Punching is often the cheapest method for creating holes in sheet materials in medium to high production volumes. When a specially shaped punch is used to create multiple usable parts from a sheet of material the process is known as blanking. In metal forging applications the work is often punched while hot, and this is called hot punching.
Punching characteristics
Punch press
Punch press, with high-speed servo hydraulic punching head
Punching characteristics:
- It is the most cost effective process of making holes in strip or sheet metal.
- It is able to create multiple shaped holes.
- Punches and dies are usually fabricated from conventional tool steel or carbides
- It is one of the quickest processes.
Equipment
Most punch presses are mechanically operated, but simple punches are often hand-powered. Major components of this mechanical press are the frame, motor, ram, die posts, bolster, and bed. The punch is mounted into the ram, and the die is mounted to the bolster plate. The scrap material drops through as the work piece is advanced for the next hole. Most common in industry are large computer-controlled punch press, called a CNC. These most commonly are of the 'turret' or 'rail' variety. A turret punch press houses punches and their corresponding dies in a revolving indexed turret, while a rail type punch stores tooling on a back rail out of the way of the work piece. These machines use hydraulic as well as pneumatic power to press the shape with enough force to shear the metal.
Related processes
Other processes such as stamping, blanking, perforating, parting, drawing, notching, lancing and bending operations are all related to punching.
How is metal sheet punching done?
Modern metal sheet punching is done with heavy machines in order to create holes in a piece of metal. The principle is relatively simple:
- The metal sheet to be punched is fixed between the puncher and the die.
- The puncher moves down into the die. It results in the metal sheet shearing from the surrounding material.
- The cut metal is collected in a container for further use / recycling.
- Repeat (if necessary).
- The special procedure used for performing individual shapes of hole is called “pinching”. Here very small holes are made individually in a long line. These connected holes can create custom-made contours for meeting special demands. In many cases, however, laser cutting is used for reaching such forms instead of metal sheet punching since it causes less physical stress on the work piece.
What can influence quality of punching?
Several critical factors determine quality of each stroke:
- Size / shape of the puncher and the die;
- Amount of force applied;
- Condition of the puncher and the die (punching tools can be used only for such number of strokes that they do not become too worn and do not prevent clear punching);
- Thickness of the metal sheet to be punched (it is more difficult to strike thicker metal); and
- Type of the metal to be punched (it is more difficult to strike heavier metals).
- In case of punching a round hole, it is usually recommended that the minimum diameter of the hole should be greater than the thickness of the metal. However, the size of the hole can be even greater for strong metal alloys.
SHEET THINCKNESSES TO BE WORKED:
- Carbon steel, cold rolled fine sheet-plate, oxygen cutting gas, combined mode, e.g. DC013 mm
- Carbon steel, cold rolled fine sheet-plate, nitrogen cutting gas, laser mode, e.g. DC012 mm
- Corrosion-resistant steel, e.g. 1.4301, combined mode, 3 mm
- Dip-galvanized sheet, e.g. DX51, laser mode: 2.5 mm
- Blanking mode: 3 mm
- Alloyed aluminium, e.g. AlMg3: combined mode, up to 3 mm
- Copper, bronze, clear aluminium (Al99.5), only blanking mode, 3 mm
LARGEST WORKING RANGE:
- Without (X x Y) overlapping in combined blanking / laser mode, 3050x1550 mm
- Without (X x Y) overlapping in laser mode, 3050x1550 mm
- Without (X x Y) overlapping in blanking mode, 3050x1550 mm
- Positioning accuracy ± 0.1 mm, repeating accuracy ± 0.03 mm
