Working Principle And Classification Of Punch Press

Working principle and classification of punch press

Working principle of punch press:

The design principle of punch press is to convert circular motion into linear motion. The main motor outputs power to drive the flywheel, which drives the gear, crankshaft (or eccentric gear), connecting rod, etc. through the clutch to achieve the linear motion of the slider. The movement from the main motor to the connecting rod is circular motion. There must be a transition point between the connecting rod and the slider for circular motion and linear motion. There are roughly two types of mechanisms in its design, one is ball type and the other is pin type (cylindrical type). Through this mechanism, the circular motion is converted into the linear motion of the slider.
The punch press applies pressure to the material to make it plastically deform and obtain the required shape and precision. Therefore, it must be matched with a set of molds (divided into upper mold and lower mold) to place the material in between. The machine applies pressure to make it deform. The reaction force caused by the force applied to the material during processing is absorbed by the punch press machine body.

Classification of punch presses:

1. According to the driving force of the slider, punch presses can be divided into mechanical and hydraulic types. Therefore, punch presses can be divided into the following types according to the driving force used:
   (1) Mechanical punch presses
   (2) Hydraulic punch presses
   Generally, most sheet metal stamping processes use mechanical punch presses. Hydraulic punch presses can be divided into oil-hydraulic punch presses and water-hydraulic punch presses according to the different liquids used. Oil-hydraulic punch presses are currently the majority, while water-hydraulic punch presses are mostly used in large machinery or special machinery.
2. Classification by slider movement: According to the slider movement, there are single-action, double-action, and triple-action punch presses. However, the most commonly used are single-action punch presses with one slider. Double-action and triple-action punch presses are mainly used in the extension processing of automobile bodies and large workpieces, and their number is very small.
3. Classification by slider driving mechanism:
   (1) Crankshaft punch presses
   Punches that use a crankshaft mechanism are called crankshaft punch presses. Most mechanical punch presses use this mechanism. The most common reason for using a crankshaft mechanism is that it is easy to manufacture, can correctly determine the lower end position of the stroke and the slider motion curve, and is generally applicable to various processing. Therefore, this type of punching is suitable for punching, bending, stretching, hot forging, warm forging, cold forging and almost all other punching processing.
   (2) Crankless punching machine
   Crankless punching machine is also called eccentric gear punching machine. Comparison of the two structural functions of crankshaft punching machine and eccentric gear punching machine: the eccentric gear punching machine structure is superior to the crankshaft structure in terms of shaft rigidity, lubrication, appearance, maintenance, etc., but the disadvantage is that the price is higher. When the stroke is long, the eccentric gear punching machine is more advantageous, and when the stroke is short, such as in the case of a special punching machine, the crankshaft punching machine is better. Therefore, small machines and high-speed punching machines are also in the field of crankshaft punching machines.
   (3) Toggle punching machine
   The use of a toggle mechanism on the slider drive is called a toggle punching machine. This punching machine has a unique slider motion curve in which the slider speed becomes very slow near the bottom dead center (compared with the crankshaft punching machine). Moreover, it can correctly determine the dead point position below the stroke. Therefore, this type of punch is suitable for compression processing such as stamping and finishing. It is now most commonly used in cold forging.
   (4) Friction punch
   A punch that uses friction transmission and a screw mechanism on a track drive is called a friction punch. This type of punch is most suitable for forging and crushing operations. It can also be used for bending, forming, stretching and other processing. It has a multi-purpose function. Because of its low price, it was widely used before the 1960s. Due to the inability to determine the lower end position of the stroke, poor processing accuracy, slow production speed, overload when the control operation is wrong, and the need for skilled technology in use, it has now been eliminated.
   (5) Screw punch
   A screw mechanism is used on the slider drive mechanism, which is called a screw punch (or screw punch). It is now rarely used.
   (6) Rack punch
   A rack and pinion mechanism is used on the slider drive mechanism, which is called a rack punch. Screw punches have almost the same characteristics as rack punches, and their characteristics are roughly the same as those of hydraulic punches. Previously, it was used for pressing bushings, extrusion of scraps and other items, oil pressing, packaging, and extrusion of shells (hot-press thinning), but it has now been replaced by hydraulic punches and is no longer used except in extremely special circumstances.
   (7) Linkage punch
   A punch that uses various linkage mechanisms on the slider drive mechanism is called a linkage punch. The purpose of using the linkage mechanism is to keep the stretching speed within the limit while shortening the processing cycle during the stretching process. By reducing the speed change of the stretching process, the speed of the approach stroke from the top dead center to the starting point of the process and the speed of the return stroke from the bottom dead center to the top dead center are accelerated, making it have a shorter cycle than the crankshaft punch to improve productivity. This type of punch has been used for deep stretching of cylindrical containers since ancient times, with a narrow bed surface, and has recently been used for processing automobile body panels with a wider bed surface.
   (8) Cam punch
   A punch that uses a cam mechanism on the slider drive mechanism is called a cam punch. The characteristic of this punch is to make an appropriate cam shape so that the desired slider motion curve can be easily obtained. However, due to the nature of the cam mechanism, it is difficult to transmit a large force, so the capacity of this type of punch is very small. It is commonly used in the general clothing industry.