Design principles for forging processing

The design of forgings begins with determining a suitable structure and material based on the part's functional requirements. Designers must consider factors such as applied loads, operating environment, service life, strength, and toughness before selecting the appropriate metal material and forging method. Since forgings achieve their final shape through plastic deformation, the design cannot simply mirror that of standard machined parts; instead, it must fully account for metal flow characteristics during the forging process. For areas subject to high stress, abrupt cross-sectional changes and sharp corners should be avoided; incorporating appropriate fillets and transition structures ensures a more uniform load distribution, thereby minimizing stress concentrations.

Forging designs must also comply with specific forging process requirements. Designs should prioritize simple, symmetrical, and easily formable geometries while avoiding excessively deep recesses, narrow grooves, or overly thin sections, as these complicate metal filling and increase the risk of defects such as laps (folds) and cracks. For closed-die forgings, the parting line must be strategically placed to facilitate easy removal from the die and simplify die manufacturing and maintenance. Appropriate forging fillets and draft angles should be incorporated to ensure smooth metal flow and reduce resistance during part ejection. Additionally, features requiring subsequent operations-such as punching or trimming-must have their machining allowances and process requirements considered during the initial design phase.

Material deformation behavior and metal flow lines are also critical considerations. During forging, metal undergoes plastic flow in the direction of the applied force; therefore, the forging sequence can be arranged to align metal flow lines with the part's primary load-bearing direction. For components subjected to heavy loads-such as shafts, gears, and connecting rods-optimizing metal flow lines enhances strength and fatigue resistance. Designers must also determine the appropriate degree of deformation based on the material's plasticity, strength, and forging temperature range, striking a balance to avoid insufficient deformation (which fails to eliminate internal defects) and excessive deformation (which can cause cracking).

Finally, the forging process design requires the proper determination of machining allowances and tolerances. Due to factors such as dimensional deviations and the formation of oxide scale during the forging process, forgings typically require a machining allowance for subsequent operations like turning, milling, and grinding. An excessive allowance increases material consumption and the volume of machining work, whereas an insufficient allowance may fail to ensure the final part's dimensional accuracy and surface quality; therefore, the allowance must be reasonably determined based on the forging method, part dimensions, and precision requirements. Additionally, factors such as forging shrinkage, deformation, and die wear must be taken into account to make appropriate adjustments to the die dimensions.