Difference Between Fusion Welding and Solid State Welding from as852123's blog

Welding is one type of manufacturing process by which two or more similar or dissimilar materials can be joined permanently by weld bead formation with or without the application of external pressure, heat or filler material. There exist different types of welding processes, each of them follows unique procedure to weld two or more components. Welding processes can be broadly classified as arc welding, gas welding, resistance welding, solid state welding and intense energy beam welding. Each of these class once again consists of several welding processes. Irrespective of the welding process, a weld bead formation is always desired to join the components by welding. This weld bead forms at the intersection of two components that are welded. It is also worth mentioning that fusion of the faying surfaces of the parent components is not necessary for weld bead formation. In some welding processes, the faying surfaces are fused with the application of heat to get the weld bead, while in other processes, weld bead can be obtained without melting the faying surfaces. On the basis of whether base materials are fused or not, welding processes can be broadly classified into two groups—solid state welding and fusion welding.

In all such welding processes where the faying surfaces of parent components along with the filler material are fused to form the weld bead are called fusion welding. Sufficient heat must be applied by external means for properly fusing the faying surfaces of base metals as well as the filler metal. Thus phase change (solid to liquid and once again liquid to solid) occurs in fusion welding. All arc welding, gas welding, resistance welding and intense energy beam welding processes are fusion welding. On the other hand, if no such melting takes place during welding, then it is termed as solid state welding. Here the joining takes place in solid state and no phase change occurs. However, in solid state welding, parent components may be heated to an elevated temperature but substantially below the melting point of the concerned material (and thus no melting occurs). Instead of external heat, application of pressure is usually necessary for this type of welding. Roll welding, diffusion welding, friction welding, etc. are considered as solid state welding processes. Following passages elaborate similarities and differences between fusion welding and solid state welding.

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Thyristors are an interesting class of semiconductor devices. They share similar characteristics with other solid-state components made from silicon, like diodes and transistors. Therefore, distinguishing thyristors from diodes and transistors could be difficult. To add to the difficulty, there are different types of thyristors available on the market.

In some instances, what sets thyristors apart from one another could be just a tiny detail.

Also, depending on the manufacturer, a given thyristor may be known by another name.

To apply thyristors successfully when designing circuits, it is important to know their unique characteristics, limitations, and their relationship with the circuit. That’s why we’re taking some time to sort it all out so that you can have a better understanding of what thyristor is most suitable for your application.

A thyristor is a four-layer device with alternating P-type and N-type semiconductors (P-N-P-N).

In its most basic form, a thyristor has three terminals: anode (positive terminal), cathode (negative terminal), and gate (control terminal). The gate controls the flow of current between the anode and cathode.

The primary function of a thyristor is to control electric power and current by acting as a switch. For such a small and lightweight component, it offers adequate protection to circuits with large voltages and currents (up to 6000 V, 4500 A).

It is attractive as a rectifier because it can switch rapidly from a state of conducting current to a state of non-conduction.

In addition, its cost of maintenance is low and, operating under the right conditions, remains functional in the long term without developing a fault.

Thyristors are used in a wide range of electric circuits, from simple burglar alarms to power transmission lines.

A thyristor with a P-N-P-N structure has three junctions: PN, NP, and PN. If the anode is a positive terminal with respect to the cathode, the outer junctions, PN and PN are forward-biased, while the center NP junction is reverse-biased. Therefore, the NP junction blocks the flow of a positive current from the anode to cathode. The thyristor is said to be in a forward blocking state. Similarly, the flow of a negative current is blocked by the outer PN junctions. The thyristor is in a reverse blocking state.

Another state a thyristor can exist in is the forward conducting state, whereby it receives a sufficient signal to switch on, and it starts conducting.

Let’s take a minute to highlight the unique properties thyristors bring to a circuit by going further into the nature of the signal and the thyristor’s response.