The process involves repeatedly hammering the metal until it achieves the desired form. Continuous hammering ensures complete filling of the die cavity. Forging dies are designed to remove excess metal (flash) which is later trimmed during finishing. While primary shaping occurs during hammering, flash removal happens in subsequent processing.

Drop forging has two primary variations: open die and closed die forging, differentiated by their die configurations. Closed die forging fully encloses the workpiece, while open die forging allows metal flow beyond the die boundaries.

Chapter 2: Types of Drop Forging

Drop forging is a powerful metal forming technique widely used in manufacturing. It applies tremendous force to reshape heated or cold metal billets into precision components with superior mechanical properties. This process benefits industries like aerospace, automotive, and construction by improving grain structure, increasing load capacity, and reducing defects.

The two main drop forging methods are open die and closed die forging. Closed die forging (or impression die forging) completely encloses the workpiece, producing complex, high-precision parts. Open die forging (or free forging) uses dies that don't fully contain the material, allowing greater flexibility for larger or custom components. Choosing between these methods depends on production volume, material properties, and application requirements.

Open Die Drop Forging

Open die forging differs from closed die forging primarily in die configuration. It uses flat, semi-round, or V-shaped dies that apply pressure without fully enclosing the billet. This versatile method can produce components ranging from small parts to massive pieces weighing several tons, making it ideal for custom or low-volume production.

The hot forging process increases material plasticity, reduces required force, and enhances ductility and toughness. Open die forging can create rough shapes or finished products with excellent strength and fatigue resistance.

Common open die forged products include discs, shafts, cylinders, and plates. This method is valued for art smithing, grain refinement, and improving machinability. It enhances fatigue strength and reduces porosity, resulting in durable, reliable components.

Open Die Forging Dies

Open die forging typically uses top and bottom dies designed for specific shapes. While most are flat, specialized options include V-dies, mandrels, and loose tools. Complex parts may require multiple dies to achieve optimal grain flow and structural integrity.

Examples of Open Die Processes

• Notching – Uses chisel-like tools to create evenly spaced impressions on rotating workpieces, commonly for axles and crankshafts.

  
  

• Shaping – Creates various profiles using fixtures to hold and rotate billets, producing components for machinery and shipbuilding.

  
  

• Cogging – Reduces billet thickness while increasing length, preparing material for further processing like closed die forging.

Closed Die Forging

Closed die forging uses precision dies to form metal into intricate shapes. The lower die remains stationary while the upper die moves with the ram, forcing material into the die cavity. This method produces complex geometries with tight tolerances for critical applications.

Unlike open die forging, closed die processes minimize flash and ensure high repeatability. Dies are designed with partition lines, draft angles, and radii to optimize metal flow and reduce wear. This method aligns grain structure with product shape, enhancing mechanical properties.

While die setup costs are higher, closed die forging is economical for high-volume production. Die life typically ranges from 5,000 to 7,000 cycles, depending on complexity and materials.

Proper die design facilitates smooth metal flow, reduces stresses, and supports precision manufacturing across industries.

td { vertical-align: middle; } .headers { font-weight: bold; text-align: center; } Advantages of Open & Closed Die Forging Advantages Improved fatigue resistance and microstructure Enhanced grain structure increases product strength Continuous grain flow and finer grain size Cost-effective for large production runs Greater strength and longer lifespan Works with various materials Minimized material waste Superior surface finish Reduced void formation Minimal machining required due to tight tolerances Significant cost savings Capable of achieving net shapes

Cold Drop Forging

Cold drop forging shapes metal at room temperature, producing precise components for automotive and electronics industries. It's ideal for soft metals like aluminum and copper, enabling high-volume production of fasteners and small parts.

This process increases material hardness while reducing ductility. Both open and closed die methods can be used, with specialized dies and lubricants required for optimal results.

Cold forging offers energy efficiency, minimal waste, and tight tolerances without extensive machining. Modern equipment supports automated, high-volume production of complex components.