Metal Forming Processes in Manufacturing

Conventional Manufacturing Processes

• Metal forming has advantages over other manufacturing processes due to high precision, minimal material wastage, and better mechanical properties.
• Metal forming is a process of plastically deforming a metal block to a desired geometry by applying a force higher than the yield strength of the material.

Bulk Metal Working Processes

• Classified into four types: rolling, forging, extrusion, and drawing.
• Forging and extrusion are frequently used forming processes since the 18th century.

Extrusion and Forging Processes

• Can be carried out under three working temperatures: hot, cold, and warm linked to recrystalization temperature.
• Cold forging and extrusion processes have more advantages compared to hot and warm processes with respect to geometrical accuracy, surface finish, and mechanical properties of the final component.

Extrusion Processes

• Classified into four types depending on the relative movement of the punch and extruded product:
  • Forward (Direct) extrusion: most common method used in industries to manufacture long products of uniform cross-section.
  • Backward (Indirect) extrusion: billet does not move relative to the container, eliminating frictional force between billet and container interface.
  • Radial (Lateral) extrusion: material flow perpendicularly to the direction of the punch movement.
  • Impact extrusion: similar to backward/indirect extrusion process, with a punch running down quickly on the blank to obtain a tubular section.

Forging Processes

• Classified into:
  • Upset forging: force applied parallel to the length direction to increase the cross-section at the expense of length.
  • Drawing out: force applied perpendicular to the length axis to decrease the cross-section area.
  • Open die forging: work is compressed between two flat dies, allowing metal to flow freely laterally.
  • Closed die or Impression die forging: work piece is compressed between two die halves to obtain a multidirectional unbroken grain flow.
  • Flashless forging: volume of the workpiece is equal to the volume of the die cavity, with no requirement of flash arrangement.

Combined Extrusion Forging Processes

• Combined forward and backward extrusion (CE): simultaneous backward and forward extrusion.
• Combined extrusion-forging (CEF): both extrusion and forging take place simultaneously to obtain a complex shape.

Dies

• Types of dies:
  • Flat faced dies: most preferred in the industry due to its simple design and low cost.
  • Taper or conical dies: have an entrance angle for metal flow.
  • Curved dies: minimize friction loss and redundant work.

Metal Spinning

• A process of forming rotationally symmetrical hollow parts from circular blanks.
• Used to produce cone-shaped, elliptical, or other concave or convex parts.
• Metal spinning yields pots, pans, vases, lamp shades, musical-instrument parts, and trophies.

Drawing

• A process of cold forming a flat precut metal blank into a hollow vessel.
• Various forms produced include cylindrical, box-shaped, and irregular shapes.
• Used to produce cups, cans, pans, cylinders, domes, hemispheres, tubes, and hoppers.

Wire Drawing

• A metalworking process used to reduce the cross-section of a wire by pulling the wire through a single, or series of, drawing die(s).
• Used to produce electrical wiring, cables, tension-loaded structural components, springs, and paper clips.

Tube Drawing

• A process similar to bar drawing, used to decrease the diameter, improve surface finish, and improve dimensional accuracy of tubes.

• A mandrel may or may not be used depending on the specific process used.### Types of Extrusion

• Direct extrusion: billet moves relative to the container

• Indirect (Backward or Reverted) extrusion: billet does not move relative to the container, die fixed on a hollow ram pushes against the billet, eliminating frictional force between billet and container interface

• Radial (Lateral) extrusion: material flow perpendicularly to the direction of the punch movement, requiring additional power to overcome friction at the die-billet interface, commonly used for production of flange type components

• Impact extrusion: similar to indirect extrusion, punch runs down quickly on the blank, resulting in a tubular section, used to produce toothpaste tubes

• Hydrostatic extrusion: billet is extruded through the die by the action of a hydrostatic liquid pressure medium, rather than direct application of load with a ram, allows for extrusion of brittle materials, can be done hot, warm, or cold