Modern invertor welding machines cover most of the needs for the production of permanent joints of metal blanks. But in some cases a device of a slightly different type will be much more convenient, in which the main role is played not by an electric arc, but by a stream of ionized gas, that is, a plasma welding machine. Acquire it for periodic use is not too cost-effective. You can make such a welding machine with your own hands.
Elements for the manufacture of plasma welding machine.
Equipment and components
It is easiest to manufacture a microplasma welding machine on the basis of an existing inverter welding machine. To perform this upgrade, you will need the following components:
- any TIG welding inverter with or without integrated oscillator;
- nozzle with tungsten electrode from a TIG-welder;
- argon cylinder with gear;
- a small piece of bar of tantalum or molybdenum with a diameter and length of up to 20 mm;
- fluoroplastic tube;
- copper tubes;
- small pieces of copper sheet with a thickness of 1-2 mm;
- electronic ballast;
- rubber hoses;
- pressure seal;
- hose clamps;
- car wiper tank with electric pump;
- Rectifier power supply for the electric pump wiper.
The device is a plasma welding machine.
Work on fine-tuning and manufacturing of new parts and components will require the use of the following equipment:
- electric soldering iron;
- torch for soldering with a balloon;
The welding machine for plasma welding can be one of 2 main types: open and closed. The main arc of an open type welding machine burns between the central cathode of the torch and the product. Between the nozzle, which serves as the anode, and the central cathode, only the arc on duty is excited to excite the main at any time. The closed type of welding machine has only an arc between the central electrode and the nozzle.
To make a durable welding machine with your own hands on the 2nd principle is quite difficult. With the passage of the main welding current through the nozzle-anode, this element experiences enormous thermal loads and requires very high-quality cooling and the use of appropriate materials. It is very difficult to ensure the heat resistance of the structure when such an apparatus is made by hand. When making a plasma machine with your own hands, for durability it is better to choose an open circuit.Back to table of contents
Schematic diagram of the plasma welding machine.
Often in the artisanal manufacture of a plasma welding machine, the nozzle is machined from copper. In the absence of an alternative, this option is possible, but the nozzle becomes a consumable material, even when only a duty current passes through it. It will have to be changed frequently. If you can get a small piece of round timber from molybdenum or tantalum, it is better to make a nozzle from them. Then it will be possible to be limited to periodic cleaning.
The size of the central hole in the nozzle is chosen empirically. You need to start with a diameter of 0.5 mm and gradually bore it to 2 mm, until the plasma flow is satisfactory.
The tapered gap between the central tungsten cathode and the nozzle-anode should be 2.5-3 mm.
The nozzle is screwed into the hollow cooling jacket, which is connected to the holder of the central electrode through a fluoroplastic insulator. Coolant circulates in the cooling jacket. As such, in the warmer months, distilled water can be used; in winter, antifreeze is better.
The control unit of the plasma welding machine.
The cooling jacket consists of 2 hollow copper tubes. The inner diameter and length of about 20 mm is located at the front end of the outer tube with a diameter of about 50 mm and a length of about 80 mm. The space between the ends of the inner tube and the outer walls is sealed with thin sheet copper. Copper tubes with a diameter of 8 mm are soldered into the shirt with the help of a gas torch. The coolant comes in and out through them. In addition, the terminal must be soldered to the cooling jacket to apply a positive charge.
In the inner tube, a thread is made into which a removable nozzle is made of heat-resistant materials. At the extended end of the outer tube is also cut the internal thread. A PTFE sealing ring is screwed into it. The center electrode holder is screwed into the ring.
An argon supply tube of the same diameter as for cooling is soldered through the wall of the outer tube into the space between the cooling jacket and the fluoroplastic insulator.
On the cooling jacket circulating fluid from the wiper tank. Power to the pump of its electric motor is fed through a separate rectifier to 12 V. The output for supply to the tank is already there, the return of the liquid can be cut through the wall or tank lid. To do this, a hole is drilled in the lid and a section of the tube is inserted through the pressure seal. Rubber hoses for circulation of liquid and supply of argon are connected to their tubes with hose clamps.
Plasma fusion of powder.
The positive charge is taken from the main power source. To limit the current through the surface of the nozzle is selected a suitable electronic ballast. The supplied electric current should have a constant value in the region of 5-7 A. The optimal current value is chosen experimentally. This should be the minimum current that ensures stable burning of the pilot arc.
Excitation of the pilot arc between the nozzle and the tungsten cathode can be carried out in one of two ways. The oscillator built into the welding machine or in its absence by the contact method. The second option requires the complexity of the design of the plasma torch. The holder of the central electrode with contact excitation is made spring-loaded with respect to the nozzle.
When pressing the rubber button of the rod connected to the electrode holder, the sharp end of the central tungsten cathode contacts the tapered surface of the rod. In the event of a short circuit, the temperature rises sharply at the point of contact, which makes it possible to initiate an arc when the cathode leads away from the anode. The contact must be very short, otherwise the surface of the nozzle will burn.
The excitation of a current by a high-frequency oscillator is preferable for the durability of the structure. But acquiring it or even making it makes an improvised plasma welding machine unprofitable.
During operation, the positive terminal of the welding machine is connected to the part without ballast. When the nozzle is at a distance of several millimeters from the workpiece, the electric current switches from the nozzle to the part. Its value rises to the value set on the welding machine, and the formation of plasma from argon is intensified. By adjusting the flow of argon and the welding current, it is possible to achieve the required intensity of plasma flow from the nozzle.Back to table of contents
The scheme of plasma welding open and closed plasma jet.
The disadvantage of this design is the consumption of argon. The cylinder is enough for several hours of continuous work. Instead of argon, you can use compressed air or water vapor. Such modifications are more suitable for plasma cutting of metals. Since these gases are not neutral and oxidize the metal.
In addition, arc burning in the atmosphere of these gases is not as stable as in argon. Work in the air accelerates wear and clogging of the nozzle. In prefabricated plasmatrons, air is pre-dried and cleaned.
In self-made devices for the supply of air using automotive compressors for 12 V with a capacity of up to 50-60 l / min. To work on the water need a portable steam generator. This may be a metal sealed container with titanium electrodes installed inside it. Fill it with distilled water. Electrodes are connected to 220 V AC.
Often, to effectively cut off oxygen over the cooling jacket, one more casing-nozzle is installed. Helium or argon is served at its entrance. The flow from this nozzle flows around the plasma flow.
It is not necessary to use an inverter or a welding rectifier as a power source. For this you can use any diode bridge withstanding current from 50 A. The exact value is regulated by an additional choke.