Abstract: A resistance projection welder for welding first and second work pieces to each other. The first work piece having a body with opposing sides with at least one projection extending from one of the opposing sides and contacting the second work piece to space the body from the second work piece and define an air gap therebetween when the first and second work pieces are properly oriented. First and second electrodes electrically couple with work pieces and apply an electrical current thereto. A source of pressurized air directs a stream of pressurized air toward an interface between the first work piece and one of the second work piece and the first electrode. An air flow sensor detects the flow rate of the air stream directed toward the interface and determines if the work pieces are properly oriented based on the detected air flow rate.