Apparatus for forming a workpiece with an inner surface and an opposed outer surface into a housing of an antipollution device for treating exhaust in which at least one preselected catalyst-bearing brick is positionable, and in which at least one mat is positionable between the at least one brick and the housing to support the at least one brick, at least part of the inner surface defining an initial chamber in the workpiece with at least one initial dimension, the apparatus comprising - a first set of members for engaging the inner surface; - a second set of members for engaging the outer surface; - a controller adapted to receive dimensional data for the at least one brick and the at least one mat and, based on the dimensional data, to determine at least one calculated dimension at least partially defining a formed chamber in a main portion of the housing, the calculated dimension being sized for compressing the mat to the preselected density when the at least one brick is positioned in the formed chamber and the mat is positioned between the at least one brick and the housing; - wherein the controller being further adapted to control the first set of members for engaging the workpiece to change the initial dimension to the calculated dimension, for compressing the mat to the preselected density when the at least one brick and the mat are positioned in the formed chamber of the housing, the apparatus being characterized in that - the controller is additionally adapted for controlling the first and second sets of members (150, 152) to form at least one end portion (144, 145) of the housing with at least one preselected dimension thereof having a predetermined relation to the at least one calculated dimension; - the controller is additionally adapted for controlling the first and second sets of members (150, 152) to form at least one transition portion (146, 147) of the housing connecting the at least one end portion with the main portion of the housing substantially without deformation of the formed chamber; and - the first set of members comprises an end sizing element adapted to cooperate with an engagement section of the second set of members to form a workpiece end part into the at least one end portion (144, 145) and the at least one transition portion (146, 147). - a first set of members for engaging the inner surface; - a second set of members for engaging the outer surface; - a controller adapted to receive dimensional data for the at least one brick and the at least one mat and, based on the dimensional data, to determine at least one calculated dimension at least partially defining a formed chamber in a main portion of the housing, the calculated dimension being sized for compressing the mat to the preselected density when the at least one brick is positioned in the formed chamber and the mat is positioned between the at least one brick and the housing; - wherein the controller being further adapted to control the first set of members for engaging the workpiece to change the initial dimension to the calculated dimension, for compressing the mat to the preselected density when the at least one brick and the mat are positioned in the formed chamber of the housing, the apparatus being characterized in that - the controller is additionally adapted for controlling the first and second sets of members (150, 152) to form at least one end portion (144, 145) of the housing with at least one preselected dimension thereof having a predetermined relation to the at least one calculated dimension; - the controller is additionally adapted for controlling the first and second sets of members (150, 152) to form at least one transition portion (146, 147) of the housing connecting the at least one end portion with the main portion of the housing substantially without deformation of the formed chamber; and - the first set of members comprises an end sizing element adapted to cooperate with an engagement section of the second set of members to form a workpiece end part into the at least one end portion (144, 145) and the at least one transition portion (146, 147).