10/02/2017

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.

10/02/2017

New manufacturing technologies and new studies in industrial applications developed some innovative methods for metal sheet cutting. These recent techniques are known as hot working processes, they convert renowned power sources (such as laser) into new applications.

We outline three important hot working process for metal cutting:

– Oxy-fuel:  metal sheet is shaped by gases through a torch (similar to a welding torch). The reaction between oxygen and acetylene heats the material (reaching  980°C/1796°F) so that it melts instantly. The oxy-fuel cutting is ideal for sheet  up to 5,9in (15cm) thick.

– Plasma cutting: this technology uses a gas jet, generally a mixture of hydrogen and nitrogen. During the process the high temperature ionization ensures local melting on the cutting line. It’s suitable for every kind of metal and it doesn’t overheat the sheet. Plasma cutting guarantees very fast and accurate results even with metal sheet up to 0,78in (20mm) thick. The whole process is guided by CAD software.

– Laser cutting: the development and the spread of these machine tools started in the 80s and it is constantly evolving.  New technological projects are testing new tools able to cut materials such as ceramic, rubber, plastic and composites.

Laser cutting machine uses an intense beam of monochromatic light, which reaches extremely high temperatures and so it allows metal sheet cutting. Engraving will be minimal as well as the metal waste. Similarly to plasma cutter, this machine is automatically controlled by CNC using CAD software. It fits for cutting sheets up to 0,78in (20mm) thick and it can’t be used with every material.

In the last few years, new kinds of laser have been tested with new power sources such as fiber, liquid-crystal and CO₂.

Pay special attention to the fiber laser. Its working is based on optical fibers as amplifiers which are fueled by injection laser diodes. It is the ideal technique for engraving, it requires low maintenance and it has an extended lifetime (the average life is 25.000 hours).