Metal and metal welding method introduction

Pressureless fusion welding is to use the pressure to bring the weldments into contact with each other, so that the contact parts are locally heated, and the mixed metal liquid is formed due to the local melting ratio of the metal surface or the edges. This metal mixture (as in the solder alloy) fills the contact gap of the joined piece. When the welding heat source is removed, the molten metal solidifies to "weld" the parts together. The heat source for pressureless fusion welding is: flame (gas welding), electric arc or electron beam.
Pressure welding is the joining of pressure to heated or unheated metal components. Among them, resistance welding requires heating and cold welding does not require heating.

    Gas welding is the welding of the welded parts by a welding torch that mixes oxygen with a flammable gas. Since this type of welding requires the use of a flux with a high gassing rate, it is used only in the welding of bulky copper or iron containers in vacuum sealed connections.

    Arc welding is a welding technique based on the heat obtained by arcing between a workpiece and an electrode or between two electrodes. Among them, atomic hydrogen (atomic arc) welding, carbon arc welding, alloy electrode welding instead of tungsten electrode argon arc welding and other methods are mostly used in vacuum sealing technology. In the atomic arc welding process, heat is obtained from an alternating current arc (60 to 100 V; 20 to 60 A) between two tungsten electrodes surrounded by hydrogen. The molecular hydrogen supplied through the electrode holder dissociates into atomic hydrogen in the arc, and recombines upon contact with the cooler metal to produce a high temperature of up to 4000 °C. The weld is even and clean, suitable for welding of iron, mild steel, aluminum and chrome. It does not apply to nickel and copper alloys. This is because hydrogen is soluble in nickel liquid (stainless steel), and when the molten metal solidifies, it will escape and cause cracks and small holes. Copper and copper alloys become brittle due to hydrogen.

    Carbon arc welding is the use of DC direct arcing (1 ~ 10A; 100V) between the carbon electrode and the workpiece or between the two carbon electrodes. This weld can be used to weld iron, nickel, aluminum or copper.

    Argon arc welding in which an alloy electrode replaces a tungsten electrode is performed by using a direct current, a consumable electrode, and a protective gas of hydrogen or argon. This process is often used in the welding of aluminum and stainless steel.

    In inert argon arc or neon arc welding, direct current or alternating current is used between the workpiece and the tungsten electrode, and the arc operates in an argon or helium atmosphere. AC (250 ~ 300A; 100V) is usually used for welding aluminum and aluminum alloy, DC (45 ~ 75V; 15 ~ 200A) is used for welding steel, stainless steel, copper, silver and titanium. Inert gas arc welding is used on vacuum seal weldments for high vacuum and ultra high vacuum.

    Since electron beam welding is performed by bombarding the heat generated by the weldment with an electron beam under a vacuum of 1.3 × 10 -3 Pa, a high quality weld can be obtained. It is mostly used for welding stainless steel, aluminum alloy, tungsten, molybdenum and niobium.

    Electric resistance welding in pressure welding is a welding process in which the weldment is welded by the resistance heat generated by the high-strength electric current when the metal welding members are pressed against each other.

    Cold welding is the welding of certain metals together in a cold state by applying sufficient pressure to the weldment. The pressure required for cold welding varies from material to material, from 170 to 250 N/mm2 for aluminum, from 500 to 750 N/mm2 for copper, and from 2000 N/mm2 for stainless steel. Cold welded weld faces must be oxide free and degreased. This process is mostly used for the sealing of vacuum-drawn metal pipes.