You would want much lower frequencies for meliting metal 50 Hz to 20 kHz or so! Higher is good for hardening and heat treatment as i understand it! I don't know what switching frequency a welder use.. But the principle is:
AC > Rectifier > H-Bridge(PWM) > Transformer > Work coil
If you have 10A DC supply... 50% Dutycycle... 10:1 Output transformer and a 15 turn work coil you should get ~700A, including losses, running trough the workpiece