Defects in metal parts offer a serious factor in the production of the forged parts and thereby it becomes very costly. Defects most commonly found in metals that have been subjected to more or less plastic shaping may be classified as follows :
1. Defects, resulting from the melting practice such as dirt or slag., blow holes, etc.
2. Ingot defects such as seams, piping, cracks, scales or bad surface and segregation.
3. Defects resulting from the improper heating and cooling of the forging such as burnt metal, decarburization, and flakes.
4. Defects resulting from improper forging such as seams, cracks, laps, etc.
5. Faulty forging design.
6. Faulty Die design.
7. Improper Placement of the metal in the die causing mismatched forging.
Defects in forging can be removed as follows :
1. Shallow cracks and cavities can be removed by chipping out of the cold forging with pneumatic chisel or with hot sets during the forging processes.
2. Surface cracks and decarburized areas are removed from important forgings by grinding on special machines. Care should also be taken to see that the workpiece is not underheated, decarburized, overheated and burnt.
3. Die design should be properly made taking into consideration all relevant and important aspects that may impair forging defects and ultimate spoilage.
4. The parting line of a forging should lie in one plane to avoid mismatching.
5. Destroyed forgings are straightened in presses, if possible.
6. The mechanical properties of the metal can be improved by forging to correct fiber line, and finally internal stresses, developed due to heating and cooling of the workpiece , are removed by annealing and or normalizing.
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