strength steels (AHSS) are generally good materials for spot welding due to their low thermal conductivity and high resistance. Spot welding zinc-coated steel is possible but it needs different welding parameters and more frequent electrode tip dressing. During the welding process, the zinc coating will be alloyed with the copper electrodes. The copper  electrode degrades  more rapidly due to this surface contamination which can result in poor weld quality. Slightly high weld force is used to squeeze out the melted zinc layer and a higher welding current may be necessary to compensate the weld force.

8. Aluminum Alloys Aluminum alloys have lower resistance and higher thermal conductivity which means it conducts electrical energy and heat very easily. The low melting point of aluminum alloys can cause the sheet materials sticking to electrodes. Therefore electrode cleaning or tip dressing is critical in spot welding of aluminum alloys. To weld aluminum, a very high current and short weld time are required. It also means cooling the electrodes is very important.

9. electrode misalignment shunt current loss between welded spots cold weld (or false weld) especially in spot welding of multiple sheets spot welding of dissimilar metals such as between aluminum and steel sheets electrode indentation on sheet surface at the welded point surface coatings surface oxides and contact resistance dynamic resistance

10. Copper Alloys Copper alloys have low resistivity and high thermal conductivity, so it is difficult to generate heat even with a high welding current, and heat will quickly transfer away. They are rather difficult to weld with resistance spot welding. Instead, copper and copper alloy are excellent materials for electrodes. In the  electrical industries , welding or brazing copper alloy is very common for electrical circuit breakers and switches. Projection welding with contact designs is one way to concentrate the heat for resistance welding. Also, surface coating or braze material such as brass, silver alloy or nickel with less conductivity can increase resistance at weld interface thus facilitate welding of copper alloys. For welding copper alloys, tungsten electrodes are often used to generate more heat in electrodes and then transfer to the joint interface.

11. SEEM WELDING In seem welding two working pieces are supported on both sides by pair of electrodes. These electrodes are in the form of rollers produce continuous weld on the work piece. Continuous spot welding is called seem welding. The working principal is similar to that od spot welding. Special seem welding machine and roller electrodes are used for the welding process. When the power is turned on the transformer supplies low voltage and high current to the roller electrodes, made up of conducting materials. These roller electrodes support pair of metal plates to be welded together. When the roller make the contact with the work piece the current flows experiences high resistance due to metal to metal interface. Thus the resistance causes heat which reaches the fusion point to weld the plats together. Weld joins two metal plates together.