According to your existing description, analyze and suggest:

1, welding current 3000~6000. If untreated common nuts are used, the original welding current is obviously too large.

2, plate and nut surface should be clean, there can be no oil, rust, paint or dust.

3. When welding, the electrode pressure should be appropriate and not too small.

The above is based on welding one nut at a time.

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