Published on : 14 April 20215 min reading time
Definition of punching
Punching is a technique whose application can vary according to the trades. But in general, we can say that punching consists of leaving a mark or punch on an object.
Furthermore, it is also defined as a perforation produced by shearing on a material using a punch and a die. Note that punching can only be done on a closed contour. In addition, a wide variety of materials can be punched.
These include, among others, vulcanized fiber, metal (sheet metal), cardboard, textiles, paper or plastic. However, it should be noted that these materials should generally be in sheet form.
Punching is used in various trades among which one can quote the dressing and the leather goods, the metallurgy,… According to your needs, the punching can give a different form to your materials. This ability to give any shape is linked to the punch-die pair that you are going to use.
It is also important to specify that the part removed following this operation is called a knockout. This can be either scrap as is the case in the manufacture of perforated sheets, or a useful part (blank) which will subsequently be used for the manufacture of another part by stamping or any other technique. machining.
To carry out a punching operation, it is necessary to have a Punching System. It is a device which allows different punching applications to be carried out.
There are three punching methods:
– Snacking. It is a technique which makes it possible to cut out an outline by multiple punches;
– Cutting to the press. It consists in making blank cuts using special tools;
– Classic punching. It consists in the removal of materials by making holes
The awl is a metal instrument made of steel and equipped with a point for drilling. It is composed of different parts such as:
– The body of the punch, the variable length of which allows the tool to be mounted and clamped.
– The clearance angle which limits friction. It is 2 to 3 °. However, tools on presses or nibblers do not have a clearance angle.
– The fly or nipple which allows the tool to be positioned in the punch cuts previously made.
– The head has sharp edges.
This is the punch impression holder. The die has in its axis a hole with the shapes and dimensions of the punch. To this set is added a play of a few tenths of a millimeter. Note that the clearance reduces the punching effort and hardening of the punched area.
Advantages and drawbacks of punching
Like any technique, punching has advantages and disadvantages. Among the advantages offered by this technique, we can note:
– The speed of execution in the realization of complex works;
– The savings made, because punching results in less wear on the tools and does not require frequent sharpening;
– The precision of the cuts;
– The possibility of forming any type of holes.
Despite these many advantages, punching has some disadvantages such as the fact that this technique is limited in thickness. It must also be said that the minimum section of the punch is also limited.
According to DIN 8588 manufacturing procedures, drilling is a mechanical separation without cutting of workpieces using cutting edges. This is a procedure which, in addition to allowing the production of large quantities of metal parts, is used in the processing of finished or semi-finished products such as sheet metal.
According to this procedure, there are three main groups of drilling: separation by cutting with steel, cutting with two approach steels and shearing.
Separation with steel involves penetrating a wedge-shaped steel into the material in order to divide it. Cutting with two steels requires two wedge steels which will penetrate the material right through.
Finally, let’s finish with shearing, which remains the most widely used process in industry. This is linked to its productivity and its great commercial importance. This practice is divided into three main stages: elastic deformation, plastic flow and cracking.
Computer numerical control (CNC) punching
CNC punching is a more modern and innovative sheet metal fabrication process. In fact, CNC punching is carried out by numerically controlled punch presses.
The CNC punching machine is the tool that allows this work to be carried out. It is programmed to move a sheet of metal in different directions. Thus, the latter is positioned precisely under the punch and ready to be perforated or deformed.
It is also possible to make perforations of 3D shapes such as dimples, electrical cutouts, screw threads …