Power Press

(1)Press
Presses are divided into hydraulic presses and mechanical presses.
The hydraulic press is also called a liquid-pressure press. It obtains the slide drive energy from oil pressure or water pressure. The pump is turned by motor revolution and sends liquid through the cylinder to move the ram up and down by the movement of the piston.
There are two types of hydraulic presses: a single action type and double action type. The single action type is a press made for general machining with one slide, and is most used.
The production speed is extremely slow compared with a mechanical press; however, the hydraulic press will easily adjust pressure speed and pressure and be able to maintain consistent pressure. In addition, there is an advantage that there is absolutely no overload on the machine.
The double action type is a press, in which in addition to a slide, has another slide operating separately. It is made for drawing work. The outside slide presses the blank holder while the inside main slide presses the punch for drawing work. The characteristics of the double-action type include the improved drawing efficiency and machine stability because most driving parts are installed at the bottom. It also elongates the product extraction or blank inserting time, and molds can easily be set. Nevertheless, there are some disadvantages that the space occupied by the machine is extremely large, and productivity and efficiency are not as good.
The mechanical press features slide drive power obtained from a mechanical system rather than oil pressure. For the most part, a C type frame is used. This type of press is suitable for most press forming, embossing, sizing, and cold-rolled forging. Available press types include crank presses, knuckle presses, and friction presses. Currently, the C type frame is used for small work weighing approximately 100 tons, and a fixed frame type (H type) is used for large work weighing more than 100 tons.
The benefits of the mechanical press include that the production speed is much faster than that of the hydraulic press, repair and maintenance are easy, accurately setting the bottom dead center is possible, working is fast, and the unit price is low compared with other types. However, compared with the hydraulic press, there is a disadvantage that overload can easily occur.

(2) Tool Set
The tool set includes a punch, die, blank holder, and drawbead. The punch (see photo), along with the die, is the part, which shapes products. Because products are processed by the punch and die, it is necessary to make the punch obtain high accuracy and good surface roughness. The material quality of the punch is determined based on the production quantity and the mold structure. While STD11 and SKH9 types are used in most cases, the use of tungsten carbides is on a rising trend. The hardness should be HRC60 or more.
In general, most dies are flat in shape. They should have a thickness capable of withstanding the pressure, considering the transformation caused by heat treatment or the grinding resulting from wear. The shapes of the die differ according to the product shape, quantity, and the accuracy. As in the case of the die, materials quality should be STD11, SKH9, or tungsten carbides, and the hardness should be HRC60 or more. When thick materials or thin-bottom products are drawn, there is of a less chance of the wrinkles occurring after forming. However, if the drawing is deep, wrinkles occur on the walls of the products. In such cases, a blank holder may be installed to prevent the occurrence of wrinkles.
If the force applied to the blank holder is excessively strong, the drawing force increases with the friction along the blank, blank holder face, and the force on the die face becomes extremely high. In such a case, the tensile strength applied to the blank in the direction of the radius increases, leading to the crack of the product in some cases. On the other hand, if the force applied to the blank holder is too small, wrinkles occur. It is therefore desirable to apply the minimum force that does not incur wrinkles to the blank holder. The drawbead increases frictional resistance partially and improves the drawing rate while the sliding resistance covering the entire container is under balance.
When a product is being shaped with curves and straight lines, the material of the curved part is compressed with its thickness growing larger, and the frictional resistance also grows compared with the rectilinear part. However, since the rectilinear part is exposed to simple bending, there is no significant resistance, and the material does not become thicker. In other words, because the rectilinear part slides better than the curved part, and there is a small clearance between the die and the blank, wrinkles occur. To prevent such phenomenon, drawbeads are placed in the rectilinear part to keep balance.