Metalworking Processes and Sheet Metal Fabrication

Hot and Cold Working Processes

Hot Working: This involves deforming a metal above its recrystallization temperature. The metal recrystallizes during the process, so it does not get harder or brittle while being worked.

Cold Working: This involves deforming a metal below its recrystallization temperature. This causes "strain hardening," making the metal stronger but also more brittle.

Metal Extrusion and Its Benefits

Extrusion can produce complex cross-sections that are impossible with rolling. It offers high material utilization (very little waste) and good mechanical properties, especially in cold extrusion. This process works for both brittle and ductile materials.

Common Applications of Extrusion

• Aluminum: Window frames, sliding door tracks, and heat sinks.
• Copper: Electrical wires and tubing.
• Lead/Tin: Collapsible tubes (creams/pastes) and solder wire.
• Steel: Gears, shafts, and structural beams.

Sheet Metal Processing and Materials

Sheet metal deals with the manual and machine-based processing of thin metal sheets, typically between 0.4 mm and 6 mm thick. The "gauge" system is used to measure thickness; a higher gauge number means a thinner sheet.

• Galvanized Iron (GI): Steel coated with zinc to prevent rust. It is most common in ductwork.
• Black Iron: Uncoated steel, used where painting or specific finishes are required.
• Aluminum: Lightweight and corrosion-resistant.
• Copper & Brass: Used for decorative work and electrical components.
• Tin Plate: Steel coated with tin, used for food containers.

Sheet Metal Cutting Operations

• Shearing: Cutting the sheet into smaller pieces.
• Blanking: Cutting a piece (the "blank") out of a sheet where the cut piece is the useful part.
• Piercing (Punching): Cutting a hole in a sheet where the removed slug is scrap.
• Notching: Removing metal from the edges of a sheet.

Sheet Metal Forming Operations

• Bending: Creating an angle (V-bend or U-bend). Beware of Springback (the tendency of the metal to partially return to its original shape after bending).
• Seaming: Joining two edges of sheet metal by folding them together (e.g., the vertical line on a tin can).
• Hemming: Folding the edge of a sheet back on itself to make it smooth and strong.
• Deep Drawing: Punching a sheet into a die to form a cup or cylinder shape (e.g., kitchen sinks, soda cans).