During the welding process of the NGW102-40 planetary reducer base made of cast iron, the key to determining whether the welding voltage and current is appropriate lies in the comprehensive evaluation of welding seam forming quality, arc stability, heat input control and post-weld inspection results. Since this type of machine base is mostly made of gray cast iron materials such as HT250, which has poor weldability and is easy to crack, defects must be avoided through precise parameter matching.
1. Assisted judgment through arc status and operating experience =
1. Listen to the sound:
When the current is moderate, the arc is stable and emits a continuous soft 'sizzling' sound;
When the current is too large, the sound turns into a 'squeaking' popping sound with loud splashing;
If the current is too small, there will be a 'crackling' arc breaking sound, and the arc will be unstable.
2. Watch the splash:
Normal welding should have only a small amount of small spatter;
If a large number of large particles of metal splash appear, it indicates that the current is too large or the voltage does not match.
3. Feel feedback:
If the welding handle shakes violently, it means that the arc is unstable, and the voltage may be too high or the current may be too low;
The operation is smooth and the molten pool is easy to control, which is a reflection of good parameter matching.
3. Quantitative verification based on process parameter standards
For the NGW102-40 machine base (material is usually HT250 or Q235), it is recommended to use nickel-based electrodes (such as Z308, Z408) for cold welding or semi-thermal welding. The specific parameters are as follows:
Notice:
Must cooperate with preheating to 300~350℃ (key requirement for iron castings);
Use low current, short arc, multi-layer and multi-pass welding, and lightly hammer to release the stress after each pass of welding;
The heat input is controlled at ≤15kJ/cm to prevent whitening and cracking.
4. Post-weld inspection is the final basis for judgment
Even if the weld looks good, internal quality still needs to be confirmed by the following tests:
Magnetic particle inspection (MT): Check whether there are micro-cracks on the surface and near the surface;
Ultrasonic flaw detection (UT): Detect internal pores, slag inclusions, lack of fusion and other defects;
Hardness test: The hardness of the heat-affected zone shall not exceed 120% of the base material, generally ≤280HV;
Dimensional re-test: Ensure that the machine base is not deformed and meets the assembly accuracy requirements.
