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Aluminium and steel frames for marquees and other temporary or portable structures are being machined twice as quickly at Tectonics UK, Alresford, since a FOM machining centre was supplied by Kasto.

The Italian-built CNC machine can process aluminium extrusion or steel bar and angle up to 7m long on three sides in a single, automatic cycle.

Positioning accuracy of +/-0.13mm and repeatability of +/-0.07mm result in faster assembly of higher-quality frames, and eliminate the re-machining of features, which was previously necessary on occasions.

A structure now produced on the FOM machine might include a 15mm diameter hole accepting a 14mm diameter pin, and it always fits first time.

In the past, 3mm clearance would have been needed to ensure trouble-free assembly.

To extend an existing building of complicated shape, customers often ask for a specialised canopy to adjoin it, so such structures are becoming ever more complex.

As in many production sectors, Tectonics uses a CAD system to produce its designs.

The resulting machining requirements were becoming difficult for production staff to fulfil by marking up the parts using a tape measure followed by manual drilling and jig sawing on the shop floor.

The FOM Flen model was chosen due to its robust build and additional spindle power, as Tectonics’ structures include a substantial amount of steel in addition to more easily machined aluminium.

Glenn Whitehouse, workshop manager, said, ‘I reckon the new machine is twice as fast as drilling and routing by hand.

‘Moreover, only two operators are now needed instead of four or five, as cleaning and deburring of parts can be carried out while the next machining cycle is in progress.

‘The FOM Flen is so quick at completing the cutting cycles that sometimes we cannot get the next piece of extrusion ready fast enough.’ The machine has eight pneumatic vices that position themselves automatically along the length of the bed under instruction from the CNC system.

It calculates where the vices should be located for maximum clamping rigidity, consistent with not impeding the spindle tooling when carrying out the required machining operations.

Any number of vices may be used together when processing long sections.

For machining shorter parts, two sets of four vices can be positioned at either end of the bed to enable tandem machining.

100m/min rapid movement of the spindle head along the bed minimises idle time.

However many vices are used to clamp a component, they close simultaneously at the touch of a button.

To run a new production batch, a DXF file of the extrusion profile is loaded from Tectonics’ CAD system into the FOM control.

The operator then keys in the relatively simple part program on the shop floor.

It involves entering the coordinates of each feature to be machined, selecting the spindle speed and feed rate for each tool according to the material being cut, and entering the overall length of the component.

The width and height are already known from the DXF file of the cross section.

It takes 15 to 20 minutes to create a new program, after which it is available in memory to be called up immediately for a repeat order.

All that remains is to key in the number of parts in the batch, load the material manually and press the start button.

In some cases, two components are loaded at a time, side by side, in which case they may be machined on two faces only in one clamping (top and outer side).

This is most often done when the components require holes, slots and other features on all four faces.

Two hits are needed in any case, and the other two faces can be accessed after reversing the extrusions.

To ensure accurate machining, it is important to carefully position the material longitudinally against a backboard and transversely against the side and lower faces of the fixed jaws on every vice.

The bottom face on the vices is adjustable to three heights to suit the size of profile.

Components are then always correct on completion of the machining cycle, which is typically 150 seconds to machine two short parts on two faces or five minutes to complete one long extrusion on three faces.

Useful features in the FOM control that assist programming include a facility that allows sections of a program created for one component in a family to be copied, scaled if necessary and pasted into another program.

On-screen simulation of the cycle checks for interference between the moving machine elements and the component, vices and bed.

The length of the cycle is calculated automatically and is summed up in a chart that shows the time taken for each element of the program, including component load/unload, clamp positioning and closure/release, tool change, rapid traverses and actual metal cutting.

The latter is broken down to show the amount of 2-axis interpolation.

Slots, recesses and the like have to be machined this way, but sometimes, circular holes are too.

If production volumes dictate, appropriately sized drills may be included in the magazine to eliminate some of the interpolative movements for hole production and speed the cutting cycle.

The machine specification includes a 12-tool magazine containing preset, mainly Guhring cutters and a 4kW/12,000 rev/min electro spindle with a -15/+195-degree A-axis for machining on three faces.

There is a choice of two lubrication systems: recirculating liquid emulsion for machining Tectonics’ steel components up to 8mm thick, or minimum-quantity, neat oil spray for processing the company’s aluminium sections, which range from 30 x 40mm to 120 x 300mm.

A swarf conveyor runs the length of the bed, to remove chips into a tank at the end, from where they are filtered from the coolant.

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