I have a multi-tool and I want to disassemble it – not for any repairing just to take it apart and take the blade for other uses – but it has no screws.
How can I disassemble it? (See image below)
The tool pictured is riveted together with solid rivets. It is not designed to be repaired, as mentioned in a comment, if it is not working correctly it should be disposed of and replaced.
It is possible to use a grinder to remove the flared head of the rivet and then punch it out. Alternately you can drill out the rivet, by drilling a hole in the exact center of the rivet. While both of these approaches theoretically allow for reassembly, they will almost certainly damage the tools body to some extent.
Re-assembly would require either a precision sized high grade bolt OR equipment to replace a solid rivet (This is NOT a blind/pop rivet). As this is a solid rivet, rivet replacements require tools not generally found in the home tool shop or home store. Bolts in this size from a home supply store will not be strong enough to handle the load. Bolts have a strength grade, small bolts from the home supply store are not designed for tool quality use.
Attempts to repair the tool pictured will cost more than a replacement tool, and most likely will leave you with a tool that is NOT safe to use.