Chapter 7 - Designing for Stamping Production
Equipment Characteristics
Fundamentally, stamping presses are machines with the space to contain
and the means to actuate dedicated metalforming tooling with the force, speed and
precision necessary to produce the desired part shape. Both mechanical and hydraulic
stamping presses are available in several basic designs, and a wide range of sizes,
tonnage capacities, stroke lengths, and operating speeds.
Mechanical presses develop energy in the flywheel and
translate the rotary motion and torque of the press drive into the reciprocating motion
and force of the press slide through a crankshaft, eccentric shaft or eccentric gear. The
two major types of mechanical presses are gap frame and straight side (see Figure 1).
Gap frame presses are available in several design variations. Open back
inclinable, open back stationary and two-point gap frame designs are the most common. As a
group they provide tonnage capacities from about 20 to 600 tons. Speeds range from about
20 to 800 strokes per minute (spm), and stroke lengths can vary from fractions of an inch
to 20 in. (0.5 m).
The gap frame concept is versatile, provides excellent accessibility to
the dies as well as convenience in feeding and ejecting parts. It is often used in
applications where the stock is manually fed.
Straight side presses have frames consisting of a crown member, two
upright side members and a bed member that supports the bolster. These components are
often secured in a preloaded position by four tie rods.
They may also be bolted and keyed together or welded into one piece. As
a result, straight side presses are stiffer vertically than gap frame units, and any
deflection under load tends to be symmetrical.
Straight side presses are suitable for progressive die and transfer die
applications and cover an enormous range of types, sizes and speeds. Tonnage capacities
range up to 6000 tons, speeds to 1500 spm.
In addition to gap frame and straight side presses a variety of special
purpose mechanical presses are in use for applications such as fineblanking, perforating,
coining, slide forming, and a wide range of precision, high-speed operations.
In general, mechanical presses are well suited for blanking parts at
high speed; blanking parts automatically fed with a short feed length; shallow drawing;
and work requiring an easily controlled depth of stroke.
Figure 2. Example of hydraulic stamping press.
Hydraulic presses deliver a controlled force generated
by hydraulic pressure used to move one or more rams in a predetermined sequence. They are
housed in a variety of types of frames, including C-frames, straight sides, H-frames,
four-column and other shapes, depending on the use (Figure 2).
Hydraulic presses cover a wide range of capabilities, and bed size,
stroke length, speed and tonnage capacity are not necessarily interdependent. Very large
bed sizes 72 in. x 48 in. (1.8 m x 1.2 m) for example, are available with only 20 tons of
pressure. Conversely, a 200-ton press may have a small 36 in. x 36 in. (0.9 m x 0.9 m) bed
area. Stroke lengths of 24 in. (0.6 m) and longer are readily available.
Important characteristics of hydraulic presses include: the ability to
deliver full power at any point in the stroke; adjustable tonnage, with overload
protection; and adjustable stroke length and speed.
In general, hydraulic presses are well suited for deep drawing; short
runs with frequent die changes; blanking with a form, or coin, or other secondary
operation in a single stroke; lower-speed high-tonnage blanking with long feed lengths;
and work requiring repeatable pressure rather than repeatable depth of stroke.
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Excerpt taken from Design Guidelines for Metal Stampings and Fabrications -- 2nd Edition copyright © 1995 Precision Metalforming Association
Purchase the new Third Edition of Design Guidelines for Metal Stampings and Fabrications copyright © 2004 Precision Metalforming Association at Marketplace today!
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