An apparatus and method for producing an exhaust processor (12) comprising: a clamping device (10, 10A) for applying a predetermined clamping pressure to clamp a case (22) or other component of the exhaust processor (12) about a substrate (28) or other component of the exhaust processor (12) to define a gap between the case (10, 10A) and substrate (28); a measuring device (212, 212A) for measuring a size of the gap during application of the predetermined clamping pressure, the measuring device (212, 212A) including a clamping pressure control system (214, 214A) for adjusting the predetermined clamping pressure of the clamping device (10, 10A) in response to the gap measurement so that the gap size is within a predetermined range; and a welder (90, 90A) for welding a portion of the case (22) to an other portion of the case (22) when the gap size is within the predetermined range. The measuring device (212, 212A) also includes a camera (334) for measuring the gap size. The measuring device (212, 212A) measures the size of the gap by taking gap measurements at a plurality of predetermined locations about the substrate (28) and averages these measurements.