Forging, a key metalworking process, involves shaping metal components through compressive forces using dies and tools while the metal is in a solid state. Originally, forging was a manual task performed by a smith using hammer and anvil, but it has evolved into a sophisticated process with engineered facilities and equipment over centuries. Dating back to 4000 B.C., forging was initially used for crafting jewelry, coins, and tools by hammering metal made of stone.
Hot forging, the most common method, operates at temperatures above the metal's recrystallization point to prevent strain hardening. This temperature, where new grains form in the metal, is crucial for maintaining ductility during deformation. Hot forging produces various components like crankshafts, gears, and connecting rods by plastically deforming simple geometry materials into complex shapes through heat and pressure.
During forging, elongation occurs plastically, enhancing ductility in the direction of elongation, with grains aligning parallel to the elongation. Defects, such as imperfections exceeding certain limits, can arise from various factors, including starting material quality, forging processes, or post-forging operations like trimming and cooling.
A connecting rod serves as the linkage between a piston and a crank or crankshaft in reciprocating engines, facilitating the conversion of reciprocating motion into rotational motion. It can also convert rotational motion into reciprocating motion, its original function. Unlike earlier mechanisms like chains that only provided pulling motion, the rigid connecting rod can transmit both push and pull forces, enabling rotation of the crank through a complete revolution. In some two-stroke engines, the connecting rod only exerts pushing force.
Today, connecting rods are predominantly associated with internal combustion piston engines, notably in automobiles. These modern designs differ significantly from earlier versions used in steam engines and locomotives.
Hot forged connecting rods, especially those made of steel for internal combustion engines, undergo a manufacturing process involving hot forging of a rough connecting rod, followed by heat treatment and machining operations.
Step 1: Rods are cut to the required size from billets using a band saw or billet shearing machine.
Step 2: The billets are heated in an oil-fired furnace to temperatures ranging from 1240β to 1270β, with approximately 15 different temperature ranges.
Step 3: The heated billets are placed between upper and lower dies using tongs, and forging is completed in two stages: forging rolling and finishing.
Step 4: Visual inspection is conducted after forging to ensure quality.
Hot forging results in connecting rods being produced in a nearly net-shaped status, reducing the need for extensive machining operations. This method is adaptable to both small and large batches and offers several advantages:
- Improved ductility
- Ability to manufacture customized parts
- Superior surface quality
- High formability ratios
- Reduced yield strength, leading to lower energy consumption
- Enhanced diffusion, reducing chemical inhomogeneity
The heat treatment process, which may occur either after rough forging or while the material is still hot, depends on the steel grade used and the desired mechanical properties.
