Questions and Answers about Welding Basics (2)

Third, welding equipment
1. What is welding power?
Answer: In an electric welder, a device that supplies the electrical energy required for welding and has electrical characteristics suitable for welding is called a welding power source.

2. Why are there special requirements for arc welding power? What are the requirements?
Answer: In order to ensure stable welding arc welding and adapt to various welding process requirements, arc welding power supply has the following special requirements:
<1> The static characteristic (or external characteristic) of the arc welding power source—that is, the relationship between the steady-state output current and the output voltage, 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 the CO2/MAG/MIG arc welding power source is the 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 output current and output voltage of arc welding power source and time is used. Characterize the ability to respond to load transients (ie, dynamic response capability), referred to as "dynamic characteristics."
<3> No-load voltage - the voltage displayed by the power supply before the arc is triggered.
<4> Adjustment characteristics - Change the external characteristics of the power supply to meet the requirements of the welding specification.

3. Why does the arc voltage change when the arc length changes?
Answer: Depending on 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 change when the wire extension length changes during CO2 welding?
Answer: The longer the wire extension length (ie dry elongation), the greater the resistance of the wire, the greater the current consumed by the resistance heat, the smaller the welding current display value, and the smaller the actual welding current. Therefore, the wire extension length is generally set within the range of 12-20 mm.

5. Why is the welding current and arc voltage strictly matched when welding CO2/MAG/MIG?
Answer: When welding CO2/MAG/MIG, adjust the welding current—that is, adjust the feeding speed of the welding wire; adjust the arc voltage—that is, adjust the melting speed of the welding wire; obviously, the melting speed and feeding speed of the welding wire must be equal to ensure The arc is stable welded.
<1> When the welding current is constant, the arc voltage is adjusted to be high, the melting speed of the welding wire is increased, the arc length is increased, and the droplets cannot be normally transitioned. Generally, large particles fly out and the splash increases.
<2> When the welding current is constant, the adjustment arc voltage is low, the melting speed of the welding wire is reduced, the arc length is shortened, the welding wire is inserted into the molten pool, the splash is large, and the weld bead is poorly formed.
<3> Best matching effect of welding current and arc voltage: The droplet transfer frequency is high, the splash is minimum, and the weld bead is beautifully formed.

6. What is arc stiffness?
Answer: Under the effect of heat shrinkage and magnetic contraction, the arc is straightened along the axial direction of the electrode.

7. Why is there a partial blow phenomenon in the welding arc?
Answer: During the welding process, the arc center deviates from the electrode axis due to the interference of the airflow, the action of the magnetic field or the eccentricity of the welding rod.

8. What is magnetic blow?
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 line or reducing the welding current and changing the angle of the electrode, the influence of the magnetic bias can be reduced.

9. What is the self-regulating characteristic of the CO2 power arc system? Why is the fine wire for CO2 welding?
Answer: Under the constant speed wire feeding system, when the arc length changes, the current and the melting speed change, so that the arc length recovery becomes the self-regulating effect of the power arc system. The finer the wire diameter used, the stronger the self-regulating effect of the arc, the more stable the arc, and the less the splash. This is the principle of fine wire for CO2 welding. Tangshan Panasonic CO2 welding machine through the advanced control technology, the arc's own regulation is the best, the performance is the most stable.

10. What is the load continuation rate of the welder?
A: The load continuation rate refers to the ability of the welding power source to work continuously under a certain current. The national standard stipulates that the manual welding rated load duration is 60%, and the automatic or semi-automatic is 60% and 100%. For example, the 500KR2 welder has a rated current of 500A at a rated load continuation rate of 60%, and a maximum welding current ≤ 387A at an actual load continuation rate of 100% (automatic welding).

11. What is the load continuation rate of the torch?
A: Refers to the ability of the welding torch to work continuously under a certain current.
<1> For example, the 350KR welding torch has a rated load continuation rate of 70% during CO2 welding and a rated current of 350A. When the actual load continuation rate is 100% (automatic welding), the maximum welding current is ≤290A. In MAG welding, the rated load duration is 35%, and the maximum welding current is ≤ 207A when the actual load duration is 100%.
<2> For example, the 500KR welding torch has a rated load continuation rate of 70% during CO2 welding and a rated current of 500A. When the actual load continuation rate is 100% (automatic welding), the maximum welding current is ≤ 418A. In MAG welding, the rated load duration is 35%, and the maximum welding current is ≤ 296A when the actual load duration is 100%.

12. What is the positive connection method?
Answer: When DC arc welding, the welding piece is connected to the positive pole of the output end of the welding machine, and the welding method of the welding gun (welding tongs) connected to the negative terminal of the output end is called "positive connection method", which is also called positive polarity.

13. What is the reverse connection method?
Answer: When DC arc welding, the welding piece is connected to the negative pole of the output end of the welding machine, and the welding method of the welding torch (welding tongs) connected to the positive terminal of the output end is called “reverse connection method”, which is also called reverse polarity. Basic welding rods (junction 507, etc.), carbon arc gouging, and CO2 welding are all reversed.

14. Why is the DC TIG welding secondary output circuit connected to DC positive connection? Which metal materials are suitable for welding?
Answer: When the DC is connected, the tungsten is extremely negative, the cathode area emits electrons, the temperature is low, the tungsten is not easy to burn, and a large welding current can be used. Suitable for welding carbon steel, stainless steel, copper, titanium and refractory active metals such as molybdenum, niobium and tantalum.

15. Why do you need to use AC TIG welding for welding aluminum, magnesium and their alloys?
Answer: When DC is reversed, tungsten is extremely positive, generating cations with higher kinetic energy, impacting the oxide film on the surface of aluminum, magnesium and its alloys, which has a cleaning effect; while tungsten is extremely anode, the temperature is very high, and the tungsten is severely burnt. Normal welding cannot be performed with a large welding current. The alternating square wave power supply is used, the positive half wave heats the workpiece, and the negative half wave cleans the oxide film to achieve high quality welding of aluminum, magnesium and its alloy.

16. What is the starting current (initial current)?
Answer: In the "Yes" state of the arc, press the arc current of the torch switch; release the torch switch and switch to the welding current.
<1> When TIG welding, the initial current is less than the welding current, used to preheat and guide the arc and the welding wire is directed to the welding station, and the welding torch switch is released to the normal welding.
<2> MIG welding aluminum, the initial current is greater than the welding current 20-30A, reducing the unfusion of the weld.
<3> MIG welded stainless steel and steel, the starting current is equal to the welding current.

17. What is the arc current?
Answer: In the "Yes" state of the arc, the current of the torch switch is the second time; generally less than 40--60% of the welding current, regardless of TIG/MIG/MAG/CO2 welding, it is used to fill the arc at the end of the weld. Pit, reduce crater defects (such as fire cracks, etc.).

18. What is the rise time?
A: The transition time from the initial current to the welding current during TIG welding.
The time from the base current to the pulse current during MIG welding.

19. What is the fall time?
A: The transition time of the welding current to the arcing current during TIG welding.
The time during which the pulse current flows to the base current during MIG welding.

20. What is pulse welding current?
A: The peak current during TIG or MIG pulse welding.

21. What is the base welding current?
A: The minimum current during TIG or MIG pulse welding (the welding current knob is adjusted during TIG welding).

22. What is the lag time?
Answer: After the welding arc is extinguished, the protective gas is delayed by 0.3-5 seconds and then the gas supply is stopped. Generally, the TIG welding aluminum, stainless steel, titanium and other metals have a lag time of 3 to 5 seconds.

23. What is arc spot welding?
Answer: Thin plate lap joints, using TIG/MIG/MAG/CO2 welding method, using a certain welding current, forming a surface nugget within a set time, connecting the upper and lower plates.

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