Medium Frequency Inveter DC Spot Welding Machine , Lamp Shade Cover Welding Machine ( Detail machine picture please see bottom page.) DESCRIPTION MF DC Inverter Spot Welder is a set of advanced welding equipment. The welding transformer is in small size but the outout energy is large. Three-phase AC will be converted into DC after being rectified. Then the DC will be converted into medium frequency 1000HZ square wave to be connected to primary welding transformer through the