FIG. 1 shows a configuration of a known door 10 for the vehicle. A door frame 1 forms as an edge of a window portion 4 of the door 10. A cross sectional view of a known common door frame 1 along a line A—A in FIG. 1 is shown in FIG. 5 as an example. Specifically, the door frame 1 made by bending a plate member comprises a frame structure portion 5 with a hollow portion 51 for being provided with its stiffness and a flange portion 54 extending from the outer portion in one direction, and an outer surface portion 6 formed on the top portion of the flange portion 54 in FIG. 5. The outer surface portion 6 is formed in approximately flat shape and assembled to be viewed from outside of the vehicle. A glass run groove 52 is formed on the right of the flange portion 54 in horizontal direction in FIG. 5 whereinto a glass run 31 inserted for engaging with a window glass 3. A seal groove 53 is formed on the left of the flange portion 54 for supporting a seal material 8 between the door 10 and the vehicle body. In this configuration, the flange portion 54 includes three layered palates which are welded each other at a welded place 9 positioned at an approximately center portion of the flange portion 54 as shown in FIG. 5.
According to the door frame 1 which is generally configured as described above, many kinds of inventions have been reported by which the weight of the door frame 1 is saved. One example of these fames comprises individually formed frame structure portion 5 and outer surface portion 6, and they are welded each other, so that each sizes of the hollow portion 51 and the outer surface portion 6 in cross sectional form are adapted to be changed in longitudinal direction. (e.g. Tokukaihei 9-216583 kouhou)
In addition, another example of these frames is formed by a sheet of plate member which is made of welded plates with difference thickness, and bended in aforementioned form. (e.g. Tokukaihei 10-297280 kouhou)
However, in the known aforementioned frame of the vehicle door, a flange portion comprising three-layered plates, which result in increasing its weight, is not necessarily for ensuring the strength of the frame. In addition, a distortion of the flange portion generated by the welding causes a distortion on the outer surface portion; as a result, it becomes difficult to achieve a smooth outer surface portion with a quality required for vehicle appearance.
Accordingly, it is an object of the present invention to provide an improved door frame structure for ensuring a quality of the outer surface portion and weight saving in which the outer surface portion is not affected by the distortion.