When selecting a processing method for metals, forging stands out for its ability to apply pressure using a
forging machine, which induces plastic deformation in the metal blank. This process not only achieves specific mechanical properties but also shapes the metal into the desired form and size. Forging is particularly effective in eliminating defects such as porosity often found in cast metals, thereby optimizing the metal's microstructure. The mechanical properties of forged items typically surpass those of their cast counterparts, thanks to the preservation of continuous metal flow lines. For critical components in high-stress environments, such as those used in machinery,
forgings are preferred over rolled sheets, profiles, or welded parts.
Types of Forging Processes
Forging can be categorized into three main types: free forging, die forging, and flashless die forging.
Free Forging: This method uses impact or pressure to deform the metal between an upper and lower anvil to create the desired shape. Free forging is divided into hand forging and mechanical forging.
Die Forging: Involves shaping the metal using a die, which gives the metal blank a specific form. Die forging can be further divided into open die and closed die forging. Methods under die forging include cold heading, roll forging, radial forging, and extrusion. At CFS Forge, we specialize in closed die forging for materials like steel, aluminum, and copper.
Flashless Die Forging: This method has no flash, leading to higher material utilization rates. It can produce complex forgings in one or several steps. Due to the absence of flash, less force is needed, and the applied load is reduced. However, careful control of the blank material volume and die positioning is necessary to minimize die wear.
Advantages of Forging
Forging offers several benefits over casting:
Improved Microstructure: Forging enhances the microstructure and mechanical properties of metals. The hot-working deformation transforms coarse dendritic crystals and columnar grains into fine, uniform equiaxed grains through recrystallization. This process helps to compact and weld original segregations, porosity, and inclusions, thus improving the metal's plasticity and mechanical properties.
Metal Flow Continuity: Forging maintains the continuity of the metal's fiber structure, ensuring the mechanical properties and longevity of the forged parts, which is superior to castings.
Rolling Process and Its Types
Rolling involves reducing the cross-section of a metal blank by compressing it between rotating rolls, thereby increasing its length. It is a common production method for steel, such as profiles, plates, and pipes. Rolling can be classified based on the motion of the rolled piece:
Longitudinal Rolling: The metal passes through two rolls rotating in opposite directions.
Cross Rolling: The motion direction of the metal is consistent with the roll axis.
Skew Rolling: The metal moves spirally, with the rolling piece and roll axis at an angle.
Advantages of Rolling
Rolling offers several key benefits:
Structural Improvement: Rolling breaks down the cast structure of steel, refining the crystalline grain and enhancing the metal's microstructure. It compacts the steel and improves its mechanical properties, especially in the rolling direction.
Defect Reduction: High temperatures and pressures during rolling help weld bubbles, cracks, and looseness formed during casting.
Challenges of Rolling
However, rolling has its drawbacks:
Inclusion Issues: Non-metallic inclusions within the steel can lead to delamination, significantly weakening the material's tensile properties.
Residual Stress: Uneven cooling during rolling creates residual stress, which can affect the steel's performance under external forces.
Dimensional Precision: The control over thickness and side width in hot-rolled steel products is less precise due to thermal expansion and contraction.
Comparing Forging and Rolling
Forging and rolling differ significantly in their effects on metal properties:
Mechanical Properties: Forged parts exhibit more uniform mechanical properties and higher isotropy compared to rolled parts, resulting in longer life spans for the forgings.
Deformation Degree: The deformation degree in forging is greater, offering better eutectic carbide breakdown than rolling.
Processing Costs: Forging is more expensive but essential for high-load, impact-resistant parts and those with complex shapes or stringent requirements.
The metal flow lines in forgings remain intact, preserving the material's structural integrity and extending the workpiece's life, unlike in rolling where the metal flow is often disrupted.
In summary, while rolling is efficient for general applications, forging is preferred for critical parts requiring superior mechanical properties and structural integrity. Choosing between forging and rolling depends on the specific requirements of the application, balancing cost and performance considerations.
