1.1 Generation of plasma arc:
(1) The concept of plasma arc:
Free arc: An arc that is not subject to external constraints, such as an arc generated by general arc welding.
Plasma arc: An arc that is subjected to compression by the influence of external restraint conditions.
The gas in the free arc arc area is not completely ionized, the energy is not highly concentrated, and the gas in the arc arc area is completely ionized, the energy is highly concentrated, the energy density is very large, up to 105~106W/cm2, and the arc temperature can be as high as 24000~ 5000K (the most free state of tungsten argon arc welding with a maximum temperature of 10,000 to 20000K and an energy density of 104W/cm2 or less) can rapidly melt metal materials and can be used for welding and cutting.
(2) Generation of plasma arc
The plasma arc generating device is shown in Figure 6-4-1.
A higher voltage is applied between the tungsten electrode and the nozzle or between the tungsten electrode and the workpiece, and the gas is ionized to form a free arc by high frequency oscillation, and the arc is subjected to the following three compressions to form a plasma arc.
1 mechanical compression effect (action) - the arc passes through a water-cooled nozzle channel with a certain aperture, so that the arc cross section is restrained and cannot be freely expanded.
Figure 6-4-1 Schematic diagram of the plasma arc generator
2Thermal compression effect——When a certain pressure and flow of argon or nitrogen is introduced, the cold airflow evenly surrounds the arc, causing the arc periphery to be strongly cooled, forcing the charged particle stream (ion and electron) to concentrate in the center of the arc column. The arc column is further compressed.
3 Electromagnetic Shrinkage Effect—The electrons and ion currents of directional motion are parallel current-carrying conductors. Under the action of the magnetic field generated by the arc column current itself, the electromagnetic force generated causes the orphan column to further contract.
After the arc is subjected to the above three compression effects, the energy is highly concentrated in the arc column with a small diameter, and the gas in the arc column is sufficiently ionized into a plasma, so it is called a plasma arc.
When a small diameter nozzle, a large gas flow rate and an increased current, the plasma flame is ejected from the nozzle at a high speed and has a large impact force. This plasma arc is called a "rigid arc" and is mainly used for cutting metal. Conversely, if the plasma arc is adjusted to a lower temperature and the impact force is small, the plasma arc is called a "flexible arc" and is mainly used for welding.
1.2 Plasma arc welding
1.2.1 Basic knowledge
The method of welding with a plasma arc as a heat source is called plasma lone welding.
The ionic gas (forming the ion arc) and the shielding gas (protecting the molten pool and the weld from the harmful effects of air) during welding are all argon.
The electrode used for plasma arc welding is generally a tungsten electrode (the same as tungsten argon arc welding, which mainly uses tantalum tungsten and tantalum tungsten, and zirconium and zirconium in foreign countries), and sometimes needs to be filled with metal (wire). Generally, the DC positive connection method (the tungsten rod is connected to the negative electrode) is adopted. Therefore, plasma arc welding is essentially a tungsten gas shielded welding with a compression effect.
1.2.2 Classification of plasma arc welding:
Plasma arc welding can be divided into high current plasma arc welding and micro beam plasma arc welding.
(1) High current plasma solitary welding:
There are two processes: one is perforated plasma arc welding and the other is fusible plasma arc welding.
1 perforated plasma arc welding:
The welding is performed under conditions such as sufficient plasma energy density and sufficient plasma flow force to generate a penetrating small hole, and the molten metal is displaced around the small hole and behind. As the plasma arc advances, the small hole also moves forward. This phenomenon is called small. Hole effect. This welding process is called perforated plasma arc welding.
The welding process is shown in Figure 6-4-2.
Figure 6-4-2 Perforated plasma arc welding
Perforated ion arc welding can ensure complete penetration. Generally, high current plasma arc welding (100~300A) adopts this method. However, the perforation effect is only formed under conditions of sufficient energy density, and the increase in energy density is limited, so the method can only be carried out within a limited plate thickness - the thickness range of current production applications is:
Carbon steel 7mm, stainless steel 8 ~ 10mm, titanium 10 ~ 12mm.
This method is most suitable for welding 3 to 8 mm stainless steel, titanium alloy below 12 mm, low carbon or low alloy structural steel of 2 to 6 mm, and butt joints of copper, brass, nickel and nickel based alloy.
2 Fused plasma arc welding - used when the ion gas flow is reduced and the perforation effect disappears.
This method is similar to general tungsten argon arc welding.
The method is applicable to the thin plate, the cover surface of the multi-layer weld and the fillet weld, and the welding wire can be added or not, and the advantage is that the welding speed is fast.
(2) Micro-plasma arc welding: refers to fusion-type plasma arc welding of 15A to 30A or less
The plasma arc jetting speed and energy density of micro-plasma arc welding are relatively small and soft, and can be used for welding foils and sheets of 0.025-2.5 mm.
1.2.3 Characteristics and applications of plasma arc welding:
Features:
(1) Microbeam plasma arc welding can weld foil and sheet.
(2) It has a small hole effect, and can realize double-sided free forming of single-sided welding.
(3) The energy density of the plasma arc is large, the temperature of the arc column is high, and the penetrating ability is strong. The steel with a thickness of 10 to 12 mm can be opened without a bevel, and the double-sided forming can be welded once, the welding speed is fast, the productivity is high, and the stress deformation is small.
(4) The equipment is complicated and the gas consumption is large, and it is only suitable for indoor welding.
Application: Widely used in industrial production, especially for welding of copper and copper alloys, titanium and titanium alloys, alloy steel, stainless steel, molybdenum and other metals used in military and advanced industrial technologies such as aerospace, such as titanium alloy missile casings, aircraft Some thin-walled containers on the top.
14.4V Drill Screwdriver Li-ion
Cordless Drill Set,Drill Screwdriver,Electric Screwdriver Drill,Cordless Screwdriver Drill
ZHENGYANG TECHNOLOGY CO.,LTD , https://www.supraone.com