Turning centre investment made to cut costs

Demands from aerospace customers to reduce costs, resulted in a subcontractor acquiring its first turning centre to be equipped with twin opposed spindles, twin turrets and C- and Y-axes control.

Kigass Aero Components in Warwick is one of many aerospace subcontractors in the UK that is being asked by Rolls-Royce and others to achieve stringent 'cost-down' targets as well as a halving of delivery lead times every three years.

Helping to reach these demanding goals is the company's latest turning machine, an Index twin-opposed-spindle, twin-turret model with C- and Y-axes supplied by Geo Kingsbury Machine Tools, Gosport.

The Index G200 Compact is the first lathe on site to have a Y-axis for off-centre prismatic machining of components in conjunction with the spindle orientation facility (C-axis).

The machine has on average reduced cycle times by 10 to 15 per cent and saved 15 per cent on set-up times compared with the 20 or so other CNC lathes on site, according to Managing Director, Peter Platt.

Kigass, which services the motorsport industry as well as aerospace customers, specialises in machining a range of metals from aluminium to exotic materials such as Inconel.

The subcontractor therefore looks for rigidity in the machines that it buys as well as single-hit production capability to achieve the required cost and lead time targets.

There is a plethora of lathes on the market able to fulfil these demands and of the eight machines reviewed by Platt, the main deciding factor in favour of the G200 was the fast and accurate tool changeover.

He commented, "Particularly with C-axis machines, we find that generally it is difficult to get a tool back on centreline; Index had the best system we looked at.

Our batch sizes can be down to 50-off, so efficient tool changeover considerably increases productivity." Prior to placing the order, Platt asked Geo Kingsbury to prove repeatability of better than 0.02mm on turned diameters when a VDI toolholder was moved from one station to another on the same turret.

A 50-off SPC run of titanium piston components was then produced whose bore diameter, overall length and outside diameter were subsequently measured.

A Cpk in excess of 1.33 was recorded.

Virtually every Kigass turned part requires machining on the reverse end, so the 20 kW power of the opposed spindle of the G200 was an important factor.

A lower power sub-spindle would have adversely affected cycle times.

The proportion of prismatic operations within a typical cycle is quite high at 20 to 30 per cent, so the generous 5.5kW / 6,000 rpm of up to 14 live tools in each of the two turrets is also useful.

Every part that comes off the Index is completely machined, including most of the deburring, ready for delivery to the customer.

Specification of the Index lathe at Kigass includes 60mm bar capacity, a maximum swing of 420 mm, a turning length of 400mm, 160mm chuck diameter and 5,000 rpm maximum speed of both main and counter spindles.

A 1.5 metre bar magazine feeds the machine.

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