Open die forging Shapes generated by open die forging are simple; examples include shafts, disks and rings. An example of open die forging in the steel industry is the shaping of a large square ingot into a round cross-section. Note : Contribution of open die hot forging is that it creates a favorable grain flow and metallurgical structure in the metal.

Operations classified as Open Die forging Fullering Edging Cogging (Incremental Forging)

Fullering Operation performed to reduce the cross-section and redistribute the metal in a work part in preparation for subsequent shape forging. It is accomplished by dies with convex shapes. Fullering die cavities are often designed into multi cavity impression dies, so that the starting bar can be rough formed before final shape.

Contd… Edging is similar to fullering, except that the dies have concave surfaces. Cogging operation consists of a sequence of forging compressions along the length of workpiece to reduce cross section and increase length. Cogging is accomplished by open dies with or slightly contoured surfaces.

Problem no. 1 A cylindrical work part with D = 30 cm, h = 30 cm is upset forged in an open die to a height of 18 cm. Coefficient of friction at interface = 0.10. The work material has a flow curve defined by K = 275 MN/m2 and n = 0.15. Determine the instantaneous force in the operation : Just as the yield point is reached (yield at strain = 0.002) At h = 27.6 cm, 22.8 cm and 18 cm.

Impression Die Forging Sometimes called as closed die forging is performed with dies that contain the inverse of the desired shape of the part.

Steps in Impression Die Forging 1. Initial contact with raw workpiece, 2. Partial compression, 3. Final die closure, causing flash to form in gap between die plates.

Impression Die forging As the die closes to final position, flash is formed by metal that flows beyond the die cavity and into the small gaps between the die. Flash formed helps or resists the bulk material to flow out of the die area. But, it increases the compression pressure significantly so that intricate details of the die cavity fills ensuring a quality product.

Impression Die Forging Because of flash formation in impression die and more complex shapes made with these die, forces in it are significantly higher and more difficult to analyze than in open die forging.

Contd… Force formula is same as that of open die forging but its interpretation is quite different: F = Kf Yf A F = Maximum force in the operation, N Kf = Forging shape factor, Yf = Yield strength of metal at elevated temperature (hot forging), MPa

Contd… “F” in the last equation applies to maximum force during the operation, since this is the load that will determine the required capacity of press or hammer used in the operation. Selecting proper flow stress (Yf) is difficult because the strain varies for complex shapes. Kf values depends upon the complexity of job.

Contd… IMPRESSION DIE FORGING : PART SHAPE Kf SIMPLE SHAPES WITH FLASH 6.0 COMPLEX SHAPES WITH FLASH 8.0 VERY COMPLEX SHAPES WITH FLASH 10.0

Contd… Note : Maximum Force (F) is reached at the end of the forging stroke, when the projected area is greatest and friction is maximum.

Precision Forging Improvements in the technology of impression die forging have resulted in the capability to produce forgings with thinner sections, more complex geometries, drastic reduction in draft requirements on the dies, closer tolerances and the virtual elimination of machining allowances. Forging process with above mentioned features is called as precision forging.

Precision Forging Example a) Conventional Impression Die forging, b) Precision Forging