In forging processes, care should be taken else few defects are likely to appear. The best forging companies take the necessary measures to avoid such defects.
Defects of metal forged product include, exterior and interior cracking, laps, cold shuts, improper grain flow and warping of a part.
- Exterior/ Interior Cracking: Cracking is caused by excessive stress, or improper stress distribution during forging. Cracking of a forged material can be a result of poorly designed forging die or excess material in the job piece. They can also be caused by high thermal gradients during the manufacturing operation.
- Laps/ Folds: This forging defect occurs in a metal forging due to buckling of the part, or too little material in the work piece.
- Cold shuts: When metal flows of different temperatures meet, they do not weld completely, i.e., they do not combine smoothly, a boundary layer known as cold shut, forms at their intersection. It can also occur due to sharp corners or high friction. It indicates that there is a problem with the metal flow in the mold.
- Improper Grain Flow: Crack propagation highly depends on grain flow and thereby properties like fatigue strength, ductility and impact toughness. This forging defect is due to improper die design. Here, the flow-lines are not close end type and are non-uniform.
- Warping: This type of forging defect occurs when thinner sections cool faster than the rest of the forging. The forged material is distorted when warpage occurs.
Defects in metal forging can be controlled by careful consideration of work material volume, good designing of the forging die and the process. The main principle is to maintain the right material distributions and the right flow of the material to accomplish these distributions. Die cavity geometry and corner radius are determined critically in forging companies in order to get defect free products.