Sheet Metal Prototyping：Terminology

Gauge

A standardized (and non-linear) measurement system for specifying the thickness of sheet metal. A lower gauge number indicates a thicker sheet (e.g., 10 Ga. is thicker than 16 Ga.).

Sheet Thickness

Often measured in millimeters (mm) or inches (in./mil) for greater precision than gauge. Common prototyping thicknesses range from 0.5mm to 3.0mm.

CRS (Cold Rolled Steel)

Steel that has been rolled at room temperature. It has a smooth surface, tighter tolerances, and higher strength than hot-rolled steel. Common for prototypes.

HRPO (Hot Rolled Pickled and Oiled)

Steel rolled at high temperatures, then pickled to remove scale and oiled to prevent rust. Has a characteristic blue-grey surface.

Aluminum (e.g., 5052, 6061)

A lightweight, corrosion-resistant metal. 5052 is excellent for forming, while 6061 is stronger but can be prone to cracking during tight bending.

Stainless Steel (e.g., 304, 316)

Known for its corrosion resistance. Type 304 is most common; Type 316 offers superior chemical resistance.

Temper

The hardness and strength of the metal, achieved through cold working or heat treatment (e.g., H32, O-temper).

Flat Pattern

The 2D shape of the part before any bending occurs. It is the "unfolded" version of the 3D model, used for cutting the blank.

Bend Allowance (BA)

The length of the neutral axis (the part that doesn't stretch or compress) between the bend lines. It is used to calculate the total flat pattern length.

Bend Deduction (BD)

The amount of material to be subtracted from the sum of the two flanges to get the correct flat pattern length. BA and BD are two sides of the same calculation.

K-Factor

A ratio used to calculate the BA. It represents the location of the neutral axis in the material thickness (t), typically a value between 0.3 and 0.5. (K-Factor = t / Material Thickness).

Bend Radius

The inside radius of a bend. The Inside Bend Radius is typically specified by the designer.

Neutral Axis

An imaginary plane within the material that neither stretches nor compresses during bending.

Flange

The bent-up wall of a part.

Hem

An edge that is folded back onto itself to create a safe, rounded edge and increase stiffness.

Tabs & Slots

Features designed into the flat pattern to aid in self-fixturing or alignment during assembly, without additional tools.

Jog

A complex bend featuring two bends in opposite directions, creating a small offset.

Laser Cutting

A process that uses a high-power, focused laser beam to melt and vaporize material. The standard for precision in sheet metal prototyping.

CNC Punching

A process where a turret punch press uses pre-made tools and dies to punch holes and shapes. Efficient for simple parts and specific hole patterns.

Waterjet Cutting

A process that uses a high-pressure stream of water mixed with an abrasive garnet to cut through material. Advantage: No Heat-Affected Zone (HAZ).

Nesting

The automated or manual process of arranging multiple flat patterns on a standard-sized metal sheet to minimize material waste.

Kerf

The width of material removed by a cutting process (laser, waterjet, plasma). "Kerf compensation" is the adjustment made to the toolpath to account for this width.

Microtab

A very small, uncut section of material that holds the finished part in the sheet skeleton after cutting, preventing it from falling out or moving.

Skeleton

The remaining scrap framework of the sheet after the parts have been cut out.

Press Brake

The machine used to bend sheet metal. A CNC Press Brake is computer-controlled for high precision and repeatability.

Punch & Die

The tooling set used in a press brake. The punch is the upper tool that presses the sheet into the V-shaped die (lower tool).

Bend Angle

The final angle of the bend, e.g., 90°, 30°, 110°.

Bend Line

The straight line on the flat pattern where the bend will occur.

Bend Order

The sequence of bends. A critical programming decision to avoid the tooling or the part itself colliding with the press brake.

Springback

The natural tendency of metal to elastically return slightly toward its original shape after bending. The press brake must over-bend the material to compensate for this.

Air Bending

The most common bending method. The punch forces the sheet into the die without the sheet touching the bottom of the die V. One set of tools can create multiple bend angles.

Bottom Bending

The punch forces the sheet to touch the bottom of the die, coining the material. It requires more tonnage but reduces springback.

Tonnage

The amount of force (in tons) required by the press brake to perform a specific bend. It is calculated based on material, thickness, and bend length.

Gooseneck Punch

A specialized punch with a curved shape that allows for bending a flange that is close to another already-formed flange.

Louvers

Formed openings in the sheet metal used for ventilation while providing some shielding.

Embossing

A raised or recessed design (like a logo or rib) pressed into the sheet metal to add stiffness or for branding.

PEM Standoff / PEM Stud

PEM is a brand name that has become generic for press-fit hardware. These are threaded or unthreaded fasteners pressed into a pre-punched hole to provide strong, permanent threads in thin sheet metal.

Weld Nut

A nut with a special base designed to be welded onto a sheet metal surface.

Rivet Nut (Nutsert)

A threaded insert that can be installed from one side of the workpiece, providing threads in a blind hole application.

Spot Welding

A resistance welding process used to join overlapping sheets of metal at discrete points. Common in automotive and enclosure manufacturing.

TIG Welding

Produces a high-precision, clean weld. Often used for aluminum and stainless steel prototypes where appearance is important.

MIG Welding

A faster, more common welding process suitable for a wider range of materials, including steel.

Deburring

The critical process of removing sharp edges and raised imperfections (burrs) left on the edges of the part after cutting.

Powder Coating

A dry finishing process where electrostatically charged powder is sprayed onto a part and then cured under heat. Durable and available in many colors.

Anodizing (Type II, Type III)

An electrochemical process for aluminum that creates a durable, corrosion-resistant oxide layer. Type II is standard; Type III (Hardcoat) is thicker for wear resistance.

Plating (e.g., Zinc, Nickel)

Electroplating applies a thin layer of another metal (like zinc) to the surface for corrosion resistance and appearance.

Hemming

A folding process used to join two sheet metal parts (e.g., a car door panel) or to create a safe, rounded edge.

GD&T (Geometric Dimensioning & Tolerancing)

A symbolic language used on engineering drawings to clearly define the permissible variation in form, orientation, and location of part features.