Sheet Metal Stamping

Stamping presses and stamping dies are tools used to produce high volume sheet metal parts. These parts achieve their shape through the effects of the stamping tooling.

Formability is the primary attribute of sheet metal material. Formability is further defined as the materials ability to be:

lBent

lStretched

lDrawn

Production stamping is generally performed on materials .020” to .080” thick, but the process also can be applied to foils as thin as .001” or the plate stock with thickness approaching 1.000”.

The metallurgical term for these qualities is “ductility”, Ductility is the materials ability to deform and elongate without fracture. The extent to which a stamping is subjected to such deformation is directly related to the part’s overall shape and geometry. Other factors also influence the material’s formability. They include:

lThe die design

lThe press

lThe press speed

lLubrication

lSheet metal feeding mechanisms

lMonitoring and control systems

The word “die” is a generic term used to describe the tooling used to produce stamped parts. A die set assembly consisting of a male and female component is the actual tool that produces the shaped stamping. The male and female components work in opposition to both form and punch holes in the stock. The upper half of the die set, which may be either the male or female, is mounted on the press ram and delivers the stroke action. The lower half is attached to and intermediate bolster plate which in turn is secured to the press bed. Guide pins are used to insure alignment between the upper and lower halves of the die set.

The most common types of dies perform cutting and forming. Cutting dies are used to shear sheet material into what is called a blank. These blanks are then exposed to blanking dies which cut the entire perimeter of the part, or to forming dies where the blank is stamped into a part. Punching is another function of cutting dies. Punching is the cutting of a slug from the sheet metal stock to produce a hole or slot. Cutting dies are also used to trim excess metal from around a formed part.

Forming is a general term used to describe a stamped part whose shape and contour is reproduced directly from the shape and contour of a die set. The main forming operations accomplished with press mounted dies are:

lDrawing

lBending

lFlanging

lHemming

Drawing, or draw forming, involved forcing a blank deeply into a die cavity and shaping it into the shape and contour of the punch face and sides. Without sufficient formability qualities, drawn blanks are subject to wrinkling, thinning, and fracturing. Draw forming required an addition to the die set called a blankholder. The function of the blankholder, usually a ring through which the punch and ram pass, is to control the metal flow as it is forced into the die cavity. In practice, the blankholder must exert less pressure against the blank than the punch, so metal can flow into the die; yet it must exert enough pressure to prevent the material from wrinkling.

Hole punching and other cutting operations require specific and carefully maintained clearance between the punch (male component) and the die (female component). The setting of the required clearances is determined by both the stock thickness and temper. In general, die clearances increase as the stock thickness increase. The depth of punch penetration into the shet metal stock will also increase as softer stock is used.