Basic knowledge of welding
Add Date:2022/1/14 Views:
What is a welding power source?
Answer: In the electric welding machine, the equipment that supplies the electric energy required for welding and has electrical characteristics suitable for welding is called welding power source.
2. Why are there special requirements for arc welding power sources? What are the requirements?
Answer: In order to ensure the stable combustion of the welding arc and adapt to various welding process requirements, the arc welding power source has the following special requirements:
<1> The static characteristics (or external characteristics) of the arc welding power source—that is, the relationship between the steady-state output current and the output voltage, which has a falling characteristic (constant current characteristic) and a flat characteristic (constant voltage characteristic).
A. The external characteristics of electrode arc welding, TIG welding and carbon arc gouging power supply are descending (constant current) characteristics;
B. The external characteristic of CO2/MAG/MIG arc welding power source is flat characteristic (constant voltage characteristic).
<2> Dynamic characteristics of arc welding power source - when the load state changes instantaneously (such as: short-circuit transition of droplets, particle transition, jet transition, etc.), the relationship between the output current and output voltage of the arc welding power source and time is used to Characterize the response ability to load transients (ie dynamic response ability), referred to as "dynamic characteristics".
<3> No-load voltage - the voltage displayed by the power supply before arc ignition.
3. Why does the arc voltage change when the arc length changes?
Answer: Determined by the external characteristics of the arc welding power source, the longer the arc, the higher the arc voltage; the shorter the arc, the lower the arc voltage.
4. Why does the current display value also change when the wire extension length changes during CO2 welding?
Answer: The longer the extension length of the welding wire (ie the dry extension length), the greater the resistance of the welding wire, the greater the current consumed by the resistance heat, the smaller the displayed value of the welding current, and the smaller the actual welding current. Therefore, the extension length of the welding wire is generally set in the range of 12--20mm.
5. Why should the welding current and arc voltage be strictly matched during CO2/MAG/MIG welding?
Answer: During CO2/MAG/MIG welding, adjust the welding current—that is, adjust the feeding speed of the welding wire; adjust the arc voltage—that is, adjust the melting of the welding wire
<1> When the welding current is constant, the arc voltage is adjusted to be high, the melting speed of the welding wire increases, the arc length increases, and the molten droplets cannot be transferred normally, generally large particles fly out, and the spatter increases.
<2> When the welding current is constant, the arc voltage is adjusted to be low, the melting speed of the welding wire is reduced, the arc length is shortened, the welding wire is plunged into the molten pool, the spatter is large, and the welding seam is poorly formed. <3> The best matching effect of welding current and arc voltage: high droplet transfer frequency, minimal spatter, and beautiful weld formation.
6. What is arc stiffness?
Answer: The degree to which the arc straightens along the electrode axis under the effects of thermal shrinkage and magnetic shrinkage.
7. Why is the welding arc blowing?
Answer: During the welding process, due to the interference of airflow, the effect of magnetic field or the influence of eccentricity of the electrode, the phenomenon that the center of the arc deviates from the axis of the electrode.
8. What is magnetic bias blowing?
Answer: During DC arc welding, the arc is blown due to the electromagnetic force in the welding circuit. By changing the position of the ground wire or reducing the welding current and changing the angle of the electrode, the influence of magnetic bias blowing can be weakened.
9. Why use thin wire for CO2 welding?
Answer: Under the constant speed wire feeding system, when the arc length changes, the current and melting speed change, so that the function of arc length recovery becomes the self-regulating function of the power arc system. The thinner the wire diameter used, the stronger the self-regulating effect of the arc, the more stable the arc and the less spatter. This is the principle of fine wire for CO2 welding. Through advanced control technology, Tangshan Panasonic CO2 welding machine has the best self-regulating effect of the arc and the most stable performance.
10. What is the load duration rate of the welding machine?
Answer: The duty cycle refers to the ability of the welding power source to work continuously under a certain current. The national standard stipulates that the rated load duration rate of manual welding is 60%, and the automatic or semi-automatic is 60% and 100%. For example, the rated current of the 500KR2 welding machine is 500A when the rated load duration is 60%. When the actual load duration is 100% (automatic welding), the maximum welding current is ≤387A.
11. What is the load duration rate of the welding gun?
A: It refers to the ability of the welding torch to work continuously under a certain current.
<1> For example: when the 350KR welding gun is in CO2 welding, the rated load duration is 70%, and the rated current is 350A; when the actual load duration is 100% (automatic welding), its maximum welding current is ≤290A. In MAG welding, the rated load duration is 35%, and when the actual load duration is 100%, the maximum welding current is ≤207A.
<2> Another example is the 500KR welding torch when the rated load duration is 70% and the rated current is 500A during CO2 welding; when the actual load duration is 100% (automatic welding), its maximum welding current is ≤418A. In MAG welding, the rated load duration is 35%, and when the actual load duration is 100%, the maximum welding current is ≤296A.
12. What is the positive connection method? Answer: During DC arc welding, the connection method of connecting the weldment to the positive pole of the output end of the electric welding machine and the welding torch (welding tongs) to the negative pole of the output end is called "positive connection", also known as positive polarity.
13. What is the reverse connection method? Answer: During DC arc welding, the wiring method of connecting the welding piece to the negative pole of the output end of the electric welding machine and the welding gun (welding tong) to the positive pole of the output end is called "reverse connection method", also known as reverse polarity. Alkaline electrodes (junction 507, etc.), carbon arc gouging, and CO2 welding all use the reverse connection method.
14. Why is the secondary output loop of DC TIG welding connected to DC positive? Which metal materials are suitable for welding?
Answer: When the direct current is connected, the tungsten electrode is the negative electrode, the cathode area emits electrons, the temperature is low, the tungsten electrode is not easy to burn, and a larger welding current can be used. Suitable for welding carbon steel, stainless steel, copper, titanium and refractory active metals molybdenum, niobium, tantalum, etc.
15. Why should AC TIG welding be used for welding aluminum, magnesium and their alloys?
Answer: When the DC is reversely connected, the tungsten pole is the positive pole, which produces cations with large kinetic energy, which hit the oxide film on the surface of aluminum, magnesium and their alloys, and have a cleaning effect; while the tungsten pole is in the anode area, the temperature is very high, and the tungsten pole is severely burned. can not
Use a higher welding current for normal welding. Using an alternating square wave power supply, the positive half wave heats the workpiece, and the negative half wave cleans the oxide film, realizing high-quality welding of aluminum, magnesium and their alloys.