logo

The Deep Drawing Process…


How It Works… And How It Can Work Better
With The Right Drawing Oil…

The Versatile Process...


Deep drawing uses multiple station transfer presses. A sequence that first blanks, then cups, draws and redraws strip metals into a variety of shapes and sizes. With experience, it is possible to draw up to 20 times longer than the diameter. In the reference books you’ll find deep drawing defined as drawn parts exceeding in length their diameter.


DeepDrawingAnimation

Deep drawing offers high-speed production. It also makes maximum use of material, which enables operators to produce complex, one-piece components. Even intricate design features can be introduced in a part, thus doing away with costly assembly or additional steps in the operation. Deep drawing proves economical. And since it employs most metals, strength-to-weight ratios can allow the production of strong yet light parts. In forming the metal, the metal’s grain structure is literally stretched. But because the properties of metals are improved by cold working, the part is actually hardened, which allows for thinner walls; providing, for example, lighter weights and better performance from parts in use, with resistance to pressing, squeezing, dropping and general usage, such as those uses to which a thin-walled writing pen will be put to in its life-cycle.

How The Drawing Process Works

It employs transfer presses. Some know these presses as eyelet machines—multiple plunger power presses used to mass-produce shells drawn from strip materials of various gauges.

In sequence, the strip is fed into the press and is worked on in a series of steps. At the first step (each step called a station), a blank for the shell about to be drawn is punched and pushed down into a transfer slide. The transfer slide carries the blank to the cupping station, or the first actual drawing operation. This is the first critical step. Care must be used to prevent tearing. A proper drawing oil must be used. (Specific drawing oil compounds for this purpose are available from Angler Industries, Inc.). The cup takes shape, reduced up to 45% or less of the blank’s initial diameter. In order to prevent the metal from wrinkling when it is drawn over the radius of the die insert, a flat flange or lip is maintained by a hold-down sleeve.

The slide moves back and forth on the die top, and with spring loaded fingers picks the part at one station and moves and places it at the next station. With each revolution of the press, the slide completes a finished part. To reduce a blank in diameter to the dimensions specified, and to increase the blank’s length in predetermined steps, 10 to 12 deep drawn stations are often used. Generally, shells do not require annealing between redraw stations when produced in this manner, because the heat generated by the draw operation, when once the machine is up and running, facilitates the material’s flow.

There is much more capability in a deep drawn operation than in basic blanking, cupping and drawing. The very same transfer power presses help achieve numerous other part designs, shapes and often ingenious configurations.


Aesthetic or functional specifications


Special requirements may require additional or secondary steps in the operation. To achieve a close tolerance hole, reaming may be required to eliminate the piercing burr. Or to achieve a perfectly flat shell, edging may be required to remove the feather edge burr. Additional steps can enhance appearances—plating, buffing, painting, metalizing, lacquering.

Achievable Tolerances

For the overall length of a part, tolerances can be kept at + 0.005 inches. By pinching the material, both the shell’s inside and outside diameter can be kept to as close as + 0.001inches. Usually, though, both dimensions are not achieved simultaneously. Flange material can be flattened if required, but its thickness is usually thicker than the starting material by as much as 0.002 to 0.003 inches.


Specifying Materials Selection

The elements to consider are—the part’s shape and size, strength stipulations, temperature, load and wear. The most used metals are cold rolled steel, copper, stainless steel, brass and aluminum. The least used metals are nickel, silver, inconel, monel and tin plate.

Using The Right Drawing Oil


Deep drawing is often called a tough assignment. Even though the parts can be small and often delicate, the job of drawing calls for an extreme pressure barrier that enhances the flow of drawn metal over die surfaces without rupturing the lubricant film itself. There are many benefits and economies resulting—protection of the die, extending of die life, superior and/or uniformity of shell’s thickness, weight, size and shape, and surfaces with minimum or no score marks.

(EDITOR’S NOTE: Cil Draw 53 is compounded especially for the precision demands of deep drawing operations).