Die

I

Introduction

Die, any of several types of tools used for the shaping of solid materials, especially those employed in the pressworking of cold metals.

In presswork, dies are used in pairs. The smaller die, or punch, fits inside the larger die, called the matrix or, simply, die. The metal to be formed, usually a sheet or precut blank, is placed over the matrix on the press bed. The punch is mounted on the press ram and is forced down by hydraulic or mechanical pressure.

A number of different forms of dies are employed for different operations. The simplest are piercing dies, used for punching holes in the blank. Blanking dies are employed to stamp out special shapes of sheet metal for later operations. Bending and folding dies are designed to make single or compound bends in the blank. Hollow, cupped shapes are formed by drawing dies; if the hollow is deep, redrawing dies are often employed in a second operation. To produce a reduced section on a hollow part, such as the neck of a rifle cartridge, special reducing dies are used. When a finished part must have a bulge at the bottom or in the middle, hydraulic dies are usually employed. In these the punch is replaced by a ram that forces oil or water into the part under pressure, thus forcing the metal outward against the matrix. Curling dies form a curved edge, or flange, on a hollow part. A special kind of curling die called a wiring die is used to form a wired edge in which the outside edges of the metal are tightly wound around a wire that is inserted for strength. A combination die is designed to perform more than one of the above operations in one stroke of the press; a progressive die permits successive forming operations with the same die.

In coining, metal is forced to flow into two matching dies, each of which bears a reverse intaglio of the relief pattern to be formed on the finished coin or part. See Mint (coin).

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II

Wiredrawing Dies

In the manufacture of wire, a drawplate is usually employed. This tool is a metal plate containing a number of tapered or bell-shaped openings, successively finer in diameter and known as wire dies. A piece of metal is pulled through the largest die to make a coarse wire. This wire is then drawn through the smaller opening, and then the next, until the wire is reduced to the desired measurement. Wiredrawing dies are subject to extreme wear and are commonly made from extremely hard materials, such as tungsten carbide or diamonds.

III

Thread-Cutting Dies

For cutting threads on bolts or on the outside of pipe, a thread-cutting die is used. It is usually made of hardened steel in the form of a round plate with a hole in the center. The hole is threaded in the appropriate form and pitch, and the threads are cut away for part of their circumference, leaving longitudinal grooves in the die. These grooves give clearance for the chips of metal formed when a thread is being cut. To cut an outside, or male, thread, the die is heavily lubricated with cutting oil and simply screwed onto an unthreaded bolt or piece of pipe, the same way a nut is screwed onto a bolt. The corresponding tool for cutting a female thread, such as that inside a nut, is called a tap.

See Die.Casting; Forging.

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