Cutting shapes from thick metal sheets.
At one large-scale precision engineering factory, sheet metal used to be cut to shape using a nibbling machine (see Figure 1). This is a large punch press fitted with a small tool which pierces the metal approximately ten times per second. The cut is made by guiding the sheet by hand so that the tool slowly ‘nibbles’ a slot at approximately 10 mm per second. The average vibration magnitude, measured at the point where the hand was holding one sheet of 3 mm steel, was 9 m/s2. The company had four such machines in use, when necessary, operated by a large pool of workers who spent the remainder of their time performing other general fabrication duties. The machine could not cut to precise dimensions, leaving a rough edge on the sheet, so that grinding was necessary to bring the components to the correct size and finish. A typical day might have included 2 hours’ grinding (with tools producing vibration magnitudes of 2 m/s2) and 1 hour on the nibbling machine. This would give a total typical daily vibration exposure of over 3 m/s2 A(8).
The company invested in a flat-bed carbon-dioxide laser cutter (see Figure 2) which, with one trained operator, does the work previously done by the four nibbling machines. The machine is computer controlled and there is no contact with vibrating surfaces. It also cuts more accurately than the nibbler so no grinding is necessary. The other staff now concentrate on other duties with no exposure to vibration.
The problem: A nibbling machine
The solution: A laser cutting machine