Types Of Presses

Classification of presses.           Types of presses for sheet metal working can be classified by one or a combination of characteristics, such as source of power, number of slides, type of frame and construction, type of drive, and intended applications. 1.) Classification on the basis of source of power. (i) Manual Presses. These are either hand or foot operated through levers, screws or gears. A common press of this type is the arbor press used for assembly operations. (ii) Mechanical presses.These presses utilize flywheel energy which is transferred to the work piece by gears, cranks, eccentrics, or levers. (iii)Hydraulic Presses. These presses provide working force through the application of fluid pressure on a piston by means of pumps, valves, intensifiers, and accumulators. These presses have better performance and reliability than mechanical presses. (iv)Pneumatic Presses. These presses utilize air cylinders to exert the required force. These are generally smaller in size and capacity than hydraulic or mechanical presses, and therefore find use for light duty operations only. 2.) Classification on the basis of number of slides. (i) Single Action Presses. A single action press has one reciprocation slide that carries the tool for the metal forming operation. The press has a fixed bed. It is the most widely used press for operations like blanking, coining, embossing, and drawing. (ii) Double Action Presses. A double action press has two slides moving in the same direction against a fixed bed. It is more suitable for drawing operations, especially deep drawing, than single action press. For this reason, its two slides are generally referred to as outer blank holder slide and the inner draw slide. The blank holder slide is a hollow rectangle, while the inner slide is a solid rectangle that reciprocates within the blank holder. The blank holder slide has a shorter stroke and dwells at the bottom end of its stroke, before the punch mounted on the inner slide touches the workpiece. In this way, practically the complete capacity of the press is available for drawing operation .Another advantage of double action press is that the four corners of the blank holder are individually adjustable. This permits the application of non uniform forces on the work if needed. A double action press is widely used for deep drawing operations and irregular shaped stampings. (iii)Triple Action Presses. A triple action press has three moving slides. Two slides (the blank holder and the inner slide) move in the same direction as in a double – action press and the third or lower slide moves upward through the fixed bed in a direction opposite to that of the other two slides. This action allows reverse – drawing, forming or bending operations against the inner slide while both upper actions are dwelling. Cycle time for a triple – action press is longer than for a double – action press because of the time required for the third action. 3.) Classification on the basis of frame and construction. (i) Arch – Frame Presses. These presses have their frame in the shape of an arch. These are not common. (ii) Gap Frame Presses. These presses have a C-shaped frame. These are most versatile and common in use, as they provide un – obstructed access to the dies from three sides and their backs are usually open for the ejection of stampings and / or scrap. (iii) Straight Side Presses. These presses are stronger since the heavy loads can be taken in a vertical direction by the massive side frame and there is little tendency for the punch and die alignment to be affected by the strain. The capacity of these presses is usually greater than 10 MN. (iv) Horn Presses. These presses generally have a heavy shaft projecting from the machine frame instead of the usual bed. This press is used mainly on cylindrical parts involving punching, riveting, embossing, and flanging edges. Credit:- https://nptel.ac.in/courses/112107144/7