Roll forging

Roll forging is a bulk forming operation in which the workpiece is deformed between rotating rolls with profiled grooves. Unlike closed-die forging, where the shape is created in a single stroke, the metal is redistributed gradually here, passing through several successive calibers. The operation is used to prepare workpieces for subsequent stamping, as well as to manufacture finished parts of elongated shape.

Process essence

The workpiece is fed into the gap between rolls rotating in opposite directions. The profiled grooves grip the metal and compress it, forcing it to flow along the workpiece axis. After each pass, the cross-section changes and the length increases. The number of passes depends on the required shape — simple workpieces are processed in one or two passes, complex ones in several.

A key advantage of the method is that deformation does not occur along the entire length simultaneously, but sequentially, section by section. This reduces tool load and allows processing workpieces of considerable length.

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Types of rolls and grooves

Roll forging is performed on equipment with various roll designs. Rolls can be solid or composite, with replaceable working inserts. Grooves on rolls can be open or closed. Open grooves are easier to manufacture but provide lower accuracy. Closed grooves ensure better surface quality and more precise cross-section.

By processing method, longitudinal and cross-wedge rolling are distinguished. In longitudinal rolling, metal flows along the workpiece axis; in cross-wedge rolling, the workpiece is processed transversely, allowing stepped parts to be produced with high productivity.

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Equipment

Roll forging is performed on forging rolls — specialized machines with two or three rolls:

  • Two-roll forging rolls — the main type of equipment.
  • Three-roll rolls for processing round workpieces.
  • Automated rolls with feeding mechanisms.

Typical parts and applications

Roll forging is used for workpieces whose length significantly exceeds transverse dimensions:

  • Blanks for connecting rods, levers, forks.
  • Axles, shafts, rods with variable cross-section.
  • Strips for knives and cutting tools.
  • Blanks for subsequent closed-die forging.

The operation is widely used in the automotive, machine-building, and tool industries.

Advantages

  • High productivity due to continuous process.
  • Metal savings — minimal waste compared to cutting.
  • Improved metal structure due to directional flow.
  • Ability to process long workpieces.
  • Reduced load on subsequent stamping equipment.

Relation to other operations

Roll forging belongs to the bulk metal forming class. The operation is often performed as a preliminary step before closed-die forging — rolling distributes metal along the length, facilitating die filling. It can also be used as an independent operation for producing finished parts.

Frequently asked questions

  • Is there hot and cold rolling using forging rolls? Yes, roll forging is performed both hot and cold. Hot rolling is used for large workpieces where it is important to reduce deformation resistance. Cold rolling is used for precise parts with clean surfaces and metal hardening.
  • What workpieces are typically processed on forging rolls? Most often, elongated workpieces with variable cross-section are processed — axles, shafts, rods, tool strips. The method is especially advantageous when the workpiece needs to be prepared for subsequent stamping.
  • Why is roll forging often used as a preforming operation? Because rolling allows pre-distributing metal along the workpiece length, forming an approximate shape. This facilitates die filling during subsequent closed-die forging and reduces tool wear.