Google? Or did you expect an answer in Vietnamese? Solder joins two pieces of metal together. The solder, typically a lead/tin alloy, melts at a lower temperature than the base metal, or pieces needing to be joined, and when the base metal is clean and appropriately treated with flux, the molten solder will adhere to the metal pieces, cool, solidify and hold them together. This is the weakest of the three processes.
Soldering is used extensively for electrical connections, joining sections of copper pipe in plumbing, for fabricating copper flashings around chimneys, and for such things as filler for the joints between the roof of a car to where it meets the rear column of the rear quarter panel. Silver Solder is a specialized solder alloy which is many times stronger than ordinary tin/lead alloy solders. I used Silver Solder to join the ends of band saw blades - I make my own, buy the band saw blade stock in long lengths. Depending on the job at hand, you would either use an electric soldering iron for most electrical work, or a propane torch for plumbing work. Auto body shops that do body solder work typically use a specialized acetylene torch.
Brazing is similar to solder in that the base metal of the pieces to be joined are not fused together, but are instead held together with the braze. Brazing is done by heating the base metal and melting the brass brazing rod, which like solder, melts at a lower temperature than the base metal, and flowing it into joints. This is used on such things as bicycle frames and for bonding carbide saw blade tips onto the steel saw blade bodies. Brazing is done at a higher heat than soldering and requires more skill. It produces a very strong joint. Brazing is usually done wth an Oxy-Acetylene torch, but can also be done with some store-bought torches, like those that use MAPP gas. I have also done brazing using the good old carbon arc torch on an electric arc welder.
Welding involves melting the pieces to be joined together so that they are fused together as one once the molten metal in the welded joint cools and solidifies again. This is used for everything from ship building to fabricating earthmoving equipment, to building things like trailers for hauling a boat or for welding together the rebar in a large concrete construction project, like, say, bridge building - and a zillion other uses.
There are a lot of different welding processes, each using its own equipment and each very different from the other. The simplest is gas welding, with an oxy-acetylene torch where you heat the area to be welded until it melts and flows together (filler rod is also often introduced here too).
Next, is simple arc welding where the work is connected to one grounding electrical lead of the arc welder and then the other pole is connected to an electrode which carries the current back to the piece, completing the circuit and with the flow of a lot electrical energy flowing through the gap, or arc, of space between the base metal and the hand-held electrode, sufficient heat is generated to melt to pieces together. The electrode is also filler material which melts in the arc and fills in the joint.
MIG welding is similar to arc welding except that it involves a specialized welding unit that automatically feeds a wire through the electrode and into the arc to make a continuous and potentially very small and fine weld. This is possible partly through the wire-feed electrode holder also incorporating shielding gas (argon or a argon/helium mixture typically), which allows the molten weld puddle to cool before it can oxidize. This welding process is used for a lot of general welding but it's especially nice for sheet metal work, like on autobody repair or fabrication.
TIG welding is lastly more complex and allows for even more specialized work, like welding difficult to weld metals. The TIG welder also uses a supply of shielding gas around the arc area, but typically the electrode only produces the electricity to make the arc (it's not a consumable filler material like the MIG welder or the arc welder electrode) and then filler material, if specified, is fed into the weld puddle by hand, not unlike oxy-acetylene welding. A TIG welder is an extremely versatile piece of equipment which provides the most control and allows the most sophisticated welding to do done.
Hi, if you were looking for an answer in Vietnamese, then here are some short definitions that might help :
Hàn gió đá (Hàn khí) (gas welding) : Phương pháp này sử dụng các khí (Acetylen hay gas) để gia nhiệt cho chi tiết hàn đạt tới trạng thái nóng chảy và liên kết với nhau. Khi hàn có thể dùng vật liệu để điền thêm (filler rod) vào vị trí hàn hoặc không. Phương pháp này thường được sử dụng trong các ngành công nghiệp nặng như đóng tàu, xây dựng,... Ngoài ra còn có phương pháp hàn hồ quang điện (arc welding).
Hàn que (hàn chấm) (soldering): phương pháp dùng để nối các vật kim loại với nhau bằng cách làm nóng chảy kim loại ở đầu que hàn (các kim loại này thường có nhiệt độ nóng chảy thấp như là chì,hợp kim thiếc,...).Các kim loại này sau khi nguội sẽ cứng lại và gắn kết các vật cần nối. Phương pháp này thường được sử dụng nhiều trong các lĩnh vực điện tử,mạch điện,...