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An assembly of sheet materials in which a first sheet of material and a second sheet of material are disposed in an overlapping relationship, with a plurality of joint portions being formed therebetween by drawing an overlapping part of the first and second sheets of materials at a plurality of posi

An assembly of sheet materials in which a first sheet of material and a second sheet of material are disposed in an overlapping relationship, with a plurality of joint portions being formed therebetween by drawing an overlapping part of the first and second sheets of materials at a plurality of positions. The plurality of joint portions includes at least one first joint portion in which the first sheet of material is laterally extruded into the second sheet of material and at least one second joint portion in which the first sheet of material and the second sheet of material are in contact with each other in a cup-like surface configuration.

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1. A method of making a cylinder assembly comprising an outer cylinder and a tubular support member disposed around and in overlapping relation with the outer cylinder, the outer cylinder and the tubular support member being joined together, the method comprising: forming an overlapping part by fitt

1. A method of making a cylinder assembly comprising an outer cylinder and a tubular support member disposed around and in overlapping relation with the outer cylinder, the outer cylinder and the tubular support member being joined together, the method comprising: forming an overlapping part by fitting the tubular support member over the outer cylinder;inserting a die device including a die cavity into the outer cylinder so that the die cavity faces an outer cylinder inner surface of the overlapping part;preparing a punch device including a stepped forward end portion, the stepped forward end portion comprisinga cylindrical base portion,a tip portion having a tip end and a base portion side opposite the tip end, the tip portion being smaller in diameter than the base portion, anda curved surface portion connecting the base portion and the tip portion, the curved surface portion being concave inwardly of the stepped forward end portion, the cylindrical base portion smoothly merging into the tip portion through the curved surface portion,the tip portion extending from the base portion side of the tip portion to the tip end without the diameter of the tip portion being enlarged; anddrawing the overlapping part by moving the punch device from a radially outer side of the tubular support member toward the die cavity of the die device until the curved surface portion of the punch device enters the tubular support member, thereby joining together the outer cylinder and the tubular support member,wherein the jointed overlapping part of the outer cylinder and the tubular support member are in contact with each other in a cup-like shape such that an angle of a tangent to the side wall inner surface of a recess of the outer cylinder, which is located forward relative to tubular support member in the drawing direction, is 90 degrees or less. 2. A method of making the cylinder assembly according to claim 1, wherein the tip portion of the punch device includes a taper portion. 3. A method of making the cylinder assembly according to claim 2, wherein the die device includes an annular groove formed in the circumferential edge of a bottom surface of the die cavity. 4. A method of making the cylinder assembly according to claim 2, wherein the thickness X2 of the bottom wall of a drawn portion formed by the drawing step is thicker than the thickness t1 of the outer cylinder, and is thinner than 1.5 times the thickness t1. 5. A method of making the cylinder assembly according to claim 2, wherein the die device comprises a plurality of dies having the die cavities which are positioned on opposing sides of an axis of the overlapping portion,the punch device comprises a plurality of punches associated with the dies, the punches being disposed on the opposing sides of the axis of the overlapping portion to face the die cavities, andin the drawing step, a plurality of portions of the overlapping part are simultaneously deformed by moving the punches such that the tubular support member is secured to the outer cylinder by staking. 6. A method of making the cylinder assembly according to claim 5, wherein the plurality of dies are radially reciprocally movable,in the die inserting step, the dies are inserted into the outer cylinder with the dies moved to their retracted positions, andthe dies are subsequently radially moved to their working positions. 7. A method of making the cylinder assembly according to claim 1, wherein the die device includes an annular groove formed in the circumferential edge of a bottom surface of the die cavity. 8. A method of making the cylinder assembly according to claim 7, wherein the thickness X2 of the bottom wall of a drawn portion formed by the drawing step is thicker than the thickness t1 of the outer cylinder, and is thinner than 1.5 times the thickness t1. 9. A method of making the cylinder assembly according to claim 7, wherein the die device comprises a plurality of dies having the die cavities which are positioned on opposing sides of an axis of the overlapping portion,the punch device comprises a plurality of punches associated with the dies, the punches being disposed on the opposing sides of the axis of the overlapping portion to face the die cavities, andin the drawing step, a plurality of portions of the overlapping part are simultaneously deformed by moving the punches such that the tubular support member is secured to the outer cylinder by staking. 10. A method of making the cylinder assembly according to claim 9, wherein the plurality of dies are radially reciprocally movable,in the die inserting step, the dies are inserted into the outer cylinder with the dies moved to their retracted positions, andthe dies are subsequently radially moved to their working positions. 11. A method of making the cylinder assembly according to claim 1, wherein the thickness X2 of the bottom wall of a drawn portion formed by the drawing step is thicker than the thickness t1 of the outer cylinder, and is thinner than 1.5 times the thickness t1. 12. A method of making the cylinder assembly according to claim 1, wherein the die device comprises a plurality of dies having the die cavities which are positioned on opposing sides of an axis of the overlapping portion,the punch device comprises a plurality of punches associated with the dies, the punches being disposed on the opposing sides of the axis of the overlapping portion to face the die cavities, andin the drawing step, a plurality of portions of the overlapping part are simultaneously deformed by moving the punches such that the tubular support member is secured to the outer cylinder by staking. 13. A method of making the cylinder assembly according to claim 12, wherein the plurality of dies are radially reciprocally movable,in the die inserting step, the dies are inserted into the outer cylinder with the dies moved to their retracted positions, andthe dies are subsequently radially moved to their working positions. 14. A method of making the cylinder assembly according to claim 1, wherein the tubular support member of the joined overlapping part by drawing the overlapping part includes a minimum wall-thickness, and the minimum wall-thickness is about 30% or more of the wall-thickness of the tubular support member, which is not drawn. 15. A method of making the cylinder assembly according to claim 1, wherein the curved surface portion includes a proximal side having a first radius of curvature and a distal side having a second radius of curvature, the proximal side being smoothly connected with the distal side, and the second radius of curvature is larger than the first radius of curvature. 16. A method of making the cylinder assembly according to claim 1, wherein the overlapping part is drawn by moving the punch device without guiding the stepped forward end portion with a guide device provided around the stepped forward end portion.