A method for cutting a continuously extruded tube into segments of lesser and predetermined length by means of a cutting machine, the cutting machine comprising:
- a guide that develops between a stroke-start and a stroke-end;
- sliding means that are movable along the guide parallel to a direction of advance of the tube along which the tube is to proceed according to a first sense of advance oriented from the stroke-start to the stroke end of the guide;
- means for actuating said sliding means along the guide;
- said sliding means comprising a first station for cutting the tube, said first cutting station comprising in turn a first shearing cutter defining a first cutting plane transverse to the direction of advance;
- said sliding means comprising:
- a second station for cutting the tube positioned upstream of the first cutting station with respect to the first sense of advance of the tube along the direction of advance, said second cutting station comprising a second shearing cutter distanced from the first shearing cutter and defining a second cutting plane that is transverse to the direction of advance of the tube;
- means for gripping tube portions, said gripping means being positioned, relative to the first sense of advance of the tube, upstream of the first cutting plane, downstream of the second cutting plane and between the first and the second cutting plane;
- said gripping means being movable between a first configuration in which they securely grip corresponding tube portions and a second configuration in which they release said tube portions;
- said cutting machine further comprising means for controlling the actuating means and means for measuring the relative displacement between said tube and said first and second cutting plane along the direction of advance;
- before every cut and on the command of the control means, the actuating means being able to synchronise with the motion of the tube the motion of each cutting station along the direction of advance, positioning the first and the second cutting plane at desired positions on the tube;
- the control means commanding said actuating means of said sliding means at least according to the information provided by said measuring means and to the desired length of the tube segments to be produced with the machine;
- once the synchronisation is completed, before each cut, said gripping means assume said first configuration to keep in position tube segments positioned at the first and at the second cutting plane, said second configuration being assumed after each cut to allow the relative motion of the tube and of the sliding means along the direction of advance of the tube;
- the method comprising the steps of:
- positioning the tube in a work area of the cutting machine;
- making the tube advance along the direction of advance according to the first sense of advance;
- positioning the first and the second cutting plane at a mutual distance equal to:
- n·(L)+K
- where:
- n:
- is a natural number greater than 0;
- L:
- is a preferential length of the desired tube segments outputted by the machine, measured along the direction of advance of the tube;
- K:
- is a first corrective coefficient to take into account the length, measured along the direction of advance of the tube, of the scrap generated by the first and/or by the second shearing cutter;
- synchronising to the motion of the tube the motion of the first and of the second cutting plane along the direction of advance;
- executing at least in part simultaneously, by means of the first and of the second cutter, a first and a second cut of the tube at the first and the second cutting plane.