David Jenkins, age 14, of Akron, Ohio, for his question:

WHAT IS METAL EXTRUSION?

Metal extrusion is the process of shaping a piece of solid material, such as steel, by forcing it through an opening. The opening is part of a die and has the same diameter as the finished object. Extrusion produces many shapes including bars and tubes.

There are three basic extrusion processes: direct, indirect or reverse and hydrostatic.

The direct process is the most widely used method of extrusion. In this process a ram or plunger in one end of a cylinder pushes against a billet or short piece of metal. The ram forces the metal through a die opening at the other end of the cylinder. Such great force is used that the metal flows out of the cylinder like toothpaste out of a tube.

The indirect or reverse process uses a die and a hollow ram. They push a billet against the closed end of a cylinder and force the metal out of the cylinder through the die opening and the ram.

The hydrostatic process resembles the direct method, except that fluid, such as castor oil, surrounds the billet. The ram pushes on the fluid and the fluid pressure forces the metal through the die opening.

Most extrusion processes shape metal that has been heated. Heat increases the flexibility of a metal. The temperature of a billet may range from 400 degrees Fahrenheit to more than 4,000 degrees Fahrenheit.

The billet and the die usually are coated with a lubricant, such as graphite or melted glass, to help the metal flow smoothly through the opening in the die.

Extrusion processes that shape metal at room temperature are called cold extrusions. There are two such methods: hooker and impact. The hooker method is a direct process and impact extrusion is an indirect method.

More pressure is needed to shape cold metal than hot metal, but cold extrusion products have greater strength.

In addition to metals, the extrusion method is also used extensively in making plastic and rubber products.

Aluminum tubing is extruded from hollow ingots. A mandrel, or tapered metal bar, extends through the center of the die. The ram forces hot metal through the space between the mandrel and the die walls. This forms the aluminum into a tube.

To make such extruded aluminum shapes as angles, T sections, window sashes and door sections, a ram in one end of a steel cylinder pushes against a heated piece of ingot. It forces the aluminum through an opening in a die at the other end of the cylinder.

The hot metal squirts out into the die, forming the desired shape.