Powerful CNC platform provides economic solution for twin-head steel cutter

CNC kernel controls 16 axes including dual oxy-acetylene cutting heads - Oxyser has dramatically increased the throughput of its oxy-acetylene steel cutting machinery, and automated the process, by developing a new twin-head machine controlled by NUM’s Axium CNC platform. In total, this powerful CNC kernel controls 16 motor axes to manage the motion of a gantry with two positioning heads - each fitted with mobile oxy-acetylene cutting torches.

The machine has just been commissioned at Grupo Ros Casares’ plant in Aviles, Spain, where it is being used initially to produce steel plate sections required to construct wind turbine generator towers. The shaped plates are typically cut with bevelled edges so that they can be welded together easily on site.

Believed to be the first of its kind, the machine introduces automatic programmed control of shape cutting in an application sector used to much simpler machines: traditionally, only three CNC-controlled axes are employed and the initial positioning of the oxy-acetylene tool for linear cuts is performed manually. The gantry runs over very long worktables. This allows raw steel plate to be loaded on one side of the gantry while cutting operations are in progress on the other side. Combined with dual cutting heads - which may be used individually or simultaneously in a master-slave configuration - the new machine more than doubles throughput.

Oxyser developed the new-generation cutting machine to improve productivity for Grupo Ros Casares, a major supplier of structural steelwork in Spain and Europe who provide a broad range of steelwork processing services including complex shape cutting. Although the cutting capability of the machine’s oxy-acetylene torch heads were conceived with the versatility needed to produce bevelled edges for the cladding of wind turbine structures, the machine will cut virtually any complex shape defined by a CAD program.

Oxyser specialise in producing plasma and oxy cutting machines, but up to now, they have typically produced smaller systems with up to five axes of control. This project marks the company’s entry into the high-end cutting market. The key technical requirement to meet the demands of this application was a much more powerful CNC kernel. NUM provided a solution in the form of its Axium platform, which offered the computational power to control the 16 axes of motion required. NUM was also able to provide all of the ancillary automation components required for the application including drives, motors, I/O and HMI panel.

The machine is enormous. The parallel worktables - one for each tool head - are 26 metres long, and eight metres wide. The gantry supports two cutting tool heads, with one slave tool following the motion of the master tool. The 4.2 cm thick steel plates being cut for the current wind turbine application typically weigh around eight tonnes each, measure around 10 x 2 metres, and have bevelled edges. To meet the end user’s production requirements, the machine currently operates for 16 hours a day. During this period it cuts up to 32 steel plates. The high degree of automation of the cutting process supported by Oxyser’s machine means that just one operator is needed, both to run the machine and remove offcuts.

The 16 axes control the X-Y movement of the gantry, plus the vertical and rotational movement axes of the two cutting heads. Inside each cutting head, three acetylene torches are positioned in a line. The middle torch is fixed in position. The outer torches are provided with a further two axes of linear and rotational movement to provide the flexibility of positioning required for cutting complex shapes and bevel edges. The torches can be used singly or in combinations.

All of the axes are powered by servo motors designed by NUM exclusively for high performance CNC applications. NUM also helped Oxyser to develop a custom operator control panel for the machine, based on the company’s standard NUMpass HMI. The program provides a simple means for the operator to enter the required cut characteristics including speed, acceleration, angle of cut, and torch power. To help Oxyser develop the machine, NUM write a utility to provide the analog signals required to control the acetylene torches. “NUM’s controller proved a cost-effective platform for this project as all the axes can be managed from one CNC kernel, together with all of the I/O. The software environment simplified the CNC programming by making it easy to set up groups of axes to break down the complexity of this large machine,” says Unai Gonzalez of Oxyser.