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How many types of presses are there?

Characteristic of the press working process is the application of large forces by press tools for a short time interval, which results in the cutting(shearing)or deformation of the work material .

Press Types

A pressworking operation, generally completed by a single application of pressure, often results in the production of a finished part in less than one second .

Pressworking forces are set up , guided , and controlled in a machine referred to as a press .

Power Presses . Essentially , a press is comprised of a frame , a bed or bolster plate , and a reciprocating member called a ram or slide which exerts force upon work material through special tools mounted on the ram and bed .

Energy stored in the rotating flywheel of a mechanical press ( or supplied by a hydraulic system in a hydraulic press ) is transferred to the ram for its linear movements .

Press Types.  An open-back inclinable (OBI ) press (Figure 1-1) , also called a Belt wheel gap-frame press has a C-shaped frame which allows access to its working space ( between the bed and the ram) . The frame can be inclined at an angle to the base , allowing for the disposal of finished parts by gravity . The open back allows the feeding and unloading of stock , workpieces , and finished parts through it from front to back .

Major components of a press are as follows :

1. Press Bed. A rectangular part of the frame, generally open in its center , which supports a bolster plate .

2. Bolster Plate. A flat steel plate , from 2 to 5in (51~127mm) thick , upon which press tools and accessories are mounted . Bolsters having standard dimensions and openings are available from press manufacturers .

3. Ram or Slide. The upper press member that moves through a stroke a distance depending upon the size and design of the press . The position of the ram , but not its stroke , can be adjusted.

The distance from the top of the bed (or bolster) to the bottom of the slide , with its stroke down and adjustment up , is the shut height of a press .

4.Knockout. A mechanism operating on the upstroke of a press , which ejects workpieces or blanks from a press tool .

5.Cushion. A press accessory located beneath or within a bolster for producing an upward motion and force ; it is actuated by air , oil , rubber , springs or a combination of mechanisms .

A straight side press of conventional design has columns (uprights) at the ends of the bed , usually with windows (square or rectangular openings) to allow the feeding and unloading of stock , workpieces , and finished parts .

With special applications, this type of press also can be used for feeding from front to back (Figure1-2).

A press brake is essentially the same as a gap-frame press except for its long bed from 6 to 20 feet (1.8~6m) or more. It is used basically for various bending operations on large sheet metal parts . It can also be used with a series of separate sets of press tools to do light piercing , notching,and forming . This allows parts of a complex design to be accurately made without a high-cost press tool by simply breaking the complex part down into several simple operations . This type of operation is used on low-run or prototype parts . The tooling cost is usually very low , but the labor cost is high as the parts are manually transferred and located in each station . The operator must follow good safety practices at all times to avoid injury .

A hydraulic press is used basically for forming operations and a slower operating cycle time than most mechanical presses . The advantages of hydraulic presses are that the working pressure , stroke , and speed of the ram are adjustable (Figure 1-3) .

A double-action press is used for large , or deep drawing operations on sheet metal parts . This type of press has an outer ram (blank holder) and a second inner ram(punch holder) . During the operating cycle , the blank holder contacts the material first and applies pressure to allow the punch holder to properly draw the part .

A triple-action press has the same inner and outer ram as the double-action press , but a third ram in the press bed moves up allowing a reverse draw to be made in one press cycle . The triple-action press is not widely used .

A knuckle press is used for coining operations . The design of the drive allows for very high pressures at the bottom of the ram stroke . This type uses a crank , which moves a joint consisting of two levers that oscillate to and from dead center and results in a short , powerful movement of the slide with slow travel near the bottom of the stroke .

These are the basic press types used in industry , although there are many more types with special applications.

Press operator safety must be a primary concern for everyone in the press area . While working under the ram the press control must be locked in the off position and safety blocks placed under the ram to prevent it from coasting down . While the press is running , the use of proper guards and safety procedures must always be followed .

Figure1-2 Single-action,straight-side, Figure1-3 Typical hydraulic press
eccentric-shaft mechanical

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