The difficult points in manufacture of the weldable WEL-TEN780A low-alloy high strength steel and the H type welding bogies applied for the 320 t depressed center flat cars are analyzed.

Based on the welding knowledge and frame structure,the category rule of components is establishecl,according to which the welded machine frame is decomposed into a series of component parts,main support members and individual members.

In order to support the whole process of design activities, a hierarchical model to represent the functional and geometrical information of welded machine frame is presented.

A welded machine frame′s computer model is proposed based on the oriented-object technology.

The UIC regulated that the fatigue strength of welded frame should be evaluated by Goodman diagram,the weldedframe has been adopted at large in speed-up and high-speed bogies, so it is very important to study the fatigue strength evalua-tion of welded frame.

Taken the mass of welded bogie frame of high speed power car as object function, and the fatigue strength of 16Mn steel base material and weld as restrictive conditions, the welded frame of high speed power car is optimized based on the strength test load according to UIC615-4.

Then on the basis of the prediction on the development tendency for freight bogies, and by considering the railway line conditions in China, a detail design for welded frame bogie is given.