Open die forging requires the shaping of heated metal parts between a top die connected to a ram and a bottom die attached to a hammer, anvil or bolster. Metal bands are worked at their appropriate heats, ranging from 500°F to 2400°F, and slowly shaped into the desired shape through the skillful hammering or pressing of the workpiece.
Open die forging is also named free forging. In open die forging, the billet is within multiple dies that do not include the metal entirely. The dimensions will be reduced by hammering and stamping the metal through a series of actions until the final dimensions come.
For open die forging, large compressive forces are imposed by the constant strike of a forging hammer to damage the metal billets. Unlike closed die forging, falls of open die forging is very simple. And secondly, the machining process is always carried out. But the defects still affect the forging. Here are some of the mistakes of the open die forging process
- Incomplete forging penetration: The Dendritic ingot structure doesn’t break at the center of forging. Actual forging happens only at the surface. This causes due to Use of light rapid hammer blows. Using forging press for full penetration can reduce this defect.
2. Improper grain flow: The grain flow can be disturbed due to Improper die design, which makes the metal not flowing in the final interred direction. Making Proper die design can help reduce this defect.
3. Residual stresses in forging: residual stresses can fall due to Inhomogeneous deformation and improper cooling (quenching) of forming. Gradual cooling of the forging in a stove or under ash cover over some time can evade the residues.
4. Flakes: These are internal ruptures. Ruptures occur due to Improper cooling of forging. Rapid cooling makes the exterior to cool fast causing internal fractures. Following proper cooling practices can reduce the flakes.
5. Die shift: Misalignment and mismatch of forging at the flash line occur by Misalignment of the die halves. Proper alignment of die halves can reduce die shift in every case.
6. Unfilled Section: Some section of die cavity not filled by the liquid metal. This is caused due to Improper design of the forging die or using forging techniques, less raw material, inadequate heating. Proper die design, Fit raw material, and right heat can help reduce this defect.
7. Cold shut (Fold): Two covers of metal fold against each other without joining ultimately. This is because of the Sharp corner (less fillet), excessive chilling, high friction. Increase fillet radius on the die can help reduce cold shut.
8. Surface cracking: this is due to Excessive working on the surface and too low temperature. Increasing the working temperature is the remedy to this defect.
9. Cracking at the flash: This crack enters into the interior after flash is cut off. This occurs due to a Very thin ray. The remedy is Increasing flash thickness, relocating the flame to a less critical region of the forging, hot trimming and stress relieving.