With the current method and apparatus a tube member is inserted into a die and the ends of the tube are engaged by sealing units. Fluid is introduced into the tube through the sealing units and pressurized to enforce stretching of the tube diameter to fill the die cavity which has the desired final shape of the expansion. Frequently in addition to and simultaneously with the pressurized fluid, an axial force is applied to one or both tube ends to assist in feeding material to the areas of expansion. This will reduce the tendency of the tube wall thickness to decrease as the diameter expands.
The currently employed technique has some serious disadvantages. The process is limited to expanding material into two adjacent cavities in the die when axial assist is employed. If the die has additional cavities, the material will be forced into the end cavities if conventional axial feed techniques are employed. The high pressure within the tube creates a large normal force between the tube and the die which results in large frictional forces when the tube diameter expands to abut the die surface. This is particularly true when the tube is attempting to expand into the center expansion cavities of the die. Another disadvantage is that the die must have at least the same length as the die. A further disadvantage is found in components having the expansion nodules formed at a distance from one end of the tube. This is related to the frictional forces that are created between the die and the tube as the fluid pressure therein is increased.
USPTO Backgrounds
USPTO Backgrounds