Five-axis for tank hatch


PRV Engineering, Pontypool, has invested in new 5-axis capacity for the manufacture of a steel hatch for an armoured tank.

The German-built Spinner U5-630 trunnion-type, 5-axis, vertical-spindle machining centre was delivered in mid-2021 by Whitehouse Machine Tools.

The U5-630 is devoted to producing a fabricated steel hatch measuring approximately 300 x 200 x 200 mm for an armoured tank in a cycle time of 5.5 hours, halving the cycle time of the previous production route. This involved milling and boring the three-part fabrication on either of two much larger 5-axis machining centres. Three setups were required and the total production time was 10 hours, which meant that it was not feasible to produce one hatch per day during a single shift.

Apart from raising the efficiency of production, another reason for investing in a machine dedicated to the job was a need to free up the larger capacity plant to fulfil an increasing amount of plate work. In any case, it is more difficult and therefore more time consuming to hold tolerance on a larger machine, as the heavier moving elements tend to cause vibration.

A factor in PRV Engineering's managing director Simon Jones and works director Alun Cox choosing the Spinner machine was its generous 630 x 530 x 465 mm working envelope in a footprint of just 2.75 x 2.53 metres.

The U5-630 has to be highly accurate, as some tolerances on the hatch fabrication, which comprises three pre-machined and welded parts, are very tight.

The run-out of two holes bored from either side of the component after rotation through 180 degrees has to be to within 0.04 mm TIR (total indicator reading), while their diameter tolerance is 25 µm total.

Better accessibility of the cutters to the workpiece on the smaller machine is a major benefit. CNC setter-programmer at the Pontypool factory, Darek Krochmalny, explained that it is possible to use shorter and therefore more rigid tools than on the larger machine, enabling faster feeds and speeds for higher productivity.

Furthermore it is now practicable to reduce the time needed to mill some features such as a locking pin pocket by interpolating all five axes simultaneously, whereas the production cycle on the B-axis machine was entirely 3+2.

Mr Cox concluded, "Over half of our turnover is defence industry work, with the rail, high voltage switchgear and Formula 1 sectors also regularly served.

"We pride ourselves on providing a full service from design-for-manufacturability through fabrication and machining to wet spray painting and powder coating. Only heat treatment and electroplating are bought in.

Photo: PRV Engineering's works director Alun Cox (right) and CNC setter-programmer Darek Krochmalny with the Spinner U5-630 5-axis VMC.