Metal cutting: Cold working

water jet cutter

 

 

Metal sheet cutting is undoubtedly one of the most important technique in metalworking and it consists in shaping the material held in a flat position. Traditionally the whole process was made entirely by shearing machines but in the last few decades new technologies developed new kinds of cut, which are more versatile and precise.

Metal cutting can be divided into two macro areas: hot working and cold working processes. In the first case, the material undergoes partial melting along the cutting line by high temperature sources; while in cold process, the metal sheet endures plastic deformation along a straight cutting line usually at ambient temperature.

 

Let’s analyze the most important cold working processes:

- shearing is the traditional technique and it involves the use of a shearing machine (mainly the guillotine). Its principle is based on two blades in very specific locations: the lowest one fixed on the shearing workbench and the moving blade that comes down to cut material. During the process a blank holder ensures stability. The higher blade can move in different positions. It can be parallel to the fixed one, so that the result will be a clean cutting at the same time along the line, or inclined for gradual cut.

Every shearing machine has its own peculiarity and specific feature but all of them can shear sheets up to 9,8-11,8 in (25-30cm) thick.

- notching machine is used basically to smooth the edge of the plates that were previously cut with other techniques. It works similarly to the shearing machine, two pairs of blades (one fixed and one moving) ensure oblique cuts by notching adjustable angles.

- waterjet cutter: a high pressure stream of water is projected on the metal sheet, the pressure can easily reach 3000-4000bar. It is a very useful and versatile method which can cut workpiece up to 5,9 in (15cm) thick and it is suitable for every kind of material. It doesn’t cause any variation in terms of chemical or physical composition so the waste is minimized. Its cutting head is controlled automatically by CNC using a CAD program.