Material elongation and thickness: General Industry Coverage

Workpiece materials have a variety of characteristics that influence how they are machined or otherwise worked to create parts. Presented here is information about elongation and thickness characteristics.

Elongation numbers provide a clue about material formability and ductility, and modulus of elasticity is a measurement that tells a material’s stiffness. The higher the number, the stiffer the material. Stiffness and strength are two very different qualities, so don’t get them mixed up.

The yield strength measurement provides a value used to determine the upper end of a material’s basic strength. Ultimate tensile strength is not as useful as a design parameter because most materials have already permanently deformed or yielded long before they see the ultimate strength. These numbers just provide a relative strength comparison. Yield strength shows at what point the material will be dimensionally altered.

Toughness indicates a material’s ability to absorb energy. Impact and notch test numbers provide a way to compare different materials. Higher numbers mean tougher materials. They also mean more sweat if you have to apply human energy.

Regarding material thickness, sheet is anything under 0.188″ thick and anything thicker is called plate.

Sheets and plates have bow (parallel to the rolling) and camber (perpendicular to the rolling) tolerances. Specifications are available from material suppliers. If they don’t want to provide the information, take your business elsewhere. Use this valuable information for real-world design efforts and tolerance analysis.

Cast aluminum tooling plate sold under various brand names is not ground flat. It is cast against a ground surface, which gives it a ground appearance, which sells more plate. This material is not particularly flat by machinist flatness standards.

First, get the specification sheet from your aluminum supplier. Then get ready for a surprise when you see how much flatness deviation they graciously allow. Keep in mind that many of the cast varieties of tooling plate offered cannot be repaired with welding. There are only a couple I know of where welding is even recommended, so screwups can be difficult or impossible to repair. The major redeeming factor is that large amounts of metal removal have little impact on workpiece geometry.